A functional ionic microgel sensor array was developed by using 1-(2-pyridinylazo)-2-naphthaleno (PAN)- and bromothymol blue (BTB)-functionalized ionic microgels, which were designed and synthesized by quaternization reaction and anion-exchange reaction, respectively. The PAN microgels (PAN-MG) and BTB microgels (BTB-MG) were spherical in shape with a narrow size distribution and exhibited characteristic colors in aqueous solution in the presence of various trace-metal ions, which could be visually distinguished by the naked eye. Such microgels could be used for the colorimetric detection of various metal ions in aqueous solution at submicromolar levels, which were lower than the U.S. Environmental Protection Agency standard for the safety limit of metal ions in drinking water. A total of 10 species of metal ions in aqueous solution, Ba2+, Cr3+, Mn2+, Pb2+, Fe3+, Co2+, Zn2+, Ni2+, Cu2+, and Al3+, were successfully discriminated by the as-constructed microgel sensor array combined with discriminant analysis, agglomerative hierarchical clustering, and leave-one-out cross-validation analysis.Keywords: metal ions; microgel; multivariate analysis; sensor array; trace analysis;

The reactivity of catechols with radicals was applied for the first time to synthesize cross-linked nanostructures, i.e. microgels, without addition of any other cross-linker. Stable microgels with narrow size distribution were successfully obtained via surfactant free emulsion polymerization (SFEP) of acrylamide-type main monomers, namely, acrylamide (AM), N,N-dimethylacrylamide (DMAA), N-vinylpyrrolidone (NVP), N-vinylcaprolactam (VCL), N-isopropylacrylamide (NIPAM), and (dimethylamino)propylmethacrylamide (DMAPM), and vinyl comonomer bearing unprotected catechol in aqueous solution at 70 °C. The formation mechanism of cross-linking network structures was mainly attributed to the reactions between unprotected catechol groups of polymer chains and the radicals of propagating chains during SFEP. With catechol chemistry, microgels with fully water-soluble polymers as scaffolds were achieved without using any surfactant stabilizer.

Thermo-sensitive degradable poly(N-isopropylacrylamide) (PNIPAm)-based microgels were prepared by surfactant-free emulsion polymerization with a redox initiator pair of potassium persulfate (KPS) and N,N,N′,N′-tetramethylethylenediamine at 50 °C. NIPAm, sodium 2-acrylamido-2-methyl-1-propanesulfonate (AMPS-Na), and N,N′-bis(acryloyl)cystamine (BAC) were used as main monomer, anionic comonomer, and degradable cross-linker, respectively. It was found that the morphology and network structure of the resultant microgels could be tuned via the controlled addition of BAC and AMPS-Na, which, in turn, strongly affected the corresponding thermo-sensitivity, stability, and degradation behavior of the microgels. The inhomogeneous network structures of the microgels could be improved by increasing the time period tBAC between KPS initiation and the addition of BAC. The morphology of microgels changed from spherical into hollow interior spherical morphology. The stability of the microgels in physiological condition could be enhanced by the controlled addition of comonomer AMPS-Na. The extent of microgel degradation increased with increasing tBAC.

It is a challenging topic to disconnect a linear polymer selectively at the mechanophore site by an external force in a “cold” fashion. In this work, the effect of the power output of ultrasonication on the selective cleavage at the centered urfuryl-maleimide Diels–Alder (DA) mechanophore of poly(methyl acrylate)s (DA-PMA-a and DA-PMA-b) were quantitatively investigated by comparative study on experimental and simulated chain scission kinetics as well as high-resolution 1H NMR spectroscopy (600 MHz). At low power output of the ultrasonication (2.10 W), DA-PMA-a with Mn of ca. 2Mlim (Mlim, below which no further chain scission was observed) presented a DI (degradation index)−t (sonication time) plot with a turnover point at ca. 1.0 and no clear variation of the molecular weight after the turnover, which met well with the calculated center cleavage mode. At 5.52 W, DA-PMA-a and a poly(methyl acrylate) that contained two centered ester bonds (ester-PMA) presented similar DI–t plots with turnover points less than 1.0 within same sonication times, while poly(methyl acrylate) with fully carbon–carbon chain (PMA) had a turnover at DI value of ca. 0.5. By way of contrast, high power output of the ultrasonication (5.52 W) caused a possible cleavage of ester bonds of DA-PMA-a, which would mask the selective cleavage at the DA site. High-resolution 1H NMR result of DA-PMA-b (115.8 kDa, Mn was slightly higher than 2Mlim) showed that DA conversions were up to 55% under 2.10 W and 38% under 5.52 W. The kinetics from GPC traces and 1H NMR results of DA-PMA-b as well as 1H NMR results of DA-PMA-c (68.4 kDa, Mn was slightly higher than Mlim) under sonication confirmed the observation that low power output favored selective chain scission at DA site. The turnover point in the DI–t plot might be used as characteristic parameter to gauge the selective chain scission at mechanophore site for single mechanophore-centered polymers.

Thermosensitive poly(VCL-4VP-NVP) ionic microgels were prepared by in situ quaternization crosslinking reaction during surfactant free emulsion polymerization (SFEP) with N-vinylcaprolactam (VCL) as the main monomer, 4-vinylpyridine (4VP) as the quaternizable co-monomer, N-vinyl-2-pyrrolidone (NVP) as the second co-monomer and 1,6-dibromohexane (6Br) as the quaternization crosslinker. The obtained ionic microgels were spherical in shape with a narrow size distribution and exhibited thermo-sensitive behavior. These ionic microgels showed low cytotoxicity at concentrations lower than 25 µg mL−1, excellent hemocompatibility at concentrations up to 1000 µg mL−1, and could be up taken into the cytoplasm regime of HEK-293 cells without entering the nucleus. It was found that these ionic microgels were suitable for the loading and sustained release of a nonsteroidal anti-inflammatory drug, diclofenac sodium (DS). The drug loading content (DLC) of DS in the microgels could reach ca. 12% with an encapsulation efficiency (EE) of up to 68%. Furthermore, 60% loaded DS could be sustainably released at 37 °C from the drug-loaded microgels within 400 min following a first-order exponential kinetics.

The fluorescent properties of a linear poly(hydroxyurethane) (P1) from carbon dioxide, siloxane (Si–O–Si)-containing bisepoxide and diamine are described. P1 showed strong photoluminescence with a quantum yield of up to 23.6%, high photostability, and broad absorption and emission spectra either in bulk or solution. The flexibility and hydrophobicity of the Si–O–Si linkage in P1 were utilized to drive the intense aggregation of hydroxyurethane chromophores which combined with the hydrogen bonding interactions lead to strong photoluminescence. P1 was used as a single phosphor film for fabricating a low voltage, cool white light-emitting diode device with competitive performances.

The chain conformations and adsorption behaviors of four thermo-sensitive poly(N-isopropylacrylamide)x–poly(propylene oxide)36–poly(N-isopropylacrylamide)x (PNIPAmx–PPO36–PNIPAmx) triblock copolymers with x values of 15, 33, 75, and 117 in dilute aqueous solutions were investigated by combined techniques of micro-differential scanning calorimetry (micro-DSC), static and dynamic light scattering (SLS & DLS), and the quartz crystal microbalance (QCM). PNIPAm15–PPO36–PNIPAm15 only exhibited the lower critical solution temperature (LCST) of the PPO block, i.e. 25 °C, because the PNIPAm block with x = 15 was too short to maintain its own LCST. With middle lengths x of 33 and 75, the LCSTs of PPO and PNIPAm blocks were observed, respectively. For the longest PNIPAm block with x = 117, only LCST of PNIPAm block dominated, i.e. 32.3 °C. DLS results revealed that the four PNIPAmx–PPO36–PNIPAmx triblock copolymers formed “associate” structures in their dilute aqueous solutions at 20 °C, which was well below the LCSTs of the PPO and PNIPAm blocks. QCM results indicated that the adsorption time constant decreased with increasing adsorption temperature but tended to increase with increasing length x of the PNIPAm block. A complex adsorption behavior with large adsorption amounts was only observed at the corresponding LCST of the PNIPAm block for PNIPAmx–PPO36–PNIPAmx with longer PNIPAm blocks with x = 33, 75, and 117. Furthermore, the adsorbed PNIPAmx–PPO36–PNIPAmx layers obtained at 20 °C were rigid with less energy dissipation.

Poly(N-isopropylacrylamide)-based ionic hydrogels were synthesized by free-radical polymerization with N-isopropylacrylamide as a monomer and imidazolium-based dicationic ionic liquid as a crosslinker. The dicationic crosslinkers [Cn(Vim)2][Br]2 were obtained by quaternizing 1-vinylimidazole (Vim) with dibromo compounds (Br-CnH2n-Br) with various alkyl chain length n, respectively. The effects of alkyl chain length and the amounts of crosslinker on the structure, swelling properties, interfacial adsorption and release of anionic dyes of the obtained ionic hydrogels were systematically investigated by using scanning electron microscopy, Fourier transform infrared spectroscopy and ultraviolet–visible spectroscopy. The obtained ionic hydrogels showed good swelling properties and typical feature of poly(ionic liquid) in aqueous solutions, of which the quaternized imidazolium moieties could interfacially interact with anionic dyes, such as methyl orange, methyl blue, congo red, orange G, thymol blue and bromothymol blue. Different kinetic and adsorption isotherm models were used to describe the interfacial adsorption and release behaviors of anionic dyes, which were strongly dependent on the chemical structures of the dyes.

We describe the enhanced mechanophore activation within nanosized core–shell micelles, which also present temperature and ultraviolet (UV) light-responsive properties. The model micelle was fabricated by the self-assembly of an amphiphilic block copolymer of poly(tert-butyl acrylate-b-N-isopropylacrylamide) with one spiropyran (SP) moiety at the midpoint of chain [SP-(t-BA88-b-NIPAM62)2, P2]. Micellization of P2 in tetrahydrofuran (THF)/water mixed solvent enhanced the reactivity of the electrocyclic ring-opening reaction of SP to merocyanine (MC) isomer under sonication because micellization caused SP-centered PtBA block entangled and partially swelled in the micellar core and the increase of the dielectric constant of the medium around the SP, which could facilitate the conversion of SP to MC. This new enhanced mechanophore activation model demonstrated here is valuable as a probe to detect stress activation within nanosized particles and to design multiple-responsive materials.

Two hydrogen (H)-bond donors, phenol and l-threonine, were added into the aqueous solutions containing crystalline micelles of a poly(ε-caprolactone)-b-poly(ethylene oxide) (PCL-b-PEO) block copolymer, respectively. Dynamic light scattering (DLS) characterization showed that the micellar size became smaller after addition of phenol. Transmission electron microscopy (TEM) results revealed that the long crystalline cylindrical micelles formed in the neat aqueous solution were fragmented into short cylinders and even quasi-spherical micelles, as the phenol concentration increased. By contrast, the spherical PCL-b-PEO crystalline micelles could be transformed into short cylinders and then long cylinders after addition of l-threonine. Reversible morphological transformation was realized for the PCL-b-PEO crystalline micelles by adding these two H-bond donors alternately. It is confirmed that both phenol and l-threonine could form H-bonds with PEO. We proposed that, the micellar corona was swollen by phenol, leading to fragmentation of the micellar core, whereas the PEO blocks in the micellar corona was dynamically cross-linked by l-threonine beacuse of its multiple H-bond-donation groups, resulting in a smaller reduced tethering density.

4-(2-Pyridylazo)-resorcinol (PAR) functionalized thermosensitive ionic microgels (PAR-MG) were synthesized by a one-pot quaternization method. The PAR-MG microgels were spherical in shape with radius of ca. 166.0 nm and narrow size distribution and exhibited thermo-sensitivity in aqueous solution. The PAR-MG microgels could optically detect trace heavy metal ions, such as Cu2+, Mn2+, Pb2+, Zn2+, and Ni2+, in aqueous solutions with high selectivity and sensitivity. The PAR-MG microgel suspensions exhibited characteristic color with the presence of various trace heavy metal ions, which could be visually distinguished by naked eyes. The limit of colorimetric detection (DL) was determined to be 38 nM for Cu2+ at pH 3, 12 nM for Cu2+ at pH 7, and 14, 79, 20, and 21 nM for Mn2+, Pb2+, Zn2+, and Ni2+, respectively, at pH 11, which was lower than (or close to) the United States Environmental Protection Agency standard for the safety limit of these heavy metal ions in drinking water. The mechanism of detection was attributed to the chelation between the nitrogen atoms and o-hydroxyl groups of PAR within the microgels and heavy metal ions.Keywords: 4-(2-pyridylazo)-resorcinol; heavy metal ion; ionic microgels; nanomolar level; optical detection;

Degradable thermosensitive ionic microgels were synthesized via surfactant-free emulsion polymerization (SFEP) of N-isopropylacrylamide (NIPAm) and 1-vinylimidazole (VIM) at 70 °C with degradable 1,4-phenylene bis(4-bromobutanoate) or 1,6-hexanediol bis(2-bromopropionate) as quaternized cross-linkers. VIM could be quaternized by 1,4-phenylene bis(4-bromobutanoate) or 1,6-hexanediol bis(2-bromopropionate), leading to the formation of degradable cross-linking network and ionic microgels. Combined techniques of transmission electron microscopy (TEM), dynamic light scattering (DLS), electrophoretic light scattering (ELS), UV–vis spectroscopy, FT-IR spectra, and gel permeation chromatography (GPC) were employed to systematically investigate the sizes, morphologies, and properties of the obtained microgels before and after degradation as well as the degradation mechanism. The obtained microgels were spherical in shape with narrow size distribution and exhibited thermosensitive behavior and controllable degradation. The disintegration of the microgels was confirmed to be resulted from the hydrolysis of ester bonds of the cross-linkers. The degradation rate of the obtained microgels could be regulated by tuning the pH value of microgel suspensions. The PNI-Ph series of microgels fabricated with 1,4-phenylene bis(4-bromobutanoate) as the cross-linking agent could gradually degrade even in neutral solution with lifetimes of 44–53 h, depending on the quaternization ratio. The degradation of PNI-Ph series of microgels experienced two reaction processes, that is, the hydrolysis of ester bonds of the cross-linkers and the oxidation of generated hydroquinone to form benzoquinone. It was also demonstrated that different silica nanostructures could be fabricated by using such degradable thermosensitive ionic microgels as the template at various temperatures.

The novel microgels, poly[di(ethylene glycol) methyl ether methacrylate-co-2-methoxyethyl acrylate] poly(DEGMMA-co-MEA) microgels, were synthesized. The poly(DEGMMA-co-MEA) microgels were thermo-sensitive and exhibited a volume phase transitive temperature (VPTT) of 14–22 °C. The incorporation of hydrophobic comonomer MEA shifted the VPTT of poly(DEGMMA-co-MEA) microgels to lower temperatures. The interfacial interaction of poly(DEGMMA-co-MEA) microgels and three model proteins, namely fibrinogen, bovine serum albumin and lysozyme, was investigated by quartz crystal microbalance (QCM). An injection sequence of “microgel-after-protein” was then established for the real-time study of the interaction of proteins and the microgels at their swollen and collapsed states by using QCM technique. The results indicated that the interfacial interaction of poly(DEGMMA-co-MEA) microgels and adsorbed protein layers was mainly determined by the electrostatic interaction. Because poly(DEGMMA-co-MEA) microgels were negatively charged in Tris-HCl buffer solution (pH = 7.4), the microgels did not adsorb on negatively charged fibrinogen and bovine serum albumin layers but strongly adsorbed on positively charged lysozyme layer. Stronger interaction between lysozyme and the microgels at collapsed state (i.e. at 37 °C) was observed. Furthermore, the incorporation of MEA might weaken the interaction between poly(DEGMMA-co-MEA) microgels and proteins.

A type of thermosensitive ionic microgel was successfully prepared via the simultaneous quaternized cross-linking reaction during the surfactant-free emulsion copolymerization of N-isopropylacrylamide (NIPAm) as the main monomer and 1-vinylimidazole or 4-vinylpyridine as the comonomer. 1,4-Dibromobutane and 1,6-dibromohexane were used as the halogenated compounds to quaternize the tertiary amine in the comonomer, leading to the formation of a cross-linking network and thermosensitive ionic microgels. The sizes, morphologies, and properties of the obtained ionic microgels were systematically investigated by using transmission electron microscopy (TEM), dynamic and static light scattering (DLS and SLS), electrophoretic light scattering (ELS), thermogravimetric analyses (TGA), and UV–visible spectroscopy. The obtained ionic microgels were spherical in shape with narrow size distribution. These ionic microgels exhibited thermosensitive behavior and a unique feature of poly(ionic liquid) in aqueous solutions, of which the counteranions of the microgels could be changed by anion exchange reaction with BF4K or lithium trifluoromethyl sulfonate (PFM-Li). After the anion exchange reaction, the ionic microgels were stable in aqueous solution and could be well dispersed in the solvents with different polarities, depending on the type of counteranion. The sizes and thermosensitive behavior of the ionic microgels could be well tuned by controlling the quaternization extent, the type of comonomer, halogenated compounds, and counteranions. The ionic microgels showed superior swelling properties in aqueous solution. Furthermore, these ionic microgels also showed capabilities to encapsulate and release the anionic dyes, like methyl orange, in aqueous solutions.Keywords: anion exchange; encapsulation and release; ionic; microgels; quaternization cross-linking; thermosensitive;

The effects of concentration, relative block length and environmental temperature as well as the surface chemical and wetting properties of solid substrates on the adsorption behaviors and mechanisms of a series of pentablock terpolymer poly(N-isopropylacrylamide)x-poly(ethylene oxide)20-poly(propylene oxide)70-poly(ethylene oxide)20-poly(N-isopropylacrylamide)x (PNIPAmx-PEO20-PPO70-PEO20-PNIPAmx or PNIPAmx-P123-PNIPAmx) with x of 10, 63 and 97 on gold were studied by using a quartz crystal microbalance (QCM) technique. It was found that increasing the solution concentration did not alter the adsorption mechanism of thickness growth mode but increase the adsorption amount of PNIPAm97-P123-PNIPAm97 on a bare gold substrate at 20 °C. Increasing the length x of PNIPAm block decreased the adsorption rate constant and shifted the adsorption mechanism from the densification adsorption process for PNIPAm10-P123-PNIPAm10 to the thickness growth mode for PNIPAm63-P123-PNIPAm63 and PNIPAm97-P123-PNIPAm97 on bare (unmodified) gold substrate at 20 °C. The adsorption mechanisms of PNIPAm97-P123-PNIPAm97 at 20 °C on the hydrophobic and hydrophilic gold surfaces were the thickness growth mode and densification adsorption process, respectively. A complex adsorption behavior with large adsorption amounts was observed at the lower critical solution temperature (LCST) of PNIPAm block, i.e. 34.7 °C, for the adsorption of PNIPAm97-P123-PNIPAm97 not only on hydrophobic gold substrates but also on hydrophilic gold substrates. The adsorption mechanism of PNIPAm97-P123-PNIPAm97 micelles at 45 °C was the densification adsorption process regardless of the surface wetting and chemical properties of gold substrate. Overall, the adsorption behavior and mechanism of PNIPAmx-P123-PNIPAmx pentablock terpolymers were mainly determined by the interactions of the pentablock terpolymers with different chain conformations in dilute aqueous solutions at various temperatures and the gold substrates with surface wetting and chemical properties.

The biocompatible poly(N-vinylpyrrolidinone) (PNVP) microgels were synthesized via surfactant free emulsion polymerization with N-vinylpyrrolidinone (NVP) as the monomer and ethylene glycol dimethacrylate (EGDMA) as the cross-linker at 60 °C. The obtained PNVP microgels are spherical in shape with hydrodynamic diameter of approximately 200 nm and narrow size distribution. The PNVP microgels show rough surfaces due to the different reaction rates of monomer NVP and cross-linker EGDMA. The obtained PNVP microgels could well disperse in phosphate-buffered saline (PBS) solution with long-term stability, which make them candidates for bioapplications. The results of 3-(4,5-dimethyl-2-thiazolyl)-2,5-diphenyltetrazolium bromide (MTT) tests indicated that the PNVP microgels are biocompatible with low toxicity even at a concentration of 1000 μg/mL. By labeling the PNVP microgels with fluorescein comonomer, it was demonstrated that the PNVP microgels could be uptaken by human embryonic kidney 293 (HEK-293) cells. The experimental results indicated that the release of isoniazid (INH, the hydrophilic model drug) could be well described by a Fickian release, whereas the microgels exhibited burst release for 5-fluorouracil (5-fu, the hydrophobic model drug).

P(TMSPMA-co-OEGMA) nanocapsules with controllable oligo(ethylene glycol) (OEG) densities and robustly cross-linked structures were successfully fabricated from the cross-linkable copolymer, poly[3-(trimethoxysilyl)propyl methacrylate-co-oligo(ethylene glycol) methacrylate] (P(TMSPMA-co-OEGMA)). The densities of OEG segments of the resultant P(TMSPMA-co-OEGMA) nanocapsules could be easily controlled by tuning the OEGMA contents of copolymer P(TMSPMA-co-OEGMA). The microenvironments of the P(TMSPMA-co-OEGMA) nanocapsules were determined to be hydrophobic. It was demonstrated that hydrophobic pyrene could be in situ loaded into the P(TMSPMA-co-OEGMA) nanocapsules during the fabrication procedure. The release rates of pyrene from the P(TMSPMA-co-OEGMA) nanocapsules were dependent on the contents of OEGMA, indicating that the permeation properties of P(TMSPMA-co-OEGMA) nanocapsules could be tuned by varying the cross-linked densities of the nanocapsule walls. It was further demonstrated that other functional groups could be easily incorporated into the resultant polymer nanocapsules by using the similar procedure. The preparation of polymer nanocapsules with various functionalities and robustly cross-linked walls without any further post modification process, any sacrificial core and surfactant would be beneficial from scientific and technical point of views.Keywords: controllable; cross-linked walls; oligo(ethylene glycol) densities; permeation properties; polymer nanocapsules;

The solution behaviors and microstructures of poly(N-isopropylacrylamide)x-poly(ethylene oxide)20-poly(propylene oxide)70-poly(ethylene oxide)20-poly(N-isopropylacrylamide)x (PNIPAmx-PEO20-PPO70-PEO20-PNIPAmx or PNIPAmx-P123-PNIPAmx) pentablock terpolymers with various PNIPAm block lengths in dilute and concentrated aqueous solutions were investigated by micro-differential scanning calorimetry (micro-DSC), static and dynamic light scattering (SLS & DLS), and synchrotron small angle X-ray scattering (SAXS). Two lower critical solution temperatures (LCSTs) were observed for PNIPAmx-P123-PNIPAmx pentablock terpolymers in dilute solutions, which corresponded to LCSTs of PPO and PNIPAm blocks, respectively. The LCST of PPO block shifted from 24.4 °C to 29 °C when the length x of PNIPAm block increased from 10 to 97. The LCST of PNIPAm is around 34.5 °C–35.3 °C and less dependent on the block length x. The PNIPAmx-P123-PNIPAmx pentablock terpolymers formed “associate” structures and micelles with hydrophobic PNIPAm and PPO blocks as cores and soluble PEO blocks as coronas in dilute aqueous solutions at 20 °C and 40 °C, respectively, regardless of the relative lengths of PNIPAm, PPO and PEO blocks. The size of “associate” structures of PNIPAmx-P123-PNIPAmx pentablock terpolymers at 20 °C increased with increasing the length of PNIPAm block. The microstructures of PNIPAmx-P123-PNIPAmx hydrogels formed in concentrated aqueous solutions (40 wt%) were strongly dependent on the environmental temperatures and relative lengths of PNIPAm, PPO and PEO blocks as revealed by SAXS. Increasing the length of PNIPAm block weakened the order structures of PNIPAmx-P123-PNIPAmx hydrogels. The microstructures of PNIPAmx-P123-PNIPAmx hydrogels changed from mixed fcc and hex structures for PNIPAm10-P123-PNIPAm10 to isotropic structure for PNIPAm97-P123-PNIPAm97. Increasing temperature led to the transition from mixed hex and fcc structure to pure hex structure for PNIPAm10-P123-PNIPAm10 hydrogel at temperature above the LCSTs.

P(NIPAm-co-TMSPMA)/Silica hybrid microgels were prepared by in-situ sol–gel process of tetraethyl orthosilicate (TEOS) in the presence of thermo-sensitive P(NIPAm-co-TMSPMA) microgels, which were synthesized via surfactant-free emulsion copolymerization (SFEP) of N-isopropylacrylamide (NIPAm) and 3-(trimethoxysilyl)propylmethacrylate (TMSPMA). At preparation temperature above the volume phase transition temperatures (VPTT) of P(NIPAm-co-TMSPMA) microgels, i.e. 50 °C, the silica nanoparticles could not penetrate into the collapsed microgels but uniformly covered on the surface of microgels and the obtained P(NIPAm-co-TMSPMA)/Silica hybrid microgels had the raspberry-like structures. Whereas, at preparation temperature below the VPTT, i.e. 25 °C, the silica nanoparticles were uniformly distributed inside the swelled microgels and the resultant P(NIPAm-co-TMSPMA)/Silica hybrid microgels exhibited uniform organic–inorganic hybrid structures. The presence of silica nanoparticles restricted the swelling–deswelling capability of P(NIPAm-co-TMSPMA)/Silica hybrid microgels and also prevented the merging of hybrid microgels during drying. Macroporous silica with ordered macropores could be easily fabricated by selectively calcinating the organic microgel component after the assembly of the P(NIPAm-co-TMSPMA)/Silica hybrid microgels.Highlights► Thermo-sensitive P(NIPAm-co-TMSPMA)/Silica hybrid microgels were prepared. ► The structures and properties of the hybrid microgels could be tuned. ► Interfacial silica nanoparticles prevent merging of hybrid microgels during drying. ► Macroporous silica with ordered macropores was fabricated from the hybrid microgels.

Organic–inorganic hybrid mesoporous polymers were successfully synthesized by using a template-directed free radical polymerization technique in aqueous solution at 0–5 °C with oxidative complexes as self-decomposed soft templates. The oxidative complexes ((CTA)2S2O8), which were formed between anionic oxidant (S2O82–) and cationic surfactant (cetyltrimethylammonium bromide, CTAB) at 0–5 °C, can be automatically decomposed due to the reduction of S2O82–. No additional treatment was needed to remove the templates. The reactive functional monomer, 3-(trimethoxysilyl)propyl methacrylate (TMSPMA), was used as main monomer. Styrene was used as the comonomer. With simultaneous free radical copolymerization of TMSPMA and styrene, condensation of methoxysilyl groups, and the self-decomposition of (CTA)2S2O8, organic–inorganic hybrid mesoporous polymers were successfully obtained. The mesoporous structures and morphologies of the resultant hybrid mesoporous polymers were found to be strongly dependent on the feed amounts of TMSPMA and styrene. In the absence of styrene, the hybrid polymer PTMSPMA exhibited mesh-like bicontinuous structures with mesopores and high surface area (335 m2/g). With the incorporation of styrene, mesoporous nanoparticles were obtained. The surface areas of the mesoporous nanoparticles decreased with the increase of styrene contents. The adsorption capabilities of such mesoporous polymers for organic dye (Congo red) and protein (bovine serum albumin) were also studied.

A facile method was developed for the fabrication of polymer nanocapsules with organic–inorganic hybrid walls and controllable morphologies from a cross-linkable polymer, poly[3-(trimethoxysilyl)propyl methacrylate] (PTMSPMA). With the combination of emulsion, hydrolysis, and condensation reaction as well as the internal phase separation, cross-linked PTMSPMA nanocapsules with classic hollow structures, collapsed hollow structures with Kippah, and multi-fold morphologies could be successfully obtained by simply mixing the toluene solution of PTMSPMA with water under vigorous stirring for 48 h at different temperatures. The hydrolysis and condensation of methoxysilyl groups resulted in the phase separation of PTMSPMA inside the toluene droplets and the migration of PTMSPMA to the interface of toluene and water. The cross-linking reaction of methoxysilyl groups further fixed the interfacial phase of PTMSPMA, leading the formation of PTMSPMA nanocapsules with robust cross-linked organic–inorganic hybrid walls. Such nanocapsules with robust cross-linking structures may find potential applications for the encapsulations of many functional species.

The adsorptions of a double thermo-sensitive pentablock terpolymer, PNIPAm110-PEO100-PPO65-PEO100-PNIPAm110 (PNIPAm110-F127-PNIPAm110), on hydrophobic gold surfaces at various temperatures were investigated by using quartz crystal microbalance (QCM), atomic force microscopy (AFM), and ellipsometry. The experimental results indicated that the adsorption kinetics, adsorbed amounts and morphologies of the adsorbed terpolymer layers were strongly dependent on the temperatures, which could be correlated with the chain conformation of PNIPAm110-F127-PNIPAm110 in aqueous solution. At the low critical solution temperature (LCST) of PPO block (i.e. 31 °C), PNIPAm110-F127-PNIPAm110 was adsorbed onto hydrophobic gold surface via a two-step adsorption process and adopted a brush-like conformation. While at the LCST of PNIPAm block (i.e. 34 °C), a complex multistep adsorption process was observed, which resulted in a large adsorption amount. By comparing with the adsorption behavior of F127 at the corresponding temperature, it was deduced that the large adsorption amount obtained at 34 °C was mainly attributed to the presence of PNIPAm blocks. The premicellar associative adsorption was thought to play an important role for the observation of this unexpected adsorption behavior at 34 °C, leading to the large adsorption amount and large aggregate structures as revealed by AFM.Graphical abstract

The influences of pH and NaCl concentration of dipping solutions and the pH and NaCl concentration of disintegration solutions on the disintegration behaviors of poly(4-vinylpyridiniomethanecarboxylate) (PVPMC)/poly(sodium 4-styrenesulfonate) (PSS) (PVPMC/PSS) multilayer films were investigated by ultraviolet–visible spectroscopy (UV–vis), Fourier transform infrared spectroscopy (FT-IR), quartz crystal microbalance (QCM) and atomic force microscopy (AFM). It was found that the disintegration rates and degrees of PVPMC/PSS multilayer films in neutral water could be well controlled by changing pH of dipping solutions and immersion time during the disintegration process. Furthermore, PVPMC/PSS multilayer films could be disintegrated completely and rapidly in pH 8 alkali solution or physiological condition (i.e., 0.15 M NaCl solution). The controllable disintegration of PVPMC/PSS multilayer films was then utilized to fabricate PEC/PSS free-standing multilayer films, in which PEC was a positively charged polyelectrolyte complex made from excessive poly(diallyldimethylammonium) (PDDA) and PSS. The experimental results indicated that the disintegration rates of PVPMC/PSS sacrificial sublayer strongly affected the integrity of the resultant PEC/PSS free-standing multilayer films. Only free-floating PEC/PSS was released from neutral water by disintegrating PVPMC/PSS multilayer sublayers. However, large size flat and tube-like PEC/PSS free-standing multilayer films with good mechanical properties were obtained facilely from pH 8 alkali solution and 0.15 M NaCl solution, respectively. The preparation of such free-standing films at physiological condition may be useful in the biological or medical application.Graphical abstractControllable disintegration of polycarboxybetaine multilayer films (PVPMC/PSS) and fabrication of tube-like free-floating films from normal saline solution.Research highlights► The disintegration rate and degree of PVPMC/PSS multilayer films can be well controlled. ► PVPMC/PSS multilayer films could be completely disintegrated in neutral water within 30 min. ► PVPMC/PSS multilayer films could be rapidly disintegrated in pH 8 alkali solution or 0.15 M NaCl aqueous solution within 2 min. ► Large size flat and tube-like PEC/PSS free-standing multilayer films with good mechanical properties were successfully prepared from 0.15 M NaCl aqueous solution.

A methodology is described for the preparation of thermosensitive organic–inorganic hybrid microgels with functional Fe3O4 nanoparticles as the crosslinker and N-isopropylacrylamide (NIPAm) as the monomer. Magnetic Fe3O4 nanoparticles were first prepared via a redox reaction in aqueous solution and then modified with 3-(trimethoxysilyl)propylmethacrylate (TMSPMA) via the silanization. The bonding of multiple TMSPMA monomers on the surface of Fe3O4 nanoparticles renders them as crosslinker. Surfactant-free emulsion polymerization (SFEP) of NIPAm was then carried out with the presence of TMSPMA-modified Fe3O4 nanoparticles at 70 °C in aqueous solution, leading to the formation of thermosensitive PNIPAm-Fe3O4 hybrid microgels crosslinked with Fe3O4 nanoparticles. Transmission electron microscopy (TEM), scanning electron microscopy (SEM), energy dispersive X-ray analysis (EDX), thermogravimetric analysis (TGA), dynamic light scattering (DLS) and physical properties measurement system (PPMS) were then used to characterize the resultant hybrid microgels. The experimental results show that the PNIPAm-Fe3O4 hybrid microgels were spherical in shape with a large size distribution and the Fe3O4 nanoparticles were randomly distributed inside the microgels. The PNIPAm-Fe3O4 hybrid microgels were thermosensitive, exhibiting a reversible swelling and deswelling behavior as a function of temperature. The PNIPAm-Fe3O4 hybrid microgels also show superparamagnetic behavior at room temperature (300 K).

Utilizing the hydrolysis and condensation of the methoxysilyl moieties, organic-inorganic hybrid poly(N-isopropylacrylamide-co-acrylamide-co-3-(trimethoxysilyl)propylmethacrylate) P(NIPAM-co-AM-co-TMSPMA) microgels were prepared via two different methods. The first method was that the microgels were post-fabricated from the crosslinkable linear P(NIPAM-co-AM-co-TMSPMA) terpolymer aqueous solutions above the lower critical solution temperature (LCST) of the terpolymer. For the second method, the microgels were directly synthesized by conventional surfactant free emulsion copolymerization of NIPAM, AM, and TMSPMA. The hydrodynamic diameter and stability of the resultant P(NIPAM-co-AM-co-TMSPMA) microgels strongly depend on the pH and temperature of the microgel aqueous solution. The hydrodynamic diameters of the microgels decreased with increasing the measuring temperature. The phase transition temperature of the microgels was found to be around 34°C, which was independent of the initial terpolymer concentration and shifted to lower temperature with increasing the preparation temperature. Increasing the initial amount of AM will enhance the instability of the microgels at high pH values. Moreover, the P(NIPAM-co-AM-co-TMSPMA) microgels obtained from the linear terpolymer had more homogeneous microstructures as compared with the corresponding NIPAM/AM/TMSPMA microgels prepared by one step emulsion copolymerization as revealed by light scattering measurements.

A novel copolymer P(MBTVBC-co-VIM) was designed and successfully synthesized for the fabrication of copolymer-coated QCM sensors to detect the heavy metal ions in aqueous solution. The copolymer P(MBTVBC-co-VIM) contains many nitrogen (N) and sulfur (S) atoms in the side groups as electron donors, which can easily form complexes with heavy metal ions. The strong interaction between the S atom and Au electrode of quartz crystal further assures the stability of copolymer thin films on the quartz crystal surface in aqueous media. The QCM results indicated that the P(MBTVBC-co-VIM)-coated sensor exhibited high sensitivity, stability and selectivity for the detection of Cu2+ in aqueous solution. The lowest detection limit can reach 10 ppm Cu2+ in aqueous solution, which resulted in the frequency shift of 3.0 Hz (ΔF3/3). The P(MBTVBC-co-VIM)-coated QCM sensors had porous surface morphologies as revealed by AFM investigation. Such porous structures enhanced the surface areas of the copolymer thin films, which increased the contacting probability of N and S atoms with heavy metal ions in solution and improved the detection sensitivity of the copolymer-coated QCM sensors.

An amphiphilic multiblock copolymer, [poly(4-vinylpyridine)-b-polystyrene-b-poly(4-vinylpyridine)]n (P4VP-PS-P4VP)n bearing trithiocarbonate moieties (–S–CS–S–), was used as capping agent to fabricate the functional copolymer-capped Au nanoparticles. Due to the amphiphilic character of the multiblock copolymer, the (P4VP-PS-P4VP)n-capped Au nanoparticles were able to be entrapped and hence form a stable monolayer thin film at the (DMF–H2O)/diethyl ether interface. Note that DMF–H2O is a good mixed solvent for P4VP and a nonsolvent for PS, whereas diethyl ether is a good solvent for PS and a nonsolvent for P4VP. A similar procedure can be applied to prepare monolayer thin film of the (P4VP-PS-P4VP)n-capped Ag nanoparticles at the (DMF–H2O)/diethyl ether interface, which exhibits enhanced surface Raman signal. We further demonstrate that the stable monolayer of (P4VP-PS-P4VP)n-capped Au nanorods can also be fabricated by using the ligand-exchange method.

The self-assembly and disintegration behavior of polyzwitterion, poly(4-vinylpyridiniomethanecarboxylate) (PVPMC), and negatively charged polyelectrolyte, poly(acrylic acid) (PAA), layer-by-layer (LbL) multilayer films were investigated in detail by using UV-vis absorption spectroscopy, quartz crystal microbalance (QCM) and atomic force microscopy (AFM). The results indicated that the PVPMC/PAA multilayer films grew linearly with increasing bilayer number. The disintegration rate of PVPMC/PAA multilayers could be well controlled by varying the concentration of salt in aqueous solution. It was found that PVPMC/PAA multilayer films could be completely disintegrated in 0.9% normal saline solution within 15 min. Such controllable disintegration behavior rendered the PVPMC/PAA multilayer as an excellent sacrificial sublayer for fabricating free-standing LbL multilayer films. Free-standing multilayer films were then successfully fabricated by LbL self-assembly of positively charged polyelectrolyte complex (PEC), made from poly(diallyldimethylammonium) (PDDA) and poly(sodium 4-styrenesulfonate) (PSS), and negatively charged PSS with PVPMC/PAA as a sacrificial sublayer, which was disintegrated in 0.9% normal saline solution. The obtained free-standing films had good mechanical properties with 24.1 MPa tensile strength at break and 0.56 GPa Young's modulus.

A linear amphiphilic multiblock copolymer (PNIPAm-PtBA-PNIPAm)m was successfully synthesized by a two-step reversible addition–fragmentation transfer (RAFT) polymerization in the presence of a cyclic trithiocarbonate as RAFT agent. The micelle behavior of (PNIPAm-PtBA-PNIPAm)m multiblock copolymer in aqueous solution was then investigated by means of normal TEM, cryo-TEM, static and dynamic light scattering. The morphology, size, and size distribution of (PNIPAm-PtBA-PNIPAm)m micelles were found to be dependent on the initial concentration of multiblock copolymer in THF. Spherical micelles, associated aggregates of spherical micelles, cage-like micelles, layered structures, and vesicular micelles were experimentally observed, which were in good agreement with the prediction of theory and simulations on linear amphiphilic multiblock copolymer in selective solvent. The (PNIPAm-PtBA-PNIPAm)m micelles also exhibit thermo-sensitive behavior in aqueous solution because of the PNIPAm blocks.

The double thermosensitive and narrow dispersed PNIPAm110-PEO100-PPO65-PEO100-PNIPAm110 pentablock terpolymer was synthesized by the typical atomic transfer radical polymerization (ATRP) method with N-isopropylacrylamide (NIPAm) as the monomer and modified poly(ethylene oxide)100−poly(propylene oxide)65−poly(ethylene oxide)100 (PEO100-PPO65-PEO100) block copolymer as the macroinitiator. Microdifferential scanning calorimetry (micro-DSC) data showed that the pentablock terpolymer exhibited two low critical solution temperatures (LCSTs) at 31 and 34 °C in the aqueous solution, which can be attributed to the thermal phase transition of the PPO block and PNIPAm block, respectively. The chain conformation of the pentablock terpolymer in aqueous solution was then studied in detail by using a combination of static and dynamic laser light scattering (SLS-DLS). The SLS-DLS results indicated that the loose “associates” and single coil chains coexisted in the aqueous solution at the low temperature, where the PEO, PPO, and PNIPAm blocks were soluble in water. These phenomena were inconsistent with those observed in other PEO-containing block copolymer systems. At the high temperature above the LCSTs of PPO and PNIPAm blocks (38−60 °C), the pentablock terplymer chains formed large and stable core−shell micelles with collapsed PPO and PNIPAm cores and swollen PEO shells. The TEM and cryo-TEM experiments provided visual images, which confirmed the formation of loose “associates” at 21 °C and large stable micelles at 38 °C. Increase of concentration hindered the formation of “associate” at low temperature, but the micelles formed at high temperature were almost independent of the solution concentration investigated.

A novel method for speedy fabrication of free-standing layer-by-layer (LbL) multilayer films in salt free media, and without the need for a sacrificial sublayer is described by using two different polyelectrolyte complex (PEC) nanoparticles as LbL self-assembly building blocks. Negatively charged polyelectrolyte complex particles (PEC−) consisting of poly(diallyldimethylammonium chloride)/sodium carboxymethyl cellulose (PDDA/CMCNa), and positively charged polyelectrolyte complex particles (PEC+) consisting of PDDA/poly(sodium-p-styrenesulfonate) (PDDA/PSSNa) were prepared and characterized by FT-IR, zeta-potential (ζ potential) and transmission electron microscopy (TEM). The LbL self-assembly of PEC+/PEC− and PDDA/PEC− was followed by quartz crystal microbalance (QCM), optical transmittance, UV-vis absorption spectroscopy and atomic force microscopy (AFM). QCM results show that the thickness growth rate of the PEC+/PEC− pair is 9 times faster than that of the PDDA/PEC− pair and this result is also supported by optical transmittance and UV-vis absorption. A robust free-standing multilayer film of (PEC+/PEC−)25 can be easily peeled off from the substrate after being cross-linked in 3.5 wt% glutaraldehyde (GA) (80 °C, 50mins). Field emission electron scanning microscopy (FESEM) indicates that both the surface and cross-section of the multilayer film display layered structures. Furthermore, multiwall carbon nanotubes (MWCNTs) can also be uniformly incorporated into the free-standing LbL multilayer film by pre-incorporating MWCNTs into PEC− particles. The experimental results show that using oppositely charged PEC particles as LbL assembly components is a speedy and convenient method to fabricate free-standing LbL multilayer films either with or without nanofillers.

A quartz crystal microbalance (QCM) consists of a resonator, which measures the resonance frequency of the quartz slab. When coupled with a network analyzer or coupled with impulse excitation technology, QCM gives additional impedance or dissipation information, respectively. This report provides a set of equations that bring the QCM community a convergence of the dissipation and impedance analysis. Equations derived from the complex frequency shift were applied to quantitatively analyze the dissipation data of polymer brushes obtained from QCM-D. The obtained viscoelastic properties of polymer brushes were then compared with those obtained by the Voigt model method. We believe that these equations will be useful in quantitative studies of interfacial phenomena accompanied with mass or viscoelasticity changes.

This paper reports a facile synthesis of thermosensitive Fe3O4 nanoparticles coated with poly(N-isopropylacrylamide)-related copolymer in aqueous solution. A functional monomer, namely 3-(trimethoxysilyl)propylmethacrylate (TMSPMA) with methoxysilyl group (-SiOCH3) was copolymerized with N-isopropylacrylamide (NIPAm) to yield a thermo-sensitive copolymer, poly[N-isopropylacrylamide-co-3-(trimethoxysilyl)propylmethacrylate] [P(NIPAm-co-TMSPMA)]. Such copolymer hence possesses the capability for the silanization of the Fe3O4 nanoparticles. Thermo-sensitive P(NIPAm-co-TMSPMA) capped Fe3O4 nanoparticles were then easily obtained by in situ synthesis of Fe3O4 nanoparticles in the presence of the copolymer in aqueous solution. The Fe3O4 nanoparticles have mean diameters around 12 nm. The P(NIPAm-co-TMSPMA) capped Fe3O4 nanoparticles show thermo-sensitive properties. With thick grafted P(NIPAm-co-TMSPMA) layer, the thermo-sensitive behavior of the composite Fe3O4 nanoparticles is reversible. For thinner grafted copolymer layer, it is irreversible. The P(NIPAm-co-TMSPMA) capped Fe3O4 nanoparticles also exhibit superparamagnetic behavior. A linear relation between the saturation magnetization Ms of copolymer-coated Fe3O4 nanoparticles and the weight percent of grafted copolymer layer is first experimentally observed. With increasing the amount of grafted copolymer, Ms of the Fe3O4 nanoparticles decreases linearly.

Hollow silica nanospheres with mesoporous shells were successfully fabricated with a new one-pot strategy by using a thermosensitive polymer, poly(N-isopropylacrylamide) (PNIPAm), as a reversible template without the need of further calcination or chemical etching. By simply regulating the solution temperature with respect to the lower critical solution temperature (LCST) of PNIPAm, PNIPAm chains can reversibly form aggregates or dissolve in aqueous solution. The thermosensitive character makes PNIPAm chains behave as soft templates for the formation of core−shell silica nanospheres at elevated temperature (>LCST), and they will then diffuse out of the cores at lower temperature (<LCST), leading to the formation of hollow silica nanospheres. The TEM, SEM, XRD, and N2 adsorption−desorption results indicate that the shells of such hollow silica nanospheres also contain large quantities of irregular mesopores. This new strategy was also tested with another thermosensitive polymer, poly(vinyl methyl ether) (PVME). However, only solid silica nanospheres with a broad size distribution were obtained when PVME was used. We speculated on the possible formation mechanism of hollow silica nanospheres with PNIPAm templates. The effects of the initial concentration of PNIPAm, the molecular weight of PNIPAm, and the pretreatment of silica precursor on the morphology and size of the resultant hollow silica nanospheres were also investigated. The PNIPAm soft templates were confirmed to be recyclable.

Three PLAx−PEG44 diblock copolymers with fixed hydrophilic PEG block and various lengths of hydrophobic PLA block were synthesized via ring-opening polymerization. The micelle formation and micelle morphologies of the PLAx−PEG44 copolymers in selective solvents were investigated by using cryogenic transmission electron microscopy (cryo-TEM) and light scattering techniques. PLAx−PEG44 diblock copolymers in aqueous solution form various micelle structures when increasing x from 56 to 212 in order to minimize the overall free energy of the systems. The micelles transform from wormlike micelles for PLA56−PEG44 into vesicles for PLA212−PEG44. Interestingly, vesicular structures with various morphologies, such as large polydisperse vesicles, entrapped vesicles, hollow concentric vesicles, ellipsoidal vesicles, open bending lamellae, vesicles with irregular shapes, etc., were found to be coexisting in PLA212−PEG44 THF/H2O and PLA212−PEG44 dioxane/H2O mixtures with 30 and 40 wt % water contents. Toroid micelles with new morphologies were also observed. These observations indicate that the vesicular micelles of amphiphilic block copolymers in mixed solvents fluctuate from time to time and are able to kinetically form different shapes of morphologies in the solutions. The membrane fluctuation of PLA212−PEG44 vesicles in mixed solvent was verified by dynamic light scattering.

Silver nanoparticles (Ag NPs) stabilized by a thermoresponsive polymer, poly(N-isopropylacrylamide) (PNIPAM), have been synthesized by the reduction of silver ions with NaBH4 in aqueous solutions. The obtained Ag NPs are very stable at room temperature due to the extended coil conformation of the PNIPAM chain at temperatures below its volume phase transition temperature (∼32 °C). At higher temperatures (such as 45 °C) above the phase transition of PNIPAM, only minute aggregation between Ag NPs was observed, showing that the collapsed PNIPAM chains still retain the ability to stabilize Ag NPs. The PNIPAM-stabilized Ag NPs were then characterized as a function of the thermal phase transition of PNIPAM by UV–vis spectroscopy, dynamic light scattering, transmission electron microscopy, and cyclic voltammeter. Consistent results were obtained showing that the phase transition of PNIPAM has some effect on the optical properties of Ag NPs. Switchable electrochemical response of the PNIPAM-stabilized Ag NPs triggered by temperature change was observed.Thermo-responsive poly(N-isopropylacrylamide) (PNIPAM)-stabilized Ag nanoparticles (Ag NPs) were successfully synthesized by simply reducing the silver salt in the PNIPAM aqueous solution. The PNIPAM-stabilized Ag NPs show tunable optical properties, which is fully reversible dependence on the phase transition of PNIPAM. The Ag NPs only show electrochemically active when the PNIPAM chains collapse. These unique properties render PNIPAM-stabilized Ag NPs as potential electrode coating materials, of which the electrochemical properties could be switched by the environmental temperature.

By utilizing the hydrolysis and condensation of the methoxysilyl groups, thermo-sensitive organic/inorganic hybrid poly[N-isopropylacrylamide-co-3-(trimethoxysilyl)propylmethacrylate] [P(NIPAm-co-TMSPMA)] microgels were successfully prepared via two different methods without addition of any surfactant. First, the microgels were obtained by a two-step method; that is, the linear copolymer P(NIPAm-co-TMSPMA) was first synthesized by free radical copolymerization, and the aqueous solution of the copolymer was then heated above its low critical solution temperature (LCST) to give colloid particles, which were subsequently cross-linked via the hydrolysis and condensation of the methoxysilyl groups to form the microgels. Second, the microgels were also prepared via conventional surfactant-free emulsion polymerization (SFEP) of the monomers NIPAm and TMSPMA. TMSPMA can act as the cross-linkable monomer. No surfactant was involved in the preparation of the hybrid microgels. The obtained microgels were rather spherical and exhibited reversible thermo-sensitive behavior. The size, morphology, swellability, and phase transition behavior of the microgels were dependent on the initial copolymer or monomer concentration, preparation temperature, and the content of TMSPMA. The size of microgels obtained by SFEP was found to be more uniform than that by the two-step method. The hybrid microgels obtained by these two methods had more homogeneous microstructures than those prepared via conventional emulsion polymerization with chemical cross-linker N,N′-methylene-bisacrylamide.

We report on a facile method for fabricating thermosensitive organic/inorganic hybrid hydrogel thin films from a cross-linkable organic/inorganic hydrid copolymer, poly[N-isopropylacrylamide-co-3-(trimethoxysilyl)propylmethacrylate] [P(NIPAm-co-TMSPMA)]. Fourier transform infrared (FT-IR) spectra confirmed the formation of hybrid hydrogel thin films after hydrolysis of the methoxysilyl groups (Si−O−CH3) and subsequent condensation of the silanol groups (Si−OH). Atomic force microscopy (AFM) images revealed that the surface morphology of the hydrogel thin films depended on the supporting substrates. Microdomains were observed for the hydrogel thin films on a gold surface, which can be attributed to inhomogeneous network structures. The thermoresponsive swelling−deswelling behavior and the viscoelastic properties of the hydrogel thin films were investigated as a function of temperature (25–45 °C) by using a quartz crystal microbalance (QCM) operated in water. The high frequency shear modulus of the P(NIPAm-co-TMPSMA) hydrogel thin films was several hundred kilopascals.

Thermosensitive poly(VCL-4VP-NVP) ionic microgels were prepared by in situ quaternization crosslinking reaction during surfactant free emulsion polymerization (SFEP) with N-vinylcaprolactam (VCL) as the main monomer, 4-vinylpyridine (4VP) as the quaternizable co-monomer, N-vinyl-2-pyrrolidone (NVP) as the second co-monomer and 1,6-dibromohexane (6Br) as the quaternization crosslinker. The obtained ionic microgels were spherical in shape with a narrow size distribution and exhibited thermo-sensitive behavior. These ionic microgels showed low cytotoxicity at concentrations lower than 25 µg mL−1, excellent hemocompatibility at concentrations up to 1000 µg mL−1, and could be up taken into the cytoplasm regime of HEK-293 cells without entering the nucleus. It was found that these ionic microgels were suitable for the loading and sustained release of a nonsteroidal anti-inflammatory drug, diclofenac sodium (DS). The drug loading content (DLC) of DS in the microgels could reach ca. 12% with an encapsulation efficiency (EE) of up to 68%. Furthermore, 60% loaded DS could be sustainably released at 37 °C from the drug-loaded microgels within 400 min following a first-order exponential kinetics.

The solution behaviors and microstructures of poly(N-isopropylacrylamide)x-poly(ethylene oxide)20-poly(propylene oxide)70-poly(ethylene oxide)20-poly(N-isopropylacrylamide)x (PNIPAmx-PEO20-PPO70-PEO20-PNIPAmx or PNIPAmx-P123-PNIPAmx) pentablock terpolymers with various PNIPAm block lengths in dilute and concentrated aqueous solutions were investigated by micro-differential scanning calorimetry (micro-DSC), static and dynamic light scattering (SLS & DLS), and synchrotron small angle X-ray scattering (SAXS). Two lower critical solution temperatures (LCSTs) were observed for PNIPAmx-P123-PNIPAmx pentablock terpolymers in dilute solutions, which corresponded to LCSTs of PPO and PNIPAm blocks, respectively. The LCST of PPO block shifted from 24.4 °C to 29 °C when the length x of PNIPAm block increased from 10 to 97. The LCST of PNIPAm is around 34.5 °C–35.3 °C and less dependent on the block length x. The PNIPAmx-P123-PNIPAmx pentablock terpolymers formed “associate” structures and micelles with hydrophobic PNIPAm and PPO blocks as cores and soluble PEO blocks as coronas in dilute aqueous solutions at 20 °C and 40 °C, respectively, regardless of the relative lengths of PNIPAm, PPO and PEO blocks. The size of “associate” structures of PNIPAmx-P123-PNIPAmx pentablock terpolymers at 20 °C increased with increasing the length of PNIPAm block. The microstructures of PNIPAmx-P123-PNIPAmx hydrogels formed in concentrated aqueous solutions (40 wt%) were strongly dependent on the environmental temperatures and relative lengths of PNIPAm, PPO and PEO blocks as revealed by SAXS. Increasing the length of PNIPAm block weakened the order structures of PNIPAmx-P123-PNIPAmx hydrogels. The microstructures of PNIPAmx-P123-PNIPAmx hydrogels changed from mixed fcc and hex structures for PNIPAm10-P123-PNIPAm10 to isotropic structure for PNIPAm97-P123-PNIPAm97. Increasing temperature led to the transition from mixed hex and fcc structure to pure hex structure for PNIPAm10-P123-PNIPAm10 hydrogel at temperature above the LCSTs.

The effects of concentration, relative block length and environmental temperature as well as the surface chemical and wetting properties of solid substrates on the adsorption behaviors and mechanisms of a series of pentablock terpolymer poly(N-isopropylacrylamide)x-poly(ethylene oxide)20-poly(propylene oxide)70-poly(ethylene oxide)20-poly(N-isopropylacrylamide)x (PNIPAmx-PEO20-PPO70-PEO20-PNIPAmx or PNIPAmx-P123-PNIPAmx) with x of 10, 63 and 97 on gold were studied by using a quartz crystal microbalance (QCM) technique. It was found that increasing the solution concentration did not alter the adsorption mechanism of thickness growth mode but increase the adsorption amount of PNIPAm97-P123-PNIPAm97 on a bare gold substrate at 20 °C. Increasing the length x of PNIPAm block decreased the adsorption rate constant and shifted the adsorption mechanism from the densification adsorption process for PNIPAm10-P123-PNIPAm10 to the thickness growth mode for PNIPAm63-P123-PNIPAm63 and PNIPAm97-P123-PNIPAm97 on bare (unmodified) gold substrate at 20 °C. The adsorption mechanisms of PNIPAm97-P123-PNIPAm97 at 20 °C on the hydrophobic and hydrophilic gold surfaces were the thickness growth mode and densification adsorption process, respectively. A complex adsorption behavior with large adsorption amounts was observed at the lower critical solution temperature (LCST) of PNIPAm block, i.e. 34.7 °C, for the adsorption of PNIPAm97-P123-PNIPAm97 not only on hydrophobic gold substrates but also on hydrophilic gold substrates. The adsorption mechanism of PNIPAm97-P123-PNIPAm97 micelles at 45 °C was the densification adsorption process regardless of the surface wetting and chemical properties of gold substrate. Overall, the adsorption behavior and mechanism of PNIPAmx-P123-PNIPAmx pentablock terpolymers were mainly determined by the interactions of the pentablock terpolymers with different chain conformations in dilute aqueous solutions at various temperatures and the gold substrates with surface wetting and chemical properties.

The chain conformations and adsorption behaviors of four thermo-sensitive poly(N-isopropylacrylamide)x–poly(propylene oxide)36–poly(N-isopropylacrylamide)x (PNIPAmx–PPO36–PNIPAmx) triblock copolymers with x values of 15, 33, 75, and 117 in dilute aqueous solutions were investigated by combined techniques of micro-differential scanning calorimetry (micro-DSC), static and dynamic light scattering (SLS & DLS), and the quartz crystal microbalance (QCM). PNIPAm15–PPO36–PNIPAm15 only exhibited the lower critical solution temperature (LCST) of the PPO block, i.e. 25 °C, because the PNIPAm block with x = 15 was too short to maintain its own LCST. With middle lengths x of 33 and 75, the LCSTs of PPO and PNIPAm blocks were observed, respectively. For the longest PNIPAm block with x = 117, only LCST of PNIPAm block dominated, i.e. 32.3 °C. DLS results revealed that the four PNIPAmx–PPO36–PNIPAmx triblock copolymers formed “associate” structures in their dilute aqueous solutions at 20 °C, which was well below the LCSTs of the PPO and PNIPAm blocks. QCM results indicated that the adsorption time constant decreased with increasing adsorption temperature but tended to increase with increasing length x of the PNIPAm block. A complex adsorption behavior with large adsorption amounts was only observed at the corresponding LCST of the PNIPAm block for PNIPAmx–PPO36–PNIPAmx with longer PNIPAm blocks with x = 33, 75, and 117. Furthermore, the adsorbed PNIPAmx–PPO36–PNIPAmx layers obtained at 20 °C were rigid with less energy dissipation.

A novel method for speedy fabrication of free-standing layer-by-layer (LbL) multilayer films in salt free media, and without the need for a sacrificial sublayer is described by using two different polyelectrolyte complex (PEC) nanoparticles as LbL self-assembly building blocks. Negatively charged polyelectrolyte complex particles (PEC−) consisting of poly(diallyldimethylammonium chloride)/sodium carboxymethyl cellulose (PDDA/CMCNa), and positively charged polyelectrolyte complex particles (PEC+) consisting of PDDA/poly(sodium-p-styrenesulfonate) (PDDA/PSSNa) were prepared and characterized by FT-IR, zeta-potential (ζ potential) and transmission electron microscopy (TEM). The LbL self-assembly of PEC+/PEC− and PDDA/PEC− was followed by quartz crystal microbalance (QCM), optical transmittance, UV-vis absorption spectroscopy and atomic force microscopy (AFM). QCM results show that the thickness growth rate of the PEC+/PEC− pair is 9 times faster than that of the PDDA/PEC− pair and this result is also supported by optical transmittance and UV-vis absorption. A robust free-standing multilayer film of (PEC+/PEC−)25 can be easily peeled off from the substrate after being cross-linked in 3.5 wt% glutaraldehyde (GA) (80 °C, 50mins). Field emission electron scanning microscopy (FESEM) indicates that both the surface and cross-section of the multilayer film display layered structures. Furthermore, multiwall carbon nanotubes (MWCNTs) can also be uniformly incorporated into the free-standing LbL multilayer film by pre-incorporating MWCNTs into PEC− particles. The experimental results show that using oppositely charged PEC particles as LbL assembly components is a speedy and convenient method to fabricate free-standing LbL multilayer films either with or without nanofillers.

The self-assembly and disintegration behavior of polyzwitterion, poly(4-vinylpyridiniomethanecarboxylate) (PVPMC), and negatively charged polyelectrolyte, poly(acrylic acid) (PAA), layer-by-layer (LbL) multilayer films were investigated in detail by using UV-vis absorption spectroscopy, quartz crystal microbalance (QCM) and atomic force microscopy (AFM). The results indicated that the PVPMC/PAA multilayer films grew linearly with increasing bilayer number. The disintegration rate of PVPMC/PAA multilayers could be well controlled by varying the concentration of salt in aqueous solution. It was found that PVPMC/PAA multilayer films could be completely disintegrated in 0.9% normal saline solution within 15 min. Such controllable disintegration behavior rendered the PVPMC/PAA multilayer as an excellent sacrificial sublayer for fabricating free-standing LbL multilayer films. Free-standing multilayer films were then successfully fabricated by LbL self-assembly of positively charged polyelectrolyte complex (PEC), made from poly(diallyldimethylammonium) (PDDA) and poly(sodium 4-styrenesulfonate) (PSS), and negatively charged PSS with PVPMC/PAA as a sacrificial sublayer, which was disintegrated in 0.9% normal saline solution. The obtained free-standing films had good mechanical properties with 24.1 MPa tensile strength at break and 0.56 GPa Young's modulus.

The fluorescent properties of a linear poly(hydroxyurethane) (P1) from carbon dioxide, siloxane (Si–O–Si)-containing bisepoxide and diamine are described. P1 showed strong photoluminescence with a quantum yield of up to 23.6%, high photostability, and broad absorption and emission spectra either in bulk or solution. The flexibility and hydrophobicity of the Si–O–Si linkage in P1 were utilized to drive the intense aggregation of hydroxyurethane chromophores which combined with the hydrogen bonding interactions lead to strong photoluminescence. P1 was used as a single phosphor film for fabricating a low voltage, cool white light-emitting diode device with competitive performances.