•The structure changes from polyamic acid fibers to polyimide fibers during ramp-heating and isothermal treatments have been traced and studied.•Higher crystallinity is the very key to improve the mechanical properties of polyimide fibers.•Isothermal treatment is more effective than ramp-heating treatment for polyimide fiber to realize better mechanical properties.Polyamic acid (PAA) fiber derived from 3,3′,4,4′-biphenyltetra-carboxylic dianhydride and p-phenylenediamine is prepared via dry-jet wet-spinning method. Polyimide (PI) fibers are obtained by applying two kinds of thermal treatment procedures on the PAA fibers. The evolution of fiber structure during thermal treatments is traced. And the influence of fiber structure on the mechanical properties is also studied. In Procedure I, the PAA fibers are heated from room temperature to 400 °C at 5 °C/min. As temperature increases from room temperature to 125 °C, relaxation behavior of PAA chains happens at first. Then, from 125 to 300 °C, imidization reaction occurs. Meanwhile, before the temperature reaches 250 °C, a significant degradation of PAA chains exists and makes the fibers too weak to measure. Crystals in fiber begin to form as temperature exceeds 250 °C and totally complete at 350 °C. The fracture strength and initial modulus of fiber are significantly improved with the formation of crystals and finally reach 0.83 GPa and 48.4 GPa at 400 °C, respectively. In Procedure II, the PAA fibers are isothermally treated at 250, 300, 350 and 400 °C for different times. When treated at 400 and 350 °C, both imidization and crystallization in fiber can happen simultaneously and complete in tens of seconds because of the high mobility of the polymer chains. While as treated at 300 and 250 °C, both these two processes are slowed down and the formation of crystals lags behind the imidization process. High crystallinity can be obtained under higher treatment temperature in a very short time. The mechanical properties of fiber highly depend on the treatment temperature rather than the treatment time. The fibers treated at 400 °C for 60 s show the highest fracture strength and initial modulus of 1.4 GPa and 70.0 GPa, respectively.Download high-res image (181KB)Download full-size image

Polyimde (PI) samples with different molecular weights were synthesized. Based on SEC coupled with multidetectors measurement and Yamakawa-Fujii-Yoshizaki (YFY) model, eight soluble samples with absolute Mw from 40,600 g/mol to 197,000 g/mol are chosen and applied to investigate the influence of molecular weight on scaling exponents and critical concentrations at 20–45 °C in dilute, semidilute unentangled, and semidilute entangled solutions. Most of the scaling exponents are higher than the theoretical values in three concentration regions, and scaling exponent increases with molecular weight; overlap concentration (C*) increases and entanglement concentration (Ce) decreases with molecular weight. Considering bead-bead interaction, corrected bead-spring model can explain the related results. Finally, the relationship among C*, Ce, and molecular weight is established at different temperatures (from 20 °C to 45 °C), and two linear equations are available at each temperature. Thus, both C* and Ce are calculated at a fixed molecular weight. And from C/C* and C/Ce ratios, the morphology of PI fiber during electrospinning can be controlled. These results are helpful to guide the preparation of polyimide solutions for different processing.

A series of macroporous adsorbents based on polyvinyl alcohol–formaldehyde (PVF) sponges was prepared using redox-initiated grafting polymerization of acrylamide (AM) followed by hydrolysis under alkaline conditions. The as-prepared sponges display average pore sizes in the range of 60–90 μm and interconnected pores with a porosity of approximately 90%. Elementary analysis confirmed that the amide groups in AM grafted PVF (PVF-g-GAM) have been rapidly converted into sodium carboxylate and the hydrolysis degree (HD) reaches approximately 65.5% within 6 h. The PVF-g-GAA (hydrolyzed PVF-g-GAM) sponges possess excellent water absorption performance with the ability to reach water absorption equilibrium within a few seconds and a saturated absorption capacity more than 300 g g−1. Importantly, the PVF-g-GAA can be used as adsorbents to remove toxic metal ions, such as Cu2+, Pb2+ and Cd2+, in wastewater efficiently due to the existence of abundant carboxylate groups in the abovementioned network. In single metal ion systems, the sponges could reach adsorption equilibrium within 10 min and the adsorption kinetics fit well with a pseudo-second order kinetic equation. The influence of pH and types of metal ions on the adsorption capacities have also been investigated extensively. PVF-g-GAA-20 displays high adsorption performances with maximum adsorption capacities for Cu2+, Pb2+ and Cd2+ up to 2.50, 3.20 and 3.15 mmol g−1 at pH 5.11, respectively. The equilibrium adsorption isotherm demonstrated that the adsorption equilibrium of the PVF-g-GAA-20 for Cu2+, Pb2+ and Cd2+ ions follows the Langmuir isotherm model very well with maximum adsorption capacities approximately 4.00, 3.97 and 3.34 mmol g−1, respectively. In the binary metal ion coexistence systems, including Cu2+/Pb2+, Cu2+/Cd2+ and Pb2+/Cd2+ mixtures, PVF-g-GAA-20 displayed excellent absorption selectivity for Cu2+ and Pb2+ and the values of and were 13.4 and 7.14, respectively. It can be noted that the adsorption capacities for the abovementioned three metal ions slightly decreased with the variation of ionic strength in the range of 0.01–0.08 M. The sample also exhibited a quick desorption procedure of less than 10 min and excellent reusability of atleast six re-cycles. The adsorption mechanism was also discussed. The PVF-g-GAA sponges are definitely ideal adsorbents for removing/separating toxic metal ions in waste/polluted water bodies.

•Hydrophilic luffa sponges are prepared successfully via grafting polymerization.•Fibers were characterized by different techniques.•The alkalization conditions, the grafting conditions, water absorption kinetics, and absorption capacities are investigated extensively.•The absorption mechanism is also discussed.Hydrophilic luffa sponges are prepared by grafting polymerization of acrylamide (AM) on luffa cylindrica and subsequent partial hydrolysis under alkaline conditions. Attenuated total reflection infrared spectroscopy is used to verify the composition of the grafted (luffa-g-PAM) and hydrolyzed (luffa-g-(PAM-co-PAANa)) samples. Alkalization conditions, including aqueous NaOH concentrations, alkalization temperature, and time, are studied extensively. Optimized conditions are then obtained. The grafting percentage (GP) of polyacrylamide increases with the feed ratios of [AM]/[OH] and [Ce]/[OH], reaction temperature, and time. Furthermore, the GP can reach up to 160%. Pristine, alkalized, grafted, and hydrolyzed luffa sponges show rapid absorption kinetics, and the pseudo second-order rate equation is applied to describe their kinetic procedure. Reaction conditions, such as [AM]/[OH], [Ce]/[OH], reaction temperature and time, influence the water absorption capacities of grafted and hydrolyzed samples. The hydrolyzed luffa sponges particularly exhibit high water absorption capacities of 75 g g−1. The absorption mechanism is also discussed.

The hybrid structures of polystyrene-b-poly(ethylene oxide) (PS-b-PEO) block copolymer and inorganic nanoparticles with good stability and biocompatibility have potential applications in drug delivery and bioimaging. Spherical co-assemblies of PS120-b-PEO318 and oleylamine-capped CdS quantum dots (QDs) are produced successfully in this work by adding water to a mixed common solvent, such as N,N-dimethylmethanamide (DMF)/chloroform, DMF/tetrahydrofuran (THF), or DMF/toluene. The energy dispersive X-ray (EDX) spectrum indicates that QDs are located at the interface between the core and shell of the spherical co-assemblies. The co-assembly process during water addition is traced by transmission electron microscopy (TEM) and turbidity measurement. Spherical co-assemblies are formed through budding from bilayers of the block copolymer and QDs. The morphology of the co-assemblies is related to the miscibility of the QD-dispersing solvents with water and the morphology changes from a spherical to a vesicle-like structure with DMF/toluene. Increasing THF content in the mixed solvent causes morphological transitions from spherical co-assemblies to multi-branched cylinders and micelles where QDs are located in the central core. Increasing chloroform content yields vesicle-like structures with protruding rods on the surface. The mechanism of the morphological transitions is also discussed in detail.

Inorganic nanoparticles play a very important role in the fabrication and regulation of desirable hybrid structures with block copolymers. In this study, polystyrene-b-poly(acrylic acid) (PS48-b-PAA67) and oleic acid-capped CdSe/CdS core/shell quantum dots (QDs) are coassembled in tetrahydrofuran (THF) through gradual water addition. QDs are incorporated into the hydrophilic PAA blocks because of the strong coordination between PAA blocks and the surface of QDs. Increasing the weight fraction of QDs (ω = 0–0.44) leads to morphological transitions from hybrid spherical micelles to large compound micelles (LCMs) and then to bowl-shaped structures. The coassembly process is monitored using transmission electron microscopy (TEM). Formation mechanism of different morphologies is further proposed in which the PAA blocks bridging QDs manipulates the polymer chain mobility and the resulting morphology. Furthermore, the size and size distribution of assemblies serving as drug carriers will influence the circulation time, organ distribution and cell entry pathway of assemblies. Therefore, it is important to prepare or isolate assemblies with monodisperse or narrow size distribution for biomedical applications. Here, the centrifugation and membrane filtration techniques are applied to fractionate polydisperse coassemblies, and the results indicate that both techniques provide effective size fractionation.

A complex branched polyethylene resin with excellent processing and film-forming properties is fractionated through solvent gradient fractionation (SGF) technique. Here, the good solvent is 1,2,4-trimethylbenzene (TMB) and poor solvent is ethyl cellosolve (ECS). The fractions are further analyzed using high-temperature gel permeation chromatography (GPC) coupled with triple detectors (refractive index (RI)-light scattering (LS)-viscometer (VIS)), and 13C-nuclear magnetic resonance spectroscopy (13C-NMR). The molecular weight distribution of SGF fractions is very narrow, most of them are less than 1.1. The molecular weights of SGF fractions gradually increase as the content of good solvent increases in the mixture. The fractions with different molecular weights all have branching structure, the short chain branching is major in all fractions and along with certain content of long chain branching. Branching distribution across the molecular weight distribution is discussed in detail, and branching distribution within a SGF fraction is also researched.

In this study, polyimide fibers at different stages of imidization were characterized by TGA, DSC, and FTIR. The imidization degree (ID) calculated by TGA was based on the weight loss of each sample, which was caused by the imidization of residual amic acid groups. The results of TGA showed good regularity with the thermal treatment temperature of the PI fibers. For DSC, the ID was calculated based on the area of endothermal peak of each sample. Compared with TGA, DSC showed a relatively higher value because the endothermal peak was reduced by the exothermic re-formation of polyamic acid which may be partially degraded during thermal treatment. The IDs obtained by the FTIR spectra generally showed poorer regularities than those obtained by both TGA and DSC, especially for the results calculated using the 730 cm−1 band. Based on the 1350 cm−1 band, the obtained IDs showed better agreement with the TGA or DSC results. The results obtained by these three methods were compared and analyzed. The ID obtained by TGA showed much more reliability among these three methods.

In this work, monodisperse giant polymersomes are fabricated by dewetting of water-in-oil-in-water double emulsion droplets which are assembled by amphiphilic block copolymer molecules in a microfluidic device. The dewetting process can be tuned by solvation between solvent and amphiphilic block copolymer to get polymersomes with controllable morphology. Good solvent (chloroform and toluene) hinders dewetting process of double emulsion droplets and gets acornlike polymersomes or patched polymersomes. On the other hand, poor solvent (hexane) accelerates the dewetting process and achieves complete separation of inner water phase from oil phase to form complete bilayer polymersomes. In addition, twin polymersomes with bilayer membrane structure are formed by this facile method. The formation mechanism for different polymersomes is discussed in detail.

•A soluble polyimide was synthesized and it can be dissolved in common organic solvents in various concentration ranges.•Deviation of scaling exponents in different concentration ranges is found.•Mechanism of the deviation of scaling exponents is discussed comprehensively.A soluble polyimide (6FDA-TFDB) was synthesized and its properties in solution were investigated. The relationship between specific viscosity and concentration is established using rheometer and applying Zimm model (dilute solution), Rouse–Zimm model (semidilute unentangled solution), and Doi–Edwards model (semidilute entangled solution). In addition, the overlapped concentration (C*) and semidilute entangled concentration (Ce) are determined. Results showed that all of the scaling exponents are higher than the theoretical values. The influence of factors, namely, electrostatic interaction, hydrogen bonding, dipole–dipole interaction and polydispersity index under different conditions (i.e., temperature, salt, and solvent) on critical concentration and scaling exponents are investigated extensively. In order to confirm the related conclusions, two soluble polyimides with different chemical structures are also synthesized and compared with the above results. The reasons for the deviation of scaling exponents are also discussed.

Novel superabsorbents based on hydrophilic and macroporous polyvinyl alcohol-formaldehyde (PVF) sponges are prepared through the grafting polymerization of hydrophilic acrylamide (AM) monomer on the PVF and PVF–GA (pre-crosslinked with glutaraldehyde) network and through subsequent partial hydrolysis under alkaline conditions. The grafting percentage (GP) increases with the feed ratio of [AM]/[OH] and can reach up to 160%. The hydrolysis degree ranges between 60% and 70%. As-prepared polyacrylamide grafted PVF (PVF-g-PAM) and PVF–GA (PVF-g-GAM), and corresponding hydrolyzed samples (PVF-g-PAA and PVF-g-GAA) present average pore sizes ranging from 60 μm to 90 μm and a high porosity of 90%. Scanning electron microscopy (SEM) images reveal an interconnected pore structure, macroscopically rough surface, and pore size ranging from several micrometers to 200 μm. As-prepared sponges also exhibit rapid absorption kinetics and they can reach absorption equilibrium in both deionized water and saline solution in 1 min. The absorption procedure described in this study is consistent with the pseudo second-order rate kinetic equation. Notably, the PVF-g-PAA sponges can absorb deionized water as high as 320 g g−1 within 60 s and can also absorb saline solution at a maximum capacity of 97.3 g g−1 in 30 s. As-prepared PVF-g-PAM sponges with an absorption capacity less than 50 g g−1 exhibit excellent reusability for at least 20 cycles. And the absorption mechanism is also discussed. Results show that these sponges with rapid absorption kinetics and high capacity can be considered as new superabsorbents for medical and sanitary applications.

Supported lipid bilayers of 1,2-dioleoyl-sn-glycero-3-phosphocholine were formed on a silicon oxide substrate, and the viscoelasticity of poly(ethylene glycol) (PEG) solutions above the bilayer was subsequently studied by quartz crystal microbalance with dissipation monitoring. No detectable adsorption of PEG molecules to the bilayer was found over a broad range of PEG molecular weight at various concentrations. The viscoelastic properties of the PEG solutions were obtained from the shifts in the resonance frequency and the energy dissipation factor of the polymer solution in contact with the resonator-supported lipid bilayer. The resulting viscoelastic properties of PEG solutions were found to be in excellent agreement with the Zimm model for linear polymer chains in a good solvent. The excluded volume scaling exponent ν for PEG in water shows an ideal-to-real crossover with increasing molecular weight. The exponent adopts a value of 0.50 for short chains and gradually increases to 0.565 for long chains. The onset of the excluded volume effect of PEG in water, a good solvent, lies in the molecular weight range between 4000 and 8000.

We report the synthesis and solution behavior of photo-, temperature-, pH-, and ion-responsive weak polyelectrolyte spherical brushes under different modes of confinement. The spherical brushes were prepared by copolymerization of N,N-dimethylaminoethyl methacrylate (DMAEMA) and 7-(2-methacryloyloxyethoxy)-4-methylcoumarin anchored to silica nanoparticles via surface-initiated atom transfer radical polymerization. The photo-cross-linking and reversibility of the nanoparticle-attached coumarin entities are detected by UV–visible spectroscopy and dynamic light scattering (DLS). The cross-linking density of poly(DMAEMA) (i.e., PDMAEMA) brushes could be easily controlled by alternating irradiation at wavelengths of 365 and 254 nm. Moreover, solution behavior under different pH levels and ionic strengths is systematically investigated in the PDMAEMA brush–polyelectrolyte chains confined only by a hard core, the cross-linked PDMAEMA brush–polyelectrolyte chains confined by a hard core and cross-linking points, and the corresponding hollow nanocapsules after removal of silica by etching-polyelectrolyte chains confined only by cross-linking points. These three models represent the different modes of confinement. DLS results indicate that the volume phase transition temperatures of the three models shift to lower temperatures with the increase in pH. The highest temperature is afforded to phase transition for hollow nanocapsules in solution, followed by the cross-linked PDMAEMA brushes. The hydrodynamic radius of the polyelectrolyte brush systems obviously decreases with the increase in ionic strength of the solution when adjusted by NaCl.

Two polyethylene (PE) resins (samples A and B) are synthesized as high-speed extrusion coatings with similar minimum coating thickness and neck-in performance but different maximum coating speeds. Both samples are separated into seven fractions using preparative temperature rising elution fractionation. The microstructures of the original samples and their fractions are studied by high-temperature gel permeation chromatography, Fourier transform infrared spectroscopy, 13C nuclear magnetic resonance spectroscopy, differential scanning calorimetry, and successive self-nucleation/annealing thermal fractionation. Compared with sample B, sample A has a broader MWD, more LCB contents, and less SCB contents. Moreover, sample A contains slightly more 30 °C and 50 °C fractions with lower molecular weights, and more fractions at 75 °C and 85 °C with higher molecular weight. The chain structure and its distribution in the two PE resins are studied in detail, and the relationship between the chain structure and resin properties is also discussed.

A series of copolymers of ethylene with 1-hexene synthesized using a metallocene catalyst are selected and mixed. The blend is fractionated via preparative temperature rising elution fractionation (P-TREF). All fractions are characterized via high-temperature gel permeation chromatography (GPC), 13C nuclear magnetic resonance spectroscopy (13C-NMR), and differential scanning calorimetry (DSC). The changes in the DSC melting peak temperatures of the fractions from P-TREF as a function of elution temperature are almost linear, thereby providing a reference through which the elution temperature of TREF experiments could be selected. Moreover, the standard calibration curve (ethylene/1-hexene) of P-TREF is established, which relates to the degree of short-chain branching of the fractions. The standard calibration curve of P-TREF is beneficial to study on the complicated branching structure of polyethylene. A convenient method for selecting the fractionation temperature for TREF experiments is elaborated. The polyethylene sample is fractionated via successive self-nucleation and annealing (SSA) thermal fractionation. A multiple-melting endotherm is obtained through the final DSC heating scan for the sample after SSA thermal fractionation. A series of fractionation temperatures are then selected through the relationship between the DSC melting peak temperature and TREF elution temperature.

A low-density polyethylene (LDPE) resin with excellent processing and film-forming properties is fractionated through temperature rising elution fractionation (TREF) technique. The chain structures of both the original resin and its fractions are further analyzed using high-temperature gel permeation chromatography (GPC) coupled with triple detectors (refractive index (RI)-light scattering (LS)-viscometer (VIS)), 13C-nuclear magnetic resonance spectroscopy (13C-NMR), Fourier transform infrared spectroscopy (FTIR), differential scanning calorimetry (DSC) and successive self-nucleation/annealing (SSA) thermal fractionation. The 13C-NMR results show that the original resin has both short chain branch (SCB) (2.82 mol%) and long chain branch (LCB) (0.52 mol%) structures. The FTIR results indicate that the methyl numbers (per 1000 C) of the fractions gradually decrease from 81 to 46 with increasing elution temperature from 25 °C to 75 °C. The TREF-GPC cross-fractionation results show that the main component is collected at around 68 °C. The molecular weight of the components in the high elution temperatures of 60 °C to 75 °C is from 2.0 × 103 g/mol to 2.0 × 106 g/mol, and the relative amount is more than 80%. In the low elution temperature region below 50 °C, the molecular weights of the components range from 1.0 × 103 g/mol to 1.6 × 104 g/mol, and the relative amount is less than 10%. In the DSC results, the melting peaks of the fractions gradually increase from 80.1 °C to 108.8 °C with elution temperature. In the SSA thermal fractionation, each resin fraction shows a broad range of endotherm with multiple melting peaks (more than eight peaks). The melting peaks shift toward high temperatures with the elution temperature. The characteristic chain microstructure for the resin is also discussed in detail.

The typical standard long chain branching (LCB) polyethylene (PE) SRM1476 is issued by the American National Bureau of Standards, which is widely used as a standard reference material in chromatographic experiments. Although some works have been reported in literatures, they are not consistent, such as the data about its molecular weight and molecular weight distribution. Therefore, it is necessary to further investigate the microstructure features of SRM1476 in order to better serve as a reference object in comparison with other unknown resins. In this study, the molecular chain heterogeneity of SRM1476 is investigated extensively and compared with the linear PE SRM1475. Based on the characterization of the original sample, SRM1476 actually has both LCB and short chain branching (SCB) structures, as well as the SCB content is more than LCB content in 13C-NMR results. After successive self-nucleation and annealing (SSA) thermal fractionation, SRM1476 shows a broad-range endotherm with multiple melting peaks (more than eight peaks), which proves the molecular chain heterogeneity in SRM1476. SRM1476 is fractionated into nine fractions by preparative temperature rising elution fractionation (TREF). At the high elution temperature region, the amounts of fractions are more than 90 %, and their molecular weights are higher. At the low elution temperature region below 50 °C, molecular weights of fractions are lower and their amounts are less than 5 %. Differential scanning calorimetry (DSC) melting curves of TREF fractions with higher elution temperatures shift toward higher temperature with sharper melting peaks. In the results of TREF-SSA cross-fractionation, each fraction shows a broad-range endotherm with multiple melting peaks that shift toward the high elution temperature region with the elution temperature. The arithmetic mean methylene sequence lengths of TREF fractions gradually increase from 33 to 105 as elution temperature increases. Results from TREF-DSC and TREF-SSA cross-fractionations indicate that SRM1476 and its TREF fractions have both intramolecular and intermolecular heterogeneity.

Macroporous materials are a class of absorbents used for oil spill cleanup. In this article, novel macroporous and hydrophobic polyvinyl formaldehyde (PVF-H) sponges were prepared by the reaction of stearoyl chloride with hydroxyl groups of hydrophilic PVF sponge at different temperatures. Attenuated total reflectance-infrared (ATR-IR) spectroscopy confirmed the successfully anchoring of hydrophobic stearoyl groups on the PVF networks. Scanning electron microscopy (SEM) images demonstrated that the as-prepared PVF-H had interconnected open-cell structures, and mercury intrusion porosimetry indicated that the average pore size ranged from 60 to 90 μm and porosity was greater than 94.8%. Such PVF-H sponges can absorb oil products effectively, such as toluene, n-hexane, kerosene, soybean oil, hydraulic oil, and crude oil up to 13.7 g·g–1 to 56.6 g·g–1, and this level of absorption was approximately 2–4 times higher than that absorbed by commercial polypropylene nonwoven mat. In low-viscosity oils, the samples can reach the saturated absorption amount only in 1 min, but in higher-viscosity oils, absorption equilibrium can be reached in 10 min. In a simulated oil slick system, these macroporous and hydrophobic sponges can still maintain high oil absorption capacities within the range of 14.4 g·g–1 to 57.6 g·g–1, whereas a relatively low absorption rate (approximately 20 min) indicated high absorption performance and excellent selectivity in the oil–water mixture. In addition, the absorbed oils were collected effectively only through a simple squeeze. The PVF-H sponges were subjected to 35 absorption–squeeze cycles and exhibited good reusability and 90% recovery for oils. The samples prepared at different temperatures differed in their absorption capacities to some extent. However, this new kind of macroporous and PVF-H sponges had excellent absorption performance on oil products.Keywords: hydropbobic sponge; macroporous absorbents; oil spill; poly(vinyl alcohol)-formaldehyde

A series of macroporous hydrophobic polyvinyl alcohol–formaldehyde sponges (PVF–Gn–Hms) are prepared via the reactions of hydrophilic polyvinyl alcohol–formaldehyde (PVF) sponges with glutaraldehyde (GA) and fatty acyl chloride. Both ATR-IR and solid-state CP/MAS 13C-NMR spectra confirm a successful substitution of alkyl chain on PVF sponges, and the calculated degree of substitution (DS) is in the range of 32.3–62.3%. PVF–Gn–Hms sponges have similar apparent densities as the pristine PVF sponges and exhibit a unimodal macropore size distribution with a peak centered at about 60 μm and a high porosity of 90%. PVF–Gn–Hms maintain the original open-cell structure well, and their surface hydrophobicity effectively increases with the n-alkyl chain length and reaction temperature. The effect of preparation conditions, including the feed ratio of crosslinker glutaraldehyde to OH groups ([GA]/[OH] = 0–4), alkyl chain length of fatty acyl chloride, reaction temperature and apparent density of pristine PVFs, on absorption behavior to organic pollutants is investigated extensively. Fourteen common solvents with solubility parameters from 7.24 to 13.40 cal1/2 cm−3/2 are selected as organic pollutants. Results demonstrate that the resultant PVF–Gn–Hms with a higher feed ratio of [GA]/[OH] (from 0 to 4) possess lower absorption capacities in most organic solvents because of a relatively higher crosslinking degree. The sponges prepared at higher reaction temperatures only exhibit slightly increased absorption capacities, and a relatively lower apparent density of pristine hydrophilic PVF facilitates higher absorption capacities. Definitely, the hydrophobic sponges with different apparent densities exhibit excellent reusability and recovery (up to 93.0%) during 35 successive absorption–squeezing cycles and excellent absorption selectivity in the water-organic solvent mixture experiment. More importantly, as-prepared sponges possess hydrophobic surfaces, open-cell structures, high porosity, as well as excellent reusability and selectivity, which make them ideal candidates as absorbents for organic pollutants.

An easy method is presented to fabricate monodisperse magnetic macroporous polymer beads (MMPBs). Waterin- oil high internal phase emulsion (HIPE) is prepared by emulsifying aqueous iron ions solution in an oil phase containing monomers. The HIPE is introduced into a simple microfluidic device to fabricate monodisperse (water-in-oil)-in-water double emulsion droplets. The droplets serve as microreactors to synthesize Fe3O4 nanoparticles and are on-line polymerized to form MMPBs. The prepared MMPBs display uniform size, interconnected porous structure, superparamagnetic behavior and uniform distribution of Fe3O4 in polymer matrix. The MMPBs are characterized by scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), transmission electron microscopy (TEM), vibrating sample magnetometry (VSM). We believe that this method is a universal technique in preparing macroporous nanocomposite beads.

Porous polymer beads (PPBs) containing hierarchical bimodal pore structure with gigapores and meso-macropores were prepared by polymerization-induced phase separation (PIPS) and emulsion-template technique in a glass capillary microfluidic device (GCMD). Fabrication procedure involved the preparation of water-in-oil emulsion by emulsifying aqueous solution into the monomer solution that contains porogen. The emulsion was added into the GCMD to fabricate the (water-in-oil)-in-water double emulsion droplets. The flow rate of the carrier continuous phase strongly influenced the formation mechanism and size of droplets. Formation mechanism transformed from dripping to jetting and size of droplets decreased from 550 μm to 250 μm with the increase in flow rate of the carrier continuous phase. The prepared droplets were initiated for polymerization by on-line UV-irradiation to form PPBs. The meso-macropores in these beads were generated by PIPS because of the presence of porogen and gigapores obtained from the emulsion-template. The pore morphology and pore size distribution of the PPBs were investigated extensively by scanning electron microscopy and mercury intrusion porosimetry (MIP). New pore morphology was formed at the edge of the beads different from traditional theory because of different osmolarities between the water phase of the emulsion and the carrier continuous phase. The morphology and proportion of bimodal pore structure can be tuned by changing the kind and amount of porogen.

A series of the copolymers of ethylene with 1-hexene (M1-M9) synthesized by metallocene catalyst Et[Ind]2ZrCl2/MAO was studied by differential scanning calorimetry and successive self-nucleation and annealing (SSA) thermal fractionation. The distribution of methylene sequence length (MSL) in the different copolymers was determined using the SSA method. The comonomer contents of samples M4 and M5 are 2.04 mol% and 2.78 mol%, respectively. Both M4 and M5 have low comonomer content and their MSL distribution profiles exhibit a monotonous increase trend with their MSL. The longest MSL of M5 is 167, and its corresponding molar percent is 43.95%, which is higher than that of M4. Moreover, the melting temperature (Tm) of M5 is also higher than that of M4. The comonomer contents of samples M7, M8, and M9 are 8.73 mol%, 14.18 mol% and 15.05 mol%, respectively. M7, M8, and M9 have high comonomer contents, and their MSL distribution profiles display unimodality. M7 has a lower peak value of 33 and a narrow MSL distribution, resulting in a Tm lower than that of M8 and M9. The MSL and its distribution are also key points that influence the melting behavior of copolymers. Sometimes, MSL and its distribution of copolymers have a greater impact on it than the total comonomer contents, which is different from traditional views.

A series of macroporous adsorbents based on polyvinyl alcohol–formaldehyde (PVF) sponges was prepared using redox-initiated grafting polymerization of acrylamide (AM) followed by hydrolysis under alkaline conditions. The as-prepared sponges display average pore sizes in the range of 60–90 μm and interconnected pores with a porosity of approximately 90%. Elementary analysis confirmed that the amide groups in AM grafted PVF (PVF-g-GAM) have been rapidly converted into sodium carboxylate and the hydrolysis degree (HD) reaches approximately 65.5% within 6 h. The PVF-g-GAA (hydrolyzed PVF-g-GAM) sponges possess excellent water absorption performance with the ability to reach water absorption equilibrium within a few seconds and a saturated absorption capacity more than 300 g g−1. Importantly, the PVF-g-GAA can be used as adsorbents to remove toxic metal ions, such as Cu2+, Pb2+ and Cd2+, in wastewater efficiently due to the existence of abundant carboxylate groups in the abovementioned network. In single metal ion systems, the sponges could reach adsorption equilibrium within 10 min and the adsorption kinetics fit well with a pseudo-second order kinetic equation. The influence of pH and types of metal ions on the adsorption capacities have also been investigated extensively. PVF-g-GAA-20 displays high adsorption performances with maximum adsorption capacities for Cu2+, Pb2+ and Cd2+ up to 2.50, 3.20 and 3.15 mmol g−1 at pH 5.11, respectively. The equilibrium adsorption isotherm demonstrated that the adsorption equilibrium of the PVF-g-GAA-20 for Cu2+, Pb2+ and Cd2+ ions follows the Langmuir isotherm model very well with maximum adsorption capacities approximately 4.00, 3.97 and 3.34 mmol g−1, respectively. In the binary metal ion coexistence systems, including Cu2+/Pb2+, Cu2+/Cd2+ and Pb2+/Cd2+ mixtures, PVF-g-GAA-20 displayed excellent absorption selectivity for Cu2+ and Pb2+ and the values of and were 13.4 and 7.14, respectively. It can be noted that the adsorption capacities for the abovementioned three metal ions slightly decreased with the variation of ionic strength in the range of 0.01–0.08 M. The sample also exhibited a quick desorption procedure of less than 10 min and excellent reusability of atleast six re-cycles. The adsorption mechanism was also discussed. The PVF-g-GAA sponges are definitely ideal adsorbents for removing/separating toxic metal ions in waste/polluted water bodies.