Polymers exhibiting an abnormal thermoresponsive behaviour, in which increase in the polymer concentration in water leads to an increase in the phase transition temperature, are few, and no plausible strategy has been addressed to prepare these polymers. For illuminating a feasible common strategy to prepare polymers with an abnormal thermoresponsive behaviour, in this study, we systematically prepared a series of hyperbranched polyglycerol (HPG) derivatives through a facile esterification reaction between HPG and aliphatic acids having different carbon numbers (X). Turbidimetry measurements demonstrate that thermoresponsive HPGs can be obtained only when HPGs are conjugated with aliphatic units of X ≤ 8. The conjugation of HPG with aliphatic units of X ≤ 4 resulted in thermoresponsive HPGs with a normal thermoresponsive behaviour. For the preparation of thermoresponsive HPGs with an abnormal thermoresponsive behaviour, X should be controlled in the range of 5–8. Fluorescence measurements with nile red as the fluorescent probe demonstrate that the existence of relatively strong hydrophobic interaction is a key factor to ensure that the polymer exhibits an abnormal thermoresponsive behaviour in water. Moreover, turbidimetry and fluorescence techniques are complementary for measuring the phase transition behaviour and suitable for different polymer concentration regions.

A series of hyperbranched poly(amidoamine)s (HPAs) were synthesized from the Michael addition copolymerization of tris(2-aminoethyl) amine (TAEA) and two bisacrylamide monomers N,N′-cystamine bisacrylamide (CBA) and N,N′-hexamethylene bisacrylamide (HMBA) at room temperature. The further modification with isobutyric anhydride led to isobutyramide terminated HPA (HPA-C4). 1H NMR and 15N NMR characterizations proved the successful preparation of these polymers. Moreover, beside the contents of TAEA, CBA and HMBA units in the composition, 15N NMR spectrometry could supply more structural information than 1H NMR spectrometry, such as the ratio of different amine groups in polymers, the transformation efficiency of reactive primary and secondary amines into C4 groups. GPC measurements not only gave the information of molecular weight and polydispersity, but also proved that all the HPA-C4s containing disulfide bonds could be degraded after being treated with dithiothreitol (DTT). Turbidimetry measurements showed that HPA-C4s had thermoresponsive property in water. The cloud point temperature (Tcp) of HPA-C4s was pH-dependent. Moreover, DTT could only affect the thermoresponsive property of HPA-C4s containing disulfide bonds due to the induced polymer degradation. Although no traditional fluorophores existed in HPA-C4s, HPA-C4s could emit blue fluorescence centered at ca. 455 nm. The fluorescence intensity was influenced pronouncedly by polymer concentration, pH, oxidizing time.

Poly(N-vinylimidazole) (PVIm) that contains a large amount of bio-active imidazole units was used as the sole carbon source to synthesize PVIm-dot through a one-pot hydrothermal method without any further modification and surface passivation. The measurements of X-ray photoelectron spectroscopy, dynamic light scattering, transmission electron microscopy and X-ray diffraction proved that only a slight carbonization occurred during the hydrothermal treatment of PVIm. The characterizations of 1H NMR, FTIR and thermogravimetric analysis verified that the obtained PVIm-dot well inherited the chemical structure of its precursor PVIm. Unlike PVIm, the obtained PVIm-dot showed an obvious excitation-dependent photoluminescence (PL) behavior, and its PL features were quite stable at different pH values and ionic strength. The PVIm-dot possessed low cytotoxicity and could enter cancer cells, making it a suitable candidate for bio-imaging. Moreover, the PVIm-dot still kept the catalytic activity of its imidazole units. With the catalytic hydrolysis of p-nitrophenyl acetate as the model reaction, it was found that the PVIm-dot showed good catalytic activity in this reaction and its catalytic efficiency was better than PVIm. What's more, the variation of PL intensity during the reaction could be used as a luminescent sensor to monitor the progress of the hydrolysis reaction.

The influences of hydrophilic dyes, including Congo Red (CR), Methyl Orange (MO), Eosin Y (EY), Fluorescein Sodium (FS) and Methylene Blue (MB), on the phase transition temperature (Tcp) of thermoresponsive hyperbranched polyethylenimine with many isobutyramide groups (HPEI-IBAm) were studied systematically. The cationic MB always showed a minor influence on the Tcp of both the cationic and the neutral HPEI-IBAm. According to the Tcp value at the 1:1 molar ratio of the dye to HPEI-IBAm, the ranking of these anionic dyes in reducing the Tcp of the cationic HPEI-IBAm (at pH 8) was CR > EY ≈ MO > FS. These anionic dyes could raise or have negligible influence on the Tcp of the neutral HPEI-IBAm (at pH 10) and their ranking in raising the Tcp of the neutral HPEI-IBAm was CR > EY > MO > FS. The pivotal interaction forces between HPEI-IBAm and the different hydrophilic dyes were interpreted through the combination of 2D 1H NMR characterization, zeta potential measurement and comparison with the influences of these dyes on the Tcp of the control thermoresponsive linear polymers. Cationic HPEI-IBAm was mixed with a mixture of anionic CR and cationic MB. The heating-induced cationic HPEI-IBAm precipitates the adsorbed CR molecules more efficiently from the CR/MB mixture that have a different effect on the Tcp. Moreover, the neutral HPEI-IBAm could separate the mixture of CR and FS molecules having a pronounced different efficiency in raising the Tcp.

Silver nanoclusters (AgNCs) functionalized with hyperbranched polyethylenimines with a certain number of trimethylacetamide groups (PEI–TMA) were prepared through three steps. The influence of the preparation conditions, including the pH value in the mixture of PEI–TMA and Ag+ and the Ag+/PEI–TMA feed ratio, on the photoluminescence properties of the obtained nanocomposite of AgNCs and PEI–TMA (AgNC–PEI–TMA) was studied. The obtained AgNC–PEI–TMA nanocomposite was characterized by transmission electron microscopy, dynamic light scattering and zeta potential measurements, verifying the formation of the nanocomposite. AgNC–PEI–TMA in water was not only thermoresponsive, but also responded to other stimuli, including pH, inorganic salts, and loaded organic guest. The cloud point temperature (Tcp) of aqueous solutions of AgNC–PEI–TMA could be modulated through changing the pH, and varying the type and concentration of the inorganic salts and the loaded organic guest. The obtained AgNC–PEI–TMA nanocomposite was photoluminescent, and its maximum emission wavelength was not influenced by outside stimuli. Its emission intensity was influenced negligibly by pH, traditional salting-out anions (Cl− and SO42−), and the relatively polar aspirin guest. However, the traditional salting-in I− anion could quench its fluorescence a little.

Hyperbranched polyethylenimine (HPEI) modified polyacrylonitrile fiber (PANF) was prepared through a water mediated hydrolysis and amidation reaction in an autoclave. The grafting amount of HPEI onto PANF could be modulated conveniently by varying the preparation conditions, such as reaction temperature, reaction time and the feed ratio of HPEI to PANF. The Young's modulus of the PANF decreased with the grafting of HPEI, especially when more HPEIs were grafted. As for the PANF-g-HPEI with low HPEI content, the Young's moduli were similar before and after loading of AuNPs, whereas the loading of AuNPs obviously deteriorated the strength of the fibers with high HPEI content. From the nitrogen adsorption and desorption isotherms, it could be seen that PANF contained nanometer sized pores, and the grafting with HPEI did not affect the pore size, but did reduce the surface area. Moreover, the loading of AuNPs into PANF-g-HPEI also did not influence the pore size, but decreased the surface area. FTIR and XPS analyses demonstrated that the obtained PANF-g-HPEI not only contained a large amount of amino groups from the HPEI moiety, but also many carboxylate ions due to the hydrolysis of the cyano groups of PANF. XRD characterization proved that the inner crystal region of PANF was partially broken by the introduction of HPEI moieties. SEM showed that the PANFs swelled up after grafting with HPEI, and the increase of the grafting efficiency led to a larger average diameter of the fibers. When the grafting amount of HPEI onto PANF reached as high as 97%, the surface of the fibers was severely impaired. The obtained PANF-g-HPEIs could be successfully used as supporters and stabilizers in the preparation of small-sized AuNPs. TEM characterization showed that the mixing time of PANF-g-HPEIs with HAuCl4 aqueous solution affected the size and size distribution of the formed AuNPs, and the optimal mixing time was around 0.5 h. The average diameter of the obtained AuNPs was around 3.0 nm at a feed ratio of amino groups of PANF-g-HPEI to Au atoms ([N]:[Au]) of 200, independent of HPEI content of the PANF-g-HPEIs used. Reducing the [N]:[Au] feed ratio increased the average size of the obtained AuNPs. The AuNPs supported by PANF-g-HPEIs could be used as efficient catalysts for the heterogeneous catalytic reduction of 4-nitrophenol by NaBH4. The PANF-g-HPEI with lower HPEI content endowed the supported AuNPs with a slightly higher catalytic rate. These heterogeneous AuNP catalysts could be conveniently recovered and reused many times, especially the AuNPs supported by the PANF-g-HPEIs containing a low content of HPEI. The turnover number (TON) values of the AuNPs supported by PANF-g-HPEI0.31 and PANF-g-HPEI0.58 could reach more than 5 × 104, which is unprecedented in the catalytic reduction of 4-nitrophenol.

The influence of aliphatic acids on the phase transition temperature of thermoresponsive hyperbranched polyethylenimine possessing a large amount of isobutyramide and amine groups (HPEI-IBAm) was studied systematically. Nine saturated aliphatic acids including formic acid (C1), acetic acid (C2), n-pentanoic acid (n-C5), trimethylacetic acid (t-C5), hexanoic acid (C6), octanoic acid (C8), decanoic acid (C10), dodecanoic acid (C12) and hexadecanoic acid (C16) were used to measure their effects on the cloud point temperature (Tcp) of HPEI-IBAm in a mixture of H2O/DMF (v/v = 9:1). For comparison, the effect of these aliphatic acids on the traditional thermoresponsive linear poly(2-dimethylaminoethyl methacrylate) (PDMAEMA) and poly(N-isopropyl acrylamide) (PNIPAm) was also studied. The influence of aliphatic acids on different thermoresponsive polymers was different. The aliphatic acids with shorter carbon chains (C ≤ 8) increased the Tcp of HPEI-IBAm, and those with long hydrocarbon chains (C > 8) depressed the Tcp. Moreover, the effect of aliphatic acids with C ≤ 5 was similar, even though their configurations might be different. The specific ranking of aliphatic acids in raising the Tcp of HPEI-IBAm was as follows: C1 ～ C2 ～ n-C5 ～ t-C5 > C6 > C8 > C10 > C12 ～ C16. With respect of the linear PDMAEMA, all the aliphatic acids employed elevated its Tcp. The specific ranking of aliphatic acids in raising the Tcp of linear PDMAEMA was similar to that for dendritic HPEI-IBAm, but with a minor difference: C1 ～ C2 ～ n-C5 ～ t-C5 > C6 > C8 > C10 > C12 > C16. In the case of the linear PNIPAM, the aliphatic acids with C ≤ 6 had almost no influence on the Tcp. Raising the carbon number to be 8 or higher leads to the obvious Tcp depression. The different effect of aliphatic acids on the phase transition of these thermoresponsive polymers was discussed, and it was mainly attributed to their structural and topological difference.

Hyperbranched polyamidoamine (HPAMAM) polymers, chemically analogous to the commercially available PAMAM dendrimer, were modified with isobutyric anhydride to result in isobutyramide (IBAm) terminated HPAMAMs (HPAMAM-IBAm). The aqueous solutions of HPAMAM-IBAm polymers had the lower critical solution temperature (LCST). The lower molecular-weight HPAMAM-IBAm exhibited higher LCST and the LCST difference was around 18 °C for one pseudo-generation variation. Further, the hyperbranched thermoresponsive polymers exhibited much lower LCSTs than the corresponding dendrimers with similar molecular weight. The LCST of HPAMAM-IBAm was pH sensitive. At pH below 10, the LCST increased significantly upon decreasing the pH, whereas, at pH above 10, the LCST decreased slowly with an increasing pH value. Nine sodium salts were used to measure the anion effect on the LCST of HPAMAM-IBAm. It was found that the LCST could also be modulated up or down in a broad range by simply adding a small amount of different kinds of inorganic anions. The specific ranking of inorganic anions in salting-out HPAMAM4-IBAm polymer was in accordance with the well-known Hofmeister series.

Thermoresponsive gold nanoparticles (AuNPs) with lower critical solution temperature (LCST) adjustable over a broad range were explored to be potentially used as colorimetric sensors. Upon raising the temperature above the LCST the surface plasmon resonance (SPR) peaks of the obtained thermoresponsive AuNPs red-shifted sharply in a narrow temperature range, accompanied by a color transition from transparent red to transparent purple–red until turbid red, which made them suitable to be used as sensitive colorimetric sensors for detecting environmental temperature variation. Moreover, the temperature range of sensitivity of the obtained thermoresponsive AuNPs could be tuned by modulating the molecular weight of core or degree of substitution of the thermoresponsive polymers employed. Furthermore, the solution colors of the thermoresponsive AuNPs were also sensitive to pH and NaCl concentration variation, as a result of which they could also be used as colorimetric sensors for detecting the variation of pH and salt concentration.

The mixing enthalpies of maltose with several typical α-amino acids (glycine, L-alanine, L-serine, L-valine, L-threonine and L-proline) and dilution enthalpies of each compound have been determined in aqueous solutions at T=298.15 K by a flow-mixing microcalorimeter. The heterotactic enthalpic pairwise interaction coefficients, hxy, of each amino acid with maltose have been calculated by the McMillan–Mayer formalism, and are discussed in terms of intermolecular interactions of the hydrated solute species.

Thermoresponsive gold nanoparticles (AuNPs) with lower critical solution temperature (LCST) adjustable over a broad range were explored to be potentially used as colorimetric sensors. Upon raising the temperature above the LCST the surface plasmon resonance (SPR) peaks of the obtained thermoresponsive AuNPs red-shifted sharply in a narrow temperature range, accompanied by a color transition from transparent red to transparent purple–red until turbid red, which made them suitable to be used as sensitive colorimetric sensors for detecting environmental temperature variation. Moreover, the temperature range of sensitivity of the obtained thermoresponsive AuNPs could be tuned by modulating the molecular weight of core or degree of substitution of the thermoresponsive polymers employed. Furthermore, the solution colors of the thermoresponsive AuNPs were also sensitive to pH and NaCl concentration variation, as a result of which they could also be used as colorimetric sensors for detecting the variation of pH and salt concentration.

Hyperbranched polyethylenimine (HPEI) modified polyacrylonitrile fiber (PANF) was prepared through a water mediated hydrolysis and amidation reaction in an autoclave. The grafting amount of HPEI onto PANF could be modulated conveniently by varying the preparation conditions, such as reaction temperature, reaction time and the feed ratio of HPEI to PANF. The Young's modulus of the PANF decreased with the grafting of HPEI, especially when more HPEIs were grafted. As for the PANF-g-HPEI with low HPEI content, the Young's moduli were similar before and after loading of AuNPs, whereas the loading of AuNPs obviously deteriorated the strength of the fibers with high HPEI content. From the nitrogen adsorption and desorption isotherms, it could be seen that PANF contained nanometer sized pores, and the grafting with HPEI did not affect the pore size, but did reduce the surface area. Moreover, the loading of AuNPs into PANF-g-HPEI also did not influence the pore size, but decreased the surface area. FTIR and XPS analyses demonstrated that the obtained PANF-g-HPEI not only contained a large amount of amino groups from the HPEI moiety, but also many carboxylate ions due to the hydrolysis of the cyano groups of PANF. XRD characterization proved that the inner crystal region of PANF was partially broken by the introduction of HPEI moieties. SEM showed that the PANFs swelled up after grafting with HPEI, and the increase of the grafting efficiency led to a larger average diameter of the fibers. When the grafting amount of HPEI onto PANF reached as high as 97%, the surface of the fibers was severely impaired. The obtained PANF-g-HPEIs could be successfully used as supporters and stabilizers in the preparation of small-sized AuNPs. TEM characterization showed that the mixing time of PANF-g-HPEIs with HAuCl4 aqueous solution affected the size and size distribution of the formed AuNPs, and the optimal mixing time was around 0.5 h. The average diameter of the obtained AuNPs was around 3.0 nm at a feed ratio of amino groups of PANF-g-HPEI to Au atoms ([N]:[Au]) of 200, independent of HPEI content of the PANF-g-HPEIs used. Reducing the [N]:[Au] feed ratio increased the average size of the obtained AuNPs. The AuNPs supported by PANF-g-HPEIs could be used as efficient catalysts for the heterogeneous catalytic reduction of 4-nitrophenol by NaBH4. The PANF-g-HPEI with lower HPEI content endowed the supported AuNPs with a slightly higher catalytic rate. These heterogeneous AuNP catalysts could be conveniently recovered and reused many times, especially the AuNPs supported by the PANF-g-HPEIs containing a low content of HPEI. The turnover number (TON) values of the AuNPs supported by PANF-g-HPEI0.31 and PANF-g-HPEI0.58 could reach more than 5 × 104, which is unprecedented in the catalytic reduction of 4-nitrophenol.