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Ring-opening polymerization (ROP) of N-carboxy-α-amino acid anhydride (NCA) of γ-benzyl l -glutamate (BLG) was investigated under frozen condition for the first time. This cryo-ROP was performed in DMSO or 1,4-dioxane below the freezing point of polymerization mixture. The kinetics was monitored with proton nuclear magnetic resonance spectroscopy and gel permeation chromatography, disclosing the well control over molecular weight, living polymerization features and considerable polymerization rate. Compared with the polymerization proceeded at 30 °C, which showed weak linearity regarding the reaction kinetics and relatively broad distribution of molecular weight, the cryo-ROP exhibited excellent first-order kinetics as well as narrow molecular distribution. [ABSTRACT FROM AUTHOR]

Ternary hydrogels composed of poly[acrylamide- co -2-(dimethylamino)ethyl methacrylate] [P(AM- co -DMAEMA)], poly(vinyl alcohol) (PVA) and β -cyclodextrin ( β -CD) were fabricated based on the multiple physical interactions such as inclusion complexation, hydrogen bonding and polymer crystallinity, and exhibited high storage modulus. To illustrate the individual role of each physical interaction, symmetrical investigation has been performed. P(AM- co -DMAEMA)s with two compositions, prepared by radical polymerization at −20 °C below the freezing point of reaction medium of water, were served as the inclusion guest for the inclusion host of β -CD. The inclusion complex between dimethylaminoethyl group of DMAEMA and β -CD was identified through 2D NOESY NMR spectroscopy. Hydrogen bonding between each pairs of hydrogel components was confirmed with FTIR analysis and contributed the second form of crosslinkage. Under freezing polymerization and further freezing-thawing treatment, PVA component tended to crystallize to serve as the third type of physical crosslinkage, which was recognized with X-ray diffraction. Rheological and thermo-gravimetrical analysis was used to inspect the modulus and thermal stability of the hydrogels, respectively. Three hydrogels of P(AM- co -DMAEMA)/PVA-g- β -CD, P(AM- co -DMAEMA)/PVA/ β -CD and P(AM- co -DMAEMA)/PVA were synthesized under the same condition to make the comparison. The whole results disclosed the strong dependence of hydrogel properties on the hydrogel components, reflecting the synergistic effects of different physical crosslinkages for the formation of those physical hydrogels. [ABSTRACT FROM AUTHOR]

Temperature-responsive macro-porous cryogels of poly(N -iospropylacryamide- co -acrylamido-2-methylpropane sulfonic acid) [P(NIPAM- co -AMPS)] were prepared through redox-initiated cryo-polymerization at −12, −18 and −24 °C. Silver or gold nanoparticles (AgNPs or AuNPs) were formed inside P(NIPAM- co -AMPS) cryogels through the thermal reduction of absorbed AgNO 3 or HAuCl 4 , resulting in hybrid cryogels immobilized with AgNPs or AuNPs. Fourier transform infrared spectroscopy, thermal gravimetric analysis and X-ray diffraction confirmed the chemical composition. Cryogel morphology and nanoparticle distribution were investigated through scanning and transmission electron microscopies. By checking swelling ratio in neutral water, the temperature response of cryogels was identified. The hybrid cryogels were used as the catalysts to reduce p -nitrophenol with NaBH 4 at different temperatures and pHs. The hybrid cryogel with AuNPs had the higher catalytic activity than the counterpart hybrid cryogel with AgNPs. The catalytic activity of hybrid cryogels increased with temperature and pH. The temperature response of cryogels facilitated their isolation from the reaction mixture. Since AuNPs were fixed tightly onto the cryogel pore-wall and hardly lost, hybrid cryogels with AuNPs demonstrated no decrease in catalytic activity for 5 cycles of p -nitrophenol reduction. P(NIPAM- co -AMPS) hybrid cryogels with gold or/and silver nanoparticle was used to catalyze the reduction of p -nitrophenol with the performances of high rate and reusability. Image 1 • Thermo-responsive and macro-porous cryogels of P(NIPAM- co -AMPS) were prepared. • AgNPs or AuNPs were incorporated through in-situ thermal reduction inside the cryogels. • Hybrid cryogels exhibited the high catalytic activity for p -nitrophenol conversion. • Cryogel morphology and metal nanoparticle affected greatly the catalytic activity. [ABSTRACT FROM AUTHOR]