Synthesis and Functionalities of Poly(N-vinylalkylamide). 13. Synthesis and Properties of Thermal and pH Stimuli-Responsive Poly(vinylamine) Copolymers

Biomimetic stimulus-responsive star diblock gelators

Novel biomimetic gelators with star diblock copolymer architectures have been synthesized by atom-transfer radical polymerization (ATRP). Two types of trifunctional ATRP initiator were used to polymerize 2-(methacryloyloxy)ethyl phosphorylcholine [MPC] at 20 degrees C, followed by sequential monomer addition of various tertiary amine methacrylates or mixtures thereof. Poor living character was achieved using an amide-based trifunctional initiator, but the analogous triester initiator gave reasonably well-defined thermo-responsive and pH-responsive star diblock copolymers. The most effective thermo-responsive gelators were obtained by the statistical terpolymerization of 2-(dimethylamino)ethyl methacrylate [DMA], 2-(diethylamino)ethyl methacrylate [DEA], and a monomethoxy-capped poly(propylene oxide) methacrylate [PPOMA], whereas pH-responsive gelators were prepared using 2-(diisopropylamino)ethyl methacrylate [DPA] as the second monomer. Star diblock copolymer gelators that were both thermo-responsive and pH-responsive were obtained by the statistical copolymerization of DMA with DPA. Copolymer compositions were assessed by 1H NMR spectroscopy, and the molecular weight distributions of the three-arm star MPC homopolymer precursors were assessed by aqueous gel permeation chromatography. Static light scattering was used to obtain weight-average molecular weights of selected star diblock copolymers and rheological measurements and variable-temperature 1H NMR were used to probe the onset of gelation.

Double stimuli-responsive behavior of aliphatic poly(urethane-amine)s derived from supercritical carbon dioxide

Copolymeric products from 2-methylaziridine and carbon dioxide showed sharp and rapid phase transitions in response to both temperature and pH; the responsive property can be controlled by varying the reaction conditions whilst maintaining the supercritical state.

Thermo- and pH-responsive biodegradable poly(alpha-N-substituted gamma-glutamine)s

New double stimuli-responsive poly(alpha-N-substituted gamma-glutamine) has been developed, which was synthesized by the reaction of poly(gamma-glutamic acid) with amino alcohols. Appropriate combinations of the amino alcohols provided the biodegradable poly(amino acid) exhibiting a sharp lower critical solution temperature (LCST) in water. Furthermore, the phase transition temperature was highly sensitive to pH changes.

Chiral stimuli-responsive gels: helicity induction in poly(phenylacetylene) gels bearing a carboxyl group with chiral amines

Poly(phenylacetylene) gels (gel-1-H and gel-2-H) bearing a carboxy pendant were synthesized either by the copolymerization of (4-carboxyphenyl)acetylene (gel-1-H) with a bis(phenylacetylene) derivative as the cross-linking reagent using a rhodium complex ([Rh(cod)(2)]BF(4): cod = 1,5-cyclooctadiene) as the catalyst or by the cross-linking of poly[(4-carboxyphenyl)acetylene] with diamines (gel-2-H). The obtained gels were found to swell in DMSO and exhibited an induced circular dichroism (ICD) in the long absorption region of the main chain in the presence of optically active amines. These results indicate that a predominantly one-handed helix can be induced in the polymer network of the gels through chiral acid-base interactions. The swelling properties and the Cotton effect intensities of the gels depend on the cross-linking ratio and the chiral amines. Gel-1-Na and gel-2-Na prepared from gel-1-H and gel-2-H, respectively, also significantly swelled in water and showed ICDs characteristic of chiral amino alcohols and free amino acids in water.