Thermoresponsive (Co)polymers through postpolymerization modification of poly(2-vinyl-4,4-dimethylazlactone)

Abstract

Poly(2-vinyl-4,4-dimethylazlactone), pVDMA, is emerging as a versatile reactive platform in polymer chemistry. Herein, postpolymerization modification of pVDMA leading to thermoresponsive homo- and copolymers is investigated. VDMA was polymerized by reversible addition–fragmentation chain transfer (RAFT) polymerization. The resulting reactive scaffolds with molecular weights ranging from 3.0 to 12.5 kg/mol were converted with a selection of alcohols and amines of varying polarity into functional poly(2-acrylamido isobutyrate)s and poly(2-acrylamido isobutyramide)s with molecular weights ranging from Mn = 4.2–65.1 kg/mol and low polydispersity indices Mw/Mn < 1.37. Spectra obtained by 1H NMR and infrared spectroscopic measurements conformed to the expected structures. While alcohols and amines producing water-soluble or water insoluble VDMA-derived homopolymers were identified, seven homopolymers were found to show a lower critical solution temperature in aqueous solution; those formed by reacting pVDMA with N-ethylamine, N-isopropylamine, N,N-dimethylamine, N,N-diethylamine, N,N-diethylaminoethylamine, Jeffamine M-600, and tetrahydrofurfurylamine (THF amine). Cloud points increased with decreasing molecular weight. With a cloud point of 31 °C, the phase separation of poly(tetrahydrofurfuryl 2-acrylamido isobutyramide) (pTAI) occurred close to body temperature, was highly reproducible, and, above a concentration of 0.5 wt %, was largely concentration independent. The transition temperature of pTAI-based copolymers could easily be tuned by reacting pVDMA with a mixture of THF amine and varying amounts of pentylamine or di(ethylene glycol) methyl ether amine.