Multifunctional poly(methacrylate ester)s-based terpolymer cryogels with basic amino groups: Correlation of elasticity and structural properties with composition

Abstract

Dual-responsive cryogel-structured materials open up a whole new field of bio-applications. Either dimethylaminoethyl methacrylate (DMAEMA) as a carrier of basic amino groups or glycidyl methacrylate (GMA) as a carrier of epoxy rings was introduced into hydroxypropyl methacrylate (HPMA) skeleton. pH/thermo-responsive cationic terpolymer cryogels were successfully prepared by varying the feeding DMAEMA/GMA mol percent ratio from 80/0 to 0/80. The presence of GMA imparts hydrophobic character that reduces swelling and provides additional crosslinks leading to a significant increase in the flexibility. Reducing the polymerization temperature below the freezing point of the solvent resulted in harder and non-brittle cryogels. Up to 48% reduction in hydration was observed for terpolymer cryogels containing 70 mol% DMAEMA upon increasing pH of bathing medium from 2.1 to 8.0. This trend confirmed pH-modulated swelling of amine-containing terpolymer gels, and pH-dependent transition point was found to be 7.7. Oscillating swelling/deswelling in response to pH cycles was studied. The water transport was strongly affected by incorporation of hydrophobic component GMA and protonation of amine functional groups. The swelling mechanism was shifted from anomalous to diffusion controlled with increasing GMA and overall swelling processes followed Schott second order dynamic equation. Lower equilibrium volume swelling at constant temperature was achieved by increasing GMA content of the terpolymers. In low temperature range, while DMAEMA-rich terpolymer gels were swollen, swelling decreased significantly when the gels were enriched in GMA and the temperature was raised above 55 °C. Regardless of salt type and Na+ or K+ hydrated ion radii, a significant difference was observed in salt-sensitive swelling in dilute salt solution (below about 10−3 M), which is controlled by the amount of DMAEMA in terpolymer structure. This study would provide novel ideas for the design of (meth)acrylate ester-based cationic terpolymer cryogels and elucidate the relationship between the gel matrix and their special swelling behavior.