POLYMER CAPSULES BY LIVING RADICAL POLYMERIZATION

Abstract

<p>A novel technique for encapsulation by in situ suspension Atom Transfer Radical Polymerization (ATRP) was developed. The capsule wall-forming material was a crosslinked terpolymer based on diethylene glycol dimethacrylate (DEGDMA) crosslinker; a hydrophobic oil-soluble monomer, methyl methacrylate (MMA), and either polar oil soluble poly(ethylene glycol) monomethyl ether methacrylate (MPEGMA) or water soluble poly( ethylene glycol) methacrylate (PEGMA). Narrow disperse (MwlMn < 1.2) and linear MMAiMPEGMA (9 - 30 mol% MPEGMA) and MMAIPEGMA (10 - 40 mol% PEGMA) copolymers of controlled molecular weight (MW) were prepared in high yields (>90 and >80 wt.%, respectively) using tosyl chloride initiator and Cu(I)Cl - dinonyl dipyridyl catalyst in diphenyl ether (DPE) solution at 70 DC. Copolymer analysis by IH and l3C NMR showed quantitative incorporation of both MPEGMA and PEGMA into the copolymers. Suspension copolymerization of MMA with either MPEGMA or PEGMA in a DPE oil phase also yielded narrow disperse (MwlMn < 1.3) copolymers of controlled MW in high yields (>80 wt.%), indicating that the ATRP catalyst was confined to the oil droplets. IH NMR confirmed the incorporation of both MPEGMA and PEGMA into the copolymers forming in the oil phase, despite significant partitioning of MPEGMA and especially PEGMA into the water phase. In crosslinking suspension ATR terpolymerizations of MMA, MPEGMA and DEGDMA cross linker, a transition in particle morphology from solid to hollow and multi-hollow capsular particles was observed upon increasing the MPEGMA content (0 - 31 mol%) in the feed. Analogous conventional free radical polymerizations (CFRP) gave only solid polymer particles. Similarly, ATR terpolyrnerization of MMA, PEGMA and DEGDMA gave capsules at 17 mol% PEGMA, while CFRP only gave capsules at higher amounts PEGMA (24 mol%) in the feed. Both systems illustrated that the slow rate of ATRP favors the thermodynamically favored capsular morphology when compared to analogous CFRP experiments, and hence should permit capsule formation for more polar fiUs compared to CFRP.</p>