Characterization of precursors of crosslinked polymers in the free-radical crosslinking copolymerization of benzyl methacrylate with polyethylene glycol dimethacrylate

Benzyl methacrylate (BzMA) was copolymerized radically with polyethylene glycol dimethacrylate [CH2=C(CH3)CO(OCH2CH2)(23)OCOC(CH3)=CH2] (PEGDMA-23) to provide novel amphiphilic polymers as precursors of crosslinked polymers governed by Flory-Stockmayer gelation theory (F-S theory). Thus, BzMA/PEGDMA-23 copolymerizations were conducted under the specified conditions where the occurrence of a thermodynamic excluded volume effect and intramolecular crosslinking as the primary and secondary factors, respectively, for the greatly delayed gelation in the free-radical monovinyl-divinyl copolymerizations was reduced: Firstly, the reasonable applicability of F-S theory was verified by the comparison of the actual gel point with the theoretical one. Secondly, the tailed molecular-weight distribution curves were observed with conversion as a result of the predominant occurrence of intermolecular crosslinking according to F-S theory. Thirdly, the applicability of F-S theory was supported by both the correlations of molecular weight versus elution volume and r.m.s. radius of gyration versus molecular weight, although the molecular size shrinkage of the resulting prepolymers consisting of rather rigid poly(BzMA) chains and flexible polyoxyethylene crosslinks would be enhanced with conversion as a result of increased crosslinking. (C) 2000 Elsevier Science Ltd. All rights reserved.