Ideal crosslinked‐polymers and their characterization in free‐radical monovinyl‐divinyl copolymerizations

Abstract

AbstractThe critical conditions in which the classical Flory‐Stockmayer gelation theory (F‐S theory) is applicable to monovinyl‐divinyl copolymerizations were pursued in detail. The resulting prepolymers or precursors of ideal crosslinked‐polymers were characterized as standard polymers for the discussion of network formation in free‐radical monovinyl‐divinyl copolymerizations. Methyl methacrylate was copolymerized with a small amount of ethylene dimethacrylate, butylene dimethacrylate or nonapropyleneglycol dimethacrylate in the presence of lauryl mercaptan, a chain transfer agent to reduce 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 and, moreover, to keep the primary chain length constant by inhibiting a gel effect. The ratio of the actual gel point to the theoretical one reached 1.1, supporting the validity of F‐S theory. The resulting prepolymers were subjected to SEC‐MALLS analysis to determine the molecular weights, the molecular‐weight distributions and the radii of gyration; the correlations of molecular weight vs. elution volume and radius of gyration vs. molecular weight were useful for the characterization of the precursors of ideal network‐polymers.