Approach to Ideal Network Formation Governed by Flory−Stockmayer Gelation Theory in Free-Radical Cross-Linking Copolymerization of Styrene with m-Divinylbenzene

The critical conditions in which the classical Flory−Stockmayer gelation theory (F−S theory) is applicable to monovinyl−divinyl copolymerizations were pursued in detail. Thus, the cross-linking copolymerizations of styrene (St) with m -divinylbenzene ( m -DVB) as a most typical monovinyl−divinyl system were discussed under the specified conditions where the occurrence of a thermodynamic excluded volume effect and intramolecular cross-linking as the primary and secondary factors, respectively, for the greatly delayed gelation in the free-radical monovinyl−divinyl copolymerizations was reduced. The ratio of the actual gel point to the theoretical one reached 1.3, supporting the good applicability of F−S theory. In addition, the more tailed molecular-weight distribution (MWD) curves were observed with conversion as a result of occurrence of intermolecular cross-linking reaction leading to ideal network formation governed by F−S theory. Also, the swelling ratio of the gel obtained just beyond the gel point was very high, suggesting no microgelation up to the gel-point conversion. On the contrary, in the solution copolymerization of St with m -DVB in toluene at a dilution of 1 / 3 in the presence of a rather high amount of cross-linker, the considerable occurrence of intramolecular cross-linking reaction was clearly reflected on the greatly delayed gelation and the markedly changed MWD curve from a tailed one at a higher conversion.