Heterogeneity in polymer networks formed by a single copolymerization reaction: II. Post-gelation structure and pendants

Abstract

Coarse-grained molecular dynamics simulations are used to study polymer formation, network growth and topology of 3- and 6-functional systems derived from reactive precursors. Part I of this sequence explored the process prior to gelation and showed that crosslinking produces heterogeneous clusters that grow and coalesce at the gel point. Not only are there small, localized defects in the network, but their dendritic structure results in poorly crosslinked regions where clusters coalesce, leading to pendant structures which persist even at high conversion. 6-functional networks exhibit a greater variety of pendants than the 3-functional networks. For 6-functional crosslinkers, some pendants have two- and three-fold connections to the elastically active network and comprise a substantial fraction of local material. Visualizations of these pendants show possible types of imperfection in crosslinked polymer networks. Crosslinked polymers used in many applications are non-ideal networks containing structural and crosslinking defects which inevitably diminish function and durability.