ASYMMETRIC SINGLE GRAFT BLOCK-COPOLYMERS - EFFECT OF MOLECULAR ARCHITECTURE ON MORPHOLOGY

This paper reports on the synthesis and morphological characterization of graft, block copolymers in which a single polystyrene (PS) arm was grafted at an asymmetric position along a polyisoprene (PI) backbone. These materials represent a model series of asymmetric simple graft ( ASG) block copolymer structures. The synthesis of these materials was carried out with methods developed for three-arm ''miktoarm'' star cop olymers using anionic polymerization high-vacuum techniques with cholo rosilane linking agents. The three arms were two polyisoprene blocks w ith different degrees of polymerization and one deuterated polystyrene block, which formed an asymmetric simple graft structure (ASG). Molec ular characterization was performed using size exclusion chromatograph y (SEC) with refractive index and UV detection, membrane osmometry, an d low-angle laser light scattering. These techniques confirmed that th e materials exhibited narrow molecular weight distributions and low co mpositional heterogeneity. The morphologies formed by these samples we re characterized using transmission electron microscopy (TEM) and smal l-angle neutron scattering(SANS). The ASG structures were compared wit h structures formed by Linear diblock copolymers and other samples hav ing miktoarm structures, like I2S (symmetric simple graft with PI back bone and one PS branch grafted from the middle) and I3S (three equal P I arms and one PS arm). Comparisons of the morphologies formed and the ir dimensions indicated that the chain stretching and lateral crowding due to the miktoarm architecture was partially alleviated by the diff erent lengths of PI blocks in ASG.