Ordered microdomain morphologies in saccharide-containing block copolymers

Abstract

Hybrid block copolymers containing both oligosaccharide and synthetic polymer components have attracted much interest in recent years as sustainable material alternatives. In particular block copolymers containing saccharides are capable of microphase separation at small molecular weights, leading to the formation of ordered morphologies with sub-10 nm feature sizes. We synthesize ABA-type triblock copolymers containing polystyrene as the synthetic mid-block and either trisaccharide maltotriose (MT) or disaccharide maltose (Mal) as the end blocks. The polymers are prepared by a combination of atom transfer radical polymerization (ATRP) and click reaction, and their bulk morphologies are examined by small-angle X-ray scattering (SAXS) and transmission electron microscopy (TEM). The MT-containing triblocks are found to form well-ordered domain structures with sub-10 nm periodicity, and morphology transition from cylinders to spheres to disordered spheres is observed with decreasing saccharide weight fraction. The Mal-containing triblocks also show microphase separation. However, the observed domain morphologies lack regular packing due to the close proximity of polymer glass transition temperature and order-disorder transition temperature. The saccharide components of the block copolymers are also found to undergo different degrees of dehydration when exposed to high temperatures. The dehydration reaction leads to the molecular change of the triblocks to form pentablock copolymers, resulting in the emergence of less ordered secondary morphologies in an irreversible manner.