Controlled grafting modification of starch and UCST-type thermosensitive behavior in water

Abstract

A controlled grafting modification starch exhibited tunable phase transition temperature in aqueous solution was prepared via reversible addition–fragmentation chain transfer (RAFT) polymerization and esterification reaction under mild condition. P(AM/AN) copolymer was grafted onto the starch backbone and endowed the grafted copolymer thermosensitivity. The molecular structure and composition of P(AM/AN) copolymers were characterized by gel permeation chromatography (GPC), FTIR, and NMR, indicating a structurally controllable side chain of the grafted copolymer. Results of X-ray diffraction (XRD) demonstrate that the crystallinity of grafted copolymer decreases compared with starch due to side chains destruct the structural regularity of starch. Scanning electron microscopy (SEM) images show that grafted copolymer displays a rough, multilayer, and irregular morphology. Dynamic light scattering (DLS) and UV tests indicate that the grafted copolymer forms aggregates in aqueous solution and the UCST of the grafted copolymer is dependent on percent grafting (PG) and molecular interactions of side chains.