Synthesis and Properties of SEPS- g -PEO Copolymers with Varying Branch Lengths

Poly(ethylene oxide) (PEO) was controllably grafted from styrene- b -(ethylene- co -propylene)- b -styrene (SEPS) backbones by combining lithiation of styrenic units and living monomer-activated anionic ring-opening polymerization of ethylene oxide (EO) monomers with the aid of co-initiators triisobutyl aluminum. The as-synthesized SEPS- g -PEO copolymers were characterized by SEC, 1 H-NMR, FTIR, SAXS, AFM and DSC. When the branch length is relatively small, increase of PEO fraction leads to the increase of the correlation length between neighboring hard domains, but the degree of correlation reduces. When the branch length is relatively large, the phase-separated structures become random both in terms of size and spatial correlation, and macro-phase separated structures appear. The crystallization behavior of the PEO branches can be effectively inhibited in SEPS- g -PEO, so no significant crystallization takes place until the fraction of PEO branches is 20.1 wt%, which greatly promotes the rapid delivery of hydrophilic drugs in the hot-melting pressuresensitive adhesives (HMPSAs) based on SEPS- g -PEO. Their cumulative release amount of a model drug could achieve 80%, more than twice the value in the HMPSAs based on linear PEO-containing styrenic block copolymers.