Synthesis and characterization of graft copolymers poly(ethylene oxide)-g-[poly(ethylene oxide)-b-poly(ε-caprolactone)] with double crystallizable side chains

Using a "grafting from" strategy, the graft copolymer poly(ethylene oxide)-g-[poly(ethylene oxide)-b-poly( epsilon -caprolactone)] [PEO-g-(PEO-b-PCL)] with double crystallizable side chains was synthesized by a sequential ring-opening polymerization (ROP) mechanism. First, the ethoxyethyl glycidyl ether (EEGE) monomers containing a protected hydroxyl group were copolymerized with ethylene oxide (EO) monomers to form poly(ethylene oxide-co-ethoxyethyl glycidyl ether) [poly(EO-co-EEGE)], and the pendant hydroxyl groups were recovered by cleavage of the protecting groups for give poly(ethylene oxide-co-glycidyl) [poly(EO-co-Gly)]. Then, using poly(EO-co-Gly) with the pendant hydroxyl groups as a macroinitiator, the graft copolymer poly(ethylene oxide)-g-poly(ethylene oxide) (PEO-g-PEO) was obtained by ring-opening polymerization (ROP) of the EO monomers, and the graft copolymer PEO-g-(PEO-b-PCL) was obtained by sequential ROP of epsilon -CL monomers. The target PEO-g-(PEO-b-PCL) and intermediates were all characterized in detail by size-exclusion chromatography (SEC) and Proton Nuclear Magnetic Resonance Spectroscopy ( super(1)H NMR). The thermal stability and crystallization behaviors were investigated by thermogravimetric analysis (TGA), differential scanning calorimetry (DSC) and X-ray diffraction (XRD). The results showed that the graft structure and compositions had important effects on the thermal stability and crystallization behaviors, and the crystallizability of graft copolymers was predominantly controlled by the outer segments.