Synthesis, characterization, crystalline morphologies, and hydrophilicity of brush copolymers with double crystallizable side chains

Novel brush copolymers with poly(2-hydroxyethyl methacrylate) (PHEMA) as polymer backbone and diblock copolymer consisting of crystallizable poly(epsilon-caprolactone) (PCL) and poly(ethylene oxide) (PEO) as side chains were synthesized successively by the combination of ring-opening polymerization (ROP) and coupling reaction. The molecular weights of poly(2-hydroxyethyl methacrylate)-graft-poly(epsilon-caprolactone) (PHEMA-g-PCL)brush copolymers were controllable, and the molecular weight distributions were in the range of 1.28-1.32. The coupling reaction efficiency of hydroxyl-terminated mPEO (mPEO-OH) with PCL-OH in the PHEMA-g-PCL to produce poly (2-hydroxyethyl methacrylate)-graft-poly(epsilon-caprolactone)-block-poly(ethy lene oxide) (PHEMA-g-(PCL-b-PEO)) ranged from 85.2% to 94.3%. The investigation of the melting and crystallization demonstrated that the values of crystallization temperature (T-c), melting temperature (T-m), and the degree crystallinity (X-c) of PHEMA-g-PCL were enhanced with the chain length increase of PCL. As for PHEMA-g-(PCL-b-PEO) brush copolymer, the T-m and X-c of the PCL blocks decreased with the chain length increase of PEO blocks. At the same time, the crystallizability of PEO segments was influenced by the brush structure of the copolymer and the PCL segments in the copolymer. Furthermore, PHEMA-g-PCL and PHEMA-g-(PCL-b-PEO) brush copolymers showed crystalline morphologies that were different from that of linear PCL according to the polarized optical micrographs and AFM images. Moreover, the hydrophilicity of copolymers could be improved and adjusted by the brush structure and the alteration of relative content of the PEO and PCL segments in the copolymers.