Synthesis of star-like hybrid POSS-(PDMAEMA-b-PDLA)8 copolymer and its stereocomplex properties with PLLA.

Although poly(lactide) (PLA), when used as biomaterials, possesses many good properties, its high hydrophobicity and slow degradation may hinder its applications. In this work, a novel star-like oligomeric silsesquioxane-(poly(2-dimethylaminoethyl methacrylate)-b-poly(d-lactide))8 (POSS-(PDMAEMA-b-PDLA)8) was first synthesized through a three-step procedure that involves Reversible Addition-Fragmentation Chain Transfer (RAFT) polymerization of DMAEMA initiated by the macroinitiator POSS-8-CTA, and then conversion of the trithiocarbonated end groups on PDMAEMA arms into hydroxyl groups by a combination of aminolysis and Michael addition followed by controlled ring-opening polymerization of D-LA. In the next step, the synthesized hybrid copolymer POSS-(PDMAEMA-b-PDLA)8 was blended with PLLA in solution to form nanocomposites to further modify the thermo-mechanical and degradation properties of PLLA. It was noted that the outer PDLA shell could facilitate POSS-(PDMAEMA-b-PDLA)8 to be well-dispersed in PLLA matrix through stereocomplex (SC) interaction, and the inner PDMAEMA shell endowed PLLA with good hydrophilicity. The SC formation between POSS-(PDMAEMA-b-PDLA)8 and PLLA was confirmed by differential scanning calorimetry (DSC) and X-ray diffraction (XRD) analyses. The surface wettability of the PLLA was enhanced due to the presence of hydrophilic PDMAEMA segments and the contact angle values decreased with increasing amount of PDMAEMA in the nanocomposites. Meanwhile, controlled degradation of PLLA in a faster pace was achieved when the nanocomposites were incubated in different pH solutions, indicating its potential in specific biomedical applications.