Synthesis and crystallization kinetics of silsesquioxane-based hybrid star poly(ε-caprolactone)

A series of silsesquioxane-based hybrid star poly(ε-caprolactone) with different arm length (SHPCL-4, SHPCL-10, SHPCL-40) were synthesized from ring-opening polymerisation of ε-caprolactone as a monomer initiated by silsesquioxane-based hybrid polyol (SBOH). Two linear poly(ε-caprolactone)s, LPCL-25 and LPCL-35, were also prepared for comparison. The sequence of LPCL-25<LPCL-35<SHPCL-4<SHPCL-10<SHPCL-40 for total molecular weights (Mn) and the sequence of SHPCL-4<SHPCL-10<LPCL-25<LPCL-35<SHPCL-40 for average molecular weight per arm ( M arm NMR ) were determined by 1H NMR and GPC measurements. The 1H NMR data also suggested that SHPCLs possess a spheric architecture with 29.2 arms in average. The crystallization kinetics study by non-isothermal DSC showed that the starting temperature of crystallization (Ts), the ending temperature (Te) and the peak temperature of exothermic curve (Tp) are in the order as: SHPCL-4<SHPCL-10<LPCL-25<SHPCL-40≈LPCL-35, while the crystallinity (Xc) follows the order of SHPCL-4<SHPCL-10<SHPCL-40<LPCL-25<LPCL-35. The corrected overall crystallization rate constant (Kc) calculated from Avrami equation were found to be in the order as: SHPCL-4<SHPCL-10<LPCL-35<LPCL-25≈SHPCL-40, which was further evidenced by the real time morphological observation with polarized light microscopy (POM). It is also found by the POM measurements that the inorganic core and star architecture greatly retards the nucleation of SHPCLs with short arms, while it helps the nucleation of SHPCL with longer arms.