Star-shaped poly(ɛ-caprolactone) with polyhedral oligomeric silsesquioxane core

A readily available octa(3-chloropropyl) polyhedral oligomeric silsesquioxane (POSS) [(ClCH2CH2CH2)8Si8O12] framework was used to prepare octa(3-hydroxypropyl) POSS [(HOCH2CH2CH2)8Si8O12], which was further used as an initiator to synthesize star poly(ɛ-caprolactone) with POSS core via ring-opening polymerization catalyzed by Stannous (II) octanoate [Sn(Oct)2]. The organic-inorganic star PCLs were characterized by means of gel permeation chromatograph (GPC), Fourier transform infrared spectroscopy (FTIR) and nuclear magnetic resonance spectroscopy (NMR). The wide-angle X-ray diffraction (WAXRD) experiments indicate that the presence of POSS cores did not alter the crystal structure of PCL. The star PCLs exhibited enhanced melting temperatures in comparison with the linear counterpart. The isothermal crystallization kinetics shows that both the overall crystallization rate and the spherulitic growth rate of the star PCLs increased with increasing the concentration of POSS (or with decreasing the arm lengths of the stars). The fold surface free energy of the star PCLs decreased with increasing the concentration of POSS. These results could be interpreted based on the effect of the heterogeneous nucleation of POSS cores, which accelerates the process of crystallization.