Angel J. Satti

Influence of amorphous block on the thermal behavior of well-defined block copolymers based on ε-caprolactone

In this work, we studied the thermal characterization of block copolymers based on ε-caprolactone. The copolymers were obtained by anionic polymerization techniques, using different co-monomers such as styrene (S) and dimethylsiloxane (DMS). Synthesized copolymers were characterized by H-nuclear magnetic resonance, size exclusion chromatography, and Fourier transform infrared spectroscopy. Isothermal crystallization was performed by differential scanning calorimetry (DSC), and Avrami’s theory was employed in order to obtain kinetics parameters of interest, such as the half-life for the crystallization process (t1/2), the bulk crystallization constant (k), and the Avrami’s exponent (n). The spherulitic growth was measured by polarized optical microscopy in order to determine the crystallization behavior. Poly(ε-caprolactone) block (PCL) crystallization was analyzed by considering the physico-chemical characteristics of the neighboring block, PS or PDMS. The chemical nature of the neighbor block in the PCL-based copolymer affects the kinetics parameters of Avrami’s equation, as can be deduced by comparing the values obtained for pure PCL and the studied block copolymers. On the other hand, the apparent thermal degradation activation energies Ead for PCL and block copolymers were determined by Ozawa’s method. The incorporation of PDMS instead of PS improves the stability of the resulting copolymer, as it was observed by thermogravimetric analysis.

Anionic Ring Opening Polymerization of ε-Caprolactone Initiated by Lithium Silanolates

Ring-opening homo- and co-polymerization reactions of ϵ-caprolactone were performed by employing anionic polymerization (high vacuum techniques) and lithium silanolates (LS) as initiators. LS were obtained by reaction between hexamethyl(cyclotrisiloxane) and sec-Bu–Li+, or from living poly(dimethylsiloxanyl)lithium chains. The results indicated that LS are efficient initiators for the ring-opening polymerization of ϵ-caprolactone, providing the respective homogeneous polymers in good yields.