Effects of copolymer composition on the crystallization and morphology of poly(epsilon-caprolactone)-block-polystyrene

The morphology and melting behavior of poly(epsilon-caprolactone)-block-pol ystyrene (PCL-b-PS) copolymers, quenched from the melt or cast from the tol uene solution, were investigated by small-angle X-ray scattering (SAXS) and differential scanning calorimetry (DSC) as a function of copolymer composi tion. The glass transition temperature of PS blocks is higher than the melt ing temperature of PCL blocks. T-m,T-PCL, in this system, so that the molec ular motion is extremely restricted when the PCL block crystallizes in temp eratures below T-m,T-PCL. DSC results showed that the quenched PCL-b-PS did not crystallize at any temperature when PCL vol%. phi(PCL), was less than 26%, whereas it crystallized partially when phi(PCL) greater than or equal to 34% and the crystallinity increased with increasing phi(PCL), suggesting that phi(PCL) affects significantly the crystallizability of PCL blocks. H owever, crystallization was observed for all PCL-b-PS copolymers cast at 20 degrees C, and the crystallinity decreased appreciably with increasing the casting temperature. SAXS results revealed that high crystallinity PCL-b-P S copolymers had an intensity peak arising from the lamellar morphology, an alternating structure consisting of crystalline lamellae and amorphous lay ers, whereas low crystallinity PCL-b-PS copolymers did not show any SAXS pe ak, indicating the morphological difference among crystallized PCL-b-PS cop olymers. The morphology formed in PCL-b-PS is discussed as a function of ph i(PCL) in terms of the lamellar morphology observed for crystalline homopol ymers.