Melt Structure and its Transformation by Sequential Crystallization of the Two Blocks within Poly(L-lactide)-block-Poly(ɛ-caprolactone) Double Crystalline Diblock Copolymers

摘要: Sequential crystallization of poly(L-lactide) (PLLA) followed by poly(epsilon-caprolactone) (PCL) in double crystalline PLLA-b-PCL diblock copolymers is studied differential scanning calorimetry (DSC), polarized optical microscopy (POM), wide-angle X-ray scattering (WAXS) and small-angle (SAXS). Three samples with different compositions are studied. The sample the shortest PLLA block (32 wt.-% PLLA) crystallizes from a homogeneous melt, other two (with 44 60% microphase separated structures. structure melt changed as at 122 degrees C (a temperature which PCL molten) forming spherulites regardless composition, even 32% PLLA. SAXS indicates that lamellar periodicity than obtained forms (for segregated samples). Where majority block, 42 following leads to rearrangement structure, observed SAXS, possibly due local melting interphases between domains. POM results showed within previously formed spherulites. WAXS data indicate unit cell modified PCL, least for samples. minority did not crystallize (well below homopolymer temperature), pointing influence pre-crystallization on crystallization, although it lower temperature. Crystallization kinetics were examined DSC WAXS, good agreement general. rate decreased increase content copolymers. increasing content. Avrami exponents general depressed both components compared parent homopolymers. Polarized micrographs during isothermal crystalli zation (a) homo-PLLA, (b) homo-PCL, (c) (d) copolymer after 30 min 15 C.