Abstract
In our previous work, crystallization from hard confinement to soft confinement under strong segregation strength in crystallizable block copolymer, poly(styrene)-block-poly(L-lactide) (PS-PLLA) (having Tg,PS ~ 85 °C, Tg,PLLA ~ 45 °C, Tm,PLLA ~ 150 °C), in microphase-separated lamellar morphology has been studied. An undulated morphology induced by crystallization in lamellar structure was observed in the PS13-PLLA24 block copolymer at Tc,PLLA > Tg,PS (i.e. soft confinement). In this study, a series of semicrystalline block copolymers PS-PLLA with lamellar microstructure were synthesized. A variety of PS-PLLA with different molecular weights, namely distinct segregated strength, were obtatined and crystallized from hard confinement (i.e., the crystallization temperature of PLLA (Tc,PLLA) < the glass transition temperature of PS (Tg,PS)) to soft confinement (i.e., Tc,PLLA>Tg,PS), where interesting morphological evolution was studied by transmission electron microscopy (TEM) and time-resolved small angle X-ray scattering (SAXS). A confined morphology for crystallized PS14-PLLA15 (high-molecular-weight samples) was observed at Tc,PLLA < Tg,PS, while at Tc,PLLA > Tg,PS, an undulated morphology was found. The effect of crystallization on microphase-separated lamellae suggests a strong dependence on the confined environments (i.e., Tg effect) justified by the ratio of Tc,PLLA and Tg,PS that plays a critical role in determining the ultimate morphology after the crystallization of PLLA. Compared to Tg effect, the effect of segregation strength on the morphological evolution is insignificant.