CRYSTALLIZATION OF MICELLES AND MATRIX IN DILUTE DIBLOCK COPOLYMER HOMOPOLYMER SOLUTIONS/

The crystallization, morphology, and crystalline structure of dilute s olid solutions of tetrahydrofuran-methyl methacrylate diblock copolyme r (PTHF-b-PMMA) in poly(ethylene oxide) (PEO) and PTHF have been studi ed with differential scanning calorimetry (DSC), X-ray, and optical mi croscopy. This study provides a new insight into the crystallization b ehavior of block copolymers. For the dilute PTHF-b-PMMA/PEO system con taining only 2 to 7 wt % of PTHF content, crystallization of the PTHF micellar core was detected both on cooling and on heating. Compared th e crystallization of the PTHF in the dilute solutions with that in the pure copolymer, it was found that the crystallizability of the PTHF m icellar core in the solution is much greater than that of the disperse d PTHF microdomain in the pure copolymer. The stronger crystallizabili ty in the solution was presumably due to a softened PMMA corona formed in the solution of the copolymer with PEG. However, the ''soft'' mice lles formed in the solution (meaning that the glass transition tempera tures (T-g) of the micelle is lower than the T-m of the matrix phase) showed almost no effects on the spherulitic morphology of the PEO comp onent, compared with that of the pure PEO sample. In contrast, signifi cant effects of the micelles with a ''hard'' PMMA core (meaning that t he T-g of the core is higher than the T-m of the PTHF homopolymer) on the nucleation, crystalline structure, and spherulitic morphology were observed for the dilute PTHF-b-PMMA/PTHF system. (C) 1998 John Wiley & Sons, Inc.