| Abstract
| - Reactive compatibilization of immiscible polymer blends is typically accomplished by graftingreactions between functional groups distributed randomly on one polymer and end-functional groups onthe other polymer. A number of model studies have focused on end coupling in polymer melts. In thiswork we compare directly reaction rate constants for an end-functional chain reacting with anend-functional chain, kE, vs reacting with a mid-functional chain, kM, using competitive reaction of phthalicanhydride end- and mid-functional poly(methyl methacrylate) (PMMA-eAn and PMMA-mAn) with amineterminal PMMA and polystyrene (PMMA-NH2 and PS-NH2). PMMA-eAn was labeled with 7-nitrobenz-2-oxa-1,3-diazole (NBD) while PMMA-mAn was labeled with anthracene. We measured the extent ofcoupling to block and graft copolymers selectively at the characteristic excitation and emission wavelengthsof NBD and anthracene using a fluorescence detector coupled with GPC. We found that coupling withthe mid-functional PMMA was slower under all reaction conditions investigated and had the increasingorder of kE/kM: homogeneous melt (1.7), solution (2.8), heterogeneous blend prepared in the mixer (2.6−3.2), and static flat interface (>10). The kinetic excluded-volume effect and steric hindrance due to thepolymer chain are considered to be the reasons for kE/kM> 1 in the homogeneous case. kE/kM in solutionwas in agreement with the value (2.1) predicted by the kinetic excluded-volume theory. The large valueof kE/kM in the static flat interface was attributed to end-group segregation at the interface. Interestingly,we found that flow affected the interfacial reaction tremendously, resulting in over 1000 times higherrate constant in heterogeneous melt blending than that in the static bilayer film.
|
