Asymmetric miscibility in random copolymer/homopolymer blends
The use of copolymers to enhance miscibility in polymer blends has been the subject of considerable investigation in recent years. In this dissertation, we have examined the interfacial and bulk properties of random copolymers with their related homopolymers, particularly poly(styrene-ran-methyl methacrylate) (S-r-MMA) with polystyrene (PS) and poly(methyl methacrylate) (PMMA). This copolymer is of specific interest because the compositionally symmetric S-r-MMA shows preferential miscibility with PMMA as compared to PS. Such “asymmetric miscibility” is not predicted by standard models of polymer blend thermodynamics, and the reasons for this unique behavior are unclear. Our objectives were to investigate the efficiency of the S-r-MMA copolymer as an interfacial strengthener and blend compatibilizer, and to explore possible causes for asymmetric miscibility in homopolymer/random copolymer blends. Neutron reflectivity studies showed that the compositionally symmetric S-r-MMA random copolymer would be an interfacial specific additive, as it readily segregates from a miscible blend with deuterated poly(methyl methacrylate) (dPMMA) to the interface with deuterated polystyrene (dPS). Further neutron reflectivity experiments performed on bilayer samples allowed us to determine interfacial widths between Sf- r-MMA and dPS or dPMMA as a function of copolymer composition, f. These reflectivity results are presented in relation to previous results on the fracture toughness of PS/PMMA joints reinforced with Sf-r-MMA. We then developed the application of forward recoil spectrometry (FRES) to measure miscibility between deuterated and hydrogenated polymers. As deuteration was found to have a strong effect on the miscibility on the (d)PS/(d)PMMA/ S-r-MMA system, we developed a new technique for measuring the coexistence compositions in blends, namely cross-sectional microscopy of thick bilayers. We investigated the miscibility behavior of several blend systems containing a homopolymer and a compositionally symmetric random copolymer, looking for a correlation between asymmetric blend miscibility, monomer size and polarity. Results from microscopy and infrared spectroscopy studies suggest that both monomer packing and polarity may contribute to asymmetric miscibility in homopolymer/random copolymer blends. A second symmetric random copolymer, poly(styrene- ran-ethyl methacrylate), was also found to exhibit preferential miscibility with one of its related homopolymers, (poly(ethyl methacrylate)) over the other (PS).
Pellegrini, Nicole N, "Asymmetric miscibility in random copolymer/homopolymer blends" (1999). Dissertations available from ProQuest. AAI9937772.