Studies on the miscibility of poly (aromatic (meth) Acrylate) s with styrene based polymers

Abstract

In spite of the vast development in polymer synthesis, even today there are only a handful of polymers which are used in bulk for technological applications. Blending offers one of the convenient ways of producing materials with varied properties. Unfortunately, due to the adverse entropy of mixing, polymers are generally not miscible. Hence, the preparation of homogeneous polymer blends is one of the major challenges in the area of polymer science. Polymers can be made miscible by promoting exothermic mixing through specific interactions such as hydrogen bonding, acid–base interaction, charge?transfer interaction, etc. Such exothermic mixing can also be achieved by the so?called ‘copolymer effect’ in a copolymer-containing blend, where the mutual repulsion between the comonomer units enforces miscibility. The ultimate properties of a blend are governed by its phase behavior, and hence there is a major emphasis on understanding their phase morphology. The various techniques employed to detect levels of miscibility show large variation in sensitivity. For example, conventional techniques like DSC are not capable of detecting micro?heterogeneities in blends. Finer techniques such as NRET and solid?state NMR relaxation methods can probe miscibility at the molecular level. In this review, a brief attempt has been made to focus attention on the physico?chemical characteristics that govern miscibility in polymer blends. PPA, PPMA, and PBMA homopolymers exhibit miscibility windows with AS copolymers. The existence of a miscibility window in these systems is the consequence of the strong repulsion between the styrene (St) and acrylonitrile (AN) units in AS copolymers, which dominates over other interactions in the blends. PBA does not show a miscibility window due to possible intramolecular hydrogen bonding. The phase behavior in PPA/AS copolymer and PBMA/AS copolymer blends has been studied with variation of AN content in AS copolymers. Phase diagrams for the miscible PPA/AS copolymer blends were constructed, and the phase compositions in partially miscible PPA/AS blends were determined. The level of miscibility was verified by NRET studies, which showed considerable narrowing of the miscibility?window limits obtained from DSC. From the miscibility?window limits, the Bij values were calculated and compared among the poly(aromatic (meth)acrylate) blends with AS copolymers. For a typical system consisting of styrene, acrylonitrile, and benzyl methacrylate monomer units, the miscibility predictions in homopolymer/copolymer and copolymer/copolymer blends were made and subsequently verified experimentally.