Calorimetric study of fluorinated methacrylic and vinyl polymer blends .1. Binary systems: determination of miscibility domains and correlation of glass transition temperatures with blends composition - application to plastic optical fibre cladding

This paper reports a calorimetric study of binary polymer blends prepared by solution mixing of fluoroalkyl methacrylic ester-methyl methacrylate (MMA) copolymers with poly(vinylidene difluoride) (PVDF) or VDF-hexafluoropropene (HFP) (or VDF-trifluoroethylene) copolymers and examines their use as materials in plastic optical fibres (POF) technology. Some interesting blends were also obtained through mechanical mixing in the molten state. As compared to the well known PVDF-poly(methyl methacrylate) (PMMA) system, miscibility domains in copolymer blends become wider when less crystalline VDF copolymers are used in place of PVDF, whereas the opposite is found for the introduction of fluorinated alkyl ester side chains in PMMA. Correlation of the observed glass transition temperatures of homogeneous phases to their compositions failed with the Fox and Gordon-Taylor relations, whereas good fits could be observed using both Kwei and Jenckel-Heutsch relations. The q and b (specific interactions) parameters in these relations are well correlated to the chemical composition, indicating the influence of strong intermolecular interactions. In fluoroalkyl methacrylic ester-containing polymers, internal interactions are competing efficiently with intermolecular ones, thus limiting the miscibility of these polymers with VDF-homo- and copolymers. Some blends of the MMA-trifluoromethyl methacrylate with VDF-HFP copolymers give good performances as POF cladding material. A more simple solution lies in the use of VDF-HFP copolymers themselves. (C) 1997 Elsevier Science Ltd.