Characterization of the miscibility of polystyrene and styrene copolymers with polymethacrylates by fluorescence techniques

Nonradiative energy transfer (NET) in systems containing polymers labeled with donor and acceptor chromophores, respectively, and excimer emission in a mixture of fluorescent and nonfluorescent polymers were used to characterize polymer miscibility. Thus, a styrene copolymer labeled with a small concentration of fluorescence donor, 2-(N-carbazolyl) ethyl methacrylate (CEMA) and styrene terpolymers containing CEMA and hydrogen bond donors of methacrylic acid (MAA), methacryloyl glycine (MAG), styrene sulfonic acid (SSA), p-(hexafluoro-2-hydroxyl isopropyl) styrene (HHIS) or p-vinyl phenol (VP) were prepared. These polymers were blended with hydrogen bond acceptors of poly(methyl methacrylate) (PMMA), poly(ethyl methacrylate) (PEMA), poly(n-butyl methacrylate) (PnBMA), or poly-(t-butyl methacrylate) (PtBMA) labeled with a fluorescence acceptor, 9-anthrylmethyl methacrylate (AMMA). The polymer blends were cast from dioxane, chloroform or toluene solution and the mutual interpenetration of the components of these blends was characterized by the relative fluorescence intensities of the donor and the acceptor. The miscibilities of these blends were found to be generally increased with an increasing content of the hydrogen bond donor in the styrene copolymers and the blend phase behavior depended strongly on the casting solvent used. The NET data also indicated that PEMA blends are most homogeneous and the relative efficiency of hydrogen bond donors employed in promoting the miscibility can be arranged in the decreasing order of HHIS, VP {dollar}>{dollar} SSA {dollar}>{dollar} MAG, MAA. This observation indicated that, in view of the larger excess of ester groups in the systems, the compatibilizing efficiency of the blends is not determined by the acidity of the hydrogen bond donors. The glass transition temperatures of PEMA and PnBMA blends with styrene copolymers determined by DSC gave consistent results with NET data.; Blends of unlabeled PS with unlabeled polymethacrylates were also characterized by excimer fluorescence in comparison with the NET method. It was found that the emission intensities of the excimer and the monomer band of PS blends with PEMA were higher than in blends with PMMA. This is in contrast with the evidence from NET data that PS/PEMA blends are more homogeneous than PS/PMMA blends. We believed that this is due to the lower rigidity of PEMA (T{dollar}sb{lcub}rm g{rcub}{dollar} = 70{dollar}spcirc{dollar}C) relative to PMMA(T{dollar}sb{lcub}rm g{rcub}{dollar} = 100{dollar}spcirc{dollar}C).