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Intimate blending of binary polymer systems from their common cyclodextrin inclusion compounds

2005-09-15
Uyar, Tamer
Rusa, Cristian C.
Wang, Xingwu
Rusa, Mariana
Hacaloğlu, Jale
Tonelli, Alan E.
A procedure for the formation of intimate blends of three binary polymer systems polycarbonate (PC)/poly(methyl methacrylate) (PMMA), PC/poly(vinyl acetate) (PVAc) and PMMA/PVAc is described. PC/PMMA, PC/PVAc, and PMMA/PVAc pairs were included in gamma-cyclodextrin (gamma-CD) channels and were then simultaneously coalesced from their common gamma-CD inclusion compounds (ICs) to obtain intimately mixed blends. The formation of ICs between polymer pairs and gamma-CD were confirmed by wide-angle X-ray diffraction (WAXD), fourier transform infrared spectroscopy (FTIR), and differential scanning calorimetry (DSC). It was observed [solution H-1 nuclear magnetic resonance (NMR)] that the ratios of polymers in coalesced PC/ PMMA and PC/PVAc binary blends are significantly different than the starting ratios, and PC was found to be preferentially included in gamma-CD channels when compared with PMMA or PVAc. Physical mixtures of polymer pairs were also prepared by coprecipitation and solution casting methods for comparison. DSC, solid-state H-1 NMR, thermogravimetric analysis (TGA), and direct insertion probe pyrolysis mass spectrometry (DIP-MS) data indicated that the PC/PMMA, PC/PVAc, and PMMA/ PVAc binary polymer blends were homogeneously mixed when they were coalesced from their ICs. A single, common glass transition temperature (Tg) recorded by DSC heating scans strongly suggested the presence of a homogeneous amorphous phase in the coalesced binary polymer blends, which is retained after thermal cycling to 270 C. The physical mixture samples showed two distinct T-gS and H-1 T-1 rho values for the polymer components, which indicated phase-separated blends with domain sizes above 5 run, while the coalesced blends exhibited uniform 1H spin-lattice relaxation values, indicating intimate blending in the coalesced samples. The TGA results of coalesced and physical binary blends of PC/PMMA and PC/PVAc reveal that in the presence of PC, the thermal stability of both PMMA and PVAc increases. Yet, the presence of PMMA and PVAc decreases the thermal stability of PC itself. DIP-MS observations suggested that the degradation mechanisms of the polymers changed in the coalesced blends, which was attributed to the presence of molecular interactions between the well-mixed polymer components in the coalesced samples.