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ABSTRACT:The bulk properties of two types of amphiphilic networks, poly(2-hydroxyethyl methacrylate)-l-polyisobutylene (PHEMA-l-PIB, H-network) and poly( N,N-dimethylacrylamide)-l-polyisobutylene (PDMAAm-l-PIB, A-network), have been investigated. Tensile strengths decreased considerably by swelling, and the decrease was more severe by swelling in water than in n-heptane. Elongations increased by swelling in water; however, the change was not consistent upon swelling in n-heptane. The hardness of dry networks decreased with increasing PIB content, while for wet networks it was similar to dry networks containing 85 wt % PIB. Small-angle X-ray scattering showed that average interdomain spacings decreased with increasing PIB content. According to dynamic mechanical thermal analysis (DMTA) the glass transition temperatures (T g ) of the respective hydrophobic and hydrophilic components shift toward each other with increasing PIB content. A ''liquid-liquid transition'' ( T ll ) above the T g of the hydrophilic component was apparent by DMTA, but could not be found by differential scanning calorimetry (DSC).

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ABSTRACT:Blends of bisphenol A polycarbonate (PC) and poly(phenyl methacrylate) (PPMA) were crystallized by tetrahydrofuran (THF) solvent to investigate the phenomena of solvent-induced crystallization. The optimum conditions for solvent induced crystallization in PC have been determined. Interaction parameter has been calculated based on the melting point depression method to estimate the extent of miscibility. A negative interaction parameter (z 12 = -0.21) obtained from the melting point depression method suggests that there is some attractive interaction between the blend components.KEY WORDS Blend / Solvent Induced Crystallization / Interaction Parameter / Polycarbonate (PC) has been widely used both as a blend partner and by itself because it has outstanding engineering properties. Furthermore, due to its remarkable transparency, PC has been recognized as a suitable plastic for optical storage disc. 1 -4 The criteria of such optical materials 4 require low birefringence, low hygroscopicity, high transmission, dimensional stability, processability, and good mechanical properties. These stringent requirements can be fulfilled by specially designed polycarbonates. 2 However, PC shows a large positive birefringence, 5 which might cause optical distortion, owing to the presence of aromatic groups in the main chain. This positive birefringence can be eliminated substantially by blending with a polymer which has negative birefringence and can form a single phase with the constituent polymer. Poly(phenyl methacrylate) (PPMA) may be chosen as the blend partner of PC to form a miscible birefringence-free blend. For this reason, the birefringence-free composition of the PC/PPMA blend may be determined. The copolymers of PPMA and their blends often been reported to be used as optical lenses 6 -16 and optical disk recording materials 1 7 because of the high refractive index (1.5706) and high transparency of PPMA. But PPMA is very brittle and has low dimensional and thermal stability. 18 On the other hand, PC shows tough and ductile properties, good processability, thermal stability, and good electrical properties, but its poor scratch resistance and thermal stresscracking with its large birefringence are disadvantages. lt can be expected, therefore, that the drawbacks of each pure component can be overcome by blending the two components. By controlling the compositions of the blends, the improvement of physical properties may be achieved.We have demonstrated that the blends of the PC/ PPMA are completely miscible 19 and the birefringence and tensile properties of the blends were excellent. It is therefore of paramount importance to identify the origin of miscibility and to estimate the extent of miscibility by determining z12 interaction parameter. It has been known that solvent-induced crystallization can occur in PC. In this paper, the phenomena of solvent-induced 970 crystallization and the melting behavior of PC in the blends have been investigated. Subsequently, z12 interaction parameter was calculated based on ...

SYNOPSISMiscibility studies on blends of polycarbonate (PC ) and poly (phenyl methacrylate) (PPMA) were undertaken by means of differential scanning calorimetry (DSC) , dynamic mechanical, and dielectric relaxation methods. PC and PPMA were mixed by dissolving in tetrahydrofuran (THF) and subsequently coprecipitated in methanol. DSC studies showed a single glass transition ( T,) that shifts systematically with composition. These Tgs are reproducible in repeated DSC heating cycles, suggesting true miscibility of the pair.The dry PC and PPMA pellets were melt mixed in a Mini-Max Mixer/Molder. The extrudates were compression molded. These melt-mixed PC/PPMA blends exhibited glasslike transparency and also showed a single Tg in the DSC scans. The true miscibility of PC and PPMA was further confirmed by dynamic mechanical and dielectric relaxation methods. The net birefringence has been reduced substantially because of the opposite sign of the intrinsic birefringence of PC and PPMA molecules. At the 12/88 PC/PPMA, the birefringence remains zero at all draw ratios, indicating the achievement of birefringencefree polymer alloys.