Mechanism of Polymer Crystallization and Control of Fine Structure under Molecular Orientation

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Molecular weight (MW) dependence of physical properties is one-of the most common characteristics in polymeric materials. For example, melt viscosity of polymer shows remarkable MW dependence and can be scaled and expressed as a 3.4 power of MW for entangled polymer chains. Also the influence of MW on polymer crystallization rate has been the most interesting subject. We studied on molecular weight dependence of crystal nucleation rate (I) and crystal growth rate for various polymers. The temperature dependence of I and G showed bell-shaped curves showing clear maximum points of Imax and Gmax. Imax and Gmax showed remarkable MW dependence. The plots of the reduced growth rate (G/Gmax) and the reduced nucleation rate (Inmax) showed a single master curve without MW dependence. Imax and Gmax are characteristic references to nucleation and crystal growth rate behaviors, respectively. The MW dependence of Imax and Gmax are scaled and expressed as I and -0.5 power of MW, respectively for a c … More hain folding crystallization.Crystallization rate of Poly(carbonate) (PC) in general is very slow, however its rate is accelerated by polymer blending with poly(ethylene oxide) (PEO). The crystallization of PC in the PC/PEO blends is completed within several seconds. During crystallization of the blends, spinodal decomposition was observed and spherulite of PC was observed in PC rich phase. The crystallization of PC was controlled by up-hill diffusion during liquid-liquid phase separation in the polymer blends.Bi-and uni-axial drawing of poly(ethylene terephthalate) (PET) and poly(ethylene 2,6 naphthalene dicarboxylate) (PEN) were performed at various strain rates and temperatures. On-line measurements of drawing stress and birefringence were carried out under several drawing conditions. The stress-optical rule (SOR) was applicable at low birefringence, and the stress-optical coefficient obtained for drawing process was similar to the reported values. Flow drawings of PET and PEN were caused at relatively high drawing temperature and low strain rate. The SOR was also applicable in flow drawing conditions. To analyze the network structure of each sample that has low crystallinity and low birefringence, the entanglement density Nc of drawn films was analyzed from the measurement of heat shrinkage and shrinkage stress applying the rubber elasticity theory for Gaussian chain. In the drawing of PEN. Nc value of drawn sample was lower when the drawing temperature was higher and strain rate was lower.Structure formation of stereo complex (racemate) polylactides fibers by high-speed melt spinning and subsequent drawing and annealing process was investigated. Distinct crystalline reflections appeared in WAXD patterns of as-spun fibers above 4 km/min. The crystal modification was co-existence of alpha-form and stereo complex crystals, and reflection intensity of stereo complex crystal increased with an increase in the take-up velocity and a decrease in the throughput rate and spinning temperature. The crystalline reflections of annealed high-speed spun fibers showed higher orientation and richer stereo complex crystallites than the fibers obtained by drawing and annealing low-speed spun fibers. From the diameter profile measurement of the spin-line, it was found that higher crystallization temperature in the spinning process leads to the preferred formation of stereo complex crystals. Less