The crystallization of the α \|and β \|form crystals of syndiotactic polystyrene ( s PS) is determined by the crystallization temperature. Being crystallized at various temperatures from the melt, sPS forms the β f...The crystallization of the α \|and β \|form crystals of syndiotactic polystyrene ( s PS) is determined by the crystallization temperature. Being crystallized at various temperatures from the melt, sPS forms the β form crystal at high temperatures above about 230℃, α form crystal at low temperatures below about 170℃ and a mixture of the α and β form at intermediate temperatures. The effect of different cooling rates is considered in more details. Since the β form crystallizes at high temperature from the melt.It will first crystallize during cooling.At low cooling rates,the crystalline phase of the β form has almost reached the maximum crystallinity of the sample by cooling to 230℃.So even the temperature for the α form formation is reached,there is no more crystallizable s PS portion remaining for the α form formation.That is the reason why the β form is always obtained by cooling at a slow or moderate rate.If cooling rate is high enough that the β form has almost no time to crystallize at high temperature,only the α form can crystallize at low temperature.That is the reason why only the α form crystal is obtained under quenching conditions.It clearly indicates that the crystallization temperature is the intrinsic factor controlling the formation the α \| and β \|form crystals.展开更多
With the help of differential scanning calorimetry, cone-plate and capillary rheometry andscanning electron microscopy, a research has been conducted on rheological behavior,crystallization and morphology of poly (but...With the help of differential scanning calorimetry, cone-plate and capillary rheometry andscanning electron microscopy, a research has been conducted on rheological behavior,crystallization and morphology of poly (butylene terephthalate) (PBT) blends containing athermotropic LCP. The blend has zero entrance pressure loss, although the LCP has rather largeone. The viscosity curve of the blend lies between those of the LCP and PBT. The crystallizationof PBT is not affected by the presence of the LCP together with no indication oftransesterification between the two ingredients. LCP spheres and ellipsoids with the size of 0. 5--1. 5 μm disperse in PBT matrix uniformly, which is related to the viscosity ratio of the two components.展开更多
文摘The crystallization of the α \|and β \|form crystals of syndiotactic polystyrene ( s PS) is determined by the crystallization temperature. Being crystallized at various temperatures from the melt, sPS forms the β form crystal at high temperatures above about 230℃, α form crystal at low temperatures below about 170℃ and a mixture of the α and β form at intermediate temperatures. The effect of different cooling rates is considered in more details. Since the β form crystallizes at high temperature from the melt.It will first crystallize during cooling.At low cooling rates,the crystalline phase of the β form has almost reached the maximum crystallinity of the sample by cooling to 230℃.So even the temperature for the α form formation is reached,there is no more crystallizable s PS portion remaining for the α form formation.That is the reason why the β form is always obtained by cooling at a slow or moderate rate.If cooling rate is high enough that the β form has almost no time to crystallize at high temperature,only the α form can crystallize at low temperature.That is the reason why only the α form crystal is obtained under quenching conditions.It clearly indicates that the crystallization temperature is the intrinsic factor controlling the formation the α \| and β \|form crystals.
基金Supported by the National Natural Science Foundation of China
文摘With the help of differential scanning calorimetry, cone-plate and capillary rheometry andscanning electron microscopy, a research has been conducted on rheological behavior,crystallization and morphology of poly (butylene terephthalate) (PBT) blends containing athermotropic LCP. The blend has zero entrance pressure loss, although the LCP has rather largeone. The viscosity curve of the blend lies between those of the LCP and PBT. The crystallizationof PBT is not affected by the presence of the LCP together with no indication oftransesterification between the two ingredients. LCP spheres and ellipsoids with the size of 0. 5--1. 5 μm disperse in PBT matrix uniformly, which is related to the viscosity ratio of the two components.
