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▼
