Isothermal crystallization of cis-1.4-polybutadiene at low temperatures

Abstract

The crystallization kinetics of commercial high cis-1.4-polybutadiene (BR) is measured by conventional differential scanning calorimetry (DSC) and fast differential scanning calorimetry (FDSC). This rubber has a glass transition temperature below -100 °C and is technically used for a wide application range.In a crystallinity range between 10 % and 30 % the ratio between the crystal and rigid amorphous fraction was determined to be about unity.Using the FDSC allows the quantitative characterization of the crystallization half time in the temperature range between the glass transition and the melting point even at low temperatures. For this, a discrete measurement method was applied. A single crystallization process was determined with the maximum crystallization rate at -50 °C.For crystallization below -40 °C, the measurements show that the melting temperature of the initially formed crystals is relatively low. The Avrami exponent is about unity. We observed comparable kinetics of nucleation and growth. A relatively large amount of an amorphous fraction with restricted mobility (the rigid amorphous fraction) is formed during crystallization at low temperatures. This finding leads to the model of self-assembled confinements for the low temperature BR crystallization.