Synthesis and Distribution of Structural Units-Thermal Property Relationship of Random and Block Butadiene-Styrene Copolymers with High Trans 1,4 Units Content Produced Using an Initiator Composed of Alkyl Aluminum, n-Butyl Lithium, and Barium Alkoxide

摘要

Random, diblock, and triblock copolymers of butadiene and styrene, with a well-defined, high number of 1,4-trans units (c.a. 80%), were synthesized by anionic living polymerization using an initiator system composed of alkyl aluminum, n-butyl lithium, and barium alkoxide. The thermal properties of the block copolymers obtained by sequential addition of monomers were basically determined by the 1,4-trans units of the polybutadiene block. Kinetic data and H-1-nuclear magnetic resonance analyses showed that simultaneous polymerization of butadiene and styrene provided copolymers with a predominantly random distribution. By increasing the styrene content, the thermal properties of these copolymers were modified; polymers with 80% content of 1,4-trans units and 5% of styrene presented an endothermic transition at or slightly below room temperature (20 degrees C), corresponding to the crystalline monoclinic form of high 1,4-trans polybutadiene, whereas copolymers with 25-50% styrene content were amorphous. The glass transition temperature of these copolymers increased significantly as the styrene content was increased. Both the block and random copolymers have a sufficient number of 1,4-trans units to display a regular distribution of structural units that makes them susceptible to strain-induced crystallization, which is important for the manufacture of products such as high-performance tires.