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

Abstract

AbstractRandom, 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 1H‐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°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. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010