ELASTOMERIC COPOLYMERS, USE AS TYRES

摘要

The invention relates to elastomeric copolymers of an aromatic vinyl compound and a conjugated diene, suitable for use in the tread portion of a pneumatic tire, which copolymers have a vinyl content of at least 30% by weight and comprise at least two polymer chains coupled to one another having a differential content of the aromatic vinyl compound at the ends of the copolymer which changes in a portion of not more than 5% of each polymer chain from a first value to a second value which is at least 25 percentage points higher than the first value, and said portion lies within the free terminal 10% portion of the copolymer chain (as determined by monomer conversion); their preparation and their use in tread portions of tires. The process of the invention is characterized by employing as structure modifier a compound of formula R1-O-CH2-CH2-O-R2 (I) wherein R1 and R2 are the same or different C2-18 alkyl groups, and on completion of polymerization, polymer chains are coupled by means of a coupling agent. The copolymers are characterized by containing a region extending over at least 50% of the polymer chain (as determined by monomer conversion) wherein the differential content of the aromatic vinyl compound in the polymer chain is at least 5% by weight less than the average content of the aromatic vinyl compound in the copolymer.