Rubber Composition for Tire Tread Balancing Fuel Efficiency and Processability

The patent changes the chemical structure parameters of the polymer by introducing specific functional groups (mercapto group and filler affinity group) at the polymer end through controlled copolymerization. This allows the polymer to achieve both improved fuel efficiency through filler interaction and maintained processability by controlling the timing and extent of functional group introduction during polymerization, rather than adding hardening agents that would increase overall hardness.

The patent controls the molecular weight parameter by using a chain transfer agent during copolymerization to achieve a specific weight average molecular weight range (5,000 to 2,000,000). This controlled molecular weight, combined with the functional groups at the polymer end, provides sufficient abrasion resistance while preventing excessive hardness that would compromise processability.

The patent adjusts the glass transition temperature parameter by controlling the composition ratio of conjugated diene monomer (5-95 mass%) and unsaturated acyclic monoester (5-95 mass%), and by selecting appropriate monomers with different Tg values. This allows optimization of wet grip performance through higher Tg while maintaining processability through controlled composition and molecular weight.

The patent controls the styrene content parameter within a specific range (1-50 mass% of the copolymer) to achieve adequate wet grip performance. By combining controlled styrene content with controlled molecular weight and functional groups at the polymer end, the patent maintains processability while still achieving the desired wet grip performance through optimized composition parameters.