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Why does cold-polymerized SBR improve tire wear resistance?

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Cold-polymerized styrene-butadiene rubber (SBR) improves tire wear resistance because the lower reaction temperature (approximately 5 °C, or 40 °F) results in polymer molecules that are more linear and possess a higher molecular weight compared to those produced through "hot" polymerization at 50 °C (120 °F).1

In contrast to hot-polymerized SBR, which tends to have more branched polymer chains, the more linear and higher-molecular-weight structure of cold-polymerized SBR enhances the material's durability and rolling resistance. To further improve wear resistance, manufacturers sometimes continue the polymerization process to create very high molecular weight products and incorporate heavy oil before coagulation, resulting in "oil-extended" elastomers that offer superior performance in tire applications.1