Tokyo (July 20, 2006) - Bridgestone Corporation has succeeded in the development of a synthesis technology for a revolutionary high cis butadiene rubber*¹ that chemically bonds with silica at its molecular chain end.

The rubber compound used in tires is a complex mixture of polymers such as natural rubber and synthetic rubber, reinforcing fillers such as carbon black and silica, together with other ingredients. One of the polymers, high cis butadiene rubber (also known as cis BR), has outstanding low-temperature flexibility, abrasion resistance and flex fatigue resistance on account of its microstructure, and its effectiveness is therefore widely known. Silica, on the other hand, displays excellent performance in wet grip and also reduces rolling resistance. As a result, efforts over the years have focused on combining these two materials, but there was a limitation coming from poor affinity of cis BR with Silica. In order to draw out the maximum advantages of the two, it was therefore necessary to greatly increase affinity. The technological tool to achieve this used to be very limited.

Bridgestone developed two new technologies to achieve this. The first technology generates a polymer chain of high cis butadiene rubber with an active site at its chain end, by redeveloping the polymerization catalyst, which converts monomer*² molecules to a polymer chain. The second technology relates to the chemical conversion of the chain-end active site to the silica-reactive functionality, by reaction with a carefully designed functionalizing agent. The integration of these two technologies led to the successful development of the end-functionalized high cis butadiene rubber (RC polymer)*³ with reactivity to silica.

With silica compounds that use RC polymers, the dispersion and the distribution of the silica in the compound is improved, thereby delivering even improved flexibility in cold conditions that allows superior contact with road surface, if used in tire tread. At the same time, such compound can retain comparative stiffness compared with compounds based on ordinary polymers in warm conditions. This makes for exceptional, balanced performance. Bridgestone has applied this new technology as a means to controlling changes in the properties of the rubber caused by changing road surface temperatures in the compound for its new studless tire in Japan.

NanoPro-Tech (Nanostructure-Oriented Properties Control Technology) is the generic name for the technology to control the affinity between the filler and the polymer at will. This is achieved through the molecular design of the polymer, the filler or other chemicals. Through this technology, the rubber morphology becomes controllable more than ever, and as a result, it is possible to fabricate compounds that can draw out the features required for different applications.

The compound achieved with NanoPro-Tech provides many benefits for the tire. It helps to reduce rolling resistance, thereby boosting environmental performance, while safety is improved, including better wet braking performance. Bridgestone plans to create various compounds using NanoPro-Tech and apply them to its tires to bring customers exceptional safety and environmental performance.

Details of this technology follow.

Technical glossary:

*1: High cis butadiene rubber (cis BR) Polymer of 1,3-butadiene can be composed of three types of microstructure; trans-1,4-, cis-1,4- and vinyl-1,2, and usually contains all of these three types. The cis BR is a type of butadiene polymer with a cis-1,4- content of more than about 90%, thus displays outstanding low-temperature characteristics, abrasion resistance and flex fatigue resistance.

*2: Monomer A chemical compound that can undergo polymerization, which is a chemical reaction in which two or more molecules combine to form larger molecules that contain repeating structural units.

*3: End-functionalized high cis butadiene rubber High cis butadiene rubber that has a special functional group at the chain end, through which it can undergo bonding reaction with given filler surface. - end - RC polymer: ReactoCis polymer