An object of the present invention is to provide a rubber composition having excellent processability while excellent heat build-up reduction effect is maintained; and a pneumatic tire that uses the rubber composition. The rubber composition of the present invention contains: a diene rubber containing from 5 to 70 mass % of a modified butadiene rubber obtained by modifying an unmodified butadiene rubber (A) with a carboxy group-containing nitrone compound (B), the unmodified butadiene rubber (A) containing from 2 to 45 parts by mass of an unmodified low molecular weight butadiene rubber (A1) having from 1.5 to 60 mol % of vinyl bonding and having a number average molecular weight (Mn) of 2000 to 60000 per 100 parts by mass of an unmodified butadiene rubber (A2) having a number average molecular weight (Mn) greater than that of the unmodified low molecular weight butadiene rubber (A1).
本发明的目的是提供一种橡胶组合物,该橡胶组合物具有优异的加工性能,同时还能保持良好的减热效果;以及一种使用该橡胶组合物的充气轮胎。本发明的橡胶组合物包含:二烯橡胶,其中含有 5 至 70 质量%的改性
丁二烯橡胶,该改性
丁二烯橡胶是通过用含羧基的腈化合物(B)对未改性
丁二烯橡胶(A)进行改性而获得的,未改性
丁二烯橡胶(A)含有 2 至 45 质量份的未改性低分子量
丁二烯橡胶(A1),该
丁二烯橡胶(A1)具有 1.5至60摩尔%的
乙烯基键,且每100份质量的未改性
丁二烯橡胶(A2)的平均分子量(Mn)大于未改性低分子量
丁二烯橡胶(A1)的平均分子量(Mn),其平均分子量(Mn)为2000至60000。