PRIMARY MOLECULAR WEIGHT AND Mc OF VULCANIZATE

Abstract

This study was undertaken to elucidate the effect of primary molecular weight and molecular weight distribution on M_C of vulcanizates. A sample of cis-polybutadiene was fractionated using the column extraction method and the fractions thus obtained were characterized mainly by the method of dilute solution measurements. The results showed that the fractions had narrow molecular weight distribution and no appreciable amount of branched molecules. A suitable condition for vulcanization of rubber was determined using the nonfractionated original sample. All fractionated samples were vulcanized under under the same condition. M_C of these vulcanizates including that of original were measured by means of Flory-Rehner's swelling method. A relationship between M_C and M_N has been established : samples having M_N10⁵ were hard to vulcanize and above this M_N, M_C decreased gradually from 2.5 × 10⁴ to 1.5 × 10⁴ with an increasing M_N. Corresponding to the relationship of Ma and M_C to the molecular weight distribution curve of the original sample, the tendency of the distribution of M_C in its vulcanizate was estimated.