CHARACTERIZATION OF POLYMERS BY GPC-LALLS (III)

Abstract

Gamma ray-irradiated EPM's, as model polymers of branched EPDM, are investigated on the relation g'=g^b, where g' is the ratio of intrinsic viscosities of the branched and linear molecules of equal molecular weight (MW), [η]_br/[η]₁, and g the ratio of mean-square radii of gyration of the two, <s²>_br/<s²>₁. The MW distributions measured by GPC-LALLS coincide well with theoretical curves of tetrafunctionally and statistically branched polymers obtained by the ideal degradation and crosslinking of the raw EPM, which assumed to have the most probable MW distribution, and the b-value is then determined to be 1.1.
EPDM samples, polymerized with a soluble vanadium compound-alkyl aluminum halide type catalyst in a contineous well-stirred pilot-reactor, are characterized on number of branching points per molecule for various MW by using the b-value. The higher the MW, the distance between neighboring crosslinking points seems to become the narrower. The reason is discussed. The unsaturated bond by dicyclopentadiene of the rubber crosslinks easier in the manufacturing process than that by 5-ethylidene-2-norbornene. The largest high-MW portion and the broadest MW distribution are observed in the EPDM with the maximum dicyclopentadiene content.