Differential thermal analysis (DTA) was carried out at higher temperatures, using graft polymers, which were obtained by solvent extraction of gross polymers, and untreated gross polymers in some cases. Polybutadiene (PBu), polystyrene(PSt) and polyacrylonitrile (PAN) were utilized as a standard homopolymer respectivly, and their DTA curves were interpreted satisfactorily. Blend polymers, random copolymers and graft polymers containing butadiene (Bu)-styrene (St) and Bu-acrylonitrile (AN) components were analyzed by DTA method. Next, DTA curves of SBR-AN, NBR-St and PBu-(AN+St) grafted polymers were analyzed and compared with those of the corresponding blend polymers. It is found that both blend and graft polymers almost retain the characteristic DTA peaks of each component homopolymer, and that exothermal peaks of graft polymers often shift to lower temperatures compared with those of homopolymers.

View full abstract

The co-crosslinking of EPDM/SBR blends was investigated by measurements of cure rate, compatibility and crosslink structure.
The results obtained are as follows. The more closely approached the cure rate of EPDM and SBR, the better physical properties of the blends were abtained.
However, since there is no compatibility of EPDM with SBR, the blends have no mutual molecular chain interactions. As a result, the co-crosslinking between different polymers was rather difficult.
On the other hand, it was found by measurements of tensile strength, Mooney-Rivlin plots, repeated tension at constant elongation, polymersolvent interaction parameter of the blends, and temperature dependence of dynamic shear modulus and tan δ that co-crosslinking between different polymers was greatly influenced by the crosslink structure.
It was thus considered that EPDM/SBR blends could co-crosslink, if the cure rates were almost the same and if the crosslink structure had polysulfide type crosslinking.

View full abstract

N, N′-Diphenyl-p-phenylenediamine (DPPD) or N, N′-diphenyl-p-quinonediimine (DPQI) was added to both peroxide and sulfur vulcanizates of IR, BR and NR by swelling method. Interconversion between DPPD and DPQI was determined during the autoxidation of vulcanizates. Conversions, (DPPD→DPQI)and (DPQI→DPPD) were observed in the oxidation of peroxide vulcanizates. Rubber hydroperoxide was assumed to participate in the conversion (DPQI→DPPD). During the oxidation of the sulfur vulcanizates, the amount of DPQI resulting from DPPD, in general, was either comparatively small or null (for NR) and the amount of DPPD from DPQI was a trace or null after 25hr oxidation. The reaction by which DPQI interacts with sulfur atom in crosslinking or with other sulfur compounds to give other products seems to compete with conversion (DPQI→DPPD).
The reason that DPPD is more effective on peroxide vulcanizates than on sulfur vulcanizates is concluded to be attributed to the interconversion (DPPD_??_DPQI) in peroxide vulcanizates.

View full abstract