Vulcanizate tensile distribution

Among the main molecular structural variables in EPDMs that are stipulated by catalyst systems and that affect the vulcanizate tensile properties we may mention molecular weight (MW) and MWD, degree of unsaturation (LG=C 1) and its distribution in the polymer, composition (C S) and monomer sequence length distribution along molecular chains, and long-chain branching if present. Effect of... 

Vj g-EPDM and VOCI3-EPDM vulcanizate tensile strength Is not simply explainable by network quality resulting from difference In the third monomer distribution in the terpolymers. 

In Figure 8 are also reproduced data (curves A and C) of the other two systems previously given Q). It is clear that although addition of ETCA to the V g-EtyV Clo system makes the DCPD distribution in the terpolymer much more heterogeneous (curve A, compared to B) and yields lower vulcanizate tensile strength (see above), the much more even distribution of DCPD in V(acac) -EPDM... 

The distribution of the thi monomer in molecular chains or in the whole polymer should affect the perfection of the vulcanizate network, free chain ends or the uncross-linked parts in the polymer making no contribution to the tensile strength but acting as a plasticizer of like structure as the polymer. 

Apart from the elfect of the overall crosslink density of NR/NBR on the tensile strength of the blend, the crosslink distribution in separate phases is of great importance. Lewan" showed that for a 50/50 blend the higher tensile strength was evident for a NR/NBR crosslink density ratio of 1.0-1.2. Further tensile strength enhancement in a NR/NBR vulcanizate was obtained when methyl methacrylate grafted NR was added to the blend instead of NR." ... 

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