Effect of polymer chain modifications on elastomer properties – Part 1

Considerable attention is paid to the influence of crosslink density and crosslink structures on behavior of polymer chains and properties of elastomers. However, a very important parameter seems to be underestimated: the modifications to the polymer chains by curatives, formed by sulfur and fragments of accelerators. The present paper intends to draw attention to this important contribution to performance of spatial networks. Emulsion styrene-butadiene rubber (E-SBR) samples, cured with tetramethylthiuram disulfide and sulfur (TMTD/S8), and zinc dialkyl dithiophosphate with sulfur (ZDT/S8), were studied. They were characterized in detail in terms of crosslink density and crosslink structures. Microscale techniques were used to obtain information about the behavior of the polymer chains: PALS to study the free volume structure; DSC and DMA to monitor the glass transition process. Properties such as static mechanical performance and thermal stability were also evaluated. All of the investigated characteristics were influenced by a combination of crosslink density, crosslink structures, and, to a large extent, by the modifications of the polymer chains. The effect of the modifications is dependent on the amount and the structure of the curatives’ molecules. On the basis of the obtained results, the reliability of “phr” unit used for calculation of the curatives’ amount has been queried. Furthermore, it has been demonstrated that DSC, DMA and PALS techniques can provide evidence for the presence of the modifications on the polymer chain by curatives. Part 1 describes how the composition of the curing system generally influences the network structure. It contains the experimental part and the comparison of the crosslink density, crosslink structures and modifications of the chains, formed as a result of curing with TMTD/S8 or ZDT/S8.