Many of the isomers of polybutadiene and polyisoprene elastomers can be characterized by thermal analysis.Tg is sensitive to side chain units (1,2 or 3,4 structure) for both polymers. Crystallinity measurements can characterizecis andtrans isomers. DMA and DEA master curves provide an idea of the heterogeneity of the chain units from the width of the loss factor
curves in theTg region. Thermal and thermooxidative degradation, as followed by DSC and DTG, can differentiate specific natural and synthetic
isomers of polyisoprenes in raw and vulcanized states.
Derivative heat flow curves give much more information about the phase heterogeneity of binary blends composed of NR, SBR
and BR elastomers thanTg. In blend compositions, the areas under the derivative heat flow curves appear to be an additive function of the concentration
of elastomers in the case of incompatible blends (NR/BR, NR/SBR). They are less than additive for either a partially compatible
blend (uncured SBR/BR) or a compatible blend (covulcanized SBR/BR). In the case of 60/40 SBR/BR blends, a DSC (T0.5) reveals a singleTg, in conformity with the earlier investigators, whereas the derivative heat flow curve shows two peaks (Tp) indicating incomplete homogenization of the phases. This is a new observation not mentioned in the published literature.
Thus, derivative heat flow traces are likely to provide a unique tool to determine compatibility of elastomers. The study
also reveals the importance of sample contact with the DSC pan in quantitative determinations.