Composition-dependent depression of the glass transition temperature of the rubber phase in a PE-SBR blend

A thermoplastic elastomeric blend was introduced based on high-density polyethylene and styrene-butadiene rubber (SBR). The morphology of the blend system was found to change from two-phase to co-continuous, depending on the polyethylene (PE) concentration. The thermo-mechanical measurements showed that, at the PE concentrations, which seemed to have a co-continuous morphology, the SBR inclusions were very fine. The fineness of the SBR domains resulted in a 20° depression of the glass transition temperature (Tg) of the SBR phase. This was attributed to the smooth interfaces at which the SBR chain sensed a higher free volume as compared with that in bulk SBR. A model correlating thin polymer thickness to the Tg of the confined polymer in the films was employed to correlate SBR domain size to the experimental Tg measured. The adjusting parameters A=129 and δ=1.45 were successfully used to fit the experimental data.

Analysis of Cured, Filled Elastomeric Compounds by 13C NMR

This paper has discussed the study of cured, filled elastomers by a newly developed 13C NMR method. This method overcomes many of the shortcomings of other methods in that the 13C method is capable of distinguishing nonstandard or experimental polymeric components in an elastomeric blend, a definite advantage for the analyst. Other advantages are that the 13C data are primary, i.e., compositional calibration standards are not necessary once a polymer's 13C carbon resonances have been assigned; the data are accurate and reproducible; the filler (carbon black, TiO2, glass fibers) does not have to be removed prior to the analysis; and, the method is sensitive to low levels of polymer concentration. The superiority of 13C quantitative data over IR data has been demonstrated. Practical examples including nonstandard and/or unique elastomeric components have been discussed.