Hyperbranched polymer/montmorillonite clay nanocomposites

Two to four pseudo-generation aliphatic hyperbranched polymers (HBPs) with -OH end-groups have been solution processed with various types of montmorillonite (MMT) layered alumino-silicate clays, and carefully dried to produce solid HBP/MMT nanocomposites. Exfoliated nanocomposites were obtained by processing the polyester HBPs with up to 20 wt% Na⁺ MMT in water, and intercalation only became dominant at higher loadings, for which the MMT layer spacing was directly dependent on the HBP pseudo-generation number. Intercalation was observed at much lower MMT contents in HBPs processed with different organically modified MMTs in THF. In this case, the absolute MMT layer spacings in the nanocomposites showed little apparent dependence on the nature of the organic modifier and the pseudo-generation number of the HBP, although the difference between the final layer spacing and its value prior to mixing increased significantly with the polarity of the organic modifier. The various HBP/MMT nanocomposites were incorporated into polyurethane formulations by melt processing in the presence of a low molar mass polyol or solution processing in THF. Na⁺MMT contents as low as 1.2 wt% led to an increase in the rubbery plateau modulus by about 60% with respect to that of the corresponding unfilled matrix, whereas much smaller relative increases were observed with unexfoliated or partly exfoliated MMT.