The miscibility and morphology of hexamine cross-linked novolac/poly(ε-caprolactone) blends

The miscibility and morphology of novolac/poly(ε-caprolactone) (PCL) blends before and after curing were investigated by optical microscopy, differential scanning calorimetry (d.s.c.) and FT i.r. It was found that PCL is miscible with uncured novolac resin, as shown by the existence of a single glass transition temperature (T g ) in each blend. FTi.r. studies revealed that hydrogen bonding interaction in novolac/PCL blend occurs between the hydroxyl groups of novolac and the carbonyl groups of PCL, which is responsible for the miscibility of the novolac/PCL blends. However, remarkable changes occurred after the novolac/ PCL blends were cured with hexamine (HMTA), which can be considered to be due to the dramatic changes in chemical and physical nature of novolac resin during the cross-linking. Phase separation in the initially miscible novolac/PCL blends occurred after curing with 15 wt% HMTA (relative to novolac content). The phase structures of the cured blends show composition dependence. The cured novolac/PCL blends with novolac content up to 70 wt% were observed to be partially miscible, whereas the 90/10 cured novolac/PCL blend was found to be miscible. The curing reduces the intermolecular hydrogen-bonding significantly, but there still exists a considerable amount of residual intermolecular hydrogen bond in the cured blends with its strength much lower than that in the uncured blends. The morphology of the novolac/PCL blends was remarkably affected by curing. The curing results in the disappearing of the T g behaviour of novolac, owing to less mobility of the novolac chain segments.