MISCIBILITY AND MORPHOLOGY OF THERMOSETTING POLYMER BLENDS OF NOVOLACRESIN WITH POLY(ETHYLENE OXIDE)

Polymer blends of novolac resin and poly(ethylene oxide) (PEG) were pr epared by solution casting from N,N-dimethylformamide (DNIF). The misc ibility and morphology of the blends before and after curing were inve stigated by optical microscopy differential scanning calorimetry (d.s. c.) and Fourier transform infrared (FTi.r.) spectroscopy. It was found that PEO is miscible with uncured novolac over the entire composition range, as shown by the existence of a single composition-dependence g lass transition temperature (T-g) FTi.r. studies revealed that hydroge n bonding interactions exist between the hydroxyl groups of novolac an d the ether oxygens of PEG. The relative amount and the average streng th of the hydrogen bonds in the blends were higher than those in the p ure novolac resin. The curing with 15 wt% hexamine (HMTA) (relative to novolac content) resulted in the disappearance of a detectable T-g in both the neat novolac and the novolac-rich blends, due to the reduced mobility of the novolac chain segments. An analysis of the reduction in T-m and crystallization rate with increasing novolac content reveal ed that the HMTA-cured blends remained completely miscible. After curi ng with HMTA, considerable hydrogen bonding interaction between the co mponents still existed, which is the driving force for the miscibility of the HMTA-cured blends. The relative amount and the average strengt h of hydrogen bonds in the cured blends were lower than those in the u ncured blends. (C) 1997 Elsevier Science Ltd.