HYDROGEN-BONDS IN POLY(METHYL METHACRYLATE) POLY(4-VINYL PHENOL) BLENDS - 2 - QUANTIFICATION NEAR THE GLASS-TRANSITION TEMPERATURE

Changes in the proportion of hydrogen bonds of poly(4-vinyl phenol) (P VPh) and poly(methyl methacrylate) (PMMA) blends have been investigate d by FTi.r. spectroscopy both above and below the grass transition tem perature T-g. Changes in three spectral regions, namely the carbonyI, hydroxyl and aromatic ring vibration regions, are attributed to variat ions in hydrogen bonding with increasing temperature. Both hydrogen bo nded O-H and C=O stretching vibrations shift to higher frequencies, in dicating a weakening of interassociated hydrogen bonds at higher tempe ratures. A clear transition is observed in the absorbance behaviour of these vibrations at T,. The reduction in total area of O-H and C=O vi bration regions is attributed not only to the breaking of hydrogen bon ds at T-g, but also to the decrease of absorption coefficients of hydr ogen bonded O-H and C=O stretching vibrations. Quantification of the d ecrease in concentration ratio of hydrogen bonds between carbonyI grou ps vs. total carbonyl groups showed a decrease of 0.5% in the number o f hydrogen bonds was occurring at T-g + 30, when T-g is taken as the m idpoint of the transition as determined by DSC, for the 30 wt% PVPh co mposition. For higher compositions, this percentage increased, reachin g 3.5% for the 80 wt% PVPh composition, which is related to the increa se in T-g of the blend. (C) 1997 Elsevier Science Ltd.