DSC AND IGC STUDIES ON BLENDS OF POLY(?-METHYL STYRENE-CO-ACRYLONITRILE) WITH COPOLYMERS OF POLYMETHACRYLATES

Abstract

The growing demand for polymer blends has generated a need for a better understanding of the thermodynamics of miscibility and phase separation in polymer systems, This in turn has created a tremendous interest in techniques which can be used to characterise the thermodynamics of polymer/polymer systems. The purpose of this study is both to gain a quantitative understanding of the intercomponent interaction of binary blends consisting of poly (?-methyl styrene-coacrylonitrile) (MSAN) with poly (methyl methacrylate)(PMMA), poly (ethyl methacrylate)(PEMA) and poly (methyl methacryiate-co-ethyl methacrylate) and to characterise the phase separation processes of these blend systems. The techniques of cloud point measurements, differential scanning calorimetry (DSC) and inverse gas chromatography (IGC) which was used to measure polymer-polymer interaction parameters were employed. MSAN was found to be miscible with two poly (methyl methacrylate-co-ethyl methacrylate) samples containing 60% and 30% by weight of methyl methacrylate (MEMA-60 and MEMA-3 0 ) respectively and with poly (methyl methacrylate-co-n-butyl methacrylate) (MBMA). All these blends exhibited lower critical solution temperature and each of them showed only one Tg. The phase separation induced on heating was not reversed on cooling due to the low mobility of the polymer chains. The interaction between MSAN and polymethacrylates decreases as the size of the pendent group increases. Miscibility of MSAN/PMMA/PEMA ternary blends studied by the use of differential scanning calorimetry (DSC), was found over a range of compositions with a high MSAN and/or PMMA content in the blend. PMMA is immiscible with PEMA, but the addition of MSAN helps make PMMA and PEMA more compatible. The favourable situation for the ternary blends to be compatible would be when the third polymer interacts well with polymers 1 and 2 whereby the phase separated area is minimal. Solubility parameter g2 of MSAN at various temperatures has been obtained according to the method developed by Di Paola-Baranyi and Guillet using inverse gas chromatography. By linear extrapolation from 180°C, the solubility parameter of MSAN was found to be 9.9 (cal/ml) 1/ 2 at 25°C, in agreement with the value of 10.4 (cal/ml) 1/2 at obtained by using Small method as reported by D.W. van Krevelen. Inverse gas chromatography (IGC) was used to measure, the polymer-polymer interaction parameter X23 for MSAN/PMMA, MSAN/MEMA-60, MSAN/MEMA-30 and MSAN/PEMA pairs. The values of X23 in all the systems vary considerably with the probes used to derive them, The solvent dependency is a result of the inadequacy of the Flory-Huggins theory to account for all of the interactions which may occur in the ternary system. This behaviour was attributed to nonrandom mixing of polymer chains in the blend or specific interaction of the probe with one of the blend components and the values of X23 measured by IGC should therefore not be interpreted in a strict and quantitative manner. Interactions of MSAN with PMMA, MEMA-60, MEMA-30 and PEMA are favoured with a high MSAN content in the blend indicating that polymer-polymer interaction parameters are also composition-dependent.