MISCIBILITY BEHAVIOUR OF METHACRYLONITRILE COPOLYMER BLENDS

Abstract

The copolymerization behaviour of methacrylonitrile (MAN) with styrene (S), pmethylstyrene (pMS), ?-methylstyrenc (?MS) and n-butyl methacrylate (nBMA) was investigated. Poly( styrene-co-methacrylonitrile) ( SMAN), poly(p-methylstyrene-comethacrylonitrile) (pMSMAN) and poly(n-butyl methacrylate-co-methacrylonitrile) (nBMAN) samples were prepared by solution polymerization and poly?:-methylstyrene-co-methacrylonitrile) (?MSMAN) samples were prepared by bulk polymerization. In terms of a terminal model, reactivity ratios for binary systems were evaluated to be 0.187 and 0.349 for MAN and styrene, 0.205 and 0.377 for MAN and pMS, 0.268 and 0.097 for MAN and ?MS, 0.754 and 0.785 for MAN and nBMA, respectively. The microstructure of these four types of copolymers was studied by 13C-NMR. The triad fractions observed by 13C-NMR are in very good agreement with those calculated from the reactivity ratios. 13C-NMR spectra of ?MSMAN copolymers showed a large difference on structural nature from those of SMAN and pMSMAN copolymers. Thermal degradation behaviour of these copolymers was investigated by thermogravimetric analysis (TGA). ?MSMAN and nBMAN copolymers showed a multi-stage thermal degradation behaviour while SMAN and pMSMAN showed a single-stage or two-stage thermal degradation behaviour depended on the copolymer composition. The miscibility behaviour of the blends of MAN copolymers, such as SMAN, pMSMAN and ?MSMAN with three types of polymethacrylates, namely poly(alkyl methacrylate)s, poly(chloroalkyl methacrylate)s and those containing bulky cyclic ester groups was studied. The blend samples were prepared by solution casting from tetrahydrofurfuran (THF) or methyl ethyl ketone (MEK). Miscibility was ascertained based on the optical clarity and glass transition temperature (Tg) criterion. The miscibility ranges of various polymer-copolymer systems were determined and segmental interaction parameters were calculated using a binary interaction model. The structural influence on miscibility behaviour is discussed. Replacement of acrylonitrile (AN) with MAN in copolymers widens the miscibility ranges with polymethacrylates. Replacement of styrene with pMS in the copolymers widens and shifts the miscibility ranges to higher MAN content with polymethaerylates. However, replacement of styrene with ?MS narrows and shifts the miscibility ranges to lower MAN content. The incorporation of chlorine atom into the pendant ester group in polymethacrylates also widens the miscibility ranges. A compatibility parameter approach has been developed based on Hoy's solubility parameter calculation and interaction parameter vectorial nature. The predicted miscibility ranges from the compatibility parameter approach are in very good agreement with the experimental results. The miscibility behaviour of poly(methacrylonitrile) (PMAN) with tertiary amide polymers, such as poly(N-vinyl-2-pyrroliclone) (PYP), poly(N,N-dimethyl acrylamide) (PDMA), poly(N-methyl-N-vinylacetamide) (PMVAc), poly(2-ethyl-2-oxazoline) (PEOx) and poly(2-methyl-2-oxazoline) (PMOx) was studied by differential scanning calorimetry (DSC) and Fourier-transform infrared spectroscopy (FTIR). FTIR studies indicate that the miscibility of PMAN with tertiary amide polymers results from polar-polar interaction between ?-electrons of the -CN group and the amide carbonyl groups. The presence of ?-hydrogen is not the only necessary requirement for specific interaction between different polymer chains. As the amide groups in PVP, PDMA and PMVAc are situated on the side chains, they show a higher degree of freedom for interaction while those in PEOx and PMOx are integral part of the main chains and their interactions are restricted by their configuration. Therefore, PEOx and PMOx blends show a lower miscibility than that of PVP, PMVAc and PDMA.