Eur. Polym. J. Vol. 31, No. 7, 665-669, 1995 pp. Copyright 0 1995 Elsevier Science Ltd Printed in Orcat Britain. All rights reserved 0014-3057/95 $9.50 + 0.00 MISCIBILITY OF POLY(STYRENE-CO-ACRYLIC ACID) WITH POLYMETHACRYLATES OR POLY(METHACRYLATE-CO-4-VINYLPYRIDINE) FATIMA FERAZ, ASSIA SIHAM HADJ HAMOU and SAID DJADOUN* Institute of Chemistry, University of Sciences and Technology Houari Boumediene, BP 32 El Alia, Algiers 16111, Algeria (Received I2 April 1994; accepted in final form 28 June 1994) Abstract-The miscibility of poly(styrene-co-acrylic acid) with polymethacrylates or poly(methacrylate- co+vinylpyridine) was studied by differential scanning calorimetry and inverse gas chromatography using decane, octane and benzene as molecular probes. The results showed that poly(isobutyl methacrylate) is immiscible with styrene-acrylic acid copolymers of different acrylic acid content as evidenced from the appearance of two glass transition temperatures determined with both techniques. Positive values of the apparent polymer-polymer interaction parameter x23 (app.) obtained with all probes in the temperature range 160-180°C over the entire blend composition confirm the immiscibility of these blends. Blends of the former styrene-acrylic acid copolymers are, however, miscible in all proportions with poly(ethy1 methacrylate), poly(ethy1 methacrylate-co-4-vinylpyridine) and poly(isobuty1 methacrylate- co-Cvinylpyridine). A single composition dependent-glass transition temperature and negative values of xz3 (app.) were obtained with these blends It is well known that polymers are generally immis- cible with each other. The miscibility of a pair of polymers has been attributed in most cases to some specific intermolecular interactions between the com- ponents of the blend [l-7]. it has also been shown that a homopolymer and a random copolymer may form a miscible blend even in the absence of specific interactions provided strong intranolecular repul- sions exist between the comonomers [8-12). Inverse gas chromatography and differential scan- ning calorimetry have been extensively used to inter- pret the miscibility of polymer blends [13-231. Polystyrene is immiscible with poly(ethyl meth- acrylate) and poly(isobuty1 methacrylate). In the pre- sent study, the miscibility of poly(styrene-co-acrylic acid) with poly(ethy1 methacrylate) or poly(isobuty1 methacrylate) or poly(ethy1 methacrylate-co-4-vinyl- pyridine) or poly(isobuty1 methacrylate-co4-vinyl- pyridine) was examined by differential scanning calorimetry (DSC) and inverse gas chromatography (IGC) using decane, octane and benzene as molecular probes. Glass transition temperatures (r,) and ap- parent polymer-polymer interaction parameters xzs were used to determine the miscibility of these blends. EXPERIMENTAL Polymerization and polymer characterization Poly(ethyl methacrylate) (PEM) and ply(isobuty1 meth- acrylate) (PIBMA) were prepared by free radical polymeriz- ation. In a similar way, controlling the conversion below *To whom all correspondence should be addressed. 15% by weight, we have also synthesized copolymers of (1) styrene and acrylic acid (SAA-20 and SAA-32) containing respectively 20 and 32 mol.% of acrylic acid and (2) of ethyl methacrylate and 4-vinylpyridine (EM4VP-8 and EM4VP- 23) and of isobutyl methacrylate and Cvinylpyridine (IBM4VP-10) containing respectively 8, 23 and 10 mol.% of 4-vinlypyridine. The styrene content in the SAA copolymers was deter- mined by U.V. spectroscopy as previously described (131 and by titration with a base in benzene-methanol mixture. The 4-vinylpyridine in the EM4VP or IBM4VP copolymers was also determined by U.V.spectroscopy and elemental analysis. Intrinsic viscosities of these polymers in butanone at 23 or 25°C are summarized in Table 1. The molecular weights of PME (Mw = 1.004 x 106) and PIBMA (M, = 1.43 x 106) were calculated from the intrinsic viscosities measured in butanone at 23°C and using the Mark-Howink-Sakurada equation [24]. IGC and DSC measurements Using Chromosorb W AWDMCS 80/ 100 mesh, obtained from Johns Mainville as a solid support, chromatographic columns of 9% polymer loading were prepared in the usual way [14]. The IGC measurements were carried out on HP 5730A gas chromatograph equipped with a dual flame ionization detector. Helium was the carrier gas and methane the non-interacting marker. A small amount (0.1 ~1) of benzene or decane or octane used as molecule probes was injected manually using a Hamilton syringe. The specific retention volume Y, (ml/g) of the molecular probe was measured in the temperature range 6C-180°C from the following relation Y,=t,.F,J,/w (1) w here J is the James-Martin correction factor, F the flow rate of carrier gas at 273 K w, the polymer or polymer mixture loading weight and tN the net retention time. A column containing the inert support only was prepared in 665