Cloud-point curves of ethylene-(meth)acrylate copolymers in fluid ethene up to high pressures and temperatures - experimental study and PC-SAFT modeling

Cloud-point pressures of ethylene-(meth)acrylic acid ester copolymers in supercritical ethene have been measured to maximum pressures and temperatures of 3000 bar and 533 K, respectively. The copolymers under investigation were prepared in a continuously operated stirred tank reactor (CSTR), which ensures production of chemically homogeneous polymer. After isolation and purification of the copolymer, the phase behavior was mapped out in a discontinuously operated high-pressure cell. The influence of the type and of the content of (meth)acrylate units within the copolymer on cloud-point behavior in mixtures with ethene was systematically studied for ethylene-ethyl acrylate (poly(E-co-EA)), ethylene-propyl acrylate (poly(E-co-PA)), ethylene-methyl methacrylate (poly(E-co-MMA)), and ethylene-butyl methacrylate (poly(E-co-BMA)) copolymers mostly covering the entire comonomer composition range including the limiting homopolymer systems ethene-polyethylene and ethene-poly(meth)acrylate. The data is compared with previously measured cloud-point pressures for ethylene-methyl acrylate and ethylene-butyl acrylate copolymers in fluid ethene. Starting from the limiting ethene-polyethylene system, cloud-point pressures decrease upon increasing the content of polar comonomer segments. For poly(E-co-MA), poly(E-co-EA), poly(E-co-MMA), and poly(E-co-BMA) this tendency is reversed at higher (meth)acrylic acid ester contents where the cloud-point pressures increase again. No such minimum in cloud-point pressure as a function of comonomer content occurs with poly(E-co-PA) and poly(E-co-BA). The variation of cloud-point pressure with copolymer composition is assigned to effects resulting from (i) short-chain branches on the polymer backbone, (ii) intersegmental interactions of carbonyl groups being shielded to different extents by the various types of alkyl ester groups, and (iii) "entropy penalty" contributions associated with the introduction of the a-methyl groups in case of the methacrylates. The experimental cloud-point-pressure curves are satisfactorily modeled by the Perturbed-chain (PC)-statistical associating fluid theory (SAFT) equation of state. The entire set of pure-component parameters and the three binary interaction parameters are independent of temperature, pressure and polymer molecular weight. The parameters from PC-SAFT modeling allow for estimates of the cloud-point behavior of ethene-poly(E-co-(meth)acrylate) systems in wide ranges of pressure and temperature. (C) 2003 Elsevier B.V. All rights reserved.