Molecular dynamics and thermal analysis study of anomalous thermodynamic behavior of poly (ether imide)/polycarbonate blends q Mingzong Zhang, Phillip Choi, Uttandaraman Sundararaj * Department of Chemical and Materials Engineering, University of Alberta, Edmonton, Canada T6G 2G6 Received 27 July 2002; received in revised form 1 January 2003; accepted 15 January 2003 Abstract Molecular dynamics simulation used to study the binary polymer blend of poly (ether imide) (PEI) and polycarbonate (PC) showed that these polymer blends are immiscible. The Flory-Huggins interaction parameter, x; calculated from simulation reached a minimum value at 80 wt% PEI. The simulation results showed that the concentration dependence of x was mainly due to electrostatic interaction and van der Waals force. The simulation results were supported by differential scanning calorimetry (DSC) measurements. The DSC measurements showed that there are two distinct glass transition temperatures for all the blends’ concentrations. However, at 80wt % PEI, the T g of PEI-rich phase reached a minimum while that of the PC-rich phase was comparable to its pure form indicating that there is some partial miscibility of PC in the PEI rich phase, but no PEI is incorporated in the PC rich phase. From simulations, the x versus concentration plot shows the same trend as the experimentally measured glass transition temperature versus concentration plot. q 2003 Elsevier Science Ltd. All rights reserved. Keywords: Polymer blends; Molecular dynamics simulation; Glass transition temperature 1. Introduction Polymer blends and alloys constitute an important part of plastics consumption and continue to grow at a rate of 9% per year [1]. An important polymer blend is the blend of poly(ether imide) (PEI) and polycarbonate (PC). PEI and PC are high performance engineering thermoplastics. The chemical structures of PEI and PC are shown in Fig. 1. PEI/PC blends can be used for aircraft interior components and household applications. The PEI/PC blends, Ultem LTXe series, have been available commercially since 1990 from GE Plastics. PEI/PC blends combine the high temperature resistance and intrinsic flame resistance of PEI with the good impact strength and ease of processing of PC. Blending PC into PEI also dilutes the cost of PEI, and reduces PEI’s notch sensitivity [2]. PEI has been blended with several other polymers such as liquid crystalline polymer (LCP), poly ether ether ketone (PEEK), liquid crystalline polyimide (PI-LC) and nitro- substituted polybenzimidazole (NO 2 –PBI) [3–8]. The blends of PC with epoxy, PMMA, high performance polystyrene, and poly(styrene-co-methacrylic acide) have been studied in recent years [9–12]. There are few papers published on PEI/PC blends. Chun et al. [13] studied the thermal properties and morphology of PEI/PC blends and found that the blends exhibited two distinct glass transition temperatures. Moreover, they found that the glass transition temperature of the PEI-rich phase changes at different loadings of PC, while that of PC-rich phase stays constant. However, the reason for this behavior was not fully explored. The primary objective of this paper is to use molecular dynamics simulation (MD) to delineate the molecular processes that lead to the anomalous observation. To this end, the Hildebrand solubility parameters of PEI and PC and Flory-Huggins interaction parameter of the blends at various concentrations are computed. In addition, blends at several concentrations are made and analyzed using differential scanning calorimetry (DSC) to obtain the full T g versus concentration curves to validate previous results. To our knowledge, no molecular dynamics simulations have been done for PEI/PC blends, but some simulation work has been done on pure PEI and pure PC. Shih et al. 0032-3861/03/$ - see front matter q 2003 Elsevier Science Ltd. All rights reserved. doi:10.1016/S0032-3861(03)00054-5 Polymer 44 (2003) 1979–1986 www.elsevier.com/locate/polymer q Portions presented at the IUPAC conference (2002). * Corresponding author. Tel.: þ 1-780-492-1044; fax: þ1-780-492-2881. E-mail address: u.sundararaj@ualberta.ca (U. Sundararaj).