Infrared and Thermal Analyses of Polybenzoxazine and Polycarbonate Blends HATSUO ISHIDA, YU-HSIN LEE Department of Macromolecular Science, The NSF Center for Molecular and Microstructure of Composites, Case Western Reserve University, Cleveland, Ohio 44106-7202 Received 15 August 2000; accepted 2 October 2000 Published online 8 May 2001 ABSTRACT: The thermal properties of physical blends containing benzoxazine mono- mer and polycarbonate (PC) were studied by nonisothermal differential scanning cal- orimetry (DSC), thermogravimetric analysis (TGA), and Fourier transform infrared spectroscopy (FTIR). The ring-opening reaction and subsequent polymerization reac- tion of the benzoxazine were inhibited significantly by the presence of polycarbonate. The glass-transition temperature of the resulting blends decreased as the concentration of polycarbonate increased and deviated markedly from the Fox equation. An earlier degradation event appeared in the blend with 11 and 33 wt % of PC. In addition, FTIR was used to study the extent of the polymerization reaction as well as the hydrogen- bonding behavior. Intermolecular hydrogen bonding between PC and cured polybenz- oxazine appeared after 1 h of isothermal curing at 180°C and continued throughout the entire curing process. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 81: 1021–1034, 2001 Key words: benzoxazine; blend; Fox equation; hydrogen bonding; polycarbonate; polymerization; reaction; ring-opening INTRODUCTION The study of miscibility of polymer blends, in which one component is crystallizable and an- other is highly crosslinked, has received attention in recent years. 1 From a thermodynamic point of view, an increase in molecular weight of either component of a miscible blend would depress the critical temperature and accelerate the phase sep- aration. Therefore, the occurrence of even partial miscibility in such polymer blends containing one component with an infinite molecular weight (i.e., highly crosslinked) is surprising and requires fur- ther comments. 1 Moreover, a crystallizable ther- moplastic polymer is cured in situ with a thermo- setting monomer; thus, how the crystallization and the polymerization are affected by the other component is of great interest and needs to be clarified. A class of ring-opening phenolic resins, the po- lybenzoxazines, has shown an excellent balance of mechanical and physical properties along with unusual thermal and physical properties. 2,3 A rich molecular design flexibility has been fully demonstrated in our laboratory by modifying functionalities of the initial raw materials, espe- cially phenolic and primary amine derivatives. 4–7 Earlier studies focused on various polybenzox- azine composite systems, to which inorganic fill- ers, such as glass fiber, 8 carbon fiber, 9 boron ni- tride, 10 or CaCO 3 , 11 were added. As a result, high- performance materials were prepared. Although a few pioneering works reported on the organic mixed system of a benzoxazine resin and an epoxy resin, 12 no investigation has reported on polyben- zoxazine/thermoplastic polymer blends. Correspondence to: H. Ishida. Journal of Applied Polymer Science, Vol. 81, 1021–1034 (2001) © 2001 John Wiley & Sons, Inc. 1021