Poly(benzoxazine-co-urethane)s: A new concept for phenolic/urethane copolymers via one-pot method Mohamed Baqar a, 1 , Tarek Agag b, * , Hatsuo Ishida b , Syed Qutubuddin a, b a Department of Chemical Engineering, Case Western Reserve University, Cleveland, OH 44106-7202, USA b Department of Macromolecular Science and Engineering, Case Western Reserve University, Cleveland, OH 44106-7202, USA article info Article history: Received 13 September 2010 Received in revised form 24 November 2010 Accepted 27 November 2010 Available online 4 December 2010 Keywords: Hydroxymethyl-benzoxazine Polyurethane Copolymers abstract Historically, applications for traditional phenolic resin/polyurethane materials are limited due to the inherently weak thermal stability of urethane-phenolic linkage and slow reaction rate. A novel concept has been developed to produce phenolic resin/polyurethane copolymers via benzoxazine chemistry. Through one-pot synthesis, a series of linear poly(benzoxazine-co-urethane) materials has been synthesized via the reaction of a newly developed dimethylol functional benzoxazine monomer with 4,4 0 -methylene diphenyl diisocyanate and poly(1,4-butyleneadipate). The structure of the copolymers has been characterized by Fourier transform infrared spectroscopy (FT-IR) and nuclear magnetic reso- nance spectroscopy (NMR). The copolymers in the film forms have been further thermally treated for crosslinking to produce crosslinked poly(benzoxazine-co-urethane) via the ring opening polymerization of cyclic benzoxazine moieties in the main-chain. The tensile properties of the films have been studied and compared with those of traditional high performance materials. The thermal properties of the crosslinked copolymers have also been studied by dynamic mechanical analysis, and thermogravimetric analysis (TGA). Ó 2010 Elsevier Ltd. All rights reserved. 1. Introduction Polyurethanes (PUs) represent one of the most versatile classes of polymers due to their advantages, which include excellent low temperature flexibility, superb oil and abrasion resistance, and extraordinary easy processability [1e3]. PUs are segmented poly- mers that consist of soft segments derived from polyols and hard segments derived from isocyanate and chain extenders. The hard segments offer stiffness to the resulting materials, whereas the soft segments act as flexible connectors between the hard segments. PUs also have a wide variety of properties, ranging from elastic to plastic behavior, which make them suitable for a broad number of applications, such as coatings and paints, flexible foams, insu- lations, adhesives, and sealants. Nonetheless, the use of PUs is associated with some disadvantages, including high water up-take, poor resistance to polar solvents, and poor thermal stability. They also undergo dissociation of urethane linkages at elevated temperatures [4]. As a result, tremendous research efforts have been reported to improve the thermal stability of PUs. Most of the reported approaches are based on copolymerization or blending with other polymers of high thermal stability such as polyimides [5e8], polyurea [9,10], polyamide [11,12], epoxy [13], and poly- diacetylene [14]. Polybenzoxazines, as a newly developed class of high perfor- mance polymers, have attracted much interest of academia and industries. They are characterized by many useful properties, such as low moisture absorption, excellent mechanical properties, self- extinguishing properties, and excellent dimensional stability [15e18]. They also offer a remarkable flexibility in molecular design of monomers and, consequently, a versatile performance as poly- mers [19e21]. Benzoxazine monomers are polymerized by the thermally activated cationic ring opening polymerization of ben- zoxazine without any added initiators, catalysts, or by-product formation [22e26]. The potential application areas of poly- benzoxazines include coatings, electronic packaging materials, printed circuit boards, frictional materials, catalysis, and matrices for composite materials. Due to the excellent thermal and mechanical properties of polybenzoxazines, they have been incorporated into PUs aiming at improving their thermal and mechanical properties. The flow chart shown in Fig. 1 represents all reported routes for preparing polybenzoxazine/PU materials. The concept adapted in all the previous studies is based on blending of either preformed * Corresponding author. Tel.: þ1 20 40 3326357; fax: þ1 20 40 3350804. E-mail address: taa16@cwru.edu (T. Agag). 1 On leave from Nasser International University-Libya Contents lists available at ScienceDirect Polymer journal homepage: www.elsevier.com/locate/polymer 0032-3861/$ e see front matter Ó 2010 Elsevier Ltd. All rights reserved. doi:10.1016/j.polymer.2010.11.052 Polymer 52 (2011) 307e317