Published: March 11, 2011 r2011 American Chemical Society 1801 dx.doi.org/10.1021/ma1029746 | Macromolecules 2011, 44, 1801–1807 ARTICLE pubs.acs.org/Macromolecules Thermally Curable Acetylene-Containing Main-Chain Benzoxazine Polymers via Sonogashira Coupling Reaction Kubra Dogan Demir, Baris Kiskan, and Yusuf Yagci* Faculty of Science and Letters, Chemistry Department, Istanbul Technical University, Maslak, TR-34469, Istanbul, Turkey b S Supporting Information ’ INTRODUCTION The interest of academics and chemical industry in 1,3- benzoxazine chemistry is growing rapidly due to many unique properties of benzoxazines and their resins. These include near- zero volumetric change upon curing, no strong acid catalysts or additives requirement for curing, high thermal stability, good mechanical performance, low water absorption, and high char yield of the cured products. 1 Accordingly, benzoxazine resins are suitable alternative materials for applications where epoxides, bismaleimides, cyanate esters, and polyimides are used. 2 And they have capability to overcome several shortcomings of con- ventional novolac and resole type phenolic resins. An additional attractive feature of benzoxazine chemistry is the ease of pre- paration of monomers which are synthesized from inexpensive, commercially available phenols, primary amines, and form- aldehyde. 3-14 Therefore, the chemistry of benzoxazine synthesis offers a wide range of molecular design flexibility by using appropriate starting materials. The polymerization of these monomers is a thermally induced ring-opening polymerization which can be accomplished without any initiator or curative and yields polybenzoxazine networks 12,15-23 (see Scheme 1). Many studies have been conducted in order to improve the properties of benzoxazine polymers and to expand their applica- tion scopes. However, processing of the benzoxazine monomers into thin films arising from its powder structure still remained as the major challenge for wider industrial applications. Moreover, the polymers obtained after curing are rather brittle as a result of the low molecular weight of the network structure. 24 A recently active concept in benzoxazine resin research is based on the synthesis of telechelic, main- or side-chain polymers containing benzoxazine moieties. 25-27 At this point, the benzoxazine behaves like an ordinary thermoplastic which has good solubility and processability and also offers the ability to prepare a varnish with low solid content that forms good quality films. 24 Hence, it is expected that the cross-linked network structure, formed from polymer and polymerization of benzox- azine, will exhibit enhanced mechanical property while preser- ving the beneficial properties of polybenzoxazine. Thus, most efforts have focused on the preparation of benzoxazine functional polymers and polybenzoxazine precursors. The latter approach seemed to be more suitable since the obtained precursors contain benzoxazine units in every repeating unit and therefore leads to the formation of highly cross-linked network structures after thermal treatment. Ishida and Takeichi groups have indepen- dently employed monomer synthesis methodology by using bifunctional amines, bisphenol A, and formaldehyde. 28-31 Jeffa- mine amine-based precursors can also be prepared via similar monomer synthesis strategy. 32,33 In addition, polyphenylene and triazole type precursors have been developed via oxidative and click coupling reactions, respectively. 34-38 Polybenzoxazine pre- cursors based on more traditional polymers such as polyesters, polyetheresters, and oligosiloxanes have also been prepared. 39-41 In those cases, appropriate functional groups incorporated to benzoxazines were conveniently used for polycondensation and Pt-catalyzed hydrosilylation reactions, respectively. As part of our continuous interest in developing alternative methods for the production of benzoxazine resins with desired properties, we herein describe preparation and characterization Received: December 30, 2010 Revised: February 15, 2011 ABSTRACT: Propargyl containing thermally curable benzox- azine precursors in the main chain have been synthesized from iodo functional bisbenzoxazine and diacetylenes by Sonogashira coupling reaction. For this purpose, 4,4 0 -isopropylidenediphe- nol (Bisphenol A) was reacted with formaldehyde and iodoani- line to form diiodobisbenzoxazine (DIBB). Sonogashira coup- ling reaction between DIBB and diacetylene bisether (DABE) or diacetylene bisbenzoxazine (DABB) catalyzed by palladium tetrakistriphenylphosphine yields the corresponding main- chain polybenzoxazine precursors with the molecular weights around 2300-3500 Da. The structures of the monomers and the resulting polymers are confirmed by FT-IR and 1 H NMR spectral analysis. Curing behaviors of both the monomer and polymers were studied by differential scanning calorimetry (DSC). Thermal properties of the cured polymers were also investigated by thermogravimetric analysis (TGA).