ELSEVIER PII: S0032-3861(96)01049-X PolymerVol. 38 No. 12, pp. 3139 3143, 1997 1997 Elsevier Science Ltd Printed in Great Britain, All rights reserved 0032-3861/97/$17.00 + 0.00 Synthesis of poly(arylene phosphine oxide) by nickel-catalysed coupling polymerization Hossein Ghassemi and James E. McGrath* Department of Chemistry and NSF Science and Technology Center." High Performance Polymeric Adhesives and Composites, Virginia Polytechnic Institute and State University, Blacksburg, VA 24061 - 0212, USA (Received 24 September 1996, revised 12 October 1996) An amorphous high molecular weight poly(arylene phosphine oxide) (PAPO) was synthesized from bis(4- chlorophenyl)phenylphosphine oxide by the nickel-catalysed carbon-carbon coupling reaction. The physical and thermal properties of PAPO were investigated. The material exhibited a glass transition temperature around 365°C and 5% weight loss around 550°C in nitrogen and air. Upon heating up to 750°C in air PAPO lost only 65% of its weight leaving significant amount of char behind which is due to the presence of phosphorous in the polymer. The polymer developed an intense red colour once the phosphine oxide groups in the polymer were reduced to phosphine. © 1997 Elsevier Science Ltd. (Keywords: polyarylenes; phosphorous-containing polymers; high-Tg materials) Introduction High performance aromatic polymers have been pre- pared by several methods. However, the majority of these methods involve the formation of carbon-heteroatom bonds. For example, the polycondensation or step polymerization of bisphenoxide anions with aromatic dihalides generates a carbon-oxygen bond. Commer- cially available poly(arylene ether sulfone)s, and poly(arylene ether ketone)s, are two examples of engineering thermoplastics which are made by nucleo- philic substitution reactions I. The oxidative polymer- ization of substituted phenols to poly(phenylene oxide)s is another example where a polY2meric chain is formed by carbon-heteroatom coupling . Polymerization involving the formation of aromatic carbon-carbon bonds are of high interest due to the expectation that such polymerizations may allow for the preparation of a variety of unique structures. Several approaches to produce carbon-carbon bonds have been investigated 3. The electrophilic Friedel-Crafts prepara- tion of poly(arylene ether ketone)s and poly(arylene ether sulfone)s, e.g. using diacidhalides or disulfonylhalides, respectively, and aromatic hydrocarbons affords high molecular weight, somewhat branched materials 4. The scope of this approach is limited to compounds capable of undergoing quantitative Friedel-Crafts acylation or sulfonylation such as biphenyl or diphenyl ether. Furthermore, this reaction requires a very large amount of Lewis acid and solvent. The palladium-mediated coupling of aromatic bro- mides with aromatic boronic acids (Suzuki coupling) has been reported as a successful method to make substituted poly(phenylene)s 5-7. Nickel coupling of aryl chlorides has been also utilized to make high molecular weight rigid-rod polymers 3'8-12. The results, described by several research groups show that using the nickel * To whom correspondence should be addressed coupling approach, a variety of polymers can be prepared by properly choosing the starting materials. Herein we describe a nickel-catalysed polymerization which employs the coupling of bis(4-chlorophenyl)phenyl- phosphine oxide as a polymer-forming reaction to synthe- size poly(4,4Ldiphenylphenylphosphine oxide) (PAPO), 1. The reaction utilized has general applicability to the synthesis of new processable engineering resins of superior thermal stability. Phosphorous-containing polymers have been widely studied in our laboratory for fire resistance and several other features 13-18. It was anticipated that the non coplanar phenyl group would produce an amorphous morphology which result in an organic soluble, but still rather rigid chain. Experimental Materials. Bis(4-chlorophenyl)phenylphosphine oxide (DCPPO) (Akzo Chemical Co.) was dried under vacuum at room temperature over night. N,N-Dimethylacetamide (DMAc, Fisher Scientific) and chlorobenzene (Aldrich) were dried over calcium hydride for 24h with constant stirring, followed by vacuum distillation and storage over 4-A molecular sieves under dry nitrogen. Triphenylphosphine (Aldrich) was recrystallized from hexane. Zn powder (Aldrich) was washed with dilute hydrochloric acid, filtered, washed with dry diethylether, and dried under high vacuum at 150°C. Nickel(II) chloride (Aldrich) was dried under vacuum at 220°C. 2,2'-Bipyridine (bpy) and phenylsilane (Aldrich) were used as received. Preparation of PAPO by polymerization of DCPPO. NiC12 (0.016g, 0.125mmol), bpy (0.02g, 0.125mmol), Zn powder (0.51g, 7.75 mmol) and (Ph)3P (0.66 g, 0.25 mmol) were added inside a dry N2 atmosphere drybag into a 50-ml flask equipped with a side tubing adapter capped by a rubber septum. After removal from the drybag, the flask was connected to a vacuum line through the side tubing for 24 h, during which the flask was purged with N2 several times. Then, it was placed in an oil POLYMER Volume 38 Number 12 1997 3139