SYNTHESIS OF SOLUBLE HALOGENATED POLYPHENYLENES - MECHANISM FOR THE COUPLING OF HALOGENATED LITHIOBENZENES

A method for the synthesis of soluble polyphenylenes that involves the polymerization of 1-halo-4-lithiobenzenes, 1-halo-3-lithiobenzenes, a nd 1,3- and 1,4-dilithiobenzenes in ethereal solvents is described. Th e lithiobenzenes are prepared from the corresponding dihalogenated ben zenes using tert-butyllithium. By varying the monomers and conditions used, a variety of soluble halogenated polyphenylenes can be obtained with weight average molecular weights (M(w)) as high as 6000 with poly dispersities (M(w)/M(n)) equal to-2.8. The prequenched polymers can ex ist as multilithiated polymers if 2.0 equiv of tert-butyllithium is us ed to form the aryllithium intermediates. The polymers are usually amo rphous and contain significant amounts of phenylated polyphenylene uni ts capped with halogens. The polymers are soluble in organic solvents such as THF, chloroform, and methylene chloride. Several of the polyme rs exhibited low melting and glass transition temperatures. The bromin ated polymers are easily dehalogenated upon treatment with tert-butyll ithium in THF at -78-degrees-C followed by quenching with water. The m olecular weights of several of the brominated polymers increased upon debromination with tert-butyllithium. When the polymerizations were ca rried out in the presence of 1,3-diphenylisobenzofuran, o-benzyne inte rmediates were trapped as their Diels-Alder adducts. LiH appears to be present in significant amounts upon completion of the polymerization.