Process for preparing polymers of p-xylylene from p-xylylene diesters

A process for preparing polymers of p-xylylene having repeating units of the formula (I) ##STR3## by pyrolysis, where n is the degree of polymerization and is.gtoreq.2, wherein ester compounds of the formula (II)

• --R--CO--O--CH.sub.2 --Ar--CH.sub.2 --O--CO--R (II)
• are pyrolyzed in one stage under conditions resulting in cleavage of the ester bonds under a partial pressure of the esters of p.ltoreq.10 mbar at temperatures T.gtoreq.500.degree. C., with the formation of corresponding derivatives of 1,4-dimethylene-2,5-cyclohexadiene, but without the latter being cleaved further in subsequent reactions, and the polymers of p-xylylene formed by spontaneous polycondensation of the derivatives of 1,4-dimethylene-2,5-cyclohexadiene were then cooled, Ar and R have the following meanings:
• --Ar-- is a 1,4-phenylene radical or another C.sub.6 -C.sub.12 aromatic or heteroaromatic radical in which the bonds are in the para position or a comparable coaxial or antiparallel position and which is unsubstituted or substituted by one or more branched or unbranched, unsubstituted or halosubstituted C.sub.1 -C.sub.4 -alkyl, alkenyl or alkoxy radicals or C.sub.6 -C.sub.12 -aryl or heteroaryl radicals, hydroxyl, nitro, nitrile or amino groups or with R*--S-- or R*--CO--O radicals, where R* is a C.sub.1 -C.sub.4 -alkyl radical or a C.sub.6 -C.sub.12 -aryl radical;
• R-- is branched or unbranched C.sub.1 -C.sub.4 -alkyl or C.sub.6 -C.sub.12 -aryl radical or an R*--CO--O radical, where R* has the meaning given above.