Polymers having the recurring units -CHR-Ar-CH2-, where R is hydrogen or a monovalent hydrocarbon radical and Ar is a bivalent aromatic unit wherein the two valences stem from the terminal carbon atoms of a chain of 2 or 4 ring atoms in an aromatic ring which may be substituted e.g. by halogen or lower alkyl radicals are made by heating to a temperature of at least 100 DEG C. in an aqueous alkali metal hydroxide solution maintained at at least 5 molal concentration one or more quaternary ammonium hydroxides or quaternary ammonium salts of strong inorganic acids in which the quaternary ammonium nitrogen is attached to three methyl groups and to a methylene radical whose remaining valency is satisfied by a carbon atom in an aromatic ring which aromatic ring has on a carbon atom thereof a hydrocarbon substituent, separated by a chain of 2 or 4 ring atoms from the methylene radical, and having at least two hydrogen atoms attached to the carbon atom of the hydrocarbon which is linked to the carbon atom of the aromatic ring. The quaternary ammonium compound containing the aromatic ring which may be carbocyclic or heterocyclic, may be trimethyl (p-methylbenzyl) ammonium bromide, chloride or hydroxide, trimethyl (o-methylbenzyl) ammonium bromide, trimethyl ( (3 - chloro - or 3 - fluoro - 4 - methylbenzyl) - ammonium chloride or fluoride, trimethyl (3-iodo-6-methylbenzyl) ammonium chloride, trimethyl (benzyl benzyl) ammonium chloride, trimethyl-(5 - methyl - 2 - furfuryl) ammonium iodide or hydroxide, trimethyl (5 - methyl - 2 - thenyl) ammonium iodide or hydroxide, trimethyl (5-p-chlorobenzyl-2-thenyl) ammonium iodide, trimethyl (4-bromo-5-methyl-2-thenyl) ammonium bromide, trimethyl (3,4-dibromo-5-methyl-2-thenyl) ammonium bromide, trimethyl (2,4-di methyl benzyl) ammonium chloride, trimethyl (4-methyl-3-phenyl) benzyl ammonium chloride trimethyl (alpha-duryl) ammonium chloride 10 - methyl - 9 - anthrylmethyltrimethyl ammonium iodide, 4,5 - dimethyl - 2 - thiazyltrimethyl ammonium chloride, (4 - methyl - 2-pyridylmethyl) trimethyl ammonium chloride, (1,5 - dimethyl - 2 - pyrrolyl) trimethyl ammonium chloride, trimethyl (2-methyl-5-pyridyl) methyl ammonium bromide, trimethyl (5- or 6-methyl- 2 or 3-pyridazinyl) methyl-ammonium chloride), trimethyl (8-methyl-5-quinolyl) methyl ammonium bromide, trimethyl (5-methyl-N - phenyl - 2 - pyrrolyl) methyl ammonium bromide and mixtures. Specified polymers are poly - p - xylylene, poly - 2 - chloro - p - xylylene, poly - 2,5 - dimethylenefuran, poly - 2,5-dimethylenethiophene, poly - 2 - p - chlorobenzlidene - 5 - methylenethiophene, poly - 3,4 - dibromo - 2,5 - dimethylenethiophene, poly - 2,3-dimethylenethiophene, poly - o - methyl - p-xylylene, poly - 2,5 - dimethyl - p - xylylene, poly - 9,10 - dimethyleneanthracene, poly - 4-methyl - 2,5 - dimethylenethiazole, poly - 2,5-dimethylene pyridine, poly - 2,5 - dimethylene-N - methyl - pyrrole, poly - 2,5 - dimethylene-pyridine, poly - 2,5 - dimethylenepyrazine, poly - 3,6 - dimethylenepyridazine, poly - 2,5-dimethylenepyrimidine, poly - 5,8 - dimethylenequinoline, poly - 5,8 - dimethyleneisoquinoline, poly - 2,5 - dimethylene - N - phenylpyrrole, and copolymers of p-xylylene/o-xylylene, alphaphenyl - o - xylylene/alpha - phenyl-p - xylylene, alpha - phenyl - o - xylylene/alpha-phenyl - p - xylylene/2,5 - dimethylenefuran, p-xylylene/2,5 - dimethyl - p - xylylene, 3 - bromo-2,5 - dimethylenethiophene/2,3 - dimethylenethiophene, 2 - benzylidene - 5 - methylenefuran/2,3 - dimethylenethiophene, 2,5 - dimethylene-furan/alpha - phenyl - o - xylylene, and 2-chloro - p - xylylene/o - xylylene. The alkali metal hydroxide may be sodium, potassium, lithium, rubidium, or cesium hydroxide. The process is preferably effected in a system containing an aqueous phase and a liquid non-aqueous phase such as toluene, p-fluorotoluene, xylene, ethylbenzene, cumene, mesitylene, chlorobenzene, bromobenzene, iodobenzene, or tetrahydronaphthalene. The polymer formation may be effected in the presence of a free radical initiator such as alpha, alpha1-azobisisobutyramidine hydrochloride or alpha, alpha1-azodicyclohexane-carbonitrile. The polymers may be made into fibres, e.g. by melt spinning, and the fibres sintered and/or drawn at elevated temperatures. The p-xylylene homopolymer is said to have a specific unimolecular thermal degradation constant k of less than 2.0 X 10-5 min.-1 when determined at 305 DEG C. in a solution in benzyl benzoate at a concentration of 0.39 gm. of polymer in 100 ml. of benzyl benzoate, where <FORM:0807196/IV (a)/1> where t is the heating time in minutes at 305 DEG C., Mm is the molecular weight of the p-xylylene unit, i.e. 104.14, and M is the molecular weight of the polymer determined from the inherent viscosity of the solution at a time t as given by the equation <FORM:0807196/IV (a)/2> and Mo is, at time zero, the molecular weight of the polymer. Specifications 650,947 and 673,651 are referred to.ALSO:Trimethyl (para-methylbenzyl) ammonium chloride, trimethyl (ortho-methylbenzyl) ammonium bromide, trimethyl (3-chloro-4-methylbenzyl) ammonium chloride, trimethyl (3-fluoro-4-methylbenzyl) ammonium chloride, trimethyl (3-iodo-6-methylbenzyl) ammonium chloride, trimethyl (benzylbenzyl) ammonium chloride, trimethyl (4-bromo - 5 - methyl - 2 - thenyl) ammonium bromide, trimethyl (3: 4-dibromo-5-methyl-3-thenyl) ammonium bromide, trimethyl (3-methyl-2-thenyl) ammonium chloride, trimethyl (2 : 4-dimethylbenzyl) ammonium chloride, trimethyl (4-methyl-3-phenylbenzyl) ammonium chloride, trimethyl (a -duryl) ammonium chloride, (10-methyl-9-anthrylmethyl) trimethyl ammonium iodide, (4 : 5-dimethyl - 2 - thiazylmethyl) trimethylammonium chloride, (4 - methyl - 2 - pyridylmethyl) trimethylammonium chloride, (1 : 5-dimethyl-2-pyrrolylmethyl) trimethylammonium chloride, (2-methyl-5-pyridylmethyl) trimethylammonium bromide, (5-methyl - 2 - pyrazinylmethyl) trimethylammonium chloride, (6-methyl-3-pyridazinylmethyl) trimethyl ammonium chloride, (8-methyl-5-quinolylmethyl) trimethyl ammonium bromide and (5-methyl-N-phenyl-2-pyrrolylmethyl) trimethylammonium bromide are prepared by quaternating trimethylamine. Trimethyl (para-methylbenzyl) ammonium hydroxide, trimethyl (3-fluoro-4-methylbenzyl) ammonium fluoride, trimethyl (5-methyl-2-furfuryl) ammonium hydroxide, trimethyl (5-methyl-2-thenyl) ammonium hydroxide, trimethyl (paramethylbenzyl) ammonium fluoride, trimethyl (3-chloro - 4 - methylbenzyl) ammonium sulphate and trimethyl (3-chloro-4-methylbenzyl) ammonium phosphate are prepared by anion exchange. 3 - Fluoro - 4 - methylbenzyl chloride, 3 - iodo-6-methylbenzyl chloride, 2 : 4-dimethylbenzyl chloride, 4-methyl-3-phenylbenzyl chloride and 10-methyl - 9 - iodomethylanthracene are prepared by appropriate halomethylation. 5 - Ethyl - 2 - furfuryldimethylamine and 5-benzyl - 2 - furfuryl dimethylamine are prepared by treating a -ethylfuran and furylphenylmethane respectively with a mixture of form-aldehyde and methylamine hydrochloride. 5 - Methyl - 2 - thenyldimethylamine and 5-parachlorobenzyl - 2 - thenyldimethylamine are prepared by treating 5-methyl-2-thiophene carboxaldehyde and 5 - para - chlorobenzyl - 2-thiophene carboxaldehyde respectively with a mixture of dimethylamine and formic acid according to the process described in J. Am. Chem. Soc. 75, 3033 (1953). Trimethyl (5 - ethyl - 2 - furfuryl) ammonium iodide, trimethyl (5 - methyl - 2 - thenyl) ammonium iodide, trimethyl (5 - para - chlorobenzyl-2-thenyl) ammonium iodide and trimethyl (5-benzyl - 2 - furfuryl) ammonium iodide are prepared by quaternating 5-ethyl-2-furfuryldimethylamine, 5 - methyl - 2 - thenyldimethylamine, 5 - para - chlorobenzyl - 2 - thenyldimethylamine and 5-benzyl-2-furfuryldimethylamine respectively. 2 - (Para - chlorobenzyl) thiophene is prepared by heating para-chlorobenzyl chloride with thiophene in presence of zinc chloride. 5 - Para - chlorobenzyl - 2 - thiophenecarboxaldehyde is prepared by reacting 2-(para-chlorobenzyl) thiophene with N : N-dimethylformamide and phosphorus oxychloride. 4 - Bromo - 5 - methyl - 2 - thienylmagnesium bromide and 3 : 4 - dibromo - 5 - methyl - 2-thienyl-magnesium bromide are prepared by treating 2 : 4-dibromo-5-methylthiophene and 2 : 3 : 4 - tribromo - 5 - methylthiophene respectively with magnesium and methyl bromide in ether. 4 - Bromo - 5 - methyl - 2 - thenyl alcohol and 3 : 4 - dibromo - 5 - methyl - 2 - thenyl alcohol are prepared by treating 4-bromo-5-methyl-2-thienylmagnesium bromide and 3 : 4-dibromo-5-methyl-2-thienylmagnesium bromide respectively with formaldehyde. 3-Methyl-2-hydroxymethylthiophene is prepared by sodium borohydride reduction of 3 - methyl - 2 - thenaldehyde. 2-Hydroxymethyl-4 : 5-dimethylthiazole is prepared by heating a mixture of benzyloxythioacetamide and a -bromoethyl methyl ketone with pyridine and ethanol, followed by further heating with aqueous NaOH. The picrate is described. 2 : 5 - Dimethyl - 4 : 6 - dihydroxypyrimidine is prepared by condensing diethyl a -methylmalonate with acetamidine. 4 - Bromo - 5 - methyl - 2 - thenyl bromide, 3 : 4 - dibromo - 5 - methyl - 2 - thenyl bromide, 3 - methyl - 2 - thenyl chloride and 4 : 5 - dimethyl-2-chloromethylthiazole are prepared by reacting 4-bromo-5-methyl-2-thenyl alcohol, 3 : 4 - dibromo - 5 - methyl - 2 - thenyl alcohol, 3 - methyl - 2 - hydroxymethylthiophene and 1-hydroxymethyl-4 : 5-dimethylthiazole respectively with hydrobromic acid or thionyl chloride. 2 : 5 - Dimethyl - 4 : 6 - dichloropyrimidine is prepared by treating 2 : 5-dimethyl-4 : 6-dihydroxypyrimidine with phosphorus pentachloride. 2 : 5 - Dimethylpyrimidine is prepared by dechlorination of 2 : 5 - dimethyl - 4 : 6 - dichloropyrimidine in presence of nickel. 2 - Chloromethyl - 5 - methylpyridine, 2-methyl - 5 - bromomethylpyridine, 2 - methyl - 5-chloromethylpyrazine, 3 - methyl - 6 - ch