Polymeric organo-tin compounds of the general formula <FORM:0694944/IV (a)/1> wherein (RO)1 represents the residue of an alcohol, R2 is the same organic group as R in the group (RO)1, R3 and R4 represent alkyl or aryl groups and n indicates the degree of polymerization, are prepared by reacting a dialkyl, diaryl or alkyl aryl tin dihalide with an alkali metal alkoxide in an anhydrous aromatic solvent, or with ammonia or a tertiary amine and alcohol in an amount not substantially exceeding the stoichiometric amount, the precipitated inorganic halide is then removed and the solvent is distilled off, the reaction and/or evaporation of the solvent being carried out at an elevated temperature, e.g. the temperature should preferably not exceed 150 DEG C. The group (RO)1 may be the residue of a saturated or unsaturated primary, secondary or tertiary aliphatic, alicyclic or aromatic alcohol, e.g. methyl, ethyl, allyl, lauryl, tertiary butyl, tetrahydrofurfuryl, benzyl, phenylethyl, cinnamyl or a hydroabietyl alcohol, any of the butyl or propyl alcohols, 2-ethylhexanol, methyl isobutyl carbinol, cyclohexanol or any of the methyl or dimethyl cyclohexanols. The alkyl chain of the alcohols may be interrupted by oxygen or sulphur, e.g. ether or thioether alcohols may be used. Suitable dialkyl or diaryl tin dihalides which may be employed include dimethyl and diethyl tin dichlorides, any of the dibutyl and diamyl tin dichlorides, dioctyl, diphenyl and dibenzyl tin dichlorides, and any of the ditolyl and dixylyl tin dichlorides as well as the corresponding dibromides. The lower polymeric tin compounds are soluble in alcohols, aromatic hydrocarbons, e.g. benzene, toluene or xylene, and also in halogenated aliphatic and aromatic hydrocarbons, e.g. ethylene dichloride, carbon tetrachloride, b ,b 1-dichloro-ethyl ether or chlorobenzene. The higher polymers are soluble in the same solvents at elevated temperatures with the exception of the alcohols. Synthetic resin compositions are obtained by incorporating the above polymeric organo-tin compounds with halogen-containing synthetic resins, e.g. by milling or by adding a solution of the polymeric organo-tin compound in one of the solvents referred to above to the resin. A monomeric organo-tin compound of the above general formula may be added to the resin and polymerized, e.g. by heat treatment, preferably in the presence of water vapour. Halogen-containing synthetic resins referred to include polymers of vinyl chloride, copolymers of vinyl chloride with vinyl esters of aliphatic acids particularly vinyl acetate, copolymers of vinyl chloride with esters of acrylic and methacrylic acids and with acrylonitrile, copolymers of vinyl chloride with diene compounds and unsaturated dicarboxylic acids or their anhydrides, e.g. copolymers of vinyl chloride with diethyl maleate, diethyl fumarate or maleic anhydride, after-chlorinated polymers and copolymers of vinyl chloride, polymers of vinylidene chloride and copolymers of the same with vinyl chloride, polymers of vinyl chloro-acetate and dichlorodivinyl ether, chlorinated polymers of vinyl acetate, chlorinated polymeric esters of acrylic and alpha-substituted acrylic acids, polymers of chlorinated styrenes, e.g. dichlorostyrene, chlorinated polymers of ethylene, polymers and after-chlorinated polymers of chlorobutadienes and their copolymers with vinyl chloride, chlorinated rubber, rubber hydrochloride and chlorinated rubber hydrochloride, and the corresponding bromides and brominated polymers. Mixtures of any of the above synthetic resins may also be used. It is preferred that the halogen-containing synthetic resins form the major constituent of the compositions, e.g. between 0.5 and 5 per cent, preferably between 1 and 3 per cent, of the polymeric tin compound based on the weight of the halogen-containing synthetic resin may be used. Plasticizers may be used in combination with the polymeric organo-tin compounds and the following plasticizers are referred to: esters of phthalic, adipic, sebacic, azelaic, citric, aconitic, tricarballic, maleic, fumaric, succinic, malonic and phosphoric acids, mercapto acids, e.g. thioglycolic acid, esters of dihydric and polyhydric alcohols, e.g. glycol, glycerol, pentaerythritol and sorbitol, esters of thioglycols, amino-alcohol derivatives, ester amides, sulphonamides, chlorinated plasticizers and carbonic acid derivatives derived from phosgene. In the examples: (1) di-n-butyl tin dimethoxide polymers are obtained either from the reaction of di-n-butyl tin dichloride and sodium methoxide in toluene followed by heating, or from the reaction of di-n-butyl tin dichloride, methyl alcohol and ammonia; the polymeric tin compounds are then added to a mixture containing vinyl chloride-vinyl acetate copolymer, dioctylphthalate, acetone and butyl acetate; the example is repeated using polymeric dimethyl tin dimethoxide; (2) di-n-amyl tin di-n-propoxide polymers are obtained from sodium propoxide and di-n-amyl tin dichloride as in (1); (3) di-n-butyl tin di-n-butoxy tin polymers are prepared as in (2) and are added to a solution of vinyl chloride-vinyl acetate copolymer in methylethyl ketone containing dioctylphthalate; polymeric di-n-butyl tin di-n-butoxides may be used in the same way; (4) di-n-butyl tin di-2-ethylhexoxide is prepared as in (2), or by heating monomeric di-n-butyl tin di-2-ethylhexoxide in alcohol; the polymeric tin compound is milled with a vinyl chloride-vinyl acetate copolymer and dioctylphthalate; (6) polymerized diethyl tin di-2-ethylhexoxide is obtained by heating diethyl tin dichloride, pyridine and 2-ethylhexanol; (7) diethyl tin di-n-butoxyethoxide polymer is prepared by heating sodium-n-butoxyethyleneglycoxide and di-n-butyl tin dichloride dissolved in xylene; the product is milled with dioctyl sebacate and a joint polymer of vinyl chloride and diethyl maleate; (8) polymeric di-n-butyl tin dibenzoxide is prepared by reacting the sodium salt of benzyl alcohol and di-n-butyl tin dichloride in toluene, distilling the toluene off under reduced pressure, heating the residue under reduced pressure and washing out any monomeric tin compound with ethanol; (9) polymeric di-n-butyl tin dialloxide is prepared as in (2) and is milled with a copolymer of vinyl chloride and vinylidene chloride and 2-ethyl hexyl phthalate; (10) polymeric di-n-butyl tin dicyclohexoxide is prepared by reacting sodium cyclohexoxide and di-n-butyl tin dichloride in toluene, and distilling off the solvent under reduced pressure, and is added to a mix containing a joint polymer of vinyl chloride and acrylonitrile and dioctyl phthalate; (11) a resinous composition is obtained by adding polymerized di-n-butyl tin butoxide to a mixture of polymerized vinyl chloride, dioctylphthalate, diisobutylketone and xylene; (12) an emulsion from which films are prepared is obtained by dissolving di-n-butyl tin dimethoxide polymer in di-octyl phthalate and adding an ionic emulsifier (an alkylated phenol reacted with ethylene oxide) together with water; (13) resinous compositions are obtained by milling at an elevated temperature vinyl chloride, vinyl acetate, dimeric din-n-butyl tin dimethoxide and each of the compounds di - 2 - ethylhexylphthalate, di - nonyl phthalate, di - isooctylphthalate, di - n - butyl tetrachlorophthalate, di - n - butoxy ethyl adipate, di-2-ethylhexyl adipate and triethylene glycol di-2-ethylhexoate. Specification 590,734 is referred to.ALSO:Organo tin compounds of the general formula <FORM:0694944/IV (b)/1> wherein (RO)1 is the residue of an alcohol, R2 i the same organic group as R in said (RO)1, R3 and R4 represent alkyl or aryl groups and n indicates the degree of polymerization, are prepared by reacting a dialkyl, diaryl or alkyl aryl tin dihalide with an alkali metal alkoxide in an anhydrous aromatic solvent, or with ammonia or a tertiary amine and alcohol in an amount not substantially exceeding the stoichiometric amount, the precipitated inorganic halide is then removed and the solvent is distilled off, the reaction and/or evaporation of the solvent being carried out at an elevated temperature, e.g. the temperature should preferably not exceed 150 DEG C. Suitable dialkyl or diaryl tin dihalides which may be employed include dimethyl and diethyl tin dichlorides, any of the dibutyl and diamyl tin dichlorides, dioctyl, diphenyl and dibenzyl tin dichlorides, and any of the ditolyl and dixylyl tin dichlorides as well as the corresponding dibromides. The group (RO)1 may be the residue of a saturated or unsaturated primary, secondary, or tertiary aliphatic, alicyclic or aromatic alcohol, e.g. methanol, ethanol, allyl alcohol, any of the butanols and propanols, 2-ethyl hexanol, lauryl alcohol, methyl isobutyl carbinol, tertiary butyl alcohol, cyclohexanol, any of the methyl and dimethyl cyclohexanols, a hydroabietyl alcohol, or tetrahydrofurfuryl alcohol, benzyl alcohol, phenyl-ethyl alcohol, or cinnamyl alcohol. The alkyl chain of the alcohols may be interrupted by oxygen or sulphur, e.g. ether alcohols or thioether alcohols may be used. The product includes some monomeric compounds of the above general formula. In the examples, compounds of the above general formula are prepared from di-n-butyl tin dichloride and sodium methoxide or methyl alcohol, di-n-amyl tin dichloride and sodium -n-propoxide, di-n-butyl tin dichloride and sodium-n-butoxide or sodium 2-ethyl hexanol, diphenyl tin dichloride and sodium methoxide, diethyl tin dichloride and 2-ethyl hexanol, di-n-butyl tin dichloride and sodium n-butoxyethylene glycoxide, sodium benzoxide, sodium allylate or sodium cyclohexoxide. Specification 590,734 is referred to.ALSO:Chlorinated rubber, rubber hydrochloride and chlorinated rubber hydrochloride are stabilized by incorporating with the rubber polymeric organotin compounds of the general formula <FORM:0694944/V/1> wherein