The invention comprises organopolysiloxanes consisting essentially of units of the general formula <FORM:0834730/IV (a)/1> where n is 2, 3 or 4, y is 0, 1 or 2, R is hydrogen or a methyl radical, and R1 is a monovalent hydrocarbon radical free from aliphatic unsaturation, and copolymers thereof with from 0.1 to 99.9 mol. per cent of conventional siloxane units. The polymers can be made by reacting a silane of the formula R1yHSiX3-y, where y is 0, 1 or 2, R1 is a hydrocarbon radical free from unsaturation and X is chlorine, bromine or an alkoxy radical, with vinyl, allyl or allylcarbinol (i.e. 3-buten-1-ol) acetate in the presence of chloroplatinic acid as catalyst. The resulting acyloxysilane is then hydrolysed, using a solvent where y is 0, to yield the corresponding siloxane which is then subjected to alcoholysis by contacting it e.g. with methanol or ethanol at 50 DEG to 100 DEG C. to produce the hydroxyalkyl polymer <FORM:0834730/IV (a)/2> an alkaline catalyst being used where n is 2 and an alkaline or acidic one where n is 3 or 4. The resulting polymer is then contacted with acrylic or methacrylic acid, preferably in the presence of H2SO4 to give the desired polymer. The copolymers are of two different types: (a) the first type is that in which the units are all of the above formula but have different R and/or R1 radicals, and can be made (i) by using a mixture of acrylic and methacrylic acids in the above described reaction, or (ii) by subjecting 2 or more homopolymers to the action of an acidic siloxane rearrangement catalyst, or (iii) by cohydrolysing a mixture of the corresponding silanes, each having different R1 radicals and/or different values for n and/or y; (b) the second type is that which contains the above defined acryloxyalkyl substituted units and units of the formula R11mSiO 4-m/2 , where each R11 is a monovalent hydrocarbon (saturated or unsaturated) or halogenated hydrocarbon radical and m is 0, 1, 2 or 3, can be made in conventional manner by copolymerization or by cohydrolysis. The disiloxanes <FORM:0834730/IV (a)/3> are made by contacting a disiloxane dialcohol [HO(CH2)nR12.Si]O with acrylic and/or meth acrylic acid followed by equilibration with (R113Si)2O, preferably in the presence of an acid catalyst. Alternatively, the disiloxane wherein n is 3 and each R1 and R11 is a methyl or phenyl radical can be made by reacting acrylic and/or methacrylic acid with a cyclic silpropoxane of the formula R12.Si.CH2.CH2.CH2.O such compounds are disclosed in Specification 817,237 followed by equilibration with a hexaorganodisiloxane. Examples are given. The products can be further polymerized by exposure to vinyl polymerizing conditions, i.e. by conventional bulk, solvent solution or suspension or emulsion polymerization techniques, using conventional catalysts (organic, inorganic or physical)-these include heat alone, ultraviolet light, ionizing radiation (e.g. X-rays and accelerated particles from nuclear reactors, radioactive isotopes and "Van de Graff generators"); hydrogen, sodium and benzoyl peroxides; t-butyl-peracetate and -perbenzoate, and a ,a 1-azo-di-isobutyronitrile. Conventional siloxane polymerization catalysts can also be added to expedite condensation of Si-OH groups present. The products can also be copolymerized with vinylic compounds, e.g. vinyl chloride, styrene, divinylbenzene, dichlorostyrene, acrylonitrile, vinylacetate, vinylalkyl ethers, vinylidene chloride, isobutylene, isopropenyl chloride, methyl- and ethyl acrylates and methacrylates, butadiene, chloroprene, isoprene, linear unsaturated polyesters such as those of ethylene glycol and maleic acid, and any silane or siloxane containing Si-bonded vinyl or allyl radicals. Uses.-As moulding and impregnating resins, electrical insulating varnishes, water repellent treatments and thermally resistant rubbers and resins. The subject-matter of Specification 754,622 is disclaimed. Specification 769,953 also is referred to.