Silanes of the general formulae <FORM:0960534/C3/1> and <FORM:0960534/C3/2> in which D is a <FORM:0960534/C3/3> , phenyl or CH3CH=CH-radical, X is a hydrocarbon radical of 1 to 6 C atoms, H or a radical of the formula <FORM:0960534/C3/4> , <FORM:0960534/C3/5> or <FORM:0960534/C3/6> , R1 is an aliphatic radical composed of C, H and O, the latter being in the form of ether or polyether linkages or -OH radicals, in R1 the ratio of C:O being not greater than 3:1, R is an alkylene radical of 1 to 4 C atoms, R111 is a monovalent hydro carbon or halohydrocarbon radical, Y is a monovalent hydrolysable atom or radical, a is 0 or 1 and b is 0, 1 or 2, are best prepared by reacting alkenyl esters of itaconic, maleic, fumaric, aconitic, citraconic, cinnamic and sorbic acids, and <FORM:0960534/C3/7> and <FORM:0960534/C3/8> with silanes of the formula <FORM:0960534/C3/9> in the presence of a Pt catalyst. Silanes in which R is a methylene radical are best prepared by reacting a tertiary amine salt of the corresponding acids or monoesters with <FORM:0960534/C3/100> , wherein Y is preferably an alkoxy radical, in the presence of a mutual solvent at 100 to 175 DEG C.; alternatively they may be made by reacting the same silane with an alkali metal salt, e.g. <FORM:0960534/C3/111> (where M=alkali metal and Q is <FORM:0960534/C3/122> , <FORM:0960534/C3/133> or <FORM:0960534/C3/144> at 50 to 150 DEG C. In these reactions the molar proportions determine whether the final silane contains 1 or 2 Si atoms. The silanes are hydrolysed at a pH of 7 to give stable solutions of the corresponding silanols, buffers such as ammonia or acetic acid, being added where necessary. The silanes per se or together with conventional silanes may be hydrolysed and condensed to give homo- or copolymers. Alternatively the polymers can be made by the above SiH addition reaction using a Pt catalyst, but starting with siloxanes containing Si-bonded hydrogen and the customary hydrocarbon (saturated or unsaturated) or halohydrocarbon radicals. In typical examples, (1) a mixture of trimethoxysilane and allylmethylmaleate was slowly added to a heated mixture of toluene and a solution of chloroplatinic acid and the resulting mixture was then heated for 1 hr at 112 DEG C. to yield, after removal of solvent and distillation of the residue, a compound of the formula CH3OOC.CH=CHCOO(CH2)3Si(OCH3)3; (7) allyl-cinnamate was similarly reacted with the same silane to yield C6H5.CH=CH.COO(CH2)3Si(OCH3)3 which was hydrolysed to yield the corresponding siloxane; (19) CH3OOC.CH=CH.COOH was reacted with <FORM:0960534/C3/155> in the presence of tributylamine to yield <F\16>. In (14) the compound HOOCCH=CHCOO(CH2CH2O)100(CH2)2 Si(CH3)-(OOCCH3)2 is prepared. Uses: the silanes are useful for treating glass, other siliceous materials and metals; the polymers are useful for copolymerization with unsaturated organic monomers or polyesters, as coating compositions with or without organic resins, and as laminating resins.