Process for making mercapto-functional silane

A process for the preparation of a mercaptofunctional silane comprising:

• a) reacting at least one organofunctional silane selected from the group consisting of:
• G1-(SiX3)s (1)
• [G3-(YG2-)kY]j-G2-(SiX3)s (2)
• and at least one mercaptofunctional silane of the general formula:
• (HS)r-G2-(SiX3)s (3)
• wherein:
• each occurrence of Y is independently selected from a polyvalent species (-Q)a[C(=E)]b(A-)c, wherein the atom (E) is attached to an unsaturated carbon atom;
• each occurrence of G1 is independently selected from the group consisting of monovalent and polyvalent groups derived by substitution of alkyl, alkenyl, aryl, or aralkyl wherein G1 can have from 1 to about 30 carbon atoms;
• each occurrence of G2 is independently selected from the group consisting of divalent or polyvalent group derived by substitution of alkyl, alkenyl, aryl, or aralkyl wherein G2 can have from 1 to 30 carbon atoms;
• each occurrence of G3 is independently selected from the group consisting of monovalent and polyvalent groups derived by substitution of alkyl, alkenyl, aryl, or aralkyl wherein G3 can have from 1 to about 30 carbon atoms, with the proviso that if G3 is monovalent, G3 can be hydrogen;
• each occurrence of X is independently selected from the group consisting of —Cl, —Br, RO—, RC(═O)O—, R2C═NO—, R2NO—, R2N—, —R, wherein each R is independently selected from the group consisting of hydrogen, straight, cyclic or branched alkyl that can or can not contain unsaturation, alkenyl groups, aryl groups, and aralkyl groups, wherein each R, other than hydrogen, contains from 1 to 18 carbon atoms;
• each occurrence of Q is independently selected from the group consisting of oxygen, sulfur, and (—NR—) and with the proviso that when Q is sulfur, b is 0;
• each occurrence of A is independently selected from the group consisting of oxygen, sulfur, and (—NR—) and with the proviso that when A is sulfur, b is 0;
• each occurrence of E is independently selected from the group consisting of oxygen, sulfur, and (—NR—);
• each occurrence of the subscripts, a, b, c, j, k, r, and s are independently integers given by a is 0 or 1;
• b is 0 or 1;
• c is 0 or 1;
• j is of from about 1 to about 3;
• k is of from about 0 to about 15;
• r is of from about 1 to about 3;
• and s is of from about 1 to about 3, and with the proviso that each of the above structures (1), (2) and (3) contains at least one hydrolysable X group;
• b) with one or more polyhydroxy-containing compounds of the general formula:
• G4(OH)d (6)
• wherein G4 is a hydrocarbon group of from 1 to about 15 carbon atoms or a heterocarbyl group of from 4 to about 15 carbon atoms containing one or more etheric oxygen atoms and d is an integer of from about 2 to about 8, under transesterification reaction conditions, wherein mixtures of silane monomers (1), (2) and/or (3) are used.