Process for the synthesis of silylated polyurethanes and silylated polyurethane composition
The present invention provides a process for the synthesis of silylated polyurethanes, comprising three sequential steps, a step (i) of preparing NCO-terminated polyurethane, a step (ii) of partial grafting of the NCO functions with silane functions and a step (iii) of total grafting of the residual NCO functions with functions that react with the NCO functions by means of polyfunctional compounds. The present invention also provides a silylated polyurethane composition that can be obtained by means of the process according to the invention, an adhesive composition comprising said silylated polyurethane composition and a self-adhesive item obtained from the adhesive composition according to the invention.
1. A process for the synthesis of a composition of silylated polyurethanes (A), said process comprising the following sequential stages:
i. polyaddition of at least one polyol (B) with at least one diisocyanate (C), in which the ratio (r1) of the number of NCO functional groups to the total number of OH functional groups, and of NH and NH 2 functional groups optionally present, is strictly greater than 1;
ii. reacting the composition obtained in stage (i) with at least one silane (E) selected from the group consisting of aminosilanes (E1) and mercaptosilanes (E2), wherein the ratio (r2) of the number of NCO functional groups to the number of amine and/or thiol functional groups ranges from 1.1 to 5;
iii. reacting the composition resulting from stage (ii) with at least one compound (G), wherein the compound (G) is selected from diols having a number average molecular weight ranging from 600 to 20,000 g/mol, and wherein during stage (iii), the ratio (r3) of the number of NCO functional groups to the number of alcohol functional groups is greater than or equal to 0.6 and less than or equal to 1.
2. The synthesis process as claimed in claim 1 , in which, during stage (iii), the ratio (r3) of the number of NCO functional groups to the number of alcohol functional groups is greater than or equal to 0.7 and less than or equal to 1.
3. The synthesis process as claimed in claim 1 , wherein the silane (E) exhibits the following structure:
X′—R 3 —Si(R 4 ) p (OR 5 ) 3-p
wherein:
X′ represents an NH 2 , NHR 7 and/or SH group,
R 7 represents a linear, branched or cyclic alkyl radical having from 1 to 12 carbon atoms or an alkenyl radical having from 2 to 12 carbon atoms or an aryl radical having from 6 to 12 carbon atoms,
R 3 represents a linear or branched divalent alkylene radical comprising from 1 to 6 carbon atoms,
R 4 and R 5 , which are identical or different, each represent a linear or branched alkyl radical comprising from 1 to 4 carbon atoms; two —OR 5 groups can optionally be involved in one and the same ring,
p represents an integer equal to 0, 1 or 2.
4. The synthesis process as claimed in claim 1 , in which the compound (G) exhibits a number-average molecular weight ranging from 100 g/mol to 80 000 g/mol.
5. The process of claim 1 , wherein the compound (G) is selected from diols having a number average molecular weight ranging from 1500 to 10,000 g/mol, and wherein during stage (iii), the ratio (r3) of the number of NCO functional groups to the number of alcohol functional groups is greater than or equal to 0.6 and less than or equal to 1.
6. The synthesis process as claimed in claim 1 , in which, during stage (iii), the ratio (r3) of the number of NCO functional groups to the number of alcohol functional groups is greater than or equal to 0.8 and less than or equal to 1.
7. The synthesis process as claimed in claim 1 , in which, during stage (iii), the ratio (r3) of the number of NCO functional groups to the number of alcohol functional groups is greater than or equal to 0.9 and less than or equal to 1.