Process for preparing resin-linear organosiloxane block copolymers
View Patent ↗A process is disclosed for preparing a resin-linear organosiloxane block copolymer by reacting in a first step an endcapped linear organosiloxane and an organosiloxane resin to form a resin-linear organosiloxane block copolymer. The resulting resin-linear organosiloxane block copolymer is then crosslinked in a second step to sufficiently increase the average molecular weight of the resin-linear organosiloxane block copolymer by at least 50%. The resin-linear organosiloxanes block copolymers prepared by the disclosed process may provide optically solid compositions which may be considered as “reprocessable”.
1. A process for preparing a resin-linear organosiloxane block copolymer comprising:
I) reacting
a) a linear organosiloxane having the formula
R 1 q (E) (3-q) SiO(R 1 2 SiO 2/2 ) n Si(E) (3-q) R 1 q ,
where each R 1 is independently a C 1 to C 30 hydrocarbyl,
n is 10 to 400, q is 0, 1, or 2,
E is a hydrolyzable group containing at least one carbon atom, and
b) an organosiloxane resin comprising at least 60 mol % of [R 2 SiO 3/2 ] siloxy units in its formula, where each R 2 is independently a C 1 to C 20 hydrocarbyl,
in c) an organic solvent
to form a resin-linear organosiloxane block copolymer;
wherein the amounts of a) and b) used in step I are selected to provide the resin-linear organosiloxane block copolymer with 40 to 90 mol % of disiloxy units [R 1 2 SiO 2/2 ] and 10 to 60 mol % of trisiloxy units [R 2 SiO 3/2 ], and
wherein at least 95 weight percent of the linear organosiloxane added in step I is incorporated into the resin-linear organosiloxane block copolymer,
II) reacting the resin-linear organosiloxane block copolymer from step I) to crosslink the trisiloxy units of the resin-linear organosiloxane block copolymer sufficiently to increase the average molecular weight (M w ) of the resin-linear organosiloxane block copolymer by at least 50%,
III) optionally, further processing the resin-linear organosiloxane block copolymer to enhance storage stability and/or optical clarity,
IV) optionally, removing the organic solvent.
2. The process of claim 1 where E is selected from an oximo, epoxy, carboxy, amino, or amido group.
3. The process of claim 1 where E is R 1 C(═O)O—, R 1 2 C═N—O—, or R 4 C═N—O—where R 4 is hydrocarbylene.
4. The process of claim 1 wherein where E is H 3 CC(═O)O—, and q is 1.
5. The process of claim 1 wherein an organosilane having the formula R 5 g SiX 4-q is added during step II), where R 5 is a C 1 to C 8 hydrocarbyl or a C 1 to C 8 halogen-substituted hydrocarbyl, X is a hydrolysable group, and q is 0, 1, or 2.
6. The process of claim 5 wherein the organosilane is an alkyltriacetoxysilane.
7. The process of claim 6 wherein the alkyltriacetoxysilane is a mixture of methyltriacetoxysilane and ethyltriacetoxysilane.
8. The process of claim 6 wherein step III is performed by reacting the resin-linear organosiloxane from step II with water and removing acetic acid.
9. The process of claim 5 wherein the amount of organosilane added provides a molar stoichiometry of 2 to 15 mol % of organosilane per mole of Si on the organosiloxane resin.
10. The process of claim 1 wherein E is (CH 3 )(CH 3 CH 2 )C═N—o—, and q is 1.
11. The process of claim 1 wherein step III is performed by reacting the resin-linear organosiloxane from step II with an endcapping compound selected from an alcohol, oxime, or trialkylsiloxy compound.
12. The process of claim 11 wherein the endcapping compound is n-butanol.
13. The process of claim 1 wherein the organosiloxane resin is a silsesquioxane resin.
14. The process of claim 13 wherein R 2 is methyl or phenyl.
15. The process of claim 13 wherein R 2 is phenyl.
16. The process of claim 13 wherein R 2 is napthyl.
17. The process of claim 1 wherein the organosiloxane resin has silanol content of at least 10 mole %.
18. The process of claim 17 wherein the organosiloxane resin has silanol content of 10 mole % to 50 mole %.
19. The process of claim 1 wherein R 1 is methyl or phenyl.
20. The process of claim 1 where the linear organosiloxane has the formula (CH 3 ) q (E) (3-q) SiO[(CH 3 ) 2 SiO 2/2 )] n Si(E) (3-q) (CH 3 ) q .
21. The process of claim 20 where E is H 3 CC(═O)O— and q is 1.
22. The process of claim 1 where the linear organosiloxane has the formula (CH 3 ) q (E) (3-q) SiO[(CH 3 )(C 6 H 5 )SiO 2/2 )] n Si(E) (3-q) (CH 3 ) q .
23. The process of claim 22 where E is H 3 CC(═O)O— and q is 1.
24. A resin-linear organosiloxane block copolymer prepared by the process of claim 1 .
25. A method of forming a coating comprising applying a film of the resin-linear organosiloxane block copolymer of claim 24 on a surface and curing the film to form a coating.
26. A solid composition comprising the resin-linear organosiloxane of claim 24 .
27. The process of claim 1 wherein the resin-linear organosiloxane block copolymer from step I) has silanol content of at least 10 mole %.
28. The process of claim 27 wherein the resin-linear organosiloxane block copolymer from step I) has silanol content of 10 mole % to 30 mole %.