Curable compositions of resin-linear organosiloxane block copolymers
AssigneeDow Corning Corporation
InventorsJohn Bernard Horstman, Steven Swier
Life of this patent
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Abstract
Curable compositions of resin-linear organosiloxane block copolymers having improved shelf stability are disclosed. A stabilizer compound is added to the resin-linear organosiloxane block copolymer which increases the temperatures needed to effect final cure of the compositions. In other embodiments, the present disclosure provides curable compositions of resin linear organosiloxane block copolymers having improved physical properties, such as improved toughness.
Claims20
A curable composition comprising:
- i) an organosiloxane block copolymer comprising:
- 40 to 90 mole percent disiloxy units of the formula [R12SiO2/2],
- 10 to 60 mole percent trisiloxy units of the formula [R2SiO3/2],
- 0.5 to 35 mole percent silanol groups [≡SiOH];
- wherein:
- R1 is independently a C1 to C30 hydrocarbyl,
- R2 is independently a C1 to C20 hydrocarbyl;
- wherein:
- the disiloxy units [R12SiO2/2] are arranged in linear blocks having an average of from 10 to 400 disiloxy units [R12SiO2/2] per linear block,
- the trisiloxy units [R2SiO3/2] are arranged in non-linear blocks having a molecular weight of at least 500 g/mol, and at least 30% of the non-linear blocks are crosslinked with each other, each linear block is linked to at least one non-linear block;
- and
- the organosiloxane block copolymer has a weight average molecular weight (MW) of at least 20,000 g/mole;
- and
- ii) a stabilizer, wherein the stabilizer comprises alkaline earth metal salt, a metal chelate, a boron compound, a silicon-containing small-molecule or combinations thereof.
A process for preparing a curable composition comprising:
- I) reacting
- a) a linear organosiloxane having the formula:
- R1q(E)(3-q)SiO(R12SiO2/2)nSi(E)(3-q)R1q,
- wherein each R1 is independently a C1 to C30 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 [R2SiO3/2] siloxy units in its formula, where each R2 is independently a C1 to C20 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 mole % of disiloxy units [R12SiO2/2] and 10 to 60 mole % of trisiloxy units [R2SiO3/2], 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 (MW) of the resin-linear organosiloxane block copolymer by at least 50%;
- III) contacting the resin-linear organosiloxane block copolymer from step II) with a stabilizer, wherein the stabilizer comprises alkaline earth metal salt, a metal chelate, a boron compound, a silicon-containing small-molecule or combinations thereof;
- and
- IV) optionally, removing the organic solvent.
A method of increasing the trouser tear strength of a solid curable film composition of a resin linear organopolysiloxane comprising adding to the composition a stabilizer comprising an alkaline earth metal salt, a metal chelate, a boron compound, a silicon-containing small molecule or combinations thereof.
Dependencies are inferred from the claim text.