Process for preparing resin-linear organosiloxane block copolymers
AssigneeDow Corning Corporation
InventorsJohn Bernard Horstman, Steven Swier
Life of this patent
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Abstract
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”.
Claims25
A process for preparing a resin-linear organosiloxane block copolymer comprising:
- I) reacting
- a) a linear organosiloxane having the formula
- R1q(E)(3-q)SiO(R12SiO2/2)nSi(E)(3-q)R1q,
- where 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 mol % of disiloxy units [R12SiO2/2] and 10 to 60 mol % 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) optionally, further processing the resin-linear organosiloxane block copolymer to enhance storage stability and/or optical clarity,
- IV) optionally, removing the organic solvent.
Dependencies are inferred from the claim text.