A composition contains an organopolysiloxane having the average chemical structure (I):

[R′R.sub.2SiO—(R.sub.2SiO).sub.m].sub.3—Si—[OSiR.sub.2].sub.n—Y—Si(OR).sub.3  (I)

where: R is independently in each occurrence selected from alkyl, aryl, substituted alkyl and substituted alkyl groups having from one to 8 carbon atoms; R′ is independently in each occurrence selected from R and terminally unsaturated alkylene groups having from 2 to 6 carbon atoms; Y is selected from a group consisting of: X, and X—(R.sub.2SiO).sub.pSiR.sub.2—X; where p has an average value in a range of one to 3; and X is independently in each occurrence selected from alkylene and substituted alkylene groups having from one to 6 carbon atoms; and the average values for subscripts m and n are each greater than zero and independently selected so that the average value for the sum of all of the average m values and the average n value is in a range of 30-200.

Provided are a polyorganosiloxane high in elasticity, high in strength and the like. The polyorganosiloxane is a polyorganosiloxane including an M unit (R.sup.1R.sup.2R.sup.3SiO.sub.1/2) at a content of 10% by mol or more relative to the total of silicon and a T unit (R.sup.6SiO.sub.3/2) at a content of 80% by mol or less relative to the total of silicon, the polyorganosiloxane having an alkoxy group bound and a reactive functional group bound to silicon, wherein the polyorganosiloxane has the alkoxy group bound at a content of 0.07 to 4% by weight based on the total weight of the polyorganosiloxane and has 3 to 12 of the reactive functional groups bound on a number basis per a molecular weight of 1000 of the polyorganosiloxane, and the weight loss of the polyorganosiloxane in heating at 110° C. under a reduced pressure of 0.15 torr for 2 hours is 5% by weight or less.

A preparation method for a spherical silica powder filler comprises the following steps: S1, providing spherical polysiloxane comprising a T unit by means of a hydrolysis condensation reaction of R.sub.1SiX.sub.3, wherein R.sub.1 is hydrogen atom or an organic group having independently selectable 1 to 18 carbon atoms, X is a hydrolyzable group, and T unit is R.sub.1SiO.sub.3—; and S2, calcining the spherical polysiloxane under the condition of a dry oxidizing gas atmosphere, the calcining temperature being between 850° C. and 1200° C., so as to obtain the spherical silica powder filler which does not contain silica particles of which the diameter is less than 50 nanometers. The spherical silica powder filler does not contain silica particles of which the diameter is less than 50 nanometers, has a low dielectric loss and a low thermal expansion coefficient, and is suitable for high-frequency high-speed circuit boards, prepregs or copper clad laminates, etc.

Curable compositions of this disclosure comprise a mixture of: a silanol, a free radical initiator, an iodonium salt; and optionally an alkoxysilane, and/or an MQ resin, and/or (meth)acrylate monomer(s). In another aspect, cured compositions of this disclosure comprise: a cured silicone, a free radical initiator or residue thereof, an iodonium salt or residue thereof; and optionally a poly(meth)acrylate and/or an MQ resin, which may comprise the cured silicone. In another aspect, cured compositions of this disclosure comprise: a continuous phase of cured silicone, a discontinuous phase of poly(meth)acrylate inclusions, and optionally an MQ resin, which may comprise the cured silicone. The poly(meth)acrylate inclusions may have an average diameter of less than 1.0 micrometer or smaller. The compositions may be pressure sensitive adhesives. The curable and cured compositions may be solvent-free.

Provided is a polymer of the formula: ##STR00001##
and compositions comprising the same. The polymers comprise a cyclic unsaturated group (Z.sup.3) within the siloxane polymer backbone. The polymers have been found to exhibit good thermal conductivity and may find utility in a variety of applications.

Processes are described for purifying acidic, preferably superacidic, in particular trifluoromethanesulfonic acid-acidified, end-equilibrated acetoxysiloxanes, wherein the acidic, preferably superacidic, in particular trifluoromethanesulfonic acid-acidified, acetic anhydride-containing and optionally acetic acid-containing equilibrated, preferably end-equilibrated acetoxysiloxane, which is optionally dissolved in an inert solvent, is contacted with a base, the precipitate is filtered off thereafter and then the filtrate obtained is optionally purified by distillation.

A white curable silicone composition provides excellent elongation characteristics while providing sufficiently great hardness, which as a result can provide a cured product having excellent toughness. The composition comprises: (A) alkenyl group-containing resinous organopolysiloxane which is represented by an average composition formula: (R.sup.1.sub.3SiO.sub.1/2).sub.a(R.sup.1.sub.2SiO.sub.2/2).sub.b(R.sup.1SiO.sub.3/2).sub.c(SiO.sub.4/2).sub.d(XO.sub.1/2).sub.e, where, in the formula, R.sup.1 are each independently a monovalent hydrocarbon group, while at least two R.sup.1 are alkenyl groups, X is a hydrogen atom or an alkyl group, 0≤a≤0.7, 0≤b≤0.2, 0≤c≤0.3, 0≤d≤0.8, and 0≤e≤0.2, a+b+c+d=1.0, and c+d>0 are satisfied; (B) linear alkenyl group-containing organopolysiloxane which is represented by R.sup.2R.sup.3.sub.2SiO(R.sup.3.sub.2SiO).sub.nSiOR.sup.2R.sup.3.sub.2, where, in the formula, R.sup.2 is an alkenyl group, R.sup.3 are each independently a monovalent hydrocarbon group other than an alkenyl group, and n is an integer of 50 or greater; (C) organohydrogenpolysiloxane having at least two hydrogen atom-bonded silicon atoms in one molecule; (D) a catalyst for curing reaction; and (E) a white pigment, wherein the component (A) is included in an amount of 20 mass % or more based on the total mass of the organopolysiloxane components, and the alkenyl group content in the components (A) to (C) is 1.7 mass % or less.

Foam control compositions along with formulations thereof and their use in various applications, including a method for making a foam control composition comprising a cross-linked polyorganosiloxane material including a dispersed silica filler, including the steps of: A) preparing a hydrosilylation reaction mixture by combining the following components: (i) silica filler, (ii) a polyorganosiloxane having at least two reactive substituents capable of addition reaction with component (iii) via hydrosilylation, (iii) a polyorganosiloxane having at least three reactive substituents capable of addition reaction with component (ii) via hydrosilylation, and (iv) a hydrosilylation catalyst; B) conducting a hydrosilylation reaction of components (ii) and (iii) until the reaction mixture at least partially gels to form a hydrosilylation reaction product; C) shearing the hydrosilylation reaction product of step B); and D) combining the hydrosilylation reaction product of step C) with a (v) silicone resin and an (vi) condensation catalyst to form a condensation reaction mixture and conducting a condensation reaction between the (v) silicone resin and the hydrosilylation reaction product of step C) to form a condensation reaction product.

A composition and uses thereof are provided, comprising a polymerization product of a reactant composition, the reactant composition comprising: (a) vinyldimethylsiloxy-terminated polydimethylsiloxane, as monomer (M.sup.VIDM.sup.VI); (b) 45-55% poly(methylhydro-co-dimethylsiloxane), α, Ω-trimethylsiloxy terminated, as crosslinker (M.sup.VIDM.sup.VI); (c) platinum-divinyltetram-CA ethyl-disiloxane complex, as catalyst; (d) 2,4,6,8-tetramethyl-2,4,6,8-tetravinylcyclotetrasiloxane, as inhibitor; and (e) a filler-like resin composition comprising one or more of dimethylvinylated silica, trimethylated silica, and tetra(trimethylsiloxy) silane, as active ingredient, and one or more of xylene, ethylbenzene and toluene (MQ-R resin).

A process for producing a silicone pressure sensitive adhesive is shown and described herein. The process comprises reacting a MQ silicone resin with a polydiorganosiloxane in the absence of a solvent. The MQ silicone resin is a solid, solventless MQ resin. The reaction may be conducted in the presence of a catalyst, a chain extension reagent, or a combination thereof, and the resulting pressure sensitive adhesive can be dissolved in a solvent and the solids content adjusted. The present method provides a manner to provide a cleaner adhesive material that is free of unwanted materials such as aromatic solvents and also substantially free of cyclic siloxane impurities.