Curable silicone composition, encapsulant and optical semiconductor device

A curable silicone composition comprising:

• (A) a resinous alkenyl group-containing organopolysiloxane containing less than two alkenyl groups per molecule on average, which is represented by average unit formula (I):
• (R13SiO1/2) a (R12SiO2/2) b (R1SiO3/2) c (SiO4/2) d (XO1/2) e, where in formula (I), each R1 is independently a monovalent hydrocarbon group, while the number of alkenyl groups per molecule is one or more and is less than two on average, X is a hydrogen atom or an alkyl group, 0≤a≤1, 0≤b≤1, 0≤c<0.9, d=0, 0≤e<0.4, a+b+c+d=1.0, and c+d>0;
• (B) an organohydrogenpolysiloxane having three or more silicon atom-bonded hydrogen atoms per molecule;
• (C) a curing reaction catalyst;
• and
• (D) an organopolysiloxane which is different from components (A) and (B), wherein the organopolysiloxane of component (D) includes a cyclic organopolysiloxane represented by general formula (III):
• (R12SiO)n,
• where in formula (III), each R1 is independently a monovalent hydrocarbon group, and n is an integer of from 3 to 50.

A curable silicone composition comprising:

• (A) a resinous alkenyl group-containing organopolysiloxane containing less than two alkenyl groups per molecule on average, which is represented by average unit formula (I):
• (R13SiO2) a (R12SiO2/2) b (R1SiO3/2) c (SiO4/2) d (XO1/2) e, where in formula (I), each R1 is independently a monovalent hydrocarbon group, while the number of alkenyl groups per molecule is one or more and is less than two on average, X is a hydrogen atom or an alkyl group, 0≤a≤1, 0≤b≤1, 0≤c<0.9, d=0, 0≤e<0.4, a+b+c+d=1.0, and c+d>0;
• (B) an organohydrogenpolysiloxane having three or more silicon atom-bonded hydrogen atoms per molecule;
• (C) a curing reaction catalyst;
• and
• (D) an organopolysiloxane which is different from components (A) and (B), wherein the organopolysiloxane of component (D) includes an epoxy group-containing resinous organopolysiloxane represented by average unit formula (IV):
• (R23SiO1/2)a(R22SiO2/2)b(R2SiO3/2)c(SiO4/2)d(XO1/2)
• where in formula (IV), each R2 is the same or different optionally halogen-substituted monovalent hydrocarbon group or epoxy group-containing organic group, at least one R2 is an epoxy group-containing organic group, X is a hydrogen atom or an alkyl group, and 0≤a≤1, 0≤b≤1, 0≤c<0.9, 0≤d<0.5, 0≤e<0.4, a+b+c+d=1.0, and c+d>0.

A curable silicone composition comprising:

• (A) a resinous alkenyl group-containing organopolysiloxane containing less than two alkenyl groups per molecule on average, which is represented by average unit formula (1):
• (R13SiO1/2)a (R12SiO2/2)b (R1SiO3/2)c (SiO4/2)d (XO1/2)e, where in formula (1), each R1 is independently a monovalent hydrocarbon group, where the number of alkenyl groups per molecule is from 1 to 1.9 alkenyl groups per molecule on average, X is a hydrogen atom or an alkyl group, a is 0≤a≤1, b is 0≤b≤1, c is 0≤c≤0.9, d=0, e is 0≤e≤0.4, a+b+c=d=1.0 and c+d>0;
• (B) an organohydrogenpolysiloxane having three or more silicon atom-bonded hydrogen atoms per molecule;
• (C) a curing reaction catalyst;
• and
• (D) an organopolysiloxane which is different from components (A) and (B).