Curable thermally conductive polysiloxane composition with increased thixotropic index

A composition comprising:

• (a) a vinyl-functional polysiloxane;
• (b) a silyl hydride functional polysiloxane having on average at least two silyl hydride groups per molecule, where the silyl hydride functional polysiloxane is a linear polysiloxane having the following general molecular structure:
• R3-hHhSiO—(HRSiO)a—(R2SiO)b—SiHh·R3-h, (II)
• where:
• R is independently in each occurrence selected from alkyl and aryl groups having from one to 6 carbon atoms;
• H is hydrogen, subscripts h and h′ refer to the average number of terminal hydrogens on the respective ends of the molecule and have a value of 0, 1, 2, or 3;
• subscript a is the average number of (HRSiO) groups per molecule and is in a range of 1 to 50;
• subscript b is the average number of (R2SiO) groups per molecule and is in a range of 01 to 150;
• subscript a is 5% to 50% of the sum of subscripts a and b;
• (c) 60 to 92 weight-percent thermally conductive filler;
• (d) a platinum hydrosilylation catalyst;
• and
• (e) 0.05 to 2.0 weight-percent of a trialkoxy-functional polysiloxane;
• where the trialkoxy-functional polysiloxane has two or more trialkoxy functionalities per molecule and a number average molecular weight of 1200 or more and where weight-percents are relative to the composition weight;
• wherein the composition is a 2-part composition comprising distinct first and second parts;
• where:
• the first part comprises:
• (i) 7 to 35 weight-percent vinyl-functional polysiloxane;
• (ii) 60 to 92 weight-percent thermally conductive filler;
• (iii) 0.05 to 2.0 weight-percent trialkoxy-functional polysiloxane;
• (iv) one to 1000 weight parts per million weight parts of first part of a platinum hydrosilylation catalyst;
• and
• (v) 0.1 to 2.0 weight-percent of treating agents;
• and
• the second part comprises:
• (i) 10 to 15 weight-percent vinyl-functional polysiloxane;
• (ii) 2 to 5 weight-percent of a silyl hydride functional polysiloxane having on average at least two silyl hydride groups per molecule;
• (iii) 60 to 92 weight-percent thermally conductive filler;
• (iv) 0.025 to 2.0 weight-percent trialkoxy-functional polysiloxane;
• (v) 0 to 1 weight-percent pigment additive;
• and
• (vi) 0 to 0.01 weight-percent platinum cure inhibitor;
• where weight-percent values are relative to the weight of the part the component is in.