Method for preparing polyorganosiloxanes

A method for preparing polyorganosiloxanes, comprising the followings steps:

• a) reacting together a hydroxyl-terminated polysiloxane of Formula I and a dialkoxysilane of Formula II or an oligomer thereof in the presence of Catalyst 1,
• where p is an arbitrary integer between 10 and 60,
• R1 is a methyl or ethyl group,
• R2 is a C6-C18 alkyl group,
• R3 is a C1-C18 alkyl group,
• q is an arbitrary integer between 1 and 8;
• b) reacting the product of Step a) by a chain scission reaction with an endcapper in the presence of Catalyst 2 to form the said polyorganosiloxane;
• wherein the endcapper has the structural formula as shown in Formula IV and/or V below:
• where t is an arbitrary integer between 0 and 20, and R4 is a C1-C6 alkyl group, and
• wherein the endcapper is used in an amount to provide 0.2-0.5 moles of vinyl groups per mole of silanol groups in the hydroxyl-terminated polysiloxane.