Sealant composition

A one-part RTV condensation curable silicone composition comprising:

• (a) an organopolysiloxane polymer of the formula
• in which each X is independently an alkoxy group, each R is an alkyl, alkenyl or aryl group, each R1 is an X group, alkyl group, alkenyl group or aryl group and Z is a divalent organic group;
• n is 0 or 1, y is 0, 1 or 2, optionally 2, and z is an integer such that the said organopolysiloxane polymer has a viscosity of from 10,000 to 150,000 mPa·s at 25° C., in an amount of from 30 to 80 wt. % of the composition;
• (b) an alkoxylated MQ silicone resin, optionally in the presence of a polysiloxane carrier fluid, having a molar ratio of M units to Q units of from 0.1:1.0 to 1.0 to 1.0;
• wherein each Q type siloxane unit has the structure SiO4/2 and the M type siloxane units either have the structure R22R8SiO1/2— or are present in the form of a mixture of R22R8SiO1/2— and R23SiO1/2— groups;
• where each R2 group is an alkyl group having from 1 to 6 carbons;
• and R8 is an alkenyl group having from 2 to 6 carbons;
• or R8 is an X3-nRnSi—Z— group with X, R, Z and n are all as previously defined;
• wherein at least 50% of the R8 groups are silicon bonded X3-nRnSi—Z— groups;
• which component (b) is present in the composition in an amount of from 7.5 to 25 wt. %;
• (c) one or more cross-linkers in the form of a silicon containing compound having at least two, optionally at least three, hydrolysable groups per molecule;
• (d) one or more reinforcing fillers selected from precipitated silica, fumed silica or precipitated calcium carbonate, which reinforcing fillers may be hydrophobically treated;
• (e) one or more silicon-containing adhesion promoters;
• (f) one or more condensation curing catalysts selected from a catalyst comprising a titanate-based compound, a zirconate-based compound or a mixture thereof;
• and optionally
• (g) one or more non-reinforcing fillers, which non-reinforcing fillers may be hydrophobically treated.