Polyurethane sealant system

A polyurethane sealant system which when exposed to ambient moisture will cure rapidly to form a seal having high tensile strength comprising

• (A) a liquid polyurethane sealant consisting essentially of (1) a polyurethane polymer containing terminal isocyanate groups in an amount of not more than about 2.0 weight % based on the weight of said polyurethane, said terminal isocyanate groups being blocked to prevent further reaction by a volatile blocking agent, said polyurethane polymer being the reaction product of (i) a liquid poly(lower) alkylene ether polyol having a molecular weight of greater than about 6,000 and from three to five hydroxyl groups, (ii) a sterically unhindered diisocyanate;
• (2) a catalytic curing effective amount of (a) an organic bismuth compound selected from the group consisting of bismuth tri-(2-ethyl hexoate) and bismuth tri-neo-decanoate and (b) an organic tin compound of the formula:
• ##STR3## wherein each of R.sub.1 and R.sub.2 is alkyl of from 1 to 12 carbon atoms and each of R.sub.3 and R.sub.4 are lower alkyl;
• (3) up to 200 weight %, based on the weight of the polyol, of inert fillers;
• and (4) up to 50 weight %, based on the weight of the polyol, of polyurethane compatible plasticizers and
• (B) a silane based primer composition which is rapidly curable in the presence of ambient moisture and consisting essentially of (1) a silane compound having isocyanate reactive groups and (2) a catalytic effective amount of a silane hydrolysis catalyst.

A method for forming a high tensile strength seal on a glass substrate which comprises priming said glass substrate which is exposed to ambient moisture with

• (A) a silane based primer composition which is rapidly curable in the presence of ambient moisture and consisting essentially of (1) a silane compound having isocyanate reactive groups and (2) a catalytic effective amount of a silane hydrolysis catalyst and applying over said silane base primer
• (B) a liquid polyurethane sealant consisting essentially of (1) a polyurethane polymer containing terminal isocyanate groups in an amount of not more than about 2.0 weight % based on the weight of said polyurethane, said terminal isocyanate groups being blocked to prevent further reaction by a volatile blocking agent, said polyurethane being the reaction product of (i) a liquid poly(lower) alkylene ether polyol having three to five hydroxyl groups and a molecular weight of greater than about 6,000 and (ii) a sterically unhindered aromatic diisocyanate;
• (2) a cataytic curing effective amount of (a) an organic bismuth compound selected from the group consisting of bismuth tri-(2-ethyl hexoate) and bismuth tri-neo-decanoate and (b) an organic tin compound of the formula:
• ##STR4## wherein each of R.sub.1 and R.sub.2 is alkyl of from 1 to 12 carbon atoms and each of R.sub.3 and R.sub.4 is lower alkyl;
• (3) up to 200 weight %, based on the weight of the polyol of inert filler and (4) up to 50 weight %, based on the weight of the polyol, of polyurethane compatible plasticizers.