BLOCKED POLYURETHANE TOUGHENERS FOR EPOXY ADHESIVES

1 . A reaction product of:

a) a first reaction product of an isocyanate terminated prepolymer, and a capping compound having a di-functional aromatic moiety, wherein the first reaction product is terminated with the capping compound;

and

b) a diglycidyl bisphenol epoxy resin;

wherein the reaction product is suitable for use as a toughener in an epoxy adhesive composition.

2 . The reaction product of claim 1 , wherein component a) comprises a reaction product of a polyether diol and an isocyanate.

3 . The reaction product of claim 2 , wherein the polyether diol comprises a PTMEG-based polymer and/or a polybutadienediol-based polymer and the isocyanate comprises an aliphatic isocyanate.

4 . The reaction product of claim 2 , wherein the aliphatic isocyanate comprises HDI and/or IPDI.

5 . The reaction product of claim 1 , wherein the first reaction product comprises free hydroxy groups from the one or more capping compounds, and substantially all of the free hydroxy groups are reacted with the diglycidyl bisphenol epoxy resin.

6 . The reaction product of claim 1 , wherein the one or more capping compounds comprises at least one of o,o′-diallyl bisphenol A and bisphenol A.

7 . The reaction product of claim 1 , wherein the isocyanate terminated prepolymer comprises a polyurethane prepolymer.

8 . The reaction product of claim 1 , wherein the diglycidyl bisphenol epoxy resin comprises a liquid diglycidyl bisphenol A epoxy resin.

9 . The reaction product of claim 1 having Mn in the range of 3,000 to 12,000 Da.

10 . The reaction product of claim 1 having Mw in the range of 4,000 to 20,000 Da.

11 . A reaction product of:

a) an isocyanate terminated prepolymer;

b) a polyphenol or a dihydroxy functional benzene compound or a derivative thereof; and

c) a diglycidyl bisphenol epoxy resin;

wherein the reaction product is suitable for use as a toughener in an epoxy adhesive composition.

12 . The reaction product of claim 11 , wherein b) comprises a bisphenol or a derivative thereof.

13 . The reaction product of claim 11 , wherein b) comprises resorcinol and/or a substituted resorcinol.

14 . An adhesive composition comprising:

i) a diglycidyl ether bisphenol epoxy resin;

ii) a toughener comprising the reaction product of claim 1 ;

iii) a hardener; and

iv) a curing accelerator.

15 . The adhesive composition of claim 14 comprising:

i) 20 to 60 wt % of the diglycidyl ether bisphenol epoxy resin;

ii) 15 to 60 wt % of the toughener;

iii) 1 to 8% of the hardener; and

iv) 0.1 to 3 wt % of the curing accelerator;

wherein the weight percents are based on the weight of the composition.

16 . A cured adhesive obtained by curing the adhesive composition of claim 14 .

17 . A composition suitable for use as a toughener in an epoxy adhesive composition, the composition comprising an epoxy terminated polyurethane coupled via a polyphenolic blocking agent.