SELF-CROSS-LINKABLE GRAFT COPOLYMER WITH BLOCKED ISOCYANATE AND OTHERFUNCTIONALITIES - SYNTHESIS, REACTIVITY AND APPLICATION TO THERMOSET COATINGS

Novel self-crosslinkable graft copolymers with complementary reactive groups, that is, a pendant blocked isocyanate in the first segment and a hydroxyl group in the second segment, were developed. In order to i ncorporate isocyanate functionality, m-isopenyl-alpha,alpha-dimethyl b enzyl isocyanate (TMI) was copolymerized with n-butyl acrylate (nBA) b y radical polymerization in solution. Subsequently, a part of the isoc yanate was reacted with 2-hydroxyethyl acrylate (HEA) in order to inco rporate a polymerizable double bond into the copolymer molecule. After blocking the remaining isocyanate groups with methyl ethyl ketone (ME K) oxime, the polymerizable prepolymer was copolymerized with methacry lates, including hydroxyl monomers, to form the graft copolymer. Anoth er process of preparing the graft polymer was also carried out; TMI/nB A copolymer was reacted with MEK oxime to block about 70% of isocyanat e groups, then poly(ol)polymer such as poly(ester)resin was added. Aft er the grafting reaction was completed, remaining NCOs were blocked by MEK oxime. Furthermore, by incorporating neutralizable functionalitie s such as carboxyl or tertiary amino groups to the second segment of t he graft copolymer, self-dispersible (self-stabilized) aqueous coating vehicles were prepared. MEK oxime blocked tertiary isocyanate from TM I in the present graft polymers exhibits fairly lower deblocking tempe rature comparing to the similar products derived from IEM (isocyanatoe thyl methacrylate) or isophorone diisocyanate-hydroxyethyl acrylate (I PDI-HEA) adduct, and hence it is possible to produce coatings curable at a lower temperature (100-120-degrees-C) while retaining satisfactor y storage stability. Owing to this curability the coatings are applica ble to the,products made of plastics such as components of automotives etc. Possible application to waterborne coatings is also described.