Branched polyester polymers and coatings comprising the same
A polyester prepared by free radical polymerization of an unsaturated polyester prepolymer, wherein the polymerization occurs primarily by reaction of the unsaturation is disclosed. Coatings comprising the same are also disclosed, as are substrates coated at least in part with such coatings.
1. A process for preparing an uncured polyester resin having a hard segment comprising:
(a) reacting an unsaturated polycarboxylic acid or anhydride or ester thereof with a polyol and with a monomer contributing a hard segment to form an unsaturated polyester prepolymer containing terminal hydroxyl groups,
(b) subjecting the unsaturated prepolymer to free radical polymerization via the unsaturation to form an ungelled, branched, crosslinkable polyester resin that has terminal hydroxyl groups and that has a weight average molecular weight greater than 15,000 and less than 10,000,000.
2. The process of claim 1 , wherein the free radical polymerization is carried out by adding a free radical initiator, the molar ratio of the initiator to degree of unsaturation is in a range from 0.001 to 1.0.
3. The process of claim 1 in which the polyester prepolymer comprises one or more polyester prepolymers.
4. The process of claim 3 in which the polyester prepolymer comprises a mixture of different polyester prepolymers.
5. The process of claim 1 , wherein the hard segment comprises an aromatic and/or cycloaliphatic polyacid.
6. The process of claim 5 , wherein the hard segment comprises isophthalic acid.
7. The process of claim 5 , wherein the hard segment further comprises benzoic acid.
8. The process of claim 1 , wherein the polyol comprises 2-methyl-1,3-propanediol and/or neopentyl glycol.
9. The process of claim 1 , wherein the unsaturated polycarboxylic acid or anhydride or ester thereof comprises maleic acid or anhydride or ester thereof.
10. The process of claim 1 , wherein the hard segment comprises isophthalic acid, the polyol segment comprises 2-methyl-1,3-propanediol and/or neopentyl glycol, and the unsaturated polycarboxylic acid or anhydride or ester thereof comprises maleic acid or anhydride or ester thereof.
11. The process of claim 1 , wherein the weight average molecular weight of the polyester resin is greater than 25,000.
12. The process of claim 1 , wherein the viscosity of the polyester resin is Z or less at 60% total solids as measured by the Gardner-Holt bubble method.
13. A coating composition comprising the polyester resin prepared in accordance with the process of claim 1 and a crosslinker.
14. The coating composition of claim 13 in which the crosslinker comprises a phenolic resin, an aminoplast an epoxy resin and/or a beta-hydroxy(alkyl)amide resin.
15. A process for the preparation of a branched, ungelled, crosslinkable polyester resin that has terminal hydroxyl groups comprising subjecting an unsaturated polyester prepolymer prepared from reacting an unsaturated polycarboxylic acid or anhydride or ester thereof and a monomer contributing a hard segment, to free radical polymerization via the unsaturation in the prepolymer to form branching of the polyester resin, the polyester resin having a weight average molecular weight greater than 15,000 and less than 10,000,000.
16. The process of claim 15 , wherein the free radical polymerization is carried out by adding a free radical initiator, the molar ratio of the initiator to degree of unsaturation is in a range from 0.001 to 1.0.
17. The process of claim 15 , wherein the free radical polymerization is carried out by adding a free radical initiator, the initiator added in portions at different times or in a continuous feed during the polymerization.
18. The process of claim 17 , wherein the viscosity of the polyester resin is Z or less at 60% total solids as measured by the Gardner-Holt bubble method.
19. The process of claim 1 , wherein the free radical polymerization is carried out by adding a free radical initiator, the initiator added in portions at different times or in a continuous feed during the polymerization.
20. The process of claim 1 , wherein the weight average molecular weight ratio of the polyester resin to the prepolymer is in a range from 1.2 to 500.
21. The process of claim 15 , wherein the weight average molecular weight ratio of the polyester resin to the prepolymer is in a range from 1.2 to 500.
22. The process of claim 1 , wherein the terminal hydroxyl groups are unreacted and provide functionality capable of reacting with a crosslinker for forming a coating.
23. The process of claim 15 , wherein the terminal hydroxyl groups are unreacted and provide functionality capable of reacting with a crosslinker for forming a coating.