Medium or high molecular weight polyester powders, powder coating compositions, and processes of making powders
A process of providing a medium or high molecular weight polyester powder, the resultant polyester polymer powder, and a powder coating composition that includes such powder; wherein the process includes: providing or forming an ester oligomer; converting the oligomer to a polyester polymer by stirring at elevated pressure and elevated temperature a reaction mixture that includes the oligomer and a nonreactive carrier capable of forming an azeotrope with water and xylenes; removing water from the reaction mixture via azeotropic reflux to provide a syrup including a medium or high molecular weight polyester polymer in the nonreactive carrier; and applying a vacuum to remove the xylenes from the syrup and form a solid (which may be in the form of a powder or subsequently formed into a powder) that includes the medium or high molecular weight polyester polymer.
1. A process for preparing a polyester polymer powder comprising a medium molecular weight polyester polymer having a number average molecular weight of 4,000 amu to 7,000 amu or a high molecular weight polyester polymer having a number average molecular weight greater than 7,000 amu, which process comprises:
a) providing or forming an ester oligomer that has a greater acid number than hydroxyl number;
b) converting the oligomer to the polyester polymer by stirring at an elevated temperature a reaction mixture comprising the oligomer and a nonreactive carrier comprising an aromatic hydrocarbon, wherein the elevated temperature is at least 200° C.;
c) removing water from the reaction mixture via azeotropic reflux to provide a syrup comprising a medium or high molecular weight polyester polymer in the nonreactive carrier; and
d) applying a vacuum to form a solid in the form of a powder comprising the medium or high molecular weight polyester polymer;
wherein the polyester polymer has an acid number of at least 17 and up to 26.
2. The process of claim 1 wherein the polyester polymer has a backbone free of or substantially free of ethylene oxide or propylene oxide groups and the syrup is free of or substantially free of alcohols, glycols, or esters that react at polycondensation temperatures with the polyester polymer.
3. The process of claim 1 wherein the polyester polymer is a medium molecular weight polymer having a number average molecular weight of 4,000 to 7,000 amu.
4. The process of claim 1 wherein the polyester polymer is a high molecular weight polymer having a number average molecular weight of more than 7,000 amu.
5. The process of claim 1 wherein the polymer has an acid number of 20 to 26.
6. The process of claim 1 wherein the nonreactive carrier comprises a mixture of solvents.
7. The process of claim 1 wherein converting the oligomer to a polyester polymer comprises stirring at a gauge pressure of at least 34 KPa and up to 500 KPa.
8. The process of claim 1 further comprising a step of allowing the pressure to rise to 100 kPa after converting the oligomer to a polyester polymer.
9. The process of claim 1 wherein providing or forming an ester oligomer comprises forming an ester oligomer in an esterification step.
10. The process of claim 9 wherein the ester oligomer is formed from at least one glycol having a boiling point greater than 196° C.
11. The process of claim 9 wherein forming an ester oligomer in an esterification step comprises providing an esterification reaction mixture having a hydroxyl:acid or hydroxyl:ester ratio of at least 0.5:1 and up to 2:1.
12. The process of claim 1 wherein the polyester polymer comprises hydroxyl functionality, carboxylic acid functionality, or a combination thereof.
13. The process of claim 1 wherein converting the oligomer to a polyester polymer comprises stirring at elevated pressure.
14. The process of claim 1 wherein converting the oligomer to a polyester polymer comprises stirring at atmospheric pressure.
15. The process of claim 1 wherein the polymer has a glass transition temperature (Tg) of greater than 20° C. and up to 70° C.
16. A process for preparing a polyester polymer powder comprising a medium molecular weight polyester polymer having a number average molecular weight of 4,000 amu to 7,000 amu or a high molecular weight polyester polymer having a number average molecular weight greater than 7,000 amu, which process comprises:
a) providing or forming an ester oligomer;
b) converting the oligomer to the polyester polymer by stirring at an elevated temperature a reaction mixture comprising the oligomer and a nonreactive carrier comprising an aromatic hydrocarbon, wherein the elevated temperature is at least 200° C.;
c) removing water from the reaction mixture via azeotropic reflux to provide a syrup comprising a medium or high molecular weight polyester polymer in the nonreactive carrier; and
d) applying a vacuum to form a solid in the form of a powder comprising the medium or high molecular weight polyester polymer;
wherein the polymer has a hydroxyl number of 1 to 3 and an acid number of 20 to 26.
17. The process of claim 16 wherein the polymer has a glass transition temperature (Tg) of greater than 20° C. and up to 70° C.
18. A process for preparing a polyester polymer powder comprising a medium molecular weight polyester polymer having a number average molecular weight of 4,000 amu to 7,000 amu or a high molecular weight polyester polymer having a number average molecular weight greater than 7,000 amu, which process comprises:
a) providing or forming an ester oligomer that has a greater acid number than hydroxyl number;
b) converting the oligomer to the polyester polymer by stirring at an elevated temperature a reaction mixture comprising the oligomer and xylene, wherein the elevated temperature is at least 200° C.;
c) removing water from the reaction mixture via azeotropic reflux to provide a syrup comprising a medium or high molecular weight polyester polymer in xylene; and
d) applying a vacuum to form a solid in the form of a powder comprising the medium or high molecular weight polyester polymer;
wherein the polyester polymer has an acid number of at least 17 and up to 26.