Method for making polymers of alpha-hydroxy acids
First Claim
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1. A method for preparing polymers of alpha-hydroxy acids by catalyzed ring opening of cyclic diesters selected from the group consisting of lactide, glycolide and mixtures thereof and comprising up to 20 weight percent of a monomer selected from the group consisting of ##STR2## where n is 4 or 5, h, i, k and m are independently 1 or 2, each R is independently selected from hydrogen or hydrocarbyl containing up to 12 carbon atoms comprising the steps of:
- a. forming a liquid phase dispersion of the cyclic diesters, monomer and ring-opening catalyst selected from the group consisting of tin compounds, yttrium compounds, compounds of lanthanum series rare earth metals having atomic numbers 57-71, titanates, zirconates, zinc compounds, antimony compounds and mixtures thereof, wherein the mole ratio of monomer to catalyst is 500-20,000;
1 and the mole ratio of organic acid to catalyst is less than 6;
1; and
b. maintaining (1) the temperature of the dispersion at 50-250 C., (2) the mole ratio of cyclic ester to catalyst at 500-20,000;
1 and (3) the mole ratio of organic acid to catalyst in the dispersion below 6;
1 to effect polymerization of the monomers to a conversion of at least 95% at a high rate.
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Abstract
A method providing a catalyzed ring opening polyester polymerization at a high reaction rate wherein the amount of organic acid in the reaction medium is maintained at an acid: catalyst ratio below 6:1.
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8 Claims
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1. A method for preparing polymers of alpha-hydroxy acids by catalyzed ring opening of cyclic diesters selected from the group consisting of lactide, glycolide and mixtures thereof and comprising up to 20 weight percent of a monomer selected from the group consisting of ##STR2## where n is 4 or 5, h, i, k and m are independently 1 or 2, each R is independently selected from hydrogen or hydrocarbyl containing up to 12 carbon atoms comprising the steps of:
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a. forming a liquid phase dispersion of the cyclic diesters, monomer and ring-opening catalyst selected from the group consisting of tin compounds, yttrium compounds, compounds of lanthanum series rare earth metals having atomic numbers 57-71, titanates, zirconates, zinc compounds, antimony compounds and mixtures thereof, wherein the mole ratio of monomer to catalyst is 500-20,000;
1 and the mole ratio of organic acid to catalyst is less than 6;
1; andb. maintaining (1) the temperature of the dispersion at 50-250 C., (2) the mole ratio of cyclic ester to catalyst at 500-20,000;
1 and (3) the mole ratio of organic acid to catalyst in the dispersion below 6;
1 to effect polymerization of the monomers to a conversion of at least 95% at a high rate. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8)
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Specification