Ethylene-vinyl alcohol copolymer and process for producing said ethylene-vinyl alcohol copolymer
The present invention provides an ethylene-vinyl alcohol copolymer which can be melt-molded at lower temperatures than conventional ethylene-vinyl alcohol copolymers to give molded objects that are inhibited from suffering undesirable coloration or having fish-eyes and that have excellent gas barrier properties. The ethylene-vinyl alcohol copolymer of the invention has a carboxylic acid ester group at a polymer terminal.
1. An ethylene-vinyl alcohol copolymer comprising:
a polymer terminal carboxylic acid ester group, and at least one polymer terminal carboxylic acid group, carboxylic acid salt group, or lactone ring group, wherein a content of the polymer terminal carboxylic acid ester group is 5-less than 20% by mole based on a total amount of polymer terminal carboxylic acid ester groups, carboxylic acid groups, carboxylic acid salt groups, and lactone ring groups;
wherein the carboxylic acid ester group does not include a cyclic ester group, and
the degree of saponification is 98% by mole or more;
wherein a content of the carboxylic acid ester group is 0.01-0.2% by mole based on a total amount of monomer units in the copolymer.
2. The ethylene-vinyl alcohol copolymer according to claim 1 , wherein the carboxylic acid ester group is a carboxylic acid alkyl ester group.
3. A process for producing an ethylene-vinyl alcohol copolymer, comprising:
copolymerizing ethylene and a vinyl ester monomer to obtain a copolymer and
performing a saponification reaction in a nonaqueous system using a saponification catalyst,
wherein performing the saponification reaction employs an alkali metal alkoxide as the saponification catalyst;
wherein performing the saponification reaction is conducted in the presence of an alcohol solvent containing no water;
and thereby obtaining an ethylene-vinyl alcohol copolymer comprising:
a carboxylic acid ester group at a polymer terminal; wherein
the carboxylic acid ester group does not include a cyclic ester group, and
the degree of saponification is 98% by mole or more.
4. An ethylene-vinyl alcohol copolymer comprising:
a polymer terminal carboxylic acid salt group, and at least one polymer terminal carboxylic acid group, carboxylic acid ester group, or lactone ring group, wherein a content of the polymer terminal carboxylic acid salt group is 5-20% by mole based on a total amount of polymer terminal carboxylic acid ester groups, carboxylic acid groups, carboxylic acid salt groups, and lactone ring groups;
wherein the carboxylic acid ester group does not include a cyclic ester group, and
the degree of saponification is 98% by mole or more;
wherein a content of the carboxylic acid ester group is 0.01-0.2% by mole based on a total amount of monomer units in the copolymer.