| 摘要 |
PROBLEM TO BE SOLVED: To produce a biodegradable polyester which does not contain any low-molecular substance and is excellent in moldability by treating a polymer which contains lactic acid units as the smallest main structural units and is a copolymer and/or a blend with another polymer in a vacuum in a molten state. SOLUTION: A comonomer to be copolymerized with lactic acid is a polyhydric alcohol, a hydroxy carboxylic acid, an aliph. polyester, an arom. polyester, an aliph. polyamide, or a cyclic compd. (e.g.β-propiolactone) and may be copolymerized in block or at random., and at least one comonomer is used. A polymer to be blended is pref. a biodegradable plastic. The degree of vacuum is kept equal to or below the vapor pressure of the low-molecular substance, generally 100mmHg or lower. Vacuum is applied in the latter half of the polymn., pref. at a conversion of about 70-95%. The heating temp. is lower than the m.p. of and higher than the decomposition point of the polymer, generally 150-350 deg.C. The low-molecular substance removed is mainly unreacted lactide.
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