Abstract: A process for the production of biodegradable aliphatic polyester particles by (co)polymerizing 2-oxetanone or a mixture containing at least 80% by weight of 2-oxetanone and up to 20% by weight of a cyclic ester or cyclic ether other than 2-oxetanone in the presence of a polymerization initiator supported on a carrier in which an ion polymerization initiator is supported on poly(2-oxetanone) in a liquid medium having a solubility parameter of about 15 to about 18 MPa.sup.1/2 and being capable of dissolving 2-oxetanone, and in a polymerizing apparatus having an internal surface formed of a material which is free of polarity or whose polarity is very small, to form a particulate aliphatic polyester; and a biodegradable aliphatic polyester melt-extrusion film, which comprises the biodegradable aliphatic polyester having a weight average molecular weight of 20,000 to 2,000,000, and having a water vapor transmission rate of 300 to 700 g/m.sup.2 .multidot.24 hours.multidot.25 .mu.

Abstract: A process for the production of biodegradable aliphatic polyester particles by (co)polymerizing 2-oxetanone or a mixture containing at least 80% by weight of 2-oxetanone and up to 20% by weight of a cyclic ester or cyclic ether other than 2-oxetanone in the presence of a polymerization initiator supported on a carrier in which an ion polymerization initiator is supported on poly(2-oxetanone) in a liquid medium having a solubility parameter of about 15 to about 18 MPa.sup.1/2 and being capable of dissolving 2-oxetanone, and in a polymerizing apparatus having an internal surface formed of a material which is free of polarity or whose polarity is very small, to form a particulate aliphatic polyester; and a biodegradable aliphatic polyester melt-extrusion film, which comprises the biodegradable aliphatic polyester having a weight average molecular weight of 20,000 to 2,000,000, and having a water vapor transmission rate of 300 to 700 g/m.sup.2 .multidot.24 hours.multidot.25 .mu.

Abstract: A resin composition which comprises 95 to 60 volume % of a resin mixture of 40 to 85% by weight of a copolymer between D-hydroxybutyrate and D-hydroxyvalerate containing 8 to 15 mol % of D-hydroxyvalerate-derived monomer unit and 60 to 15% by weight of poly-.epsilon.-caprolactone, and 5 to 40 volume % of an inorganic filler or fillers, a porous film produced from the resin composition and having a void volume of 10 to 70%, and a process for producing the porous film are disclosed. The film can be produced by melting the resin composition, forming it into a film, and stretching the film in at least one direction. The porous film can easily be degraded by microorganisms. Examples of the inorganic filler include barium sulfate, with the particle size being preferably 0.1 to 10.0 .mu.m.