The present invention relates generally to a polyvinyl alcohol composition having higher amorphous polyvinyl alcohol polymer content, a process for making such a polyvinyl alcohol composition, and various end uses thereof.

Provided is an interlayer film for laminated glass capable of effectively enhancing the sound insulating property at 6300 Hz while effectively preventing deterioration in sound insulating property at 3150 Hz in laminated glass. An interlayer film for laminated glass according to the present invention has a one-layer structure or a two or more-layer structure and includes a resin layer containing a resin and a plasticizer. The interlayer film has a resonance frequency X of 550 Hz or more and 740 Hz or less, a loss factor Y in a secondary mode of 0.35 or more, and satisfies a formula: Y>0.0008X−0.142 in a measurement of resonance frequency in a secondary mode in a damping test for laminated glass according to a central exciting method of laminated glass, when the laminated glass is obtained by arranging the interlayer film between two glass plates of 25 mm wide, 300 mm long and 2 mm thick.

Provided is an interlayer film for laminated glass capable of effectively enhancing the sound insulating property at 6300 Hz while effectively preventing deterioration in sound insulating property at 3150 Hz in laminated glass. An interlayer film for laminated glass according to the present invention has a one-layer structure or a two or more-layer structure and includes a resin layer containing a resin and a plasticizer. The interlayer film has a resonance frequency X of 550 Hz or more and 740 Hz or less, a loss factor Y in a secondary mode of 0.35 or more, and satisfies a formula: Y>0.0008X−0.142 in a measurement of resonance frequency in a secondary mode in a damping test for laminated glass according to a central exciting method of laminated glass, when the laminated glass is obtained by arranging the interlayer film between two glass plates of 25 mm wide, 300 mm long and 2 mm thick.

Provided is a method for producing a polyvinyl alcohol having improved mechanical strength without significantly impairing productivity. A method for producing a polyvinyl alcohol having an average degree of polymerization of 5.0×10.sup.3 or more and 1.5×10.sup.4 or less, the method including steps of: subjecting a vinyl ester-based monomer to suspension polymerization at a polymerization temperature of 10° C. or more and 50° C. or less with a polymerization rate of 10% or more and 70% or less to obtain a vinyl ester-based polymer; dissolving the vinyl ester-based polymer in an alcohol-based solvent; and carrying out a saponification reaction by adding a saponification catalyst to an alcohol-based solution of the dissolved vinyl ester-based polymer.

Provided is a method for producing a polyvinyl alcohol having improved mechanical strength without significantly impairing productivity. A method for producing a polyvinyl alcohol having an average degree of polymerization of 5.0×10.sup.3 or more and 1.5×10.sup.4 or less, the method including steps of: subjecting a vinyl ester-based monomer to suspension polymerization at a polymerization temperature of 10° C. or more and 50° C. or less with a polymerization rate of 10% or more and 70% or less to obtain a vinyl ester-based polymer; dissolving the vinyl ester-based polymer in an alcohol-based solvent; and carrying out a saponification reaction by adding a saponification catalyst to an alcohol-based solution of the dissolved vinyl ester-based polymer.

Provided is a dispersion assistant useful for suspension polymerization of vinyl-based compounds. The dispersion assistant comprises a polyvinyl alcohol-based polymer (A) comprising a constituent unit represented by the general formula (1) shown below at 0.1 to 10 mol % per polyvinyl alcohol monomer unit and having a saponification degree of 15 to 70 mol %. ##STR00001##
(In the formula, R denotes an alkyl group.)

Provided is a dispersion assistant useful for suspension polymerization of vinyl-based compounds. The dispersion assistant comprises a polyvinyl alcohol-based polymer (A) comprising a constituent unit represented by the general formula (1) shown below at 0.1 to 10 mol % per polyvinyl alcohol monomer unit and having a saponification degree of 15 to 70 mol %. ##STR00001##
(In the formula, R denotes an alkyl group.)

[Problem to be solved] To provide a traceable vinyl acetate, a polymer containing the vinyl acetate, and a vinyl alcohol polymer which is a saponified product of the polymer.

[Solution] Vinyl acetate having a ratio of carbon-14 to total carbon of 1.0×10.sup.−4 or more, a vinyl acetate polymer containing the vinyl acetate as a monomer unit and a vinyl alcohol polymer obtained by saponifying the vinyl acetate polymer.

Embodiments of the present disclosure describe a method of removing an end group from a polymer comprising contacting a polymer having a thiocarbonylthio end group, or a solution containing such a polymer, with an excess of a borane compound in the presence of oxygen. Embodiments of the present disclosure further describe a method of polymerization comprising contacting one or more monomers with an initiator and a chain transfer agent to form a polymer having a thiocarbonylthio end group in a reaction solution and contacting the polymer with a borane compound in the presence of oxygen to remove the thiocarbonylthio end group from the polymer.

Embodiments of the present disclosure describe a method of removing an end group from a polymer comprising contacting a polymer having a thiocarbonylthio end group, or a solution containing such a polymer, with an excess of a borane compound in the presence of oxygen. Embodiments of the present disclosure further describe a method of polymerization comprising contacting one or more monomers with an initiator and a chain transfer agent to form a polymer having a thiocarbonylthio end group in a reaction solution and contacting the polymer with a borane compound in the presence of oxygen to remove the thiocarbonylthio end group from the polymer.