Abstract: Acido-basic properties of a system containing a polymer fragment obtained by oxidative cleavage of a carbon-carbon double bond of a diene rubber polymer and a functional molecule having in a structure thereof an alkoxysilyl group and at least one functional group selected from the group consisting of an aldehyde group and a carbonyl group are changed such that the system becomes basic when acidic, and becomes acidic when basic, thereby combining the polymer fragment with the functional molecule to form a modified diene rubber polymer having an alkoxysilyl group incorporated therein. A silane monomer comprising tetraalkoxysilane and/or alkyl trialkoxysilane is added to the system containing the modified diene rubber polymer, followed by condensation polymerization, thereby forming silica.

Abstract: Acido-basic properties of a system containing a polymer obtained by decomposing by oxidative cleavage of a carbon-carbon double bond, and a trifunctional molecule having an alkoxysilyl group in the structure as represented by the formula (A) are changed such that the system is changed into a basic system when the system is acidic and the system is changed into an acidic system when the system is basic to combine the decomposed polymer and the trifunctional molecule, thereby introducing the alkoxysilyl group into the main chain. Furthermore, acido-basic properties of a system containing a polymer obtained by decomposing by oxidative cleavage of a carbon-carbon double bond to decrease the molecular weight, and a functional molecule having an alkoxysilyl group as represented by the formula (a) are changed in the same manner as above to combine the decomposed polymer and the functional molecule, thereby introducing the alkoxysilyl group in a molecular terminal.

Abstract: A modified diene polymer is obtained by decomposing a diene polymer having a carbon-carbon double bond in a main chain by oxidative cleavage of the carbon-carbon double bond to reduce a molecular weight, changing acido-basic properties of a system containing polymer fragments obtained such that the system is changed into a basic system when the system is acidic and the system is changed into an acidic system when the system is basic to combine the polymer fragments, thereby obtaining an intermediate polymer having an altered structure, and epoxidizing a carbon-carbon double bond moiety of a main chain of the intermediate polymer.

Abstract: A polymer having a carbon-carbon double bond in a main chain is decomposed by subjecting the carbon-carbon double bond to oxidative cleavage using an oxidizing agent such as periodic acid to decrease the molecular weight, polymer chains of the decomposed polymer are combined by changing acido-basic properties such that a system containing the decomposed polymer becomes basic when acidic and becomes acidic when basic, and a modified polymer in which the structure has been changed is obtained. By this, a functional group can be incorporated in the main chain structure of a polymer. A rubber composition comprising a rubber component containing the modified polymer, and a filler compounded therewith, and a pneumatic tire comprising the rubber composition are provided.

Abstract: Acido-basic properties of a system containing a polymer fragment obtained by oxidative cleavage of a carbon-carbon double bond of a diene rubber polymer and a functional molecule having in a structure thereof an alkoxysilyl group and at least one functional group selected from the group consisting of an aldehyde group and a carbonyl group are changed such that the system becomes basic when acidic, and becomes acidic when basic, thereby combining the polymer fragment with the functional molecule to form a modified diene rubber polymer having an alkoxysilyl group incorporated therein. A silane monomer comprising tetraalkoxysilane and/or alkyl trialkoxysilane is added to the system containing the modified diene rubber polymer, followed by condensation polymerization, thereby forming silica.

Abstract: Acido-basic properties of a system containing a polymer obtained by decomposing by oxidative cleavage of a carbon-carbon double bond, and a trifunctional molecule having an alkoxysilyl group in the structure as represented by the formula (A) are changed such that the system is changed into a basic system when the system is acidic and the system is changed into an acidic system when the system is basic to combine the decomposed polymer and the trifunctional molecule, thereby introducing the alkoxysilyl group into the main chain. Furthermore, acido-basic properties of a system containing a polymer obtained by decomposing by oxidative cleavage of a carbon-carbon double bond to decrease the molecular weight, and a functional molecule having an alkoxysilyl group as represented by the formula (a) are changed in the same manner as above to combine the decomposed polymer and the functional molecule, thereby introducing the alkoxysilyl group in a molecular terminal.

Abstract: A modified diene polymer is obtained by decomposing a diene polymer having a carbon-carbon double bond in a main chain by oxidative cleavage of the carbon-carbon double bond to reduce a molecular weight, changing acido-basic properties of a system containing polymer fragments obtained such that the system is changed into a basic system when the system is acidic and the system is changed into an acidic system when the system is basic to combine the polymer fragments, thereby obtaining an intermediate polymer having an altered structure, and epoxidizing a carbon-carbon double bond moiety of a main chain of the intermediate polymer.

Abstract: A polymer having a carbon-carbon double bond in a main chain is decomposed by subjecting the carbon-carbon double bond to oxidative cleavage using an oxidizing agent such as periodic acid to decrease the molecular weight, polymer chains of the decomposed polymer are combined by changing acido-basic properties such that a system containing the decomposed polymer becomes basic when acidic and becomes acidic when basic, and a modified polymer in which the structure has been changed is obtained. By this, a functional group can be incorporated in the main chain structure of a polymer. A rubber composition comprising a rubber component containing the modified polymer, and a filler compounded therewith, and a pneumatic tire comprising the rubber composition are provided.