A conjugated diene-based polymer comprising a structural unit derived from a conjugated diene compound and having, at a terminal of the polymer, at least one nitrogen-containing group represented by formula (1) is used. In formula (1), R.sup.1 is a hydrocarbyl group, and the symbol * is a bonding site.

##STR00001##

Provided are modified plant fibers suitable for addition to rubber; an additive for rubber comprising the modified plant fibers which can be micronized and dispersed easily and highly when adding to rubber; a method of preparing the additive for rubber; and a rubber composition comprising the additive for rubber. Modified plant fibers (A) in which plant fibers (a) and a modified synthetic rubber (B) are covalently bonded wherein the ratio of the modified synthetic rubber (B) relative to 100 parts by weight of the plant fibers (a) is 5 to 100 parts by weight. An additive for rubber comprising 20 to 75 weight % of the modified plant fibers (A) according to claim 1 and 25 to 80 weight % of a processing agent for rubber (C), wherein the number average molecular weight of the processing agent for rubber (C) is 400 to 60,000, and the glass transition point of the processing agent for rubber (C) is 100 C. or less, and wherein the additive for rubber includes plant fibers in the ratio of 10 to 65 weight %.

Cold flow-reduced polymers having good processing characteristics have, at the ends of the polymer chains, a silane-containing carboxyl group of the formula (I) ##STR00001##
where R.sup.1 and R.sup.2 are the same or different and are each an H, alkyl, alkoxy, cycloalkyl, cycloalkoxy, aryl, aryloxy, alkaryl, alkaryloxy, aralkyl or aralkoxy; R.sup.3 and R.sup.4 are the same or different and are each an H, alkyl, cycloalkyl, aryl, alkaryl or aralkyl radical; A is a divalent organic radical.

Cold flow-reduced polymers having good processing characteristics have, at the ends of the polymer chains, a silane-containing carboxyl group of the formula (I) ##STR00001##
where R.sup.1 and R.sup.2 are the same or different and are each an H, alkyl, alkoxy, cycloalkyl, cycloalkoxy, aryl, aryloxy, alkaryl, alkaryloxy, aralkyl or aralkoxy; R.sup.3 and R.sup.4 are the same or different and are each an H, alkyl, cycloalkyl, aryl, alkaryl or aralkyl radical; A is a divalent organic radical.

Process for functionalizing a polymer by treating said polymer at a temperature in the range 80-250 C. with a monoazide of the formula wherein m is 0 or 1, n is 0 or 1, n+m=1 or 2, X is a linear or branched, aliphatic or aromatic hydrocarbon moiety with 1-12 carbon atoms, optionally containing heteroatoms, R.sub.b is selected from the group consisting of hydrogen, linear and branched alkyl groups with 1-6 carbon atoms optionally substituted with O, S, P, Si, or N-containing functional groups, alkoxy groups with 1-6 carbon atoms, and halogens, and each R.sub.a is individually selected from hydrogen, linear or branched alkyl groups with 1-6 carbon atoms, or may form a saturated or unsaturated aliphatic or aromatic ring structure with at least one other R.sub.a.

##STR00001##

Process for functionalizing a polymer by treating said polymer at a temperature in the range 80-250 C. with a monoazide of the formula wherein m is 0 or 1, n is 0 or 1, n+m=1 or 2, X is a linear or branched, aliphatic or aromatic hydrocarbon moiety with 1-12 carbon atoms, optionally containing heteroatoms, R.sub.b is selected from the group consisting of hydrogen, linear and branched alkyl groups with 1-6 carbon atoms optionally substituted with O, S, P, Si, or N-containing functional groups, alkoxy groups with 1-6 carbon atoms, and halogens, and each R.sub.a is individually selected from hydrogen, linear or branched alkyl groups with 1-6 carbon atoms, or may form a saturated or unsaturated aliphatic or aromatic ring structure with at least one other R.sub.a.

##STR00001##

Polymers are functionalized at chain ends thereof with silane-containing carboxyl groups of the formula (I) ##STR00001##
where R.sup.1 and R.sup.2 are the same or different and are each an H, alkyl, alkoxy, cycloalkyl, cycloalkoxy, aryl, aryloxy, alkaryl, alkaryloxy, aralkyl or aralkoxy radical; R.sup.3 and R.sup.4 are the same or different and are each an H, alkyl, cycloalkyl, aryl, alkaryl or aralkyl radical; and A is a divalent organic radical.

Polymers are functionalized at chain ends thereof with silane-containing carboxyl groups of the formula (I) ##STR00001##
where R.sup.1 and R.sup.2 are the same or different and are each an H, alkyl, alkoxy, cycloalkyl, cycloalkoxy, aryl, aryloxy, alkaryl, alkaryloxy, aralkyl or aralkoxy radical; R.sup.3 and R.sup.4 are the same or different and are each an H, alkyl, cycloalkyl, aryl, alkaryl or aralkyl radical; and A is a divalent organic radical.

Preparing a microbially desulfurized crumb rubber includes combining microorganisms capable of breaking crosslinked sulfur bonds, sulfur-containing crumb rubber, and a salt solution to yield a mixture; combining a buffer with the mixture to yield a buffered mixture, thereby adjusting a pH of the mixture; providing oxygen to the buffered mixture; incubating the buffered mixture for a length of time to yield a microbially desulfurized mixture; combining the microbially desulfurized mixture with bitumen to yield a precursor; and heating the precursor to yield the microbially desulfurized crumb rubber. The microbially desulfurized crumb rubber can be combined with bitumen to yield a modified bitumen. The modified bitumen can be combined with asphalt to yield a modified asphalt.

Preparing a microbially desulfurized crumb rubber includes combining microorganisms capable of breaking crosslinked sulfur bonds, sulfur-containing crumb rubber, and a salt solution to yield a mixture; combining a buffer with the mixture to yield a buffered mixture, thereby adjusting a pH of the mixture; providing oxygen to the buffered mixture; incubating the buffered mixture for a length of time to yield a microbially desulfurized mixture; combining the microbially desulfurized mixture with bitumen to yield a precursor; and heating the precursor to yield the microbially desulfurized crumb rubber. The microbially desulfurized crumb rubber can be combined with bitumen to yield a modified bitumen. The modified bitumen can be combined with asphalt to yield a modified asphalt.