Nitrile group-containing copolymer rubber

Abstract

A nitrile group-containing copolymer rubber including 10 to 60 wt % of an α,β-ethylenically unsaturated nitrile monomer unit and 1 to 60 wt % of an α,β-ethylenically unsaturated dicarboxylic acid monoester monomer unit, and having an iodine value of 120 or less, wherein a processability index Ipro (Ipro=CC×SA) is 0.0030 or less, where the processability index Ipro is the product of the carboxyl group content CC, which is the number of moles of carboxyl groups per 100 g of nitrile group-containing copolymer rubber, and the absorbance area SA of a carboxylic anhydride group determined by infrared spectroscopy.

1 . A nitrile group-containing copolymer rubber comprising 10 to 60 wt % of an α,β-ethylenically unsaturated nitrile monomer unit and 1 to 60 wt % of an α,β-ethylenically unsaturated dicarboxylic acid monoester monomer unit, and having an iodine value of 120 or less,
 wherein a processability index I pro  (I pro =C C ×S A ) is 0.0030 or less, where the processability index I pro  is the product of the carboxyl group content C C , which is the number of moles of carboxyl groups per 100 g of nitrile group-containing copolymer rubber, and the absorbance area S A  of a carboxylic anhydride group determined by infrared spectroscopy. 
 
     
     
         2 . The nitrile group-containing copolymer rubber according to  claim 1 , wherein a conjugated diene monomer unit is contained in an amount of 20 to 89 wt %. 
     
     
         3 . The nitrile group-containing copolymer rubber according to  claim 1 , wherein a content of the α,β-ethylenically unsaturated dicarboxylic acid monoester monomer unit is 1 to 10 wt %. 
     
     
         4 . The nitrile group-containing copolymer rubber according to  claim 1 , wherein the α,β-ethylenically unsaturated dicarboxylic acid monoester monomer unit is at least one selected from the group consisting of a mono-n-butyl maleate unit, a mono-n-butyl fumarate unit, and a monocyclohexyl fumarate unit. 
     
     
         5 . A cross-linkable rubber composition comprising the nitrile group-containing copolymer rubber according to  claim 1  and a cross-linking agent. 
     
     
         6 . The cross-linkable rubber composition according to  claim 5 , further comprising a basic cross-linking accelerator having a cyclic amidine structure. 
     
     
         7 . A cross-linked rubber prepared by cross-linking the cross-linkable rubber composition according to  claim 5 .