Relationship Between Molecular Structure of Nitrile Butadiene Rubber and Low-Temperature Properties

The nitrile butadiene rubbers （NBR） with different acrylonitrile （ACN）content and Mooney viscosity were studied， and the effects on glass transition temperature （Tg）， low-temperature shrink temperature（TR） and compressive cold resistance coefficient （CCRC） were reported. The results show that： the Tg of NBR is linearly proportioned to ACN content， （coefficient of determination R2=0.9711）， which is the dominated factor of Tg. On the other hand， the molecular sequence of Butadiene within NBR is affected by ACN content， resulting in the temperature range of glass transition （ΔTg） varying from 4.24 ℃ to 12.55 ℃ and the max loss tangent （tanδmax） of NBR rubber varying from 0.83 to 1.19， both of which displays linear relationship （R2= 0.9628）. In the TR experiment test， TR temperature with the same shrinking level for NBRs of different ACN content displays linearly relationship with Tg， with the linear relationship of initial temperature of TR （TRs） and Tg tested by DSC （Tg-DSC） （R2=0.9991）. Meanwhile， the result of TR and CCRC keeps highly consistency. MV is the secondary factor of NBR rubbers， higher MV results in lower TR and high CCRC. In the compound of NBR mixtures， NBR compounds with different ACN show properties of partly compatible mixtures. Within the range of 25%~75% for NBR mixtures with at least two NBRs， NBR with low ACN is beneficial to the low-temperature properties， but the NBR with high ACN dominates the final properties， the Tg of which shows well consistency with TRs and R2=0.9964. As a result， for the compounds with the same ACN content， one NBR with the homogenous ACN distribution in the molecules shows better low-temperature properties than the mixtures of NBR with different ACN mole fraction