1 H NMR study of monomer sequence distributions in some commercial acrylonitrile‐butadiene copolymers

A ratio of acrylonitrile groups (A) and 1,2‐ and 1,4‐bonded butadiene (B) in SKN‐18, SKN‐26 and SKN‐40 nitrile rubbers has been determined by means of a 250 MHz NMR spectrometer. The amounts of the corresponding units in mol% were as follows: 20; 28; 39 for A and 12; 7‐9; 4‐3 for B 1.2 . Block‐bonded acrylonitrile has been detected only in SKN‐40 where the ratio of the triad sequences AAB and BAB is 3:97. Quantitative data on the BBB, BBA and ABA triads of 1,4‐butadiene have been obtained by using the signals of the double bond methine protons at 5‐20‐5‐67 ppm. A clearly outlined decreasing trend of the proportion of the B trans :B trans sequence with respect to both the B trans :B cis and B cis :B cis dyads in the order SKN‐18, SKN‐26 and SKN‐40 was found. It was suggested that the signals located in the ‐02‐5‐20ppm region relate to the AB 1.2 B and probably to the AB 1.2 A triad sequences.