Dichlorocarbene Modified Natural Rubber

Natural rubber dissolved in chloroform was reacted with aqueous NaOH using a phase transfer reagent or with solid NaOH to produce dichlorocarbene modified natural rubber. The 13C n.m.r. spectrum of the 100% modified natural rubber showed the presence of diastereoisomers due to two modes of addition of dichlorocarbene units as previously observed in epoxidation. There was no evidence of cis‐trans iso‐merisation, occurrence of other side reactions or of chain scission (shown by measurements of intrinsic viscosity). Partially dichlorocarbene modified natural rubber gave rise to a complex 13C n.m.r. spectrum that was assigned in terms of triad structures (for methylene carbon atoms)and pentad structures (for olefinic carbon atoms). Using 13C n.m.r. and measurements of glass transition temperature, it was found that reaction with aqueous NaOH and with solid NaOH both gave a random distribution of dichlorocarbene units, as compared with a block copolymer structure observed by previous workers with dichlorocarbene modified polybutadiene. The thermal stability of natural rubber is intermediate between that of the more stable 100% dichlorocarbene modified rubber and the less stable partially modified rubber.