Chemical modification of polydienes, 2. Properties of polybutadiene and nitrile rubbers grafted with poly(tetrahydrofuran)

Thermal analysis by differential scanning calorimetry (DSC) indicated that graft copolymers of poly(tetrahydrofuran) (PTHF) on a nitrile rubber containing 39 wt.‐% acrylonitrile have a two‐phase morphology comprising crystalline PTHF and amorphous rubber. In rubbers with an 18 wt.‐% acrylonitrile content the PTHF is more compatible with the rubber and exerts a plasticising effect; crystallinity of the PTHF is not as well developed. cis‐1,4‐Polybutadiene and PTHF are partially miscible and in grafts on these two the melting endotherm of the latter was not detected. The relative values of the solubility parameters of PTHF and the three rubbers are consistent with this behaviour. All graft copolymers have a fairly low thermal stability and begin to decompose under N2 below 200°C. Degradation appears to be initiated at the PTHF grafts. Graft copolymers of PTHF with nitrile rubbers are less resistant to petroleum than the ungrafted rubbers.