The conformational origin of flexibility and stiffness in poly(olefin sulphones) demonstrated by means of dynamic C n.m.r. measurements

From previous calculations of electrostatic energies which cause third order Markov correlations of orientation of the dipoles in poly(olefin sulphones) ---(SO₂---C---C---)_nSO₂---, the lack of a strong interaction of one dipole with its immediate neighbour is predicted in the alternating copolymers prepared with symmetrical olefins. Using an approach developed by Bovey to detect stiffness in polysulphones in solution by means of C¹³ spin-lattice relaxation time measurements upon carbons in the main chain it is shown that poly(but-2-ene sulphone) and poly(cyclohexene sulphone) do have significantly shorter correlation times for motion of their backbones, and are thus more flexible than poly(but-1-ene sulphone). In the flexible polymers the C---C bonds are predominantly trans in conformation so that neighbouring sulphone groups are sufficiently well separated in space that each has thermal motions independently of the other. Stiffness in poly(1-olefin sulphones) is thus a consequence of their C---C bonds being predominantly in a gauche conformation, which permits the close approach of each pair of adjacent dipoles and the development of strong mutual ordering through the dipoles' electric fields.