"Living" chain association during the lithium-initiated polymerization: Dependence on the chain length and effect on the process kinetics

The degree of the "living" chain association and the association-dissociati on equilibrium constants : were studied as functions of the propagating cha in length during the lithium- initiated polymerization. The number of possi ble conformations of a starlike molecule was calculated for various numbers and lengths of star arms using the model of chains without self- intersect ions on a cubic lattice. It is established that the probability of existenc e of these chain conformations drops according to the power law with increa sing chain length, the drop rate growing with the number of star arms. For the polymerization degrees below 1000, a change in the degree of associatio n (dimer or trimer) with increasing chain length is low probable and has no significant effect upon the polymerization kinetics. The ratio between cyc lic and acyclic associates of bifunctional macromolecules was studied as de pendent on their length, with an allowance for the probability of cyclizati on, It is demonstrated that the fraction of cyclic forms must rapidly decre ase according to a power law with increasing chain length. The fractions of the main types of bifunctional chain associates were calculated as functio ns of chain length were calculated taking into account the dimer and tetram er association equilibrium constants for poly(butadienyldilithium) macromol ecules.