Intra- and intermolecular chain transfer to macromolecules with chain scission. The case of cyclic esters

摘要

Chain transfer to macromolecules with chain scission is the most often observed "side" reaction in the polymerization of heterocyclics. In our previous works we analysed quantitatively the intramolecular chain transfer to the own macromolecule (back-biting). This paper gives a general treatment of the kinetics of polymerization with propagation and intermolecular chain transfer to macromolecules, accompanied with chain scission. The numerical solution developed allows determining the k(p)/k(tr) ratio from the dependence of (M) over bar(W)/(M) over bar(n) on monomer conversion. This treatment was applied to the polymerization of L,L-lactide and k(p)/k(tr) ratios were measured for covalent alcoholate active species bearing Al, Fe, Ti, Sm, and La. In this way selectivities of active species (expressed with k(p)/k(tr)) were for the first time measured and finally correlated with the atomic number of the corresponding metal atoms, related to the strength of the bond involved in the monomer addition. [References: 16]