INTRAMOLECULAR AND INTERMOLECULAR CHAIN TRANSFER TO MACROMOLECULES WITH CHAIN SCISSION - THE CASE OF CYCLIC ESTERS

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 chai n transfer to the own macromolecule (back-biting). This paper gives a general treatment of the kinetics of polymerization with propagation a nd intermolecular chain transfer to macromolecules, accompanied with c hain 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 polymeriza tion of L,L-lactide and k(p)/k(tr) ratios were measured for covalent a lcoholate active species bearing Al, Fe, Ti, Sm, and La. In this way s electivities of active species (expressed with k(p)/k(tr)) were for th e first time measured and finally correlated with the atomic number of the corresponding metal atoms, related to the strength of the bond in volved in the monomer addition.