Intermolecular chain transfer to polymer with chain scission: General treatment and determination of k(p)/k(tr) in L,L-lactide polymerization

A general kinetic treatment of the system with intermolecular chain transfer followed by fast reinitiation is given. It leads to the broadening of the molecular weight distribution (MWD), the number of growing chains being invariable. Thus, this system can be considered as a special case of living polymerization. A general method has been elaborated allowing the determination of the ratio of the rate constant of propagation (k(p)) to the rate constant of the bimolecular transfer (k(tr)((2))) from the dependence of the MWD on monomer conversion. Numerical values of k(p)/k(tr)((2)) equal to approximate to 10(2) and 25 were thus determined for the polymerization of L,L-lactide (L,L-dilactide) initiated with aluminium tris(isopropoxide) trimer ({Al((OPr)-Pr-i)(3)}(3)) and tributyltin ethoxide ((Bu3SnOEt)-Bu-n), respectively.