Macromol. zyxwvut Rapid zyxwvuts Commun. zyxwvuts 18,325-333 zyxwv (1997) zyxwv 325 Intermolecular chain transfer to polymer with chain scission: general treatment and determination of k,/kt, in L,L-lactidepolymerization Jolanta Baran, Andrzej Duda, Adam Kowalski, Ryszard Szymanski, Stanislaw Penczek" Polish Academy of Sciences, Center of Molecular and Macromolecular Studies, Department of Polymer Chemistry, Sienkiewicza 112,90-363 Lodz, Poland (Received: November 22, 1996; revised manuscript of January 2,1997) SUMMARY 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 consid- ered 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 zy ($) to the rate constant of the bimolecular transfer (kf)) from the dependence of the MWD on monomer conversion. Numerical values of k,/kf) equal to =lo2 and 25 were thus deter- mined for the polymerization of L,L-lactide (L,L-dilactide) initiated with aluminium tris(isopropoxide) trimer ({ Al(O'Pr),) zyxwv 3) and tributyltin ethoxide ("Bu$nOEt), respec- tively. Introduction We have recently described a method allowing the determination of the kJk$n) ratio (see Eq. (1)) from the kinetics of the intramolecular, unimolecular chain trans- fer (ba~k-biting)'-~). In order to correlate the structure of the active centers to the efficiency of transfer we have introduced a parameter j? = kplkh;'n, where kp is the rate constant of propagation and k$) the rate constant of the intramolecular trans- fe? (back-biting), leading to the formation of cyclic oligomers with a degree of polymerization equal to zyxwvut n (DP = n). For example, in the case of the polymerization of 8-caprolactone (ECL) we have: Mt = metal 0 --OMt + & where - O M t is ionic --O-Mt+ or covalent (polarized) -O&Mts+ species, zy kp and kd are the rate constants of propagation and depropagation, respectively; kun) is the oligomer with n repeating units; jy&!) is the rate constant of the corresponding back reaction, i. e. addition of this cyclic oligomer to the growing species. zyx (1) rate constant of the unimolecular intramolecular) transfer with formation o f a cyclic 0 1997, Hiithig & Wepf Verlag, Zug CCC 1022-1336/97/$02.50