Poly molar mass decrease ratio

Figure 4.9 Variation of molar mass decrease ratio of poly-L-lactide (PLLA), PLT95/5, PLTG terpolymers, and PLTG95/5/5C during in vitro degradation.

Bulk polymerization of POx at 90-150 "Cyields poly(POx) with molar masses limited to about 6000 gmol", which corresponds to the ratio of the apparent rate constant and the rate constant of chain transfer to monomer (fep/fetriu) of 100. In HMPA at 40 °C, this ratio is equal to 75. Indeed, several factors influence the extent of this chain transfer reaction temperature, initiator, and nature of the counterion. Chain transfer to monomer decreases in the order Na > K > Cs , in agreement with interactions between the metal cation and the oxygen of the monomer. 

Grafting of other living anionic polymers has also been reported and it was found that the maximum number of grafted chains depends on the nucleophiUdty of the terminal carbanion [51]. This behavior is not unexpected as the reactivity of the fuUerene decreases with each addition. For ejample, for the carbanions isoprenyl and 1,3-cyclohexadienyl, which have about the same reactivity as the carbanion styryl, a maximum of six polyisoprene (PI) or poly(l,3reaction with, respectively, polyisoprenyUith-ium (PILi) [51, 70] and poly 1,3-cyclohexadienyllithium [71] in a non-polar solvent Some other factors like steric effects or stability of the carbanion may interfere in this latter case, and a recent publication concluded that only four arms are attached, based on a ratio = 4.37 [72]. However, these molar masses were deter-... 

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