Living anionic polymerization polydispersity index

The ratio M IMn approaches unity asymptotically as increases. Narrow molecular weight distributions should thus be obtained in living ionic polymerizations with fast initiation in the absence of depropagation, termination, and chain transfer reactions. Values of polydispersity index (PDI) below 1.1 -1.2 are indeed found for many living polymerizations. Molecular weight-standards for polystyrene, poly-isoprene, poly(a-methylstyrene), and poly (methyl methacrylate) are thus synthesized by living anionic polymerizations. However, the termination reactions in methyl methacrylate polymerizations and depropagation in or-methylstyrene polymerizations tend to broaden the PDI in these systems. 

The sample used in this study was a PS-PI prepared by living anionic polymerization with jec-butyllithium as an initiator and cyclohexane as a solvent. The number-averaged molecular weight, M determined by GPC (HLC-8020, THOSO, Co, Ltd.) is 4,4x1 O and the polydispersity index, is 1.02 with My, being the weight-... 

Consistently, Anderson and coworkers showed that the polymerization of MMA in THF at —78 °C is living when initiated by DPHLi (10), which is nothing but the model of the diphenylalkyl anion (9) of the PS macroinitiator used in the synthesis of PS-fcZock-PMMA (equation 21). It must be noted that DPHLi (10) results from the direct addition of DPE (8) to n-Buli (equation 22)". The molecular weight of PMMA is predetermined by the monomer-to-initiator molar ratio and the MMA conversion. The polydispersity index is low (1.04 < Mw/Mn < 1.16). The livingness of this polymerization was confirmed by the successful resumption of the polymerization of lauryl methacrylate (LMA), and formation of the parent PMMA-fc/ock-PLMA diblocks. The anionic polymerization of MMA in THF at —78°C is thus living , provided that sterically hindered initiators are used. 

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