Thiocarbonylthio Compounds (SC(Z)S−R) in Free Radical Polymerization with Reversible Addition-Fragmentation Chain Transfer (RAFT Polymerization). Effect of the Activating Group Z

Abstract

Free-radical polymerization in the presence of suitable addition-fragmentation chain transfer agents [SdC(Z)S-R] (RAFT agents) possess the characteristics of a living polymerization (i.e., polymer products can be reactivated for chain extension and/or block synthesis, molecular weights are predetermined by RAFT agent concentration and conversion, narrow polydispersities are possible). Styrene polymerizations (110 °C, thermal initiation) were performed for two series of RAFT agents [SdC(Z)S-CH 2Ph and SdC(Z)S-C(Me)2CN]. The chain transfer coefficients decrease in the series where Z is Ph. N(alkyl)2 (only the first five in this series provide narrow polydispersity polystyrene (< 1.2) in batch polymerization). More generally, chain transfer coefficients decrease in the series dithiobenzoates > trithiocarbonates ∼ dithioalkanoates > dithiocarbonates (xanthates) > dithiocarbamates. However, electron-withdrawing substituents on Z can enhance the activity of RAFT agents to modify the above order. Thus, substituents that render the oxygen or nitrogen lone pair less available for delocalization with the CdS can substantially enhance the effectiveness of xanthates or dithiocarbamates, respectively. The trend in relative effectiveness of the RAFT agents is rationalized in terms of interaction of Z with the CdS double bond to activate or deactivate that group toward free radical addition. Molecular orbital calculations and the estimated LUMO energies of the RAFT agents can be used in a qualitative manner to predict the effect of the Z substituent on the activity of RAFT agents.

Chain Transfer in Degenerative RAFT Polymerization Revisited: A Comparative Study of Literature Methods

“…In contrast, the value of C −tr,0 has a pronounced infl uence on the accuracy at which C tr,0 can be determined, as discussed further. It is clear from Table 4 that the accuracy of the method of Moad and co-workers [26][27][28] (Equation ( 8) 3,5,6). This is in line with expectations as the contribution of R 0 species reacting with macro-RAFT CTA will decrease accordingly and, hence, the underlying assumption for the derivation of Equation ( 8) will be more closely met.…”

“…[ 6,[10][11][12] Specifi cally for the RAFT polymerization process, Moad and co-workers developed an experimental method to directly determine C tr,0 based on the measured decay of the R 0 X concentration. [26][27][28] Assuming the PSSA for the concentration of the macroradicals and R 0 species they reported that…”

“…As explained above, other methods to determine C tr,0 for the RAFT exchange reactions with R 0 X were developed by Moad and co-workers [26][27][28] (Equation ( 8) and Barner-Kowollik and co-workers [ 15,29 ] (Equation ( 9) . The former method relies on the assumption that the reaction of R 0 species with macro-RAFT CTA can be neglected ( C −tr,0 ), while the latter method can only be applied to monomer/RAFT CTA combinations that display a strong hybrid behavior.…”

“…Equation ( 7) can be used to estimate both C tr,0 and C −tr,0 . Moreover, if reverse degenerative transfer ( C −tr,0 ) becomes negligible compared to transfer with R 0 X ( C tr,0 ), it enables the direct evaluation of C tr,0 from the slope of a plot of ln([R 0 X]) versus ln([M]) [26][27][28] ) ) ( (…”

Tin(IV) oxide nanoparticles grafted with N,N-dimethylacrylamide–allyl butyl ether for xylene adsorption

“…Radical polymerization has significant advantages over ionic and coordination polymerization. The reaction conditions are usually less demanding and exhibit tolerance of trace impurities, and it is possible to polymerize a variety of monomers (Chiefari et al 2003).…”