Polymerization trithiocarbonates xanthates

Substantial effort has been directed toward the control of vinyl acetate (VAc) radical polymerization using living radical polymerization (LRP) methods, including atom transfer radical polymerization, degenerative transfer through alkyl iodide,dialkyl tellurium, trithiocarbonate, xanthate, and cobalt acetylacetonate The focus of... 

Living radical polymerization using thiocarbonylthio RAFT agents (including dithioesters, trithiocarbonates and xanthates) was first described in a patent published in 1998.40S The first paper describing the process also appeared in 1998.1R Other patents and papers soon followed. Papers on this method, along with NMP and ATRP, now dominate the literature on radical polymerization. 

Living polymerization is another rapidly developing area where the degenerative transfer of xanthates and related derivatives (e.g. dithioesters, dithiocarbamates, trithiocarbonates) is having a significant impact [38] (see also Volume 1, Chapter... 

Multifunctional dithioesters, trithiocarbonates, or xanthates can be used to generate arm-first star polymers by reversible addition fragmentation chain transfer (RAFT) polymerization, via the so-called Z-group approach (XXV to XXVII) [42]. 

A whole variety of thiocarbonylthio compoimds have been S5mthesized and used in RAFT polymerization. The initial work was focused to some extent on the use of dithioesters. More recently the range of RAFT agents is expanded to trithiocarbonates, dithiocarbamates, and xanthates. 

Both RAFT and NMP controlled/living techniques are suitable for the direct poljunerization of acrylic acid. The RAFT polymerization of AA has been reported in DMF (24,105), various alcohols (106,107), water (108), and dioxane (109) em-plojdng a variety of RAFT CTAs including dithioesters, xanthates, dithiocarba-mates and trithiocarbonates. AA is also susceptible to controlled polymerization by NMP (110,111). 

A RAFT polymerization system consists of an initiator, monomer, solvent and a chain transfer agent, defined as RAFT agent, which mediates the polymerization via a reversible chain transfer process. RAFT agents are thiocarbonylthio compounds, including dithioesters, dithiocarbamates, trithiocarbonates and xanthates, and characterized by the presence of two different functionalities a Z group, which affects the stability of the C=S bond and controls the effectiveness radicals addition to the growing chain, and a R group, able to initiate new polymeric chains (Fig. 1.10). 

Good control over the polymerization of LAMs requires use of a less active RAFT agent such as a dithiocarbamate (Z = NR 2) or a xanthates (Z=OR ) with R = alkyl or aryl. The more active RAFT agents Z = R (dithioesters) or SR (trithiocarbonates) strongly retard or inhibit polymerization of LAMs. The choice of the R group is also critical. Inhibition periods due to slow reinitiation are expected for RAFT agents such as 37 (R = 2-cyano-2-propyl) and 38 (R = benzyl). 

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