Backbiting-fragmentation

The high temperature polymerization of acrylates with the backbiting-fragmentation process has been used to synthesize macromonomers based on acrylate esters. 277,312 Interestingly, fragmentation shows a strong preference for giving the polymeric macromonomer 64 and a small radical 65. 276.277 An explanation for this specificity has yet to be proposed. 

The high-temperature polymerization of acrylates with the backbiting-fragmentation process has been used to synthesize maaomonomers based on acrylate esters. " " " ... 

Copolymerization of macromonomers formed by backbiting and fragmentation is a second mechanism for long chain branch formation during acrylate polymerization (Section 4.4.3.3). The extents of long and short chain branching in acrylate polymers in emulsion polymerization as a function of conditions have been quantified.20 ... 

Recent work has shown that backbiting is prevalent in polymerizations and copolymerizations of acrylate esters.It is also observed in styrene polymerization at high temperature and probably occurs to some extent during polymerizations of most monosuhstituted monomers. At high temperatures, and at low temperatures in very dilute solution, backbiting may be followed by fragmentation (Scheme 4 lower temperatures short chain... 

Keywords backbiting chain length dependent termination (CLDT) kinetics reversible addition fragmentation chain transfer (RAFT) simulations... 

Transfer may be intramolecular ( backbiting ) giving small fragments such as dimer, trimer, etc, or intermolecular, producing a macroradical in which the radical centre is not at the chain end this undergoes scission, so that intermolecular transfer leads to a rapid drop in the molecular weight (MW) of the polymer. 

Only the former of the macroradicals (A) and (B) is believed to lead directly to production of volatile products (Scheme 15). Monomer production involves depropagation of radical (A) by reaction (a) in Scheme 15, whilst backbiting intramolecular transfer (reactions b, c) account for the dimer, etc. Fragments such as the trimer, etc. can be formed in the same way by H abstraction at subsequent tertiary H sites along the chain. 

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