End group initiation

R,R(x) total radical concentration which may be a function of x in the presence of end group initiation. 

End-group initiation first-order and disproportionation termination narrow distribution... 

Fig. 11. End-group initiation, initial most probable distribution [19]. The effect of chain transfer on (a) the relative rate of weight loss, (dAf( ldt)l(dMt ldt)0, against conversion, and on (b) the relative d.p., x/x°, against conversion. Curves are plotted atone value of the ratio of initial zip length to initial d.p., (1/7° )/x° = 0.01, for several values of the initial transfer parameter times initial d.p., O0x° = (k R/ke)x0.

Using multi-wavelength transmission spectroscopy together with labeled compounds additional quantitative information on the reaction can be readily obtained. For example, Figure 5 shows the analysis of end groups (initiation radicals) per molecule as a function of conversion, in a methyl-methacrylate polymerization reaction. The initiator used in this case is benzoyl peroxide, a strong chromophore in the ultraviolet portion of the spectrum. " ... 

Addition of L-lactide monomer to preformed active PCL chains gave 98% conversion of lactide monomer and formation of block copolymer. That is, the PCL end groups initiated the ring-opening polymerisation of L-lactide. It was also demonstrated that there was no transesterification reaction during the polymerisation the end groups of the propagating lactide chain did not attack the preformed PCL chain. 

The thermal instability of polycyanoacrylate is of particular importance both to the manufacturer and the consumer of cyanoacrylate adhesives. The degradation of cyanoacrylate oligomer has been described in general terms previously, as an important step in the production of cyanoacrylate monomer. Heating PECA above 150°C results in the steady production of cyanoacrylate monomer in high yield. This process is end group-initiated... 

Wang, Y., Chen, S., and Huang, J. (1999). Synthesis and characterization of a novel macroinitiator of poly(ethylene oxide) with a 4-hydroxy-2,2,6,6-tetramethylpiperidinyloxy end group initiation of the pol5merization of styrene by a living radical mechanism. Macromolecules, 32(8) 2480-2483. 

This reaction can be catalysed by both acids or bases. Also, the reaction product, RCOOH, is able to accelerate ester hydrolysis according to a phenomenon named autocatalysis. In the case of aliphatic polyesters, chain cleavage at ester bond level is autocatalysed by carboxyl end groups initially present or generated by the degradation reaction ... 

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