Ring-opening polymerisation mechanisms

D. J. Brunelle (Ed), Ring Opening Polymerisation Mechanisms, Catalysis, Structure, Utility, Hanser, Munich (1996)... 

Characteristic of these models of active sites is the appearance of the OZn O Zn(0)Et species. Considering the structural properties of the discussed catalysts as well as the polymer chain microstructure and the structure of the end groups of poly(propylene oxide) obtained with the PhOZnOCeHi ( -Bu)OZnEt catalyst, a concerted mechanism of epoxide ring-opening polymerisation with catalysts containing multinuclear species, including those with condensed zinc atoms, has been postulated [65,74] ... 

M. Morton and M. Wu in Ring-Opening Polymerisation Kinetics, Mechanisms and Synthesis, Ed., J.E. McGrath, ACS Symposium Series No.286, American Chemical Society, Washington, DC, USA, 1985, p.175. 

Figure 21.1 Possible mechanisms for anionic ring-opening polymerisations of non-substituted lactones showing both acyl-oxygen scission (a) as well as alkyl-oxygen scission (b).

Figure 21.3 Proposed mechanism for cationic ring-opening polymerisations initiated through alkylating agents. Adapted from [30].

The most widely applied catalyst systems in organocatalytic ROP include N-heterocyclic carbenes [62, 64, 67], guanidine and amidine bases [51,65] and phosphorane-based compounds [68,69]. Strong organic acids are excluded from this section as their mechanism follows the one described for cationic ring-opening polymerisations [70, 71]. 

Scheme 4.3 Proposed mechanism of cationic ring-opening polymerisation of six-membered cyclic carbonates.

Scheme 4.8 Proposed mechanism of lipase-catalysed ring-opening polymerisation of trimethylene carbonate.

Figure 1.5 Commonly accepted mechanism for the ring-opening polymerisation of hexachlorophosphazene...

Regardless of the methods used to synthesise lactic acid-based polymers, the monomers must be purified [34]. The ring-opening polymerisation of lactides can be initiated or catalysed by many compounds acting via different general mechanisms. Protic acids (hydrobromic acid (HBr), hydrochloric acid (HCl), triflic acid and so on). 

A mechanism was proposed for carbonate ring opening polymerisation (Scheme 12.6). The mechanism was based on the identification of propanediol, a dimer of trimethylene carbonate (DTMC) and a trimer of trimethylene carbonate (TTMC) in the reaction mixture, along with the presence of symmetrical hydroxyl end group structures in the low and high molecular weight TMC polymerisation products. 

Ring-opening polymerisation initiated by metal alkoxides according to the insertion-coordination mechanism. 

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