Ring-opening polymerization base-initiated mechanism

Acheson process, 566 Acid-initiated ring-opening polymerization comparison widi base-initiated process, 79 kinetics, 79-80 mechanism, 79-81 rate retardation by water, 81 relative reactivities of cyclosiloxanes, 79 step-growth process, 79 Acyclic oligosilanes, photochemical transformations, 432/-433/ Acylsilanes... 

The subsequent mechanism of the base-catalyzed polymerization of caprolactam is complicated. Ring opening of the initiated monomer does not occur. Since the lactam anion is stabilized by resonance, viz.,... 

It was also shown that functional zinc alkoxides are also effective initiators for the ring-opening polymerization of -caprolactone imder very mild conditions via a polymerization mechanism described for aluminum alkoxides (345). Tin octoate, Sn(0(0)CCH(C2H5)C4H9)2, is another type of initiator to synthesize telechelics based on PCL. In particular, when it is used in conjunction with hydroxyl functional compounds or prepolymers, telechelics, linear and star-shaped block copolymers, or networks can be obtained via corresponding alkyl octoate formation (346-354). More recently, novel end-chain and mid-chain telechelics functionalized with photoactive groups of PCL were synthesized (355). 

Braune and Okuda have shown the possibility to substitute porphyrin initiators by simpler systems based on the association of ammonium salts with a bulky aluminum bis(phenolate) electrophile. According to their study, the ring-opening polymerization of PO cannot occur at simple Lewis add centers, but that nucleophilic ate complexes must be present at the same time. However, so far, only the synthesis of PPO oligomers with MWs less than 5000 has been reported for this system. The important contribution of Braune and Okuda is that they confirmed the Vandenberg binudear mechanism earlier proposed for epoxide polymerization (see Figure 12). °- ... 

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