Abstract
AbstractRing‐opening polymerizations of ε‐caprolactone (εCL) were conducted in bulk at 120 °C with triphenyl bismuth, Ph3Bi, as an initiator or catalyst. Variation of the monomer–initiator ratio (M/I) allowed for a variation of the molecular weight, but not an accurate control. With an M/I ratio of 1 000:1 and ultra‐dry εCL, a number average molecular weight (corrected $\overline M _{\rm n}$) of 285 kDa was obtained corresponding to a degree of polymerization around 2 500. Addition of tetra(ethylene glycol) resulted in incorporation of this coinitiator and allowed for a better control of the molecular weight. Time–conversion curves revealed a long induction period followed by a conspicuous acceleration upon addition of a coinitiator (tetraethylene glycol). Model experiments demonstrated that Ph3Bi is unstable at 120 °C in the presence of water, oxygen, or alcohols and slowly a precipitate is formed which mainly consists of (PhBiO)x. Ph2BiOR groups formed by side reactions seem to be the true initiators.magnified image
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