Alternating Copolymerization Reaction of Propylene Oxide and CO: Variation of Polymer Stereoregularity and Investigation into Chain Termination

Abstract

The cobalt‐catalyzed alternating copolymerization reaction of racemic propylene oxide and CO affords regioregular but atactic poly(hydroxybutyrates). The application of enantiomerically pure (R)‐ or (S)‐propylene oxide results in the formation of isotactic, optically active and crystalline materials. In contrast to the perfect isotactic microstructures that are available via the microbial pathway, our approach allows to tailor the stereoregularity of the polymer products, and hence their melting points by application of mixtures of the epoxide enantiomers. Investigations into the polymer stereochemistry show that the epoxide units undergo a clean regioregular incorporation into the polymer chain with retention of configuration at the stereogenic carbon centers. MALDI‐TOF and online ATR‐IR experiments give insight into the mechanism of chain termination reactions.

Synthesis and characterizations of new isotactic homopolyesters, statistical and block copolyesters derived of poly((S)‐3,3‐dimethylmalic acid) via the lactone route

“…If only a single peak is visible, it can be identified as chiral polymer, representing syndiotactic or isotactic polymer. 31 The above synthetic methodology of stereoregular PDMMLA was quite convenient and efficient. Thus, obtaining racemic and chiral PDMMLAs in hand and comparing carbonyl peak around 167 ppm corresponding to stereopolymers with data obtained from a series of racemic triads, we were able to confirm the isotacticity of stereoregular PDMMLA and accurately attribute the isotactic or syndiotactic sequence peaks for racemic PDMMLAs.…”

Metal‐Catalyzed Synthesis of Alternating Copolymers

“…The group of Rieger also reported the polymerization of (R)-PO or (S)-PO with CO to give optically active PHB. [74] It was shown that the resulting polyester exhibits an optical rotation identical to that of (R)-PHB obtained from natural sources. The mechanism of the copolymerization of CO/epoxides using cobalt carbonyl complexes as initiators has been investigated by in situ IR spectroscopy.…”

Synthesis of a polyester macromonomer via the cobalt‐catalyzed alternating copolymerization of propylene oxide and carbon monoxide

“…In contrast, the combination of Co 2 (CO) 8 and N ‐heteroaromatic compounds provided oligomers with higher molecular weights and with much smaller concentrations of crotonate end groups (Table 1, runs 8–10) 12. As shown in run 8, the M calcd value is much larger than the M n value, indicating the minor population of the end‐functionalized copolymer.…”

“…Possible reaction mechanisms, including Co 2 (CO) 8 as precursor, have been reported as follows. Acidic HCo(CO) 4 operates as an initiator in the Co 2 (CO) 8 /hydroxypyridine system, whereas [L(CO) n Co] + [Co(CO 4 )] − has been proposed to initiate the polymerization in the Co 2 (CO) 8 /amine system in the absence of any proton source 11–13, 15. The initiation is the nucleophilic attack of [Co(CO 4 )] − against propylene oxide activated by a Brønsted acid or Lewis acid (A), and then the insertion of CO into the resulting CoC bond gives the corresponding acyl–cobalt complexes (Scheme ).…”