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Synthesis of a new mononuclear magnesium complex with a bulky bis(alkoxide) ligand environment and its reactivity in ring-opening polymerization (ROP) and ring-opening copolymerization (ROCOP) are reported. Reaction of n -butyl- sec -butylmagnesium with two equivalents of HOR (HOR = di- tert -butylphenylmethanol, HOC t Bu 2 Ph) formed Mg(OR) 2 (THF) 2 . The reaction proceeded via the Mg(OR)( sec -Bu)(THF) 2 intermediate that was independently synthesized by treating n -butyl- sec -butylmagnesium with one equivalent of HOR. Mg(OR) 2 (THF) 2 led to active albeit not well-controlled ROP of rac -lactide. In contrast, well-controlled ROCOP of epoxides with cyclic anhydrides was observed, including efficient and alternating copolymerization of phthalic anhydride with cyclohexene oxide as well as rare copolymerization of phthalic anhydride with limonene oxide and terpolymerization of phthalic anhydride with both cyclohexene oxide and limonene oxide. In addition, novel copolymerization of dihydrocoumarin with limonene oxide is described.
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Chain transfer agents utilized in epoxide and CO 2 copolymerization processes
This tutorial deals initially with a comparison of the mechanistic aspects of living and immortal polymerization processes. The living polymerization pathway originated with the anionic polymerization of styrene by Szwarc, whereas immortal polymerization was first described by Inoue for the homopolymerization of epoxides using an aluminum complex. A similar behavior would be anticipated for the copolymerization of epoxides and carbon dioxide catalyzed by well-defined metal complexes. The major difference between these two pathways is rapid and reversible chain transfer reactions involving protic impurities or additives in the latter case, that is, the stoichiometry of the monomer/initiator ratio changes as a function of the nature and concentration of the chain transfer agent (CTA). For instance, in early studies of the copolymerization of epoxides and CO 2 where adventitious water was present in the copolymerization reactions, there was little control of the molecular weight of the resulting copolymer product. Presently, the presence of chain transfer with protic CTAs during the copolymerization of epoxides and CO 2 is a major positive factor in this process's commercialization. Specifically, this represents an efficient production of polyols for the synthesis of CO 2 -based polyurethanes. Studies of the use of various CTAs in the synthesis of designer polymeric materials from CO 2 and epoxides are summarized herein.
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- Award ID(s):
- 1665258
- PAR ID:
- 10106214
- Date Published:
- Journal Name:
- Green Chemistry
- Volume:
- 21
- Issue:
- 9
- ISSN:
- 1463-9262
- Page Range / eLocation ID:
- 2214 to 2223
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1039/C9GC00620F
