Lactone Ring-Opening Equilibria in Methanol by ¹H NMR Analysis: An Assessment of the Ring-Opening Polymerizability of Lactone Monomers

Abstract

The purpose of this study was to learn if a convenient 1H NMR method could be developed to serve as a tool for estimating the propensity of a given lactone to participate in ring-opening transesterification polymerization (ROTEP). The methanolysis of each of 18 lactones was initially examined in CD3OD solution in the presence of sulfuric acid as a Brønsted catalyst at ambient temperature. Once equilibrium was established, the ratio of remaining lactone to the ring-opened methyl ester/alcohol could be readily measured by NMR spectroscopy. The observed thermodynamic driving force observed for the methanol ring openings is roughly in line with the extent of ROTEP for the various classes of lactones. This is the case even though the reaction conditions for these methanolyses versus ROTEP reactions are substantially different. Qualitative evaluations of the rates of the ring-opening methanolyses were also performed, and several non-obvious relative reactivities were observed. Finally, employing this simple NMR methanolysis using low concentrations of methanol in CDCl3 is recommended as the preferred protocol for the initial evaluation of the polymerizability of any new lactone monomer that researchers may prepare in the future.

Sustainable Copolymer Synthesis from Carbon Dioxide and Butadiene

“…Second, the conjugated olefin is a typical Michael acceptor that may react with potential chain-end alkoxides to terminate chain-propagating processes in anionic ROPs, similar to that observed by Eagan . In fact, although ring-opening homopolymerizations of six-membered lactones with 0 to 1 substituents on the ring have been well-known, early efforts for ROP of the disubstituted counterpart failed. , Model studies of the thermodynamics of ring-opening polymerization of various EVP derivatives by Hoye suggest that ROP of EVP and its derivatives should be thermodynamically feasible, further indicating that the challenges of EVP ROP may mostly be a consequence of the kinetics of competitive Michael addition . The question of Michael addition can be overcome through hydrogenation of the conjugated olefin to produce one of two new disubstituted six-membered lactones, fully hydrogenated 3,6-diethyltetrahydro-2 H -pyran-2-one (DEtP) and partially hydrogenated 3-ethyl-6-vinyltetrahydro-2 H -pyran-2-one (EtVP) (Scheme ).…”

“…Though with a low efficiency, a conjugated addition/ring-opening homopolymerization of EVP was developed to afford main-chain degradable polymers. Although direct ROP of EVP to form recyclable polyesters was calculated to be feasible by Hoye et al, 75 there is still a lack of suitable catalytic systems that favor ROP over selfconjugated addition. Furthermore, current polymerization systems usually suffered from low polymerization efficiency, while lacking regio-and stereoselectivity control.…”

“…71,74 Model studies of the thermodynamics of ring-opening polymerization of various EVP derivatives by Hoye suggest that ROP of EVP and its derivatives should be thermodynamically feasible, further indicating that the challenges of EVP ROP may mostly be a consequence of the kinetics of competitive Michael addition. 75 The question of Michael addition can be overcome through hydrogenation of the conjugated olefin to produce one of two new disubstituted six-membered lactones, fully hydrogenated 3,6-diethyltetrahydro-2H-pyran-2-one (DEtP) and partially hydrogenated 3-ethyl-6-vinyltetrahydro-2H-pyran-2-one (EtVP) (Scheme 7).…”

Efficient all polymer active layers with long-range ordered 1D p–n nanoheterojunctions confirmed by TEM tomography

“…The P(NDI2OD-T2) with a crystalline character is well known to form a 1D nanowire (NW) structure in a certain solvent. 42,43 In general, solution-state crystallization-driven assembly of polymer can be induced using a marginal solvent or mixed solvent having a limiting solubility. The compatibility between P(NDI2OD-T2) and the solvent used in this study was predicted considering the HSP space (R a ) (see ESI †).…”

Novel conversions of a multifunctional, bio-sourced lactone carboxylic acid

“…This is consistent with the thermodynamic reluctance of 6 to undergo methanolysis in 2 vol% methanolic chloroform, a proxy we recently reported for evaluating the suitability of any lactone to function as a ROTEP monomer. 17 Only 6.5% of the methyl ester 8 was formed at equilibrium; for comparison, γ-butyrolactone (another reluctant ROTEP monomer) and δ-valerolactone (a competent ROTEP monomer) produced their corresponding methyl esters to the extent of 18.7% and 86.8%, respectively, in the same assay. 17 (Notably, radical ring-opening polymerization of the thionolactone analog of 6 was recently reported.…”