Alternating Chain Growth Copolymerization of Isothiocyanates and Epoxides

Abstract

A class of heteroatom polymers through anionic chain growth copolymerization of epoxides and isothiocyanates has been successfully obtained under mild conditions via initiation by a simple salt of lithium alkoxide. The resulting polymers have characteristics of controlled molecular weights and low dispersity with a well-defined backbone of carbonimidothioate repeat units (-OC­(=N)­S-) at 100% alternating degree, which have been confirmed in the 1H-13C heteronuclear multiple bond correlation NMR spectrum and mass spectrum. Side reactions have been greatly suppressed in the copolymerization, and no more than 5% cyclic small molecular byproducts have been produced. We have revealed the special role of lithium bonds in regulating the alternating copolymerization of these two types of monomers, which are involved in activating isothiocyanates as well as binding the incoming monomers to the growing chain ends due to the especial coordination capability of lithium ions to multiple nucleophilic sites. The proposed mechanism of the alternating copolymerization process is supported by density functional theory calculations. Moreover, the copolymerization exhibits first-order kinetics with respect to the monomers and a quasi-living feature. Our strategy is expected to shed light on the incorporation of different types of cumulated double bonds as comonomers into polymer backbones, and the high availability of epoxides and isothiocyanates of various substitutions will forge the development of such kinds of heteropolymers.

Lithium catalysed sequence selective ring opening terpolymerisation: a mechanistic study

“…[9][10][11][12][13][14][15][16] Sustainable catalysts featuring main-group metals are enjoying increasing popularity, but the associated reaction pathways are only partially understood and it is often unclear which mono-or multimetallic, cooperative or uncooperative and neutral or zwitterionic routes occur. [17][18][19][20][21][22][23][24][25] Polymerising more complex ROCOP monomer mixtures with such catalysts can achieve the selective one-pot construction of higher order polymer architectures. For example, ternary mixtures comprising cyclic anhydrides, CO 2 and epoxides can be selectively polymerised into polyester-b-polycarbonate blockpolymers, i.e.…”

Thioanhydride/isothiocyanate/epoxide ring-opening terpolymerisation: sequence selective enchainment of monomer mixtures and switchable catalysis

“…1). 12 Therefore, we investigated the terpolymerisation of PTA/ PhNCS/BO at different monomer ratios and catalyst loadings at 80 °C with lithiumbenzyloxide (LiOBn) as the catalyst (Table 1). Gratifyingly, we find that mixtures comprising 15 eq.…”

“…This can be rationalized by kinetic competition between O/S or LiOCH 2 Ph (LiOBn). 12,17,19 rearrangement and propagation from alkoxide intermediates. In these cases, we also observe the onset of PhNCS/BO ROCOP to form poly(monothioimidocarbonates) once all PTA is consumed as confirmed by 1 H (Fig.…”

“…[7][8][9] However, sulfur-containing variants also exist and relevant to this study are recent reports on isothiocyanate/epoxide ROCOP forming poly(monothioimidocarbonates), isothiocyanate/thiirane ROCOP forming poly (dithioimidocarbonates), cyclic thioanhydride/epoxide ROCOP forming poly(ester-alt-thioesters). [10][11][12][13][14][15][16][17][18] Recently we realised alternating ring-opening terpolymerisation (ROTERP) of ternary monomer mixtures comprising thiophtatlic anhydride (PTA), CS 2 and butylene oxide (BO). 19 Here, a simple lithium catalyst (e.g.…”

Lithium Catalysed Sequence Selective Ring Opening Terpolymerisation: A Mechanistic Study

“…[9][10][11][12][13][14][15][16] Sustainable catalysts featuring main-group metals are enjoying increasing popularity, but the associated reaction pathways are only partially understood and it is often unclear which mono-or multimetallic, cooperative or uncooperative and neutral or zwitterionic routes occur. [17][18][19][20][21][22][23][24][25] Polymerising more complex ROCOP monomer mixtures with such catalysts can achieve the selective one-pot construction of higher order polymer architectures. For example, ternary mixtures comprising cyclic anhydrides, CO2 and epoxides can be selectively polymerised into polyester-b-polycarbonate blockpolymers, i.e.…”