The Fluorocarbene Exploit: Enforcing Alternation in Ring-Opening Metathesis Polymerization

Abstract

Fluoroalkenes are known to be notoriously reluctant substrates for olefin metathesis due to the generation of thermodynamically stable Fischer-type fluorocarbene intermediates, which invariably fail to undergo further reaction. In the present disclosure, we find that fluorine substitution on the sp 2 carbon also strictly suppresses homopolymerization of norbornene derivatives (NBEs), and this can be harnessed to achieve alternating ring-opening metathesis polymerization (ROMP) with an appropriately electron-rich comonomer. Dihydrofuran (DHF) is thereby shown to undergo alternating ROMP with fluorinated norbornenes, the perfectly alternating structure of the resulting copolymer having been unambiguously elucidated by 1 H, 19 F, and 13 C NMR analyses. Furthermore, we find that the degradability of the resultant copolymers in acidic media via hydrolysis of enol ether moieties in the backbone can be predictably modulated by the number of fluorine atoms present in the NBE comonomer, affording an opportunity to engage with the desirable physical properties of fluorinated polymers while limiting their attendant environmental degradability issues.

Non‐Symmetrical Tetrafluoroalkadienes Synthesized by ROCM of 3,3,4,4‐Tetrafluorocyclobutene

“…Surprisingly, examples of ROM of fluorinated substrates are extremely scarce, polymerization of fluorinated norbornene derivatives being the only known example [19] . Simultaneously with our work, a ROCM of ethyl vinyl ether with norbornene derivatives bearing fluorine atoms on the sp 2 carbons was studied and very recently published [20] …”

“…[19] Simultaneously with our work, a ROCM of ethyl vinyl ether with norbornene derivatives bearing fluorine atoms on the sp 2 carbons was studied and very recently published. [20] The presence of fluorine atoms in a molecule modifies its properties and thus fluorinated compounds found wide applications as pharmaceuticals, [21] agrochemicals [22] or biomolecules. [23] Increasing attention is paid to compounds bearing a tetrafluoroethylene unit.…”

Effect of Ligand Steric Hindrance on Catalytic Polymerization of Cycloolefin Polymer (COP)

“…[26][27][28][29] In the study of branched or polar olefin polymers, researchers found that large steric ligands increased the rigidity, limited the rotation, and improved electron donating to catalysts, giving the catalysts good thermal stability, long life, good selectivity, and less chain transfer, so such catalysts had high catalytic activity and high molecular weight. [30][31][32][33] For example, Long et al synthesized αdiimide Ni complex with 2,6-diphenyl-substituted aniline, and this catalyst had very good thermal stability and could efficiently catalyze ethylene polymerization at 100 °C. Moreover, the existence of this large steric aromatic ring could effectively inhibit the chain transfer reaction, devoting to a narrow molecular weight distribution (M w /M n < 1.5) under high temperature conditions.…”

Long-Range Kinetic Effects on the Alternating Ring Opening Metathesis of Bicyclo[4.2.0]oct-6-ene-7-carboxamides and Cyclohexene

“…This innovation provides rapid access to copolymers with well-defined backbone sequences 12,13 and copolymers with backbone degradability. 14,15 AROMP has been used to create materials with unique and interesting properties. 12,13,16 However, in order to create more advanced functional materials using AROMP, it is important that we understand the kinetics of the ring openings of the bicyclooctene and the subsequent ring opening of CH.…”

“…Hence, ROMP has been limited to high strain energy monomers such as norbornenes, cyclooctadienes, and cyclobutenes. − However with recent developments and innovations, low strain cyclic olefins such as cyclohexene (CH), which traditionally is impractical for ROMP, can be incorporated into alternating copolymers via ROMP (AROMP) − and cascade enyne metathesis polymerization. − When CH is combined with specific monomer types that undergo only a single metathesis cycle and do not homopolymerize, the monomers will cross-react to form precisely alternating copolymers. − Bicyclooctenes , and disubstituted cyclopropenes are prominent examples of single addition monomers that can form highly alternating copolymers with cyclohexene and other low strain cyclic olefins. This innovation provides rapid access to copolymers with well-defined backbone sequences , and copolymers with backbone degradability. , …”