Heterocycle/Heteroallene Ring‐Opening Copolymerization: Selective Catalysis Delivering Alternating Copolymers

Abstract

Heteroatom‐containing polymers have strong potential as sustainable replacements for petrochemicals, show controllable monomer–polymer equilibria and properties spanning plastics, elastomers, fibres, resins, foams, coatings, adhesives, and self‐assembled nanostructures. Their current and future applications span packaging, house‐hold goods, clothing, automotive components, electronics, optical materials, sensors, and medical products. An interesting route to these polymers is the catalysed ring‐opening copolymerisation (ROCOP) of heterocycles and heteroallenes. It is a living polymerization, occurs with high atom economy, and creates precise, new polymer structures inaccessible by traditional methods. In the last decade there has been a renaissance in research and increasing examples of commercial products made using ROCOP. It is better known in the production of polycarbonates and polyesters, but is also a powerful route to make N‐, S‐, and other heteroatom‐containing polymers, including polyamides, polycarbamates, and polythioesters. This Review presents an overview of the different catalysts, monomer combinations, and polymer classes that can be accessed by heterocycle/heteroallene ROCOP.

Heterocycle/Heteroallene Ring‐Opening Copolymerization: Selective Catalysis Delivering Alternating Copolymers

“…[116] Endo and co-workers pioneered DHC/glycidyl ether ROCOP, using imidazole catalysts, to produce polyesters with 99% selectivity, moderate activity and low molar mass (TOF 30-50 h -1 , 120 ºC, 2 mol%, Mn < 3 kg/mol, 94-99%). [117][118][119][120] Using a bifunctional DHC, in which two lactones are connected through a benzene core, copolymerisation with epoxides resulted in polyesters featuring pendant lactones.…”

“…[147,148] Figure 21: COS/epoxide ROCOP illustrating different chemo-and regioselectivities. [149] In 2013 Zhang and co-workers successfully achieved both chemo-and regioselective COS/PO ROCOP using a Cr(III) salen/PPNCl catalyst system to produce monothio-PPC (TOF 288 − 332 h −1 , 25 °C, 0.1 mol%, Mn = 21.9 -25.3 kg/mol). [149] The selectivity O/S scrambling.…”

“…[149] In 2013 Zhang and co-workers successfully achieved both chemo-and regioselective COS/PO ROCOP using a Cr(III) salen/PPNCl catalyst system to produce monothio-PPC (TOF 288 − 332 h −1 , 25 °C, 0.1 mol%, Mn = 21.9 -25.3 kg/mol). [149] The selectivity O/S scrambling. [150] The Cr(III) salen/PPNCl catalysts also showed good activity in COS ROCOP with other epoxides, e.g.…”

“…[163] Isotactic COS/PO and COS/PGE copolymers, prepared from enantiopure epoxides, were amorphous but the COS/EO polymer was semicrystalline (Tm = 128 °C, Tc = 66 °C; note that the all oxygen variant poly(ethylene carbonate) from CO2/EO ROCOP is amorphous (Tg = 0 -10°C). [149,152,158] The catalyst system was a DBU-tethered Cr(III)…”

Mg(ii) heterodinuclear catalysts delivering carbon dioxide derived multi-block polymers

“…Subsequently, many other equivalently selective and controlled homogenous mono-, [21][22][23][24] dinuclear metal catalysts 25,26 and organocatalysts were reported. 27,28 A few catalysts are exceptions to the selectivity preference, including poorly dened heterogeneous catalysts that result in illcontrolled random or tapered copolymers. [29][30][31] In 2014, we reported a new type of self-switchable polymerization catalysis, whereby a Zn(II)Zn(II) catalyst was directed between epoxide/carbon dioxide ROCOP and lactone ringopening polymerization (ROP) to deliver well controlled poly(ester-b-carbonates).…”