All-Polycarbonate Graft Copolymers with Tunable Morphologies by Metal-Free Copolymerization of CO₂ with Epoxides

Abstract

Brush-type macromolecules (BMs) have attracted much attention over the past decades because of their unique properties and potential applications in nanoscience, drug-delivery systems, and photonics. A two-step strategy of synthesis of polycarbonate-grafted copolymers with either star-shaped or brush-typed morphologies using a “grafting from” approach is reported; the backbone in these all-polycarbonate graft copolymers is made of poly­(cyclohexene carbonate) (PCHC), and the side grafts are made of poly­(propylene carbonate) (PPC). In the first step, poly (vinyl-cyclohexene carbonate) (PVCHC) backbones of two different sizes (PVCHC35, PVCHC283) were prepared by copolymerization of vinyl-cyclohexene oxide (VCHO) with CO2 in the presence of triethylborane (TEB), using tetrabutyl ammonium succinate (TBAS) as the initiator. In the second step, the dangling vinyl double bonds of PVCHC were transformed into carboxylic acid groups. After partial neutralization of the latter using tetrabutyl ammonium hydroxide, the PPC grafts could be grown from the backbone carboxylic sites by copolymerization of propylene oxide (PO) with CO2 in the presence of TEB. Before attempting the synthesis of the above all-polycarbonate grafted copolymers, we check the viability of the above synthetic strategy by preparing graft copolymers made of a polymethacrylate backbone and PPC side grafts. In the latter case, the backbone was generated by reversible addition–fragmentation chain-transfer (RAFT) polymerization of methacrylic acid (MAA), followed by the growth of PPC side grafts using the backbone carboxylates as initiating sites. In both cases (PVCHC-g-PPC and PMAA-g-PPC), two types of architectures corresponding to two different morphologies were synthesized: star-shaped morphologies were obtained from rather short backbones, and relatively long grafts, on the one hand, and semiflexible cylinders were grown from rather long backbones and short grafts. These various structures were characterized by nuclear magnetic resonance (NMR) and gel permeation chromatography/light scattering (GPC/LS), and their morphologies were further investigated by atomic force microscopy (AFM). The reported synthetic method provides a robust way to synthesize well-defined polycarbonates with either star-type or brush-type morphologies and graft copolymers made of polyacrylate backbones and polycarbonate grafts. Thermal and mechanical properties of these graft copolymers were also investigated.

Tertiary and Quaternary Phosphonium Borane Bifunctional Catalysts for CO2/Epoxide Copolymerization: A Mechanistic Investigation Using In Situ Raman Spectroscopy

“…This strategy can be further extended to highly active bifunctional Co − and Al systems featuring pendant ammonium cations (Chart ). It has been proposed that the ammonium cation can interact with the anionic polymer chain-end, whereas the metal center binds/activates CO 2 and epoxide. , Owing to these advances, novel random/block copolymers of polyalkylene carbonates have been developed with emerging applications. − …”

Orthogonally grown polycarbonate and polyvinyl block copolymers from mechanistically distinct (co)polymerizations

“…Distinct polymerizations using TTC-COOH in a dual role of an initiator and a chain transfer agent For our initial attempt at growing a polycarbonate block, we relied on our previous contributions where the use of carboxylate salts as initiators of the ROCOP of CO 2 /epoxides was described; 9,10,13 we thus used 4-cyano-4-[(dodecylsulfanylthiocarbonyl) sulfanyl] pentanoic acid (TTC-COOH) playing a dual role as an initiator for the ROCOP of CO 2 /epoxides and a transfer agent for the RAFT polymerization of vinyl monomers (Scheme 1). The tetrabutylammonium carboxylate salt (TTC-COO − , Bu 4 N + ) obtained after the deprotonation of TTC-COOH using tetrabutylammonium hydroxide was characterized by 1 H NMR to check its structure (Fig.…”

“…Over the past decade, several examples of successful syntheses of aliphatic polycarbonates through metal-based catalytic systems, [1][2][3][4][5][6][7][8] and more recently through metal free systems, have been disclosed. [9][10][11][12][13][14][15] These chemistries described efficient ring-opening copolymerizations (ROCOP) of CO 2 with epoxides, leveraging the direct utilization of over-emitted CO 2 as a means to reduce carbon footprint and avoid fossil feedstock. However, applications derived from CO 2 -based polymers are still very limited due to their rather poor mechanical and thermal properties.…”

“…13 More recently, using a polycarbonate backbone carrying multiple tetrabutylammonium carboxylate salts as the initiator, well-defined all-polycarbonate graft copolymers could be obtained: in such a macromolecular structure all grafts were grown from each of the carboxylate sites of the backbone. 10 In addition, the carboxylate groups serving as ROCOP initiating sites are generally compatible with other functional groups that are suitable for the initiation of other chain polymerizations. In this investigation, we describe the synthesis of di- and triblock copolymers using TTC-COOH in the dual role of an initiator for the ROCOP of epoxide/CO 2 from its carboxylic acid group and of a transfer agent for the RAFT polymerization of vinyl monomers through its trithiocarbonate function (Scheme 1).…”

Progress in the catalytic reactions of CO2 and epoxides to selectively provide cyclic or polymeric carbonates

“…This result strikingly differs from terpolymerization of a mixture of epoxides, cyclic anhydrides, and CO 2 catalyzed by metal catalysts in a one-pot process to provide poly(ester-b-carbonate)s. 88,89 In a two-step process, metal-free catalyzed copolymerization of vinyl-cyclohexene oxide (VCHO) and CO 2 has provided poly (vinyl-cyclohexene carbonate)s (PVCHC) backbones for synthesizing polycarbonate-grafted copolymers with brush typed morphologies. 90 Following the synthesis of PVCHC employing a TEB/tetrabutylammonium succinate catalyst at 60 °C, the dangling PVCHC double bonds were subjected to thiol-ene click chemistry with 3-mercaptopropanoic acid to afford PVCHC-COOH. Upon partial deprotonation of PVCHC-COOH with Bu 4 NOH, the carboxylate side chains were utilized as initiators for the copolymerization of PO and CO 2 in the presence of TEB to yield all-polycarbonate side chains (Scheme 7).…”