Polycarbonates were successfully synthesized for the first time through the anionic copolymerization of epoxides with CO2, under metal-free conditions. Using an approach based on the activation of epoxides by Lewis acids and of CO2 by appropriate cations, well-defined alternating copolymers made of CO2 and propylene oxide (PO) or cyclohexene oxide (CHO) were indeed obtained. Triethyl borane was the Lewis acid chosen to activate the epoxides, and onium halides or onium alkoxides involving either ammonium, phosphonium, or phosphazenium cations were selected to initiate the copolymerization. In the case of PO, the carbonate content of the poly(propylene carbonate) formed was in the range of 92-99% and turnover numbers (TON) were close to 500; in the case of CHO perfectly alternating poly(cyclohexene carbonate) were obtained and TON values were close to 4000. The advantages of such a copolymerization system are manifold: (i) no need for multistep catalyst/ligand synthesis as in previous works; (ii) no transition metal involved in the copolymer synthesis and therefore no coloration of the samples isolated; and (iii) no necessity for postsynthesis purification.

Tetrabutylammonium carbonate (TBAC) which is obtained by treating CO 2 with tetrabutylammonium hydroxide is shown to perform as an ideal difunctional initiator for the copolymerization of carbon dioxide (CO 2) and propylene oxide (PO) in the presence of triethylborane (TEB). In this system, CO 2 thus serves as the initiating moiety of its own copolymerization with epoxides when used in the form of a carbonate salt. Based on this remarkable result, mono-, tri-, and tetrafunctional ammonium carboxylate initiators and also other difunctional carboxylate initiators were synthesized and used for the synthesis of well-defined ωhydroxyl-polycarbonates with linear and star structures. Well-defined telechelics, three-and four-armed star samples of molar mass varying from 1 kg/mol to 10 kg/mol, with around 95% carbonate content, were successfully synthesized. The structure of the obtained polycarbonate ω-polyols were characterized by 1 H NMR, MALDI-TOF, and GPC. The terminal hydroxyl functionality of polycarbonate diol was further used for polycondensation with diisocyanates to afford polyurethanes. Finally, taking TBAC as an example, the recyclability of this ammonium-based initiator is demonstrated for the preparation of polycarbonate diols. 65 polycarbonate diols and polyols eventually obtained under 66 these conditions are contaminated with monofunctional 67 chains, which is detrimental to the subsequent polycondensa-68 tion applications. As clearly demonstrated by Sugimoto et al., 69 polycarbonate tetrol and hexeol samples using

Poly­(ester-carbonate) copolymers were synthesized through triethylborane (TEB)-activated, one-pot copolymerization of epoxides with anhydrides (AH) and CO2. Depending upon the feeding ratio of AH to the epoxides, poly­(ester-carbonate) copolymers with random and tapered ester structures could be derived due to the much higher reactivity of AH toward growing oxanions compared to the reactivity of CO2. Anhydrides like succinic anhydride (SA) and phthalic anhydride (PA) when tried in terpolymerization with epoxides, like propylene oxide (PO) and cyclohexene oxide (CHO), and CO2 indeed exhibited such high reactivities in comparison to CO2 that tapered block structures were eventually obtained for high feeding ratios of AH to PO and random copolymers for the AH-to-epoxide feeding ratio lower than 10%. Terpolymerization with different feeding ratios of anhydrides to epoxides was thus systematically investigated. In an alternate path, diblock poly­(ester-b-carbonate)­s were prepared by sequential copolymerization of epoxide/anhydride and epoxide/CO2. All of the obtained copolymers were characterized by 1H nuclear magnetic resonance (NMR), diffusion-ordered spectroscopy (DOSY), gel permeation chromatography (GPC), and differential scanning calorimetry (DSC). The structures and properties of copolymers obtained by terpolymerizations and block copolymerizations were compared.

Glycidyl azide polymer or poly(glycidyl azide) which is considered as an excellent energetic binder or plasticizer in advanced solid propellants is generally obtained by post-modification or azidation of poly(epichlorohydrin). Here we report that glycidyl azide can be directly homopolymerized through anionic ring-opening polymerization to access poly(glycidyl azide) using onium salts as initiator and triethyl borane as activator. Molar masses of poly(glycidyl azide) up to 11.0 Kg/mol are achieved in a controlled manner with a narrow polydispersity index (PDI ≤ 1.2). Similarly, alternating poly(glycidyl azide carbonate) are also prepared through alternating copolymerization of glycidyl azide with carbon dioxide. Lastly, the copolymerization of glycidyl azide with other epoxide monomers is carried out; the azido functions carried by glycidyl azide which are successfully incorporated into the backbones of polyethers and polycarbonates based on cyclohexene oxide and propylene oxide subsequently served to introduce other functions by click chemistry.

Achieving simultaneously high selectivity and high rate in the coupling reaction of CO 2 with poorly reacting oxetanes remains a major challenge. Here is described the selective and nearly quantitative conversion of the coupling reaction of oxetanes with CO 2 into six-membered cyclic organic carbonates (COCs) when a binary metal-free system composed of commercially available alkyl borane and onium iodide salts is used under 10 bar CO 2 pressure between 90 and 110 o C. Kinetic investigations provide quantitatively the enthalpy and entropy of activation [ΔH ‡ = 6.7 ± 1.2 kcal/mol and ΔS ‡ = -57 ± 4 cal/(mol•K)] of the back-biting, cyclic formation reaction. In addition to forming borate complexes with the anions responsible for the CO 2 /oxetane coupling reaction, these alkyl boranes activate the cyclic ethers as unambiguously confirmed by DFT studies. Upon selecting onium salts other than iodide-based ones, in particular those with poor leaving ability, the process is driven towards chain growth and the formation of linear polycarbonates. This metal-free system also exhibits both versatility and an activity comparable to that of metal catalysts (turnover frequency values of 14 -124 h -1 ) for the synthesis of various fivemembered COCs from epoxides and CO 2 .