Cascade (Dithio)Carbonate Ring Opening Reactions for Self-Blowing Polyhydroxythiourethane Foams

Synthesis of polyurethanes through the oxidative decarboxylation of oxamic acids: a new gateway toward self-blown foams

Polyurethane (PU) thermoplastics and thermosets were prepared through the step-growth polymerization of in situ generated polyisocyanates through the decarboxylation of polyoxamic acids, in the presence of phenyliodine diacetate (PIDA), and polyols. The CO2 produced during the reaction allowed the access to self-blown polyurethane foams through an endogenous chemical blowing. The acetic acid released from ligand exchange at the iodine center was also shown to accelerate the polymerization reaction, avoiding the recourse to an additional catalyst. Changing simple parameters during the production process allowed us to access flexible PU foams with a wide range of properties.

Aminocyclopropenium as a novel hydrogen bonding organocatalyst for cycloaddition of carbon disulfide and epoxide to prepare cyclic dithiocarbonate

The smallest Hückel aromatic ring cyclopropenium substituted by electron-donating C-amino groups produced a aminocyclopropenium electron-rich cation. A bifunctional aminocyclopropenium halide catalyst installed with bis-(hydroxyethyl) functions on the amino group was then designed. A typical (diethanolamino)cyclopropenium halide catalyst C5·I was screened optimally for the cycloaddition of carbon disulfide into an epoxide to produce cyclic dithiocarbonate with an excellent conversion (95%) and high selectivity (92%). The electrostatic enhancement of alkyl C-H HBD capability was implemented via vicinal positive charges on the cyclopropenium core, and the acidity of the terminal O-H hydrogen proton increased by intramolecular H-bonding between the two hydroxy groups on the diethanolamino group (O-H⋯O-H). Then, a hybrid H-bond donor comprising enhanced alkyl C-H and hydroxy O-H was formed. The hybrid HBD offered by aminocyclopropenium was vital in activating the epoxide and stabilizing the intermediate, resulting in reduced O/S scrambling. Moreover, weakly coordinated iodide anion served as a nucleophilic reagent to open the ring of the epoxide. The cooperative catalytic mechanism of the HBD cation and halide anion was supported by NMR titrations and control experiments. Eleven epoxides with various substituents were converted into the corresponding cyclic thiocarbonate with high conversion and selectivity under mild conditions (25 °C, 6 h) without a solvent. The cycloaddition of carbon disulfide with epoxides catalyzed by aminocyclopropenium developed a new working model for hydrogen bonding organocatalysis.

Cascade Exotherms for Rapidly Producing Hybrid Nonisocyanate Polyurethane Foams from Room Temperature Formulations

For decades, self-blown polyurethane foams─found in an impressive range of materials─are produced by the toxic isocyanate chemistry and are difficult to recycle. Producing them in existing production plants by a rapid isocyanate-free self-blowing process from room temperature (RT) formulations is a long-lasting challenge. The recent water-induced self-blowing of nonisocyanate polyurethane (NIPU) formulations composed of a CO2-based tricyclic carbonate, diamine, water, and a catalyst successfully addressed the isocyanate issue, however failed to provide foams at RT. Herein, we elaborate a practical solution to empower the NIPU foam formation in record timeframes from RT formulations. We generate cascade exotherms by the addition of a highly reactive triamine and an epoxide to the formulation of the water-induced self-foaming process. These exotherms, combined to a fast cross-linking imparted by the triamine and epoxide, rapidly raise the temperature to the foaming threshold and deliver hybrid NIPU foams in 5 min with KOH as a catalyst. Careful selection of the monomers enables producing foams with a wide range of properties, as well as with an unprecedented high biobased content up to 90 wt %. Moreover, foams can be upcycled into polymer films by hot pressing, offering them a facile reuse scenario. This robust cheap process opens huge perspectives for greener foams of high biobased contents, expectedly responding to the sustainability demands of the foam sector. It is potentially compatible to the retrofitting of industrial foaming infrastructures, which is of paramount importance to accommodate existing foam production plants and address the huge foam market demands.

Influence of Phosphorus Structures and Their Oxidation States on Flame-Retardant Properties of Polyhydroxyurethanes

This article focuses on the synthesis of polyhydroxyurethane (PHU) materials containing novel phosphorus flame retardants (FR). Four different phosphorus compounds were grafted onto cyclic carbonate: 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO), diethyl phosphite (DEP), diphenyl phosphite (DPP) and dibenzo[d,f][1,3,2]dioxaphosphepine 6-oxide (BPPO). Thus, three novel phosphorus reactive cyclic carbonates which have never been reported so far were synthetized. Phosphorus FR containing PHU materials were characterized by FTIR to evidence the total conversion of the cyclic carbonate. Moreover, the gel contents up to 80% confirmed the formation of the polymer network. Then, the thermal stability and the flame-retardant properties were investigated by thermogravimetric analyses, cone calorimeter and pyrolysis combustion flow calorimeter. The mode of action of phosphorus compounds, depending on the oxidation state, was especially highlighted. Phosphonate (+III) provided better action in a condensed phase than phosphinate thanks to a more efficient char formation. Among phosphonates, differences were observed in terms of char-formation rate and expansion. DEP provided the best flame-retardant properties, with a reduction of 76% of pHRR with 2 wt% of phosphorus in cone calorimeter analysis. Therefore, this article highlighted the different modes of action of phosphorus flame retardants, depending on the oxidation state of phosphorus, in PHU materials.

Water-Induced Self-Blown Non-Isocyanate Polyurethane Foams

For 80 years, polyisocyanates and polyols were central building blocks for the industrial fabrication of polyurethane (PU) foams. By their partial hydrolysis, isocyanates release CO₂ that expands the PU network. Substituting this toxic isocyanate-based chemistry by a more sustainable variant-that in situ forms CO₂ by hydrolysis of a comonomer-is urgently needed for producing greener cellular materials. Herein, we report a facile, up-scalable process, potentially compatible to existing infrastructures, to rapidly prepare water-induced self-blown non-isocyanate polyurethane (NIPU) foams. We show that formulations composed of poly(cyclic carbonate)s and polyamines furnish rigid or flexible NIPU foams by partial hydrolysis of cyclic carbonates in the presence of a catalyst. By utilizing readily available low cost starting materials, this simple but robust process gives access to greener PU foams, expectedly responding to the sustainability demands of many sectors.