Catalyst‐Controlled Dual Dynamic Networks in Polyhydroxyurethanes from Six‐Membered Cyclic Carbonates

The transient shear rheology of a thermotropic liquid crystalline polymer in the super-cooled state

Unique Ligand Exchange Dynamics of Metal–Organic Polyhedra for Vitrimer-like Gas Separation Membranes

In this work, three different cyclic carbonates are obtained from renewable diols and transformed into carbamates by reacting them with renewable 11‐amino undecanoic acid methyl ester to synthesize non‐isocyanate poly(ester urethane)s in a sustainable manner. A procedure using 2,3‐butanediol (2,3‐BDO) as a renewable starting material to synthesize a cyclic carbonate with dimethyl carbonate (DMC) is introduced, catalyzed by 1,5,7‐triazabicylco[4.4.0]dec‐5‐ene (TBD). Three purification strategies, i.e., column chromatography, extraction, and distillation, are compared regarding their E‐Factors. Propylene glycol (PG) and ethylene glycol (EG) are used as alternative starting materials to broaden the substrate scope and compare material properties, their cyclic carbonates likewise react to carbamates with 11‐amino undecanoic acid methyl ester. All carbamates are then polymerized in a bulk polycondensation reaction, yielding non‐isocyanate polyurethanes (NIPUs), specifically poly (ester urethane)s, with molecular weights (Mn) up to 10 kDa. Complete characterization is reported using differential scanning calorimetric (DSC), size exclusion chromatographic measurements (SEC), 1H‐NMR as well as IR spectroscopy. The rheological properties of the poly(ester urethane)s are investigated in the framework of small amplitude oscillatory shear (SAOS) and uniaxial elongation.

In the current context of sustainable chemistry development and new regulations, aminolysis of cyclic carbonate is one of the most promising routes to nonisocyanate polyurethanes, also called polyhydroxyurethanes (PHU). In this study, a new kind of shape memory PHU vitrimers with outstanding mechanical properties and chemical recyclability is prepared. The monomer employed for aminolysis to form the PHUs is bis(six-membered cyclic carbonate) of 4,4'-biphenol (BCC-BP), which is synthesized by bi(1,3-diol) precursors and CO2. The synthetic strategy, isocyanate-free and employing CO2 as a building block, is environmentally friendly and suits the concept of carbon neutrality. The thermal properties, mechanical properties, and dynamic behaviors of the PHUs are explored. The maximum breaking strength and elongation at break of the resultant PHUs reach 65 MPa and 452%, respectively, exceeding other reported PHU-based materials in combined performance. Such a PHU material can also lift up a load 4700 times heavier than its own weight by a shape recovery process. Finally, the bi(1,3-diol) can be regenerated through the alcoholysis of PHUs to realize chemical recycling. This work provides a feasibility study for a green synthetic approach and for designing a novel PHU material with outstanding properties.

Glycerol carbonate acrylate is a 5-membered cyclic carbonate synthesized from glycerol that is used as a chemical coupling agent and has proven highly suitable for use in the synthesis of multifunctional polyhydroxyurethanes (PHUs). The multifunctionality of the structure of PHUs is determined by the density of the carbon-amine groups generated by the Aza-Michael reaction and that of the urethane groups and adjacent primary and secondary hydroxyl groups generated by aminolysis. Glycerol carbonate acrylate is polymerized with polyfunctional mono-, di-, tri, and tetra-amines, by type-AB polyaddition, either in bulk or in solution, through stepwise or one-pot reaction strategies in the absence of added catalysts. These approaches result in the generation of linear, interchain, and crosslinked structures, through the polyaddition of linear and branched amines to the ethylene and cyclic carbonate sites of glycerol carbonate acrylate. The resulting collection of organic molecules gives rise to polyethylene amino ester PHUs with a high molar mass, exceeding 20,000 g·mol−1, with uniform dispersity.

Hybrid polyhydroxyurethanes: How to overcome limitations and reach cutting edge properties?

A sol/gelcuring method is used in this work to synthesize hybridpartially bio-based polyhydroxyurethanes (PHUs) from dicarbonatesderived from glycerol and various diamines. The method consists ofend-capping the PHU prepolymers with moisture-sensitive groups, sosealants and adhesives can be produced from partially sustainablehybrid PHUs (HPHUs), similar to their preparation from end-cappedconventional polyurethanes. Diglycerol dicarbonate (DGC) is synthesizedand polymerized with different diamines of various chain lengths,and the resulting structural and thermal properties of the PHUs arequalitatively and quantitively characterized. This characterizationled to two potential candidates: PHU 4, made of DGC and a poly(propyleneglycol) diamine, and PHU 10, prepared from DGC and a poly(dimethylsiloxane)diamine. These polymers, with respective relative number-average molecularweights of 3200 and 7400 g/mol, are end-capped and left to cure underambient lab conditions (22 °C and 40–50% humidity), andthe curing processes are monitored rheologically. Notably, moisturecuring does not require any catalyst. The chemical stability of theresulting hybrid PHUs (HPHUs) 4 and 10 in pure water is investigatedto check the viability of applying them under outdoor conditions.Only HPHU 10 is found to be resistant to water and shows hydrophobicitywith a contact angle of 109°. Tensile tests are conducted onHPHU 10 samples cured under lab conditions for a week and others curedfor another week while being immersed in water. The mechanical properties,tensile strength and elongation at break, improve with the samplescured in water, indicating the high-water repellency of HPHU 10.

Bis-benzimidazolium salts as bifunctional organocatalysts for the cycloaddition of CO2 with epoxides

In this work, the isothermal crystallization of compounded polylactide (PLA) and PLA-flax fiber composites was investigated by means of rheometry using small amplitude oscillatory shear (SAOS). The rheological measurements were carried out in parallel plate flow geometry at a crystallization temperature (T c ) ranging from 110 to 140 °C. In addition, the effect of shear on polylactide crystallization was studied at 140 °C. Rheological behavior in the molten state was employed to predict the initial viscosity in the T c interval by applying time-temperature superposition, and results were found to be in agreement with experimental values at low crystallization rates. A simple empirical model was also used to determine the crystallization induction time in a wide range of supercooling conditions. The evolution of the complex viscosity under quiescent conditions of the PLA-based flax-fiber composite indicated an enhancement of the rate of crystallization due to the presence of cellulosic fibers, while shear flow effectively accelerated the crystallization of neat PLA. This work shows that rheometry is an accurate technique for analyzing the crystallization behavior of polymers in a temperature range which presents low to very low crystallization rates, which is the case for PLA at T ≥ 130 °C.

The evolution of linear viscoelasticity during cross‐linking of a stoichiometrically imbalanced polydimethylsiloxane (PDMS) was measured by small amplitude oscillatory shear. At the gel point (GP), stress relaxation was found to follow a power law, St−n, as described by the previously suggested gel equation. However, while stoichiometrically balanced gels (PDMS, polyurethanes) gave the specific exponent value of n=1/2, a higher exponent value, 1/2<n<1, was measured on a stoichiometrically imbalanced PDMS sample. Transformation of the data from the frequency to the time domain required the hypothesis that the power law behavior extends over the entire frequency range, 0<ω<∞. The imbalanced gel exhibited a higher loss than storage modulus, G″(ω)>Gv′(ω), and a higher rate of stress relaxation. GP was found to occur before the crossover point of the loss and storage moduli, G″(ω0,t), and G′(ω0,t), as measured during the cross‐linking reaction (reaction time, t) at constant frequency, ω0. This suggests new methods for localizing GP, for instance by the detection of a loss tangent independent of the frequency. All the experiments were performed with end‐linking networks far above the glass transition temperature. The network junctions were assumed to be due to chemical cross‐links only and not due to any other association phenomenon such as crystallization or phase separation.

1. A study has been made of interchain-exchange reactions, reading to the synthesis of polyesters and polyamides, in compounds having amide and ester linkages. 2. It has been shown that, in presence of free hydroxyl, carboxyl, or amino groups, exchange reactions of the alcoholysis, acidolysis, or aminolysis types respectively occur at ester linkages. Amide linkages are broken only by amino and carboxyl groups; they are stable toward hydroxyl groups. 3. It has been found that no exchange reaction occurs between diethyl adipate and N,N′-hexamethylenebisacetamide in absence of catalyst; it occurs only in presence of an acid catalyst. 4. It has been shown that a narrow fraction of a polyester undergoes considerable change when subjected to prolonged heating: interchain exchange reactions occur, resulting in the formation of a more heterogeneous material, the distribution curve for which is similar to that of the original unfractionated polyester obtained by the polycondensation of adipic acid with ethylene glycol.

We here report the synthesis of two types of six‐membered cyclic carbonate monomers equipped with various drug molecules through ester linkages. The target compounds can be isolated in good yields and feature diagnostic IR and 13C NMR spectroscopic fingerprints in line with their proposed connectivities. As a potential application, we investigated their ring‐opening polymerization (ROP), showing that the nature of the cyclic carbonate is crucial towards macromolecular carbonate formation. The functionalized polycarbonates have molecular weights of up to 10 kg/mol, controllable functionality and a variable drug‐to‐carbonate ratio. This work demonstrates the adaptive synthesis of new types of functionalized six‐membered cyclic carbonates with potential as precursors to polycarbonate‐drug type macromolecules.

Nanocomposites made of poly(lactic acid), poly(butylene succinate), and organically modified montmorillonite were prepared by melt blending in a twin screw extruder. The influence of the organoclay content on nanocomposite properties was investigated. The nanocomposite structure has been characterized by various techniques at different scales. X‐ray diffraction showed an intercalated structure whereas rheological investigations in small amplitude oscillatory shear indicated a partial exfoliation. It was also shown that organoclay was evenly dispersed in the matrix even though some large aggregates were also observed. The mechanical properties of nanocomposites were measured in uniaxial tensile test. Oxygen and water vapor permeability was also characterized. It was shown that dispersed organoclay and aggregates have a direct impact on mechanical properties and permeability. An increase of Young's modulus by 41% and a decrease of permeability by 40% could be obtained with 7 wt % organoclay. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014, 131, 40364.

In this study, a green and sustainable strategy was opted for the synthesis of a novel biobased non-isocyanate polyurethane (NIPU) or polyhydroxyurethane (PHU). NIPU or PHU was synthesized from microbially converted hydroxy fatty acid-based cyclic carbonate and diamine cross-linker. Initially, oleic acid was biotransformed into 7,10-dihydroxy-8(E)-octadecenoic acid (DOD) using Pseudomonas aeruginosa. The cell-free approach was chosen for DOD production due to its high yield and productivity. Afterward, DOD was modified into DOD-based tricyclic carbonate by a two-step method. The prepared monomeric material was characterized using Fourier transform infrared (FTIR) spectroscopy, 1H nuclear magnetic resonance (1H NMR), and 13C NMR analyses. A series of DOD-based PHUs (DOD PHUs) were synthesized with different amine contents, and their structures were studied by FTIR and 1H NMR analyses. The morphological, mechanical, and thermal properties of DOD PHU were further analyzed. The tensile strength and elongation at break of the prepared DOD PHU were in the range of 2–6 MPa and 39–76%, respectively. The glass transition temperature of the material was in the range of 4–27 °C. Thermogravimetric analysis exhibited that thermal stability increases with the increase in amine content. The gel content was in the range of 73–100%, suggesting that the polymers are highly cross-linked. In addition, the synthesized DOD PHU displayed excellent ultraviolet and water resistance properties. The green synthesized DOD PHU depicts suitability for a wide range of applications, particularly in the coating and packaging industries.

A series of poly(thiourethanes) (PTUs) from biobased monomers have been synthesized. Limonene and squalene were transformed into polyfunctional thiols by thiol-ene reaction with thioacetic acid and further saponification. They were then reacted in different proportions with hexamethylene diisocyanate (HDI) in the presence of a catalyst to prepare bio-based poly(thiourethane) vitrimer-like materials. The different functionalities of squalene and limonene thiols (six and two, respectively) allow for changing the characteristics of the final material by only varying their relative proportions in the reactive mixture. The proportions of thiol and isocyanate groups were stoichiometric in all the formulations tested. An acidic and a basic catalyst were tested in the preparation of the networked polymers. As the acidic catalyst, we selected dibutyltin dilaurate (DBTDL), and as the basic catalyst, a tetraphenylborate salt of 1,8-diazabicyclo(5.4.0)undec-7-ene (BGDBU), which has the advantage of only releasing the base at high temperatures. The materials obtained were characterized by thermogravimetry and thermomechanical analysis. The vitrimeric-like behavior was evaluated, and we could see that higher proportions of the limonene derivative in the formulations led to faster stress relaxation of the material. The use of the base catalyst led to a much shorter relaxation time. The materials obtained demonstrated good self-healing efficiency.