Non-isocyanate Poly Hydroxyurethanes Research Articles

Poly(ethylene oxide) bis(cyclic carbonate) based hydrophilic non-isocyanate polyhydroxyurethanes: Polymer-water interactions and glass transition behavior

Hydrogen bonding, glass transition, water absorption, and plasticization are studied as a function of hydrogen bond donor concentration in the chain of a non-isocyanate polyhydroxyurethane system, synthesized by solvent-free aminolysis of a poly(ethylene oxide) (PEO) based cyclic carbonate. The concentration of hydrogen bond donors is controlled by varying the ratio of diaminobutane (DAB) and triethylenetetramine (TETA) in the amine component. Introduction of secondary amino groups enhances hydrogen bonding and rigidity of the chain, and, as a result, slows down dynamics, as evidenced by an increase in glass transition temperature. Hydroxyurethane groups are the primary hydration sites despite the hydrophilicity of the polyether. Secondary amino groups act as secondary hydration sites which further increases water sorption capacity. The Couchman-Karasz model describes excellently the dependence of glass transition temperature on composition in both dry and hydrated systems.

Structure-Glass Transition Relationships in Non-Isocyanate Polyhydroxyurethanes.

The molecular dynamics, with an emphasis on the calorimetric and dynamic glass transitions, of non-isocyanate polyhydroxyurethanes (PHUs) produced by the equimolar polyaddition of polyether-based dicyclic carbonates (P-CCs) and various short diamines was studied. The diamine component consisted of a short aliphatic diamine (1,4-diaminobutane, DAB) and a more complex 'characteristic' diamine. The study was conducted to investigate (i) the chemical structure of the characteristic amine, (ii) its molar ratio, and (iii) the structure and molar mass of the P-CC. Infrared spectroscopy, differential scanning calorimetry, and broadband dielectric spectroscopy were employed. The P-CC, constituting the bulk of the systems, was the most crucial component for the glass transition. The characteristic amine influenced the glass transition as a result of its bulky structure, but also presumably as a result of the introduction of free volume and the formation of hydrogen bonds. The dynamic glass transition (α relaxation) trace in the Arrhenius plots showed a subtle change at a certain temperature that merits further study in the future. The charge mobility was fully coupled with the molecular mobility, as evidenced by dc conductivity being directly proportional to the characteristic frequency of α relaxation. The fluctuation in carbonyl units (β relaxation) was mildly affected by changes in their immediate environment.

Physicochemical and Mechanical Properties of Non-Isocyanate Polyhydroxyurethanes (NIPHUs) from Epoxidized Soybean Oil: Candidates for Wound Dressing Applications.

Only 0.1% of polyurethanes available on the market are from renewable sources. With increasing concern about climate change, the substitution of monomers derived from petrochemical sources and the application of eco-friendly synthesis processes is crucial for the development of biomaterials. Therefore, polyhydroxyurethanes have been utilized, as their synthesis route allows for the carbonation of vegetable oils with carbon dioxide and the substitution of isocyanates known for their high toxicity, carcinogenicity, and petrochemical origin. In this study, polyhydroxyurethanes were obtained from carbonated soybean oil in combination with two diamines, one that is aliphatic (1,4-butadiamine (putrescine)) and another that is cycloaliphatic (1,3-cyclohexanobis(methylamine)). Four polyhydroxyurethanes were obtained, showing stability in hydrolytic and oxidative media, thermal stability above 200 °C, tensile strength between 0.9 and 1.1 MPa, an elongation at break between 81 and 222%, a water absorption rate up 102%, and contact angles between 63.70 and 101.39. New formulations of bio-based NIPHUs can be developed with the inclusion of a cycloaliphatic diamine (CHM) for the improvement of mechanical properties, which represents a more sustainable process for obtaining NIPHUs with the physicochemical, mechanical, and thermal properties required for the preparation of wound dressings.

Water-polymer interactions and mechanisms of water-driven glass transition decrease in non-isocyanate polyhydroxyurethanes with varying hydration sites

Non-isocyanate polyurethanes (NIPUs) with varying content of secondary amino groups along their chain were studied with respect to water absorption and plasticization. Secondary amino groups promote water uptake. Water sorption isotherms in the water activity range 0–0.97 are discussed in terms of various sorption models. Secondary amino groups act as additional hydration sites, increasing monolayer capacity. The red shift of the IR band assigned to the carbonyl of the urethane and the simultaneous blue shift of the urethane N–H bending band show cleavage of the polymer-polymer hydrogen bonds upon water uptake, due to strong interactions between water molecules and hydroxyurethanes constituting the primary hydration sites. A decrease in glass transition temperature (Tg) is observed with increasing water content. The effect is discussed in terms of plasticization and slaving mechanisms, while a peculiar decrease of Tg at very low hydrations is attributed to a mechanism not following common mixing laws.

Assembling a dense grid structure with green polyhydroxyurethane and a high-capacity Si-based anode for lithium ion batteries

Interweaving a non-isocyanate polyhydroxyurethane synthesized through an eco-friendly route and polyacrylic acid results in a grid structure network that stabilizes high-capacity anodes.

‘Spider-like’ POSS in NIPU webs: enhanced thermal stability and unique swelling behavior

PEO-based non-isocyanate polyhydroxyurethane (NIPU, PHU) networks physically modified with octa(3-hydroxy-3-methylbutyldimethylsiloxy)POSS (8OHPOSS) were synthesized via one-pot one-step approach. POSS was introduced into the polymer matrix in the amount of 1–10 wt%. Polar hydroxyls on the vertex groups of POSS allowed for uniform dispersion even up to high loadings (10 wt%). Composites exhibit enhanced thermal stability in comparison to the pristine matrix. FTIR analysis confirmed that POSS strengthens the hydrogen bonding in the material. Upon POSS introduction, plasticization was observed with a peculiar trend change at POSS loadings over 5 wt%. Glass transition temperature of highly crystalline 8OHPOSS was measured and reported to be at around 3 °C. NIPUs at hand exhibit high water absorption (around 200 wt%) typical for hydrogels. Swelling studies show that 8OHPOSS enhances PHUs hydrogels absorption capacity in phosphate-buffered saline (PBS). Higher absorption capacity in PBS solution in comparison to distilled water is an uncommon phenomenon in hydrogels.

Tailoring the physical properties of non-isocyanate polyurethanes by introducing secondary amino groups along their main chain

A series of linear non-isocyanate polyhydroxyurethanes (NIPUs) were synthesized by aminolysis of a PPO bis-cyclic carbonate with two diamines, one of which (triethylenetetramine, TETA) contains non-reacting secondary amino groups. Thus, varying the composition of the diamine component modulates the density of proton donors. Fourier Transform Infrared Spectroscopy (FTIR) showed that with increasing TETA content in the amine components (20–100 wt%) carbonyl groups tend to form progressively more double hydrogen bonds (HBs). Interestingly, the system without this amine deviates from the trend. In the whole composition range, a higher amount of double HBs correlates monotonously with reduced molecular mobility as observed by differential scanning calorimetry (DSC), dielectric relaxation spectroscopy (DRS), and dynamic mechanical analysis (DMA). It also correlates with the mechanical properties of studied NIPUs which range at room temperature from a viscous liquid to a dimensionally stable, flexible, and durable elastomer, depending on the density of double hydrogen-bonded carbonyls. Hence, the herein proposed approach allows for tailoring thermomechanical properties of NIPUs by modulating density of double hydrogen-bonded carbonyls.

Original Fluorinated Non-Isocyanate Polyhydroxyurethanes

New fluorinated polyhydroxyurethanes (FPHUs) with various molar weights were synthesized via the polyaddition reaction of a fluorinated telechelic bis(cyclocarbonate) (bis-CC) with a diamine. The fluorinated bis-CC was initially synthesized by carbonylation of a fluorinated diepoxide, 1,4-bis(2',3'-epoxypropyl)perfluorobutane, in the presence of LiBr catalyst, in high yield. Then, several reaction conditions were optimized through the model reactions of the fluorinated bis-CC with hexylamine. Subsequently, fluorinated polymers bearing hydroxyurethane moieties (FPHUs) were prepared by reacting the bis-CC with different hexamethylenediamine amounts in bulk at 80 °C and the presence of a catalyst. The chemoselective polymerization reaction yielded three isomers bearing primary and secondary hydroxyl groups in 61-82% yield. The synthesized fluorinated CCs and the corresponding FPHUs were characterized by 1H, 19F, and 13C NMR spectroscopy. They were compared to their hydrogenated homologues synthesized in similar conditions. The gel permeation chromatography (GPC), differential scanning calorimetry (DSC), and thermogravimetric analysis (TGA) data of the FPHUs revealed a higher molar mass and a slight increase in glass transition and decomposition temperatures compared to those of the PHUs.

Biodegradation of novel bioplastics made of starch, polyhydroxyurethanes and cellulose nanocrystals in soil environment

Plastic pollution is recognized as a major environmental problem in many countries. Over the last decade, academics have embraced research on bioplastics to discover newer high-end green materials. However, the end-of-life environmental fate of such materials is not adequately understood. Non-isocyanate polyhydroxyurethanes (PHUs) are green engineering materials with huge potential to replace traditional polyurethanes. Despite this immense potential, a number of questions about their environmental fate remain unanswered. The present study investigated the extent and mechanisms underlying soil biodegradation of PHUs and determined whether the deterioration of PHUs within starch bioplastics (ST) can improve the biodegradation of starch (ST)-PHU hybrids. Soil microbiomes managed to effectively and quickly digest not only PHUs but also ST-PHU hybrids. All ST-PHU hybrids were characterized by exceptional biodegradability with mass losses of up to ~88% following a soil burial time of only 120 days. The biodegradation of ST-alone bioplastics was 69% under identical conditions. The presence of cellulose nanocrystals (CNC) reduced the potential for the soil microbial community to degrade nanohybrids (ST-PHU-CNC). Microbially digested bioplastics with PHU presented less stages of thermal degradation, and reduced intensities of FTIR, NMR and XPS signals compared to the original films, indicating improvement of the biodegradation mechanism. These findings suggested the positive environmental implications of PHU in improving the bioplastic's degradation and their potential for future applications.

Highly Efficient MOF Catalyst Systems for CO2 Conversion to Bis-Cyclic Carbonates as Building Blocks for NIPHUs (Non-Isocyanate Polyhydroxyurethanes) Synthesis

The present paper describes a greener sustainable route toward the synthesis of NIPHUs. We report a highly efficient solvent-free process to produce [4,4′-bi(1,3-dioxolane)]-2,2′-dione (BDC), involving CO2, as renewable feedstock, and bis-epoxide (1,3-butadiendiepoxide) using only metal–organic frameworks (MOFs) as catalysts and cetyltrimethyl-ammonium bromide (CTAB) as a co-catalyst. This synthetic procedure is evaluated in the context of reducing global emissions of waste CO2 and converting CO2 into useful chemical feedstocks. The reaction was carried out in a pressurized reactor at pressures of 30 bars and controlled temperatures of around 120–130 °C. This study examines how reaction parameters such as catalyst used, temperature, or reaction time can influence the molar mass, yield, or reactivity of BDC. High BDC reactivity is essential for producing high molar mass linear non-isocyanate polyhydroxyurethane (NIPHU) via melt-phase polyaddition with aliphatic diamines. The optimized Al-OH-fumarate catalyst system described in this paper exhibited a 78% GC-MS conversion for the desired cyclic carbonates, in the absence of a solvent and a 50 wt % chemically fixed CO2. The cycloaddition reaction could also be carried out in the absence of CTAB, although lower cyclic carbonate yields were observed.

Synthesis of novel plant oil-based isocyanate-free urethane coatings and study of their anti-corrosion properties

In this study, a bio-resource resin was synthesized via epoxidation and carbonation of linseed oil (LO) in acidic conditions, and then in the presence of tetra ‐ n ‐ butyl ammonium bromide (TBAB) and under purging of CO2 gas, respectively. The synthesized resins were characterized using FTIR spectroscopy, NMR analysis, and titration method. The resins were cured with diethylenetriamine to form non-isocyanate polyhydroxy-urethane networks. Rheometry analysis and DSC were utilized for determining the proper time and temperature of the curing process. The physical and mechanical properties of the mild steel coated samples were evaluated using various techniques. Finally, the corrosion resistance of the coated samples was assessed via Electrochemical Impedance Spectroscopy (EIS) and the results were compared with commercial polyurethane-based coated samples.The characterization tests confirmed the formation of epoxy and cyclo-carbonate groups as a result of the epoxidation process and carbonation reaction of LO, respectively. The various tests showed the appreciation of the mechanical properties of the coating samples with different carbonation weight percentages. The results revealed the improvement of adhesion and hardness properties and reduction of the flexibility of the coating samples with increasing the conversion % of carbonation. As the carbonation content increases, more hydroxyl groups were formed in the final polyhydroxy-urethane structure due to the reaction of the cyclo-carbonate with the amine, resulting in increased adhesion strength and mechanical properties of the polymer. EIS study revealed increasing of the anti-corrosion properties first and then decreasing it by increasing the percentage of carbonation. The 75% carbonated sample revealed the best corrosion performance, which was comparable with PU-based coated samples.

Oligomeric ricinoleic acid synthesis with a recyclable catalyst and application to preparing non-isocyanate polyhydroxyurethane

As a consequence of the great demand and extended application of polyurethanes in various fields, the development of green processes for their production and functional polyurethane materials has received widespread attention. In this regard, the biomass-derived polyurethane via the non-isocyanate route could be promising. In this work, the castor-based polyurethanes were designed and synthesized through a non-isocyanate route by employing ricinoleic acid as the starting material, in which the oligomeric ricinoleic acid (ORA) with variable average polymerization degree was used as the key intermediate. To access the ORA with different average polymerization degree, the solid Lewis acid tin(II) oxide (SnO) was developed as the efficient and recyclable catalyst and the average polymerization degree of ORA was regulated by the reaction time at 210 °C. After sequential esterification, epoxidation, cycloaddition with CO2 and polyaddition with 1,6-hexamethylene diamine (HMDA) or isophorone diamine (IPDA), a series of polyhydroxyurethanes (PHUs) with different tensile strength and elongation at break as well as the thermal stability and the glass transition temperature were obtained depending on the type of diamine and the average polymerization degree of ORA, indicating the functional role of the polymerization degree of ORA in regulating the mechanical and thermal properties of the resulting materials. This protocol for the castor-based PHUs preparation in this work not only represents a green and sustainable way to produce bio-based material, but also provides a convenient way to change the average polymerization degree of ORA and then alter the properties of resulting polyurethanes.

Lysine‐Functionalized Gibbsite Nanoplatelet Dispersions for Nonisocyanate Polyhydroxyurethane Nanocomposites and Translucent Coatings

AbstractThe lysine functionalization of ultrathin γ‐Al(OH)3 single‐crystal nanoplatelets (ly‐gibbsite) having an average thickness below 100 nm and a width ranging between 0.5 and 1.5 µm renders them organophilic and enables their agglomerate‐free dispersion in nonisocyanate polyhydroxyurethane (NIPU) thermosets prepared by amine cure of polyfunctional cyclic carbonates. Whereas most other nanoparticles drastically increase viscosity even at very low content, NIPU processing tolerates up to 40 wt% ly‐gibbsite without impairing its uniform dispersion. The amine groups of ly‐gibbsite can react with cyclic carbonate groups of NIPU to afford interfacial coupling. Contrary to the NIPU composites containing corundum and spherical gibbsite particles, ly‐gibbsite/NIPU nanocomposites exhibit substantially higher stiffness as reflected by high Young’s modulus up to 9500 MPa. Moreover, ly‐gibbsite/NIPU coatings remain translucent even at high ly‐gibbsite content when the nanoplatelet length is below 1 µm. As verified by transmission electron microscopic imaging of coatings, the ly‐gibbsite nanoplatelets are aligned parallel to the surface. At high ly‐gibbsite content, NIPU thermosets are rendered flame retardant in the absence of halogen and other flame retardants. The NIPU coatings tolerate the addition of aluminum flakes to produce metallic NIPU varnishes.

Graphenated Ceramic Particles as Functional Fillers for Nonisocyanate Polyhydroxyurethane Composites

AbstractGraphenation of corundum and silicon carbide filler particles simultaneously improves mechanical properties and electrical conductivity of nonisocyanate polyhydroxyurethanes (NIPU) composites prepared by amine cure of polyfunctional cyclic carbonates. Typically, the ceramic fillers coated with either glucose, polydopamine, or graphite oxide (GO) are thermolyzed to produce an ultrathin graphene shell around the ceramic core, as verified by transmission electron microscopy. As compared to a blend of corundum particles with the thermally reduced graphite oxide (TRGO) nanofiller, graphenation of corundum with GO at a similar total carbon content significantly improves the Young’s modulus (7000 MPa, +184%) of trimethylolpropane glycidylether carbonate (TMPGC) cured with diethylenetriamine (DETA). Moreover, up to 30 wt% of the graphenated corundum filler is uniformly dispersed, whereas a few percent of neat TRGO account for intolerable high viscosity. Furthermore, NIPU composites containing graphenated ceramic fillers exhibit electrical conductivities of up 2.58 × 10−5 S m−1 well below the percolation threshold of neat TRGO in the same NIPU matrix. Hence, the graphenation of inorganic particles represents a facile and universal synthetic route toward tailoring functional fillers and combines the two worlds of functionalized graphene and inorganic fillers in an economic way by eliminating the tedious syntheses and handling typical for graphene nanofillers.

Synthesis of Bio‐Based Cyclic Carbonates Using a Bio‐Based Hydrogen Bond Donor: Application of Ascorbic Acid to the Cycloaddition of CO2 to Oleochemicals

AbstractOleochemicals such as functionalized fatty acid esters and vegetable oils are classes of renewably sourced compounds that are increasingly attracting attention in sustainable chemistry as replacement for fossil‐fuel based chemicals. The possibility of coupling CO2 with epoxidized fatty acids esters (EFAEs) and epoxidized vegetable oils (EVOs) to afford compounds that are attractive as additives or chemical intermediates in the synthesis of non‐isocyanate polyhydroxyurethanes (NIPU) can conjugate highly sought‐after CO2 valorization with the exploitation of bio‐based substrates. In this context, there have been very few attempts to employ organocatalytic hydrogen bond donors (HBDs) in the cycloaddition reaction of CO2 to EFAEs and EVOs and no studies focusing on bio‐based and readily available HBDs. In this work we show that ascorbic acid is an efficient HBD for the cycloaddition of CO2 to EFAEs and EVOs under mild reaction conditions of temperature (80–100 °C) and pressure (5–10 bar) that could be applied to several kinds of substrates (monounsaturated EFAEs, polyunsaturated EFAEs and EVOs). In all cases, the formed by‐products (ketones, allylic alcohols, cyclic ethers etc.) were identified and the reaction conditions were tuned in order to obtain the target carbonates, generally, in high yields and selectivity.

En route to CO2-containing renewable materials: catalytic synthesis of polycarbonates and non-isocyanate polyhydroxyurethanes derived from cyclic carbonates.

Combining CO2-chemistry with biomass conversion allows renewable polymeric materials including polycarbonates and polyhydroxyurethanes (PHUs) to be generated. The demand for robust materials with modular properties that can be prepared on an industrial scale is important and, to date, the most important polymeric materials are derived from petrochemicals. These materials inevitably result in CO2 emissions, and therefore making robust materials from renewable sources will contribute to a more sustainable society. An attractive way to address this challenge is to combine biomass transformations with CO2-fixation and material science. An identified target that combines all three aspects involves the preparation of PHUs (or non-isocyanate polyurethanes, NIPUs) via the polymerization of fully renewable cyclic carbonates derived from biomass and CO2 with a diamine compound that can also been derived from biomass sources. In this review, we critically analyze the progress in catalyst development for the efficient transformation of epoxides and CO2 to cyclic carbonates and polycarbonates. We also discuss the synthesis of PHUs from cyclic carbonates and diamines (not restricted to fully renewable compounds), including challenges in regiocontrol and biodegradability, as well as the role catalysts play in the synthesis of these polymers.

Liquid sorbitol ether carbonate as intermediate for rigid and segmented non-isocyanate polyhydroxyurethane thermosets

The facile chemical fixation of 18wt.% carbon dioxide by catalytic carbonation of sorbitol glycidyl ether, monitored by means of NMR and FTIR spectroscopy, affords sorbitol-based cyclic ether carbonate (SEC) as versatile intermediate for producing renewable non-isocyanate polyhydroxydroxyurethane (NIPU) materials. In sharp contrast to the solid, crystalline and highly insoluble pure sorbitol tricarbonate (STC), melting above 200°C close to its decomposition temperature, SEC is liquid at room temperature and fully miscible with a wide variety of polyfunctional amine curing agents. Despite high SEC carbonate functionality (4.2mol/kg), both gel time and pot-life time measurements confirm easy processing by curing SEC with polyfunctional aliphatic amines to produce new families of sorbitol-based NIPU materials. Particularly, blends combining flexible long-chain diamines such as dimer fatty acid based diamine (Priamine™ 1074) or polyether triamine (Jeffamine™ T403), respectively, with rigid short-chain diamines such as 1,6-hexamethylene diamine (HMDA), 1,12-dodecyl diamine (DDA), 2,2,4-trimethylhexamethylene diamine (TMHMDA) and isophorone diamine (IPDA), enable the simultaneous incorporation of soft and hard segments into NIPU networks. Moreover, miscible blends of SEC with STC remain liquid up to high STC content. Unparalleled by conventional bio-based NIPU chemistry, the curing of SEC or miscible SEC/STC blends, respectively, with IPDA yields sorbitol-based NIPU thermosets exhibiting significantly improved thermal and mechanical properties, as reflected by high glass transition temperatures surpassing 180°C and Young moduli exceeding 4000MPa.

Triple-Shape Memory Materials via Thermoresponsive Behavior of Nanocrystalline Non-Isocyanate Polyhydroxyurethanes

Crystallization of long n-alkyl side chains within the confined environment of nonisocyanate polyhydroxyurethane (PHU) networks renders PHUs thermoresponsive, enabling thermomechanical programming of temperature-induced shape changes. Key intermediates of shape memory PHUs are highly branched, semicrystalline polyamidoamine curing agents tailored by amidation of a polyamine-terminated hyperbranched polyethylenimine with semicrystalline long chain behenic acid. Both cure temperature and content of n-alkyl side chains, varied independently, govern crystallization behavior, phase separation and mechanical properties of semicrystalline PHU networks obtained by curing pentaerythritol-based polyfunctional cyclic carbonates with hyperbranched, semicrystalline polyamidoamines. As compared to conventional PHUs, the incorporation of hydrophobic, crystalline n-alkyl side chains significantly lowers hydrophilicity. Typically, the n-alkyl side chains of behenic amides in PHU networks melt at temperatures varying betwe...

High Purity Limonene Dicarbonate as Versatile Building Block for Sustainable Non-Isocyanate Polyhydroxyurethane Thermosets and Thermoplastics

Oxidation and subsequent catalytic carbonation of limonene, gained from orange peels, afford high purity limonene dicarbonate (LC) as a versatile building block for tailoring linear and cross-linked non-isocyanate polyurethanes (NIPU) from renewable resources. Spectroscopic investigations reveal so far unknown highly colored carbonation byproducts which are successfully removed to yield crystalline LC. Melt-phase polyaddition of a dimer fatty acid based diamine and its diamine-terminated LC-prepolymers with carbonated 1,4-butanediol diglycidyl ether (BDGC) produces 100% bio-based linear NIPU thermoplastics. Side-reactions occurring during polymerization account for decreasing molar mass with increasing LC content. Curing carbonated pentaerythritol glycidyl ether (PGC)/LC blends with 1,5-diaminopentane, gained from lysine, enables tailoring of 100% bio-based NIPU thermosets exhibiting unconventional property profiles. The incorporation of small amounts high purity LC substantially improves NIPU glass tempe...

Isocyanate-Free Route to Poly(carbohydrate–urethane) Thermosets and 100% Bio-Based Coatings Derived from Glycerol Feedstock

Glycerol serves as the exclusive bio feedstock for the preparation of high purity sorbitol tricarbonate (STC) as new intermediate for poly(carbohydrate–urethane) thermosets and 100% bio-based non-isocyanate polyhydroxyurethane (NIPU) coatings. In this process, glycerol-based acrolein is dimerized, carbonated, and oxidized, thus producing the highly reactive diepoxy functional ethylene carbonate (DOC), which by facile chemical CO2 fixation yields high purity STC. Opposite to most state-of-the-art multifunctional five-membered cyclic carbonates and regardless of the feedstock used for its manufacture, STC enables amine curing at ambient temperature even in the absence of catalysts. According to FT-IR and NMR spectroscopic analyses of the amine/carbonate reaction kinetics, the internal cyclic carbonate group is 3 times more reactive with respect to the two terminal carbonate groups. This is attributed to the electron-withdrawing effect of terminal cyclic carbonates. Curing STC with a blend of bio-based flexi...