Chemo-Enzymatic Synthesis and Characterization of Renewable

Research Article pubs.acs.org/journal/ascecg

Chemo-Enzymatic Synthesis and Characterization of Renewable Thermoplastic and Thermoset Isocyanate-Free Poly(hydroxy)urethanes from Ferulic Acid Derivatives Raphael̈ Ménard,†,‡ Sylvain Caillol,*,‡ and Florent Allais*,†,§ †

Chaire Agro-Biotechnologies Industrielles (ABI), AgroParisTech, CEBB, 3 rue des Rouges Terres, 51110 Pomacle, France Institut Charles Gerhardt - UMR 5253, CNRS, UM, ENSCM - 8 rue de l’Ecole Normale, 34296 Montpellier, France § UMR 782 GMPA, INRA, AgroParisTech, CNRS, Université Paris-Saclay, Avenue Lucien Brétignières, 78850 Thiverval-Grignon, France

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‡

S Supporting Information *

ABSTRACT: This study presents the syntheses and characterization of renewable nonisocyanate polyurethanes (NIPUs) from a new family of aromatic C5-cyclocarbonate precursors with different functionalities obtained from nontoxic ferulic acid derivatives by glycidylation and carbonation under high carbon dioxide pressure. Depending on the functionality, linear NIPU chains (thermoplastics) or cross-linked NIPU networks (thermosets) have been obtained. The thermoplastic NIPUs molar masses were determined using SEC and 1H NMR. The thermal and thermo-mechanical properties of the NIPUs were assessed by DSC, DMA (for thermosets), and TGA to determine the influence of the NIPU chemical structure on its properties. The range of Tg obtained (17−72 °C) was efficiently correlated with the degree of freedom and the molar mass of the NIPU repeat unit. KEYWORDS: Chemo-enzymatic synthesis, Nonfeed product valorization, CO2 sequestration, Ferulic acid, Fully biobased NIPU, Thermosets and thermoplastics, Tunable material properties

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INTRODUCTION Since the 1930s, polyurethanes (PUs) constitute an increasing part of the polymer market, and the market was estimated to be14 Mt in 2010 and should reach 18 Mt in 2016 according to Research and Markets.1−4 The strong development of polyurethane materials is linked to their versatile adaptable properties and application fields such as thermoplastics, thermosets, or elastomers used in everyday life as coatings, sealants, adhesives, or fibers.5,6 However, despite their exceptional properties, PUs are typically obtained by the reaction between harmful diisocyanates or polyisocyanate and diols or polyol oligomers. However, isocyanates are not only toxic compounds but are also made from even more toxic reagents. Indeed, the wellknown human toxicity7,8 of isocyanate-containing compounds has been illustrated by the 1984 Bhopal disaster in India which killed officially almost 4000 persons the first night and more than 20,000 persons in total. In addition to its dangerousness, isocyanate synthesis requires harmful phosgene and generates waste that needs disposed. Moreover, some polyisocyanates are carcinogen, mutagenic, or toxic and tend to be substituted as they are listed in the annex XVII of REACH. Thus, there is a current need to develop safer alternatives to polyisocyanates. In order to avoid these harmful precursors, the synthesis of © 2016 American Chemical Society

nonisocyanate PUs (NIPUs) has recently gained increasing interest in the chemical industry. Two different synthetic pathways can be used to access NIPUs. The first one relies on the polycondensation of dicarbonates or dicarbamates with diamines or diols, respectively, leading to linear NIPUs. The second consists of polyaddition by ring-opening polymerization of polyfunctional cyclic carbonates with diamines that does not produce any byproduct waste. This last synthetic pathway is considered as a promising alternative to the conventional one as it allows the synthesis of poly(β-hydroxyurethane) by stepgrowth polymerization with diamine. The cyclocarbonate-amine reaction, described for the first time in the 1930s by Carothers et al.,9−11 has been widely studied and used since the 1960s12,13 and allows us to dispense with isocyanate in polyurethane synthesis. Thus, this NIPU route has attracted the attention of the polymer community14−19 for the syntheses of poly(hydroxy)urethane materials and led to the development of some commercial systems. The five-membered cyclocarbonate may be synthesized by various methods,20,21 but the most common and effective one consists Received: August 21, 2016 Revised: December 12, 2016 Published: December 16, 2016 1446

DOI: 10.1021/acssuschemeng.6b02022 ACS Sustainable Chem. Eng. 2017, 5, 1446−1456

Research Article

ACS Sustainable Chemistry & Engineering of an addition of carbon dioxide onto oxirane rings.22,23 Indeed, this reaction is very interesting since carbon dioxide is both inexpensive and renewable. However, this reaction has to be catalyzed to achieve good yield. A wide range of catalysts has been tested for the carbonation reaction: different metal salts22,24 or complexes,25−27 some polymers,28,29 or silicasupported compounds.30 Some efforts are currently made to develop carbonation catalysts efficiently under mild conditions, such as quaternary phosphonium salt,31 that allow complete oxirane conversion in bulk under atmospheric pressure of carbon dioxide. The presence of the pendant hydroxyl groups induces some differences between common PUs and NIPUs. Indeed, the hydroxyl groups increase the polarity of the urethane functions as reported by Kihara et al.14 who investigated the influence of pendant hydroxyl groups on polymer properties studying PU and NIPU with analogue backbone and highlighted the equivalent molar masses of the two polymers. Ochiai et al.32 also showed that the glass transition temperature of the NIPUbased polymer is higher than that of the PU-based polymer due to their higher hydrogen interchain bonds content. This higher polarity also implies a lower solubility in organic media33 and a higher water uptake. However, the main drawbacks of this approach are the lower reactivity17 of the five-membered cyclocarbonate with amine at ambient temperature and the low molar masses of the NIPU synthesized compared to the isocyanate alcohol-based PUs. Many teams17,21,34−36 tried to overcome these drawbacks using thio-carbonate, six-membered or seven-membered cyclocarbonates, but their syntheses requires carbon disulfide, phosgene, or derivatives, which are harmful compounds to humans. With the increasing need to substitute petrobased polymer building blocks, the isocyanate substitution dynamic has recently joined the sustainable one, leading to some biobased isocyanate-free polyurethane. Indeed, the literature presents various examples of NIPUs derived from various fractions of the biomass. Carré et al.37 valorized the biomass oil-fraction through polymerization of sebacic acid-based biscyclocarbonate or a carbonated fatty acid dimer.38 Even fully biobased NIPU thermosets were reported by Javni et al.39 from a soybean oilbased polyfunctionnal cyclocarbonate cured with biobased diamine, resulting in highly flexible NIPU materials exhibiting low glass transition temperatures (Tg). As shown by Bähr et al.,40 the linseed oil-based carbonate leads to higher Tg values due to the higher cyclocarbonate functionality. The terpene fraction has also been valorized in 2012 as a cyclocarbonate NIPU precursor by Bähr et al.,41 who reported the preparation of some limonene dicarbonate-based NIPU exhibiting Tg values up to 70 °C. It appears from these studies that the sterically hindered limonene carbonate is less reactive than terminal cyclocarbonate obtained by glycidyl groups carbonation. Indeed, for the latter, the presence of the electro-withdrawing ether function leads to a more electropositive carbonate that can be attacked by a nucleophilic diamine. This difference in reactivity between the internal and the terminal cyclocarbonate was also highlighted by Boyer et al.42 with fatty ester derivatives. The major parts of the biobased NIPUs reported to date used vegetable oil as the raw material. Indeed, the high functionality and the varied structures of unsaturated triglycerides lead to various thermosets of low glass transition temperature (Tg). In order to produce biobased NIPU materials with higher mechanical properties and rigidity, it seemed interesting to use

aromatic building blocks. Indeed, the aromatic moieties in the NIPU could balance with the low molar masses generally obtained. Lignocellulose represents a huge source of biobased phenolic synthons. Indeed, lignocellulosic biomass such as forest residues or agricultural wastes is the most abundant renewable resource for the potential replacement of the aromatic fossil raw materials. Nevertheless, to the best of our knowledge, only one team reported the synthesis of a biophenol-based NIPU. Indeed, Chen et al.43 recently used a creosol-based renewable bisphenol,44 which is first glycidylated then carbonated, leading to an aromatic biobased biscyclocarbonate. Vanillin has also been used by Fache et al.45 as the raw material for the synthesis of a biobased biscyclocarbonate, but it has not yet been polymerized. Ferulic acid is one of these accessible aromatic synthons from lignocellulosic biomass and is present in numerous nonedible bioresources such as bagasse, rice bran, wheat bran, and beetroot pulp. Its valorization represents a potential added value to some bioresources already industrially used for sugar production. Indeed, Pion et al.46 developed an efficient sustainable chemo-enzymatic process to synthesize different bis- and trisphenols from ferulic acid and various biobased diols under mild conditions. Moreover, the antiestrogenic activity47 of that family of phenolic architectures has been investigated48 highlighting that they do not show the endocrine disruption observed with Bisphenol A, making them ideal candidates for the fossil aromatic building blocks substitution. These phenolic precursors bearing two or three functionalizable hydroxyl groups possess the aromatic structures needed to confer polymer with good properties. They have already been used successfully as polymer building blocks for the synthesis of new copolyesters,49 isocyanate-based copoly(ester-urethane)s,50 and poly(ester-alkenamer)s51 via acyclic diene metathesis (ADMET) polymerization. These biobased phenolic ferulic derivatives have also recently been glycidylated using a NaOHmediated route,48 hydrolyzing partly the internal ester functions, or by the TEBAC (triethylbenzylammonium chloride)-mediated route52 to preserve the building block structures, leading to various biobased epoxy precursors. The latter were then cured with biobased diamines to provide fully biobased epoxy thermosets.52 In this paper, we aim at assessing the potential of these ferulic acid-based phenolic architectures as building blocks for the synthesis of new biobased aromatic NIPUs. The strategy relies on the preparation of new aromatic cyclocarbonate precursors through the carbonation of the renewable ferulic acid-based epoxy precursors previously described.52 The final cyclocarbonate functionality will confer thermoplastic or thermoset behavior to the NIPU materials. Eager to offer renewable NIPU materials and lower the carbon footprint of their preparation, the ferulic acid-based cyclocarbonates are combined with four diamines, two of which are biobased.

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EXPERIMENTAL SECTION

Reagents. Ferulic acid, benzyltriethylammonium chloride, palladium supported on carbon, lithium bromide, and dimethylformamide were purchased from Sigma-Aldrich. Glycerol, isosorbide, and 1,4butanediol were purchased from Alfa Aesar. 1,4-Butanediamine and epichlorohydrine were purchased from Acros Organics. Isophorone diamine (IPDA) was purchased from TCI. CAL-B supported on acrylic bead was purchased from Novozymes. Decane diamine (DA10) was kindly provided by Arkema and EDR148 by Huntsmann. CO2 was purchased from Linde. All reactants were used as received. 1447


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ACS Sustainable Chemistry & Engineering

H12), 4.05 (t, 3JH2−H1 = 6 Hz, H2), 4.22 (dd, 3JH14−H15 = 12 Hz, JH13−H15 = 3 Hz, 2H, H15), 4.28 (dd, 3JH14−H15 = 12 Hz, 4JH13−H15 = 3 Hz, 2H, H13), 4.57 (dd, 3JH13−H14 = 9 Hz, 4JH13−H15 = 6 Hz, 2H, H13), 4.69 (t, 2H, H15), 5.15 (m, 2H, H14), 6.77 (dd, 3JH7−H8 = 6 Hz, 4 JH7−H11 = 3 Hz, 2H, H7), 6.91 (s, 2H, H11), 6.93 (d, 3JH7−H8 = 6 Hz, 2H, H8). 13 C NMR (75.5 MHz, acetone-d6, ppm): δ 26.0 (t, C1), 31.2 (t, C5), 36.4 (t, C4), 56.2 (q, C12), 64.3 (t, C15), 66.8 (t, C2), 70.3 (d, C14), 75.9 (t, C13), 113.9 (d, C11), 116.7 (d, C8), 121.2 (d, C7), 136.3 (s, C6), 147.3 (s, C9), 151.1 (s, C10), 155.7 (s, C16), 173.0(s, C3). HRMS (TOF MS, ES+): m/z calcd for [C32H38O14Na] 669.2159; found: 669.2147. Yield: 89% (white powder, mp 46 °C). Overall yield from ferulic acid: 72%. IDF2Cy. 1H NMR (300 MHz, acetone-d6, ppm): δ 2.61 (t, 3JH5−H6 = 9 Hz, 4H, H5), 2.86 (m, 4H, H6), 3.81 (s, 6H, H9), 3.85 (s, 4H, H2), 4.22 (dd, 3JH16−H15 = 12 Hz, 4JH16−H14 = 3 Hz, 2H, H16), 4.28 (dd, 3 JH14−H15 = 12 Hz, 4JH13−H15 = 3 Hz, 2H, H14), 4.35 (d, 3JH1−H3 = 6 Hz, 1H, H1), 4.57 (dd, 3JH14−H15 = 9 Hz, 4JH14H16 = 6 Hz, 2H, H14), 4.69 (t, 3 JH16−H15 = 6 Hz, 2H, H16), 4.75 (t, 3JH3−H2 = 3 Hz, 1H, H3), 5.07 (d, 3 JH1−H3 = 6 Hz, 1H, H1), 5.15 (m, 1H, H3), 5.15 (d, 2H, H15), 6.77 (dd, 3JH8−H9 = 6 Hz, 4JH8−H12 = 3 Hz, 2H, H8), 6.91 (s, 2H, H12), 6.93 (d, 3JH7−H8 = 6 Hz, 2H, H9). 13 C NMR (75.5 MHz, acetone-d6, ppm): δ 31.1 (t, C6), 36.4 (t, C5), 56.2 (q, C13), 66.8 (t, C16), 70.4 (d, C15), 71.3 (t, C2), 73.5 (t, C2), 74.9 (d, C3), 76.0 (t, C14), 78.8 (d, C3), 81.7 (d, C1), 86.8 (d, C1), 114.0 (d, C12), 116.8 (d, C9), 121.2 (d, C8), 136.3 (s, C7), 147.4 (s, C10), 151.1 (s, C11), 155.7 (s, C17), 172.4 (s, C4). HRMS (TOF MS, ES+): m/z calcd for [C34H38O16Na] 725.6518; found: 725.6528. Yield: 83% (yellow viscous liquid). Overall yield from ferulic acid: 65%. GTF3Cy. 1H NMR (300 MHz, acetone-d6, ppm): δ 2.61 (m, 6H, H4), 2.86 (m, 6H, H5), 3.81 (s, 9H, H12), 4.20−4.40 (m, 10H, H2,13,15), 4.57 (m, 3H, H13), 4.70 (t, 3JH7−H8 = 6 Hz, 3H, H15), 5.15 (m, 3H, H14), 5.25 (m, 1H, H1), 6.77 (dd, 3JH7−H8 = 6 Hz, 4JH7−H11 = 3 Hz, 3H, H7), 6.91 (s, 3H, H11), 6.93 (d, 3JH7−H8 = 6 Hz, 3H, H8). 13 C NMR (75.5 MHz, acetone-d6, ppm): δ 31.1 (t, C5), 36.1 (t, C4), 56.3 (q, C12), 60.6 (t, C2), 62.8 (t, C15), 66.8 (d, C1), 70.3 (d, C14), 75.9 (t, C13), 113.9 (d, C11), 116.7 (d, C8), 121.2 (d, C7), 136.2 (s, C6), 147.3 (s, C9), 151.1 (s, C10), 155.7 (s, C16), 172.7 (s, C3). HRMS (TOF MS, ES+): m/z calcd for [C45H50O21Na] 949.2742; found: 949.2751. Yield: 67% (brown viscous liquid). Overall yield from ferulic acid: 52%. Syntheses of NIPU Compounds. The C5-precursor (BDF2Cy, IDF2Cy, or GTF3Cy) is melted around 60−70 °C before adding the adequate amount of diamine (IPDA, DA10, DIFFA, or EDR148) considering that C5-rings react only once with a primary amine. The system is manually homogenized, introduced in a rectangular rubbery mold, and cured. In the case of the GTF3Cy-based NIPU thermosets, in order to avoid freezing of the system during curing and to ensure optimal cross-linking, it is necessary to slow down the cross-linking reaction. Therefore, materials were first cured at 80 °C (a temperature inferior to the temperature of cross-linking as determined by DSC) then at 100 °C (a temperature superior to the temperature of crosslinking as determined by DSC). For the homogeneity of the study, the same curing process was applied to all NIPU materials: 5 h at 80 °C followed by 10 h at 100 °C. Table S5 summarizes the weight formulations. The NIPU materials are named according to the C5precursor used, followed by the diamine formulated (e.g., BDF2CyDIFFA).

Characterizations. Carbonations were made in a 100 mL Paar autoclave equipped with overhead mechanical stirring. Silica gel flash chromatography was performed on an Interchim puriflash 4100 using a variable cyclohexane/ethyl acetate gradient of elution. Chemical structures of the prepared compounds were determined by 1H and 13C NMR spectroscopy with a Bruker Fourier Ultrashield 300 MHz spectrometer at room temperature in (CD3)2CO or (CD3)2SO. Trimethylsilane was used as external references for 1H NMR, and shifts are given in ppm. The FT-IR spectrum was recorded on an Agilent Cary 630. High resolution mass spectroscopy (HRMS) was recorded by the PLANET platform at URCA on a Micromass GCTOF. Differential scanning calorimetry (DSC) analyses were carried out on a TA Q20 calorimeter. Constant calibration was performed using indium, n-octadecane, and n-octane standards. Nitrogen was used as the purge gas. The thermal properties were analyzed at 10 °C/ min between 20 and 200 °C to observe the glass transition temperature determined as the inflection value in the heat capacity jump. Thermogravimetric analyses were performed using a TA Q500 at a heating rate of 10 °C/min under nitrogen atmosphere. Molar masses distributions were analyzed by size exclusion chromatography (SEC) using a Varian Q50 GPC with a differential refractive index detector and a column set consisting of two PL-gel Mix-C at 35 °C. Tetrahydrofuran was used as eluent at 1.0 mL/min. Calibration of the GPC equipment was carried out with polystyrene standards (Varian Standards). Dynamic mechanical analyses (DMA) were performed on a Metravib DMA 25. The DMA samples had a rectangular geometry (length: 10 mm; width: 20 mm; thickness: 2.5 mm). Uniaxial stretching of samples was performed while heating at a rate of 3 °C/ min from 50 to 200 °C, keeping frequency at 1 Hz. In order to perform measurements in the linear viscoelastic region, deformation was kept at 0.001%. The storage modulus (E′) and tan δ curves as a function of temperature were recorded and analyzed using the software Dynatest 6.8. E′ is the elastic response of the material and is related to the mechanical energy stored per cycle upon deformation. E″ is the viscous response and is related to the dissipated energy per cycle when the sample is deformed. The loss factor is defined as tan δ = E″/E′, with δ being the angle between the in-phase and out-of phase components of the modulus in the cyclic motion. The temperatures Tα of the relaxation processes, corresponding to the relaxation of the networks starting to coordinate large-scale motions, were determined as the temperatures at the peak maximum of the tan δ curves. Syntheses of C5-Precursors. The three biobased epoxy precursors (BDF2EP, IDF2EP, and GTF3EP) have been prepared from ferulic acid using the chemo-enzymatic procedure previously described.52 Ferulic acid was first transformed into ethyl dihydroferulate using a one-pot−two-step reaction process involving a Fisher esterification and a palladium-catalyzed hydrogenation (85%). Ethyl dihydroferulate was then transesterified with 1,4-butanediol, isosorbide, and glycerol in the presence of immobilized Candida antarctica lipase B (aka CAL-B or Novozyme 435) to provide bis-Odihydroferuloyl 1,4-butanediol (BDF, 95%), bis-O-dihydroferuloyl isosorbide (IDF, 92%), and tris-O-dihydroferuloyl glycerol (GTF, 92%), respectively. The latter were then epoxidized using TEBAC (triethylbenzylammonium chloride), epichlorohydrin, and sodium hydroxide, providing the corresponding epoxy precursors BDF2EP, IDF2EP, and GTF3EP in overall yields of 72%, 65%, and 52%, respectively. General Carbonation Procedure. Epoxy precursor (BDF2EP, IDF2EP, or GTF3EP) (1 equiv) and lithium bromide (0.05 eq/ glycidyl groups) were dissolved in DMF (3 mL/g of epoxy precursor) and introduced into a 100 mL autoclave. Then, 20 bars of carbon dioxide were added to the system, and the latter was heated at 80 °C under stirring for 24 h. After cooling and degassing the system, the solvent was removed by distillation to give the crude product which is then solubilized in ethyl acetate and washed with distilled water and brine to remove the DMF traces. The organic phase was dried over anhydrous MgSO4 and concentrated using a rotary evaporator to provide the C5-cyclocarbonates (BDF2Cy, IDF2Cy, and GTF3Cy). BDF2Cy. 1H NMR (300 MHz, acetone-d6, ppm): δ 1.62 (m, 4H, H1), 2.61 (t, 3JH4−H5 = 9 Hz, 4H, H4), 2.86 (m, 4H, H5), 3.81 (s, 6H,

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RESULTS AND DISCUSSION Syntheses of Biobased Cyclocarbonate Precursors and DIFFA. As mentioned above, the metallic salt-catalyzed (lithium bromide) addition of carbon dioxide onto oxirane rings seems to be the simplest way to access five-membered 1448


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ACS Sustainable Chemistry & Engineering Scheme 1. Syntheses of Biobased NIPU from Ferulic Acid

Figure 1. 1H NMR spectrum of the BDF2Cy C5-precursor.

cyclocarbonates. Recently, our teams reported52 an efficient pathway to access different ferulic acid-based epoxy precursors and highlighted the influence of the epoxy precursor linker

structure (linear vs cyclic, di- vs trifunctionality, ester vs amide containing) on the final cross-linked thermosets thermomechanical properties, showing that a higher epoxy function1449


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cyclocarbonate/amine ratio is fixed to 1/1 for all the formulations. As shown in Figure 2, which pictures the BDF2Cycontaining thermoplastic series, materials are translucent,

ality has lower influence on thermoset properties than the presence of a rigid cyclic linker between the ferulic units. To determine structure−NIPU thermo-mechanical properties relationships, we used these biobased epoxy precursors as raw materials and performed the carbonation using a catalytic amount of lithium bromide (5 mol %/oxirane) under high carbon dioxide pressure (20 bar) at 80 °C (Scheme 1). The conversion of the oxirane rings into cyclocarbonates is quantitative after 24 h as determined by NMR spectroscopy. In 1H NMR, the conversion of the oxiranes into the corresponding C5-carbonate rings is highlighted by the total disappearance of the signal of the glycidyl moiety, while those of the cyclocarbonates appear at 5.15, 4.69, 4.57, 4.28, and 4.22 ppm (Figure 1). 13C NMR spectrometry can also be used to monitor the conversion; for instance, Figure S3 shows the total conversion of oxirane into cyclocarbonate for BDF2Cy. The final C5-cyclocarbonate precursor functionality is determined by integrating the signal at 5.15 ppm corresponding to the proton on the tertiary carbon of the cyclocarbonate ring (1.95 for BDF2Cy, 1.85 for IDF2Cy, and 2.40 for GTF3Cy). It is noteworthy to mention that the integration for the final C5functionality is close to the initial epoxy one, demonstrating the almost quantitative conversion of the oxiranes. 1H NMR spectra of IDF2Cy and GTF3Cy are given in Figures S1 and S2, respectively. In the case of NIPUs, one cyclocarbonate only reacts once with a primary amine. Thus, the trifunctional C5-precursor GTF3Cy allows us to access cross-linked NIPU networks due to its C5-functionality higher than 2, whereas difunctional C5precursors BDF2Cy and IDF2CY lead to linear NIPU chains. With the successful preparation of BDF2Cy, IDF2Cy, and GTF3Cy, three NIPU series were prepared via their polyaddition with diamine. As ferulic acid-based epoxy precursors exhibit low melting temperature and various studies53 having shown that the reaction of cyclic carbonate and diamine occurs faster in bulk than in solvent, the reactants are mixed without any solvent, and polyadditions were performed in bulk without adding any catalyst. NIPU thermosets and thermoplastics were then prepared by mixing the C5-precursor with the adequate amount of diamine, considering that a primary amine reacts with only one C5cyclocarbonate. Four diamines with various structures were chosen as curing agents: the oil-based aliphatic and cycloaliphatic amines and EDR148 from Huntsman and isophorone diamine (IPDA), respectively, but also two biobased diamines, the aliphatic decane diamine (DA10) from castor oil and the aromatic difurfural amine (DIFFA) which can be synthesized from renewable resources. The synthesis of biobased diamines became a topic of interest for the polymer community and for many fields looking for renewable alternatives to the oil-based diamine. The difurfuryl amine (DIFFA) that can be produced from furfural, a biobased aromatic compound potentially available from agricultural wastes and byproducts of solvent wood pulping, has attracted interest. DIFFA has already been used as curing agent for epoxy thermosets, leading to good material properties.54,55 Holfinger et al.56 have reported a single-step synthesis of DIFFA and described the mechanism involved. We decided to follow this procedure. The 1H NMR spectrum of the DIFFA synthesized is given in Figure S4. Each C5-precursor is formulated with each diamine, leading to 12 different NIPUs. It is worth noting that among the 12 NIPU polymers prepared half of them are fully biobased. The C5-

Figure 2. Picture of the BDF2Cy-containing NIPU series.

except for the IPDA-containing one. The same trend is observed for the three series. We assume that the opacity of the IDPA-containing material is due to the slight foaming during polymerization. This gas emission may be correlated to the partial carbonated state of the IPDA that leads to carbon dioxide release during heating. The various diamine structures led to NIPUs with different physical properties, from flexible and elastic materials with low Tg to rigid and brittle ones with higher Tg. Characterization of Ferulic Acid-Based NIPUs. 1H and 13 C NMR and FT-IR Analyses of Thermoplastic NIPUs from BDF2Cy and IDF2Cy. The structures of the linear prepared NIPUs were confirmed through FT-IR and 1H and 13C NMR analyses. First of all, the formation of the urethanes has been confirmed by FT-IR and 13C NMR spectroscopy with the presence of the signals at 1722 cm−1 (νCO,urethane) and 1569 cm−1 (δN−H) and the new peaks at 156.7 and 158.8 ppm, respectively (Figures S6 and S7 ). The potential transamidification of the internal esters of the ferulic acid-based cyclocarbonates by the amines has been ruled out as the specific signals of the amide were not observed in the FT-IR spectrum (νCO stretch at 1690−1630 cm−1) nor in the carbonyl region of the 13C NMR spectrum (ca. 173 ppm). The regioselectivity of the ring-opening polyaddition was also determined. Figure 3 shows the 1H NMR spectrum of BDF2Cy-DIFFA NIPU. First, one can observe the presence of a new signal between 7.5 and

Figure 3. Chromatogram of the BDF2Cy-IDPA. 1450


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ACS Sustainable Chemistry & Engineering Scheme 2. Mechanisms of the Two C5-Ring-Opening Routes

Table 1. Experimental Data from TGA, DSC, SEC, and 1H-NMR TGA

a

DSC

1

SEC

NIPU

T5 (°C)

wt %char at 900 °C

Tg(exp)/Tg(calc) (°C)

M̅ n (g/mol)

Đ

BDF2Cy-IPDA BDF2Cy-DA10 BDF2Cy-DIFFA BDF2Cy-EDR148 IDF2Cy-IPDA IDF2Cy-DA10 IDF2Cy-DIFFA IDF2Cy-EDR148 GTF3Cy-IPDA GTF3Cy-DA10 GTF3Cy-DIFFA GTF3Cy-EDR148

276 269 278 267 238 276 265 264 248 260 241 249

11.3 10.4 19.3 15.1 13.4 9.8 19.4 13.3 18.5 15.0 26.3 22.3

40/37 18/17 33/35 17/18 56/51 34/33 43/48 34/35 72/68 38/40 61/65 45/43

7700 9500 4400 5000 3500 5700 4200 3600 X X X X

1.1 1.8 1.7 1.7 1.1 1.4 1.1 1.5 X X X X

H NMR

DMA

DPn

C5-conv. (%)

DPn

RI/II

9 11 5 6 4 6 4 4 X X X X

88 >95 84 >95 79 85 75 87 X X X X

5 X 5 X 5 7 3 5 X X X X

54/46a 35/65 30/70 45/55 n.d 40/60 33/67 27/63 X X X X

Tα (°C)

E0 °C (GPa)

E120 °C (Mpa)

− − − − − − − − − 19/39 61/102 16/48

− − − − − − − − − 1.4 1.1 2.8

− − − − − − − − − 1.5 0.2 0.9

Determined from primary and secondary hydroxyl group signals.

amine and assuming that the residual C5-groups are end-chain groups, it is possible to calculate the NIPU chains DPn; for instance, 83% of conversion corresponds to 10 C5-groups opened and 2 closed. In the case of BDF2Cy-DIFFA, a DPn of 5 is calculated. The values of the as calculated DPn are given in Table 1. Gel Permeation Chromatography. The linear NIPUs from BDF2Cy and IDF2Cy were solubilized into THF in the presence of toluene as a flow marker and analyzed by SEC, with the molecular weights of the NIPU determined according to PS standards. Molecular weights of the NIPU prepared ranged between 4,000 and 10,000 g/mol, which correspond to low polymerization degrees (i.e., DPn between 4 and 11). The discrepancies between the DPn values obtained via SEC and the DPn values determined by 1H NMR (Table 1) are due to the fact that PS standards and our materials do not have the same molecular weight for a given hydrodynamic volume. Moreover, the presence of a minor part of the NIPU oligomers of lower DPn (Figure 3) induces a DPn error and minimizes the polydispersity (Đ). That is why the NIPU BDF2Cy-IDPA presents a Đ of 1.1, whereas the other NIPUs, which show a more homogeneous distribution of the molar mass, present a higher Đ of 1.7, as expected for a polyaddition. The difference observed between the SEC- and NMR-determined DPn values is also due to the presence of hydrogen bonds which minimize the hydrodynamic radius value of the solubilized NIPU chain compared to the PS standards one. The low molar masses observed for the NIPUs may be linked to the incomplete conversion of the C5-functions during the polyaddition reaction as previously determined by 1H NMR. We assume that these low conversions may be due to the increasing viscosity of the NIPU system that does not allow enough molecular motions

7.7 ppm attributed to the N−H signal of the urethane functions formed by the cyclocarbonate ring-opening during the polymerization. Two new distinct chemical shifts were also observed at 5.18 and 3.57 ppm and are attributed to the primary and secondary hydroxyl groups formed by the ringopening polyaddition through the two routes as shown in Scheme 2. The ratio of the primary hydroxyl group and secondary hydroxyl group (RI/II) was determined by integrating the signal 11 and 11′ (e.g., for BDF2Cy-DIFFA NIPU, RI:II = 0.76/1.48 = 34/66). Because of the overlapping of the −OH signals in some NIPU 1H NMR spectra, the N−H signals can also be used to calculate the RI:II. Indeed, Figure S16 shows the proton on the nitrogen of the urethane function between 7.5 and 7.7 ppm integrating for 0.45 and 1.06, respectively, and attributed to NH with primary OH group and to NH with secondary OH group, respectively. In this way, a new RI:II is obtained (0.45/1.06 = 30/70). These RI:II values show that the formation of secondary OH prevails over the formation of the primary −OH groups. This result is consistent with the literature16,57 as Tomita et al.18 already demonstrated that the electron-withdrawing group PhOCH2− stabilizes more efficiently the transition state for the secondary hydroxyl group structure, thus favoring the formation of secondary −OH compared to primary −OH. The RI:II of the BDF2Cy- and IDF2Cy-containing series calculated from the N−H signals are given in Table 1 and follow the trend described. The 1H NMR spectrum also shows a residual C5-group signal (19) at 5.09 ppm, corresponding to the proton on the tertiary carbon of the cyclocarbonate ring. The integration of this signal allows us to calculate the C5-ring conversion. For the BDF2Cy-DIFFA NIPU, this conversion is equal to [(1.93−0.32)/1.93] × 100 = 84%. As the spectrum does not show the presence of residual 1451


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thermolysis of the internal ester functions that are the more sensitive functions in these NIPUs. Concerning the high temperature char content, in the three series, DIFFA leads systematically to the highest char content of a NIPU series. Indeed, the aromaticity brought by its two furanic rings favors the charring mechanism of the NIPU during its thermal degradation. The linear DA10 provides the lowest char content since the aliphatic chains present a very low charring propensity. The IPDA and EDR148 lead to intermediate char content. We assume that the cyclic structure of IPDA and the EDR148 oxygen content may favor the cyclization and dihydroxylation mechanism, respectively. One can also notice that for the same diamine the GTF3Cycontaining NIPUs present a higher char content at 900 °C (Table 1). This is due to their cross-linked structures, which favor the charring mechanism,53 an important feature for fireretardation properties. Finally, despite their different physical properties (hard/soft), ferulic acid-based NIPUs exhibit very close thermal behaviors. Differential Scanning Calorimetric Analyses. The physical properties of a polymer may be assessed by measuring its glass transition temperature (Tg) by DSC. DSC analyses were thus performed on all NIPUs prepared and curves of the IPDA-, DA10-, DIFFA-, and EDR148-containing polymers are presented in Figure S12. Tg values obtained from the DSC curves are presented in Figure 5 and are given in Table 1. Data

for a quantitative reaction. Although the viscosity of the system may be decreased by performing the curing at higher temperature, this was not attempted as transamidation and/or chain scission may occur.6 In addition, it is noteworthy to mention that even if these NIPUs are obtained in lower molecular weights with regards to the conventional PUs and aliphatic NIPUs these molecular weights are comparable to that of fossil-based aromatic NIPUs obtained in solvent and without catalyst.6 Thermal Characterizations. Thermogravimetric Analyses. Thermal degradations of all NIPU materials were characterized by TGA under nitrogen flow to assess the influence of the monomer structure on the thermal stability and the charring propensity of the polymer. T5 represents the temperature at which the polymer loses 5 wt % of its initial mass and is representative of the thermal stability of a material; wt %char corresponds to the content of the high temperature (900 °C) stable residue. Table 1 presents the T5 and the wt %char for all the thermosets prepared. Figure 4 shows the

Figure 4. Thermograms of the DA10-containing series (10 °C/min under nitrogen).

thermograms of the DA10-containing NIPU. Thermograms of the IPDA-, DIFFA-, and EDR148-containing NIPUs are presented in Figures S8, S9, and S10, respectively. In terms of thermal degradation, the NIPU materials exhibit good thermal stabilities as their T5 range between 241 and 278 °C. It is generally observed that, for the same diamine, the BDF2Cycontaining NIPU exhibits the highest thermal stability. As the BDF2Cy-containing NIPU presents equivalent thermal stabilities (Figure S11), we assume that the thermal stability of the NIPU system is mainly correlated with the stability of the internal ester of the C5-precursor. IDF2Cy and GTF3Cy possess at least one secondary carbon in the α-position of the ester, while BDF2Cy only possesses a primary one. As the alkyl groups are inductive donator groups, our assumption is that the higher inductive effect in the case of IDF2Cy and GTF3Cy destabilized further their ester compared to the BDF2Cy one, which is subjected to a lower inductive effect. This assumption is in agreement with the observations made on the corresponding epoxy thermosets52 but also with different polyester thermal stabilities.58 One can observe that the crosslinked structure of the GTF3Cy-based NIPU does not seem to influence the thermal stability of the NIPU. It is assumed that the thermal degradation of all the NIPU starts by the

Figure 5. Tg values of the three NIPU series.

show that low molar mass NIPUs exhibit Tg values ranging between 17 and 72 °C, probably due to the aromaticity of the NIPU and to the hydrogen bonds between the carbamate functions and the primary and secondary hydroxyl group formed during the C5-cyclocarbonate ring opening. The influence of the C5-precursor is first investigated. By comparing BDF2Cy- and IDF2Cy-containing NIPU series, one can observe that, with the same diamine, the Tg values of the BDF2Cy-contining NIPU are systematically around 15 °C lower. As BDF2Cy and IDF2Cy present equivalent C5functionnalities, this difference in Tg value is most likely due to the rigidity (degree of freedom) of the linker between the ferulic units. Indeed, IDF2Cy possesses a rigid bicyclic linker (isosorbide), whereas the butane linker of the BDF2Cy is more flexible. The influence of the structure of the NIPU on its Tg is also illustrated in each series between the IDPA-containing NIPUs and DA10-contaning ones. Indeed, for the same C5precursor, IPDA-containing NIPUs present Tg values 20 °C 1452


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combinations give access to glass transition temperatures ranging from 17 to 72 °C as shown in Figure 5. A semiempirical method based on the mass-per-flexible bond (M/f) principle59 was used to explain the large range of glass transition temperatures of the ferulic acid-based NIPU. In this discussion, the chemical structure of the NIPU is assumed to be the most important factor which may influence the Tg value. Each flexible bond (allowing a free rotation around its axis) of the NIPU segment (BDF2CY, IDF2Cy, GTF3Cy, IPDA, DA10, DIFFA, and EDR148) is taken into account. In the case of GTF3Cy, we consider that the repeat unit is formed by 1 GTF3Cy and 1.5 diamine. According to the literature, C−OH and C−CH3 bonds are not considered as mobile due to the small size of the hydrogen atoms. A p-phenyl is assigned to a flexibility of 1.5 due to the rotation of the principle axis of the linear and the rotation of the single bond of the aromatic ring, which has almost no change in molecular shape. In this way, the C5-cyclocarbonate precursors segment of the NIPU, BDF2Cy, IDF2Cy, and GTF3Cy, present f values of 26, 23, and 36.5, respectively. The diamines segments of the NIPU, IPDA, DA10, DIFFA, and EDR148, present f values of 3, 11, 9, and 6, respectively. From the molar masses of the repeat units, we can calculate the mass-per-flexible bond (M/f) of each NIPU; the (M/f) values are given in Table 2.

higher than those of the corresponding DA10-containing NIPUs. This result is due to the structure of the diamine polymerized: DA10 is linear, whereas IPDA is cyclic. In summary, by playing with both the structure of the linker of the C5-precursor and that of the diamine, one can tailor the Tg and thus NIPU properties. The influence of the C5-functionality on the Tg values of the NIPU systems was then investigated by comparing the Tg values of the BDF2Cy- and GTF3Cy-containing NIPUs. For the same diamine used, GTF3Cy-containing NIPUs exhibit Tg values between 20 and 30 °C higher than those of BDF2Cycontaining ones. These results highlight the influence of the interchains covalent bonds which strongly rigidify the NIPU structure and increase the thermal energy required to provide some mobility to the segments of the network, thus increasing Tg values. Moreover, GTF3Cy-containing NIPUs remain in the solid state at temperatures higher than their Tg, whereas the difunctional C5-precursor-containing NIPUs are viscous when temperature exceeds their Tg values. One can also notice that the difunctional C5-precursor-containing NIPUs do not present any fusion enthalpy (Figure S12) due to their amorph structures. This result implies that, just like classic thermoplastics, BDF2Cy- and IDF2Cy-containing NIPUs are processable after their syntheses as shown in Figure 6, representing

Table 2. Molar Masses (M) and Number of Flexible Bonds ( f) per Repeat Unit and Mass-per-Flexible Bond alculated (M/f)

Figure 6. Picture of extruded BDF2Cy-IPDA.

BDF2Cy-IPDA NIPU that has been extruded at 80 °C. The choice of the C5-precursor is thus very important as its C5functionnality governs the type of polymer obtained: thermoplastics for C5-functionnality of 2 or thermosets for C5functionnality higher than 2. Finally, when it comes to the influence of the structure of the diamine, the following trend was observed for each NIPU series: Tg IPDA > Tg DIFFA > Tg DA10 ∼ Tg EDR148. Aromatic DIFFA brings lower properties than cycloaliphatic IPDA. The two aliphatic links between the amine functions and the furanic ring of DIFFA allow free rotation of the system and provide some mobility to balance the rigidity brought by its aromaticity. Cyclic IPDA has only one −CH2− group as the rotation axis and brings more rigidity to the system. The same trend has previously been observed52,55 with biobased epoxy thermosets. The lower Tg values are obtained when using the diamines EDR148 and DA10 due to their aliphatic linear structures, which provide almost equivalent properties to the NIPU obtained. It is worth noting that these 12 C5-precursor/diamine

NIPU

molar mass of repeat unit, M (g/mol)

number of flexible bond per repeat unit ( f)

mass-per-flexible bond (M/f)

BDF2Cy-IPDA BDF2Cy-DA10 BDF2Cy-DIFFA BDF2Cy-EDR148 IDF2Cy-IPDA IDF2Cy-DA10 IDF2Cy-DIFFA IDF2Cy-EDR148 GTF3Cy-IPDA GTF3Cy-DA10 GTF3Cy-DIFFA GTF3Cy-EDR148

817 819 881 795 873 875 937 851 1182 1185 1278 1149

29 37 35 32 26 34 29 32 41 53 45.5 50

28.17 22.14 27.53 22.70 33.58 25.74 32.31 26.60 28.83 22.36 28.09 22.98

On the basis on the arguments presented above, the Tg values were plotted against the computed (M/f) values of all the NIPUs (Figure 7). For equivalent (M/f) values, GTF3Cycontaining NIPUs lead to higher Tg values than those of the BDF2Cy due to the cross-linked structure. A good correlation for the BDF2Cy- and GTF3Cy-series and a correct one for the IDF2Cy-series were observed. This correlation can be highlighted by calculating Tg values from these linear fits. Shown in Figure 7 are the equations of the linear fits for each C5-precursor series allowing the determination of the values of the a and b coefficients in the following equation:Tg = a M/f + b, which now allows calculating Tg values from the mass-per-flexible-bond. The calculated Tg values are given in Table 1. A very good correlation between the experimental Tg values and the M/f is observed as the linearity coefficients (r2) range from 84% to 96%. These results demonstrate that the chemical structure of the NIPU is a

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thermo-mechanical characterization allows us to observe a twotime mechanical relaxation phenomenon which has not been highlighted by thermal characterization (DSC). Indeed, the EDR148- and DA10-containing NIPUs present two distinct tan δ peaks, whereas GTF3Cy-DIFFA presents a clear shoulder on the trace, allowing us to determine two mechanical transitions for each sample (Table 1). Interestingly, the Tg determined by DSC corresponds to one of the two Tα determined by DMA. Indeed, the NIPU thermosets present a tan δ peak corresponding to the Tg value previously determined around 40 °C for DA10 and EDR148 and around 60 °C for the DIFFA. The two aliphatic diamines lead to a second mechanical transition at a temperature lower than the Tg of the material, around 20 °C, whereas the DIFFA-containing NIPU presents a second mechanical transition at temperatures higher than the Tg of the material around 100 °C. It is assumed that these additional mechanical transitions are linked to the diamine structure. The 16−19 °C mechanical transitions may correspond to the relaxation of the linear aliphatic segment of the DA10 and EDR148 diamines and the one at 102 °C to that of the diaromatic segment of the DIFFA, whereas the 39−61 °C transitions are attributed to the GTF3Cy network segments. These results tend toward structured thermosets with soft segments (fully reacted diamines but also potential partially reacted diamines that act as plasticizers) and hard segments (GTF3Cy), the latter being impacted by the soft ones as suggested by the rather large range observed for the transitions attributed to GTF3Cy. Such two-time mechanical transitions are of great interest as they allow the NIPUs to exhibit intermediate mechanical behavior, between the glassy and the rubbery state, in a short temperature range. Even if DMA is not ideal to determine precisely the elastic modulus (E′) of the NIPU thermosets, it gives an order of magnitude for these values (Table 1), showing the strong mechanical behavior of these materials with E′ > 1 GPa below their Tg. At the rubbery state, DIFFA leads to lower elastic modulus than those of the DA10 or EDR148. This is representative of the lower cross-link density of the DIFFAcontaining thermoset linked to its higher molar mass.

Figure 7. Experimental Tg values plotted against the calculated massper-flexible-bond.

parameter of great importance as it seems to govern mainly the Tg of the polymer. Thermomechanical Characterization of Ferulic AcidBased Thermosets. Dynamic Mechanical Analyses (DMA). To assess the mechanical properties of the cross-linked NIPU materials, the thermosets prepared from GTF3Cy were characterized by DMA. Unfortunately, due to the slight foaming of the GTF3Cy-IPDA thermosets, this NIPU could not be mechanically characterized. The considered parameters were the elastic modulus values at the glassy state and at the rubbery state, and the Tα values that are given in Table 1. The DMA curves of the DA10-, EDR148-, and DIFFA-containing thermosets are presented in Figure 8. First, GTF3Cy-

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CONCLUSION With the low availability and fluctuating prices of fossil resources, and new regulations that restrict the use of harmful precursors, it becomes urgent to find renewable and safe alternatives to the current petrobased building blocks used in polymers and materials. In this study, a new and efficient method for the chemo-enzymatic syntheses of renewable aromatic C5-bis- and triscyclocarbonates from CO2, ferulic acid, and biobased diols (glycerol, isosorbide, etc.) has been reported. This method is not only greener but also avoids the use of harmful precursors since the phenolic precursors do not exhibit any endocrine disruptive activity. These C5-cyclocarbonates then were used as building blocks for the preparation of different NIPU in the presence of four diamines under solvent-free and catalyst-free conditions, biobased diamines DIFFA and DA10 leading to fully biobased NIPUs. Thermo-mechanical properties characterization of these NIPUs revealed not only the importance of the C5-cyclocarbonate functionality to obtain linear thermoplastic chains or crosslinked thermoset networks but also the structure of the diol/ triol used as linker as it governs the physical behavior of the material (linear vs cyclic, thermoplastic vs thermoset). Moreover, the structure of the diamine influences strongly the Tg

Figure 8. DMA E′ (top curves) and tan δ traces (bottom curves).

containing NIPUs exhibit thermoset thermo-mechanical behaviors. Indeed, below their transition temperature, the three NIPUs show a glassy plateau (rigid material). At temperatures higher than their Tg, the value of the elastic modulus is reduced until a rubbery plateau showing a particular structuration of the polymer due to cross-linking points. Furthermore, the presence of a rubbery plateau for each NIPU sample reveals an elastomeric behavior for these materials. It is also observed that the two aliphatic based-NIPUs show equivalent and low Tα, while the DIFFA-containing NIPU exhibits a higher transition as observed by measuring the Tg values. Concerning the NIPU thermal transition behavior, the 1454


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(5) Sardon, H.; Pascual, A.; Mecerreyes, D.; Taton, D.; Cramail, H.; Hedrick, J. L. Synthesis of Polyurethanes Using Organocatalysis: A Perspective. Macromolecules 2015, 48, 3153−3165. (6) Maisonneuve, L.; Lamarzelle, O.; Rix, E.; Grau, E.; Cramail, H. Isocyanate-Free Routes to Polyurethanes and Poly(hydroxy Urethane)s. Chem. Rev. 2015, 115 (22), 12407−12439. (7) Karol, M. H.; Jin, R.; Lantz, R. C. Immunohistochemical detection of toluene diisocyanate (TDI) adducts in pulmonray tissue of guinea pigs following inhalation exposure. Inhalation Toxicol. 1997, 9 (2), 63−84. (8) Karol, M. H.; Kramarik, J. A. Phenyl isocyanate is a potent chemical sensitizer. Toxicol. Lett. 1996, 89 (2), 139−146. (9) Hill, J. W.; Carothers, W. H. Studies of Polymerization and Ring Formation. XXI. Physical Properties of Macrocyclic Esters and Anhydrides. New Types of Synthetic Musks. J. Am. Chem. Soc. 1933, 55 (12), 5039−5043. (10) Hill, J. W.; Carothers, W. H. Studies of Polymerization and Ring Formation. XX. Many-Membered Cyclic Esters. J. Am. Chem. Soc. 1933, 55 (12), 5031−5039. (11) Spanagel, E. W.; Carothers, W. H. Macrocyclic Esters. J. Am. Chem. Soc. 1935, 57 (5), 929−934. (12) Whelan, J. M., Jr.; Hill, M.; Cotter, R. J. Multiple Cyclic Carbonate Polymers. U.S. Patent 3072613, 1963. (13) Mikheev, V. V.; Svetlakov, N. V.; Sysoev, V. A.; Gumerova, R. Kh. Zh. Org. Khim. 1983, 19 (3), 498−501. (14) Kihara, N.; Endo, T. Synthesis and properties of poly(hydroxyurethane)s. J. Polym. Sci., Part A: Polym. Chem. 1993, 31 (11), 2765−2773. (15) Kihara, N.; Kushida, Y.; Endo, T. Optically active poly(hydroxyurethane)s derived from cyclic carbonate and L-lysine derivatives. J. Polym. Sci., Part A: Polym. Chem. 1996, 34 (11), 2173−2179. (16) Tomita, H.; Sanda, F.; Endo, T. Structural analysis of polyhydroxyurethane obtained by polyaddition of bifunctional fivemembered cyclic carbonate and diamine based on the model reaction. J. Polym. Sci., Part A: Polym. Chem. 2001, 39 (6), 851−859. (17) Tomita, H.; Sanda, F.; Endo, T. Polyaddition behavior of bis(five- and six-membered cyclic carbonate)s with diamine. J. Polym. Sci., Part A: Polym. Chem. 2001, 39 (6), 860−867. (18) Tomita, H.; Sanda, F.; Endo, T. Model reaction for the synthesis of polyhydroxyurethanes from cyclic carbonates with amines: Substituent effect on the reactivity and selectivity of ring-opening direction in the reaction of five-membered cyclic carbonates with amine. J. Polym. Sci., Part A: Polym. Chem. 2001, 39 (21), 3678−3685. (19) Figovsky, O. L.; Shapovalov, L. D. Poly(hydroxy urethane) coatings prepared from copolymers of 3-(2-vinyloxyethoxy)-l,2propylene carbonate and N-phenylmaleimide. Macromol. Symp. 2002, 187 (1), 325−332. (20) Benyahya, S.; Boutevin, B.; Caillol, S.; Lapinte, V.; Habas, J.-P. Optimization of the synthesis of polyhydroxyurethanes using dynamic rheometry. Polym. Int. 2012, 61 (6), 918−925. (21) Besse, V.; Foyer, G.; Auvergne, R.; Caillol, S.; Boutevin, B. Access to nonisocyanate poly(thio)urethanes: A comparative study. J. Polym. Sci., Part A: Polym. Chem. 2013, 51 (15), 3284−3296. (22) Rokicki, G.; Kuran, W. Cyclic Carbonates Obtained by Reactions of Alkali Metal Carbonates with Epihalohydrins. Bull. Chem. Soc. Jpn. 1984, 57 (6), 1662−1666. (23) Reithofer, M. R.; Sum, Y. N.; Zhang, Y. Synthesis of cyclic carbonates with carbon dioxide and cesium carbonate. Green Chem. 2013, 15 (8), 2086−2090. (24) Liang, S.; Liu, H.; Jiang, T.; Song, J.; Yang, G.; Han, B. Highly efficient synthesis of cyclic carbonates from CO2 and epoxides over cellulose/KI. Chem. Commun. 2011, 47 (7), 2131−2133. (25) Paddock, R. L.; Nguyen, S. T. Chemical CO2 Fixation: Cr(III) Salen Complexes as Highly Efficient Catalysts for the Coupling of CO2 and Epoxides. J. Am. Chem. Soc. 2001, 123 (46), 11498−11499. (26) Kilic, A.; Ulusoy, M.; Durgun, M.; Tasci, Z.; Yilmaz, I.; Cetinkaya, B. Hetero- and homo-leptic Ru(II) catalyzed synthesis of cyclic carbonates from CO2; Synthesis, spectroscopic characterization

values (linear vs cyclic, aliphatic vs aromatic). Another important feature of these NIPUs is that their low molar masses do not prevent to reach high Tg values. Indeed, NIPU with Tg ranging from 17 to 72 °C may be prepared from these ferulic acid-based C5-precursors, leading to soft and flexible or hard and brittle materials. Equally remarkable, the thermosets presented show a two-time mechanical transition which could lead to structured materials of interest for PU applications. This work demonstrates the great potential of this new class of biobased aromatic architectures to design new C5-cyclocarbonate precursors for health and environmentally friendly NIPU syntheses. Although the NIPUs were obtained with relative low molecular weights, the latter may be increased further by performing the polymerization in a polar solvent such as DMSO and in the presence of a catalyst. To continue the expansion of the polymer material market, original mechanical behaviors are desired, especially in the shock absorption field with composites. To go further in the “greening” of the polymer market, the influence of hemp fiber content on mechanical properties of the thermoplastics NIPU for the preparation of fully biobased hemp/NIPU composites will be studied and reported in due course.

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ASSOCIATED CONTENT

* Supporting Information S

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acssuschemeng.6b02022. DSC and TGA traces and SEC chromatograms, as well as 1 H and 13C NMR spectra. (PDF)

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AUTHOR INFORMATION

Corresponding Authors

*E-mail: [email protected] (S.C.). *E-mail: fl[email protected] (F.A.). ORCID

Florent Allais: 0000-0003-4132-6210 Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS The authors thank Dr. Claire Negrell and Dr. Vincent Ladmiral for their help with SEC analyses and Dr. Marine Janvier for her help on the purification of cyclocarbonates. The authors are also grateful to the Region Champagne-Ardenne, the Conseil Départemental de la Marne, and Reims Métropole for their financial support.

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REFERENCES

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