Synthesis of bio-based building blocks from vegetable oils : a platform chemicals approach

In recent years, the sustainability is becoming increasingly important for the chemical industry; thus, the use of renewable resources has gained interest in polymer applications. Indeed, overall demand for chemical products will increase by 50% in volume by 2020 (Prudhon, 2010). Thus, American studies estimate that 90% of organic chemicals will come from renewable resources by 2090 (Eissen et al., 2002). However, it is not sufficient to synthesize exactly the same chemicals from renewable resources, even if they are harmful. Biobased chemicals could also be very dangerous. Newprocesses have to be developed to replace hazardous reactives by harmless, biobased ones. Vegetable oils are extracted primarily from the seeds of oilseed plants. Their competitive cost, worldwide availability, and built-in functionality (ester functions and insaturations) make them attractive. The development of oleochemicals has been carried out from two distinct ways. The first one corresponds to the double-bond modification (Gunstone et al., 2001) of crude oils or fatty acid derivatives. The second one is the carboxylic acid group modification of vegetable oils (Corma et al., 2007). The chemical functionalizations of unsaturated oils to produce polyols have been widely developed to prepare new polyurethane structures, which depend on triglyceride and isocyanate reagents used (Zanetti-Ramos et al., 2006; Yeganeh et al., 2007; Guo et al., 2000). Demand for renewable resources is also increasing for polymers and composite applications. This demand is particularly strong for polyurethanes (PUs) and epoxy resins (ER) with a global production of respectively 14 Mt and 2 Mt per year (Shen et al., 2009). These polymers became among the most dynamic groups of polymers, exhibiting versatile properties suitable for use in practically all the fields of polymer applications – foams, elastomers, thermoplastics, thermosets, adhesives, coatings, sealants, fibers, and so on. In this context, our team synthesized new building blocks from vegetable oils in order to synthesize biobased PUs and ER materials. Experimental conditions and characterizations of these works were previously reported and scale-up was performed by Specific Polymers Company, Av. de l’Europe, 34830 Clapiers France.

In recent years, the sustainability is becoming increasingly important for the chemical industry; thus, the use of renewable resources has gained interest in polymer applications.Indeed, overall demand for chemical products will increase by 50% in volume by 2020 (Prudhon, 2010).Thus, American studies estimate that 90% of organic chemicals will come from renewable resources by 2090 (Eissen et al., 2002).However, it is not sufficient to synthesize exactly the same chemicals from renewable resources, even if they are harmful.Biobased chemicals could also be very dangerous.New processes have to be developed to replace hazardous reactives by harmless, biobased ones.Vegetable oils are extracted primarily from the seeds of oilseed plants.Their competitive cost, worldwide availability, and built-in functionality (ester functions and insaturations) make them attractive.The development of oleochemicals has been carried out from two distinct ways.The first one corresponds to the double-bond modification (Gunstone et al., 2001) of crude oils or fatty acid derivatives.The second one is the carboxylic acid group modification of vegetable oils (Corma et al., 2007).The chemical functionalizations of unsaturated oils to produce polyols have been widely developed to prepare new polyurethane structures, which depend on triglyceride and isocyanate reagents used (Zanetti-Ramos et al., 2006;Yeganeh et al., 2007;Guo et al., 2000).Demand for renewable resources is also increasing for polymers and composite applications.This demand is particularly strong for polyurethanes (PUs) and epoxy resins (ER) with a global production of respectively 14 Mt and 2 Mt per year (Shen et al., 2009).These polymers became among the most dynamic groups of polymers, exhibiting versatile properties suitable for use in practically all the fields of polymer applicationsfoams, elastomers, thermoplastics, thermo-sets, adhesives, coatings, sealants, fibers, and so on.In this context, our team synthesized new building blocks from vegetable oils in order to synthesize biobased PUs and ER materials.Experimental conditions and characterizations of these works were previously reported and scale-up was performed by Specific Polymers Company, Av. de l'Europe, 34830 Clapiers France.

Polyurethane precursors
PUs are obtained by the reaction of an oligomeric polyol (low molecular weight polymer with terminal hydroxyl groups) and a diisocyanate (or polyisocyanate).However, diisocyanates are not biobased and are generally very harmful reactants for human health.Thus, most used diisocyanates, methylene diphenyl diisocyanate (MDI) and toluene diisocyanate (TDI) are CMR products.Therefore the substitution of these compounds is crucial.To answer Abstract: This review reports the synthesis of various building blocks from vegetable oils in one or two-steps syntheses.Thiol-ene coupling allows to synthesize new biobased reactants with various function and functionality with reaction conditions in agreement with green chemistry principles: it does not use neither solvent nor initiator or need simple purification step, feasible at industrial scale.Esterification and amidification were also used to insert ester or amide groups in fatty chains in order to modifiy properties of thereof synthesized polymers.Building blocks synthesized have various functions and functionality: polyols, polyacids, polyamines and dicyclocarbonates from vegetable oils and from glycerine derivatives.They were used for the synthesis of biobased polyurethanes, polyhydroxyurethanes and epoxy resins.
these questions, we proposed various solutions (figure 1).In a first approach, since polyols correspond to 70% w/w of PU we synthesized new biobased polyols from vegetable oils.In a second approach, we used a reaction which is currently gaining much attention as an alternative route for the synthesis of PUs: step-growth polyaddition of dicyclocarbonates and diamines (Whelan et al., 1963;Mikheev et al., 1983).This method is quite interesting since no hazardous isocyanates are used and dicyclocarbonate reactants can be obtained from renewable resources such as glycerin.Moreover, this route allows the synthesis of polyhydroxyurethanes (PHUs) with hydrogen bonds, which have higher chemical resistance and better hydrolysis behavior.

Synthesis of di-and polyols by thiol ene coupling
On one hand, Soybean oil was reacted with mercaptoethanol in presence of an initiator (figure 2).The study of the addition of mercaptoethanol on oleic acid allowed defining the experimental conditions (Desroches et al., 2011): synthesis was done in mass, with a ratio of thiol/double bonds of 3:1, at 808C in the presence of AIBN with a ratio initiator/double bonds of 0.1/1.( Caillol et al., 2012).On the other hand, we have developed a synthetic strategy, which allows reaching a wide range of soft pseudo-telechelic diols from vegetable oils methyl esters.The soft segments of vegetable oils were comprised of either ester groups (one or two) or amide groups (one or two) with various spacer lengths between hydroxyl groups (figure 3).Thus, the synthetic pathway was the following: 1) transesterification with a diol or amidification with hydroxylamine reactant; 2) thiolene radical coupling in presence of mercaptoethanol (Desroches et al., 2012).Two main parameters seemed to govern the physical properties of these pseudo-telechelic diols: the nature of ester/amide group and the spacer length.These parameters positively or negatively influenced the hydrogen bonding between pseudo-telechelic diols and thus modified their physical properties.For instance, the glass transition temperature decreased when the spacer length increased, whereas the melting temperature of amide containing pseudo-telechelic diols was much higher than that of ester containing pseudo-telechelic diols.
These pseudo-telechelic diols were reacted with MDI to elaborate PUs.It is particularly interesting to note that the thermostability of these PUs was lowered in the presence of amide groups.In the other hand, PUs with amide groups exhibited the highest glass transition temperatures (around 608C), due to hydrogen bonding enhancement.Furthermore, chain length between functional groupsester and amidemodified the rigidity of corresponding PUs.Finally, we demonstrated that amide groups influence the curing behavior through a catalytic effect onto the isocyanate-alcohol reaction (gel times around 40 min for diols with amide groups and around 200 min for diols with ester groups).

Polyols by epoxide ring opening
We also worked on epoxidized vegetable oils which are interesting industrial biobased resources.We thus synthesized biobased polyols by epoxide ring opening of epoxidized vegetable oils, with three different acids (figure 4): lactic and glycolic acids were selected since they are both biobased and present respectively a secondary and a primary hydroxyl group.Acetic acid, without hydroxyl group, was selected due to its low cost and widespread use in chemical industry.The polyol obtained from lactic acid is the most interesting in terms of renewable carbon content.It is noted that reactions occurred in mass, at relatively low temperatures, without initiator or purification, which meets the principles of green chemistry (Caillol et al., 2012).
The three synthesized polyols led to materials with similar thermal and mechanical properties (Tg values around 508C, tensile strengths at break > 20 MPa and Young Moduli > 900 N/mm 2 at 238C), except the gel time which strongly depended on the type of hydroxyl function of the precursor (from 370 min for glycolic acid polyol, which exhibits primary alcohols, to 690 min for acetic acid polyol, which bears only secondary alcohols).The tree PUs obtained from these polyols present a high content of renewable carbon, around 70%.The synthesis of PUs from vegetable oil based polyols was extensively reported in the literature.It is possible to compare PU from biobased polyols reacted with pure or modified MDI, with a NCO/OH ratio ranging from 1.00 to 1.05 (figure 5).(Petrovic et al., 2000) (Ep-HCl, Ep-HBr), or by acids (Miao et al., 2010) (Ep-lactiq, Ep-glycolic, Ep-acetic) or alcohols (Pechar et al., 2006) (Ep-MeOH).Amide diols synthesized by our team (MAD, DAD or MAT) led also to high Tg-PUs.(hydroxymethyl)-1,3-dioxolan-2-one (glycerin carbonate) (Benyahya et al., 2011).Dicyclocarbonate was synthesized by UV thiol-ene coupling of AGC with a 2,20-oxydiethanethiol (figure 6).This photochemical thiol-ene reaction was carried out under air, with neither solvent nor photoinitiator.

Hardeners for epoxy resins
The development of ecofriendly curing agents for epoxy resins is of great importance.Few solutions of nontoxic amine hardeners are reported in literature (Fenouillot et al., 2010).The diamines the most used in industry are methylenedianiline (MDA) and diaminodiphenylsulfone (DDS).However, DDS is toxic and MDA is a CMR chemical.Therefore their use is very harmful and should be avoided.Others amines are also used as epoxy resin hardeners, such as isophorone diamine and N-aminoethyl piperazine, but these amines remain toxic for human and environment.Besides amines, acid hardeners lead to interesting curing properties and some studies have proposed nontoxic or biobased acid hardeners for epoxy resins.Thus, a study reports the use of abietic acid and maleic acid to synthesize a diacid for epoxy curing (Wang et al., 2011).Acid functionalized lignin was also reported as epoxy hardener (Hiroko et al., 2009).Modified lignin with acid derivatives of mono and disaccharides were also used as hardeners (Hirose et al., 2003).
Hardening of epoxy resins is performed at 1308C with reaction time between 6 and 10 hours.Moreover poly(styreneco-acrylic acid) or poly(acrylic acid) was also used as acid hardener (Heba et al., 2003).The curing is rather slow, and uncompleted even at 1008C.Amino acids have also been studied, particularly lysine and tryptophan (Li et al., 2006).
In both cases curing were performed above 1508C, even with a catalyst.All these works showed that only few acids and amine hardeners for epoxy have been synthesized in the past from renewable resources.Moreover, the applied methodologies lead generally to mono or difunctional precursors or imply multistep processes with low yields and formation of many byproducts.Thus, we present the synthesis of polyacids based on unsaturated triglycerides thanks to the thiol-ene coupling and polyamine thanks to the amidification reaction (figure 7).

Polyacids synthesized by thiol-ene coupling
New vegetable acids hardeners were prepared using thioglycolic acid by thiol-ene coupling (figure 8).The resulting polyacid exhibited a mean functionality of 3.

Polyamines synthesized by amidification reaction
Amine harderners were also synthesized by amidification of vegetable oils with diethylene triamine (figure 9).The product of the reaction is an amido-amine with an average functionality of 3.
The monoadduct was used as amine hardener with BADGE epoxy precursors.
The resin obtained exhibited a Tg of 328C.Other amines were designed from vegetable oils, by dimerization followed by amidification (Fomina, 2010), by thiol-ene coupling (Stemmelen et al., 2011), by nitrile synthesis (Dubois, Gillet, 2008) or by a 3 step reaction from epoxydized oil (Zao et al., 2008).But our method allows to synthesize fatty amidoamine in a one-step reaction.

Conclusion
We developed a real chemical toolbox based on thiol-ene coupling and amidification/esterification to synthesize a library of biobased building blocks with various functions and functionality from vegetable oils.The synthesized building blocks reported in this contribution are polyols, polyacids, polyamines and dicyclocarbonates from vegetable oils and from glycerine derivatives.They led to polymer synthesis such as polyurethanes, polyhydroxyurethanes and ep-oxy resins.These biobased building blocks led to polymers with various properties: low Tg polymers for coating or higher Tg polymers for composites.

Figure 5 .
Figure 5. Tg comparison of PUs obtained from functionalized vegetable oils and MDI-based isocyanate (blue for literature, green for our syntheses) (determined by DSC).
Synthetic pathways from vegetable oils to epoxy resins precursors.Dicyclocarbonate synthesis by thiol ene coupling on AGC.

Table 1 .
Gel time at different curing temperature of epoxy resins.