Review on synthesis of isocyanate free polyurethane using sustainable routes and its applications

Excerpt: Polyurethane(PU) is most commonly used polymer in various of applications due to its excellent properties.

Abstract

Polyurethane(PU) is most commonly used polymer in various of applications due to its excellent properties. Conventional polyurethane are mostly synthesized by the reaction of isocyanates, polyols and chain extenders. Isocyanates used in this process increases a various health issue. To overcome come all these drawback of PU alternative method of polyurethane synthesis is developed. In this review Sustainable routes for the synthesis of Non-isocyante polyurethane(NIPU) reported . Currently few method of NIPU synthesis reported such as polyaddition, polycondensation, rearrangement and ring opening polymerization are presented in this article. Attention has been given by researchers towards the synthesis of non-isocyanate polyurethane(NIPU),polyhydroxylurethane(PHU) by using most popular and industrially important by the reaction of cyclic carbonate with diamine. This review also summarizes the synthesis of cyclic carbonate from various routes.

Keywords: Non-isocyanate polyurethane; Poly(hydroxyurethane); Transurethanization; cyclic carbonate

Introduction

POLYURETHANE (PU) synthesis started in the 1930s, Ottos and coworkers. They reported reaction between polyol and diisocynate to get first PU which shows outstanding adhesive properties1. Polyurethane are refer as most adaptable polymer till a decade's for wide range of application. The major application area are flexible foam, elastomers, coatings, sealants, adhesives. Polyurethane become most versatile polymer due to its various properties such as high elasticity, thermal and chemical stability, abrasion resistances and other excellent properties. In a last few days polyurethane found application as biomedical material due to their excellent biocompatibility and biostability2.

Polyurethane are the sixth most widely used polymers with a global production of 18 Mt in 2016 based on the annual worldwide production . The major part of polymer production completed in Asia and then Europe and finally in United State of America and the key player of polyurethane production , Covestro AGC(Germany),BASF SE(Germany),The Dow(US),Huntsman(US) and Yantai Wanhua(China) secure for over 35% share of total market.

Conventional polyurethane are synthesized from diisocyanate or polyisocyanate ,polyol, and chain extender. The first step involves the reaction between a polyol and an excess of diisocyanate which gives a polyurethane prepolymer with NCO end terminals. In the second step of reaction prepolymer react with extender. This two step process allows to overcome the differencs of reactivity between polyol and hence improve the material property(Scheme 1)3. Isocyanate is main starting material in urethane production. Isocyanates requires use of phosgene, to convert amine into isocyanate. Phosgene is a colorless, highly reactive and highly toxic gas. Discloser to this toxic gas causes several ocular irritation and burn to the eye and skin. Most commonly used isocyanates in PU industry are MDI(methylenediphenyl diisocyanate) and TDI(Toluene diisocyanate) these material have very dangerous effects on human health and environments. These material are categories as carcinogenic, Mutagenic and Reprotoxic.4,5 These creates a need to development of an alternative method for polyurethane synthesis. The latest advances in PU research focus on the replacement of isocyanate.

Synthesis of non-isocyanate polyurethane from non-toxic route

Non-isocyanate polyurethane (NIPU) can be synthesized from four routes: polycondensation, ring-opening polymerization, polyaddition and rearrangement reaction. Lise et al. discus the different terms of chemistry and polymer properties from chemical point of view and review the routes towards phosgene free6. Dyer and Scott first time used of ethylene carbonate and primary amine to produce isocyanate free urethane.2-Hydroxyethylycarbamate synthesized by reacting ethylene carbonate with primary amine with removal of ethylene glycol as a by product under vacuum distillation at 1500C in presences catalytic amount of barium oxide(Scheme-2 a) also substituted polyurethane synthesized by reacting ethylene carbonate with amino alcohol such as 10amino-1-decanol and 4-aminomethylbenzyl alcohol(Scheme-2b).7

NIPU from Transurethanization process

Condensation process of NIPU mainly depends upon the reaction between carbamate with alcohol and this reaction is called as transurethane reaction(scheme 3). PU synthesized from polycondensation have a same properties and structure like PU synthesized from polyaddition reaction of polyol and diisocyanate. Deepa et al. developed new solvent and isocyanate free transurethanization process for synthesis of PU.. This work is more beneficial for synthesis of aliphatic and cycloaliphatic polyurethane and condensation of A+B,A-A+B,A-A+B-B aliphatic and cycloaliphatic urethane linkage.8 Lijing et al. synthesized bio-based diisocyanate free unsaturated poly(ester urethane) by metal catalyzed melt polycondensation of itaconic acid with urethane diols.9 There are three main routes for Isocyanate-free polyurethane synthesis through transurethanization process;

  • AB types monomer synthon
  • Bis-alkylcarbamate
  • Bishydroxylalkylcarbamte

AB type monomer synthesis process

This type of polymerization requires a difuctional monomer for perform the polymerization. More et al, prepared AB-type self condensable reaction of hydroxyl-acyl azide moiety to obtaine vegetable oil based polyurethane10,12(Scheme 4). Calle et al. prepared PU and PUrs (polyurea) from castor oil by AB type monomer approach to synthesized Ѡ-Hydroxy- or Ѡ-amino methyl carbamate ester precursor monomer under mild condition from crysteamine methyl carbamate by thiol-ene addition. They obtained good PU conversion at 120° C for 8and 14h in presences of Ti(OBu)4 catalyst (Scheme 5).13 Sardon et al. Synthesized catalyst and isocyanate free polyurethane via polycondensation of diamine with activate carbonates in aqueous media. They reported preparation of high molecular weight PU in a aqueous media using homogeneous polymerization method.14 Bhaskar et al. synthesized poly(amide-urethane) from e-caprolactum, amino alcohol and phenyl or ethylene carbonate in three step. These prepared polymer containing alternate amide and urethane linkage. In a last step polycondensation of α-hydroxy-Ѡ-O hydroxyethyl urethanes and α-hydroxy-Ѡ-O hydroxyethyl urethanes perform at 150°C and 90° C respectively. They found that due to presences of urea group the polymer chain the melting point of these polymer are lower and they can be used for building block for power coating.15

Polyurethane from Bis-Hydroxyalkylcarbamate

PU synthesis by polycondnsation of Bis-hydroxylurethane with diol. Bis-Hydroxyalkylcarbaamte are directly obtained by reacting cyclic carbonate with diamine . Rokicki et al. synthesized bis-hydroxyethyloxycarbonylamino) hexane and bis-hydroxyethyloxycarbonylamino)butane at room temperature by preparing reaction between ethylene carbonate and 1,6-hexanediamin and 1,4-butanediamine in methylene chloride(Scheme 6).16 Bungo et al. synthesized and studied the self polycondensation of 1,6-bis(hydroxyethyloxy carbonyl amino)hexane (BHCH) and used to prepare polyurethane.17 Similarly Richard et al. used an enzymatic pathway for synthesis of novel polyurethane by using Candida Antarctica lipase B. These new polymer have potential used in biomaterial and bioplastics application(scheme 7).18 Chenguo et al. synthesized high molecular weight PU prepared by melt transurethane polymerization of hydroxyl functional urethane diol with HO Terminal group (H2N-PA-OH) . This Poly(amide-urethane ) having short nylon 6 segment. This PU has good tensile strength but brittle. New PU with Tm above 128°c has very good toughness and tensile strength.19 Wang et al synthesized Non-isocyanate thermoplastic polyurethane(NI-TPUs) containing dibutylene terephthalate in unit. They first prepared bis(4-hydroxybutyl) terephthalate(BHBT) by condensation of dimethyl terephthalate with excess 1,4-butandiol.NI-TPUs synthesized by transurethane polycondensation of 1,6-bis (hydroxyethyloxy carbonyl amino)hexane with BHBT at different molar ratio under reduced pressure(scheme 8) . NIPUs containing aromatic units improves the mechanical properties of polymer.NI-TPU exhibits a Mn above 14200,Mw above 19700,Tm ranging from 123.8 to 141.1 °C and tensile strength up to 37.89 MPa with strain at break of 475.28%.20 For the first time Mariusz et al. studied the wettability and surface energy of NIPU coating based on the bis(2,3-dihydroxylpropyl)ethyl dicarbamate. They also extensively study on contact angle of NIPU coating with dispersed and polar solvent. Their result indicates the limitation of application of NIPU coating in high humidity conditions.21

Polyurethane from Bis-Alkylcarbamate

Earlier bis-alkylcarbamate can be directly synthesized by reacting diisocyanate with alcohol. In order to remove the use of isocyanate, bisalkylcarbonate directly react with diamine to get bisalkylcarbamate. The most commonly used dicarbonate is dimethyl carbonate(DMC). It was originally formed by phosgene route. Currently it is synthesized by reacting phosgene free route by the reaction of CO2 , methanol, and dioxygen.22 It is directly synthesized from CO2 and methanol. Later on Maike et al. synthesized NIPU by polycondensation of bis(methylcarbamates) with diols in presences of TBD (1,5,7-triazabicyclo[4.4.0]dec-5-ene)catalyst. The key step for synthesis of bis(methyl carbonate) monomer from plant oil derived dicarboxylic acid is based on a sustainable base‐catalyzed Lossen rearrangemen.23Later on Charloatte et al.also reported a fully renewable NIPU using transurethanization approach by using TBD as catalyst. First they synthesized dicarbamate molecules by reacting several linear and branched diamine with excess of DMC. They reported linear and branched NIPU, both showed good thermal stability compared to those of commodity polymer and such polymer are used to modify the properties of existing PU or as powder coating.24

Martin et al. synthesized new biobased allyl terminated renewable polyurethane and Polyureas by using transurethanization approach for different application in coating. Allyl terminated oligomer shows a good thermal stability and crystalline behavior. These PUras and PU crosslink by using benzophenone as a photoinitiataor.25

Cyclic carbonate pathway(Polyaddition)

In 1957,Dyer and Scott reported the polyaddition reaction of five membrane(CC5) cyclic carbonate with amine for the synthesis of urethane. They found that bis(2,hydroxylethyl carbamate)s synthesized from ethylene carbonate and primary amine with removal of ethylene glycol under vacuum distillation in presences of catalyst.7 It is also possible to prepare NIPU from 6-membrane(CC6) 26, 7-membrane(CC7) cyclic carbonate27 and 8-membrane(CC8).28 Yuen et al. aminolysis of 5CC- membrane and 6CC-membrane required a high temperature to obtain NIPU with high molecular weight as compared 7-CC membrane and 8-CC membrane. N-substituted 8-membrane carbonate show high reactivity towards amine at low temperature and obtained high molecular weight NIPU.

Reactivity of cyclic carbonate and amines reaction

During the process of NIPU formation ,the addition of polyamine or amines to cyclic carbonate is referred as nucleophilic attack followed by deprotonation reaction. In the first step of reaction amine attack on the carboxyl group of cyclic carbonate which form a tetrahedral intermediates . The ring opening reaction of cyclic carbonate with amine observed very slow at room temperature due to its chemical stability. In the second step another amine group attack on the tetrahedral intermediate which result in removal of hydrogen. Carbon oxygen bond is then broken and which in turn leads to generation of the alkyl-oxygen anion.35,36 This newly generating alkyl-oxygen ion combines with hydrogen ion which result in rapid formation of NIPU. This polyaddition reaction of cyclic carbonate and amine generally gives two isomers as shown in scheme 10.

Synthesis of cyclic carbonate

Most beneficial way of synthesizing cyclic carbonate is by ring opening and insertion of carbon dioxide on oxirane ring. John et al. review on the cyclic alkylene carbonate as reactive intermediate and they have numerous application in polymer, surfactant, plasticizers, cross-linking agents and many more.37 Also Michel North et al. review on the conversion of inexpensive ,waste CO2 in to useful product and benefits of from this 100% economical reaction and eliminating hazardous phosgene as a reactant for cyclic carbonate synthesis . Most commonly used catalyst in synthesis process are Sn(II),Mn(II),Fe(II),oxides and carbonates.38,39 Many organic or inorganic compound is use such as amines, phosphanes, organic halide, alkali metal salt, magnesium oxide in fixation of carbon dioxide.40 Recently Jing review progress in synthesis cyclic carbonate and their reaction mechanism and different application using NIPU.41

Synthesis of 5-membrane cyclic carbonate

There are so many routes available to 5-membrane cyclic carbonate synthesis. Currently cyclic carbonate such as ethylene and propylene carbonate synthesized from respective oxides and CO2 on industrial level. 38 Synthesis of cyclic carbonate mainly take placed in presences of lewis acid or base catalyst which requires high temperature and pressure. The epoxide ring mostly activated by interaction oxygen with levis acid. Most of the catalytic system developed for levis acid ,nucleophilec attack on oxirane ring which cause the opening of epoxide ring. Many of the catalytic system developed for this reaction which contain levis acid site for the activation of electrophiles and lewis base for activation of nucleophiles.39 Hendrik et al recently review on the various approaches for the synthesis of cyclic carbonate (Scheme 11) ,The development in catalyst system which able to obtained conversion of oxirane at low CO2 concentration and pressure. Metal catalyst shows higher reactivity as compared to organomettalic catalyst42. Metal catalyst requires oleum salt as co-catalyst.43 Li et al synthesized another promising method for direct synthesis of cyclic carbonate from oleum and CO2 by using N-bromosuccinimide(NBS) together with 1,8-diazabicyclo[5.4.0]undecenc-7-ene(DBU)in water or by using a catalytic amount of bromide ion together with aqueous H2O(Scheme-12).44

Alkali metal salt seems to be active catalyst for reaction of epoxide with carbon dioxide, introduction of phase transfer agent or crown ether to increase the catalytic activity. This cause the activation of respective anion to increases the cyclic alkylyne carbonate yield at mild condition.45

Quaternary ammonium salt is also used as active catalyst for cyclic carbonate synthesis. They describe as tetrabutylammonium bromide (TBAB) and tetraethyl ammonium bromide as easily availabled and highly active in synthesis of ethylene carbonate because of ammonioum ion in the structure. Activation of epoxide by using quaternary ammonium salt as shown in scheme 13.43

imidazolium based ionic liquid catalysts is used as fixation of CO2 for the synthesis of cyclic carbonate . ionic liquid immobilized on carboxylmethyl cellulose(cmc) which shows higher catalytic activity and selective addition of carbon dioxide on propylene oxide resulting in formation of propylene caabonate under mild and solvent free condition.46

Haritz et al. demostrted organomettalic catalyst for convention isocyanate based PU and NIPU .In this they have reported both levis acid and levis base for polyaddition reaction and compared with the metal based catalyst (scheme 14).42,47

Glycerol carbonate(GC) is one of the most important derivative till a decades and it is obtained from glycerol and carbon dioxide, it is consider as green chemical and is used in replacement of petroleum based compound. This monomer is key compound used in synthesis of multiple cyclic carbonate ,which is further used for NIPU preparation.

Matthieu and group review the reactivity and application of glycerol carbonate. Currently GC becoming more versatile material for the synthesis of cyclic carbonate Glycerol carbonate is starting to be used as is (direct applications) or as intermediate (indirect applications) for various industrial and synthetic application.48

Very good conversion and yield obtained from glycerol carbonate by transesterification of glycerol with dimethyl carbonate. Author has studies the effect of different acid and basic homogeneous and heterogeneous catalyst on a reaction. They found that catalytic activity is very low for acid catalyst that indicates the reaction rate is very slow .catalytic activity is increases with base catalyst .The best result is, shown with heterogeneous catalyst Cao. It lead to 100% conversion and 95% yield in 1.5 hr at 95°C.49

Hydroxyapatite(HAP) modified salt with different metal salt prepared by wet-impregnation method and used as catalyst for synthesis of glycerol carbonate via transesterification process. They have prepared a catalyst with various metal such as M=K, La, Zr, Li ,Ce, KF (M/HAP). They have observed that with KF modified HAP showed good heterogenous catalyst activity which is comparable to Homogenous catalyst K2CO3, the conversion and yield of glycerol carbonate obtained 99.3% and 99% respectively. This catalyst can be easily recovered and recycle.51

For the first time silicate catalyst was used for synthesis of glycerol carbonate by transesterification of glycerol with dimethyl carbonate (DMC). Sodium silicate calcined at 200°C (Na2SiO3-200) has the satisfactory performance in transesterification reaction of glycerol with DMC. The highest catalytic activity of Na2SiO3-200 achieved under the condition i.e 4:1 molar ratio of DMC to glycerol was reacted at 75°C for 2.5 h. This catalyst can be five time without drop in previous activity(Scheme-15).50

Ionic liquid (IL)can be used as catalyst for transesterification of glycerol with DMC glycerol. Dicyanamide based ILs appear to be suitable catalysts for this reaction. In the presence of [Mor1,4]N(CN)2, it is possible to obtain a practically complete conversion of glycerol in glycerol carbonate in 13 h by working at 120°C. no reactions observed in the case of neutral ILs like [bmim][Tf2N] and [bmim][PF6], whereas [mmPyrr][MeOCO2] gives relevant amounts of by products.52

A new Cu6 cluster [Cu6(μ4-O)2(SO4)4(DMA)6] based catalyst have a very good active site for the fixation of CO2 into cyclic carbonate without use of any solvent under room temperature and atmospheric pressure. The preparation procedure is very simple and low in cost which is more important for industrial application.53

Recently glycerol carbonate also synthesized from glycerol and dimethyl carbonate by using Trisodium phosphate(TSP) and under various reaction condition, of at 70°C, glycerol/DMC molar ratio 2,for 60 min with 3% catalyst get 99.5% conversion and yield.TSP is a reusable heterogeneous catalyst. The reaction is proceed via catalytic carboxylation pathway.54

Hu j et al. shows that glycerol carbonate can be directly produce from the catalytic oxidative corboxylation of PdCl2(phen) as the catalyst with CuI. Excellent conversion was obtained with low amount of catalyst under mild conditions,in this glycerol react with carbon monoxide and oxygen(Scheme 16).55

Novel cyclic-functionalized polysiloxanes was successfully prepared by reaction of epoxy-functionalized polysilaxanes with carbon dioxide using TEAB in conjugation with ethylene glycol as catalyst. Author found that properties of NIPU depends on chemical structure of amine ,carbonate content. NIPU coatings containing polysiloxane segments exhibited good water resistance and mechanical properties(scheme 17).56

Wang et al synthesized NIPU by thermo-curing of polyamine and cyclic carbonate terminated polyester. Cyclic carbonate terminated polyester was synthesized from the reaction of the carbon dioxide and epoxidized polyester which was prepared from the polyester polyol with the epichlorohydrin under the catalyst(scheme 18).57

Hannes and coworker synthesized highly versatile solvent-free multifunctional polyhedral oligomeric silsesquioxanes, gives a mono and polydispersed multifunctional POSS cyclic carbonate becoming as intermediate for new family of 100%NIPU hybrid material and coating. POSS synthesized by of chemical fixation of carbon dioxide with glycidyl ether functionalized polyhedral oligomeric silsesquioxanes. POSS carbonate are extraordinary regarding the fixation of 15.4-20.8 % CO2 as well as 28.5-42.1% wt silica. Incorporation of POSS in NIPU thermoset coating reduces the water intake without damaging the resistances to organic solvent and slightly improve the thermal stability.58

Synthesis of 6CC-membrane, 7CC-Membrane and 8CC- membrane cyclic carbonate

Cyclic carbonate plays important role on the carbonate/amine kinetics of reaction. 6CC membrane cyclic carbonate can also be prepared by using same method used for 5CC carbonate synthesis. 1,3-diol or 1,4-diol with alkyl carbonate used to synthesized 6 CC membrane and 7CC membrane .6,59

Candy and coworker synthesized 5CC and 6CC membrane cyclic glycerilic carbonates having exocyclic urethane functions, as potential monomers for polyurethanes and polycarbonates, was prepared by two different routes. Phosphazene showed the best catalytic activity and provided 5CC and 6CC in appreciable amounts whereas the other catalysts favored 5CC formation. An increase in molar ratio of DMC increased the yield and the conversion.60 Rokicki et al. developed a new method for synthesis of 6CC membrane. They obtained 1,3-bis(alkoxycarbonyloxy)propane obtainted from 1,3 propane diol and DMC was subjected to disproportionation at 200-350°C in the presences of colloidal silica or Sn(II). They observed that anionic catalyst yielded the linear polycarbonate with alkylcarbonate as pendant group no crosslink product obseved.61

Georgina and coworker synthesized a 6CC membrane from natural sugar mannose by using CO2 as a C1 building block at room temperature and atmospheric pressure. Author observed These aliphatic polycarbonates exhibit high-temperature resistance and demonstrate potential for post polymerization functionalization, suggesting future application as high-performance commodity and biomedical materials(scheme 19).62

Novel 7CC membrane synthesized from triphosgene and 2-allylbutane-1,4-diol,which was synthesized from reduction of allylsuccinic anhydride with LiAlH. In this, they report the synthesis and polyaddition of a bis(seven-membered cyclic carbonate) with diamines, along with the model reaction of a seven membered cyclic carbonate with amines.27

5-CC and 6-CC membrane cyclic carbonate have been successfully synthesized, aminolysis of these carbonate required high temperature to get high yield and high molecular weight NIPUs. It was reported that 8CC cyclic carbonate could be synthesized from naturally rich epoxides, diamine and dimethyl carbonate by using sustainable routes. This N-substituted 8 membered cyclic carbonates seems to be more reactive than 5CC and 6CC. Due to this reason reactivity increases and they obtained high molecular weight NIPUs by using various diamine.28

Preparation of highly reactive 6CC,7CC and 8CC and their synthesis required harmful reactant. 5 CC carbonate has low reactivity compared to 6CC,7CC and 8CC, The 5CC carbonate and its synthesis extensively studied.29

Synthesis of bis-cyclic carbonate

In order to synthesize PHU by polyaddition process ,various routes has been developed to synthesize bis(cyclic carbonate). The synthesis of five membrane cyclic carbonate become the basic production for bis or multi(cyclic carbonate)(Scheme 20).

One of the most extensively studied bis(cyclic carbonate) is a derivative of bisphenol A with two glycerol carbonate attach to phenol OH group. A bis(cyclic carbonate) was obtained via glycidylation of lignin-based bisphenol followed by cycloaddition with CO2. The lignin-derived bisphenols-glycerol-HMDA based polyurethane has higher Tg than that of traditional BPA-glycerol HMDA based NIPUs. Firstly, they used lignosulfonic acid, a green, effective and biomacromolecule derived catalyst for the synthesis of bisphenol through the para-para condensation reaction with a maximal 52.7% yield between creosol and formaldehyde in water. The integrated use of biobased feedstocks and CO2 via atom economic reaction and green catalysis for PUs synthesis outlined a good example in sustainable polymer chemistry with low carbon footprint. (Scheme 21).63

A renewable aromatic cyclic carbonate was synthesized from syringaresinol with excellent yield and purity. This study confirms the syringarsinol is greener and safer alternative to bisphenol A. syringarsinol is a naturally occurring bisphenol derive from sinapic acid . A five membrane cyclic carbonate has been prepared by CO2 fixation on bis-epoxy monomer (scheme 22).64

Elise and coworker developed a telechelic polyclooctene(PCOEs) by ring-opening metathesis polymerization(ROMP) of cyclooctene (COE)using Grubbs as second generation catalyst in the presents of epoxide functionalized chain transfer agent(CTAs). In this they mentioned about the monofunctional oxiran-2-ylmethylmethyl acrylate CTA(1) and difunctional epoxide CTAs ,bis(oxirane-2-ylmethyl) fumarate, selectively afforded the corresponding α-(glycidyl alkenote),Ѡ-alkenote telechelic PCOEs(DF) along with minor amount of cyclic nonfunctional PCOE.CTA mechanium is proceed through the tendam one-pot ROMP process. ROMP is very effective with the Z- than E- configurated CTAs, due to the presences of methylene group in between the C=C double bond and glycidy moiety. Later on dithiocarbonation of α,Ѡ-diepoxide telechelic PCOEs reaction with CS2 in presences of LiBr is the first example of cyclo(di)thiocarbonate end functionalized PCOEs(Scheme 23).65

Renjian and coworker synthesizes bis(cyclic carbonate) and propylene carbonate through the coupling reaction of CO2,bisepoxide and propylene oxide without addition of external solvent by using a nanolamellar zinc-cobalt double metal cyanide complex (Zn–Co(III) DMCC) as the catalyst and cetyltrimethyl-ammonium bromide (CTAB) as the co-catalyst. They obtained high monomer conversions (PO: 93.6%, bisepoxides: 82.9%).66.

Lise et al prepared bis(cyclic carbonate) from methyl 10-undecenote.In the first step involves transesterification of methyl 10-undecenote in the presences of ester or amide function of hydrogen bond through amide linkage and cyclic carbonate was found to drastically modify the PHU properties (scheme 24).67

Bis(cyclic carbonate) was successfully synthesized from the reaction of D-sorbitol (Sorb-BisCC) with DMC as a reactant through an sustainable route. The reaction was carried out in the presences of 1.3.5-triazabicyclo[4.4.0]dne-5-ene(TBD) as a catalyst and continuous a DMC was added to limit the side reaction or loss of reactant by azeotropic flux. The reaction was carried out solvent free reaction at low temperature ..Sorb-.Sorb-BisCC has proved to be an efficient biobased platform molecule for large no of products using different chemical pathway with excellent properties(scheme 25).68

Carre et al. developed two method for the preparation of dimer-based cyclic carbonate by the reaction of Sebacoyl chloride and glycerol carbonate(scheme 26). This cyclic carbonate and its derivative are subsequently used for synthesis of NIPU. The important stochiometric ratio affect the average functionality. Increasing the average functionality crosslink network is form. It was observed that dimeric structure affect the properties of NIPU and particularly increases the thermal stability of the polymer. A small percentage of trimer in bis(cyclic carbonate)or diamine seems to increase in crosslink density.69,70

Natural rubber (NR;cis-1,4-polyisoprene) is an ecofriendly material obtained from a renewable resource. It is gathered from Hevea brasiliensis tree in latex form. They investigated to produce both linear and crosslink PHU with amino telechelic oligo-isoprenes or amino telechelic natural rubber and cyclic carbonate telechelic natural rubber.71 Zhijun et al. synthesized the cyclic carbonate polymer from diglycidylether of bisphenol A and CO2 under the 0.6 MPa at 130°C for 6 hr. NIPU coating form prepolymer having cyclic carbonate group react with isophorone diamine ,the cured film of NIPU coating showed good thermal properties, excellent solvent resistances, adhesion and flexibility. First application of being the wood coating. (Scheme-27).72

Maria et al prepared cyclic carbonate from the carbonation of glycerol, trimethylolpropane and pentaerythritol glycidyl ether, after curing citric acid amide in the presences of cellulose carbonate. The glycidyl ether react with carbon dioxide in presences of tetrabutylammonium salt as a hetreogenous catalyst to synthesized cyclic carbonate of glycerol carbonate(GCC), pentaerythritol (PEC), and trimethylolpropane (TMC). Most of the 5-CC required elevated temperature for curing, the addition of 1,4-diazabicyclo[2.2.2] octan (DABCO) as a catalyst in a urethane formation enables cureing at room temperature. This is most attractive application of NIPU in coating. It observed that GGC has very low carbonate functionality, impairing the amine-mediated crosslinking, it can be added as a reactive diluent to PEC, lowering resin viscosity and substantially improving both thermal and mechanical properties of PEC. 73

Isosorbide another renewable and biobased sources which is used for synthesis of bis(cyclic carbonate). Using carbonation method cyclocarbonate was synthesized from isosorbide.(scheme-28).74

Cashew nut shell liquid (CNSL) are also becoming renewable material for the synthesis of new cyclic carbonate. Sabnis et al . reported a new versatile renewable material for cyclic carbonate synthesis. It is observed that CNSL based cyclic carbonate can used as component for coating formulation and its properties can be improved by selecting suitable curing agent(Scheme-29).75 Recently published researched on cyclic carbonate from bio-based dimer acid(DACC),DACC is prepare from glycerol carbonate and sapium sebiferum oil derived dimer in presences of NOVOZYM 435 (candida antartica lipase B) as a biocatalyst.DACC was further used for synthesis of NIPU indicating that it give good physiochemical properties and unique material quality(scheme-30).76

A novel bis(cyclic carbonate) synthesized from 2,5-furandicarboxylic acid(FDCA) with fixation of carbon dioxide. This bis(cyclic carbonate) was used for synthesis of NIPU via polyaddition reaction. FDCA referred as new renewable material for synthesizing new products. A main drawback of for PHU synthesis is it requires high temperature to get sensible reaction due to low reactivity of FDCA based cyclic carbonate (scheme-31).77

Moritz et al. reported a new versatile linear routes for the synthesis of Bis(cyclic carbonate) for linear as well as crosslink terpenes based NIPU. The carbon fixation on epoxide was carried out by using homogeneous TBAB and heterogeneous silica supported 4-pyrrolidinopyridinium iodide (SiO2-(I)) catalyst. With systematic variation of catalyst type , CO2 pressure and temperature permits the carbonation in bulk and incorporates 34.4% CO2 in to limonene. As compared to plant oil based cyclic carbonate these terepenes based cyclic carbonate fix more CO2 with less amount of ester group due to absences of ester group it is essential to prevent the side reaction while curing with amine(Scheme 32).78

Alexander et al reported a bifunctional cyclic carbonate from fixation CO2 with diglycidyl terephthalate, it is used for polyaddition reaction with amine to synthesized NIPU. The reaction was carried out in atmospheric pressure using LiCl as a catalyst at room 100°C 79. Another one step reaction was developed for the synthesis of dicyclic carbonate from terepthalic acid and glycerol carbonate (Scheme 33).

Aguiar et al reported a Poly(dimethyl siloxane), PDMS, with terminal cyclic carbonate was prepared by fixation of CO2 on epoxide ring, tetra alkyl-ammonium bromide as a catalyst. The process is carried out in under molded pressure condition and temperature(<200°C). The relatively low viscosity of the bis(cyclic carbonate)PDMS allows the future use of this compound for solvent-free reactions with components containing nucleophilic groups like for instance amines, thiols or alkoxides (Scheme 34).80

Karolina et al synthesized a new one pot tetrahydrofuran derivative which were synthesized under basic intermolecular etherification of substituted five membrane cyclic. carbonate. The development provides a new environmentally friendly approach to the synthesis of five membered cyclic ether derivatives under non-acidic conditions. At the β-position of alcohols with vicinal hydroxyl groups and additional OH groups leading to form 3-hydroxytetrahydrofuran derivatives under intermolecular etherification. Those reactions were also studied for compounds having from 2 to 6 hydroxyl groups per molecule, and the mechanism was studie. It was observed that the lowering the temperature reduces the extent of etherification. In the reaction of meso-erythritol with an excess of DMC carried out at 70 °C in the presence of K2CO3 biscyclic carbonate(Scheme 35). 81

PRÖMPERS and coworker synthesized bis(ethylene carbonate) monomers 3,4-O-isopropylidene-D-mannitol, 2:5,6-dicarbonate and D-mannitol-1,2:5,6-dicarbonate from D-Mannitol. Preparation of bis(carbonate) requires multistep. Synthesized cyclic carbonate containing terminal cyclic ring with two pendant hydroxyl group. Ethyl chloroformate was used as carbonate bond for synthesized Cyclic carbonate. The polyurethanes with pendant hydroxy groups are stable up to 200°C, they exert hydrophilic properties and a high potential for adjusting the properties to the demands of a respective application(Scheme 36).82

Maxence and coworker used vaniline as a renewable building block for synthesis 22 biobased polymer compound. Monomers having epoxy, cyclic carbonates, allyl, amine, alcohol and carboxylic acid moieties was synthesized from biobased vaniline. They can be used, among many others, in epoxy, polyester, polyurethanes, and non-isocyanate Polyurethanes (NIPU) polymer synthesis. Cyclic compound was synthesized between epoxy and CO2 (Scheme 37).83 Mariusz and coworker synthesized bis(2,3-dihydroxypropyl)ether dicarbonate from a commercially available diglycerol by one step process. The synthesized bis(cyclic carbonate) was used as a precouser for synthesis of NIPU. NIPU prepared by non solvent process which has Spectral, thermal and rheological properties. The obtained NIPUs exhibited high thermal stability accompanied by low Tg (Scheme 38).84

Recently Tryznowsk and coworker synthesized novel high reactive bifuctional 5CCand 6CC from commercially available diglycerol. bicyclicdiglycerol dicarbonates having five-membered and six-membered rings have been never reported earlier. The obtained diglycerol biscarbonate was used as a monomer for polycarbonate and non-isocyanate poly(hydroxyurethane)(Scheme-39).85

From natural resources to cyclic carbonate

Vegetable oil is represented as most versatile material for synthesis of polymeric material. vegetable oil are easily available, cost effective and easy to produced. Vegetable oil have found a practical application in biodiesel, lubricants paints and coating and along with other application.86 Vegetable oil and its derivatives are mostly used for the synthesis of polyol and polyurethane. Fatty acid, fatty acid ester, crude glycerol can be synthesized from hydrolysis and transesterification process. Many researchers have reviewed vegetable oil based polyol and polyurethane.87

Hamid and coworker reported a new polyurethane network based on the castor oil as renewable resources for polyol and poly(ethylene glycol)with high biodegradation rates as potential application for inplants and tissue engineering which is prepared through the reaction of epoxy terminated polyurethane prepolymer with 1,6-hexamethylene diamine as curing agent.88

Tamami et al prepare a non isocyanate polyurethane through the conversion of epoxide soyabean oil to carbonated soyabean oil contacting five-membrane cyclic carbonate in the presence tetrabutylammonium bromide as a catalyst at 110°C in high yield.89

For the first time Albert et al. synthesized NIPU elastomer with significantly high biomass content (85%) from two different biomasses i.e ligin and soyabean oil. Carbonated soyabean oil was reacted with coupling agent, 3-aminopropyltriethoxysilane to form urethane bridge and lignin was used to produce sustainable PU.90

Hannes et al.was the first to reported a new and sustainable polyurethane foam. They synthesized PHUs at room temperature by step growth polymerization of cyclic carbonate and diamine. Trimethylolpropane tricarbonate and polypropylene oxide bis-carbonate were copolymerized with EDR148 diamine with thiourea as catalyst and Poly(methylhydrogenosiloxa-ne) was used as blowing agent. Thermal conductivity values were slightly increased compared to a classical PU foam but the potential thermal insulation ability of NIPU foams are promising due to a low thermal diffusivity. Finally, the presence of hydroxyurethane groups slightly reduced the thermal stability. Hence improvement of thermal and mechanical properties could be proposed by the modification of chemical structure of carbonate soft segments 91

Mortiz et al. synthesized soya and linseed oil based polyurethane with a different diamine. cyclic carbonate formation reaction was catalyzed with tetra-butylammonium bromide (TBAB) and silica-supported 4-pyrrolidinopyridinium iodide(SiO2–(I) to get conversion of soya oil using carbon dioxide. Catalyst was readily recovered without requiring the conventional purification by solvent extraction of TBAB. The reaction was monitored as a function of catalyst type and pressure, indicating slower conversion rates for the supported catalyst.92

Recently new NIPU synthesized by reacting cyclic carbonate with diamine new bis cyclic carbonate derived from renewable diphenolic acid and carbon dioxide. furthermore they demonstrated the good dispersion of these PHU in water by adding chemically bonded carboxylic anions into a molecular backbone to form a stable aqueous emulsion with well control particle sized and further used in water borne coating PHU coating with good thermal and mechanical properties (scheme 40).93

Manjeet et al. present a new study the successful carbonation of epoxidized canola oil with carbondioxide using 5,10,15‐tris(pentafluorophenyl) corrole as novel catalyst under mild conditions. It was found that use of 5,10,15‐tris(pentafluorophenyl)corrolato‐manganese(III) complex as catalyst can effectively reduce the reaction time to 1/4th of the time taken by conventional catalysts.94

Donald and coworker recently reported successful electrospinning of NIPU into fiber mats and their physical characterization in comparison to annealed, compression-molded films. Their work revolved around electrospining NIPU into fibrous mats for biomedical applications. In this, melt polymerization of a plant oil-based cyclic carbonate monomer with polyether soft segments and various diamines yielded isocyanate-free, segmented poly(amide hydroxyurethane)s (PAHUs). Electrospinning of segmented PAHUs afforded ductile, free-standing fibrous mats with Young's modulus values between 7 and 8 MPa, suitable for tissue scaffold applications. PAHU fiber mats exhibited 3–4 times greater water uptake than the electro spun TPU control, demonstrating potential utility in drug delivery.95

Marion et al. synthesized isocyanate free condensed tannin based polyurethane from maritime pine ,mimosa and radita pine barks,and quebracho wood were first reacted with dimethyl carbonate then hexamethylenediamine was added to form urethane linkage. Product obtained was tested for wood coating application under high temperature and pressure.96

The nonisocyanate polyurethane/silica nanocomposite coatings was synthesized from cyclic carbonate functional soybean oil and polypropylene glycol resins. Cyclic carbonate functional alkoxysilane (4-((3-(trimethoxysilyl)propoxy)methyl)-1,3- dioxolan-2-one, CPS). The silica particles about 150–200 nm in size were prepared successfully, morphology study indicated that the cyclic carbonate modified silica nanomaterial can be dispersed in carbonated polypropylene glycol (CPPG) contain better formulation than soyabean oil based formulation and from this thermal, mechanical and other coating properties of CSBO-CPPG based PU/silica nanocomposite improved well. 97

In this section we have summarize literature regarding the synthesis of cyclic carbonate functional unsaturated monomer. Free radical homo- or copolymerization of an unsaturated monomer containing the cyclic carbonate functionality which is one of most important method of for producing cyclic carbonate functional polymers. It was found that monomer having at least two reactive group one group for copolymerization and other for another reaction. In the following there are some examples of such polymers prepared from monomer containing cyclic group.

Propylene carbonate methacrylate it is one of the most available monomer having five membrane cyclic carbonate. Many researchers have synthesized propylene carbonate methacrylate by using different routes. These methods included. (1) reaction of glycidyl methacrylate with insertion of CO2.(2) transesterification of glycerol carbonate with methyl methacrylate.(3) reaction of glycerin carbonate with methacryloyl chloride.(4) reaction of glycerin carbonate chloroformate with methacrylic acid.98 Later on it was reported first time, a complete study of free radical polymerization of of (2-oxo-1,3-dioxolan-4-yl) methyl methacrylate or glycerin carbonate methacrylate. Methacrylic acid monomer allows to produces polymers having cyclic carbonate functionality which can be further used as crosslinker to form urethane linkages.99

Vinyl ethylene carbonate(VEC) is one such a cyclic carbonate monomer synthesized from the reaction of epoxybutane with addition CO2 (Scheme 41).100 Polymer with pendent cyclic carbonate functionality was synthesized by both solution and emulsion free polymerization process. In solution polymerization researchers found that VEC copolymerizes completely with vinyl ester monomers over a wide compositional range. Due to its electronic structure, monomer shows low reactivity in radical polymerization.101 Melvin et al synthesized a new monomer from chlorination ethylene carbonate followed by the dehydrochlorination of chlroethylene carbonate. A different types of chlorinating agent were used but triethyleneamine showed best result. When ethylene carbonate was chlorinated under optimum conditions(70-80°C) for monochlorination ,some dichlroethylene carbonate was obtainted.102

and coworker synthesized (2-Oxo-1,3-dioxolan-4-yl) methyl vinyl ether (OVE) by addition reaction of glycidyl vinyl ether with insertion of CO2 in the presence of TBAB as a catalyst. OVE can also be produced by reacting β-butyrolactone or sodium hydrogencarbonate in the presence of TBAB as the catalyst. Poly [ (2-oxo-1,3- dioxolan-4-yl) methyl vinyl ether] [ P (OVE) ] has highest yield for cationic polymerization of OVE catalyzed using boron trifluoride diethyl ether complex in dichloromethane. The reaction with CO2 also showed good yield.103

Takahiro and coworker successfully synthesized a 4-vinylbenzyl 2,5-dioxoran-3-ylmethylether (VBCE) by addition of carbon dioxide to 4-vinylbenxyl glycidyl ether (VBGE) in the presences of lithium bromide as catalyst. 2,2'-azo-bisisobutyronitrile as an initiator was used to obtained VBCE This is a styrene based monomer having five membrane cyclic carbonate structure(Scheme 42).104

Balaka et al synthesized methacrylic monomer which has pendant cyclohexane cyclic carbonate by the reaction of 1, 2 cyclohexene epoxide methacrylate monomer with insertion CO2 in the presencs of lithium bromide as catalyst. This is very efficient method adopting low temperature (RT-450) and normal pressure (1 atm) to covert epoxide into cyclic carbonate the aid of CO2 fixing N-Methyltetrahydropyrimidine (MTHP) and Lewis-type epoxide activating LiBr as catalysts(Scheme 43).105

Bassam and coworker recently reported a new five membrane cyclic carbonate monomer and hyroxylyurethane isomer were synthesized in solvent and catalyst reaction conditions. These new monomer upgraded with both amine and ester group, which provide a novel and enviromentfriendly monomer for synthesis of new biobased polyhydroxyurethane.106

Sudo et al. synthesized a norbornene monomer having cyclic carbonate(NB-CC) functionality from the reaction of epoxy moiety with CO2 under atmospheric pressure in the presences of lithium bromide catalyst. It was reported that NB-CCand 5-butyl-2-norbornene were copolymerized by the methods of ROMP and palladium-catalyzed addition polymerization to afford the corresponding poly(norbornene)s having cyclic carbonate pendants, which can react with amine to permit potential utilization of the polymersas scaffolds for polymer architectures involving networked poly(norbornene)(Scheme 44).107

Rearrengement reaction

NIPU can also be synthesis by rearrangement reaction . Various type of rearrangement reaction are involved. Curtius rearrangement108,Hoffman rearrangement109 and losson rearrangement110 as isocyanate is produces in reaction, it is not suitable for production of NIPU. Many researchers have reported carbamates synthesis using this

Peng et al reported a simple and efficient method for the synthesis of 1,3-disubstituted ureas and carbamates from amides by using iodosylbenzene as the oxidant by Hoffman rearrangement reaction. Heterocyclic products can be easily obtained up to 92% yield using this method. Ureidopeptides can also be prepared in good yield by this method(scheme 45). 111

Recently Borah and coworker reported a new efficient synthesis of methyl carbamate from the corresponding amides via the Hofmann rearrangement using N,N-dibromo-p-toluenesulfonamide (TsNBr2) in the presence of DBU in methanol. The reaction takes 10–20 min at 65°C to produce the corresponding carbamate of excellent yield. Although the reaction works well at room temperature, use of a higher temperature could push the reaction forward at a much faster rate.112

Ring opening polymerization

Hall et al. was the first to that reported NIPU can also be prepared from ring opening polymerization of aliphatic cyclic carbamates. The polymerization process was carried out at near about 250°C in the presences of sodium hydride or N-acetylcaprolactam as a

Stephan and coworker synthesized a poly(trimethylene urethane) from the cationic ring opening polymerization of trimethylene urethane(TU). The polymerization reaction was carried out at 100°C and at different TU to initiators ratio with TfOMe and TfOH as initiators (Scheme 46).114

Bhaskar and coworker synthesized a poly(amide urethane ) by the reaction of ε-caprolactam, amino alcohols and diphenyl carbonate. These polymers contain amide and urethane groups thus combining the properties of two important classes of technical polymers. The microstructure of the resulting poly(amide urethane)s differs by the content of urea groups in the polymer chains, which is 5% for poly(amide urethane)s prepared from a-hydroxy-Ѡ-Ophenyl urethanes and 15% for poly(amide urethane)s prepared from a-hydroxy-Ѡ-O-hydroxyethyl urethanes.115

Osamu et al synthesized a novel thermoresponsive polyurethanes from the reaction of 2-methylaziridine d CO2 under supercritical conditions. The product was obtained with a high content of urethane units and unique temperature-sensitive phase transitions in water. The copolymers exhibited lower critical solution temperatures (LCSTs) in aqueous solution, with a sharp phase transition over a wide range of 41°–85° C (Scheme 47).116

Conclusion

The convention polyurethane synthesizes from the reaction of polyol and very toxic isocyanates. Isocyanates is very dangerous to humans health and environments so to avoid this drawback researchers focus on the synthesis of NIPU. NIPU can be synthesized by many routes, they used diols, polyols, CO2 and diamines as they enviromentfriendly materials. The recent progress focus on the NIPU synthesis pathways which involves polycondensation, polyaddition ,rearrangement and ring opening polymerization reaction. But most convenient routes of NIPU synthesis by the reaction of cyclic carbonate is with diamine. Recent development in cyclic carbonate synthesis and their polymer shows a promising application in many field. Six-membrane, seven-membrane and eight-membrane cyclic carbonate will provides a great opportunity in synthesis of NIPU. But most beneficial cyclic carbonate is five-membrane due its safe and economical preparation process. A varity of cyclic carbonate having functional group in their structure prepared and polymerized are used for large number of industrial application.

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Author Details

Bhagyashree Waghmare and Dr. Prakash Mahanwar

Institute Of Chemical Technology, Mumbai.