Aromatic Bioplastics with Heterocycles - ACS Symposium Series (ACS

Chapter 14

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Aromatic Bioplastics with Heterocycles Sumant Dwivedi and Tatsuo Kaneko* Graduate School of Advanced Science and Technology, Energy and Environment Area, Japan Advanced Institute of Science and Technology, 1-1 Asahidai, Nomi, Ishikawa 923-1292, Japan *E-mail: [email protected].

In the interest of establishing sustainable societies, the production of polymers from bio-based renewable materials has gained momentum owing to the availability of raw materials at low costs from fermented materials. White-biotechnology has catalyzed the production of bio-based raw materials and plays a significant role in lowering final product costs. Various kinds of bio-based aliphatic plastics have been developed for several decades, and high-performance polymers having heterocyclic and/or aromatic structures have been commercialized. The wide expansion of bioplastics is driven by outstanding progress in the processes for refining biomass feedstocks. These feedstocks produce the building blocks that allow versatile and adaptable polymer chemical structures to achieve tailored properties and functionalities. In this chapter, the recent progress in bioplastics composed of heterocyclic and/or aromatic structures, such as polyamides, polyureas, and polyimides, is described and their molecular structure-performance relationships are reviewed. Additionally, the recent scientific achievements regarding high-spec engineering-grade bio-based polymers are discussed.

Introduction Prior to the 1960s, the polymer industry relied heavily on petroleum-derived chemistry, refinery, and engineering processes. The industrial perspectives on the high-economy generation processes had not changed until the negative impact on the environment reached a critical level by the late 20th century. The 21st century © 2018 American Chemical Society Cheng et al.; Green Polymer Chemistry: New Products, Processes, and Applications ACS Symposium Series; American Chemical Society: Washington, DC, 2018.

began with two serious challenges for the polymer industry: global warming and dwindling fossil resources. One of the promising methodologies for combating these problems is to use sustainable resources rather than fossil-based resources. Biomass feedstocks are a promising resource because of their continuous availability and sustainability. Biomass feedstocks can be converted into raw materials for polymer production, and the resulting polymers are called “bio-based polymers.” Currently, several kinds of bio-based polymers such as polylactides (PLA), poly(hydroxy alkanoates) (PHAs), succinate derived polymers, and others are gaining pace through rapid development and commercialization as a response to waste accumulation problems largely encountered in the agricultural, marine fishery, and construction industries (1–6). The progress made in bio-derived polymers is recognized as one of the most successful innovations in the polymer industry for addressing environmental issues. In terms of market development, it has been projected that in the case of bio-based polymers, their production capacity will triple from 5.1 metric tonnes in 2013 to 17 million tonnes in 2020 (7). Bio-based drop-in substitutes for PET and the new polymers PLA and PHA show the fastest rates of market growth. The lion’s share of capital investment is expected to take place in Asia (8–11). The bio-based production capacity of 5.1 million tonnes represented a 2% share of the overall structural polymer production of 256 million tonnes in 2013 (12). The bio-based polymer turnover was about €10 billion worldwide in 2013. There are several successful examples of commercialization of these polymers, including the pilot-scale production of polylactide (PLA) at NatureWorks and Corbion/Total; poly(trimethylene terephthalate) (PTT) at DuPont; poly(isosorbide carbonate) at Mitsubishi Chemicals; bio-based polyamides at Arkema, Toray, BASF, DSM, and others; and poly(ethylene 2,5-furandicarboxylate) (PEF) at Synvina (12, 13). Bio-based polymers are being applied to general and engineering situations. For example, because of the improvements in the physical durability and processability of PLA, it has been used in the packaging industry (1, 14, 15). In addition, owing to the superior gas barrier properties of PEF, it is being used in bottles, films, and other packaging materials in the food and beverage industry. Furthermore, bio-based PTT is analogous to petroleum-derived PTT, and its bio-based, sustainable nature and intrinsically flexible chain properties afford comfortable stretching and shape recovery properties that make it attractive and promising. The current general approach for bio-based plastic processability entails physical modification and optimization of polymer processing, including the optimization of processing parameters, extruder screw design, selection of appropriate additives, and post-orientation for strain-induced crystallization (16–21). These developments in the processing conditions have made bio-based polymers analogous to certain petroleum-derived polymers and have helped to establish a sizeable market. The aforementioned bio-based polymers have been remarkably well developed because of their high mechanical strengths. However, it was estimated that these polyesters will only replace a small percentage of the nondegradable plastics currently in use owing to their poor thermal resistance (22). As a result, high-performance environmentally friendly polymers from bio-based materials that are degradable after usage into natural molecules are urgently desired in 202 Cheng et al.; Green Polymer Chemistry: New Products, Processes, and Applications ACS Symposium Series; American Chemical Society: Washington, DC, 2018.

order to improve human life. Many nondegradable engineering plastics have rigid conjugated rings, such as benzene, benzimide, benzoxazole, benzimidazole, or benzothiazole (23). The introduction of a heterocyclic and/or aromatic component into a thermoplastic polymer backbone is an efficient method for intrinsically improving material performance. Additionally, the continuous sequence of aromatic rings can be a mesogenic group. Molding in the thermotropic liquid crystalline (LC) state can induce molecular orientation, imparting anisotropy to mechanical performance, which sometimes dramatically increases mechanical strength and Young’s modulus (24). Outstanding reviews and textbook knowledge are available for bio-based polyesters and other kinds of aliphatic bio-derived polymers (25–29); however, a systematic review for the aromatic and heterocyclic bio-based engineering plastics is lacking. This chapter reviews the recent important developments in the preparation of various rigid polymers derived from phytochemical monomers and other fermented products. Moreover, an exhaustive discussion on the significant progress in heterocyclic/aromatic bio-based polyamides (PAs), polyureas (PU), and polyimides (PIs), as well as their (nano)composites is included for a better understanding of structure-performance relationships and value addition through material hybridization.

Bio-Based Polyamides Polyamides (PAs or Nylon) are widely used as engineering thermoplastics because of their unique physicochemical properties, and their high thermomechanical properties attract many researchers in polymer industries (30–32). The amide linkages exhibit hydrogen bonding, and thereby good thermal stability and mechanical properties. Conventional PAs account for a significant fraction of the thermoplastics field. However, based on the previously mentioned background of environmental issues, several PA scientists in both industry and academia have trialed the process conversion from petro-chemistry to white-biotechnology by incorporating cost-performance tradeoffs. Most of the development began with the syntheses of aliphatic bio-based monomers for PAs by DSM, Evonik, Arkema, and others (12, 13). Figure 1 illustrates the structures of various bio-based PAs with minimized carbon footprint, such as PA11 derived from castor oil and other PAs. PA6,10 is synthesized by the interfacial polymerization of hexamethylenediamine and sebacoyl chloride, which was also derived from castor oil to afford a wide variety of molecular designs involving PAs. Furthermore, the properties of the bio-derived PAs were benchmarked with the commercial PA6 and PA6,6. Several aliphatic bio-polyamides such as PA4 and PA4,6 showed quite good thermomechanical properties. These PAs exhibit a wide range of applications, from flexible tubes to high-end electronic devices.

203 Cheng et al.; Green Polymer Chemistry: New Products, Processes, and Applications ACS Symposium Series; American Chemical Society: Washington, DC, 2018.

Figure 1. Syntheses of bio-derived polyamides.

The introduction of aromatic/heterocyclic moieties in the bio-based PA backbone improved their thermomechanical properties. Several industries attempted to prepare “partially” bio-derived PAs, in which only the aliphatic component was bio-derived. Mitsubishi Chemical Corporation prepared poly(m-xylylene adipamide) (MXD-6) by polycondensation of m-xylylene diamine with bio-derived adipic acid. MXD-6 exhibits a glass transition in the 204 Cheng et al.; Green Polymer Chemistry: New Products, Processes, and Applications ACS Symposium Series; American Chemical Society: Washington, DC, 2018.

range 85–100 °C and a melting point in the range 235–240 °C (1, 3). QianaTM developed by DuPont is an aliphatic-aromatic nylon fiber with a melting point of 275 °C (1–3, 33–36). In general, PAs absorb moisture ranging from 2 to 10% owing to the amide linkage interacting with the water molecules via hydrogen bonding, which has a plasticizing effect and reduces their melting point, glass transition temperature, and mechanical properties (37–40), although the impact strength and resilience increase. Since PAs with longer interconnecting alkyl chains have lower contents of amide linkages, they reveal lower water absorption. However, the potential of bio-PAs to provide superior material performance has yet to be exploited by incorporating heterocyclic and/or aromatic structures in the PA backbone. Reactive alicyclic or aromatic structures do not widely exist as biomolecules for exploitation in monomer production. Furthermore, the toxicity of these superior moieties for bio-PAs renders their biological availability quite low. Itaconic acid (IA, Figure 1), which is widely produced by the fermentation of Aspergillus terreus, possesses two carboxylic groups separated by a vinylidene group adjacent to a carboxylic group as a α,β-unsaturated compound (41). The conventional polycondensation reaction of IA with a diamine in the solution phase was extremely difficult to accomplish due to the three-way branching resulting from the Michael addition and amidation of three amines to the double bond and two carboxylic acids of IA, respectively. Therefore, the polymerization of the complex monomer was conducted using 1:1 organic salts of IA and diamine followed by melt condensation, leading to the formation of rigid five-membered pyrrolidone groups along the bio-PA backbone with superior thermomechanical properties (41, 42). The heterocyclic ring enhances the fatigue resistance and wearing durability, and promotes strong intermolecular hydrogen bonding. Its glass transition temperature can be attributed to the molecular motion of the amorphous regions, such as translation motion, the alkyl chain length, atomic vibrations, movability of the crystal lattice, net amide content, and chain uncoiling. The amide content plays a critical role in deciding the Tg as a result of hydrogen bonding, which leads to better lattice arrangement and a greater degree of crystallization. The Tg of PA increases with increasing crystallization. Greater crystallinity impacts the major properties of PAs such as high moisture absorption, abrasion resistance, high stiffness, high density, high moduli, high chemical resistance, and better dimensional stability, but decreases elongation, impact resistance, thermal expansion, and gas permeability (43, 44). The melting temperatures of aliphatic PAs are greatly affected by the alternation of odd or even alkyl chain length in the diamine moiety. It was observed that PAs with odd numbers of methylene groups have higher melting temperatures than those with even numbers of methylenic groups, owing to the varying levels of inter/intra-molecular hydrogen bonding. For instance, the melting temperatures of PA4,6, PA6,6, PA6,10, and PA6,12 are 300 °C, 260 °C, 225 °C, and 210 °C, respectively (45). In the case of PAs and coPAs with varying degrees of crystallinity, the polymer molecular weight greatly affects the melting point. Similar trends were also observed with the heterocyclic IA-based bio-PA. One of the motivations for the development of bio-based polymers was their biodegradability, which is becoming increasingly important due to strong public 205 Cheng et al.; Green Polymer Chemistry: New Products, Processes, and Applications ACS Symposium Series; American Chemical Society: Washington, DC, 2018.

concerns about waste management. It is worth mentioning that the pyrrolidone ring was opened by ultraviolet (UV) irradiation and through composting in a landfill for extensive periods of time, leading to a reduction in the molecular weight of the polymer, thereby demonstrating the degradation ability of bio-based engineering thermoplastics (41). Aromatic PAs with very high glass transition temperatures (156–242 °C) have also been synthesized from bio-based monomers that introduce a heterocyclic ring (42). IA reacted with aromatic diamines such as 4,4′-diaminodiphenylether, p-phenylenediamine, m-xylenediamine, and p-xylenediamine, leading to the syntheses of aromatic bio-PAs. Out of these structures, the p-phenylenediamine-based bio-PA reveals the highest thermal stability due to the absence of ether and methylene linkages among the aromatic groups. Owing to their rigid backbones, especially the entirely p-substituted derivative, aromatic PAs have high thermomechanical properties (tensile and impact resistance), are chemically resistant to alkali, and are hydrolytically stable. The two most famous commercial aramids are NomexTM and KevlarTM. Morgan (DuPont) discovered NomexTM in 1958 and it was later commercialized in 1961 (1, (46, 47)). On the other hand, KevlarTM was discovered by Kwolek (DuPont) in 1965 and it was later commercialized in 1971. NomexTM was synthesized by the polymerization of m-phenylene diamine and isophthaloyl chloride. NomexTM has a high melting point (400 °C) and thermal stability, and allows easy processing in the form of fibers from aprotic polymer solutions (1–3). However, owing to the poor solubility of aromatic bio-PAs in the commonly used organic solvents, the processing becomes difficult, which limits their applications. The behavior of hybrid composites is a balance of the advantages and disadvantages of each component, in which the advantages of one type of fiber could compensate for the lack of it in another fiber. A small content of carbon fibers was found to be capable of significantly improving the mechanical properties of PA11, including stiffness, elastic deformation before yield, and creep properties (43–45). However, carbon fiber is not renewable and quite expensive compared to other fiber types because of the high consumption of energy during its manufacturing. Compared to wood fiber composites (30% wood fiber), hybridization with carbon fiber (10% wood fiber and 20% carbon fiber) increased the tensile and flexural moduli by 168% and 142%, respectively (46). The Izod impact strength of the hybrid composites exhibited a good improvement compared to that of the wood fiber composites. Hence, hybridization of a small amount of carbon fibers with natural fiber could be another cost‐effective alternative for developing high-performance biocomposites. The addition of inorganic fillers in the PA matrix that act as nucleating sites enhances the net crystallinity and abrasion resistance of the resulting composite material. Nanohybridization of the IA-based bio-PA with montmorillonite (MMT) clays enhances not only the moduli through improved molecular orientation from cryogenic treatment but also the elongation degree for Na-MMT. The increment in the strain energy density observed from improved elasticity was attributed to the greater flexibility of the polymer backbone due to the catalytic hydrolysis of the pyrrolidone moiety through interactions with the silicate layers (42). 206 Cheng et al.; Green Polymer Chemistry: New Products, Processes, and Applications ACS Symposium Series; American Chemical Society: Washington, DC, 2018.

Transparent high-performance PAs possess largely amorphous structures, which are controlled by a precise molecular design of monomers having aromatic units interlinked with (cyclo)aliphatic units (47). Path-breaking advancement requires connecting the dots along the multidisciplinary scientific progress. Producing a bio-based diamine with an aromatic structure in the backbone requires precise molecular design. Takaya et al. developed an artificial biosynthetic route to 4-aminocinnamic acid (4ACA) in Escherichia coli (E. coli) cells to obtain 4-aminophenyl alanine (4APhe; Figure 2) from glucose followed by deamination (48). However, the yield of 4ACA was too low for realistic commercialization of the technology. Adopting white-biotechnology led to the improved yield of 4ACA through genetically engineered E. coli that was at least 30 times more than that obtained using the conventional deamination techniques with 90% purity (47). A microbial catalyst was employed to reduce 4ACA to 4-aminohydrocinnamic acid (4AHCA), and this molecule was utilized for polycondensation to yield a PA with a very high glass transition temperature of more than 240 °C and 10 % weight loss temperature above 390 °C. On the other hand, the synthesis of diamine through the [2+2] photocycloaddition reaction of the 4ACA salt yielded 4,4′-diaminotruxillic acid-based monomers (4ATA-acid/methyl/ethyl ester). The polycondensation of 4ATA-acid and 4ATA-methyl ester led to the formation of a bio-PA with transparency over 95% at 550 nm and a tensile strength of over 400 MPa (the highest among transparent plastics and borosilicate glass). The ultrahigh mechanical strength of the bio-PA was attributed to the prospective spring-like flexible function of the phenylenecyclobutanyl backbone. However, it is interesting to note that the spring function of the phenylenecyclobutanyl backbone is also responsible for degradation under UV irradiation, due to the ease of cleavage along the strained ring. This suggests photo-degradation, which is an indispensable aspect of the biopolymers development. These bio-PAs may be utilized for versatile applications in the manufacturing of automobile parts, flexible electronic devices, sensors, and other optical materials as well.

Bio-Based Polyureas Polyurea (PU) is an elastomeric polymer suitable for application in ballistic protection owing to its characteristic set of properties: light weight, high elasticity, high flexibility, heat resistance, impact resistance, and high energy absorbing capacity (49, 50). It is also one of the most successful materials used in the coating industry, having multiple applications in many fields of activity owing to its fast curing, chemical resistance, low flammability, good stability and durability, and excellent bonding properties to all types of surfaces, especially metals (51). The synthesis of PU elastomeric films consists of a rapid polyaddition reaction between two oligomeric species: a diamine and a diisocyanate. The PU films described in the literature are generally obtained by simply mixing two commercial components: an isocyanate component (Isonate 143L, Basonat HI-100, Vestanat IPDI) and an oligomeric diamine (Versalink P-1000, Jeffamine D-2000 and D-400, Jefflink 754, Clearlink 1000) (52–54). 207 Cheng et al.; Green Polymer Chemistry: New Products, Processes, and Applications ACS Symposium Series; American Chemical Society: Washington, DC, 2018.

Figure 2. Biosyntheses of 4-aminocinnamic acid using genetically-manipulated Escherichia coli (studied by Prof. N. Takaya of Tsukuba University, Japan). Reproduced from ref. (67). Copyright © 2014 American Chemical Society.

The aforementioned PUs have an interesting microstructure consisting of two distinct microphases with different characteristics: aromatic ring regions (hard domains) that are chemically bonded and homogenously distributed throughout the aliphatic polymer chain matrix (soft domains) (55). Depending on the composition, the properties of a PU coating change dramatically. Thus, a higher aliphatic chain content increases the flexibility, but decreases the strength, whereas a higher content of aromatic rings leads to increased strength but lower elasticity. Another important aspect related to the PU coatings is their transition from the glassy to a rubbery state during the deformation process, which occurs earlier in the case of high impact forces (49, 56). The amount of energy dissipated through the PU film is comparable to its loading-unloading behavior, which is related to the hysteresis area under the stress–strain curve. The PU properties for a certain type of application can be designed by choosing the right components and the adequate proportions between them. Thus, the behavior of these materials can be controlled by the synthesis parameters. Several kinds of bio-based PUs based on 4-aminophenylalanine (4-APhe, available from genetically modified E. coli., as presented in Figure 2) and 4-APhe methyl ester along with several kinds of diisocyanates (varying degrees of aromaticity: MDI, MMDI, 1,3 PDI, and 1,4 PDI) were synthesized (57, 58), as shown in Figure 3. Overall, almost all of these bio-based PUs have higher thermal degradation temperatures of up to 200 °C, whereas the carboxylic acid containing 4-APhe shows superior thermomechanical properties than the PU obtained from methyl-ester-based 4-APhe, with unified diisocyanate structures. This observation was attributed to the interchain hydrogen bonding of carboxylic acid with the amide and carbonyl units. Furthermore, bio-based PUs with a greater degree of hydrogen bonding and rigid aromatic backbone showed superior tensile properties. On the contrary, flexible interlinked aromatic structures containing bio-based PU exhibited better ductilities and higher strain energy densities (above 208 Cheng et al.; Green Polymer Chemistry: New Products, Processes, and Applications ACS Symposium Series; American Chemical Society: Washington, DC, 2018.

10 Jcm–3). In general, these bio-based PUs showed better thermal stability and mechanical properties than conventional aliphatic PUs or the PU spray elastomer (Spandex) (49, 57).

Figure 3. Syntheses of bio-based polyureas.

On the other hand, introducing ionic interactions among the repetitive units (4ATA-acid and aromatic diisocyanate MDI, Figure 3) in PU results in a significant transition from a highly transparent film to a colored one due to the formation of a metal-ligand charge transfer complex (47). Furthermore, the 4ATA-acid based PU reveals significant swelling characteristics in alkaline solutions that lead to highly improved mechanical properties, especially for multivalent cationic interactions with the 4ATA-carboxylate repetitive unit. The high solubility of these bio-based PUs in aprotic solvents ensures easy processability and is comparable with those of conventional PUs. During the past decades, great progress has been made in the development of segmented thermoplastic polyurethanes/polyureas (TPUs), which are applied in many areas such as the automotive industry, clothing, sportswear, and medical applications (59, 60). Conventionally, TPUs are prepared from polymeric diols (which act as the soft segment (SS)), diisocyanates, and low molecular diol or diamine chain extenders (the low molecular compounds together form the hard segment (HS)). However, the toxicity of the diisocyanates should not be ignored, especially for the TPUs employed in biomedical applications. Several 209 Cheng et al.; Green Polymer Chemistry: New Products, Processes, and Applications ACS Symposium Series; American Chemical Society: Washington, DC, 2018.

isocyanate-free routes have been developed for preparing TPUs, starting from carbonylbiscaprolactam, di-tert-butyltricarbonate, cyclocarbonates, transition metal catalyzed transurethanization, etc. (61). A metal-free organic catalyst was utilized as an isocyanate-free route for synthesizing a series of segmented PUs from renewable resources: dimethylcarbonate (DMC, metabolic engineered E. coli.), diamino-terminated polypropylene glycol (PPGda, potentially bio-based and originating from propylene oxide), and 1,4-diaminobutane (DAB or putrescine) (62). The renewable segmented PUs contain monodisperse HSs. Dynamic mechanical analysis of the PUs reveals a sharp glass transition, a sharp flow transition, and a flat rubbery plateau. The flow and maximum use temperature (FL) of PUs increases with the increasing number of urea groups in the corresponding dicarbamates. In addition, for a constant HS length, varying the length of the SS allows the modulation of the thermomechanical properties of PUs, enabling their application as adhesives, soft elastomers, or rigid plastics.

Bio-Based Polyimides The development of PAs and PUs as engineering plastics triggered the evolution of highly chemically and thermally resistant and mechanically strong polymers through the incorporation of aromatic/heterocyclic rings in the polymer backbone. In the 1950s, DuPont employed pyromellitic dianhydride and 4, 4′-oxydianiline as monomers and invented a new class of polymers with repetitive imide units, polyimides, and commercialized the material as Kapton® (63). Since then, many scientific reports have been published on the development of more advanced polyimides, though scarcely any report has mentioned the synthesis of biopolyimides. The recent progress in the preparation of a bio-based polyimide from the exotic amino acid 4ACA (Figure 2) has drawn special attention due to the advanced optical, thermo-mechanical, and memory characteristics of the polyimide (64–66). The various kinds of diamine synthesis as monomers from 4ACA have been prepared through photo-cycloaddition reactions. The low thermal stability of cyclobutane in the truxillate backbone motivated researchers to dimerize 4ACA through alternative routes (67–71). Grubb’s olefin metathesis was utilized to prepare 4, 4′-diaminostilbene (DAS) and its reduced counterpart 4, 4′-(ethane-1,2-diyl)dianiline (EDDA) for polyimide synthesis (68). Furthermore, a salt of 4, 4′-diaminotruxillate was utilized for the preparation for polyimide-hybrid materials (70). Figure 4 represents the preparation of a polyimide using the 4ACA-based diamine monomer, and mostly comprised thermal imidization, except in the case of polyimide-metal oxide as a hybrid material. Among all the products of polycondensation, CBDA exhibits the highest inherent viscosity, irrespective of the diamine type, which can be attributed to the higher reactivity of the anhydride unit attached to the aliphatic cyclobutane ring that produces a positive inductive effect (67, 72). Furthermore, the biopolyimide possesses high chemical resistance, especially the DAS-based polyimides, which are insoluble in non-polar/protic-polar/aprotic solvents; this may be attributed to 210 Cheng et al.; Green Polymer Chemistry: New Products, Processes, and Applications ACS Symposium Series; American Chemical Society: Washington, DC, 2018.

the conjugated trans-stilbene unit of the diamine, which provides structural rigidity. However, EDDA-based diamine and ATA-methyl/ethyl ester are soluble only in concentrated sulfuric acid, probably due to the coplanar rings of the aromatic-imide structures (68). These synthesized biopolyimides have an amorphous nature, except the polyimide from CBDA, which may be ascribed to the cyclobutane rings, phenylenes, and imide rings that induce partial crystallization. It is important to mention that a slight change in the monomer structure can significantly affect the polymer crystallinity, e.g., replacing the methyl with ethyl in the ATA-ester in CBDA-based polyimide decreases the crystallinity by 20% (73). The copolymers also show high chemical resistance to non-polar/polar-protic/aprotic solvents; however, all the co-polyimides exhibit solubility in concentrated sulfuric acid and trifluoro acetic acid. Nevertheless, it was found that reducing the torsional energy of the dianhydride ring significantly improves the solubility of the biopolyimide in aprotic solvents (69). Moreover, a water-soluble biopolyimide has been introduced through the neutralization of the carboxylic acid moieties in each repetitive unit (72). One-step chemical imidization of the ATA salt and BCDA was performed in the presence of isoquinoline, and thereafter, the ATA salt neutralized with an acid. The polyimide resulting from chemical imidization reveals less chemical resistance, as it showed solubility in a series of aprotic solvents, which in turn offers an opportunity for the sol-gel condensation reaction. The sol-gel reaction comprises the hydrolysis and condensation of metal alkoxide units. Titanium and zirconium alkoxide precursors were added to a solution of polyimide in DMAc with acidic catalysts to yield a polyimide-metal oxide composite film as a hybrid material. Furthermore, the content of the metal oxide was varied 10–50 wt% and the average particle size of the oxide was around 5 nm (for 50 wt% TiO2 or ZrO2) (70). The transmittance of the 4ATA-derived homo/co-polyimide film was measured for a normalized thickness of 10–20 μm with a cutoff wavelength of 450 nm (T450). In general, it was observed that poly(amic acid) (PAA) from all 4ATA-derived monomers exhibit an almost transparent to pale-yellow color (T450 > 88%) due to the variation in dianhydride. Aromatic dianhydrides exhibit more intense colors than their aliphatic counterparts due to the electron-rich benzenes of ATA and dianhydrides that induce strong charge-transfer (CT) interactions (67). However, it is important to mention that all the 4ATA-derived polyimides were more transparent than Kapton®. Usually, transmittance increases with the loss of conjugation in the polymer backbone (67–74). The optical properties of the 4ATA salt and BCDA-based polyimide show outstanding transmittance, presumably due to the alicyclic dianhydride, which induces weak intra and intermolecular CT interactions. It is important to mention that metal oxide particle dispersion in the polymer matrix and the band gaps of ZrO2 (5.0–5.85 eV) and TiO2 (3.2 eV) critically affect film transparency, with a greater band gap resulting in a higher transparency (75, 76). The refractive index and Abbe number of the polyimide hybrids increase with metal oxide content, and indicate the sol-gel reaction between the 4ATA salt and M-OH (M = Ti, Zr) to form M-O-M structures (70, 77). In other words, controlling the amount of metal oxide 211 Cheng et al.; Green Polymer Chemistry: New Products, Processes, and Applications ACS Symposium Series; American Chemical Society: Washington, DC, 2018.

in the polyimide matrix provides an opportunity to tune the refractive index of the composite, as well as its Abbe number, for advanced optical applications.

Figure 4. Syntheses of bio-based polyimides. The DAS-based polyimide exhibits exceptionally high thermal resistance compared to the EDDA-based counterpart due to the extended conjugation in the polymer backbone structure. The aromaticity in the polymer backbone is responsible for the greater thermal resistance. In other words, CBDA-based polyimides with DAS or EDDA show lower thermal resistances than the other aromatic dianhydrides due to the absence of π-electron conjugation. The 10% weight loss temperatures (Td10) of the DAS- and EDDA-based polyimides were in the range 400 °C to 600 °C. In particular, the OPDA-DAS-based polyimides show an exceptionally high Td10 value of 600 °C, which is the highest reported for any polyimide (68). On the other hand, the 4ATA-based homopolymer exhibits satisfactory thermal resistance, with Td10 values ranging from 399 °C to 425 °C, which are lower than DAS/EDDA due to the presence of the strained and non-conjugated cyclobutane ring of truxillic acid along the diamine unit, compared to DAS. Along similar lines, 4ATA-based copolymers show a Td10 value around the arithmetic mean of the corresponding values of the individual dianhydride-based homopolymers. The glass transition temperature was sufficiently high for several polyimides (> 250 °C) and difficult to determine for most polyimides. However, the polymer backbone with lower torsion energy exhibits glass transition behavior and promotes easy processability in aprotic solvents (67, 68). Furthermore, the 212 Cheng et al.; Green Polymer Chemistry: New Products, Processes, and Applications ACS Symposium Series; American Chemical Society: Washington, DC, 2018.

incorporation of metal oxides in polyimides increases the Tg, as well as Td10, of the polymer hybrids due to the uniform dispersion of rigid inorganic components. Contact angle measurements of the 4ATA-based polyimide revealed the film surface to be hydrophobic. The cell compatibility of biopolyimide was tested based on its adherence to L929 fibroblast cells. All the polyimides exhibit similar results with good cell compatibility with increasing incubation time, which is similar to Kapton®. The mechanical properties of super-engineering plastics have always been the center of attention and are mostly expressed in terms of Young’s modulus (E), elongation at break (ε), tensile strength (σ), and strain energy (U). Monomer structure and polymer molecular weight are among the significant factors that affect the mechanical properties. For instance, the kinked sulfone unit of DSDA increases polymer flexibility (good ε, high σ, and E), whereas the rigid cyclobutane/a-single benzene of PMDA makes the polymer brittle (low ε). In general, the DAS/EDDA-based polymers reveal high tensile strengths (σ = 54–132 MPa), moduli (E = 2.3–4.3 GPa), and a large window of polymers with varying degrees of elongation (ε = 1.5–7.8%) (67, 74). In general, most of the 4ACA-derived polymers show higher moduli than Kapton®. The 4ATA-based polyimide exemplifies a large window of modulation of the mechanical properties modulation (σ = 28–114 MPa, E = 3–13 GPa, and ε = 0.9–9.4%) by varying the structure of the dianhydride(s). This observation can be envisaged to the structural disordering that renders interchain stacking difficult and improves the ability of the carbonyl-connecting groups to rotate the benzene rings of the tetra-acid (74). Furthermore, the copolyimide ductility of the copolymer substantially increased compared to the corresponding homopolymer, which can be suitably used in foldable devices. Recently, it was observed that the greater surface hydrophilicity of the biopolyimide induces stronger interfacial interactions with the ITO nanolayer, resulting in high transparency, smoothness, and high robustness against mechanical deformation (78). Hybridization of polyimide with graphite is important for application in electronic devices (79). The adhesion strength of the ATA-based homopolyimide on a carbon substrate was found to be equivalent to that of a conventional instant super glue prepared from α-cyanoacrylate polymers. The HOMO and LUMO levels calculated from cyclic voltammetry, and the amalgamation of the information with molecular simulations based on the density functional theory provides a detailed insight of the memory characteristics of these 4ATA salt/BCDA polyimide hybrids. It was found that the introduction of TiO2/ZrO2 as electron acceptors into the neat polyimide matrix results in a lower LUMO level, which is one of the basic requirements of memory devices, and facilitates as well as stabilizes the CT interactions. In other words, the type of memory greatly depends on the content of the metal-oxide (0–50 wt%). The neat polyimide showed no memory properties, but introducing TiO2/ZrO2 up to 5 wt% yields dynamic random access memory (DRAM); up to 10 wt%, the polyimide-hybrids behave as static random access memory (SRAM), while beyond 10 wt%, the materials act as write once read many (WORM). In other words, the memory device revealed longer retention time and lower threshold voltage with increasing TiO2/ZrO2 and exhibited bi-switchable characteristics (70, 78, 80). The introduction of 213 Cheng et al.; Green Polymer Chemistry: New Products, Processes, and Applications ACS Symposium Series; American Chemical Society: Washington, DC, 2018.

SiO2 in the 4ATA-ester/CBDA polyimide leads to improved optical, dielectric, and dielectric breakdown strengths. On the other hand, the 4ATA-ester/CBDA polyimide hybrid with silica showed lower transparency and electrical properties due to prospective localized interactions with carboxylic acid and silanols (71). These observations clearly exemplify the opportunity of these hybrid materials in transparent memory, display, and insulating devices with high robustness.

Future Outlook In the pursuit of sustainable development and reduction of environmental impact, bio-based polymers are among the best materials to tackle global environmental concerns. Undoubtedly, the production of various kinds of monomers from bio-based precursors presents an alternative to the conventional dependence on fossil-based monomers for biobased polymer production.

Figure 5. Transparent sheets of high-performance bioplastics. Reproduced from ref. (47). Copyright © 2016 American Chemical Society. The bioderived engineering plastics show either equivalent or better thermomechanical characteristics with good transparency (Figure 5) compared to the conventional engineering plastics. Many biomolecules are multifunctional, which is advantageous in the molecular design of heterocyclic polymers having high thermal/mechanical performances. Furthermore, hybridization of biopolymers with various fillers leads to superior properties. In particular, the application of biopolyimides (hybridized with metal oxides) offers an opportunity for the development of advanced materials such as transparent memory devices or as an ophthalmological material. Further strategic exploration of bio-based monomers, as well as the design of new monomers, presents an outstanding prospect for new and expanded horizons for bio-based polymer chemistry.

References 1. 2.

3.

Steinbuchel, A. Biopolymers; Wiley-VCH: Weinheim, Germany, 2001. Domb, A. J.; Kost, J.; Wiseman, D. M; Handbook of Biodegradable Polymers; Harwood Academic Publishers: London, 1997; ISBN 90-5702-153-6. Klass, D. L. Biomass for Renewable Energy, Fuels, and Chemicals; Academic Press: San Diego, CA, 1998; ISBN 0-12-410950-0. 214 Cheng et al.; Green Polymer Chemistry: New Products, Processes, and Applications ACS Symposium Series; American Chemical Society: Washington, DC, 2018.

4. 5.

6. 7. 8. 9. 10. 11. 12.

13.

14. 15. 16. 17. 18. 19. 20. 21. 22. 23. 24. 25. 26.

Ladmiral, V.; Jeannin, R.; Fernandes Lizarazu, K.; Lai-Kee-Him, J.; Bron, P.; Lacroix-Desmazes, P.; Caillol, S. Eur. Polym. J. 2017, 93, 785–794. Toledo, P. V.; Limeira, D. P.; Petri, D. Abstracts of Papers, 255th ACS National Meeting & Exposition, New Orleans, LA, United States 2018, PMSE-271. Watanabe, H.; Fujimoto, A.; Nishida, J.; Ohishi, T.; Takahara, A. Langmuir 2016, 32, 4619–4623. Llevot, A.; Grau, E.; Carlotti, S.; Grelier, S.; Cramail, H. Macromol. R. Commun. 2016, 37, 9–28. Krishnaswamy, R. K.; Van Walsem, J.; Peoples, O. P.; Shabtai, Y.; Padwa, A. R. US Pat. Appl. 20150132512 A1 20150514, 2015. Kaneko, T.; Tran, H. T.; Matsusaki, M.; Akashi, M. Chem. Mater. 2006, 18, 6220–6226. Wei, L.; McDonald, A. G. Mater. 2016, 9, 1–23. Babu, R. P.; O’Connor, K.; Seeram, R. Prog. Biomater. 2013, 2, 1–16. Avantium Report. Renewable Chemicals into Bio-Based Materials: From Lignocellulose to PEF. http://biobasedperformancematerials.nl/ upload_mm/3/5/7/651bed82-390b-4435-a006-7909570de736_BPM %202017%20-%20Speaker%2006%20-%20Ed%20de%20Jong %20-%20Renewable%20chemicals%20into%20biobased%20materials%20-%20from%20lignocellulose%20to%20PEF.pdf (accessed May 19, 2018). Avantium Report. PEF, a 100% Bio-Based Polyester: Synthesis, Properties & Sustainability. http://euronanoforum2015.eu/wp-content/ uploads/2015/06/PlenaryII_PEF_a_100_bio-based_polyester_GertJanGruter_11062015_final.pdf (accessed May 19, 2018). Fukushima, K.; Yoshiharu, K. Polym. Int. 2006, 55, 626–642. Ikada, Y.; Jamshidi, K.; Tsuji, H.; Hyon, S. H. Macromolecules 1987, 20, 904–906. Duan, Y.; Liu, J.; Sato, H.; Zhang, J.; Tsuji, H.; Ozaki, Y.; Yan, S. Biomacromolecules 2006, 7, 2728–2735. Serizawa, T.; Yamashita, H.; Fujiwara, T.; Kimura, Y.; Akashi, M. Macromolecules 2001, 34, 1996–2001. Cicala, G.; Latteri, A.; Saccullo, G. J. Polym. Environ. 2017, 25, 750–758. Yonezawa, N.; Okamoto, A. Polym. J. 2009, 41, 899–928. Zachariades, A. E.; Economy, J. Polym. Eng. Sci. 1983, 23, 266–270. Saulnier, B.; Ponsart, S.; Coudane, J.; Garreau, H.; Vert, M. Macromol. Biosci. 2004, 4, 232–237. Nagarajan, V.; Singh, M.; Kane, H.; Khalili, M.; Bramucci, M. J. Polym. Environ. 2016, 14, 281–287. Imai, Y. High Perform. Polym. 1995, 7, 337–345. Kaneko, T.; Tran, H. T.; Shi, D. J.; Akashi, M. Nature Mater. 2006, 5, 966–970. Ricarda, N.; Anthony, J. M.; Cathie, M. Nature Biotechnol. 2004, 22, 746–754. Mathews, A. S.; Kim, I.; Ha, C. S. Macromol. Res. 2007, 15, 114–128. 215 Cheng et al.; Green Polymer Chemistry: New Products, Processes, and Applications ACS Symposium Series; American Chemical Society: Washington, DC, 2018.

27. Lu, Y.; Hu, Z.; Wang, Y.; Fang, Q. X. J. Appl. Polym. Sci. 2012, 125, 1371–1376. 28. Garrison, T. F.; Murawski, A.; Quirino, R. L. Polymers 2016, 8, 262. 29. Nakajima, H.; Dijkstra, P.; Loos, K. Polymers 2017, 9, 523. 30. Kawasaki, N.; Nakayama, A.; Yamano, N.; Takeda, S.; Kawata, Y.; Yamamoto, N.; Aiba, S. Polymer 2005, 46, 9987–9993. 31. Winnacker, M.; Rieger, B. Macromol. Rapid Commun. 2016, 37, 1391–1413. 32. Moran, C. S.; Barthelon, A. B.; Pearsall, A.; Mittal, V.; Dorgan, J. R. J. Appl. Polym. Sci. 2016, 133, 43626. 33. Schouwer, F. D.; Claes, L.; Claes, N.; Bals, S.; Degrèvec, J.; Vos, D. E. D. Green Chem. 2015, 17, 2263–2270. 34. Winnacker, M.; Vagin, S.; Auer, V.; Rieger, B. Macromol. Chem. Phys. 2014, 215, 1654–1660. 35. Jasinska, L.; Villani, M.; Wu, J.; van Es, D.; Klop, E.; Rastogi, S.; Koning, C. E. Macromolecules 2011, 44, 3458–3466. 36. Vanhaecht, B.; Rimez, B.; Willem, R.; Biesemans, M.; Koning, C. E. J. Polym. Sci., Part A: Polym. Chem. 2002, 40, 1962–1971. 37. Koning, C. E.; Teuwen, L.; DeJong, R.; Janssen, G.; Coussens, B. High Perform. Polym. 1999, 11, 387–394. 38. Gaymans, R. J.; van Utteren, T. E. C.; van Berg, J. W. A.; Schuyer, J. J. Polym. Sci., Part B: Polym. Chem. 1977, 15, 537–545. 39. Steeman, P.; Nijenhuis, A. Polymer 2010, 51, 2700–2707. 40. Hasan, M. M.; Zhou, Y.; Mahfuz, H.; Jeelani, S. Mater. Sci. Eng. 2006, 429, 181–188. 41. Ali, M. A.; Tateyama, S.; Kaneko, T. Polym. Degrad. Stab. 2014, 109, 367–372. 42. Ali, M. A.; Kaneko, T. Microbial Applications; Springer-Verlag: Berlin Heidelberg, 2017; Vol. 2, pp 279−289. 43. Wang, Z.; Wei, T.; Xue, X.; He, M.; Xue, J.; Song, M.; Wu, S.; Kang, H.; Zhang, L.; Jia, Q. Polymer 2014, 55, 4846–4856. 44. Coiai, S.; Passaglia, E.; Pucci, A.; Ruggeri, G. Materials 2015, 8, 3377–3427. 45. Nikiforov, A. A.; Vol’fson, S. I.; Okhotina, N. A.; Rinberg, R.; Hartmann, T.; Kroll, L. Russ. Metallurgy 2017, 4, 279–282. 46. Zhao, M.; Yi, D.; Camino, G.; Frache, A.; Yang, R. RSC Adv. 2017, 7, 861–869. 47. Tateyama, S.; Msuo, S.; Suvannasara, P.; Oka, Y.; Miyazato, A.; Yasaki, K.; Teerawatananond, T.; Muangsin, N.; Zhou, S.; Kawasaki, Y.; Zhu, L.; Zhou, Z.; Takaya, N.; Kaneko, T. Macromolecules 2016, 49, 3336–3342. 48. Kawasaki, Y.; Nag, A.; Minakwa, H.; Masuo, S.; Kaneko, T. Appl. Microbiol. Biotechnol. 2018, 102, 631–639. 49. Toader, G.; Rusen, E.; Teodorescu, M.; Diacon, A.; Stanescu, O. P.; Rotariu, T.; Rotaiu, A. J. Appl. Polym. Sci. 2016, 133, 43967. 50. Sasaki, K.; Crich, D. Org. Lett. 2011, 13, 2256–2259. 51. Grujicic, M.; Pandurangan, B.; He, T.; Cheeseman, B. A.; Yen, C. F.; Randow, C. L. Mater. Sci. Eng. A 2010, 527, 7741–7751. 216 Cheng et al.; Green Polymer Chemistry: New Products, Processes, and Applications ACS Symposium Series; American Chemical Society: Washington, DC, 2018.

52. Holzworth, K.; Jia, Z.; Amirkhizi, A. V.; Qiao, J.; Nemat-Nasser, S. Polymer 2013, 54, 3079–3085. 53. Leventis, N.; Chidambareswarapattar, C.; Mohite, D. P.; Larimore, Z. J.; Lu, H.; Sotiriou-Leventis, C. J. Mater. Chem. 2011, 21, 11981–11986. 54. Aries, R. S. US Patent No. 2,945,841 (7-19-1960). 55. Reinecker, M.; Soprunyuk, V.; Fally, M.; Sanchez-Ferrer, A.; Schranz, W. Soft Matter 2014, 10, 5729–5738. 56. Qian, X.; Song, L.; Yu, B.; Yang, W.; Wang, B.; Hu, Y.; Yuen, R. K. K. Chem. Eng. J. 2014, 236, 233–241. 57. Grewal, M. S.; Taya, K.; Tateyama, S.; Kaneko, T. Macromol. Symp. 2017, 375, 1600194. 58. Shin, H.; Tateyama, S. J. Mater. Life Soc. 2014, 26, 25–31. 59. Tan, Y.; Liu, Y.; Chen, W.; Liu, Y.; Wang, Q.; Li, J.; Yu, H. ACS Sustainable Chem. Eng. 2016, 4, 3766–3772. 60. Jin, X.; Tateyama, S.; Kaneko, T. Polym. J. 2015, 47, 727–732. 61. Versteegen, R. M.; Kleppinger, R.; Sijbesma, R. P.; Meijer, E. W. Macromolecules 2006, 39, 772–783. 62. Tang, D.; Mulder, D. J.; Bart, A.; Noordover, J. Macromol. Rapid Commun. 2011, 32, 1379–1385. 63. Andrady, A. L. Plastics and Environment; Wiley-Intersciences, 2003; Vol. 1, pp 418−466. 64. Kitazume, T.; Tanaka, A.; Takaya, N.; Nakamura, A.; Matsuyama, S.; Suzuki, T.; Shoun, H. Eur. J. Biochem. 2002, 269, 2075–2082. 65. Kane, K. F.; Fiske, M. J. J. Bacteriol. 1985, 161, 963–966. 66. Tribe, E. D. Novel microorganism 4 method, U.S. Patent Number 4,681,852, 1987. 67. Suvannasara, P.; Tateyama, S.; Miyasato, A.; Matsumura, K.; Shimoda, T.; Ito, T.; Yamagata, Y.; Fujita, T.; Takaya, N.; Kaneko, T. Macromolecules 2014, 47, 1586–1593. 68. Kumar, A.; Tateyama, S.; Yasaki, K.; Ali, M. A.; Takaya, N.; Singh, R.; Kaneko, T. Polymer 2016, 83, 182–189. 69. Dwivedi, S.; Kaneko, T. Polymer 2018, 10, 368. 70. Huang, T. T.; Tsai, C. L.; Tateyama, S.; Kaneko, T.; Liou, G. S. Nanoscale 2016, 8, 12793–12802. 71. Dwivedi, S.; Sakamoto, S.; Kato, S.; Mitsumata, T.; Kaneko, T. RSC Adv. 2018, 8, 14009. 72. Kaneko, T.; Sakamoto, S.; Kobayashi, T.; Dwivedi, S. 255th ACS National Meeting & Exposition POLY-634, New Orleans, LA, United States, March 18–22, 2018. 73. Althues, H.; Henle, J.; Kaskel, S. Chem. Soc. Rev. 2007, 36, 1454–1465. 74. Shin, H.; Wang, S.; Tateyama, S.; Kaneko, D.; Kaneko, T. Ind. Eng. Chem. Res. 2016, 55, 8761–8766. 75. Zhang, S.; Li, Y.; Lin, D.; Wang, X.; Zhao, X.; Shao, Y.; Yang, S. Eur. Polym. J. 2005, 41, 1097–1107. 76. Chen, C. J.; Hu, Y. C.; Liou, G. S. Polym. Chem. 2013, 4, 4162–4171. 77. Tsai, C. L.; Chen, C. J.; Wang, P. H.; Lin, J. J.; Liou, G. S. Polym. Chem. 2013, 4, 4570–4573. 217 Cheng et al.; Green Polymer Chemistry: New Products, Processes, and Applications ACS Symposium Series; American Chemical Society: Washington, DC, 2018.

78. Dwivedi, S.; Kaneko, T. J. Appl. Polym. Sci. 2018 DOI:10.1002/ app.20180278. 79. Fang, Y.; Hester, J. G. D.; Su, W.; Chow, J. H.; Sitaraman, S. K.; Tentzeris, M. M. Sci. Rep. 2016, 6, 39909. 80. Harnett, M. E.; Alderman, J.; Wood, T. J. Colloid Surf. B: Biointerfaces 2007, 55, 90–97.

218 Cheng et al.; Green Polymer Chemistry: New Products, Processes, and Applications ACS Symposium Series; American Chemical Society: Washington, DC, 2018.