Singapore

Dimaleimide-substituted tetraphenylethene (TPE-2MI), which is non-emissive due to photo-induced electron transfer (PET) between maleimide (MI) and tetraphenylethene (TPE) groups, was synthesized and used to cross-link random copolymers of methyl, decyl, or lauryl methacrylate with furfuryl methacrylate. The mixture of the copolymers and TPE-2MI in DMF showed reversible fluorescence with “turn on/off” behavior depending on the Diels–Alder (DA)/retro-DA temperature adjustable process. At high temperatures, the retro-DA reaction dominates, and the fluorescence is quenched by PET mechanism. In contrast, at low temperatures, the emission recovers as the DA reaction takes over. A transparent PMFM/TPE-2MI polymer film was prepared to show an accurate response to the external temperature with tunable fluorescent “turn on/off” behavior. This study proposes possible applications in areas such as information security and transmission.

MATERIALS FOR HUMANITY (MH 21)

Diels–Alder Polymer Networks with Temperature-Reversible Cross-Linking-Induced Emission

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technical paper

Hydroxyapatite (HA) is a calcium phosphate bioreactive and biocompatible material which is an essential element for bone regeneration in human and animal bodies. HA can be found abundant in bones and shells of aquatic animals. The extraction or recovery of HA from aquatic species play an important role in future biomedical applications such as drug delivery, implant coatings, scaffolds for bone grafts, etc. [1]. Therefore, in our study, a wet chemical method was utilized for extraction of HA from bones of different types of seafood wastes (Oreochromis spp, Channa striata, Thunnus albacares, Notopterus notopterus, Salmo salar, Pangasius krempfi). The extracted HA powders were characterized by different characterization methods such as FTIR, XRD, Optical microscope and ICP-MS. Their bioactivity was also evaluated by the immersion of HA powders in stimulated body fluids. The results showed that the extracted HA powders from bones of Channa striata species had the best biocompability and be a good candidate material for bone regeneration, particularly when they existed at a nano-scaled size.

Recovery of Hydroxyapatite From Bones of Seafood Wastes and Its Bioactivity Evaluation

The increasing contamination of organic micropollutants in environmental and biological systems is one of the serious issues faced by humanity. The potentially harmful effects of organic micropollutants (pesticides, pharmaceuticals, and dyes) on human health and aquatic ecosystems have raised worldwide concerns. The releasing of organic micropollutants to freshwater causes serious health hazards because most of them are mutagenic or carcinogenic in nature. Comparing with absorbents, membrane technology possesses merits of high separation performance, low energy consumption, mild operation temperature, cost efficiency, and no cross-contamination, etc.
Here, we propose 2D covalent organic framework (COF) membranes for molecular separation. Azobenzene derivatives act as linkers, which can be photo-switched between trans- and cis-isomers by irradiation under ultraviolet (UV) or visible light. The resultant smart COF membrane has nanopores that can be switched between On- (big pores) and Off-state (small pores) valves for molecular separation. The COF membranes were tested in different organic solvents and exhibit permeances as high as 56.7 L m-2 h-1 bar-1, in the following order: acetonitrile > acetone > methanol > ethanol > isopropanol > DMF. Interestingly, the smart cis-COF membranes with Off-state valves under UV show higher rejection for dye molecules than the trans-COF analogue with On-state valves. Different from the traditional membranes with immutable pore channels, the pore size of COF membranes can be remotely tuned by controlling the trans-to-cis isomerization of azobenzene via UV/Vis light, therefore, the permeance and separation factor can be adjusted as needed.
The ingenious design strategy endows traditional membranes with new fascination and opens up new perspectives for separation science and technology. The development of COF based smart membranes with a periodic honeycomb lattice could be a promising solution for a wide variety of separations such as catalyst and solvent recycle, wastewater treatment (organic micropollutant or heavy metal removal), valuable drug purification from organic solvents in pharmaceutical industry (vitamin or antibiotic refinement), oil extraction and purification in food industry, and other challenging separations (hemodialysis or chiral pharmacology separation).

Smart light-responsive COF membrane for molecular separation

Concerns over dwindling oil reserves, carbon dioxide emissions from fossil fuel sources and associated climate change is driving the need for clean, renewable energy supplies. If average global temperature rises induced by greenhouse gases are not to exceed 1.5 °C, then estimates indicate that a large proportion of crude oil, gas and coal reserves must remain untouched.1 Biomass, derived from agricultural and forestry residues, or non-food sources of triglycerides are a sustainable source of carbon that can provide low cost solutions for transportation fuels and organic chemicals. Akin to petroleum refining, biorefining will integrate biomass conversion processes to produce fuels, power, and chemicals, thereby increasing the economic viability of bio-derived processes. Indeed, the US DoE identified a range of sugar derived ‘Platform Chemicals’ produced via chemical or biochemical transformation of lignocellulosic biomass as potential targets for manufacture in biorefineries.2 Catalytic technologies played a critical role in the economic development of both the petrochemical industry and modern society, underpinning 90 % of chemical processes and contributing to over 20% of all industrial products. In a post-petroleum era, catalysis will underpin biorefinery technology, and researchers will need to rise to the challenge of synthesising chemical intermediates and advanced functional materials and fuels from such non-petroleum based feedstocks.3 

This presentation will discuss the challenges faced in catalytic biomass processing, and highlight recent successes in catalyst design facilitated by advances in nanotechnology and careful tuning of catalyst formulation. Specific case studies will explore (i) how the effects of pore architecture and acid strength can impact upon process efficiency in biodiesel synthesis;4,5 (ii) how catalytic pre-treatments improve transportation fuel production from pyrolysis oil,6 and (iii) the role of bifunctional catalysts in the hydrodeoxygenation of phenolic components in bio-oils,7 and the aqueous phase processing of sugars to important platform chemicals and fuel precursors such as 5-HMF derivatives.8



References. 
1. M. Jakob, J. Hilaire, Nature, 517 (2015) 150.
2. J.J. Bozell, G.R. Petersen, Green Chemistry, 12 (2010) 539.
3. K. Wilson, A. F. Lee Phil. Trans. R. Soc. A, 374 (2016) 20150081.
4. A.F. Lee, K Wilson, Catalysis Today, 242 (2015) 3. 
5. M.A. Isaacs, C.M.A. Parlett, N. Robinson, L.J. Durndell, J.C. Manayil, S.K. Beaumont, S. Jiang, N.S. Hondow, A.C. Lamb, M.L. Johns, K. Wilson, A.F. Lee, Nature Catalysis, 3 (2020), 921.
6. L. Ciddor, J.A. Bennett, J.A. Hunns, K. Wilson, A.F. Lee J. Chem. Tech. Biotech., 90 (2015) 780. 
7. A. Shivhare, J.A. Hunns, L.J. Durndell, C.M.A. Parlett, M.A. Isaacs, A.F. Lee, K. Wilson, ChemSusChem, 13 (2020), 4771.
8. A. Osatiashtiani, A.F. Lee, D.R. Brown, J.A. Melero, G. Morales, K. Wilson, Cat. Sci. Tech., 4 (2014), 333. 


Catalysts for a Sustainable Future

Sulfur-containing polymer is promising to the application of the optical, anti-corrosion and antifouling materials. Using sulfur-containing C1 building blocks [i.e. carbonyl sulfide (COS), carbon disulfide (CS2)] to copolymerize with epoxides have been rapidly developed in our group and others. This talk reports two metal-free routes for the reaction of COS with epoxides.
1) The inhibition of oxygen-sulfur exchange reaction (O-S ER)1 for synthesizing poly(monothiocarbonate)s. Two types of organocatalysts will present, one is the combination of Lewis bases including amidine, guanidine, or quaternary onium salts with triethyl borane.2 A highly transparent and colorless poly(monothiocarbonate)s are obtained with > 99% tail-to-head content and high Mns of up to 92.5 kg/mol. O-S ER that would generate random thiocarbonate and carbonate units, were totally suppressed in most instances. The turnover frequency (TOF) of these Lewis pairs are as high as 240 h-1 at ambient temperature. The other is the combination of organic bases and thioureas via cooperative catalysis.3 Poly(monothiocarbonate)s are obtained with 100 % alternating degree, > 99% tail-to-head content, high Mns of up to 98.4 kg/mol and narrow molecular weight distributions (1.13-1.23). TOFs of the catalysts are up to 112 h−1 at 25 °C. 
2) The utilization of O-S ER for synthesizing poly(thioether)s using COS and epoxides as the starting materials.4 This route undergoes the coupling reaction of COS with epoxides, decarboxylative ring-opening polymerization (ROP) of the generated mixed cyclic thiocarbonates with releasing CO2(a little bit COS). And this method is also applied to the reaction of carbon disufide with epoxides, providing a new pathway to produce COS and poly(thioether)s simultaneously. 
Finally, we’ll present the transformation of poly(monothiocarbonate)s to poly(thioether)s by using O-S ER process, which is a polymer A to polymer B method for recycling the polymers.

Organocatalytic Synthesis of Sulfur-containing Polymers

Composites, and especially carbon fibre reinforced plastics (CFRP), have impressively demonstrated their mechanical performance in several applications in the last years, starting from aerospace, finding their way into sports and commodities and just recently having a significant increase in the wind energy sector. These materials are often referred to as “a material with high potential”. The question is: potential to what? The potential to be a solution to the CO2-problem due to lightweight construction capabilities and the possibility to contribute to fuel savings during the lifetime of an aircraft, a truck or a car, to provide clean energy with more efficient next-gen wind turbines? Or is it the potential to be part of the problem, as the material is very difficult to recycle and currently causes trouble in waste incineration plants and in many cases just ends up in landfills. The presented talk will address the state of the art of recycling CFRP-materials: in a first step the different components of the materials (fibres and plastics, the so called matrix) need to be separated. This can be done via pyrolysis on a commercial scale, or by different alternatives with lower TRL levels. After that the recovered fibres are processed into semi-finished products, such as nonwovens, that are suitable to replace the first-gen materials in terms of handling and processing. All along the way, it is necessary to monitor the properties of the materials, in order to be able to identify correlations of process-parameters and resulting properties, both for quality assurance in a future supply chain, as well as identification of further demand for continuing R&D-activities. Finally, the stakeholders in a circular economy are adressed: why should a company invest in the improvement of recycle-ability of their products? This discussion is not limited to CFRP-materials only, but is open to interaction with other material classes with emerging circularity.

Recycling of fibre reinforced plastics - state of the art and outlook

Flexible electronics are of critical importance for medical devices, portable electronics, smart textiles, energy storage, communication and sensor systems [1,2]. However, the lifetime of electronics is becoming shorter, which poses a growing ecological problem. Therefore, it is urgent and necessary to find sustainable and cost-efficient materials to replace the crude oil-derived polymers that are commonly used in flexible electronics. To this end, fish gelatin (FG) extracted from fish scales could provide an eco-friendly and biodegradable alternative to plastic for use in flexible electronics. Fish scales are inedible and malodorous kitchen waste, and >2 million metric tons of fish scales are discarded each year. This talk will introduce our recent works on FG-based flexible electronics, including flexible electroluminescent devices and triboelectric nanogenerators (TENGs) [3-6]. The properties of FG films, the structure design and the performance of flexible electronic devices will be briefly discussed. These works may pave a new way to green and sustainable flexible electronics.

References
1. S. Xu, A. Jayaraman, J. A. Rogers. Skin sensors are the future of health care. Nature, 2019, 571, 319-321.
2. G.-H. Lee, H. Moon, H. Kim, G. H. Lee, W. Kwon, S. Yoo, D. Myung, S. H. Yun, Z. Bao, S. K. Hahn. Multifunctional materials for implantable and wearable photonic healthcare devices. Nat. Rev. Mater., 2020, 5, 149–165.
3. X. P. Zhang, T. Y. Ye, X. H. Meng, Z. H. Tian, L. H. Pang, Y. J. Han, H. Li, G. Lu, F. Xiu, H. D. Yu, J. Q. Liu, W. Huang. Sustainable and transparent fish gelatin films for flexible electroluminescent devices. ACS Nano, 2020, 14, 3876-3884.
4. T. F. Jiang, X. H. Meng, Z. Zhou, Y. Y. Wu, Z. H. Tian, Z. D. Liu, G. Lu, M. Eginlidil, H. D. Yu, J. Q. Liu, W. Huang. Highly flexible and degradable memory electronics comprised of all-biocompatible materials. Nanoscale, 2021, 13, 724-729.
5. Y. J. Han, Y. F. Han, X. P. Zhang, G. Lu, H. D. Yu, W. Huang. Fish gelatin-based triboelectric nanogenerator for harvesting biomechanical energy and self-powered sensing of human physiological signals. ACS Appl. Mater. Interfaces, 2020, 12, 16442-16450.
6. Q. Z. Sun, H. C. Wang, L. Wang, X. P. Yue, L. R. Zhang, G. Z. Ren, D. H. Li, Y. J. Han, L. L. Xiao, G. Lu, H. D. Yu, W. Huang. Fully sustainable and high-performance fish gelatin-based triboelectric nanogenerator for wearable movement sensing and human-machine interaction. Nano Energy, in revision.

Sustainable Flexible Electronics Based on Fish Gelatin

Chitin is the second most abundant biopolymer, after cellulose. It is present in the shell of crustaceans, in the cuticle of insect and even in some fungi. Chitin can be converted into chitosan, a highly praised material in the biomedical sector for its antibacterial properties, which finds also important application as a fertilizer, water treatment flocculant and food additive. Yet today's technologies for chitosan production from biomass rely on the use of corrosive treatments, high energy input and large quantities of by product effluents. Herein we are presenting our group's effort to tackle this question. We showed that mechanochemistry and aging could be used effectively for the deacetylation of chitin.1 This process yielded high molecular weight chitosan with minimal use of energy and solvent. This method is versatile and applicable to a number of chitin sources, including crude crustacean and insect shells, yielding deacetylation up to 98% and remarkably high molecular weights. This process affords chitosan in a safer fashion and with less materials and energy usage compared to the classic hydrothermal one. We have also extended this method to the fabrication of chitosan nanocrystals from chitin nanocrystals.2 Chitin and chitosan nanocrystals featured enhanced properties are nanocatalysts supports.3,4 We have also developed hydrogels from chitosan and chitin nanocrystals, with exceptional gelling properties and demonstrated their applicability for slow drug release.

Upcycling biomass: from crustacean waste to functional materials

Biopolymers such as chitosan, cellulose and alginate from biomass have demonstrated huge potential in many important and rapidly growing applications, it is always challenging to create advanced biopolymer materials cost-effectively. Herein, we present our progress in preparing a series of biopolymer composite materials with unexpected properties using a facile “dry”, thermomechanical method. Chitosan/CMC composite films created in this way showed much better hydrolytic stability, compared to chitosan-only films. This is so despite inclusion of the CMC in the chitosan matrix even increasing the surface hydrophilicity. We propose that our processing method led to the polyelectrolyte complexation between chitosan and CMC generating physical crosslinking points in the materials. These crosslinks stabilised the films in water although hydration disrupted hydrogen bonding between polysaccharide chains leading to dramatically decreased tensile strength and increased elongation at break. 
Besides, we found chitosan/silk peptide (SP) polyelectrolyte-complexed materials prepared in the same way had extraordinary mechanical properties. Moreover, we prepared chitosan/alginate composites using the same processing protocol and demonstrate that inclusion of graphene oxide could enhance polysaccharide plasticisation, leading to enhanced mechanical properties and surface hydrophobicity. 
The method of materials hybridisation without chemical reactions demonstrated in this work could provide an insight into the development of cost-effective biopolymer materials with competitive properties as plastic replacements in certain applications, where biodegradability, biosafety, and biocompatibility are indeed required (e.g. functional food packaging and antimicrobial wound healing).

Thermomechanically Processed, Polyelectrolyte-Complexed Polysaccharide Composites with Enhanced Hydrolytic Stability and Mechanical Properties

Plastics have become indispensable in the modern society. However, plastics pollution has also become a global environmental crisis that is projected to grow. The most common approaches to manage plastics pollution include mechanical recycling and pyrolytic waste-to-energy processes, but these methods inevitably lead to the increase in greenhouse gas emissions. In this presentation, I will summarize my team’s early contributions to using exclusively Earth-abundant elements and renewable energy to upcycle plastics. In particular, I plan to focus on our efforts at applying molecular vanadium complexes for selective, ambient condition, photoredox C-C cleavage reactions.1 We conducted detailed kinetic measurements to identify the fastest catalyst and the critical functional groups required in the substrates.2 The vanadium photocatalysts were then utilized for the C-C bond cleavage and oxygenation of over 30 substrates, including unactivated, commercially sourced alcohols and even non-biodegradable plastics.3-6 

Figure 1. Photocatalytic upcycling of non-biodegradable polyethylene to formic acid, a liquid organic hydrogen carrier as a fuel.

References
1. Gazi, S.; Ng, W. K. H.; Ganguly, R.; Moeljadi, A. M. P.; Hirao, H.; Soo, H. S. Chem. Sci. 2015, 6, 7130-7142.
2. Gazi, S.; Dokić, M.; Moeljadi, A. M. P.; Ganguly, R.; Hirao, H.; Soo, H. S. ACS Catal. 2017, 7, 4682-4691.
3. Gazi, S.; Dokić, M.; Chin, K. F.; Ng, P. R.; Soo, H. S. Adv. Sci. 2019, 6, 1902020.
4. Dokić, M.; Chin, K. F.; Soo, H. S. Trends Chem. 2020, 2, 485-488.
5. Zhao, X.; Boruah, B.; Chin, K. F.; Dokić, M.; Modak, J. M.; Soo, H. S. Adv. Mater. 2021, in press.
6. Estahbanati, M. R. K; Kong, X. Y.; Eslami, A.; Soo, H. S. ChemSusChem, 2021, in press.

Photocatalytic Upcycling to Sustainably Reuse Plastics

High dielectric constant and low dielectric loss are desirable electrical properties for next generation polymer films for capacitive energy storage. Unfortunately, the dielectric constant of polymers is often limited to 2-5, much lower than that of inorganic dielectrics, because of the nature of hydrocarbon covalent bonds for electronic and atomic polarizations. It is essential to understand the fundamental physics of different types of polarization and the associated loss mechanisms in polymers. Among various approaches for high dielectric constant and low loss polymers, the multilayer film technology is of particular interest because a multilayer film is a unique one-dimensional system with tailored material choices, layer thicknesses, and interfaces. By minimizing the disadvantageous polarizations and enhancing the advantageous polarizations, multilayer films hold promise as advanced dielectrics for future polymer film capacitors.

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Organocatalytic Synthesis of Sulfur-containing Polymers