Low-temperature Depolymerization Research Articles

Chemical recycling of bromine-terminated polymers synthesized by ATRP.

Chemical recycling of polymers is one of the biggest challenges in materials science. Recently, remarkable achievements have been made by utilizing polymers prepared by controlled radical polymerization to trigger low-temperature depolymerization. However, in the case of atom transfer radical polymerization (ATRP), depolymerization has nearly exclusively focused on chlorine-terminated polymers, even though the overwhelming majority of polymeric materials synthesized with this method possess a bromine end-group. Herein, we report an efficient depolymerization strategy for bromine-terminated polymethacrylates which employs an inexpensive and environmentally friendly iron catalyst (FeBr2/L). The effect of various solvents and the concentration of metal salt and ligand on the depolymerization are judiciously explored and optimized, allowing for a depolymerization efficiency of up to 86% to be achieved in just 3 minutes. Notably, the versatility of this depolymerization is exemplified by its compatibility with chlorinated and non-chlorinated solvents, and both Fe(ii) and Fe(iii) salts. This work significantly expands the scope of ATRP materials compatible with depolymerization and creates many future opportunities in applications where the depolymerization of bromine-terminated polymers is desired.

Hydroxyl radicals-mediated oxidative cleavage of the glycosidic bond in cellobiose by copper catalysts and its application to low-temperature depolymerization of cellulose

As the most abundant source of biomass in nature for sustainable production of fuels and chemicals, efficient depolymerization of cellulose under mild conditions, due to the difficulty in selective cleavage of its β-1,4-glycosidic bonds, still remains challenging. Here, we report a novel method for oxidative cleavage of the glycosidic bonds by free radicals. Probed by the cellobiose reaction, it was found that ·OH radicals, generated from the decomposition of H2O2 catalyzed by CuSO4 or CuO/SiO2, were efficient for selective conversion of cellobiose to glucose and gluconic acid at a low temperature of 333 K, and their selectivities reached 30.0% and 34.6%, respectively, at 23.4% cellobiose conversion. Other radicals, such as ·SO4−, also exhibited high efficacy in the cellobiose reaction. Mechanistic studies suggest that the oxidative cleavage of the β-1,4-glycosidic bond by the free radicals involve formation of the carbon radical intermediate via abstraction of the H atom dominantly at the C1 position. Following this oxidative mechanism, treatment of microcrystalline cellulose with ·OH by impregnation with H2O2 and CuSO4 catalyst at 343 K led to significant enhancement in its hydrolysis efficiency. These results demonstrate the effectiveness of this new method in the oxidative cleavage of glycosidic bonds, and its viability for the efficient depolymerization of cellulose at low temperatures, which can be further improved, for example, by exploring new free radicals and optimizing their reactivity and selectivity.

Solvolysis of Sugarcane Bagasse: Strategy To Increase the Yields of Secondary Fuel Precursors

Low-temperature depolymerization of biomass sugars is a less capital-intensive way to produce secondary fuel precursors. Solvolysis of bagasse using polyol cosolvents reduces sugar dehydration and limits unwanted side reactions. Ethylene glycol (EG) as cosolvent (50 v/v%) was found to increase formic acid, levulinates, and furfural yields from 71 to 100 mol %, 59 to 70 mol %, and 44 to 59 mol %, respectively, based on the theoretical yield of the cellulose component of bagasse. The exceptionally high formic acid yield is attributed to it being produced not only from cellulose but also via hemicellulose and EG conversion pathways. Increasing concentrations of EG proportionally reduced furfural yield. Delignification of bagasse prior to solvolysis with 50 v/v% EG decreased the yields of both formic acid (84 mol %) and furfural (52%) but increased the levulinates yield to 80 mol %.

Low temperature depolymerization and polycondensation of a slag-based inorganic polymer

Abstract In this paper, the depolymerization and polycondensation process, compressive strength, gel content and conductance of an alkali-activated slag (AAS) (an inorganic polymer or high-calcium geopolymer) paste cured at low temperature (−25 °C~25 °C) were studied. The results showed that gel content of the AAS inorganic polymer sample first increased and then decreased with the decreasing of the curing temperature for 24 h, reaching a maximum value of 37.8 wt% in the samples cured at 0 °C. Chemical structural data are obtained by nuclear magnetic resonance (NMR) spectroscopy for 6-coordinated (octahedral) aluminum can be observed at low temperature (

Low-temperature depolymerization of polysiloxanes with iron catalysis.

The easy accessibility and high adjustability of polymers mainly accounts for the great impact of such materials on modern society. Besides this great success, an important matter is the accumulation of large amounts of end-of-life polymers, which are mainly deposited in landfills or converted by thermal recycling or down-cycling to low-quality materials. In contrast to that, the depolymerization of end-of-life polymers to monomers, which can be applied as feedstock in polymerization chemistry for high-quality polymers, is only carried out for a small fraction of waste. Polysiloxanes are extensively used in a diverse array of technological applications. Based on intrinsic properties of polymers, depolymerization is challenging and only a few high-temperature or less environment-friendly processes have been reported. In this regard, we have set up a capable low-temperature protocol for the depolymerization of poly(dimethylsiloxane) in the presence of catalytic amounts of simple iron salts in combination with different depolymerization reagents. The application of benzoyl fluoride, benzoyl chloride/potassium fluoride, or benzoic anhydride/potassium fluoride as depolymerization reagents affords difluorodimethylsilane or 1,3-difluoro-1,1,3,3-tetramethyldisilxanes as products, which are interesting building blocks for the synthesis of new polymers and allow an overall recycling of polysiloxanes.

UV photostability of PMMA-C60 fullerene composition

Thermal decomposition of pure poly(methyl methacrylate) (PMMA) and its composition with C60 fullerene before and after UV irradiation has been studied by thermodesorption mass spectrometry (TDMS). It is established that low-temperature depolymerization of UV-irradiated PMMA is suppressed in its composition with C60. Possible molecular stabilization mechanisms are discussed.

Low temperature depolymerization from a copper-based aqueous vinyl polymerization system

A low temperature strategy for the aqueous polymerization of N-isopropylacrylamide (NIPAM) has been developed. The radical polymerization system is featured with the exclusive use of CuCl and tris(2-dimethylaminoethyl)amine (Me6TREN), devoid of any externally added organic atom transfer radical polymerization (ATRP) initiator. The polymerization reaction is tolerant of variation on the N-substitution pattern, as demonstrated by the synthesis of a homopolymer of acrylamide (AM) and a copolymer of NIPAM and N,N-dimethylacrylamide (DMAA). Importantly, an intriguing phenomenon of depolymerization has been observed at 0 °C with the addition of either 2,2,6,6-tetramethylpiperidinooxy (TEMPO) or 1,4-benzoquinone (BQ) to the polymerization system. A control experiment carried out with conventional 2,2′-azobisisobutyronitrile (AIBN) radical system indicates that copper is required in the depolymerization process. The depolymerization reaction is therefore proposed to proceed through β-alkyl elimination from CuII coordination center. These observations provide a likely starting point for the establishment of new synthetic paradigms for the precision recycling of vinyl monomers under mild and benign conditions.

Photoluminescence and paramagnetic defect formation in PMMA-C60 fullerene nanocomposite

The dynamics of thermoinduced defect formation and the photoluminescent properties of a poly(methyl methacrylate)-fullerene (PMMA-C60) composite have been studied using a combination of spectroscopic techniques. Quantum-chemical calculations with implicit allowance for the presence of oxygen have been performed for a MMA-C60 model complex. The generation of defects and the quenching of photoluminescence, which take place in the same temperature interval where the macromolecules exhibit low-temperature depolymerization in the presence of C60, can be precursors of the depolymerization process.

Modeling of low-temperature depolymerization of poly (methyl methacrylate) promoted by ion beam

The role played by the ion beam in the depolymerization of poly(methyl methacrylate) (PMMA) is the creation of initiators for the unzipping reaction at relatively low temperatures [lower than the ceiling temperature of PMMA (TC=220 °C)]. Monomer (MMA) evolution out of the polymeric film is thus governed by the kinetics of the chemical reaction and also by the diffusion of monomer inside the polymeric film. In this work this phenomenon has been described by using simple models in which both one- and two-dimension monomer diffusion is considered. Exact analytical solutions of the models are provided. The theory fit well the experimental data and allows for the determination of important parameters such as the kinetics constant of the depolymerization and the monomer diffusion coefficient, D, inside the polymer film. Thus, the pulsed ion beam technique, here modeled, is useful not only for extracting D values of slow diffusants in polymers, but even for measuring kinetics constants of depolymerization at a temperature well below that needed for the formation of suitable thermal initiators.

96/03797 Low-temperature depolymerization of coal under the influence of electron acceptors

96/03797 Low-temperature depolymerization of coal under the influence of electron acceptors

Preservation of 2-D Crystals of Tubulin for Electron Crystallography

Zinc-induced sheets of tubulin are two-dimensional crystalline polymers that constitute an ideal sample for high resolution studies of tubulin by electron crystallography. We show that these 2-dimensional tubulin crystals can be stabilized by taxol against low-temperature depolymerization and degradation with time, easing the way for the preparation of electron microscopy samples. The preservation of the crystals to high resolution has been tested with different embedding media. While glucose-embedded samples diffract poorly, samples embedded in tannin consistently diffract to a resolution of at least 3.5 Å. Even better results are obtained by embedding with a combination of tannin and glucose, which improves the flatness of the crystals and allows the collection of isotropic high-resolution data from tilted specimens.

High resolution Chromatographic characterization of depolymerized coals of different rank: aliphatic and aromatic hydrocarbons

A selective, low temperature depolymerization procedure has been applied to four coals of different rank to obtain products that are representative of the original structural units (monoclusters) of the coal macromolecular component, and that are amenable to Chromatographic analysis. The monocluster products of this depolymerization procedure retain most of their original aromatic-hydroaromatic structures, whereas functional groups serving as intercluster linkages, e.g. alkylene and etheric groups, undergo predictable modification. A comparison of liquid 13C n.m.r. spectra of the products and solid state 13C n.m.r. spectra of the original coals showed only minor changes in the aromaticities between the solid and depolymerized products, but some loss of carbonyl carbons was detected in all of the coals. Both the tetrahydrofuran pre-extract and the depolymerized products of the four coals were separated into chemical classes by adsorption chromatography. Two of these fractions were found to consist predominantly of aliphatic hydrocarbons (paraffins and naphthenes) and alkylsubstituted bi-, tri- and (some) tetracyclic arenes. The fractions were analysed using gas chromatography-mass spectrometry. Structural identifications were based on a combination of Chromatographic retention and mass spectral fragmentation data. For the lower rank coals, the compositions of the pre-extracts were quite different from the corresponding depolymerized coal products, and contained various molecular biological markers. The compositions of the pre-extracts became closer to those of the depolymerized coal products as rank increased.

Recent Progress on Coal Chemistry

The analysis of extract of coal, hydrolysis, low temperature depolymerization, hydrogenolysis and oxydation of coal were reviewed.