Decrosslinking Reaction Research Articles

Mechano-Activated Self-Immolation of Hydrogels via Signal Amplification.

Cellular organisms possess intricate mechano-adaptive systems that enable them to sense forces and process them with (bio)chemical circuits for functional adaptation. Inspired by such processes, this study introduces a hydrogel system capable of mechanically activated and chemically transduced self-destruction. Our judiciously designed hydrogels can mechanically generate radicals that are processed and amplified in a self-propagating radical de-crosslinking reaction, ultimately leading to mechanically triggered self-immolation. We put such systems to work in mechano-induced debonding, and in a bilayer actuator, where swelling-induced bending generates sufficient force for selective degradation of one layer, leading to autonomous self-regulation associated with unbending. Our work helps define design criteria for molecularly controlled adaptive and self-regulating materials with embodied mechano-chemical information processing, and showcases their potential for adhesives and soft robotics.

Chemical Communication and Protocell‐Matrix Dynamics in Segregated Colloidosome Micro‐Colonies

AbstractDespite an emerging catalogue of collective behaviours in communities of homogeneously distributed cell‐like objects, microscale protocell colonies with spatially segregated populations have received minimal attention. Here, we use microfluidics to fabricate Janus‐like calcium alginate hydrogel microspheres with spatially partitioned populations of enzyme‐containing inorganic colloidosomes and investigate their potential as integrated platforms for domain‐mediated chemical communication and programmable protocell‐matrix dynamics. Diffusive chemical signalling within the segregated communities gives rise to increased initial enzyme kinetics compared with a homogeneous distribution of protocells. We employ competing enzyme‐mediated hydrogel crosslinking and decrosslinking reactions in different domains of the partitioned colonies to undertake selective expulsion of a specific protocell population from the community. Our results offer new possibilities for the design and construction of spatially organized cytomimetic consortia capable of endogenous chemical processing and protocell‐environment interactivity.

Chemical Communication and Protocell-Matrix Dynamics in Segregated Colloidosome Micro-Colonies.

Despite an emerging catalogue of collective behaviours in communities of homogeneously distributed cell-like objects, microscale protocell colonies with spatially segregated populations have received minimal attention. Here, we use microfluidics to fabricate Janus-like calcium alginate hydrogel microspheres with spatially partitioned populations of enzyme-containing inorganic colloidosomes and investigate their potential as integrated platforms for domain-mediated chemical communication and programmable protocell-matrix dynamics. Diffusive chemical signalling within the segregated communities gives rise to increased initial enzyme kinetics compared with a homogeneous distribution of protocells. We employ competing enzyme-mediated hydrogel crosslinking and decrosslinking reactions in different domains of the partitioned colonies to undertake selective expulsion of a specific protocell population from the community. Our results offer new possibilities for the design and construction of spatially organized cytomimetic consortia capable of endogenous chemical processing and protocell-environment interactivity.

Thermally reversible polymer networks for scratch resistance and scratch healing in automotive clear coats

This study investigated the application of a thermally reversible polymer network fabricated using Diels-Alder (DA)/retro-DA (rDA) reactions for use as a scratch-healing automotive clear coat. For this purpose, a new scratch-healing poly(urethane acrylate) network containing a DA adduct unit (DA-CL) was prepared, and its material properties and scratch-healing performance were compared to the properties of a commercial clear coat system (C-CL). The thermally reversible crosslinking and de-crosslinking reactions among the DA-CL, via DA and rDA reactions, were systematically evaluated using in-situ oscillatory rheology coupled with FT-IR spectroscopy. The material properties of the DA-CL and C-CL materials, including the thermal stability, thermal transitions, hardness, and scratch resistance, were measured using thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), nanoindentation, and nanoscratch test methods. The scratch-healing performance of the DA-CL was quantitatively characterized and compared to the performance of the C-CL using a nanoscratch tester equipped with an optical microscope (OM) and an atomic force microscope (AFM). The DA-CL polymer network exhibited superior scratch healing and scratch resistance compared to the C-CL polymer network. These data indicated that the DA self-healing polymer network is potentially useful as a scratch-healing clear coat for the automotive industry.

Lowering the Healing Temperature of Photoswitchable Dynamic Covalent Polymer Networks.

To reduce the environmental footprint of the modern society, it is desirable to elongate the lifetime of consumer products, for example by implementing healable coatings and protective layers. However, since most healing processes carried out by heat or light suffer from material degradation, improving the robustness and integrity of healable materials is of tremendous importance to prolong their lifetime. In recent work, a prototype is created of a dynamic covalent polymer network, whose thermal healing ability can be switched "on" and "off" by light to provide a means to locally control repair of a damaged coating. Based on the initial concept, herein a new set of difunctional crosslinkers and linear polymers of various compositions is presented to form dynamic covalent polymer networks, in which the barrier for the retro Diels-Alder decrosslinking reaction is decreased. The approach results in lower healing temperatures and thus a longer lifetime of the material.

Crosslinking of poly(vinyl alcohol) and poly(vinyl acetate) using poly(maleic anhydride‐alt−2,4‐dimethyl‐1,3‐pentadiene) as polyfunctional crosslinker and decrosslinking by ozone degradation

ABSTRACTCrosslinking and decrosslinking reactions of poly(vinyl alcohol) (PVA) and poly(vinyl acetate) (PVAc) using an alternating copolymer of maleic anhydride and 2,4‐dimethyl‐1,3‐pentadiene (PMAD) as the polyfunctional crosslinker and subsequent ozone degradation are reported. PVA and PVAc are heated at 200 °C for 0.5 to 3 h in the presence of 5 to 30 wt % of PMAD in the solid state to obtain the corresponding crosslinked polymers. The reactions of a hydroxy group of PVA and an acetate group of PVAc with an anhydride group of PMAD slowly proceed to give insoluble polymers with a loose crosslinking structure. Almost no change in the thermal decomposition temperatures and the IR spectra is observed during the crosslinking reactions. The crosslinked PVA produces hydrogels with a high swelling ratio of 500 to 1700%, which are readily degradable during a reaction with ozone in water at 0 °C. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017, 134, 44229.

Decrosslinking reaction kinetics of silane-crosslinked polyethylene in sub- and supercritical fluids

Supercritical methanol is a popular fluid as a supercritical medium for decrosslinking reaction of crosslinked polyethylene. However, due to its toxicity, a safe alternative medium is much to be desired. In this work, various sub- and supercritical fluids with different polarity characters were investigated to find a safe alternative medium for continuous decrosslinking of silane-crosslinked polyethylene (S-XLPE). Like methanol, all examined fluids, including ethanol, propanol, and water, exhibited first-order reaction kinetics regarding the gel content in the continuous decrosslinking process. The reaction rate constant values were observed as 2.806, 2.569, 2.383, and 2.130 min−1 in supercritical methanol, supercritical ethanol, supercritical 2-propanol, and subcritical water at 380 °C, respectively. As a non-toxic fluid with reaction kinetics very comparable to that of methanol, ethanol was found to be the best alternative medium for the continuous decrosslinking reaction of S-XLPE.

A kinetic study on the supercritical decrosslinking reaction of silane-crosslinked polyethylene in a continuous process

For the first time, a kinetic study on the supercritical decrosslinking reaction of silane-crosslinked polyethylene (S-XLPE) in a continuous process was conducted. The decrosslinking reaction in a continuous process was corresponding to the first-order reaction model in which the reaction rate was linearly proportional to the gel content. The residual gel content exponentially decreased with reaction time. Reaction constant was observed exponentially related to the reaction temperature. The continuous decrosslinking reaction revealed kinetic constants of 1.355 ± 0.103, 2.715 ± 0.177, and 4.348 ± 0.218 min−1 at 360, 380 and 390 °C, respectively and activation energy of 132.36 kJ mol−1.

Introduction of reversible crosslinker into artificial marbles toward chemical recyclability

Organic/inorganic composites containing thermally breakable crosslinker were prepared for exploring the possibility in fabrication of recyclable artificial marble composed of acrylic resin and aluminum hydroxide. The breakable crosslinker was fabricated using Diels–Alder reaction from furfuryl methacrylate and bismaleimide. De-crosslinking reaction was also triggered by retro-Diels–Alder reaction. The basic properties of artificial marbles fabricated by breakable crosslinker, i.e chemical, thermal, mechanical and coloring properties, are compared to that of conventional one, which is based on unbreakable crosslinker.

Dynamic crosslinked poly(styrene-block-butadiene-block-styrene) via Diels–Alder chemistry: an ideal method to improve solvent resistance and mechanical properties without losing its thermal plastic behavior

Poly(styrene-block-butadiene-block-styrene) (SBS) is a typical example of thermal plastic elastomers (TPE).

Synthesis and Characterization of Coumarin-containing Hyperbranched-star Copolymers

Coumarin-containing inimer was prepared and used in the self-condensing vinyl polymerization(SCVP) of 2-(2-methoxyethoxy)ethyl methacrylate(MEO2MA). The molar ratio of inimer/MEO2 MA was set as 1︰7, and the reaction was carried out at 50 ℃ for 80 h to afford hyperbranched poly(2-(2-methoxyethoxy)ethyl methacrylate)(H-PMEO2MA). The molecular weight of H-PMEO2 MA is 5400 g/mol and Mw/Mn is 1.56. The content of coumarin group in the hyperbranched polymer is consistent with the feed ratio. Then the resultant H-PMEO2 MA was used as macroinitiator in the following atom transfer radical polymerization(ATRP) of dimethylaminoethyl methacrylate(DMAEMA), and thermo-responsive hyperbranched-star copolymers with different molecular weights were achieved. NMR and GPC were utilized to characterize the hyperbranched-star copolymers. Lower critical solution temperature(LCST) of H-PMEO2 MA is below room temperature, thus the hyperbranched-star copolymers can self-assemble to form micelles in water at room temperature. TEM and DLS were utilized to characterize the morphology and size of the micelles. Coumarin group has the potential to photodimerize via a cycloaddition to form a cyclobutane ring under irradiation of UV light at λ310 nm, and the dimer can be reversibly divide into two coumarin groups under irradiation of UV light at λ260 nm. In this case, when exposed to irradiation of UV light at λ=320 nm, the micelles were core-crosslinked via photodimerization of the coumarin groups. This procedure has been monitored by the UV-Vis spectrum. With increasing irradiation time, the absorbance of coumarin group at 320 nm decreased. After 30 min, the absorbance almost disappeared, indicating that most of coumarin groups dimerized. Under irradiation at λ=254 nm, de-crosslinking reaction of the crosslinked micelles occurred, with the division of dimer into two coumarin groups. During the self-assembly, Nile Red as the model drug was loaded, and the release of Nile Red under different conditions was investigated. When placed at 25 ℃, both core cross-linked and uncross-linked micelles exhibit a relatively slow release behavior, which suggest the good stability of the micelles. While at 0 ℃, a burst release of the uncross-linked micelles was observed due to the disassembling of micelles. However, the morphology of core cross-linked micelles was kept well, and only a small amount of Nile Red was released.

Continuous supercritical decrosslinking extrusion process for recycling of crosslinked polyethylene waste

ABSTRACTThis work demonstrates that extrusion process can be used as a continuous reactor for the recycling of crosslinked polyethylene (XLPE) via supercritical methanol decrosslinking reaction. The multistage single screw extruder (L/D = 36, D = 40 mm) with methanol injection pump was customized for the continuous supercritical decrosslinking reaction. Reaction temperature was ranged from 360°C to 390°C. The amount of methanol was varied from 0 to 7 mL/min. The extruder provided the crosslinked polymers with the supercritical conditions of methanol during continuous process. The gel content of XLPE decreased with the increase in the reaction temperature and methanol content. Although XLPE experienced supercritical methanol for less than 2 min retention time in the continuous supercritical extruder, it was completely decrosslinked above 390°C at the methanol feeding rate of 7 mL/min. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015, 132, 41442.

Foaming of recycled crosslinked polyethylenes via supercritical decrosslinking reaction

AbstractFoaming of decrosslinked crosslinked polyethylene (DCXLPE) was investigated to assess the feasibility of recycled crosslinked polyethylene for polyolefin foam applications. DCXLPE was recycled from irradiation‐induced crosslinked polyethylene using the supercritical methanol process. As the concentration of crosslinking agents increased, the gel fraction and hardness of the DCXLPE foam sheets increased, while the expansion ratio and cell size decreased. The resulting foam products not only revealed a viable foam structure and properties comparable with those of conventional polyethylene foam from virgin low‐density polyethylene resin but also are expected to open new applications for recycled crosslinked polyolefin via supercritical decrosslinking reaction. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012

초임계 메탄올에서 가교폴리프로필렌과 가교폴리에틸렌의 재활용성 비교

Decrosslinking of crosslinked polypropylene(XLPP) in supercritical methanol was investigated compared with that of crosslinked polyethylene(XLPE). Effect of reaction temperature and initial gel contents was studied using a batch reactor. Gel contents of samples before and after reaction were measured for quantitative analysis. As reaction temperature and initial gel contents increased, the decrosslinking rate increased. The rate of decrosslinking reaction is dependent linearly on the gel contents. Experimental results indicated that the decrosslinking of XLPP was faster than that of XLPE, and it was confirmed quantitatively by the calculation of kinetic constants. In conclusion, it is considered that XLPP has better recyclability than XLPE.

A Thermo-Sensitive Laser Imaging Composition Derived from a Modified Phenolic Resin

The performances of CTP plate depend heavily on polymer binder and those capable of producing large image contrast by exposure are keys to quality plate. This research proposed a polymer resin containing hydrophilic spices in the side chain which could be sheltered by the thermal induced crosslinking reaction during plate manufacturing process and released upon imaging exposure. The resin was prepared through esterification reaction of maleic anhydride with phenolic resin, and its chemical structure was characterized by IR spectrum. Plate coatings were formulated with the modified polymer as binder resin, 2,2-bis(4- (2-(vinyloxy)ethoxy)phenyl)propane as the crosslinking agent, a near infrared absorbing dye and crystal violet as the tracing agent. Solubility of the exposed and unexposed coatings in diluted aqueous alkaline was investigated in situ using a home-made dissolving rate tester. It was found that polymer containing 4-6% mole carboxyl groups led to high image contrast and this contribution came directly from the cross-linking and decrosslinking reactions. Preliminary test indicated that this polymer coating generated positive image of high contrast after exposure and could be used as CTP plate coating for thermal laser imaging.

A Modified Phenolic Resin and its Effectiveness as Polymer Binder in Thermo-Sensitive Imaging Composition

The performances of CTP plate depend heavily on polymer binder and those capable of producing large image contrast by exposure are keys to quality plate. This research proposed a polymer resin containing hydrophilic spices in the side chain which could be sheltered by the thermal induced crosslinking reaction during plate manufacturing process and released upon imaging exposure. The resin was prepared through esterification reaction of maleic anhydride with phenolic resin, and its chemical structure was characterized by IR spectrum. Plate coatings were formulated with the modified polymer as binder resin, 2,2-bis(4-(2-(vinyloxy)ethoxy)phenyl)propane as the crosslinking agent, a near infrared absorbing dye and crystal violet as the tracing agent. Solubility of the exposed and unexposed coatings in diluted aqueous alkaline was investigated in situ using a home-made dissolving rate tester. It was found that polymer containing 4-6% mole carboxyl groups led to high image contrast and this contribution came directly from the cross-linking and decrosslinking reactions. Preliminary test indicated that this polymer coating generated positive image of high contrast after exposure and could be used as CTP plate coating for thermal laser imaging.

A kinetic study of the decross-linking of cross-linked polyethylene in supercritical methanol

The recycling of cross-linked polyethylene (XLPE) by a decross-linking reaction in supercritical methanol was studied using a batch reactor. XLPEs with initial gel contents of 45, 55 and 65% were employed and subjected to reaction temperatures between 320 and 360 °C. Complete decross-linking of XLPE was achieved in 10 min in supercritical methanol at 360 °C and 15 MPa. For the first time, chemical kinetics for the decross-linking reaction is proposed based on the gel concentration, and applicable to the reactor design. With respect to the gel concentration, the first-order reaction model agreed well with the experimental results. The evaluated kinetic constant was 0.0867 ± 0.0082 cm 3/mg min at 350 °C, and the activation energy was 578 ± 25 kJ/mol.

A Novel Thermo-Sensitive Polymer Film and its Imaging Properties

Three copolymers containing isobutyl p-styrenesulfonate (IBSS) and carboxyl units, i.e. methyl methacrylate (MMA) and methacrylic acid (MAA), were synthesized and their chemical structures and thermal behaviors were investigated by using TGA, DSC, FTIR and other methods. Films were prepared by using the synthesized copolymers in combination with a bisvinyl ether compound, i.e. 2,2-bis(4-(2-(vinyloxy)ethoxy)phenyl)propane (BVPP), to applied onto an aluminum plate. Crosslinking and de-crosslinking reactions would readily take place when the polymer films were baking treated at 100 oC and 200 oC for a short period of time, respectively. Along with the chemical structural changes during thermal treatments, an affinity change was achieved from being insoluble to completely soluble in neutral water. A positive-working and neutral water-developable imaging material was proposed and preliminary studies on the imaging properties were conducted.

Novel thermo-sensitive polymer matrixes and their imaging properties

Three novel terpolymers, i.e. P-1, P-2 and P-3, were prepared from the terpolymerization of butyl p-styrenesulfonate (BSS), methyl methacrylate (MMA) and methacrylic acid (MAA). Thin films composed of the prepared terpolymers, 2,2-bis(4-(2-(vinyloxy)ethoxy)phenyl)propane (BVPP) and an IR dye (in case of laser scanning) were made onto an aluminum substrate. Crosslinking and de-crosslinking reactions would readily take place when the films were treated at 80 °C and 220 °C for a short period of time, respectively. Along with the chemical structural changes during thermal treatment, great solubility changes could be achieved. It was found that the crosslinked polymer matrix was more resistant to aqueous solution and insoluble in neutral water, whereas the de-crosslinked one such as P-1 matrix could become soluble in neutral water. Based on these properties, a positive-working and neutral water-developable imaging material was proposed and preliminary studies on the imaging property were conducted.

Role of supercritical carbon dioxide for selective impregnation of decrosslinking reagent into isoprene rubber vulcanizate

The behavior of supercritical CO 2 (scCO 2)/low molar mass molecule/crosslinked rubber ternary system was investigated in relation to the impregnation of reagent into the isoprene rubber (IR) vulcanizates, which was the first step of new decrosslinking reaction. The diffusion coefficient of decrosslinking reagent, diphenyl disulfide (DD), into the IR network in scCO 2 was 3.2×10 −11 m 2/s. The distribution coefficient ( K c ) of DD between the solvent and IR matrix was also determined for scCO 2 and toluene. The K c for scCO 2 was higher about four orders of magnitude than that for toluene. DD was uniformly dispersed in the crosslinked IR matrix under 10 MPa at 313 K in scCO 2. These phenomena are advantages of use of scCO 2 for the effective decrosslinking reaction of IR vulcanizate.