Polymer Scission Research Articles

Fast and Selective Main-Chain Scission of Vinyl Polymers Using the Domino Reaction in the Alternating Sequence for Transesterification.

This communication reports on vinyl polymers capable of selective and fast main-chain scission (MCS). The trick is the domino reaction in an alternating sequence of methyl 2-(trimethylsiloxymethyl)acrylate and 5,6-benzo-2-methylene-1,3-dioxepane, a cyclic ketene acetal for radical ring-opening polymerization. Removal of the trimethylsilyl group using Bu4N+·F- readily led to MCS via irreversible transesterification of the ester backbone, affording a five-membered lactone fragment. The molar mass decreased drastically within 5 min, and no side reactions were observed. Control experiments suggest that the formation of a five-membered ring via a domino reaction is critical for fast and selective MCS. The terpolymers with methyl methacrylate and styrene also exhibited a large decrease in molar mass within 5 min. In addition, MCS was also observed for the heterogeneous reaction system in acidic aqueous media; treatment of the binary copolymer in a 50 wt % acetic acid solution resulted in a significant decrease in molar mass after 30 min. These results suggest efficient construction of degradable sites using a binary monomer system corresponding to the pendant trigger and ester backbone. Because this molecular design using a binary monomer system provides selective and fast MCS for terpolymers containing other vinyl monomers, it can provide various degradable vinyl polymers.

Increasing polymer scission rate by tying an overhand knot

Increasing polymer scission rate by tying an overhand knot

Memory and scission effects of polymers on the flow regime of polyethylene oxide solutions in continuous abrupt contraction–expansion microchannels with different cavity lengths

This study experimentally observes the flow regimes of polyethylene oxide solutions in continuous, abrupt contraction–expansion microchannels. In dilute solutions (0.5 × 10−3–1.5 × 10−3 wt. %), the effects of flow rate, concentration, and cavity length on flow characteristics in the contraction and expansion parts of each cavity are analyzed, including quantified calculations of normalized vortex lengths and extension rates. The results indicate that polymer memory and scission affect the flow transitions. Memory effects enhance vortex growth and scission weakens flow, and these effects occur continuously within the channel. Increased flow rates and cavity lengths intensify polymer scission, accelerating the transitions from elastic instability to corner vortex, lip vortex, and then to steady vortex-free flows in the contraction parts and from steady vortex-free flows to lip and corner vortices in the expansion parts. The flow-regime transitions for concentrations from 0.01 to 0.4 wt. % for dilute and unentangled semi-dilute solutions at various flow rates are summarized in the Reynolds and Weissenberg number spaces. Polymer chains tend to become entangled in higher-concentration solutions, rendering the solution rigid and inducing complex flow regimes.

Impact of Mixing Shear on Polymer Binder Molecular Weight and Battery Electrode Reproducibility

The viscosity and microstructure of Li-ion battery slurries and the performance of the resulting electrodes have been shown to depend on the mixing protocol. This work applies rheology to understand the impact of shear during mixing and polymer molecular weight on slurry microstructure and electrode performance. Mixing protocols of different shear intensity are applied to slurries of LiNi0.33Mn0.33Co0.33O2 (NMC), carbon black (CB), and polyvinyldiene difluoride (PVDF) in N-methyl-2-pyrrolidinone (NMP), using both high-molecular-weight (HMW) and low-molecular-weight (LMW) PVDF. Slurries of both polymers are observed to form colloidal gels under high-shear mixing, even though unfavorable interactions between high molecular weight PVDF and CB should prevent this microstructure from forming. Theoretical analysis and experimental results show that increasing shear rate during the polymer and particle mixing steps causes polymer scission to decrease the polymer molecular weight and allow colloidal gelation. In general, electrodes made from high molecular weight PVDF generally show increased rate capability. However, high shear rates lead to increased cell variability, possibly due to the heterogeneities introduced by polymer scission.

Effects of Activation Barriers on Quenching to Stabilize Prebiotic Chemical Systems.

We have previously shown in model studies that rapid quenches of systems of monomers interacting to form polymer chains can fix nonequilibrium chemistries with some lifelike properties. We suggested that such quenching processes might have occurred at very high rates on early Earth, giving an efficient mechanism for natural sorting through enormous numbers of nonequilibrium chemistries from which the most lifelike ones could be naturally selected. However, the model used for these studies did not take account of activation barriers to polymer scission (peptide bond hydrolysis in the case of proteins). Such barriers are known to exist and are expected to enhance the quenching effect. Here, we introduce a modified model which takes activation barriers into account and we compare the results to data from experiments on quenched systems of amino acids. We find that the model results turn out to be sensitive to the width of the distribution of barrier heights but quite insensitive to its average value. The results of the new model are in significantly better agreement with the experiments than those found using our previous model. The new parametrization of the model only requires one new parameter and the parametrization is more physical than the previous one, providing a chemical interpretation of the parameter p in our previous models. Within the model, a characteristic temperature Tc emerges such that if the temperature of the hot stage is above Tc and the temperature of the cold stage is below it, then the 'freezing out', in a quench, of a disequilibrium ensemble of long polymers is expected. We discuss the possible relevance of this to models of the origin of life in emissions from deep ocean rifts.

The role of ubiquitous metal ions in degradation of microplastics in hot-compressed water

Hydrothermal processing (HTP) is an efficient thermochemical technology to achieve sound treatment and resource recovery of sewage sludge (SS) in hot-compressed subcritical water. However, microplastics (MPs) and heavy metals can be problematic impurities for high-quality nutrients recovery from SS. This study initiated hydrothermal degradation of representative MPs (i.e., polyethylene (PE), polyamide (PA), polypropylene (PP)) under varied temperatures (180–300 °C) to understand the effect of four ubiquitous metal ions (i.e., Fe3+, Al3+, Cu2+, Zn2+) on MPs degradation. It was found that weight loss of all MPs in metallic reaction media was almost four times of that in water media, indicating the catalytic role of metal ions in HTP. Especially, PA degradation at 300 °C was promoted by Fe3+ and Al3+ with remarkable weight loss higher than 95% and 92%, respectively, which was ca. 160 °C lower than that in pyrolysis. Nevertheless, PE and PP were more recalcitrant polymers to be degraded under identical condition. Although higher temperature thermal hydrolysis reaction induced severe chain scission of polymers to reinforce degradation of MPs, Fe3+ and Al3+ ions demonstrated the most remarkable catalytic depolymerization of MPs via enhanced free radical dissociation rather than hydrolysis. Pyrolysis gas chromatography-mass spectrometry (Py GC–MS) was further complementarily applied with GC–MS to reveal HTP of MPs to secondary MPs and nanoplastics. This fundamental study highlights the crucial role of ubiquitous metal ions in MPs degradation in hot-compressed water. HTP could be an energy-efficient technology for effective treatment of MPs in SS with abundant Fe3+ and Al3+, which will benefit sustainable recovery of cleaner nutrients in hydrochar and value-added chemicals or monomers from MPs.

Mock-Ups in Plastic Conservation Research: Processing and Aging of 3D Celluloid Specimens Simulating Historical Objects.

The preparation of mock-ups in heritage science studies represents a valid alternative for investigation purposes, avoiding extensive sampling of cultural heritage objects. This work presents for the first time the successful preparation of three dimensional (3D) mock-ups made of celluloid, considering a combination of historical industrial production strategies and small-scale lab facilities. Prefabricated transparent celluloid sheets were acquired and then shaped through compression molding for creating mock-ups with 3D geometries. These reflected common and representative shapes encountered in the collection of the Deutsches Museum. Visual inspection of the mock-ups allowed determining the best compression molding conditions. Attenuated total reflection Fourier-transform infrared spectroscopy (ATR-FTIR) confirmed the absence of molecular heterogeneity due to the processing method. Artificial aging of the mock-ups was conducted to reach degradation states comparable with naturally aged objects. ATR-FTIR investigation offered first insights into the induced artificial degradation. Ion chromatography (IC) and gel permeation chromatography (GPC) analyses allowed to assess the extent of the artificial aging of the celluloid mock-ups and confirmed the occurrence of loss of camphor, denitration, and main chain polymer scission, the latter being the predominant decay path. The comparison with historical objects highlighted that the mock-ups are representative of moderately aged artifacts. As such, this study paves the way for implementing moderately aged celluloid 3D mock-ups in heritage science research, enabling in-depth testing for the scope of conservation.

Thermal pre-processing before extraction of polyhydroxyalkanoates for molecular weight quality control

Past studies have repeatedly demonstrated the technical feasibility to produce polyhydroxyalkanoate (PHA) using bacterial biomass of mixed microbial cultures (MMCs). Commercial quality grades of poly(3-hydroxybutyrate-co-3-hydroxyvalerate), PHBV, can be produced with control of average monomer composition. However, demonstration of PHBV production and recovery with quality control of molecular weight (MW) distribution has been lacking in the research literature. Towards this goal, a workflow has been developed for characterizing molecular weight control by thermal treatment pre-processing of dried PHA-rich biomass before solvent extraction. Dimethyl carbonate (DMC) was a suitable solvent in this workflow in the routine evaluation of extractable PHA. From assessments of DMC extraction using differential scanning calorimetry, 125 °C was selected for nominally 100 percent extraction yield independent of polymer 3-hydroxyvalerate (3HV) content (2 to 41 wt.% 3HV) and molecular weight (100 to 1400 kDa). Intrinsic viscosity measurements of PHBV in DMC at 60 °C was used for molecular weight monitoring. Mark-Houwink constants, α (0.738 ± 0.010) and LogK (-2.016 ± 0.025), were estimated for a PHBV co-polymer blend having 36 wt.% 3HV. A model of random scission supported that weight average molecular weight (Mw) was a more robust metric, compared to number average molecular weight (Mn), for assessing the polymer scission rates. During isothermal heat treatment for a given biomass batch, interpreted scission rate was reproducible and commonly, but not always, constant in time. Scission rates between biomass batches were also variable. Measured properties of the polymer in the biomass (thermal stability, biomass PHA content, PHBV grade, initial moisture content) could not be correlated to this observed batch-to-batch variation of scission rate. Molecular weight loss before extraction did not influence the melting temperatures of the co-polymer blends of PHBV evaluated over a wide sub-eutectic range of average 3HV content. Molecular weight changes for these PHBV co-polymer blends were considered to have likely influenced the nature of blend 3HV distribution, and consequently, crystallization behaviour. Molecular weight loss effects on crystallization behaviour at constant PHBV average 3HV wt.% content could then have contributed to the observed variability for glass transition temperatures and melting enthalpies. However, a reproducible correlation between this variability and MW change was not observed.

Mechanical scission of a flexible polymer (polyethylene oxide) under highly turbulent flows through abrupt contractions

We analyze the polymer scission of a flexible polymer (polyethylene oxide) in a turbulent flow in pipelines, including abrupt contractions. The role played by these local occurrences is studied for an extensive range of concentrations and molecular weight over time (passes through our system). We pointed that the final value of the drag reduction parameter (DR) is independent of the initial value of molecular weight. This behavior is different for flows in straight tubes in the absence of local occurrences. We propose a model for DR as a function of concentration, molecular weight, contraction rate, and the number of passes through the system. We also showed that the fall of DR is linearly dependent on the molecular weight decrease.

Effect of high-energy electrons on the thermal, mechanical and fire safety properties of fire-retarded polypropylene nanocomposites

Fire-retarded nanocomposites (FRNC) based on polypropylene, clay and allylamine polyphosphate (PP-FRNC) was processed firstly. Effect of high-energy electrons on the thermal, mechanical and fire safety performances of PP-FRNC were then investigated systematically. After that the relevant fire safety mechanism of irradiated PP-FRNC was discussed. The thermal and mechanical properties of the irradiated PP-FRNC were increased by (electron beam) EB treatment at suitable dose, whereas these properties reduced by high-energy electrons because of the degradation or chain scission of polymer at higher dose. Moreover, the increase dose of EB treatment could improve the LOI values of PP-FRNC. Furthermore, EB treatment modified PP-FRNC improved better quality char residue, which effectively enhance fire safety of PP-FRNC. Particularly, the results suggest that EB treatment is a sustainable green and efficacious surface modification for heat and smoke suppressions rate of FRNC.

Glass transition temperature of Risø B3 radiochromic film dosimeter and its importance on the post-irradiation heating procedure

Full-color development and stability of measured absorbance of the commercially used Risø B3 radiochromic film dosimeter can be achieved by applying a post-irradiation heat treatment procedure, typically at 60 °C for 10 min. However, the choice of post-irradiation heating duration and temperature has only been based on a trial and error method, and thus, the thermal stability of the material has not been fully studied before. We show that B3 film undergoes a rapid thermal decomposition of the PVB polymer base at 400 °C, with an initiation of the process at 70 °C. It means that higher irradiation temperatures, which can occur e.g. at high-dose electron beam irradiation, may cause polymer degradation. We also show that the post-irradiation heating temperature agrees with the polymer material's glass transition temperature as measured by differential scanning calorimetry (DSC). The post-irradiation heating procedure successfully removes the film's thermal history. This can be seen as an endothermic peak in the first heating cycle, which becomes smaller for higher irradiation doses. Glass transition temperatures of irradiated and post-irradiation heated B3 film are lower than those of the non-irradiated film, and decrease with increasing the dose. That implies a probable chain scission or degradation of the base polymer upon irradiation using high dose rates with no irradiation temperature control.

Effect of additives on the thermal stability of SBS modified binders during storage at elevated temperatures

Styrene-butadiene-styrene modified binders (SBS-MBs) exhibit significant property deterioration during storage at elevated temperatures (≥180 °C) in closed containers due to the degradation of the SBS molecules. This study examines the effect of waxes, polyphosphoric acid (PPA), thermal stabilizers, sulfur, aromatic oils, and oxidized binders on the thermal stability of SBS-MBs. The result shows that iscowax and PPA successfully reduced property deterioration in SBS-MBs during storage at 180 °C by up to 30–40 %. On the other hand, thermal stabilizers are ineffective in enhancing the thermal stability of SBS-MBs in closed containers where the presence of air/oxygen is limited. Similarly, sulfur, aromatic oil, and oxidized binders do not alter the thermal stability of SBS-MBs. SBS polymer with high vinyl content (≥30%) showed excellent thermal stability during storage at 180 °C. The shifting of the CC bond from the main chain to the side chain (vinyl content) shields the chain scission of the SBS polymer at elevated temperatures. This study provides practically implementable mitigation strategies, such as using iscowax, PPA, and high vinyl content SBS polymer, to safeguard the properties of SBS-MBs during storage and transportation. These strategies can be adopted by users and suppliers of SBS-MBs in scenarios where prolonged storage at elevated temperatures is required.

A Brief Review on the High-Energy Electromagnetic Radiation-Shielding Materials Based on Polymer Nanocomposites.

This paper revises the use of polymer nanocomposites to attenuate high-energy electromagnetic radiation (HE-EMR), such as gamma radiation. As known, high-energy radiation produces drastic damage not only in facilities or electronic devices but also to life and the environment. Among the different approaches to attenuate the HE-EMR, we consider the use of compounds with a high atomic number (Z), such as lead, but as known, lead is toxic. Therefore, different works have considered low-toxicity post-transitional metal-based compounds, such as bismuth. Additionally, nanosized particles have shown higher performance to attenuate HE-EMR than those that are micro-sized. On the other hand, materials with π-conjugated systems can also play a role in spreading the energy of electrons ejected as a consequence of the interaction of HE-EMR with matter, preventing the ionization and bond scission of polymers. The different effects produced by the interactions of the matter with HE-EMR are revised. The increase of the shielding properties of lightweight, flexible, and versatile materials such as polymer-based materials can be a contribution for developing technologies to obtain more efficient materials for preventing the damage produced for the HE-EMR in different industries where it is found.

Multicolor Mechanofluorophores for the Quantitative Detection of Covalent Bond Scission in Polymers.

The fracture of polymer materials is a multiscale process starting with the scission of a single molecular bond advancing to a site of failure within the bulk. Quantifying the bonds broken during this process remains a big challenge yet would help to understand the distribution and dissipation of macroscopic mechanical energy. We here show the design and synthesis of fluorogenic molecular optical force probes (mechanofluorophores) covering the entire visible spectrum in both absorption and emission. Their dual fluorescent character allows to track non‐broken and broken bonds in dissolved and bulk polymers by fluorescence spectroscopy and microscopy. Importantly, we develop an approach to determine the absolute number and relative fraction of intact and cleaved bonds with high local resolution. We anticipate that our mechanofluorophores in combination with our quantification methodology will allow to quantitatively describe fracture processes in materials ranging from soft hydrogels to high‐performance polymers.

Polymer scission in turbulent flows

Abstract

Effect of property deterioration in SBS modified binders during storage on the performance of asphalt mix

SBS modified binders (SBS-MBs) are vulnerable to property erosion during storage and transportation in closed containers at temperatures exceeding 160 °C. If proper precautionary measures are not taken, the quality of pavements may also be affected. This investigation is focused on determining the effect of property deterioration in SBS-MBs during storage in closed metal containers on the performance of the asphalt mixture. In the first phase, optimum SBS content was determined based on binder and mixture studies. In the second part, studies were carried out comparing the performance of asphalt mixes prepared using fresh (0 days stored) and stored SBS-MBs at 150 °C and 180 °C for 14 days in closed metal containers. The asphalt mix performance was assessed through Marshall stability, rut depth, and fatigue tests. The results show that the properties of the SBS-MB remained stable during storage at 150 °C, and the performance of the asphalt mixes prepared using such SBS-MBs remained intact. On the contrary, during storage at 180 °C, significant erosion in the properties of the SBS-MBs with 4.5 wt% SBS content (optimum dosage) was observed. Gel permeation chromatography (GPC) results clearly showed chain scission of SBS polymer due to the non-oxidative thermal degradation. It can be concluded that the decline in the performance of the asphalt mix prepared using 4.5 wt% SBS-MB stored at 180 °C was substantial (50–100%). The Marshall stability value of the mixes decreased by up to 30% and rut depth increased by almost 50% when the asphalt mix was prepared using SBS-MB stored at 180 °C for 7 days. Such a massive reduction in the performance of asphalt mixes will severely impact the overall life and stability of the pavements, and contribute to its premature failure.

Toward Drug Release Using Polymer Mechanochemical Disulfide Scission.

Traditional pharmacotherapy suffers from multiple drawbacks that hamper patient treatment, such as the buildup of antibiotic resistances or low drug selectivity and toxicity during systemic application. To overcome these challenges, drug activity can be controlled by employing delivery, targeting, or release solutions that mostly rely on the response to external physicochemical stimuli. Due to various technical limitations, mechanical force as a stimulus in the context of polymer mechanochemistry has so far not been used for this purpose, yet it has been proven to be a convenient and robust method to site-selectively rearrange or cleave bonds with submolecular precision in the realm of materials chemistry. Here, we present an unprecedented mechanochemically responsive system capable of successively releasing small furan-containing molecules, including the furylated fluorophore dansyl and the drugs furosemide as well as furylated doxorubicin, by ultrasound-induced selective scission of disulfide-centered polymers in solution. We show that mechanochemically generated thiol-terminated polymers undergo a Michael-type addition to Diels-Alder (DA) adducts of furylated drugs and acetylenedicarboxylate derivatives, initiating the downstream release of the small molecule drug by a retro DA reaction. We believe that this method can serve as a blueprint for the activation of many other small molecules.

Greener approach for synthesis of N,N,N-trimethyl chitosan (TMC) using ternary deep eutectic solvents (TDESs)

N,N,N-trimethyl chitosan (TMC), quaternized hydrophilic derivative of chitosan, has been projected to have wide applications in the pharmaceutical industry owing to its improved solubility at physiological conditions. However, the conventional synthesis of TMC involves toxic organic agents, which complicates its use for biological applications. Moreover, these reactions result into unwanted O-methylation and scission of the parent polymer. In the present study we have addressed these limitations by employing a green approach to synthesize TMC, by using lipase as the biocatalyst and dimethyl carbonate (DMC) as the green methylating agent, in a reaction medium comprising of ternary deep eutectic solvents (TDESs). Synthesis of TMC was carried out by using two different lipases from Burkholderia cepacia and Candida rugosa. The resulting TMC was characterized by using FTIR, 1H NMR, DSC, XRD. Methylation was confirmed by FTIR analysis (-CH at 1666 cm−1) and 1H NMR (?? = 3.3 ppm). DSC study revealed a lower thermal stability of TMC as compared to chitosan. These results indicated the possibility of using DMC as a green methylating agent, along with TDESs as green and sustainable solvents, for lipase catalyzed reactions. TMC was successfully synthesized and exhibited a degree of quaternization of about 12.5%, 15.69%, when synthesized used lipases from Burkholderia cepacia and Candida rugosa, respectively.

Mechanoradicals in tensed tendon collagen as a source of oxidative stress

As established nearly a century ago, mechanoradicals originate from homolytic bond scission in polymers. The existence, nature and biological relevance of mechanoradicals in proteins, instead, are unknown. We here show that mechanical stress on collagen produces radicals and subsequently reactive oxygen species, essential biological signaling molecules. Electron-paramagnetic resonance (EPR) spectroscopy of stretched rat tail tendon, atomistic molecular dynamics simulations and quantum-chemical calculations show that the radicals form by bond scission in the direct vicinity of crosslinks in collagen. Radicals migrate to adjacent clusters of aromatic residues and stabilize on oxidized tyrosyl radicals, giving rise to a distinct EPR spectrum consistent with a stable dihydroxyphenylalanine (DOPA) radical. The protein mechanoradicals, as a yet undiscovered source of oxidative stress, finally convert into hydrogen peroxide. Our study suggests collagen I to have evolved as a radical sponge against mechano-oxidative damage and proposes a mechanism for exercise-induced oxidative stress and redox-mediated pathophysiological processes.

Scission of flexible polymers in contraction flow: Predicting the effects of multiple passages

When injected through a contraction, high molecular weight polymer solutions exhibit a sharp increase of apparent viscosity which originates from stretching polymer chains above a critical extension rate. This chain stretching can also induce polymer scission, which then decreases the extensional viscosity. In practice, the two phenomena are difficult to separate. Moreover, these phenomena are often observed in situation where flow instabilities appear. In order to disentangle the two effects we have measured the pressure-flux relation for polymer solutions passing through a hyperbolic contraction. The ratio of the pressure drop to that of the (Newtonian) solvent has a maximum due to the competition between polymer extension and scission. We find a geometry-dependent relation between the flow rates at which the maximum occurs for successive passages in a given contraction, which appears to be independent of molecular weight, concentration, solvent quality and viscosity, and can be used to predict the scission under successive passes.