Chain Rearrangement Research Articles

Polydimethylsiloxane enabled triple-action water-resistant coating with desirable relaxation rate in clear aligner

Clear aligners undergo rapid stress relaxation in warm, moist oral environments, compromising therapeutic effectiveness and longevity of treatment. To develop an innovative multilayer composite material with improved stability and reduced stress release, we have engineered an innovative coating characterized by the surface aggregation of polydimethylsiloxane (PDMS), which imparts a pronounced hydrophobic effect. In addition, the chemically and physically cross-linked structure of the coating reduces the free volume created by molecular chain rearrangement owing to the presence of water molecules, thereby minimizing water penetration into the coating. Concurrently, the coating’s internal structure is enriched with numerous polar functional groups to capture water molecules that penetrate into the inside of the coating. Through combination of these mechanisms, water molecules are effectively sequestered, thereby impeding their penetration into the polyethylene terephthalate glycol (PETG) substrate. The impact of the polydimethylsiloxane content on the triple-action water-resistance mechanisms was thoroughly examined using attenuated total reflection (ATR)-Fourier transform infrared (FTIR), water absorption rate, water swelling rate, and X-ray photoelectron spectroscopy. The low surface energy cross-linked polyurethane coating is applied to the polyethylene terephthalate glycol (PETG) substrate to create a novel composite material with specific mechanical properties and reduced stress relaxation. The composite material remains stable in simulated oral environment with linear swelling rate of 0.58 % upon water absorption. Additionally, the stress release rate of the composite material within 336 h is notably lower (23.64 %) than that of PETG (62.29 %).

Pyrolysis and oxidation mechanisms of ethylene and ethanol blended fuel based on ReaxFF molecular dynamics simulation

To gain detailed atomic-level insights into the reaction mechanisms associated with the oxy-fuel combustion of ethylene and ethanol, ReaxFF reactive force field molecular dynamics simulations were performed to analyze the behavior of their high-temperature pyrolysis and oxidation. Results showed that the main reaction of pure ethylene involves the formation of long carbon chains by C–C polymerization in an oxygen-free environment. The polycondensation-cyclization of long carbon chains significantly contributes to the formation of polycyclic aromatic hydrocarbons (PAHs). The addition of ethanol enriches the initial reaction pathways of ethylene. For instance, ethanol participates in the following reactions: C2H4 + C2H6O → C4H10O, C2H6O + C2H4 → C2H5 + C2H5O, and C2H6O + C2H4 → C2H5 + H2O + C2H3. Ethanol inhibits the growth of long carbon chains, with a more pronounced effect at higher ethanol concentrations. In an oxygen atmosphere, the decay rate of ethylene decreases significantly, and its main reaction pathway involves dehydrogenation and oxidation with the assistance of OH, HO2, H, and O2. The final products are released in the form of CO, CO2, and H2O. In addition, the formation of soot particles is mainly divided into three steps: (i) ethylene aggregates to form long carbon chains, (ii) rearrangement and cyclization of long carbon chains, and (iii) growth of PAHs.

Complete detection of FR1 to FR3 primer-based PCR patterns of immunoglobulin heavy chain rearrangement in the BIOMED-2 protocol is associated with poor prognosis in patients with diffuse large B-cell lymphoma.

Somatic hypermutations (SHMs) in the variable region (VH) of the immunoglobulin heavy chain (IgH) gene are common in diffuse large B-cell lymphoma (DLBCL). Recently, IgH VH SHMs have become known as immunogenic neoantigens, but few studies have evaluated the prognostic impact of the frequency of VH SHMs in DLBCL. The BIOMED-2 protocol is the gold standard polymerase chain reaction (PCR) for clonality analysis in lymphoid malignancies, but can produce false negatives due to the presence of IgH VH SHMs. To overcome this problem, three primer sets were designed for the three framework regions (FR1, FR2, and FR3). We evaluated the predictive value of this PCR pattern in patients with DLBCL. To evaluate the prognostic impact of complete detection of the clonal amplifications (VHFR1-JH, VHFR2-JH, and VHFR3-JH) in the BIOMED-2 protocol, we retrospectively analyzed 301 DLBCL patients who were initially treated with anthracycline-based immunochemotherapy. Complete detection of the FR1 to FR3 primer-based IgH VH PCR patterns in the BIOMED-2 protocol was associated with low frequency of VH SHMs (p<0.001). Patients who were positive for all these three PCRs (n=79) were significantly associated with shorter 5-year overall survival (OS; 54.2% vs. 73.2%; p=0.002) and progression-free survival (PFS; 34.3% vs. 59.3%; p<0.001) compared to patients with other PCR patterns (n=202). Specifically, the successful FR3-JH detection was associated with significantly worse OS (p<0.001) and PFS (p<0.001). PCR patterns of complete IgH rearrangement using the BIOMED-2 protocol are clinically meaningful indicators for prognostic stratification of DLBCL patients.

Impact of manufacturing variables on product performance of contraceptive levonorgestrel intrauterine systems

The development of Levonorgestrel Intrauterine Systems (LNG-IUSs) stands as a formidable challenge due to their intricate design and reliance on specialized manufacturing methods. Pharmaceutical manufacturers face a labyrinth of process variables that demand precise identification and comprehension to establish a robust product design to ensure consistent performance. The current manuscript navigates through this complexity, describing a small-scale processing method for LNG-IUSs via addition and condensation curing processes, as well as investigating the influence of key manufacturing variables on LNG-IUS product performance. Different mixing speeds and time exhibited distinct impact on drug content uniformity within the IUS drug-polymer reservoirs. Surprisingly, no variation in drug release rates were observed. Curing temperature and time were the critical processing parameters of IUSs which were dependent on the polymer type (polydimethylsiloxane, PDMS) and drug loading. At lower curing temperatures, crosslinking in PDMS remained relatively unaffected, irrespective of drug loading. By contrast, elevating curing temperatures resulted in a drastic reduction in PDMS crosslinking densities at higher drug loading. This was attributed to increased drug volume fraction within the matrix, impeding optimal prepolymer chain mobility and rearrangement which is crucial for complete crosslinking. Interestingly, rapid curing led to increased PDMS crystallinity, thereby retarding drug release rates while concurrently compromising mechanical properties. PDMS curing chemistry, such as condensation cure (no filler) and addition cure (cured at room temperature), did not affect drug release rates of the LNG-IUSs. In the condensation cure-based LNG-IUS, the formulations prepared without filler had higher drug release rates than those containing silica or diatomaceous earth fillers. Overall, the present study unravels the intricate interplay between PDMS characteristics, processing variables, and product performance, offering fundamental insights into product design and manufacturing of brand and generic LNG-IUS products.

Study on poly(butylene adipate‐co‐terephthalate)/thermoplastic starch/poly((R)‐3‐hydroxybutyrate‐co‐(R)‐3‐hydroxyhexanoate) biodegradable films with enhanced gas barrier properties

AbstractBioplastic films with excellent barrier properties were successfully prepared from poly(butylene adipate‐co‐terephthalate) (PBAT), thermoplastic starch (TPS), and poly((R)‐3‐hydroxybutyrate‐co‐(R)‐3‐hydroxyhexanoate) (PHBHHx). The rheological, mechanical, barrier, dynamic mechanical properties, and microstructure of the PBAT/TPS/PHBHHx films were studied. The transition of the continuous phase in the blend significantly affects the properties of the films. The increase in PHBHHx content results in its transition from a dispersed phase to a continuous phase. This phase transition, along with the consequent increase in the crystallinity of PHBHHx, greatly enhances the barrier properties of the film. The percentage crystalline degree of PHBHHx increased from 10.9% to 25.1% with increasing PHBHHx content from 0% to 50%. The film containing 50% PHBHHx showed a significant decrease in both water vapor permeability (WVP) and oxygen permeability (OP) by 75.1% and 69.6%, respectively. It found that the film containing 50% PHBHHx exhibited a decrease of elongation at break from 505% to less than 10% but an unusual increase of tensile strength after a 72‐hour aging test, which is different from PBAT and PBAT/TPS films. However, this indicates that the extensibility of PHBHHx is more susceptible to the effects of aging test, leading to the rearrangement of polymer chains from disordered to ordered morphology.

Multiscale damage evolution and fracture for thermal aging energetic material based on mesoscopic observation and molecular dynamics simulation

As a composite energetic material composed of filler and matrix, the mechanical properties of HTPB propellants change constantly due to the aging of each component and component interfaces during long-term storage. However, the study of a single component or performance parameter limits disclosure of the complex aging mechanism and mechanical property evolution. Therefore, based on accelerated thermal aging experiments, this study integrated gas detection, contact angle testing, in situ loading experiments, digital image correlation numerical analysis, and all-atom molecular dynamic simulations to explore the underlying mechanism of structural morphology and mechanical property changes during propellant aging. The results showed that the aging reaction was dominated by degradation chain breaking in the early stage and oxidative crosslinking in the later stage. Degradation chain breaking enhanced interfacial bonding between the two phases, while oxidative crosslinking deteriorated interfacial bonding. Compared with lossless specimens, short-term thermal aging weakened the strength of the matrix and enhanced bonding interfaces. During in situ loading, interfacial pore expansion and matrix damage and fracture occurred simultaneously and the matrix became the key damage source. However, with the extension of thermal aging time, the strength of the matrix increased, bonding interface weakened, and bonding interfaces became a weak point of loading. This made the high-strain area change from the matrix at the initial loading stage to the bonding interface and the damage of the bonding interface caused whole fracture of the specimen. The external loading resulted in the rearrangement of interfacial molecular chains, change of molecular spacing, and initiation and expansion of micropores between molecular chains. The tractor-separation curve conformed to the exponential cohesion model and the damage mode of the interface layer changed between adhesion and cohesion due to thermal aging.

Advancing spin-coating technique for semi-crystalline low-density polyethylene thin films

Polymeric thin films are widely used for coating substrates or as freestanding materials. They are prepared using physical/chemical vapor deposition, dip coating, solution casting, or spin coating. Among these, spin-coated films offer uniform thickness and reproducible results. These films are typically made from amorphous polymers, which are soluble in solvents at ambient temperature, making it easier to coat the polymer solution on the substrate. Despite the advantages of this technique, it has hardly been used for semi-crystalline polymers. In this work, we report the synthesis of freestanding porous thin films using semi-crystalline polymers, specifically low-density polyethylene (LDPE), through the utilization of spin coating. The effect of polymer concentration and porosity on thickness and strength was investigated. The as-prepared thin film was characterized by XRD, XPS, FTIR, and SEM techniques. The increase in crystallinity (14 % change) of the thin film was attributed to the rearrangement and uniform alignment of the polymer chains, which further resulted in relatively higher tensile strength.

Convoluted micellar morphological transitions driven by tailorable mesogenic ordering effect from discotic mesogen-containing block copolymer

Solution-state self-assemblies of block copolymers to form nanostructures are tremendously attractive for their tailorable morphologies and functionalities. While incorporating moieties with strong ordering effects may introduce highly orientational control over the molecular packing and dictate assembly behaviors, subtle and delicate driving forces can yield slower kinetics to reveal manifold metastable morphologies. Herein, we report the unusually convoluted self-assembly behaviors of a liquid crystalline block copolymer bearing triphenylene discotic mesogens. They undergo unusual multiple morphological transitions spontaneously, driven by their intrinsic subtle liquid crystalline ordering effect. Meanwhile, liquid crystalline orderedness can also be built very quickly by doping the mesogens with small-molecule dopants, and the morphological transitions are dramatically accelerated and various exotic micelles are produced. Surprisingly, with high doping levels, the self-assembly mechanism of this block copolymer is completely changed from intramolecular chain shuffling and rearrangement to nucleation-growth mode, based on which self-seeding experiments can be conducted to produce highly uniform fibrils.

Clinical utility of 7-probe FISH panel in multiple myeloma in a resource-constrained setting: A retrospective and prospective observational study

ABSTRACT Background: A 7-probe fluorescence in situ hybridization (FISH) panel identifying abnormalities such as immunoglobulin heavy chain (IGH) rearrangement, deletion 17p (TP53 – tumor protein 53), hyperdiploidy, and amplification of 1q, t(11;14), t(14;16), and t(4;14) aids in diagnosis and treatment planning for patients with multiple myeloma, particularly for high-risk patients and short-survival rates. Objectives: The primary objective of the study was to stratify patients with multiple myeloma based on the risk of developing the disease. The secondary objective was to assess the frequency of triple- and double-hit myeloma. Materials and Methods: This retrospective and prospective observational study was conducted in the Department of Cytogenetics, Amrita Institute of Medical Science, Kochi, Kerala, India from January 2020 to September 2022. Bone marrow samples were analyzed using the 7-probe FISH panel and stratification for myeloma and risk-adapted therapy (mSMART) classification for risk stratification. Results: We included 123 samples in the study. Results showed hyperdiploidy as the most common abnormality among newly diagnosed patients (110), with 54.5% (n = 60/110) classified as high-risk and 45.5% (n = 50/110) as standard-risk. Amplification of 1q was the most common abnormality in high-risk, while hyperdiploidy prevailed in standard-risk. Out of the 110 patients, 20.9% (n = 23) patients exhibited double-hit myeloma, and only two out of 110 (1.8%) had triple-hit myeloma. Among relapsed cases (13, 11.8%), all were high-risk, with amplification of 1p1q being the most common abnormality. Out of the 13 relapsed cases, five (38.4%) were double-hit myeloma, and one (7.7%) was triple-hit myeloma. In the remaining 7 (53.8%) cases, either one of the standard risk or high-risk abnormalities or both were observed. Conclusion: The 7-probe FISH panel was found to be a better and more comprehensive tool for risk stratification, molecular classification, and further management of multiple myeloma patients, and it led to improved patient care. Karyotyping, in contrast, did not yield any additional information and thus can be avoided.

Fast-setting multi-stimuli responsive silk hydrogels tailored with dual network interface

Silk fibroin, a naturally occurring and versatile polymer with broad range of material forms and applications, presents numerous advantages. Notably, hydrogels are noteworthy among these advantages due to their inherent hydrophilicity, biocompatibility, and flexibility. Nevertheless, their practical utility has been hindered by intricate preparation procedures and limited mechanical strength. In this investigation, we introduce a straightforward and cost-effective method for producing a novel silk hydrogel. Subsequent to the hydrogel synthesis, an ethanol treatment was employed to induce the preferential formation of β-sheet conformations. The developed system exhibits rapid gelation (gelation time: 3 min) and non-swelling behavior (swelling ratio = 0.47). This suggests its potential suitability for biomedical devices without imposing strain on adjacent tissues. Conformational rearrangement of polymeric chains induced by ethanol treatment contributed to heightened material crystallinity, resulting in a remarkable 55.9% increase in Young's modulus and a substantial 91.2% enhancement in ultimate tensile strength for the ethanol-treated hydrogels (SF/AG/Gly/Eth) when compared to their non-ethanol-treated counterparts (SF/AG/Gly). Additionally, in-situ biodegradation studies on silk hydrogels confirmed the material's degradability, with a notable 94.75% weight loss within 3 days, following pseudo-second-order kinetics (R2 = 0.991). This degradation is attributed to action of proteolytic enzymes on the amino acid units of silk fibroin, alleviating concerns regarding waste generation. Moreover, these pH and water-responsive hydrogels can be harnessed in the fabrication of intelligent biomedical devices. Further, drug release studies on silk hydrogels showed that both ethanol-treated and non-treated samples displayed sustained drug release following the Korsmeyer−Peppas model, with an entrapment efficiency of 65.6% and 48.2%, respectively.

Evaluation of next-generation sequencing versus next-generation flow cytometry for minimal-residual-disease detection in Chinese patients with multiple myeloma

PurposeTo evaluate the efficacy of next-generation sequencing (NGS) in minimal-residual-disease (MRD) monitoring in Chinese patients with multiple myeloma (MM).MethodsThis study analyzed 60 Chinese MM patients. During MRD monitoring in these patients’ post-therapy, clonal immunoglobulin heavy chain (IGH) rearrangements were detected via NGS using LymphoTrack assays. MRD monitoring was performed using NGS or next-generation flow cytometry (NGF), and the results were compared. Additionally, the sensitivity and reproducibility of the NGS method were assessed.ResultsThe MRD detection range of the NGS method was 10–6–10–1, which suggested good linearity, with a Pearson correlation coefficient of 0.985 and a limit of detection of 10–6. Intra- and inter-assay reproducibility analyses showed that NGS exhibited 100% reproducibility with low variability in clonal cells. At diagnosis, unique clones were found in 42 patients (70.0%) with clonal IGH rearrangements, which were used as clonality markers for MRD monitoring post-therapy. Comparison of NGS and NGF for MRD monitoring showed 79.1% concordance. No samples that tested MRD-positive via NGF were found negative via NGS, indicating the higher sensitivity of NGS. MRD could be detected using NGS in 6 of 7 samples before autologous hematopoietic stem-cell transplantation, and 5 of them tested negative post-transplantation. In contrast, the NGF method could detect MRD in only 1 sample pre-transplantation.ConclusionCompared with NGF, NGS exhibits higher sensitivity and reproducibility in MRD detection and can be an effective strategy for MRD monitoring in Chinese MM patients.

Butyryl group distribution modulates the structure and properties of butyrylated maize starch focused on amylose contents

In this study, four types of maize starch with different amylose contents (3 %, 25 %, 40 %, and 70 %) were used to prepare butyrylated starches. Based on amylose contents, the influence of butyryl group distribution on the structure, thermal and digestive properties of butyrylated maize starch was investigated. The butyrylation reaction mainly substituted butyryl groups on amylose, and the butyryl groups were most easily substituted for the hydroxyl group at the C6 position. The degree of substitution of butyrylated starch reached its maximum when the amylose content was 40 %, and the degree of substitution did not correlate linearly with the amylose content. The butyrylation reaction increased the surface roughness, decreased the crystallinity, enthalpy value and molecular weight of native starch granules, resulting in a decrease in the degree of internal order of the starch and inducing the rearrangement of the amylose molecular chains in the amorphous region of the starch. The combination of the amylose content and the substitution of butyryl groups on amylose affected the digestibility of starch and ultimately increased its resistance. The Pearson correlation coefficient further confirmed the correlation between the distribution of butyryl groups and the structure and properties of butyrylated starch.

Protein‐Mediated ZnO Synthesis for Self‐Healing in Natural Rubber

AbstractNatural rubber (NR) consists of mainly cis‐1,4‐polyisoprene with proteins as notable nonrubber components that significantly influence its properties. A relatively unexplored aspect is the role of these proteins in reducing and stabilizing metal ions to form metallic particles. Here, the NR/ZnO composite is successfully prepared by in situ generation of ZnO in the NR latex for the first time. With the aid of the proteins, the amount of ZnO is slightly higher than that formed in the saponified NR latex (SPNR), where some proteins are removed. Importantly, the noncovalent bonds between the proteins and/or amino acids with the ZnO formed in the NR latex can provide the self‐healing behavior of the NR/ZnO composite. However, heating at ≈40 °C is still necessary for reducing the healing time and increasing the self‐healing efficiency of the composite. Nevertheless, greater noncovalent bonds within NR/ZnO hinder rubber molecular chain interdiffusion and rearrangement essential for self‐healing behavior in uncross‐linked rubber, resulting in lower healing efficiency compared to SPNR/ZnO. This study underscores the significance of proteins and/or amino acids on NR's properties, despite their minor presence. Without sophisticated NR modification, this is a very simple and low‐cost technique to achieve the NR/ZnO composite with self‐healing behavior.

Electrical Chain Rearrangement: What Happens When Polymers in Brushes Have a Charge Gradient?

Under the influence of electric fields, the chains in polyelectrolyte brushes can stretch and collapse, which changes the structure of the brush. Copolymer brushes with charged and uncharged monomers display a similar behavior. For pure polyelectrolyte and random copolymer brushes, the field-induced structure changes only the density of the brush and not its local composition, while the latter could be affected if charges are distributed inhomogeneously along the polymer backbone. Therefore, we systematically study the switching behavior of gradient polyelectrolyte brushes in electric fields for different solvent qualities, grafting densities, and charges per chain via coarse-grained molecular dynamics simulations. Similar to random copolymers and pure polyelectrolytes, these brushes show a mixed-phase transition: intermediate states between fully stretched and collapsed are characterized by a bimodal chain-end distribution. Additionally, we find that the total charge of the brush plays a key role in the critical field required for a complete transition. Finally, we find that gradient polyelectrolyte brushes are charge-enriched at the brush-solvent interface under stretched conditions and charge-depleted under collapsed conditions, allowing for control over the local composition and thus the surface charge of the brush due to the inhomogeneous charge along the grafted chains.

Molecularly Mixed Composite Membranes for Gas Separation Based on Macrocycles Embedded in a Polyimide.

Polyimides are a polymer class that has been extensively investigated as a membrane material for gas separation owing to its interesting permselective properties in a wide range of operation temperatures and pressures. In order to improve their properties, the addition of different filler types is currently studied. p-tert-Butylcalix[n]arene macrocycles (PTBCs) with different cavity sizes (PTBC4, PTBC6, PTBC8) were used as fillers in a commercial thermoplastic polyimide, with a concentration in the range 1-9 wt%, to develop nanocomposite membranes for gas separation. The selected macrocycles are attractive organic compounds owing to their porous structure and affinity with organic polymers. The nanocomposite membranes were prepared in the form of films in which the polymeric matrix is a continuous phase incorporating the dispersed additives. The preparation was carried out according to a pre-mixing approach in a mutual solvent, and the solution casting was followed by a controlled solvent evaporation. The films were characterized by investigating their miscibility, morphology, thermal and spectral properties. The gas transport through these films was examined as a function of the temperature and also time. The results evidenced that the incorporation of the chosen nanoporous fillers can be exploited to enhance molecular transport, offering additional pathways and promoting rearrangements of the polymeric chains.

The novel mechanical and recovery behaviors of 3D printed EVA under cyclic tensile loading

In this study for the first time, the cyclic mechanical properties and shape recovery behavior of 3D printed EVA were investigated. EVA with high elastic capability was successfully printed by direct material extrusion method and then a novel cyclic shape recovery test was conducted in which the tensile test was performed at three different strain levels (250, 500 and 1000%) in six cycles and after the end of each cycle by heating the samples, their recovery was measured. The results showed that in all strain levels and tensile cycles, the full recovery is observed, which is completed in two steps after unloading and after heating the sample. Upon exposure to hot water, the disruption of intermolecular forces facilitated the recovery of the material's original shape through increased molecular mobility and rearrangement of polymer chains. However, it was observed that with increasing strain levels (from 250% to 1000%), the recovery process became less effective, leading to a decline in mechanical properties. Also, by increasing the number of tensile cycles, the tensile stress value at the desired strain level and the rate of change decreases and after the second cycle, the cyclic behavior under tensile loading almost reaches a constant trend.

CI:Mor interactions in the lysogeny switches of Lactococcus lactis TP901-1 and Staphylococcus aureus φ13 bacteriophages.

Aim: To structurally characterize in detail the interactions between the phage repressor (CI) and the antirepressor (Mor) in the lysis-lysogeny switches of two Gram-positive bacteriophages, the lactococcal TP901-1 and staphylococcal φ13. Methods: We use crystallographic structure determination, computational structural modeling, and analysis, as well as biochemical methods, to elucidate similarities and differences in the CI:Mor interactions for the two genetic switches. Results: By comparing a newly determined and other available crystal structures for the N-terminal domain of CI (CI-NTD), we show that the CI interface involved in Mor binding undergoes structural changes upon binding in TP901-1. Most importantly, we show experimentally for the first time the direct interaction between CI and Mor for φ13, and model computationally the interaction interface. The computational modeling supports similar side chain rearrangements in TP901-1 and φ13. Conclusion: This study ascertains experimentally that, like in the TP901-1 lysogeny switch, staphylococcal φ13 CI and Mor interact with each other. The structural basis of the interaction of φ13 CI and Mor was computationally modeled and is similar to the interaction demonstrated experimentally between TP901-1 CI-NTD and Mor, likely involving similar rearrangement of residue side chains during the formation of the complex. The study identifies one CI residue, Glu69, which unusually interacts primarily through its aliphatic chain with an aromatic residue on Mor after changing its conformation compared to the un-complexed structure. This and other residues at the interface are suggested for investigation in future studies.

An entropy generation approach to the molecular recoiling stress relaxation in thin nonequilibrated polymer films.

In polymers, the equilibrium state is achieved when the chains have access to the maximum number of conformational states, which allows them to explore a larger conformational space, leading to an increase in the entropy of the system. Preparation of thin polymer films using the spin-coating technique results in polymer chains being locked in a nonequilibrium state with lower entropy due to possible stretching of chains during the process. Allowing enough time for recovery results in the relaxation of the spin-coating-induced molecular recoiling stress. Annealing such a film generates entropy due to its inherent irreversibility. We employed the dewetting technique to determine the molecular recoiling stress relaxation time in poly-(tertbutyl styrene) thin films. Furthermore, we qualitatively differentiated the metastable states achieved by the polymer film using entropy generation in a relaxing polymer film as an effect of thermal entropy and associated it with the conformational entropy of polymer chains utilizing the molecular recoiling stress relaxation time. This enabled us to explain molecular recoiling stress relaxation using a rather simplistic approach involving segmental level molecular rearrangements in polymer chains by attaining transient metastable states through an entropically activated process driving toward equilibrium.

Shock and spallation behavior of ultrahigh molecular weight polyethylene

We investigate dynamic compression and fracture of ultra-high molecular weight polyethylene (UHMWPE) with plate impact experiments, high-speed velocimetry, and postmortem X-ray computed tomography. The Hugoniot equation of state of UHMWPE up to peak shock stress of ∼2.0 GPa is obtained via reverse impact. Spall strength and corresponding tensile strain rates are determined via symmetric impact. With increasing impact velocity, spall strength is nearly a constant (∼70 MPa) up at first, and then decreases continuously as a result of competition between increasing tensile strain rate, shock heating and strain softening; the damage degree increases first and then decreases rapidly at the expense of more damage nucleation sites. The void size distributions follow a power law. The small voids are closer to spheres and voids/cracks becomes flatter as void volume increases, likely because of the rearrangement and breakage of linear polymer chains of UHMWPE.

Expanding Diterpene Complexity and Diversity via Photoinduced Ring Distortions.

Natural products and their semi-synthetic derivatives undoubtedly constitute an important source of therapeutic agents. Their importance lies in their own origin and evolution, since they have great chemical diversity, biochemical specificity, and pharmacological properties. Currently, there is a renewed interest in the development of methodologies capable of efficiently modifying the chemical structure of these bioactive platforms. In this work, the photoderivatization of the diterpene solidagenone was performed using a complexity-to-diversity-oriented approach. By exploring [2+2]-photocycloaddition, photoinduced-hydrogen abstraction, and photoxygenation reactions, a set of solidagenone derivatives was obtained, showing different ring fusions, side chain rearrangements, and modifications of the original furan ring's substitution pattern. The derivatives obtained were characterised by NMR methodologies. To evaluate the structural diversity of the labdane-derived compounds, their physicochemical properties, structural similarity, and chemical space were analysed. These results suggest that photochemical reactions are a useful tool for performing ring distortion transformations, generating derivatives of natural compounds with wide diversity, structural complexity, and with potential biological properties.