Low Molecular Polymers Research Articles

3D Printed Drug Delivery Systems in Action-Magnetic Resonance Imaging and Relaxometry for Monitoring Mass Transport Phenomena.

The hypothesis of the study was that (1) 3D printed drug delivery systems (DDS) could be characterized in situ during drug release using NMR/MRI techniques in terms of mass transport phenomena description (interfacial phenomena), particularly for systems dealing with two mobile phases (e.g., water and low molecular weight liquid polymer); (2) consequently, it could be possible to deduce how these interfacial mass transport phenomena influence functional properties of 3D printed DDS. Matrix drug delivery systems, prepared using masked stereolithography (MSLA), containing poly(ethylene glycol) diacrylate (PEGDA) and low molecular weight polyethylene glycol (PEG) with ropinirole hydrochloride (RH) were studied as example formulations. The PEGDA to PEG (mobile phase) concentration ratio influenced drug release. It was reflected in spatiotemporal changes in parametric T2 relaxation time (T2) and amplitude (A) images obtained using magnetic resonance imaging (MRI) and T1-T2 relaxation time correlations obtained using low-field time-domain nuclear magnetic resonance (LF TD NMR) relaxometry during incubation in water. For most of the tested formulations, two signal components related to PEG and water were assessed in the hydrated matrices by MRI relaxometry (parametric T2/A images). The PEG component faded out due to outward PEG diffusion and was gradually replaced by the water component. Both components spatially and temporally changed their parameters, reflecting evolving water-polymer interactions. The study shows that dynamic phenomena related to bidirectional mass transport can be quantified in situ using NMR and MRI techniques to gain insight into drug release mechanisms from 3D printed DDS systems.

Characterization and optimization of colon specific nanosponges immobilized polymeric microbeads formulation for the combined delivery of 5-fluorouracil and curcumin

Introductionand purpose: Site-specific delivery systems are highly advantageous for local cancer treatment as they allow a more significant delivery of the drug to the tumor with minimal systemic side effects. Furthermore, combination therapy is a promising approach that attracts more attention in cancer treatment due to its synergistic effects. In this work, nanosponges immobilized polymeric microbeads for colon-specific delivery systems were developed for a drug combination of 5-fluorouracil and curcumin to treat colorectal cancer. MethodsSodium alginate and low molecular chitosan polymers were used to create microbead-based formulations containing curcumin-encapsulated nanosponges and 5-fluorouracil. To improve curcumin's low solubility, Diphynylacarbonate (DPC) hyper cross-linking of β-CD was used to create curcumin-loaded β-CD nanosponges that further incorporated in the polymeric microbeads along with free 5-fluorouracil. ResultsThe optimized microbeads were spherical with a mean particle size of 1.1 ± 0.05 mm. The produced beads were subsequently coated with a multilayer coating of ethyl cellulose and Eudragit S100 polymers, which functioned as pH-dependent and time-dependent coatings to ensure drug delivery to the colon. The developed formulation (Coated MB5) showed controlled release of the drug and sustained cytotoxic effect. The release profiles of 5-fluorouracil and curcumin from Coated MB5 were best described by zero-order followed by first-order release functions. About 66.4 % of 5-FU and 73.1 % of curcumin were released for 24 h. In vivo roentgenographic evaluation in a rabbit model indicated that the optimized coated microbeads successfully reached the colon 7–9 h after administration. ConclusionsAs a prospective colon-specific drug delivery system, a successful formulation (Coated MB5) was developed for the combined delivery of 5-fluorouracil and curcumin. More in vivo studies are needed to demonstrate the therapeutic efficacy of optimized formulations and their potential to improve colorectal cancer therapy by providing a more targeted administration of combination medicines with fewer undesirable side effects.

Long-Term Prevention of Biofilm Formation by Polycatechol-Based Supramolecular Assemblies with Low Molecular Weight Polymers on Surfaces.

Achievement of a stable surface coating with long-term resistance to biofilm formation remains a challenge. Catechol-based polymerization chemistry and surface deposition are used as tools for surface modification of diverse materials. However, the control of surface deposition of the coating, surface coverage, coating properties, and long-term protection against biofilm formation remain to be solved. We report a new approach based on supramolecular assembly to generate long-acting antibiofilm coating. Here, we utilized catechol chemistry in combination with low molecular weight amphiphilic polymers for the generation of such coatings. Screening studies with diverse low molecular weight (LMW) polymers and different catechols are utilized to identify lead compositions, which resulted in a thick coating with high surface coverage, smoothness, and antibiofilm activity. We have identified that small supramolecular assemblies (∼10 nm) formed from a combination of polydopamine and LMW poly(N-vinyl caprolactam) (PVCL) resulted in relatively thick coating (∼300 nm) with excellent surface coverage in comparison to other polymers and catechol combinations. The coating properties, such as thickness (10-300 nm) and surface hydrophilicity (with water contact angle: 20-60°), are readily controlled. The optimal coating composition showed excellent antibiofilm properties with long-term (>28 days) antibiofilm activity against both Gram-negative (Escherichia coli) and Gram-positive (Staphylococcus aureus) strains. We further utilized the combination of optimal binary coating with silver to generate a coating with sustained release of silver ions, resulting in killing both adhered and planktonic bacteria and preventing long-term surface bacterial colonization. The new coating method utilizing LMW polymers opens a new avenue for the development of a novel class of thick, long-acting antibiofilm coatings.

An optimized polymeric delivery system for piggyBac transposition.

The piggyBac transposon/transposase system has been explored for long-term, stable gene expression to execute genomic integration of therapeutic genes, thus emerging as a strong alternative to viral transduction. Most studies with piggyBac transposition have employed physical methods for successful delivery of the necessary components of the piggyBac system into the cells. Very few studies have explored polymeric gene delivery systems. In this short communication, we report an effective delivery system based on low molecular polyethylenimine polymer with lipid substitution (PEI-L) capable of delivering three components, (i) a piggyBac transposon plasmid DNA carrying a gene encoding green fluorescence protein (PB-GFP), (ii) a piggyBac transposase plasmid DNA or mRNA, and (iii) a 2 kDa polyacrylic acid as additive for transfection enhancement, all in a single complex. We demonstrate an optimized formulation for stable GFP expression in two model cell lines, MDA-MB-231 and SUM149 recorded till day 108 (3.5 months) and day 43 (1.4 months), respectively, following a single treatment with very low cell number as starting material. Moreover, the stability of the transgene (GFP) expression mediated by piggyBac/PEI-L transposition was retained following three consecutive cryopreservation cycles. The success of this study highlights the feasibility and potential of employing a polymeric delivery system to obtain piggyBac-based stable expression of therapeutic genes.

Permeability reduction techniques: Plain and fiber HPAM gels in fractured cores

The aim of this study is to investigate how fibers influence the ability of polymer gels to resist washing out from fractures. For this purpose, synthetic and mineral wool fibers were integrated into polymer gels. These fiber-gels were compared to plain gels using bottle tests, viscosity measurements, and fractured core flooding experiments.The bottle tests show no effect of 13-mm-long synthetic fibers on gel strength. However, inside a constricted fracture, the polymer-synthetic fiber gel exhibited 8.4 times higher resistance to the flow of brine compared to the plain gel. This is explained by the retention of the fibers at the constriction point. In low salinity brine, mineral wool fibers allowed a substantial improvement in gel strength, while, at the same time, a reduction in the concentration of chemicals by 40% was made possible.Furthermore, with the addition of 0.6 wt.% mineral wool fibers, the viscosity of the 0.3 wt.% polymer gel increased from 560.5 to 106,920 cp. In fact, in a 1-mm-wide fracture, a gel containing 0.3 wt.% polymer and 0.6 wt.% mineral wool fiber achieved a post-flush pressure gradient that was 58 times higher than a 0.75 wt.% plain polymer gel. Unfortunately, the choice of a makeup brine with an increased salinity resulted in the deterioration of fiber-gel strength. Nonetheless, a substantial improvement of gel strength can be achieved by adding 0.6 wt.% mineral wool fibers, even if the salinity is as high as 143 g/L. Moreover, in experiments in which the permeability of the adjacent matrix was very low, 0.018 mD, a gel of 0.3 wt.% polymer and 0.6 wt.% mineral wool fiber prepared in 242.6 g/L brine, was still superior to a 0.75 wt.% plain gel prepared in low salinity brine.Experimentation with large fracture widths of 2.55 mm and 4 mm was also done to confirm gel effectiveness. For example, a gel of 0.3 wt.% polymer and 0.6 wt.% mineral wool fiber, prepared in 14 g/L brine, provided a 1.46 times higher post-flush pressure gradient in a 2.55-mm-wide fracture, as compared to that of a 0.75 wt.% plain polymer low salinity gel in a 1-mm-wide fracture. With an increase in the salinity, to 234.6 g/L, of the makeup brine used with a fiber-gel, the resistance to the flow of brine in a 2.55-mm-wide fracture became comparable to that of a plain gel in a 1-mm-wide fracture. In a 4-mm-wide fracture, a gel with 0.3 wt.% polymer prepared in 234.6 g/L brine and one of 0.5 wt.% polymer prepared in 14 g/L brine, each with 0.6 wt.% mineral wool fiber, provided maximal post-flush pressure gradients equal to 12–14 psi/ft. This is the same range usually expected from a 0.5 wt.% relatively low molecular weight plain polymer gel in a 1-mm-wide fracture.Although, fibers improved the ability of gels to resist washing out from fractures, in a 4-mm-wide fracture such a fiber-gel could not provide notable resistance to the flow of brine with an increase in the superficial flow velocity higher than 1,000 ft/d. Discovering formulas that would increase the resistance of gels to being washed out of wide fractures must continue.

Unraveling the cytotoxicity and cellular uptake of low, medium and high molecular weight polyethylene glycol polymers in MCF-7 cells by green UPLC-MS/MS methods

Unraveling the cytotoxicity and cellular uptake of low, medium and high molecular weight polyethylene glycol (PEG) in cells is important for evaluation of therapeutic efficacy and toxicity of PEGylated drug delivery systems. In this study, cellular uptake of PEG600, PEG2K, PEG4K and PEG10K in MCF-7 cells was first studied by an UPLC-MS/MS assay coupled with collision induced dissociation (CID) in source technique. The CID of PEG in source with high values of declustering potentials generates numerous PEG-related product ions. These PEG-related fragment ions can be further broken into specific product ions in the collision cell as alternative ions for detection of PEG. The quantification of PEG was finally performed with the MRM transition (m/z 221.0 → 89.0). The experimental results indicated that the toxicity of PEG600, PEG2K, PEG4K and PEG10K was not significant at concentrations of 5–1200 μg/mL and the amounts of PEG polymers entry into MCF-7 cells at was small. The greenness of the developed analytical methods was also assessed by Analytical Eco-Scale, Analytical Greenness calculator (AGREE) and Green Analytical Procedure Index (GAPI) in this study.

The relaxation dynamics and dielectric properties of cyanobiphenyl-based nematic tripod liquid crystals

We present a detailed investigation of the phase behaviour, molecular relaxation dynamics, rheology and dielectric properties of two cyanobiphenyl-based liquid crystal (LC) tripods, differing only in the length of their spacer units (6 or 9 carbons). These LC tripods combine properties of low molecular weight LCs and LC polymers, resulting in a range of advantageous properties including a wide nematic range (ΔT>90 K) and a large birefringence (0.3 at T−TNI=-80 K for the 6 spacer tripod). Using broadband dielectric relaxation spectroscopy, calorimetry, oscillatory and steady state shear rheology, we identified four molecular relaxation processes: the structural (α) relaxation (defining the glass transition temperature, Tg); the δ relaxation (reorientation of the mesogen unit around its short axis); the β relaxation (reorientation around its long axis); and the γ relaxation (internal tripod arm fluctuations). The β and γ relaxations follow Arrhenius temperature dependencies in the glass, whereas the α and δ relaxations merge above, but near Tg, where they follow a non-Arrhenius VFT behaviour. For higher temperatures, the two relaxations separate and for T>T⁎, where T⁎ marks a dynamic crossover, the α relaxation transitions from VFT to Arrhenius behaviour. For the two tripods, ratios of T⁎/Tg=1.14 and T⁎/Tg=1.13 were observed respectively, consistent with the ratio observed for many side-chain LC polymers (and other LC systems), and consistent with the ratio where a dynamic crossover is typically observed also for non-LC glass-formers. However, for non-LC systems, the transition to Arrhenius behaviour happens at significantly higher temperatures relative to Tg and the dynamic crossover at T⁎ is typically observed as a transition between two different VFT behaviours. We argue that for the tripods these differences arise from differences in the molecular relaxation mechanisms induced by the LC order. Finally, for temperatures where δ and α relaxations are separated, we find that ion conductivity decouples from the α relaxation, instead following the δ relaxation; this demonstrates that the ion transport properties for the tripods can be tuned by the design of the tripod mesogen arm.

New mode of HPLC separation for multi‐charged polymers, peptides, and proteins

AbstractThis article explores a new mode of chromatographic separation named BIST™ (Bridge Ion Separation Technique) that is designed specifically for the retention and separation of charged molecules. The proposed mechanism is supported by multiple examples. The separation technique is especially useful for analysis of low molecular weight charged polymers, the class of molecules where ion‐exchange, ion‐exclusion and size exclusion modes of separation do not work effectively. Among low molecular weight polymers, many compounds are of high importance for biological, medicinal, agricultural, and consumer applications. Some examples include heparin, poly amino acids, insulin, polyethyleneimine, as well as other peptides. The wide variety of applications of many charged polymers necessitates a high‐quality analytical technique for testing and research of these compounds.

Effect of the structure of macromonomer in polycarboxylate superplasticizer on slump-retention of concrete

Three kinds of slump-retention polycarboxylate superplasticizers(52HPC4, 52IPC4, and 52EPC4) were synthesized by using HPEG, IPEG, or EPEG as macromonomers. The effects of polycarboxylate superplasticizers on the slump-retention of cement and concrete were investigated. The mechanism of action was explained by the composition of PCE polymers and monomer sequences (EHE, HHE, or HHH), which were investigated by using conductivity, GPC, 1H-NMR, and 13C-NMR. The results indicated that the slump flow of cement paste mixed with 52EPC4 was increased quickly within 120 min, while 52IPC4 doesn’t change within 240 min. Concrete mixed with 52IPC4 had the best slump-retention performance reaching 440 mm after 150 min, but concrete mixed with 52HPC4 was almost no fluidity after 120 min which had the largest slump flow loss through time than that containing other PCEs, and the conductivity of 52IPC4 aqueous solution decreased more slowly than other PCEs. Because of the highest content of effective PCE polymers, and the largest steric hindrance to ester bond resulting in the concrete had the best slump-retention performance when mixed with 52IPC4, because of the smallest steric hindrance to ester bond resulting in the fastest increase spread flow of cement paste which mixed 52EPC4, because of the highest content of low molecular polymers and the lowest content of effective PCE polymers in 52HPC4 resulting in the smallest initial slump flow of concrete, and the largest slump flow loss through time of concrete, even though the steric hindrance effect was larger than 52EPC4.

Construction of fracturing fluid with excellent proppant transport capacity using low molecular weight hydrophobic association polymer and surfactant

Slick water fracturing fluid is widely used for fracturing unconventional reservoirs such as shale and tight gas, and it has aided in developing unconventional oil and gas reservoirs. However, the problem of slick water in terms of its weak proppant transport capacity has not been effectively solved. Conventional methods of increasing the proppant transport capacity of a fracturing fluid by increasing viscosity and pumping rate have resulted in serious reservoir damage and increased costs, showing more and more limitations. To address this issue, a low molecular weight polymer/surfactant (LMPS) fracturing fluid system was developed. LMPS increased the fluid elasticity through the interaction between the hydrophobic groups on the polymer and the surfactant while maintaining low viscosity, thus obtaining excellent proppant transport capacity. The low molecular weight polymer is a type of hydrophobic association water-soluble polymer (HAWSP) prepared by photoinitiation. Its viscosity-average molecular weight was determined to be 1.24 × 106 g/mol, much more than that of a typical drag reducer of traditional slick water (about 1 × 107 g/mol). The low molecular weight of HAWSP is conducive to preparation, dissolution, pumping, and reducing the damage of polymer to the reservoir. When 300 mg/L of sodium dodecyl benzene sulfonate (SDBS) surfactant was added to a 0.2 wt% HAWSP solution, it formed a robust self-assembled network that significantly enhanced the elasticity and raised the storage modulus G' from 0.11 to 5.95 Pa. The 20/40 mesh ceramsite proppant remained suspended in the LMPS solution (36 mPa·s) for 30 min, whereas ceramsite completely settled within 30 s in an ordinary linear polymer solution with similar viscosity. Simultaneously, despite having a lower molecular weight, the drag reduction rate test shows that the drag reduction performance of the LMPS fracturing fluid was similar to the tested conventional commercial linear polymer. The self-assembled network of HAWSP/surfactant can increase the viscoelasticity of the fracturing fluid, which is expected to overcome the weakness of insufficient proppant transport capacity of slick water, thus improving development efficiency of unconventional gas reservoirs.

Recycling of ammonia-cured epoxy resin by oxidative degradation of nitric acid assisted by swelling agent

Because of its high crosslinking density, compact structure and stable performance, epoxy resin is difficult to be degraded, which leads to serious environmental pollution problems. In this work, using dipropylene glycol dimethyl ether as swelling agent and nitric acid as oxidant, the degradation of amine cured epoxy resin was studied. Results are as follows: The degradation rate obtained by swelling agent assisted oxidation degradation method is much higher than that obtained by oxidation degradation method only. And the degradation rate of the epoxy resin even reached 100 % at 100 °C only in an hour under the condition of swelling agent assisted nitric acid. FT-IR and GC–MS showed that the degradation was mainly caused by that the CN bond in the molecular chain was gradually weakened and fractured finally. The molecular weight of the degradation product was relatively dispersive, which was composed of low molecular polymer and small fragments, and the molecular weight of low molecular polymer was about 2167. And the degradation products primarily contain 4-isopropylphenol and (allyloxy)benzene rings. This work provides a new way to solve the problem about the degradation, recycling and pollution of epoxy resin.

Practical Route for Catalytic Ring-Opening Metathesis Polymerization.

Norbornene derivatives are typical monomers for ring-opening metathesis polymerization (ROMP) for synthesizing highly functional polymers. However, the lack of catalytic methods, that is, the lack of readily available chain transfer agents (CTAs) for these monomers has been a significant cost limitation when large-scale syntheses are required. Here, we report commercially available styrene and its derivatives as efficient regioselective CTAs for the catalytic synthesis of metathesis polymers requiring up to 1000 times less ruthenium than in classical ROMP experiments. The molecular weight of the synthesized polymers was controlled by the monomer-to-CTA ratio. Low molecular weight ROMP polymers known for their antimicrobial properties were also synthesized on a gram scale in this report. Polymers were characterized by SEC, 1H NMR spectroscopy, and isotopically resolved MALDI-TOF MS. This approach describes a greener, more cost-effective, and eco-friendly methodology for the preparation of metathesis-based materials on the multigram scale.

A novel low molecular quaternary polymer as shale hydration inhibitor

Polymer inhibitors for deep shale gas drilling have poor temperature resistance and can influence the rheological attributes of the drilling muds. To overcome this issue, a high temperature resistant and low molecular weight quaternary polymer DVAA was prepared by hydrothermal radical polymerization. The characterizations of the DVAA were evaluated by IR, NMR, TG, and GPC, and the inhibition, rheology, and filtration parameters were examined. The shale inhibition mechanism was evaluated by the SEM, zeta potential, contact angle, and XRD. Initial decomposition temperature of DVAA is 354.83 °C and Mp is 4583. The performance test outcomes suggest that using DVAA could lead to a linear expansion reduction rate of MMT at 73.4%, whereas the rolling recovery rate of cuttings was 86.25%. The API filtration of 4% MMT after hot-rolling is 13.6 ml. The mechanism of DVAA showed that DVAA and MMT form ionic bonds and hydrogen bond through electrostatic attraction and can still maintain a good structure under elevated temperature conditions. DVAA can effectively weaken the surface hydration by entering the crystal layer to replace the inter-layer cations, where it forms a polymer-film on the bentonite surface. In summary, the research and development of the DVAA can provide an effective guarantee for the stability of the wellbore during the development of deep shale gas reservoirs.

Mechanical reinforcement of isoprene rubbers via metal-coordinated crosslink of carboxyl-terminated telechelic polymers

Telechelic carboxyl-terminated polyisoprene and carboxyl-terminated polynorbornene were synthesized by Ru-catalyzed cross-metathesis of maleic acid with polyisoprene and polynorbornene, respectively. The molecular weight of the telechelic polymer can be controlled by varying the molar ratio of monomer units to catalyst or maleic acid. These telechelic polymers were used as modifiers for isoprene rubbers and resulted in accelerated vulcanization. Moreover, iron ions were used as “sutures” to form a cross-linked network of low molecular weight telechelic polymers through iron-carboxyl coordination bonds, and another cross-linked network was generated by sulfur-induced vulcanization, resulting in dual-cross-linked network and mechanical reinforcement of isoprene rubbers. • Telechelic carboxyl-terminated polyisoprene and polynorbornene are synthesized. • Metal-coordinated crosslink lead to mechanical reinforcement of isoprene rubbers. • Telechelic polymers result in accelerated vulcanization of isoprene rubbers.

Investigation of different molecular weight Polyvinylidene Fluoride (PVDF) polymer for the fabrication and performance of braid hollow fiber membranes

ABSTRACT In the current study, braid reinforced membranes were fabricated from polyvinylidene fluoride (PVDF) polymers with two different molecular weights, and the blending of the polymers in a 1:1 ratio to upgrade the performance of the membrane. Characterization, filtration studies, and membrane bioreactor (MBR) application were done to evaluate membrane performance by applying the same operation conditions on each membrane. Characterization studies indicated that the fabricated membrane from blending polymers was a hydrophilic structure with a contact angle of 50.78° and smoother surface properties compared to the other fabricated membranes. According to the MBR results, at the end of the operation process, TMP levels of the membrane from the blending method are found 150 mbar, membrane from high molecular weight PVDF polymer had 250 mbar, and membrane from low molecular weight PVDF polymer had 800 mbar. As a consequence of the investigation, it is seen that the hydrophilic structure of the membrane allows the pollutant to adsorb less to the blend membrane surface, and the lower roughness is also a factor in reducing fouling.

Fracturing fluid applications of carboxylate-terminated low molecular weight PEI and CTAB formulations

It is imperative to develop new viscoelastic surfactants (VES) based fluid formulations that show promise as fracturing fluids for a more efficient hydrocarbon recovery. In this study, a novel hyperbranched polymer having multiple terminal carboxylate (C-PEI) functional groups was prepared using a simple one-pot, two-step synthesis method and characterized using 1HNMR, FTIR, and TGA. The terminal carboxylate moieties are employed as a chelating agent along with a cationic surfactant cetyltrimethylammonium bromide (CTAB) to develop different viscoelastic formulations of a low molecular weight polymer and a surfactant system. The amounts of C-PEI (2.5–7.5%) and CTAB (2.5–7.5%) that were used in 1:1 wt/wt percent with CaCl2 (10–30%) solutions at a temperature range of RT to 90 °C under the influence of shear rate (1–100 s−1) to find an optimum formulation and the most convenient conditions for exhibition of better viscoelastic properties. The shear-based viscosity was investigated to ascertain the typical viscoelastic behavior of a carboxylate terminated polymer and a cationic surfactant using a rheometer. The results showed that the concentrations of C-PEI and CTAB (7.5%:7.5% wt/wt) in the presence of 30% CaCl2 solution (85%) exhibited apparent viscosity of ~680 cPs at 90 °C under a shear rate of 100 s−1. The stability of optimized viscoelastic formulations was also assessed, and it was realized that there was no appreciable change in viscosity with respect to time. The gel-breaking results indicate that the addition of ~8.5% commercial diesel reduced the maximum apparent viscosity 682 cPs to 12 cPs at 90 °C. This novel viscoelastic system comprising of a low molecular weight hyperbranched polymer C-PEI and CTAB may potentially offer a more robust and efficient system for enhanced recovery of hydrocarbons from oil reservoirs.

Self-Healing and Electrical Properties of Viscoelastic Polymer-Carbon Blends.

Self-healing polymer-carbon composites are seen as promising materials for future electronic devices, which must be able to restore not only their structural integrity but also electrical performance after cracking and wear. Despite multiple reports about self-healing conductive elements, there is a lack of a broad fundamental understanding of correlation between viscoelasticity of such composites, their electrical properties, and self-healing of their mechanical as well as electrical properties. Here, it is reported thorough investigation of electromechanical properties of blends of carbon black (CB) as conductive filler and viscoelastic polymers (polydimethylsiloxanes (PDMS) and polyborosiloxane (PBS)) with different relaxation times as matrices. It is shown that behavior of composites depends strongly on the viscoelastic properties of polymers. Low molecular polymer composite possesses high conductivity due to strong filler network formation, quick electrical, and mechanical properties restoration, but for this the ability is sacrificed to flow and ductility at large deformation (material is brittle). In contrary, high relaxation time polymer composite behaves elastically on small time and flows at large time scale due to weak filler network and can heal. However, the electrical properties are worse than that of carbon and viscous polymer and degrade with time.

Homoleptic and Heteroleptic Substituted Amidomethylpyridine Iron Complexes: Synthesis, Structure and Polymerization of rac‐Lactide

AbstractThe synthesis of iron complexes bearing amidomethylpyridine ligands, one homoleptic [2‐[(2,6‐iPr2‐C6H3)NC(Me)]C5H4N]2Fe (1) complex and two heteroleptic silylamide iron complexes [2‐[(2,6‐iPr2‐C6H3)NC(Me)]‐6‐R‐C5H4N]Fe(N(SiMe3)2)C5H5N (R=H, 2Py and R=Me, 3Py), are described together with their application as catalysts for the Ring‐Opening Polymerization (ROP) of rac‐lactide (rac‐LA). The determination of the crystal structure of the three iron complexes is reported as well as their behavior in solution by means of 1H NMR studies. All of these complexes have shown to be active for the polymerization of rac‐LA at 50 °C in toluene, producing, among others, high molecular weight polylactides (PLA) according to SEC analysis, along with a portion of low molecular weight cyclic polymer (cPLA) on the basis of MALDI spectra.

Small Molecule Modifications Significantly Increase the Transfection Efficiency of Low-Molecular Polymer.

Gene vectors with high biocompatibility and transfection efficiency are critical for successful gene therapy. PEI 25K (Polyethyleneimine 25K) is a common polymeric gene vector that has been employed as a positive control material in gene transfection studies due to its good performance in endosome escape. PEI 25K's indegradability and abundance of positive charges, on the other hand, cause toxicity in cells, limiting its use. In this study, we developed the PEI-ER non-viral vector by adding an endoplasmic reticulum (ER) targeting ligand to low molecular weight PEI 1.8K. These small molecule modifications dramatically improved PEI transfection efficiency while barely interfering with compatibility. PEI-ER/DNA complexes were discovered to enter the cell via caveolin-mediated endocytosis, avoiding destruction in the endosome. We believe that this little chemical alteration is a simple solution to enhance the efficacy of cationic polymer vectors in gene transport, and it has a lot of medicinal applications.

Multi-functional oilfield production chemicals: maleic-based polymers for gas hydrate and corrosion inhibition

Several chemical problems can occur during the production of oil and gas through flow lines. This includes corrosion, scale deposition and gas hydrate plugging. Three separate chemicals may be needed to treat these issues. Kinetic hydrate inhibitors (KHIs) are used in cold oil or natural gas production flow lines to prevent the formation and plugging of the line with gas hydrates. They are often injected concomitantly with other production chemicals such as corrosion and scale inhibitors. KHIs are specific low molecular weight water-soluble polymers with amphiphilic groups formulated with synergists and solvents. However, many corrosion inhibitors (CIs) are antagonistic to the KHI polymer, severely reducing the KHI performance. It would be preferable and economic if the KHI also could act as a CI. We have explored the use of maleic-based copolymers as KHIs as well as their use as film-forming CIs. KHIs were tested using a natural gas mixture in high pressure rocking cells using the slow constant cooling test method. A terpolymer from reaction of vinyl acetate:maleic anhydride copolymer with cyclohexy lamine and 3,3-di-n-butylaminopropylamine (VA:MA-60% cHex-40% DBAPA), gave excellent performance as a KHI, better than the commercially available poly(N-vinyl caprolactam) (PVCap). CO2 corrosion inhibition was measured by Linear Polarization Resistance (LPR) in a 1 litre CO2 bubble test equipment using C1018 steel coupons. The new terpolymer gave good CO2 corrosion inhibition in 3.6 wt% brine, significantly better than PVCap, but not as good as a commercial imidazoline-based surfactant corrosion inhibitor. The terpolymer also showed good corrosion inhibition efficiency at high salinity conditions, (density 1.12 g/cm3). VA:MA-60% cHex-40% DBAPA shifted the open-circuit potential to more positive values and significantly decreased the corrosion rate.