Increase In Polymer Molecular Weight Research Articles

Synthesis and Modeling of Poly(L-lactic acid) via Polycondensation of L-Lactic Acid.

We present synthetic experiments of lactic acid (LA) polycondensation to produce poly(lactic acid) (PLA) as well as kinetic modeling calculations that capture the polymer molecular weight increase with time, given the initial concentrations. Tin-octoate-catalyzed polycondensation of (D,L)- or L-lactic acid was carried out in pre-dried toluene after azeotropic dehydration for 48-120 h at 130-137 °C. The polymerization was optimized by varying lactic acid and catalyst concentrations as well as the temperature. Gel permeation chromatography was used to experimentally follow the evolution of molecular weights and the products were characterized by NMR, TGA, DSC and IR. Under optimal conditions, PLLA with weight-average molecular weight (Mw) of 161 kDa could be obtained. The rate equations that describe polycondensation kinetics were recast in a condensed form that allowed very fast numerical solution and calculation of the number-average molecular weight with time. Deviations with respect to the experiment were minimized in a least-squares fashion to determine rate constants. The optimized kinetics parameters are shown to reproduce the experimental data accurately.

Study on Compatibility between Complex Mode Micropore Structure and Polymer Solution of Different Formulation for Conglomerate Reservoir

In this paper, the conglomerate reservoir is selected as the object to investigate the micropore structure and the compatibility of polymer solutions. Firstly, the characteristics of complex mode pore structure are analyzed based on casting thin sections, scanning electron microscope, and capillary pressure curve. Then the conglomerate reservoir is divided into five types by use of the K-means clustering algorithm, and the differences in micropore structure among the different reservoir types are also clarified. Secondly, the dynamic light scattering technology is used to directly determine the hydrodynamic diameter of different polymer formulations. As the polymer molecular weight increases, the average hydrodynamic diameter becomes larger, and with the same polymer molecular weight, the average hydrodynamic diameter becomes gradually larger as the solution concentration increases. Based on the above research results, the matching relationship between five reservoir types and polymer solutions is determined through laboratory experiments. The experimental results show that when the polymer molecular weight is determined, the volume of pore volume that can be effectively swept by polymer hydration molecules gradually decreases as the concentration of the solution increases. When the polymer molecular weight and its concentration are both determined, the pore volume of effective displacement of polymer-hydrated molecules also gradually reduces with becoming worse reservoir pore structure. The scope of application of different polymer formulations becomes progressively smaller as the microscopic pore structure of type I to type V reservoirs becomes deteriorated. The compatibility between the micropore structure of different conglomerate reservoir types and polymer solution is determined to provide the geological basis for the reasonable formulation of the polymer flooding scheme.

1,1,3,3-Tetramethylguanidine-Mediated Zwitterionic Ring-Opening Polymerization of Sarcosine-Derived N-Thiocarboxyanhydride toward Well-Defined Polysarcosine.

Zwitterionic ring-opening polymerization (ZROP) of sarcosine-derived N-thiocarboxyanhydrides (Me-NNTAs) can be induced by using 1,1,3,3-tetramethylguanidine (TMG) initiators in CH2Cl2 at 25 °C, rapidly producing well-defined polysarcosine polymers with controlled molecular weights (Mn = 1.9–37 kg/mol) and narrow molecular weight distributions (Đ = 1.01–1.12). The reaction exhibits characteristics of a living polymerization, evidenced by pseudo-first-order polymerization kinetics, the linear increase of polymer molecular weight (Mn) with conversion, and the successful chain extension experiments. The polymerization is proposed to proceed via propagating macro-zwitterions bearing a cationic 1,1,3,3-tetramethylguanidinium and an anionic thiocarbamate chain end. The TMG not only initiates the polymerization but also serves to stabilize the thiocarbamate chain end where the monomer addition occurs. Because of the enhanced hydrolytic stability of Me-NNTA, the polymerization can be conducted without the rigorous exclusion of moisture, further enhancing the appeal of the method to access well-defined polysarcosine.

Horizontally and Vertically Concerted Steric Strategy in α‐Diimine Nickel Promoted Ethylene (Co)Polymerization†

Main observation and conclusionSteric bulk plays a significantly paramount role in late transition metal promoted olefin (co)polymerization in terms of polymer molecular weight and catalyst thermal stability. Numerous sterically encumbered nickel and palladium catalysts have been developed, but they are usually uni‐directional. In this contribution, from a bi‐directional side the distinctive horizontally and vertically concerted steric strategy was well‐developed and applied to α‐diimine nickel catalysts. In ethylene polymerization, the increase of vertically steric bulk (H, Ph, Biph) led to an enhanced polymer molecular weight, a slightly ascended branching density; likewise increasing horizontally steric bulk (Ph, Nap, Ant) further resulted in the increase of polymer molecular weight and branching density. As a result, in sharp contrast to Ni1(H) without steric bulk, Ni5(Ant) with horizontally and vertically concerted steric bulk was thermally stable, showed very high activities at a level of 107 g·mol–1·h–1, and produced polyethylenes with the highest molecular weight of 518.8 × 104 g·mol–1 and the broader range of branching density from 2.4/1000C to 27.8/1000C. In the copolymerization of ethylene with methyl 10‐undecenoate, Ni5(Ant) also provided the highest copolymer molecular weight but gave the lowest incorporation of co‐monomer. This work sheds light on the steric effect on olefin (co)polymerization.

2,4,6‐Triphenylpyridinium: A Bulky, Highly Electron‐Withdrawing Substituent That Enhances Properties of Nickel(II) Ethylene Polymerization Catalysts

AbstractThe reactivity of NiII and PdII olefin polymerization catalysts can be enhanced by introduction of electron‐withdrawing substituents on the supporting ligands rendering the metal centers more electrophilic. Reported here is a comparison of ethylene polymerization activity of a classical salicyliminato nickel catalyst substituted with the powerful electron‐withdrawing 2,4,6‐triphenylpyridinium (trippy) group to the ‐CF3 analogue. The trippy substituent is substantially more electron‐withdrawing (σmeta=0.63) than the trifluoromethyl group (σmeta=0.43) which results in a ca. 8‐fold increase in catalytic turnover frequency. An additional advantage of trippy is the high steric bulk relative to the trifluoromethyl group. This feature results in a four‐fold increase in polymer molecular weight owing to enhanced retardation of chain transfer. A significant increase in catalyst lifetime is observed as well.

Investigation into the effect of branch length of polyolefin and its statistical distribution on the flow improving performance

Ultra high molecular weight polyolefins as the main category of drag reducing agents play the main role in energy transportation. The present study seek to thoroughly investigate, the implications of several determining factors, such as catalyst structure, monomer type and concentration, in the coordinative polymerization of 1-olefins coupled with the corresponding accumulative effect of these precursors on the potential behavior of drag reducing macromolecules. The results showed that polymerization temperature is the most important parameter affecting polymer performance in drag reduction due to the increase in polymer molecular weight with decreasing the polymerization temperature. It was also observed that a type of monomer plays an important role in the drag reduction. The results showed that polyhexene had a higher performance than the polydecene, due to the amorphous structure of the polymer, which can evidently be corroborated by DSC analysis. The experimental results verified that polymers produced with late transition metal catalysts have lower performance in drag reduction efficiency than polymers synthesized with Ziegler-Natta catalysts. Having considered the distribution and the length of side chains in macromolecules chain (synthesized via ZN and Late transition metal ones) as well as their performance, it can surely be assumed that uniformity of side chain branches in the boosting of polymer capacity concerning drag reduction efficiency is of paramount significance. This is definitely an issue of paramount significance in tailoring functional structures.

Influence of the Polymer Glass Transition Temperature and Molecular Weight on Drug Amorphization Kinetics Using Ball Milling.

In this study, the putative correlation between the molecular mobility of a polymer and the ball milling drug amorphization kinetics (i.e., time to reach full drug amorphization, ta) was studied using different grades of dextran (Dex) and polyvinylpyrrolidone (PVP) and the two model drugs indomethacin (IND) and chloramphenicol (CAP). In general, IND had lower ta values than CAP, indicating that IND amorphized faster than CAP in the presence of the polymers. In addition, an increase in polymer molecular weight (Mw) also led to an increase in ta for all systems investigated up to a critical Mw for each polymer, which was in line with an increase of the glass transition temperature (Tg) up to the critical Mw of each polymer. Hence, the increase in ta seemed to correlate well with the Tg/Mw of the polymers, which indicates that the polymers’ molecular mobility had an influence on the drug amorphization kinetics during ball milling.

Chain‐growth polymerization of azide–alkyne difunctional monomer: Synthesis of star polymer with linear polytriazole arms from a core

ABSTRACTThis article reports a chain‐growth coupling polymerization of AB difunctional monomer via copper‐catalyzed azide–alkyne cycloaddition (CuAAC) reaction for synthesis of star polymers. Unlike our previously reported CuAAC polymerization of AB n (n ≥ 2) monomers that spontaneously demonstrated a chain‐growth mechanism in synthesis of hyperbranched polymer, the homopolymerization of AB monomer showed a common but less desired step‐growth mechanism as the triazole groups aligned in a linear chain could not effectively confine the Cu catalyst in the polymer species. In contrast, the use of polytriazole‐based core molecules that contained multiple azido groups successfully switched the polymerization of AB monomers into chain‐growth mechanism and produced 3‐arm star polymers and multi‐arm hyperstar polymers with linear increase of polymer molecular weight with conversion and narrow molecular weight distribution, for example, Mw/Mn ~ 1.05. When acid‐degradable hyperbranched polymeric core was used, the obtained hyperstar polymers could be easily degraded under acidic environment, producing linear degraded arms with defined polydispersity. © 2019 Wiley Periodicals, Inc. J. Polym. Sci. 2020, 58, 84–90

γ-valerolactone (GVL) as a bio-based green solvent and ligand for iron-mediated AGET ATRP

AbstractIn this paper, γ-valerolactone (GVL), a bio-based polar solvent, was applied as green solvent for iron(III)-catalyzed AGET ATRP without any external ligand. GVL is a fully degradable, non-toxic green solvent and has complex ability to iron halide complexes through –OCO- group. GVL as the solvent and the ligand for AGET ATRP of MMA in a controlled manner, as proved by kinetic study, the low PDI values and the increase in polymer molecular weight versus monomer conversion. Chain re-initiation experiments and 1HNMR characterization were conducted to further confirm the living feature.

Design and optimisation of a microwave reactor for kilo-scale polymer synthesis

Current industrial production of polymer resins is generally undertaken in large multi-tonne stirred tank reactors. These are characterised by relatively slow heating and cooling cycles, resulting in long vessel cycle times and extended production campaigns. In this work we present a design for a hybrid microwave/oil jacket proof of concept system capable of producing up to 4.1 kg of polymer resin per batch. By exploiting rapid volumetric heating effects of microwave energy at 2.45 GHz, we have optimised the synthetic regime, such that a 3.7 kg batch of polyester resin pre-polymer can be made in only 8 h 20 min, with higher molecular weight (Mn 2100) compared to the conventional process taking 22 h 15 min (Mn 1200), yielding an increase in synthesis rate of at least 265%. The increase in polymer molecular weight also suggests a higher conversion was achieved over a shorter time scale.

Impact of Ultraviolet Irradiation on Stress–Strain Behavior of Syndiotactic 1,2-Polybutadien: The Role of Oxidation

We studied the impact of ultraviolet (UV) irradiation on stress–strain characteristics, derived from uniaxial stretching measurements, and the molecular structure (photoinduced changes) of syndiotactic 1,2-polybutadien, a polymer with thermoplastic elastomer properties. Uniaxial stretching stress–strain curves are recorded for samples subjected to UV irradiation for different times and the effects UV irradiation has on the stress–strain behavior of polymers are analyzed. Long UV irradiation is found to markedly increase the hardening of polymers: Young’s modulus and yield strength increase, while the fracture strain decreases. At the same time, we observe a sharp increase in polymer molecular weight and its considerable oxidation that particularly involves surface layers. The mechanisms of cross-linking between macromolecules and their simultaneous oxidation induced by exposure to UV light are discussed along with the role these processes play in evolution of the physical mechanical properties under UV irradiation.

Partitioning of cefazolin in aqueous two-phase systems containing poly (ethylene glycol) and sodium salts (citrate, tartrate, and sulphate)

Aqueous two-phase systems (ATPSs) have been recognized as potential alternative techniques for extraction or purification of biomolecules. In this work, partitioning behavior of cefazolin has been investigated in polymer-salt ATPSs. Thus, systems containing polyethylene glycol (PEG) with two different molecular weights (6000 and 8000) and three forms of sodium salts, including sodium citrate, sodium tartrate, and sodium sulfate were examined. Firstly, the binodal curves were determined at 300 K and then correlated with Merchuk equation. Results indicate that the system PEG8000/sulfate owns a wider two-phase area. Then, the tie-lines were plotted for the systems under study, and their validity was evaluated using the Othmer-Tobias and Bancroft equations. Finally, the partition coefficient of cefazolin was investigated in 6 different two-phase systems and 28 tie-lines overall. Effect of salt type, polymer molecular weight and its concentration on partition coefficient were discussed. On the basis of the results it can be declared that as the polymer concentration increases, the partition coefficient increases but the increase of polymer molecular weight leads to partition coefficient reduction. Sodium citrate was better than the other salts used for studying the cefazolin partitioning, that is in good accordance with the excluded volume theory. The maximum amount of partition coefficient equals to 13.4 with a 90.5 recovery percentage in the top phase which belongs to the system combined of PEG6000 (16% w/w) and sodium citrate (14% w/w).

Влияние ультрафиолетового облучения на деформационные свойства синдиотактического 1,2-полибутадиена: роль окисления

AbstractWe studied the impact of ultraviolet (UV) irradiation on stress–strain characteristics, derived from uniaxial stretching measurements, and the molecular structure (photoinduced changes) of syndiotactic 1,2-polybutadien, a polymer with thermoplastic elastomer properties. Uniaxial stretching stress–strain curves are recorded for samples subjected to UV irradiation for different times and the effects UV irradiation has on the stress–strain behavior of polymers are analyzed. Long UV irradiation is found to markedly increase the hardening of polymers: Young’s modulus and yield strength increase, while the fracture strain decreases. At the same time, we observe a sharp increase in polymer molecular weight and its considerable oxidation that particularly involves surface layers. The mechanisms of cross-linking between macromolecules and their simultaneous oxidation induced by exposure to UV light are discussed along with the role these processes play in evolution of the physical mechanical properties under UV irradiation.

Synthesis of Nickel Nanoparticles by the Reduction of Its Salts Using the Modified Polyol Method in the Presence of Sodium Polyacrylates with Various Molecular Weights

Nickel nanoparticles were synthesized by the reduction of its salts by hydrazine hydrate in a polyol medium in the presence of sodium polyacrylates with molecular weights of 1200, 5100, and 8000. The nanoparticles were characterized by X-ray diffraction, scanning and transmission electron microscopy, IR spectroscopy, and thermogravimetric analysis. The effect of the synthesis conditions, such as temperature, molecular weight of sodium polyacrylate, and polyol and precursor types, on the reduction products were studied. It was shown that the average particle sizes, their aggregation and polydispersity degrees increase as the polymer molecular weight increases.

Influence of polymeric carrier on the disposition and retention of 20(R)-ginsenoside-rg3-loaded swellable microparticles in the lung.

The objective of this study was to investigate the influence of differently charged biocompatible polymers, including chitosan (CS), hyaluronic acid (HA), and hydroxypropyl cellulose (HPC), on the disposition and retention of 20(R)-ginsenoside-rg3 (Rg3)-loaded swellable microparticles in the lung. A high-pressure homogenization method combined with spray drying was used to prepare Rg3-loaded microparticles. In vitro aerodynamic performance of different microparticles was characterized by the Next Generation Impactor (NGI). Retention of the swellable microparticles in the rat lung was investigated using bronchoalveolar lavage fluid method. Influence of drug loading, polymer molecular weight, and polymer charge on the properties of the swellable microparticles was investigated. It was found that drug loading had no significant influence on experimental mass median aerodynamic diameter (MMADe) and fine particle fraction (FPF). Increasing polymer molecular weight caused no remarkable change in MMADe value, but the FPF value decreased with the increase of polymer molecular weight. At the same molecular weight level, polymer structure and charge had no statistical influence on the in vitro aerodynamic properties of the microparticles and lung disposition, but it influenced the swelling and bioadhesion behavior and therefore lung retention profile. Desirable phagocytosis escapement and inhibition of A549 cell proliferation were achieved for the developed swellable microparticles. In conclusion, the lung retention of swellable microparticles can be adjusted by selecting polymeric carriers with different structure and charge.

Copolymerization of Glycolide and ɛ-Caprolactone Using 12-Aminolauric Acid Modified Montmorillonite

Poly(glycolide-co-ɛ-caprolactone) (PGLYCL) nanocomposites were prepared by copolymerization glycolide (GLY) and ɛ-caprolactone (ɛ-CL) in the presence of varying loadings 12-aminolauric acid (12-ALA)-modified montmorillonite. Copolymerization was successfully achieved based on the increase in polymer molecular weight after the reaction determined by gel permeation chromatography (GPC). The amount of the poly(glycolide) block and poly(ɛ-caprolactone) block units in the copolymer, identified by proton nuclear magnetic resonance (1H-NMR) spectroscopy, suggested that the increase in organo-clay loading cause a reduction GLYL: ɛ-CLL ratio. The arrangement of the monomers in the polymer products was elucidated to have an ABA triblock structure, where PCL block is the central block and the PGLY is found at both end of the copolymer. The presence of intercalated and exfoliated silicates in the nanocomposites were observed by x-ray diffraction (XRD) analysis. The biocompatibility of the nanocomposites with NCTC 292 mouse normal fibroblast was high relative to untreated cell cultures using tetrazolium bromide (MTT)-dye reduction assay.

Mucoadhesive Properties of Thiolated Pectin-Based Pellets Prepared by Extrusion-Spheronization Technique

The aim of this study was to develop mucoadhesive pellets on a thiolated pectin base using the extrusion-spheronization technique. Thiolation of pectin was performed by esterification with thioglycolic acid. The molecular weight and thiol group content of the pectins were determined. Pellets containing pectin, microcrystalline cellulose, and ketoprofen were prepared and their mucoadhesive properties were evaluated through a wash-off test using porcine intestinal mucosa. The in vitro ketoprofen release was also evaluated. Thiolated pectin presented a thiol group content of 0.69 mmol/g. Thiolation caused a 13% increase in polymer molecular weight. Pellets containing thiolated pectin were still adhering to the intestinal mucosa after 480 min and showed a more gradual release of ketoprofen. Conversely, pellets prepared with nonthiolated pectin showed rapid disintegration and detached after only 15 min. It can be concluded that thiolated pectin–based pellets can be considered a potential platform for the development of mucoadhesive drug delivery systems for the oral route.

Amidine-Mediated Zwitterionic Ring-Opening Polymerization of N-Alkyl N-Carboxyanhydride: Mechanism, Kinetics, and Architecture Elucidation

Zwitterionic ring-opening polymerization (ZROP) of N-butyl N-carboxyanhydrides (Bu-NCAs) has been investigated using 1,8-diazabicycloundec-7-ene (DBU), a bicyclic amidine initiator. It was found that poly(N-butylglycine)s (PNBGs) with molecular weight (Mn) in the 3.5–32.4 kg mol–1 range and polydispersity index (PDI) in the 1.02–1.12 range can be readily obtained by systematically varying the initial monomer to initiator feed ratio. The polymerization exhibits characteristics of a controlled polymerization, as evidenced by the linear increase of polymer molecular weight with conversion and the successful enchainment experiments. Kinetic studies revealed that the reaction is first-order dependent on the monomer and the DBU concentration. The rate of initiation is comparable to that of the propagation. Random copolypeptoids of poly[(N-propargylglycine)-r-(N-butylglycine)]s [P(NPgG-r-NBG)s] were also synthesized by DBU-mediated copolymerization of Bu-NCA and N-propargyl N-carboxyanhydride (Pg-NCA). Subsequen...

Mechanochemical Strengthening of a Multi-mechanophore Benzocyclobutene Polymer.

The mechanical stresses that materials experience during use can lead to aging and failure. Recent developments in covalent mechanochemistry have provided a mechanism by which those stresses can be channeled into constructive, rather than destructive, responses, including strengthening in materials. Here, the synthesis and mechanical response of a polymer containing multiple benzocyclobutene (BCB) mechanophores along its backbone are reported. When solutions of the BCB polymer were exposed to the normally destructive elongational flow forces generated by pulsed ultrasonication, the number of intermolecular bond-forming reactions was greater than the number of bond-breaking reactions, leading to a net increase in polymer molecular weight. The molecular weight increase could be turned into gelation by introducing a bismaleimide cross-linker that reacts with the ortho-quinodimethide intermediate generated by mechanically assisted ring opening of the BCB mechanophores and using polymer concentrations in excess of the critical overlap concentration. Unlike a previous mechanically induced gelation of a mechanophore-based polymer, the BCB cross-linking requires no ionic components and represents an attractive, second platform for stress-strengthening materials.

P‐54: WCS Material Development of FIT M+ Structural for Reduce the Power Consumption of a Large Size UHD TV

LGD has developed M+ technology for reduces power consumption. The core technology is the development of WCS photoresist. We developed in the following two technologies. 1. The binder polymer molecular weight increase to 20,000. 2. Synthesized the PDI to 2.0. LGD‐WCS developed at UHD large size TV into mass production.