Increase In Molecular Weight Research Articles

New contributions from thermal and dielectric techniques to the understanding of the dynamic properties of medium to long chain poly (propylene glycols)

AbstractThe molecular mobility of poly (propylene glycols) with molecular weights between 2000 and 18,200 g mol−1 was studied in the amorphous solid state, in the region of the glass transition and in the rubbery state; the experimental techniques used were differential scanning calorimetry (DSC) and thermally stimulated depolarization currents (TSDC). It was found that the glass transition temperature increases slightly with MW and tends to a limit value: TgDSC = −67°C, TgTSDC = −73°C.The different types of molecular mobility were analyzed: below Tg the secondary relaxations, and above this temperature the normal mode, were characterized in detail using TSDC; in the glassy transformation region, around Tg, the main relaxation was analyzed by both DSC and TSDC. It was found the dynamic fragility, m, behaves as independent of the molecular weight in the studied range: mDSC = 74 and mTSDC = 92. The TSDC results also show that, without influencing the kinetics of the segmental relaxation, the increase in molecular weight slows down the chain relaxation.

Microwave-assisted RAFT polymerization of N-(2-hydroxypropyl) methacrylamide and its relevant copolymers

A rapid and eco-friendly reversible addition-fragmentation chain transfer (RAFT) polymerization reaction of the N-(2-hydroxypropyl) methacrylamide (HPMA) monomer under microwave irradiation (MWI) was demonstrated. A systematic investigation to determine the optimal conditions for the polymerization, such as the reaction time, solvents, monomer stoichiometry and RAFT agents, was implemented. The polymerization kinetics were obtained using two different chain transfer agents (CTAs), namely, commercial 4-cyano-4-(phenylcarbonothioylthio)pentanoic acid and synthesized 4-cyano-4-(((ethylthio)carbonothioyl)thio)pentanoic acid, in the presence of 4,4′-azobis(4-cyanovaleric acid) as the initiator in various solvents. The controlled living character of the RAFT polymerization under MWI conditions was demonstrated by the linear increase in the number-average molecular weight (Mn) with monomer conversion. Moreover, good agreement between the theoretical and experimental Mn values was verified with pseudo-first-order kinetic plots, with low dispersities (Đ ≤ 1.04) if a favorable solvent and/or CTA was chosen. In addition, the ability of MWI to facilitate copolymer formation was demonstrated by the preparation of relevant copolymers, such as poly(HPMA-b-bocAPMA), poly(HPMA-b-MABH) and poly(HPMA-b-PDPA). Altogether, these facile synthetic approaches can find applications for the synthesis of PHPMA-based homo- and copolymers that have already been clinically tested and serve as hydrophilic high-potential alternatives to polyethylene oxide.

Hydration of α-pinene catalyzed by oxalic acid/polyethylene glycol deep eutectic solvents

A series of carboxylic acid-functionalized deep eutectic solvents(DES) wereconstructed by a natural organic dicarboxylic acid, oxalic acid (OA), as the hydrogen bond donor and the polyethylene glycol (PEG)with different polymerization degrees as the hydrogen bond acceptors, which are used in the hydration of α-pineneto produce α-terpineol. Fourier transform infrared spectroscopy (FT-IR), proton nuclear magnetic resonance spectroscopy (1H NMR), and thermogravimetric analysis (TGA) were used to prove the hydrogen bonding between OA and PEG. It is found that the presence of PEG has a less impact on the acid strength of DES. However, an increase in both molecular weight and dosage of PEG results in a decrease in total acidity and catalytic activity.Among them, OA/0.6PEG200, a DES catalyst prepared by PEG with the smallest molecular weight, exhibits a favorable catalytic performance. Under an optimal reaction condition with 0.03 mol of DES (based on OA), 0.06 molof α-pinene, 0.3 mol of water,at 75°C for 8 h, anα-pinene conversion of 81.5% and an α-terpineol selectivity of 51.2% are obtained. The catalyst phase can be separated by refrigerating overnight after reaction and reused directly with relatively stable catalytic performance. Thus, OA/0.6PEG200, as a DES catalyst prepared by a simple and highly atom economical process, will offer a clean catalytic route for the one-step production of α-terpineol.

Synthesis and Characterization of Methyl Acrylate-Copolymerized Medium-Chain-Length Poly-3-hydroxyalkanoates

Methyl acrylate (MA) and medium-chain-length poly-3-hydroxyalkanoates (mcl-PHA) underwent “grafting through” copolymerization in an inert atmosphere with benzoyl peroxide as sole radical initiator. The effects of different concentrations of MA on the yield and properties of the graft copolymers (PHA-g-MA) were investigated. Successful grafting of mcl-PHA and poly-methyl acrylate (PMA) was validated from the increase in molecular weight (Mw) of starting mcl-PHA and the presence of methyl acrylate backbone indicated by two additional peaks in proton nuclear magnetic resonance (1H-NMR) spectrum. The hydrophobic graft materials were more resistant to strong alkali condition than neat mcl-PHA in addition to strong acid resistivity. Copolymerization affects the amorphous character of mcl-PHA, as evidenced by a significant reduction in glass transition temperature (Tg). Nonetheless, the degradation temperature (Td) of mcl-PHA was increased about 20 °C higher after copolymerization which indicates excellent thermal stability of grafted mcl-PHA. The graft copolymers also displayed increased dielectric constant (e′) value except for PHA-g-MA synthesized from the highest concentration of MA (0.12 M) whereby it showed similar glass-to-rubbery transition and dielectric behavior to the neat mcl-PHA. Based on the results, the mechanism of the copolymerization is proposed.

Mechanical properties and water sensitivity of soybean protein isolate film improved by incorporation of sodium caseinate and transglutaminase

This study addresses the classic problems of high water solubility, hydrophilicity and low tensile strength of soybean protein isolate films. The effects of incorporation of sodium caseinate and transglutaminase treatment on the properties of film-forming solutions and their resultant films were systematically studied, changes in the former explaining improved properties of the latter. Increases in protein molecular weight, particle size, and viscosity, and decreases in lysine residue content of the solutions confirmed the formation of new macromolecular proteins following transglutaminase cross-linking. Increased hydrophobicity of proteins revealed the reason for decreases in water sensitivity of the films. The tensile strength and the hydrophobicity of the films significantly increased, while water solubility, water vapor permeability and elongation at break decreased by 37 %, 32 % and 71 %, respectively, in the presence of sodium caseinate and transglutaminase. In general, the coexistence of sodium caseinate and transglutaminase treatment significantly improve critical properties of soybean protein isolate-based films, particularly water sensitivity and tensile strength, and expand their potential applications in humid environments.

Biobased Thermoplastic Elastomers: Structure-Property Relationship of Poly(hexamethylene 2,5-furanodicarboxylate)-Block-Poly(tetrahydrofuran) Copolymers Prepared by Melt Polycondensation.

A series of poly(hexamethylene 2,5-furanodicarboxylate)-block-poly(tetrahydrofuran) (PHF-b-F-pTHF) copolymers were synthesized using a two-stage procedure, employing transesterification and polycondensation. The content of pTHF flexible segments varied from 25 to 75 wt.%. 1H nuclear magnetic resonance (NMR) and Fourier transformed infrared spectroscopy (FTIR) analyses were applied to confirm the molecular structure of the materials. Differential scanning calorimetry (DSC), dynamic mechanical measurements (DMTA), and X-ray diffraction (XRD) allowed characterizing the supramolecular structure of the synthesized copolymers. SEM analysis was applied to show the differences in the block copolymers’ morphologies concerning their chemical structure. The influence of the number of flexible segments in the copolymers on the phase transition temperatures, thermal properties, as well as the thermo-oxidative and thermal stability was analyzed. TGA analysis, along with tensile tests (static and cyclic), confirmed the utilitarian performance of the synthesized bio-based materials. It was found that an increase in the amount of pTHF caused the increase of both number-average and weight-average molecular weights and intrinsic viscosities, and at the same time causing the shift of the values of phase transition temperatures toward lower ones. Besides, PHF-b-F-pTHF containing 75 wt.% of F-pTHF units was proved to be a promising thermoplastic shape memory polymer (SMP) with a switching temperature of 20 °C.

Influence of the molecular weight on mechanical behavior and associated strain-induced structural evolution of Poly(ethylene 2,5-furandicarboxylate) upon biaxial stretching

The mechanical behavior of Poly(ethylene 2,5-furandicarboxylate) upon biaxial stretching and the associated strain-induced structural evolution is studied in the light of its molecular weight. Besides it is shown that the increase of molecular weight favors strain-induced crystallization (SIC) and that SIC in PEF occurs when a critical molecular orientation ratio is achieved. The earlier occurrence of SIC in the case of the higher macromolecular weight is explained by the faster macromolecular orientation due to a more robust entanglement network.Regarding the mechanical behavior, it appears that a strain-hardening stage is observed whatever the molecular weight, this stage originates from both macromolecular orientation and formation of crystals upon stretching. Finally, it is shown that biaxial orientation (BO) has a positive effect on both oxygen barrier properties and mechanical properties. Particularly it was highlighted that, while as-cast PEF is brittle, BO PEF films are ductile when a critical biaxial draw ratio is achieved.

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.

Effects of sludge age on anaerobic acidification of waste activated sludge: Volatile fatty acids production and phosphorus release

Effects of sludge age on volatile fatty acids (VFAs) production and Phosphorus (P) release during anaerobic acidification of waste activated sludge (WAS) were investigated. Sequencing batch reactors (SBR) fed with simulating domestic sewage were applied to produce WAS of different sludge ages, and batch tests were used for anaerobic acidification. The maximum dissolved total organic carbon, release of PO43+−P, and accumulation of acetate (C2), propionate (C3), butyrate (C4), and valerate (C5) decreased by 56.2%, 55.8%, 52.6%, 43.7%, 82.4% and 84.8%, respectively, as the sludge age of WAS increased from 5 to 40 days. Limited degradation of protein played a dominating role in decreasing DTOC and VFAs production. Moreover, the increase in molecular weight of organics and organic nitrogen content in the supernatant after acidification suggested that the refractory protein in WAS increased as sludge age extended. Although the production of C2, C3, C4, and C5 from WAS decreased as the sludge age increased, the proportions of C2 and C3 in VFAs increased, which might be due to the declined production of C5 from protein and the faded genus Dechlorobacter. Keeping sludge age of WAS at a relatively low level (<10 days) is more appropriate for anaerobic acidification of WAS as internal carbon sources and P resource.

Синтез блок-сополимера бутилакрилата с винилбу-тиловым эфиром с использованием инициирующей сис-темы триэтилборан – кислород компенсационным спо-собом

The synthesis of a copolymer of butyl acrylate with vinyl butyl ether was carried out by a compensatory method in boiling vinyl butyl ether, at its excess, in the presence of triethyl boron isolated from the complex with hexamethylenediamine and an oxidizing agent. The resulting copolymer was used as a macroinitiator by adding a new portion of butyl acrylate to boiling vinyl butyl ether. Several samples of macroinitiators were obtained with different copolymerization times. As the formation of macromolecules upon copolymerization of butyl acrylate with vinyl butyl ether occurs along two centers of chain growth: oligomeric, formed due to the capture of initiating and growing radicals with a small number of copolymer units by boroxyl radicals, and one with low molecular weight, formed by conventional radical chain termination during initiation by alkyl and alkoxyl radicals, the composition of the isolated copolymer contains an oligomer and a low molecular weight copolymer. In the oligomeric fraction of the copolymer, there are more labile bonds with the boroxyl radical at the end of the chain than in the low molecular weight copolymer; as a result, the addition of butyl acrylate to the solution in vinyl butyl ether of the copolymer isolated from the reaction mixture leads to the formation of a block copolymer with a higher molecular weight, while the molecular weight increases after this, due to the addition of new copolymer units most of all to the oligomeric part of the sample. An increase in the molecular weight of the copolymer due to the grafting of new units predominantly onto the oligomer via a labile bond according to the reversible inhibition scheme leads to an increase in the mass of the samples and noticeable changes in the molecular weight distribution curve. If the sample synthesis time significantly exceeds the dosing time, the revealed effects are weaker, which is associated with the recombination of radicals formed according to the scheme of reversible inhibition, due to the usual radical termination. The presented data indicate that the copolymer of butyl acrylate with vinyl butyl ether synthesized in the presence of triethyl boron and an oxidizing agent during compensatory copolymerization in an excess of vinyl butyl ether is a macroinitiator of the block copolymerization of butyl acrylate with vinyl butyl ether, due to the labile bond of the terminal boroxyl radical.

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.

The signal-to-noise issue in mass spectrometric analysis of polymers

Mass spectrometric approaches to polymer analysis become increasingly ineffective as average molecular weight increases. This perspective explains these fundamental limits of MS for determining molecular weight distribution of high polymers.

Molecular weight effect on the structural detail and chain characteristics of 33-armed star polystyrene

In this study, synchrotron X-ray scattering and quantitative data analysis were performed on a series of 33-armed polystyrenes with four different arm molecular weights in cyclohexane (CHX, Θ solvent) and tetrahydrofuran (THF, good solvent). The quantitative scattering analysis was successfully done, providing molecular structure details and their responses to the solvent change. Each star system is confirmed to be prepared in a very narrow unimodal size distribution; the distribution is slightly broadened with increasing the arm molecular weight. It has an oblate ellipsoid shape, which is composed of two phases, a denser and smaller core and a less dense and thicker fuzzy shell; the ellipsoidicity ranges in 0.56–0.62. The core and shell phases are enlarged and thickened respectively by the arm molecular weight increases. Both the phases are further expanded in THF. Interestingly, the THF-induced expansion is predominant in the core against the fuzzy shell with a Gaussian like density gradient. Overall, the 33-armed star polystyrenes in various molecular weights are quite unique in the structural details and performance in solvent changes, which would be beneficial for advanced applications in various technological areas including smart deliveries of desired molecules (drug, gene, imaging agent, etc.).

Thermal Property Analysis and Characteristic Study of Ploy Ethylene Glycol with Diverse Molecular Weight for Thermal Energy Storage Material

In this study, the investigation on thermal property and characteristic analysis of Poly Ethylene Glycol (PEGs) material by varying the molecular weights is examined. In this context, the study on thermal energy material storage is explored by using the different techniques such as Differential Scanning Calorimetry (DSC) for persistent heating rate and Thermal Gravity Analysis (TGA) for determining the amount of change of mass of the material in addition to the function of increasing temperature. Subsequently, the characterization of PEGs with different molecular weight is carried out to explore the property and insight of the material by using the Scanning Electron Microscopy (SEM) and Transmission Electron Microscopy (TEM) by examining the surface topology, crystallography in addition to this the X-Ray Diffraction (XRD) techniques for catch a glimpse of the crystal structure is studied. As an outcome, in the DSC techniques the results made known when the molecular weight increases, correspondingly the melting temperature and solidification temperature similarly increases however, the heat of fusion during the freezing cycle increases. In the TGA techniques, similarly specified increases in the volume of PEG with different molecular weight has resulted in an increase in the temperature. Subsequently, in the characterization of the PEGs, the SEM has shown an enormous amount of insignificant sphere-shaped crystal-like structures which are joined together and impinging on their neighbour’s which paved the way for the formation of a multi-layered lamellar structure in due course activated rise in the solidification temperature in its molecular weight. Henceforth, from the analytical studies, it’s been evident that the molecular weight greatly influences the mechanical and thermal properties of PEGs. In this concern, the PEGs blends are a potential benefit to replace pure components.

Tunable Lower Critical Solution Temperature of Poly(butyl acrylate) in Ionic Liquid Blends

We describe the lower critical solution temperature (LCST)-type phase behavior of poly(butyl acrylate) (PBA) dissolved in hydrophobic 1-alkyl-3-methylimidazolium bis{(trifluoromethyl) sulfonyl}amide ionic liquids (ILs). The temperature-composition phase diagrams of these PBA/ILs systems are strongly asymmetric with the critical composition shifted to low concentrations of PBA. As the molecular weight increases from 5.0×103 to 2.0×104, the critical temperature decreases by about 67 °C, and the critical composition shifts to a lower concentration. Furthermore, the LCST of PBA/ILs system increases as increasing the alkyl side chain length in the imidazolium cation. Using IL blends as solvents, the LCST of PBA can be tuned almost linearly over a wide range by varying the mixing ratio of two ionic liquids without modifying the chemical structure of the polymers.

Transfer of ellagitannins to unclarified juices and purees in the processing of selected fruits of the Rosaceae family

The present study investigated the transfer of ellagitannins (ETs) from selected berry fruits of the Rosaceae family to the products of their processing - unclarified juices and purees, as well as ET retention in pomace. Percentage distribution was calculated not only for total ETs, but also separately for each ET identified by HPLC-MS.In the case of all fruits tested, ET transfer to purees was two to six times greater as compared to juices. The content of oligomeric ETs in juices was five times lower than that of low molecular weight compounds, while the transfer of high molecular weight compounds (>1569 Da) to purees ranged from 56% to 87%. An increase in molecular weight from 1569 Da to 3740 Da resulted in a fivefold decrease in ET transfer for raspberry juice, a twofold decrease for blackberry and wild strawberry juices, and a fourfold decrease for strawberry juice.

Effect of plasticizers and polymer blends for processing softwood kraft lignin as carbon fiber precursors

Plasticizers depress the glass transition temperature (Tg) of polymers and produce a flowable material at lower temperatures. The use of plasticizers to depress Tg of lignin is important, since at high processing temperatures lignin crosslinks, making it intractable. The goal of this study was to assess plasticizers and polymer blends for the ability to retard a commercial softwood kraft lignin from crosslinking and also serve as thermal and rheological property modifiers during thermal processing in the attempt to produced moldable and spinnable lignin for lignin and carbon fiber products. The Tg of the lignin and the lignin mixed with various amounts of plasticizers and with different thermo-mechanical mixing were determined using differential scanning calorimetry. The Tg and the change in heat capacity at the glass transition (ΔCp) decreased and increased, respectively, about linearly within this plasticizers range with increased plasticizer weight percentage. Gel permeation chromatography results for extruded lignin as well as extruded lignin-plasticizer blends with glycerol, N-allyurea, citric acid with and without sodium hypophosphite, and oleic acid indicate that the presence of these materials reduced the rate of molecular weight increase at temperatures between 100 and 200 °C. Continuous, homogenous films and fibers could be produced by thermal processing with plasticized lignin samples and plasticized lignin-polymer blends, but not with lignin alone. These fibers could be carbonized, yielding up to about 50% of carbon. The present findings have shown the advantages of plasticizers in thermally processing a commercial softwood kraft lignin.

Fabrication of ultrafiltration membranes by poly (aryl ether nitrile) with poly (ethylene glycol) as additives.

A new kind of flat sheet ultrafiltration membrane was prepared by a promising membrane material, poly (aryl ether nitrile) (PEN), via non-solvent induced phase separation. The effect of solvents, N-methyl-2-pyrrolidone (NMP) and dimethyl acetamide (DMAc), as well as additive of poly (ethylene glycol) (PEG) with different molecular weights on the structure and permeation performance of synthesized membranes were investigated. Comparing with NMP, DMAc is more suitable for the casting solution preparation due to better solubility. A gradually changing pore from sponge-like to finger-like can be observed when PEG was added with DMAc as solvent, while a finger-like pore structure always appears in the NMP system with or without PEG. In both systems, the formation of macrovoids is effectively promoted by the addition of PEG, and higher porosity membranes can be obtained by PEG with higher molecular weight. With the increase of PEG molecular weight from 400 to 10,000 Da, the permeate flux increases from 74.5 to 114.3 L·m-2·h-1 and from 102.0 to 130.8 L·m-2·h-1 under a 100 kPa pressure-driven when NMP and DMAc were used as solvents, respectively. The membranes prepared by DMAc exhibit outstanding rejection of BSA with rejections all above 96.5%.

Structure and properties of polycarboxylic acid dispersants synthesized by RAFT method

Polycarboxylic acid dispersants (PCs) with comb‐like molecular structure have become the focus of dispersants. However, there are many contradictions in the study of molecular structure of polycarboxylic acids. In this article, a series of PCs with different molecular structures were prepared from acrylic acid (AA) and methyl allyl alcohol polyoxyethylene ether (TPEG) by reversible addition fragmentation chain transfer (RAFT) polymerization. The structural characteristics of PCs were characterized by flourier transform infrared spectrometer (FT‐IR), 1H nuclear magnetic resonance (NMR) spectroscopy and gel permeation chromatography (GPC). The dispersion performance of PCs to cement was measured by the fluidity and adsorbing capacity. The results show that the dispersion performance and adsorbing capacity of PCs are significantly related to its structure. The adsorption and dispersion properties increase with the increase of carboxyl content and molecular weight. However, this phenomenon is limited to a certain range that the acid ether ratio in this range is no greater than 5:1, and the molecular weight is no greater than PC‐4 (Mw = 82 125, Mn = 63 889).

The Contribution of PEG Molecular Weights in PEGylated Emulsions to the Various Phases in the Accelerated Blood Clearance (ABC) Phenomenon in Rats.

PEGylated preparations will be cleared rapidly from blood circulation when they are administrated twice in the same animal at a time interval, referred to as the "accelerated blood clearance" (ABC) phenomenon. Commonly, the study of the ABC phenomenon was investigated in two aspects: induction phase and effectuation phase. Herein, we report the influence of physicochemical properties (PEG molecular weights) in the induction phase and effectuation phase on the ABC phenomenon. In the experiment, on one hand, PEGylated emulsions with different molecular weights of PEG (refer to PEn, n = 400, 600, 800, 1000, 2000, and 5000) were injected for the first dose (induction phase) and induced PE2000 to produce ABC phenomenon. On the other hand, after PE2000 injected, PEn was injected for the second dose (effectuation phase). The results indicated that PE2000 and PE5000 induced an intense ABC phenomenon by their long-circulating characteristic. Interestingly, PE400, PE600, PE800, and PE1000 produced a consistent ABC phenomenon but different circulation time. Apparently, the induction of the ABC phenomenon is not only determined by the circulation time but also by the PEG molecular weights. When PEn is in the effectuation phase, the extent of the ABC phenomenon was not positively related to the molecular weights of PEG, increasing first and then weaken with the increase of molecular weights of PEG. These suggest that the number of -(CH2CH2O)n- repeat units of PE2000 was more conducive to interact with anti-PEG IgM. The results reported here clearly indicate that both the PEG molecular weights of prior dose and the subsequent dose of emulsion strongly influence the extent of the ABC phenomenon. Taken together, our observations in this study complete the effect of PEG molecular weights at a different phase of the ABC phenomenon. Furthermore, our findings have a significant impact on the choice of molecular weights for PEGylated formulations for use in cross-administration.