Terms Of Molar Mass Research Articles

Effect of adduct synthesis parameters on the ethylene polymerization kinetics of Ziegler Natta catalysts

AbstractHere, it is aimed to clarify the structure‐performance relationship in MgCl2 based Ziegler Natta catalysts toward ethylene polymerizations. In this regard, 11 different adduct precursors were prepared through industrially appreciated melt quenching method employing various: (i) reaction times for dissolving magnesium chloride inside ethanol; (ii) ethanol/MgCl2 molar ratios in the feed; (iii) heating rates during thermal dealcoholation; (iv) N2 flows during thermal dealcoholation and (v) alcohol content after thermal dealcoholation. Among the studied parameters, heating rate and N2 flow during thermal dealcoholation have the most pronounced effect on the porosity and particle size of the resulted adducts. Related Ziegler Natta catalysts were subsequently employed in ethylene polymerizations. According to the kinetic curves, catalyst productivity and form of kinetic curve (as decay or build‐up type) can be precisely tailored by proper choosing of the mentioned variables during adduct synthesis. Microstructure analysis of the prepared polyethylenes reveals that alcohol content in the final adduct has the most significant effect on the H2 response, in terms of molar mass and its distribution, of the related Ziegler Natta catalysts. The overall results help polyethylene producers in choosing proper reaction conditions during adduct synthesis for the production of different polymer grades, when productivity or H2 response is targeted.

Marine Exopolysaccharide Complexed With Scandium Aimed as Theranostic Agents.

(1) Background: Exopolysaccharide (EPS) derivatives, produced by Alteromonas infernus bacterium, showed anti-metastatic properties. They may represent a new class of ligands to be combined with theranostic radionuclides, such as 47Sc/44Sc. The goal of this work was to investigate the feasibility of such coupling. (2) Methods: EPSs, as well as heparin used as a drug reference, were characterized in terms of molar mass and dispersity using Asymmetrical Flow Field-Flow Fractionation coupled to Multi-Angle Light Scattering (AF4-MALS). The intrinsic viscosity of EPSs at different ionic strengths were measured in order to establish the conformation. To determine the stability constants of Sc with EPS and heparin, a Free-ion selective radiotracer extraction (FISRE) method has been used. (3) Results: AF4-MALS showed that radical depolymerization produces monodisperse EPSs, suitable for therapeutic use. EPS conformation exhibited a lower hydrodynamic volume for the highest ionic strengths. The resulting random-coiled conformation could affect the complexation with metal for high concentration. The LogK of Sc-EPS complexes have been determined and showing that they are comparable to the Sc-Hep. (4) Conclusions: EPSs are very promising to be coupled with the theranostic pair of scandium for Nuclear Medicine.

Poly(ethylene glycol) or poly(2-ethyl-2-oxazoline) – A systematic comparison of PLGA nanoparticles from the bottom up

In times of drastically increasing numbers of scientific reports dealing with the drawbacks of poly(ethylene glycol) (PEG), the search of PEG alternatives has never been more urgent. This study describes a one–to–one comparison of poly(2-ethyl-2-oxazoline)-b-poly(lactic-co-glycolic acid) (PEtOx-b-PLGA) to commercial PEG-b-PLGA from the bottom up in order to verify the similarity of both polymer classes when applied in nanoparticle formulation processes. For this purpose, a library of block copolymers with molar masses (Mn) ranging from 6500 to 60,000 g mol−1 was synthesized via tin-(II)-ethyl hexanoate (SnOct2) catalyzed ring-opening polymerization (ROP) of lactide and glycolide utilizing PEtOx-OH as a macroinitiator in the melt. The PEtOx-b-PLGA polymers were adjusted in terms of molar mass, dispersity and lactide to glycolide ratio of the PLGA block. Nanoparticle formulations showed a similar behavior for both polymer libraries. Zeta potentials as well as hydrodynamic diameter measured by laser light scattering were in excellent agreement, demonstrating the eligibility of PEtOx-b-PLGA as an alternative to formulate “stealth” nanoparticles.

Well-Defined Conjugated Macromolecules Based on Oligo(Arylene Ethynylene)s in Sensing

Macromolecules with well-defined structures in terms of molar mass and monomer sequence became interesting building blocks for modern materials. The precision of the macromolecular structure makes fine-tuning of the properties of resulting materials possible. Conjugated macromolecules exhibit excellent optoelectronic properties that make them exceptional candidates for sensor construction. The importance of chain length and monomer sequence is particularly important in conjugated systems. The oligomer length, monomer sequence, and structural modification often influence the energy bang gap between the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) of the molecules that reflect in their properties. Moreover, the supramolecular aggregation that is often observed in oligo-conjugated systems is usually strongly affected by even minor structural changes that are used for sensor designs. This review discusses the examples of well-defined conjugated macromolecules based on oligo(arylene ethynylene) skeleton used for sensor applications. Here, exclusively examples of uniform macromolecules are summarized. The sensing mechanisms and importance of uniformity of structure are deliberated.

Comprehensive two-dimensional liquid chromatography for the characterization of acrylate-modified hyaluronic acid.

Hyaluronic acid and its acrylate derivatives are important intermediates for various pharmaceutical, biomedical, and cosmetic applications due to their biocompatibility and viscoelasticity properties. However, these polymers are inherently difficult to characterize due to their significant heterogeneity regarding molar mass and chemical composition (degree of substitution, DS). The present study describes the development of a comprehensive online two-dimensional liquid chromatography (2D-LC) approach to characterize hyaluronic acid and its acrylate derivatives (DS ranging from 0.4 to 3.1) in terms of molar mass and degree of substitution. In the first dimension of the 2D-LC method, separation according to chemical composition/DS was achieved by using a stepwise solvent gradient and a reversed phase C8 column. Fractions from the first dimension were automatically transferred to the second dimension comprising size exclusion chromatographic separation of the fractions according to molar mass. It was found that the hyaluronic acid derivatives were broadly distributed with regard to both chemical composition and molar mass. Fractions with different degrees of substitution were identified, and their molar mass distributions were determined. The study proved that comprehensive 2D-LC is a powerful approach to reveal the complex nature of hyaluronic acid and its derivatives. Graphical abstract.

Combining SEC & MALDI for characterization of the continuous phase in dispersion polymerization

Dispersion copolymerization of styrene (St) with either acrylonitrile (AN) or methyl methacrylate (MMA) in 1-propanol/deionized water medium were carried out using Bisomer S20W (polyethylene oxide macromonomer with a methacrylic end group) as stabilizer. The serums of the St/AN and St/MMA latexes were characterized in terms of molar mass and composition by the combination of Size Exclusion Chromatography (SEC) and Matrix Assisted Laser Desorption Ionization Time of Flight Mass Spectrometry (MALDI-TOF MS). This work demonstrates that the combination of SEC and MALDI techniques is necessary for an accurate identification of the composition and molar mass of the oligomeric species present in the continuous phase of a dispersion polymerization that cannot be achieved by using either SEC or MALDI alone. For the particular latexes analyzed in this work it was found that unreacted macromonomer was present in both copolymer systems. However, in the case of the copolymerization with AN besides the presence of the macromonomer there were also some pAN oligomers.

Characterization of the chemical structures and physical properties of exopolysaccharides produced by various Streptococcus thermophilus strains

Exopolysaccharides (EPS) produced by some lactic acid bacteria are often used by the dairy industry to improve the rheological and physical properties of yogurt, but the relationship between their structure and functional effect is still unclear. The EPS from different species, or different strains from the same species, may differ in terms of molar mass, repeating unit structure, and EPS yield during fermentation of milk. This study aimed to characterize the detailed properties of EPS produced from 7 strains of Streptococcus thermophilus, which is one of the key cultures used for yogurt manufacture. Milk was fermented with strains DGCC 7698, DGCC 7710, DGCC 7785, ST-10255y, St-143, STCth-9204, and ST4239. These strains were selected because they have been used in previous studies on yogurt texture, but a complete description of their EPS structural properties has not yet been reported. All strains were fermented under a similar acidification rate by adjusting the level of supplementation with peptone or the inoculation level, which allowed for a comparison of EPS yields under similar growth conditions (reconstituted skim milk at 40°C). The EPS from each strain was isolated and the weight-average molar mass and z-average root mean square radius determined using size-exclusion chromatography multiangle laser light scattering. The monosaccharide composition of EPS was determined using gas chromatography-mass spectrometry, and repeating unit structure was determined using nuclear magnetic resonance spectroscopy. The weight-average molar mass values of EPS ranged from 0.14 to 1.61 × 106 g/mol. All 7 EPS samples were uncharged. The strains ST-10255y and ST4239 had EPS with the same repeating unit structure. The monosaccharide compositions of the various EPS were mainly composed of glucose and galactose, with low levels of rhamnose in the EPS isolated from DGCC 7698, and N-acetylgalactosamine in the EPS from DGCC 7785, ST-10255y, and ST4239. The yields of EPS (measured when fermented milks reached pH 4.6) ranged from 8.0 to 76.4 mg of glucose equivalents/kg. In addition to (free) EPS, some strains were also able to produce capsular polysaccharide (associated with the bacterial cells) when observed with negative staining technique. The results of our study will help the dairy industry to better understand the mechanism by which different strains of Streptococcus thermophilus affect yogurt texture.

ChemInform Abstract: Beyond Stereoselectivity, Switchable Catalysis: Some of the Last Frontier Challenges in Ring‐Opening Polymerization of Cyclic Esters

AbstractReview: [37 refs.

Beyond stereoselectivity, switchable catalysis: some of the last frontier challenges in ring-opening polymerization of cyclic esters.

Metal-based catalysts and initiators have played a pivotal role in the ring-opening polymerization (ROP) of cyclic esters, thanks to their high activity and remarkable ability to control precisely the architectures of the resulting polyesters in terms of molar mass, dispersity, microstructure, or tacticity. Today, after two decades of extensive research, the field is slowly reaching maturity. However, several challenges remain, while original concepts have emerged around new types or new applications of catalysis. This Review is not intended to comprehensively cover all of these aspects. Rather, it provides a personal overview of the very recent progress achieved in some selected, important aspects of ROP catalysis--stereocontrol and switchable catalysis. Hence, the first part addresses the development of new metal-based catalysts for the isoselective ROP of racemic lactide towards stereoblock copolymers, and the use of syndioselective ROP metal catalysts to control the monomer sequence in copolymers. A second part covers the development of ROP catalysts--primarily metal-based catalysts, but also organocatalysts--that can be externally regulated by the use of chemical or photo stimuli to switch them between two states with different catalytic abilities. Current challenges and opportunities are highlighted.

Degradable polyurethane nanoparticles containing vegetable oils

AbstractsThe development of colloidal delivery systems from degradable polyurethanes (PU) has attracted increasing interest as the highly variable synthetic chemistry of PU may be exploited to generate polymers having properties ranging from very soft elastomers to very rigid plastics. In this work, the synthesis of PU nanoparticles using isophorone diisocyanate, castor oil, and poly(ϵ‐caprolactone) as monomers and containing high amounts of vegetable oils as açaí oil and crodamol GTCCwas studied. The effect of surfactants Tween 80 and sodium dodecyl sulfate (SDS) and of poly(ethylene glycol) molar masses 400, 600, and 1000 g/mol on the stability, size, and nanoparticle morphology was evaluated. Stable dispersions with sizes between 50–70 nm and 170–250 nm were achieved when, respectively, SDS and Tween 80 were used as surfactant. The polyol type used in the step polymerization in miniemulsion had a major effect on the molar mass of the resulting PU nanoparticles. The effect of poly(ethylene glycol) molar masses was more pronounced when Castor oil and Tween 80 were employed. Increasing the molar mass of PEG increased the average particle size and the molar mass of the PU. Finally, a strong reduction of the molar mass of the PU nanoparticles was observed in degradation assays when those were maintained during 30 days at 37°C and pH 7.0.Practical applications: Using natural renewable oil as polyol to obtain polyurethane nanoparticles combined with incorporation of other vegetable oil therein showed good results in terms of molar mass and nanoparticle size. The simple and straightforward procedure to prepare polyurethane nanoparticles containing vegetable oils by step polymerization in miniemulsion contributes to improve the application range of these polymers.

Extraction of short-chain-length poly-[(R)-hydroxyalkanoates] (scl-PHA) by the “anti-solvent” acetone under elevated temperature and pressure

A novel method was developed for extraction of short-chain-length poly(hydroxyalkanoates) (scl-PHA) from microbial biomass by the well-known "scl-PHA anti-solvent" acetone at elevated temperature and pressure in a closed system combining components for extraction, filtration, and product work-up. Recovery of scl-PHA using this new approach was compared with established methods using chloroform at ambient pressure. The new method performs similar regarding product purity (98.4 vs. 97.7%) and extraction yield (96.8% by both methods), and is by far faster than established chloroform extraction (20 min vs. 12 h). Separation of the polymer from acetone is simply achieved by cooling down the acetone solution of scl-PHA, thus allows for a nearly quantitative recovery of the solvent that conveniently can be reused. Characterization of scl-PHA extracted by both methods does not reveal any significant difference in terms of molar mass and thermo analytical parameters.

In vitro hemocompatibility and cytotoxicity study of poly(2‐methyl‐2‐oxazoline) for biomedical applications

AbstractSince poly(2‐methyl‐2‐oxazolines) (PMeOx) attract high attention for the potential use in drug delivery, cytotoxicity, and hemocompatibility of a set of PMeOxs with molar masses in the range from 2 to 20 kDa are systematically investigated under standardized conditions in terms of molar mass, concentration and time dependency. PMeOx polymers are well tolerated in red blood cell aggregation and hemolysis assays without any damaging effects even at high concentrations up to 80 mg/mL. Only in long term cytotoxicity tests PMeOx polymers moderately influence cell viability in a time, concentration, and molar mass dependent manner. Referring to these results it can be concluded that PEtOx could be promising nonionic hydrophilic polymers for many biomedical applications without any cyto‐ and hemotoxic effects at typically used therapeutic doses. © 2013 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2013

PP-based WPCs-Influence of the molar mass of matrix and coupling agent

Six commercial polypropylene (PP) homopolymer grades, ranging from 2 to 125 g/10 min in MFR (230°C/2.16 kg), and from 530 to 180 kDa in terms of molar mass (mass average; Mw), have been tested as matrix polymers in wood polymer composites (WPCs) with a wood content of 40%. To check for possible molecular weight controlled interactions between matrix and additives, five different maleic anhydride grafted PP (MA-PPs) coupling agents (CAs) have been included in the screening as well. Flexural properties, impact strength, and water absorption of the resulting composites served as responses. In addition, crystallinities, surface contact angles (on solid specimens), and rheological properties of the melt were measured for several compounds. The most important outcome of the study is that matrix polymer properties, as influenced by molar mass, are largely reflected in the resulting WPCs. Surprisingly, water absorption of the composites increases with matrix MFR, a phenomenon as yet not published for PP-based compounds. Furthermore, dynamic rheometry results indicate that the interaction of wood particles with PP melts is dependent on polymer and coupling agent Mw. © 2013 Society of Plastics Engineers

Coassembly of Poly(ethylene oxide)-block-poly(methacrylic acid) and N-Dodecylpyridinium Chloride in Aqueous Solutions Leading to Ordered Micellar Assemblies within Copolymer Aggregates

Formation of polyelectrolyte–surfactant (PE–S) complexes of poly(ethylene oxide)-block-poly(methacrylic acid) (PEO705–PMAA476) and N-dodecylpyridinium chloride (DPCl) in aqueous solution was studied by static and dynamic light scattering (SLS, DLS), small-angle neutron scattering (SANS), small-angle X-ray scattering (SAXS), and cryogenic transmission electron microscopy (cryo-TEM). While it was found previously [Macromolecules1997, 30, 3519] by microcalorimetric titration that in a similar system (PEO176–PMAA186) crystallization of aliphatic tails of N-dodecylpyridinium bromide did not occur, in our system it was evidenced by SAXS that upon addition of DPCl to fully ionized PEO705–PMAA476 the ordered arrangement of the surfactant occurs in a certain range of PEO705–PMAA476 concentrations and surfactant-to-polyelectrolyte charge molar ratio (Z). Our data suggest a four-step process in the behavior of the PEO705–PMAA476/DPCl system: (i) coexistence of loose aggregates of electrostatically bound surfactants to PMAA block with free and almost unperturbed copolymer coils at Z ≪ 1, (ii) formation of aggregates containing ill-defined cores formed by DPCl micelles attached to coiled PMAA chains (beads-on-a-string nanoparticles) in the range around Z = 0.5, (iii) formation of compact core–shell nanoparticles with a core formed by densely packed ordered (crystalline) DPCl micelles and PEO shell starting slightly before charge equimolarity (Z = 1), and (iv) the region of coexistence of the core–shell nanoparticles with free DPCl micelles in excess above equimolarity (Z ≫ 1). In the region around Z = 0.5, the nanoparticles with nonordered cores coexist in a mixture either with a fraction free chains and large swollen nanoparticles decorated by surfactant micelles (at lower Z) or with the core–shell nanoparticles (at higher Z). PE–S complexes were characterized in detail in terms of molar mass, size, shape, and internal structure.

The kinetics of chitosan depolymerisation at different temperatures

The stability (in terms of molar mass) of chitosan potentially plays an important role in its behaviour and functional properties in a wide range of applications and therefore any changes over time must be understood. The weight-average molar masses and intrinsic viscosities of chitosan solutions at different temperatures (4, 25 and 40 °C) have been investigated using size exclusion chromatography coupled to multi-angle laser light scattering (SEC-MALLS) and a “rolling ball” viscometer respectively. The weight-average molar mass ( M w) and the intrinsic viscosity ([ η]) both decrease with increased storage time, although this phenomenon is more pronounced at elevated temperatures. Good correlation was found between the changes in molar mass and intrinsic viscosity with time and these parameters were used to determine the depolymerisation constant ( k) and the activation energy ( E a). Knowledge of the effect of storage conditions ( e.g. temperature) is important in the understanding the stability of chitosan solutions, but whether or not chitosan depolymerisation will be detrimental to its intended application will depend on the functional significance of the changes that occur.

Do‐it‐yourself functionalized silicones part 1: basic methods for characterization of commercial products

AbstractConventional silicone fluids of varying composition, microstructure, and functionality are commercially available with a view to prepare films, elastomers, or resins. This paper is the first of a series of papers devoted to the synthesis, characterization, and application of vinyl and hydrido‐functionalized silicones. We present some basic analytical techniques useful to unacquainted people to fully characterize silicone fluids in terms of molar mass, purity, composition, structure, and functionality. Some commercial polymers were thus examined by size exclusion chromatography (SEC), from which molar masses were checked and compared with those from the provider (derived from viscosities). Two SEC‐derived techniques were used to confirm the perfect linearity of the chains. 1H and 29Si NMR spectrograms were recorded, from which chemical shifts gave the position of the functional groups (either at both chain‐ends or inside the chains) and from which intensities of the NMR signals provided quantitative data, namely number‐average molar mass Mn and contents of functional groups. In the final part, special emphasis is laid on the microstructure of the chains. Copyright © 2008 John Wiley & Sons, Ltd.

Condensation kinetics of polyphthalamides. II. Polyesters and diamines

AbstractPolyphthalamides are distinguished by outstanding properties. Only their price keeps them from replacing PA66 in many applications, in particular, in automobiles. This article deals with a simple, economically attractive process of upcycling postconsumer polyethylene terephthalate (PET) waste to polyphthalamides. Basic studies on the amidation of acids and esters were described in Part I. The amidation of esters is accompanied by a side reaction of amine alkylation, which, in the case of polyesters, leads to branching and crosslinking. But the crosslinking can be avoided in mixtures with excessive diamine. Therefore, a heterogeneous amidation process was developed in which solid PET granules are simultaneously dissolved in and amidated by a liquid diamine. As long as the PET‐diamine system is heterogeneous, it reacts under amino excess conditions. Later, when all PET is dissolved, it comes back to stoichiometric conditions again, so long‐chained polyamides can be obtained. In terms of molar mass and viscosity, this amidation of solid PET proceeds very similarly to the amidation of terephthalic acid (TPA), which is so far the common route towards polyphthalamides. PET waste could replace TPA. POLYM. ENG. SCI., 47:1600–1609, 2007. © 2007 Society of Plastics Engineers

Atom Transfer Radical Polymerization of Styrene and Methyl Methacrylate from Mesoporous Ordered Silica Particles

AbstractSummary: Mesoporous silica was used as substrate for the grafting of alkyl halides initiators. The control over the surface‐initiated polymerization of styrene and MMA, in terms of molar mass and molar mass distribution, was successfully achieved using an ATRP mechanism. The occurrence of the polymerization inside the mesopores was confirmed by thermogravimetric analysis.Transmission electron microscopy and schematic representation of mesoporous silica functionalized by the anchored iniator (left) and the grafted polymer (right).magnified imageTransmission electron microscopy and schematic representation of mesoporous silica functionalized by the anchored iniator (left) and the grafted polymer (right).

Gamma-ray attenuation studies of [formula omitted] glass system

PbO – BaO – B 2 O 3 glass system has been investigated in terms of molar mass, mass attenuation coefficient and half value layer parameters by using gamma-ray at 511,662 and 1274 keV photon energies. Gamma-ray attenuation coefficients of the prepared glass samples have been compared with tabulations based upon the results of XCOM. Good agreement has been observed between experimental and theoretical tabulations. Our results have uncertainty less than 3%. Radiation shielding properties of the glass system have been compared with some standard radiation shielding concretes.

Solution properties of well-defined 2-(dimethylamino)ethyl methacrylate-based (co)polymers: A viscometric approach

Well-defined poly(2-(dimethylamino)ethyl methacrylate)-based (co)polymers with various molar masses were synthesized by atom transfer radical polymerization (ATRP) using CuBr ligated with 1,1,4,7,10,10-hexamethyltriethylenetetramine (HMTETA) as catalyst, and ethyl 2-bromoisobutyrate (EBiB) or α-methyl, ω-(2-bromoisobutyrate) poly(ethylene glycol) (mPEG x -BiB) as (macro)initiator. The solution properties of these (co)polymers were investigated by viscometry either in pure water or in concentrated buffer solutions. It comes out that reduced viscosity in pure water is strongly affected by the molar mass of poly(2-(dimethylamino)ethyl methacrylate) block but also by the quaternization degree of tertiary amino groups. In fact, a polyelectrolyte effect can only be detected when the charge density per macromolecule reaches a critical value either in terms of molar mass or quaternization degree. Fitting of viscometry data according to either Huggins or Fuoss and Fedors equation also allows calculating the intrinsic viscosity and approaching the overlap concentration.