Molar Mass Range Research Articles

Controlled degradation of polyisoprene and polybutadiene: A comparative study of two methods

Low molar mass carbonyl telechelic cis,1–4 polyisoprene (CTPI) and aldehyde telechelic cis, 1–4 polybutadiene (ATPB) were easily prepared by the controlled degradation of high molar mass 1,4-cis polyisoprene (PI) and 1,4-cis polybutadiene (PB) in a molar mass range of 5000–80 000 g mol−1. Two methods are compared: the direct one using only the periodic acid (H5IO6) to randomly cleave the chain and a second one where the chain are first epoxidized before being cleaved by the periodic acid. In both cases, a control of the final chain length was observed with nevertheless a better control of the final chain length, dispersity and chain-ends using the 2-steps procedure. Importance of the washing step in order to avoid side reactions on the carbonyl chain-ends is also discussed.

POx as an Alternative to PEG? A Hydrodynamic and Light Scattering Study

Poly(ethylene glycol)s (PEG) are widely and intensely used in the pharmaceutical industry and biomedical applications, and due to this fact, antibodies have recently been reported. Poly(2-oxazoline)s (POx) are promising candidates for potential replacement of PEG in related applications, and as such, their hydrodynamic properties and characteristics derived from light scattering experiments are important to reconcile their behavior in solution. In this study, we have investigated the molecular hydrodynamic characteristics of poly(2-methyl-2-oxazoline)s and poly(2-ethyl-2-oxazoline)s in the pharmaceutical molar mass range as base candidates for such applications, prepared by cationic ring-opening polymerization in a microwave reactor. A combined viscometry and sedimentation–diffusion analysis by using sedimentation velocity experiments in an analytical ultracentrifuge includes (i) the study of intrinsic viscosities, (ii) sedimentation coefficients, and (iii) derived translational diffusion coefficients. Th...

Synthesis and fractionation of poly(phenylene methylene)

ABSTRACTPoly(phenylene methylene) (PPM) was isolated in a broad range of molar masses by optimization of the catalytic polymerization of benzyl chloride with SnCl4 or FeCl3, followed by fractionation by Soxhlet extraction or phase separation in concentrated solutions in poor solvents. Low molar mass products were also obtained by quenching the reaction at moderate monomer conversions. Products with number average molar masses (Mn) ranging from 200 to 61,000 g mol−1 were isolated, the latter being an order of magnitude above the previously reported values. DSC analysis of polymers of different molar masses revealed that the glass transition temperature follows the Flory‐Fox equation reaching a plateau value of 65 °C at a molar mass between 10,000 and 20,000 g mol−1. The onset of decomposition temperature of higher molar mass products proceeds above 450 °C (maximum decomposition rate at 515 °C), according to TGA. Furthermore, the substitution pattern of PPM was discussed by study of chemical shifts of the methylene group by extensive NMR spectroscopy (1H, 13C, DEPT, and HSQC) and by comparison with two mono‐substituted derivatives of PPM—poly(2,4,6‐trimethylphenylene methylene) and poly(2,3,5,6‐tetramethylphenylene methylene)—which were synthesized analogous to PPM. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2018, 56, 309–318

Molecular Simulations of Free and Graphite Capped Polyethylene Films: Estimation of the Interfacial Free Energies

We present a reliable simulation strategy for estimating the surface tension, the work of adhesion, and all related macroscopic work functions of fluid/vacuum and fluid/solid interfaces, directly from the atomic-level stresses in the system. Our methodology employs efficient algorithms (developed here and from the literature) for fast and reliable simulations of high molar mass polymer melts and is applied to the well-tested molten polyethylene/graphite interface, as well to the free surface of molten polyethylene, using a united atom model for the polymer. The surface thermodynamic properties are obtained for a broad range of molar masses and temperatures and are compared to experimental data, theoretical models, and earlier simulation studies. The individual components of the stress tensor are isolated, and their profiles along the aperiodic dimension are correlated to the orientational and structural features of the polymer chains near the interfaces. The distributions of end segments in free and cappe...

Molecular and structural analysis via hydrodynamic methods: Cationic poly(2-aminoethyl-methacrylate)s

Pharmaceutically relevant cationic linear poly(2-aminoethyl-methacrylate)s were synthesized by reversible addition-fragmentation chain transfer polymerization resulting in a homologous series of the homopolymers in a wide range of molar masses (10,000<M<130,000gmol−1) and relatively narrow dispersities (Ð:1.3±0.4). The polymers were studied in 0.2MNaCl and 0.2MNaOH in water, applying combined analytical approach comprising of complementary hydrodynamic and optical methods such as analytical ultracentrifugation, intrinsic viscosity, translation diffusion, flow birefringence and asymmetric flow field-flow fractionation (AF4) as well as standard characterization technique (SEC). The efforts were focused on the evaluation of solution (solvation), molecular (absolute molar masses), conformational (equilibrium rigidity, diameter of the polymer chain) and optical (anisotropy of optical polarizability of the monomer unit) characteristics of the polymers. Consequently the absolute values of the molar masses were determined by the sedimentation-diffusion analysis and AF4 resulting in well consistent results. The corresponding scaling relationships in 0.2MNaCl water ([η]=0.0031×M0.83; s0=0.0324×M0.39; D0=3,909×M−0.64) show linear trends in whole range of molar masses revealing random coil conformation of the macromolecules. Conformational characteristics were determined in 0.2MNaCl (equilibrium rigidity A=5.3±1.5nm) and 0.2MNaOH (A=1.3±0.1nm) revealing an influence of uncompensated charges on the polymer conformation.

Absolute characteristics and conformation of cationic polymers by hydrodynamic approaches: Poly(AEMA-co-MAEMA-co-DMAEMA)stat copolymers

Сationic poly((2-aminoethyl)-methacrylate–co-N-methyl-(2-aminoethyl)-methacrylate-co-N,N-dimethyl-(2-aminoethyl)-methacrylate) copolymers were synthesized by reversible addition-fragmentation chain transfer polymerization in a wide range of molar masses 16,000<M,g mol-1<130,000 and narrow dispersities. The copolymers were investigated by a wide range of characterization techniques such as sedimentation velocity, intrinsic viscosity, translation diffusion, asymmetric flow field-flow fractionation, as well as standard SEC and NMR analysis. As a result a matrix of self-consistent parametric macromolecular characteristics and the absolute molar masses were obtained. Consistent Kuhn-Mark-Houwink-Sakurada scaling relationships were found for 0.2MNaCl water ([η]=0.002×M0.85, s0=0.0231×M0.41, D0=2,349×M-0.59) and 0.2MNaOH water ([η]=0.022×M0.50) solvent system. The corresponding conformational characteristics of the macromolecules, that define the polymer behavior in solution – equilibrium rigidity and diameter of the polymer chain, were determined to be A = 4.3 nm and A = 1.1 nm for 0.2MNaCl and 0.2MNaOH respectively. Additionally, the anisotropic optical properties were studied by the flow birefringence revealing information about optical anisotropy of the monomer unit (Δa=-1.5×10-25cm3). The presented study exemplifies the in-depth analytical characterization of cationic/charge polymers by the fundamental hydrodynamic approaches resolving the essential macromolecular characteristics and solution behavior.

Supercritical continuous precipitation polymerization of acrylic acid in a droplet-based millifluidic device

In this work, a high pressure droplet-based millifluidic device was developed to achieve the continuous precipitation polymerization of acrylic acid in a green reaction medium: a supercritical mixture of 10 wt% ethanol in CO2 (15/19.5 MPa and 75 °C). To avoid clogging the tubular reactor of 762 µm ID, a segmented flow of an aqueous solution of monomer dispersed in the supercritical mixture (containing the initiator) was generated. During the reaction, the droplets were used as reservoirs which enable the continuous transfer of the monomer to the CO2-rich phase. This work shows that a large range of molar masses of poly(acrylic acid) (from 20,000 to 120,000 g.mol−1) with low polydispersity index (from 1.35 to 1.70) can be obtained. Due to the rapid transfer of the monomer compared to its conversion and the resulting low monomer concentration in the reactive medium, the molar mass distributions are not dependent on the residence time but rather on the initial monomer and initiator concentrations only. Hence in the investigated experimental conditions, the continuous reactive extraction process helps to achieve the precipitation polymerization without clogging the tubular reactor and in mastering the molar mass distribution. The effect of pressure influencing the molar mass distribution of poly(acrylic acid) as well as the competition between two possible loci of polymerization are also discussed.

Effect of molar mass on enthalpy relaxation and crystal nucleation of poly (l-lactic acid)

The effect of the chain length/molar mass of poly (l-lactic acid) (PLLA) on the formation of homogeneous crystal nuclei below and above the glass transition temperature (Tg) has been analyzed by fast scanning chip calorimetry, employing Tammann’s nuclei development method. It has been found that the kinetics of crystal nucleation below Tg is independent on the chain length within the investigated range of molar masses from about 60 to 600kDa, similar as the kinetics of enthalpy relaxation. In contrast, at temperatures well above Tg there is detected that crystal nucleation is slower in samples of higher molar mass. This observation is confirmed by non-isothermal nucleation experiments which showed that suppression of nucleation occurs on cooling at rates of 200, 100, and 30K/s in samples with molar masses of around 60, 100, and 600kDa, respectively. The different effect of molar mass on crystal nucleation in the glass and well above Tg is discussed in terms of the length-scale of required chain-mobility and of the critical size of nuclei.

Characterization of polymeric substance classes in cereal-based beverages using asymmetrical flow field-flow fractionation with a multi-detection system.

Cereal-based beverages contain a complex mixture of various polymeric macromolecules including polysaccharides, peptides, and polyphenols. The molar mass of polymers and their degradation products affect different technological and especially sensory parameters of beverages. Asymmetrical flow field-flow fractionation (AF4) coupled with multi-angle light scattering (MALS) and refractive index detection (dRI) or UV detection (UV) is a technique for structure and molar mass distribution analysis of macromolecules commonly used for pure compound solutions. The objective of this study was to develop a systematic approach for identifying the polymer classes in an AF4//MALS/dRI/UV fractogram of the complex matrix in beer, a yeast-fermented cereal-based beverage. Assignment of fractogram fractions to polymer substance classes was achieved by targeted precipitations, enzymatic hydrolysis, and alignments with purified polymer standards. Corresponding effects on dRI and UV signals were evaluated according to the detector's sensitivities. Using these techniques, the AF4 fractogram of beer was classified into different fractions: (1) the low molar mass fraction was assigned to proteinaceous molecules with different degrees of glycosylation, (2) the middle molar mass fraction was attributed to protein-polyphenol complexes with a coelution of non-starch polysaccharides, and (3) the high molar mass fraction was identified as a mixture of the cell wall polysaccharides (i.e., β-glucan and arabinoxylan) with a low content of polysaccharide-protein association. In addition, dextrins derived from incomplete starch hydrolysis were identified in all fractions and over the complete molar mass range. The ability to assess the components of an AF4 fractogram is beneficial for the targeted design and evaluation of polymers in fermented cereal-based beverages and for controlling and monitoring quality parameters.

Free Radical Copolymerization of Ethylene with Vinyl Acetate under Mild Conditions

This work highlights a medium pressure and temperature radical polymerization process in organic solvents for the synthesis of ethylene–vinyl acetate copolymers (EVA). Organic solvents play a crucial role in copolymerization yields, copolymer molar masses, chemical composition, and branching degree. THF and dimethylcarbonate (DMC) were selected, yielding EVA copolymers exhibiting molar masses from 1000 up to 35000 g mol–1 and vinyl acetate contents between 4 and 32 mol %. In the case of DMC, an additional transfer agent (propanal) was required to reach the molar-mass range targeted for the specific application of EVA copolymers as cold flow improver (CFI): an essential diesel fuel additive.

Conformational features of poly-l- and poly-d,l-lactides through molecular optics and hydrodynamics

Poly(l-lactide) and poly(d,l-lactide) samples have been synthesized through ring-opening polymerization. The homological series of two poly(lactide)s have been studied in 1,4-dioxane solutions by a complex of methods: molecular hydrodynamics, molecular optics, NMR, and optical rotation. The 1H and 13C NMR spectroscopy and optical rotation proved the different stereo isomeric composition of poly(l-lactide) and poly(d,l-lactide) polymer series. The P-l-LA series are isotactic polymers, whereas the P-d,l-LA polymer series are atactic or syndiotactic ones. The hydrodynamic volume of poly(l-lactide) macromolecules was found to be larger than that for poly(d,l-lactide) macromolecules. Hydrodynamic studies were performed for P-l-LA series in the range of molar masses: 3.5<M×10−3, g/mol<81, whereas for P-d,l-LA series in the range: 1.6<M×10−3, g/mol<200. Poly-l-lactide chains in solution exhibit higher equilibrium rigidity than poly-d,l-lactide chains, which is explained by different chain tacticity. For the first time the birefringence of solution of two investigated types of poly(lactide) macromolecules in mechanical and electrical fields was studied. Both birefringence methods demonstrate the net differences between optical properties of P-l-LA and P-d,l-LA chains and confirm the conclusion made from the hydrodynamic study. Comparisons with the literature data concerning intrinsic viscosity values and chain rigidity parameters have been made.

CCQM-K103 key comparison melanine in milk powder

Under the Comité Consultatif pour la Quantité de Matière (CCQM), a key comparison, CCQM-K103, was coordinated by the National Institute of Metrology (NIM) and Government Laboratory, Hong Kong, China (GLHK). The comparison was designed to demonstrate NMIs/DIs ability to analyze traces of melamine in milk and milk powder at concentration levels resulting from requirements for food safety. Seven NMIs or DIs participated in the comparison. Final reference value (KCRV) is 0.286 mg/kg, with standard uncertainty of the median as 0.011 mg/kg (3.8 %). The k-factor for the estimation of the expanded uncertainty was chosen as k = 2.57 ( t (0.05;5) ), thus the expanded uncertainty is 0.028 mg/kg (9.8%). The degrees of equivalence with melamine in milk powder KCRV for each participant were reported. The measurement results and degrees of equivalence should be indicative of the performance of a laboratory's measurement capability for IDMS in determining mass fractions in the range from 0.1 to 5.0 mg/kg of analytes with low molar mass (range 50-300 Da) with high polarity (pKow > -2.0) in milk and milk products. Extension to other analytes and matrices should be applied with care since there is a close linkage to other relevant parameters as e.g. sample preparation procedures (liquid/liquid extraction, SPE clean-up) and analytical separation techniques (e.g., GC-MS, LC-MS/MS etc).Main textTo reach the main text of this paper, click on Final Report. Note that this text is that which appears in Appendix B of the BIPM key comparison database kcdb.bipm.org/.The final report has been peer-reviewed and approved for publication by the CCQM, according to the provisions of the CIPM Mutual Recognition Arrangement (CIPM MRA).

Hydrodynamic Analysis Resolves the Pharmaceutically-Relevant Absolute Molar Mass and Solution Properties of Synthetic Poly(ethylene glycol)s Created by Varying Initiation Sites.

The solution behavior originating from molecular characteristics of synthetic macromolecules plays a pivotal role in many areas, in particular the life sciences. This situation necessitates the use of complementary hydrodynamic analytical methods as the only means for a complete structural understanding of any macromolecule in solution. To this end, we present a combined hydrodynamic approach for studying in-house prepared, low dispersity poly(ethylene glycols)s (PEGs), also known as poly(ethylene oxide)s (PEOs) depending on the classification used, synthesized from varying initiation sites by the living anionic ring opening polymerization. The series of linear PEGs in the molar mass range of only a few thousand to 50 000 g mol-1 have been studied in detail via viscometry and sedimentation-diffusion analysis by analytical ultracentrifugation. The obtained estimations for intrinsic viscosity, diffusion coefficients, and sedimentation coefficients of the macromolecules in the solution-based analysis clearly showed self-consistency of the followed hydrodynamic approach. This self-consistency is underpinned by appropriate and physically sound values of hydrodynamic invariants, indicating adequate values of derived absolute molar masses. The classical scaling relations of Kuhn-Mark-Houwink-Sakurada of all molar-mass dependent hydrodynamic estimates show linear trends, allowing for interrelation of all parametric macromolecular characteristics. Differences among these are ascribed to the observation of α-end and chain-length dependent solvation of the macromolecules, identified from viscometric studies. This important information allows for analytical tracing of variations of scaling relationships and a physically sound estimation of hydrodynamic characteristics. The demonstrated self-sufficient methodology paves an important way for a complete structural understanding and potential replacement of pharmaceutically relevant PEGs by alternative macromolecules offering a suite of similar or tractably distinct physicochemical properties.

Consequences of linking charged and uncharged monomers to binary copolymers studied in dilute solution. Part I: Viscometric behavior of the homopolymers, the effects of charging, and uncommon salt effects

Intrinsic viscosities, generalized intrinsic viscosities and viscometric interaction parameters were measured for aqueous solutions of poly(ethylene oxide) [PEO], poly(N,N-dimethyl aminoethyl methacrylate) [PR] (uncharged) and for poly{[2-(methacryloyloxy)ethyl] trimethylammonium iodide} [PR+] (charged) within a wide range of molar masses. In this manner it was possible to establish the information required for the study of non-additivity effects upon the formation of binary copolymers from the monomers specified above. The following additional items were of particular interest: The effects of charging PR to PR+ and the composition dependence of the coil overlap in the case of saline (NaCl, CaCl2 and NaI) solvents. NaCl turned out to be much less efficient in shielding the electrostatic interactions than the other salts due to its large tendency to form ion pairs in solution.

Analysis of β-glucan molar mass from barley malt and brewer’s spent grain with asymmetric flow field-flow fractionation (AF4) and their association to proteins

β-Glucan benefits are related with its molar mass and it would be of interest to better understand how this parameter can be changed by processing and variety for design of food with specific health effects. For this purpose, extracts from barley malts and brewers' spent grain, processed at different conditions, were analysed regarding β-glucan content, molar mass, and protein content. Molar mass distribution was assessed using asymmetric flow field-flow fractionation (AF4) with multiangle light scattering (MALS), differential refractive index (dRI) and fluorescence (FL) detection. β-Glucan was detected in a wide molar mass range, <2000 to approximately 6.7×106g/mol. Differences in molar masses were more noticeable between barley varieties and steeping malting conditions than by mashing of malt. Barley products processed to preserve β-glucan contained more β-glucan of high molar mass with potential to shift the fermentation site to the distal colon. Enzymatic degradation of proteins indicated presence of aggregates containing β-glucan and protein.

Cross-Contamination From Vial Caps for SEC Analysis Determined by MALDI-TOF Mass Spectrometry.

Cross-contamination from the polymeric material of the vial caps used in size exclusion chromatography (SEC) and high-performance liquid chromatographyautosamplers in the low molar mass (LMM) range (<2000 Da) of polymer samples was demonstrated with the help of matrix assisted laser desorption ionization time of flight mass spectrometry (MALDI-TOF MS) analysis. It is shown that polyethylene (PE) caps, if exposed to either short or long periods intetrahydrofuran solvent, might extract oligomers that contaminate the LMM end of the SEC chromatograms. On the other hand, polytetrafluoroethylene (PTFE)/silicone caps have shown to be inert if used properly; namely, the PTFE part in contact with the sample solution. However, care should be taken if accidentally the silicon part is exposed to the solution because silicone oligomer peaks have been detected by MALDI-TOF MS analysis that might mislead the results.

Filling the gap: Calibration of the low molar-mass range of cellulose in size exclusion chromatography with cello-oligomers

Degraded celluloses are becoming increasingly important as part of product streams coming from various biorefinery scenarios. Analysis of the molar mass distribution of such fractions is a challenge, since neither established methods for mono- or disaccharides nor common methods for polysaccharide characterization cover the intermediate oligomer range appropriately. Size exclusion chromatography (SEC) with multi-angle laser light scattering (MALLS), the standard approach for celluloses, suffers from decreased scattering intensities in the lower-molar mass range. The limitation in the low-molecular range can, in principle, be overcome by calibration, but calibration standards for such “short” celluloses are either not readily available or structurally remote and thus questionable. In this paper, we present the calibration of a SEC system— for the first time – with monodisperse cellooligomer standards up to about 3400gmol−1. These cellooligomers are “short-chain celluloses” and can be seen as the “true” standard compounds, by contrast to commonly used standards that are chemically different from cellulose, such as pullulan, dextran, polystyrene, or poly(methyl methacrylate). The calibration is compared against those commercial standards and correction factors are calculated. Calibrations with non-cellulose standards can now be adjusted to yield better fitting results, and data already available can be corrected retrospectively.

Lithium naphthalenides in non-polar or in low-polarity media: some insights regarding their use as initiators in anionic polymerizations

The synthesis of bidirectional anionic initiators by the reaction between metallic lithium (Li) and naphthalene (Naph), under mild conditions, in non-polar (benzene) or low-polarity media (benzene/THF mixtures) is reported. The efficiency of these initiators to provide macromolecules with well-defined structures was demonstrated. Model linear homopolymers from styrene (S) or hexamethyl(ciclotrisiloxane) (D3) monomers were synthesized using classical anionic polymerization (high-vacuum techniques). The model polymers obtained were analyzed using the conventional analytical techniques, and showed narrow molar mass distributions, a broad range of molar masses (from 3000 to 1,000,000 g/mol) and polydispersity indexes (Mw/Mn) lower than 1.1. High molar mass polymers were obtained using pure benzene as solvent, whereas lower molar masses were obtained in benzene/THF mixtures in which the concentration of THF was lower than 10 % v/v. The ratio [Li]/[Naph] and the nature of the reaction medium are the experimental parameters to be controlled to obtain the desired lithium naphthalenides.

μPET imaging of the pharmacokinetic behavior of medium and high molar mass 89Zr-labeled poly(2-ethyl-2-oxazoline) in comparison to poly(ethylene glycol)

Poly(2-oxazoline)s are a promising class of polymers for biomedical applications and a versatile alternative to poly(ethylene glycol)s (PEG). In this work, the pharmacokinetic behavior of well defined 89Zr-labeled poly(2-ethyl-2-oxazoline)s (PEtOx) was evaluated and compared to that of 89Zr-labeled PEG, both with varying molar mass. Amine-terminated PEtOx of low dispersity in a molar mass range of 20 to 110kDa and PEG of 20 and 40kDa were functionalized with a desferrioxamine chelator and radiolabeled with 89Zr. The tissue distribution of both radiolabeled PEtOx and PEG polymers was studied by means of micro Positron Emission Tomography (μPET) molecular imaging in mice longitudinally up to 1week post injection, followed by ex vivo biodistribution.As previously described for other classes of non-ionic polymers, the blood clearance of PEtOx decreased with molar mass. The cut off for glomerular filtration of PEtOx is likely to be around 40kDa. The head to head comparison of PEG and PEtOx revealed that the biodistribution is mostly dominated by polymer chain length and not polymer molar mass. This study constitutes an important addition to further establishing PEtOx as a promising polymer in biomedical applications.

Hyperbranched Poly(ethylene glycol) Copolymers: Absolute Values of the Molar Mass, Properties in Dilute Solution, and Hydrodynamic Homology

Hyperbranched poly(ethylene glycol) copolymers were synthesized by random anionic ring-opening multibranching copolymerization of ethylene oxide with glycidol as a branching agent, leading to poly(ethylene glycol) structure with glycerol branching points. Extending the available range of molar masses by novel synthesis strategies, a limited extent of control over the degree of polymerization was achieved by variation of the solvent in this copolymerization. Generally, absolute molar mass characterization of hyperbranched polymers still represents an unresolved challenge. A series of the hyperbranched poly(ethylene glycol)-co-(glycerol) copolymers (hbPEGs) of a wide range of molar masses (1400 < M < 1 700 000 g mol–1), degree of branching (DB) = 0.04–0.54, and moderate polydispersity (Mw/Mn) ≈ 2.1 ± 0.2 were studied, in both water and dimethylformamide by the methods of molecular hydrodynamics. Analytical ultracentrifugation, intrinsic viscosity, translational diffusion measurements, and SEC were combined....