Aqueous phase size exclusion chromatography of polyvinylalcohols of different degrees of hydrolysis

The aqueous-phase size exclusion chromatography (SEC) represents a suitable method for the analysis of molecular weight distribution (MWD) of polyvinylalcohols (PVOHs) of different degree of hydrolysis ranging from 72 to 98 mol-% applying the Suprema columns. Eluents of different composition were used consisting of either a mixture of water and acetonitrile for the lower degrees of hydrolysis (72 - 88 mol-%) or 0.1 M LiNO₃ solution for the higher degrees of hydrolysis (88 - 98 mol-%). By knowing the M̄_w̄ values of commercially available PVOHs samples of a given degree of hydrolysis and using the commercial water soluble narrow distribution standards, a principle of the constant hydrodynamic equivalence ratios was applied to obtain the absolute values of the molecular weights of PVOHs of different degree of hydrolysis. The effect of a various number of extrusion cycles on MWD of different PVOHs was used to demonstrate the sensitivity of the selected SEC conditions.     

Thermosetting of wheat protein based bioplastics: modeling of mechanism and material properties

Structural investigation of gluten-glycerol blends subjected to heat-treatment was carried out by size-exclusion high performance liquid chromatography (SEC) and stress-strain tests. SEC is a valuable tool to investigate the size distribution of gluten protein chains, while the molecular weight between network junctions (M_e) can be estimated from the elastic plateau modulus. Wheat gluten aggregation upon thermosetting seems to proceed through direct covalent cross-linking between glutenin oligomers and the gluten macropolymer. The time course of the reaction, which showed a slow-down of the reaction rate with time, was described by a simple mechanistic model. The deceleration of the reaction rate was presumably due to the development of a three-dimensional protein network, which decreased the accessibility of reactive groups. The network formation could be evidenced separately by the decrease of M_e during the heat-treatment.     

High-resolution melting analysis for detection of fusion allele of FUT2

The secretor status of ABH antigens, determined by FUT2 polymorphisms, affects susceptibility to various infectious diseases. In addition to many SNPs responsible for the nonsecretor phenotype, five nonfunctional alleles (se) resulting from copy number variations have been reported. One of the five alleles generated by an unequal crossover between FUT2 and a pseudogene (SEC1), is se^fus. This allele may be misidentified as a functional allele if only common inactivating SNPs are genotyped because it contains the 3ʹ region of the functional FUT2. Therefore, accurate detection of se^fus is desirable. For this purpose, a high-resolution melting (HRM) analysis is developed for detection of se^fus in which a 284bp fragment of SEC1 and se^fus but not FUT2, are amplified. This HRM analysis detected se^fus reliably. Thus, an initial screening or prescreening for se^fus using HRM analysis seems to be useful for association studies of FUT2.     

Mean‐Field Calculation of MZ for Randomly Branched Condensation Polymers

The mean‐field theory of Flory–Stockmayer for randomly branched polymers in the regime of strong chain overlap is extended to a calculation of M_Z via the recursive method of Miller and Macosko. The formalism includes condensation polymers, copolymers, chain stoppers, bifunctional diluents to control the chain length between branch points, multiple branching agents, and arbitrary stoichiometries. M_Z closely approximates the largest branched polymer in the system and is therefore a key parameter describing static scaling behavior near the gel point. Nonuniversal static scaling of M_Z is illustrated with examples from the literature. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2019 , 57, 1415–1422     

Dehydropolymerisation of Methylamine Borane and an N-Substituted Primary Amine Borane Using a PNP Fe Catalyst

Dehydropolymerisation of methylamine borane (H₃B⋅NMeH₂) using the well-known iron amido complex [(PNP)Fe(H)(CO)] (PNP=N(CH₂CH₂PiPr₂)₂) ( 1 ) gives poly(aminoborane)s by a chain-growth mechanism. In toluene, rapid dehydrogenation of H₃B⋅NMeH₂ following first-order behaviour as a limiting case of a more general underlying Michaelis–Menten kinetics is observed, forming aminoborane H₂B=NMeH, which selectively couples to give high-molecular-weight poly(aminoborane)s (H₂BNMeH)_n and only traces of borazine (HBNMe)₃ by depolymerisation after full conversion. Based on a series of comparative experiments using structurally related Fe catalysts and dimethylamine borane (H₃B⋅NMe₂H) polymer formation is proposed to occur by nucleophilic chain growth as reported earlier computationally and experimentally. A silyl functionalised primary borane H₃B⋅N(CH₂SiMe₃)H₂ was studied in homo- and co-dehydropolymerisation reactions to give the first examples for Si containing poly(aminoborane)s.     

Size‐exclusion chromatography coupled to multiangle light scattering detection of long‐chain branching in polyethylene made with phillips catalyst

Size‐exclusion chromatography coupled to multiangle light scattering (SEC‐MALS) has been used to detect long‐chain branching (LCB) in polyethylene (PE) from Cr/silica catalysts for the first time. The observed LCB response to several catalyst and reactor variables mostly confirms earlier conclusions drawn from rheological measurements. However, SEC‐MALS has also shed additional light on a few previously unanswered questions. Above all, SEC‐MALS shows the placement of branching within the MW distribution, which was not previously known, and which may explain some of the unique molding behavior of Cr‐derived PE. This new SEC‐MALS data also provide insight into the mechanism of LCB formation, which is discussed. Like earlier studies based on rheology, this new study demonstrates that the commonly accepted view of macromer incorporation may be overly simplistic. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

Design of Experiment (DoE) as a Tool for the Optimization of Source Conditions in SEC‐ESI‐MS of Functional Synthetic Polymers Synthesized via ATRP

Design of experiment (DoE) is applied to establish the optimum ionization conditions for analyzing synthetic polymers via coupled size exclusion chromatography electrospray ionization mass spectrometry (SEC‐ESI‐MS) yielding maximum ionization efficiency. The ion source conditions were optimized with regard to the ionization efficiency, the amount of fragmentation, as well as the formation of salt adducts. A D ‐optimal experimental design was employed for this purpose and the recorded data were evaluated by a quadratic response surface model, accounting for possible interactions between the individual source settings. It was established that the ionization efficiency can be improved by up to one order of magnitude without compromising the softness of the ionization process and that optimal ionization conditions are found at similar source settings regardless of the charge state. The present optimization exercise therefore provides a hands‐on guide for the use of experimental design to determine optimum ionization conditions during the SEC‐ESI‐MS of functional polymers.

     

Rapid UV Light‐Triggered Macromolecular Click Conjugations via the Use of o‐Quinodimethanes

Shining a light on click chemistry: The use of UV‐radiation as trigger signal provides a facile means to obtain spatial and temporal control over polymer conjugation reactions in addition to providing a further means of achieving orthogonality in click transformations. In the current contribution, UV‐radiation was employed to induce a highly efficient Diels–Alder conjugation of polymeric building blocks via the photo‐induced in situ formation of highly reactive cis‐dienes from a 2‐methylbenzophenone precursor.

     

Poly(vinyl phosphonic acid): Hydrodynamic Properties and SEC‐Calibration in Aqueous Solution

Poly(vinyl phosphonic acid) (PVPA) as obtained by free radical polymerization of aqueous vinyl phosphonic acid was studied by light scattering (SLS, DLS) and size exclusion chromatography (SEC) in dilute aqueous solutions containing sufficient salt in order to screen long range electrostatic interactions. Samples of 37< < 110 × 10³ were studied. The polymers showed positive A₂‐values in aqueous NaH₂PO₄ solution (0.04 M ), and self‐diffusion behavior and R_H/R_G—ratios indicative of the structure of random coiled chains. A comparison of the SEC‐elugrams of the PVPA‐samples with those of commercially available standards of poly(acrylic acid) sodium salt gave a fit to the same calibration curve described by log P_n(PVPA) = −0.21ν_e + 7.0(+0.1) which correlates the number average degree of polymerization (P_n) with the elution volume ν_e. This indicates that PVPA and PAA have the same hydrodynamic structure under given solution conditions.

     

Environmental application of elemental speciation analysis based on liquid or gas chromatography hyphenated to inductively coupled plasma mass spectrometry—A review

In recent years the number of environmental applications of elemental speciation analysis using inductively coupled plasma mass spectrometry (ICP-MS) as detector has increased significantly. The analytical characteristics, such as extremely low detection limits (LOD) for almost all elements, the wide linear range, the possibility for multi-elemental analysis and the possibility to apply isotope dilution mass spectrometry (IDMS) make ICP-MS an attractive tool for elemental speciation analysis. Two methodological approaches, i.e. the combination of ICP-MS with high performance liquid chromatography (HPLC) and gas chromatography (GC), dominate the field. Besides the investigation of metals and metalloids and their species (e.g. Sn, Hg, As), representing “classic” elements in environmental science, more recently other elements (e.g. P, S, Br, I) amenable to ICP-MS determination were addressed. In addition, the introduction of isotope dilution analysis and the development of isotopically labeled species-specific standards have contributed to the success of ICP-MS in the field. The aim of this review is to summarize these developments and to highlight recent trends in the environmental application of ICP-MS coupled to GC and HPLC.