Polyamide‐6,6‐based blocky copolyamides obtained by solid‐state modification

Copolyamides based on polyamide‐6,6 (PA‐6,6) were prepared by solid‐state modification (SSM). Para‐ and meta‐xylylenediamine were successfully incorporated into the aliphatic PA‐6,6 backbone at 200 and 230 °C under an inert gas flow. In the initial stage of the SSM below the melting temperature of PA‐6,6, a decrease of the molecular weight was observed due to chain scission, followed by a built up of the molecular weight and incorporation of the comonomer by postcondensation during the next stage. When the solid‐state copolymerization was continued for a sufficiently long time, the starting PA‐6,6 molecular weight was regained. The incorporation of the comonomer into the PA‐6,6 main chain was confirmed by size exclusion chromatography (SEC) with ultraviolet detection, which showed the presence of aromatic moieties in the final high‐molecular weight SSM product. The occurrence of the transamidation reaction was also proven by ¹H nuclear magnetic resonance (NMR) spectroscopy. As the transamidation was limited to the amorphous phase, this SSM resulted in a nonrandom overall structure of the PA copolymer as shown by the degree of randomness determined using ¹³C NMR spectroscopy. The thermal properties of the SSM products were compared with melt‐synthesized copolyamides of similar chemical composition. The higher melting and higher crystallization temperatures of the solid state‐modified copolyamides confirmed their nonrandom, block‐like chemical microstructure, whereas the melt‐synthesized copolyamides were random. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013 , 51, 5118–5129     

Speciation of essential and toxic elements in edible mushrooms: size‐exclusion chromatography separation with on‐line UV–inductively coupled plasma mass spectrometry detection

Size‐exclusion liquid chromatography was coupled to UV and inductively coupled plasma mass spectrometry (ICP‐MS) for detection to perform elemental speciation studies on different edible mushrooms. Molecular weight (MW) distribution patterns of several elements among different fractions present in various edible mushrooms are presented. The association of the elements with the high and low MW fractions was observed using sequential detection by UV and ICP‐MS. Separation was performed using a Superdex 75 column. Variability of the fractionation patterns with three different extraction media (0.05 mol l^?1 NaOH; 0.05 mol l^?1 HCl; hot water at 60°C) was evaluated for mushroom species. A comparative elemental speciation study was performed in order to determine the differences in the fractionation patterns of silver, arsenic, cadmium, mercury, lead, and tin in Boletus edulis, Agaricus bisporus, and Lentinus edodes. Differences in the fractionation patterns of the elements were found to depend on the mushroom species and the extraction medium. Most of the elements were associated with high mw fractions. It was not possible to assess the trace metal contributions from the mushroom growth media. Copyright © 2004 John Wiley & Sons, Ltd.     

Ethylene/1‐pentene copolymers synthesized using the metaloxycarbene complex catalyst system [(CO)5W=C(Me)OZr(Cp)2Cl]/MAO

Ethylene/1‐pentene copolymers were prepared using a [(CO)₅W= C(Me)OZr(Cp)₂Cl] (1)/MAO catalyst system. 1‐Pentene incorporation in the copolymer was monitored using ¹³C‐NMR spectroscopic methods. The weight average molecular weights (M_w) of the copolymers were between 142,000 and 629,000 g/mol, with polydispersity indexes (PDIs) ranging from ≈ 2 to 90, as analyzed by size exclusion chromatography (SEC). Melting and crystallization temperatures, determined using differential scanning calorimetry (DSC) and crystallization analysis fractionation (CRYSTAF), decreased linearly as the amount of 1‐pentene in the copolymer increased. SEC‐FTIR revealed that the 1‐pentene is predominantly incorporated in the low molecular weight fraction. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 5121–5133, 2004     

pH‐Responsive ampholytic terpolymers of acrylamide,sodium 3‐acrylamido‐3‐methylbutanoate,and (3‐acrylamidopropyl)trimethylammonium chloride. I. Synthesis and characterization

Low-charge-density ampholytic terpolymers composed of acrylamide, sodium 3-acrylamido-3-methylbutanoate (NaAMB), and (3-acrylamidopropyl)trimethylammonium chloride were prepared via free-radical polymerization in 0.5 M NaCl to yield terpolymers with random charge distributions. NaOOCH was used as a chain-transfer agent during the polymerization to eliminate the effects of the monomer feed composition on the degree of polymerization (DP) and to suppress gel effects and broadening of the molecular weight distribution. The terpolymer compositions were obtained via ¹³C NMR spectroscopy, and the residual counterion content was determined via elemental analysis for Na⁺ and Cl⁻. The molecular weights (MWs) and polydispersity indices (PDIs) were determined via size exclusion chromatography/multi-angle laser light scattering (SEC–MALLS); the terpolymer MWs ranged from 1.3–1.6 × 10⁶ g/mol, corresponding to DPs of 1.6–1.9 × 10⁴ repeat units, with all terpolymers exhibiting PDIs of less than 2.0. Intrinsic viscosities determined from SEC–MALLS data and the Flory–Fox relationship were compared to intrinsic viscosities determined via low-shear dilute-solution viscometry and were found to agree rather well. Data from the SEC–MALLS analysis were used to analyze the radius of gyration/molecular weight (R_g–M) relationships and the Mark–Houwink–Sakurada intrinsic viscosity/molecular weight ([η]–M) relationships for the terpolymers. The R_g–M and [η]–M relationships revealed that most of the terpolymers exhibited little or no excluded volume effects under size exclusion chromatography conditions. Potentiometric titration of terpolymer solutions in deionized water showed that the apparent pK_a value of the poly[acrylamide-co-sodium 3-acrylamido-3-methylbutanoate-co-(3-acrylamidopropyl)trimethylammonium chloride] terpolymers increased with increasing NaAMB content in the terpolymers and increasing ratios of anionic monomer to cationic monomer at a constant terpolymer charge density. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 3236–3251, 2004     

示差折光和光散射双检测体积排除色谱的绝对定量化

讨论了示差折光和光散射联用双检测体积排除色谱的绝对定量化的原理,强调指出了试样注入量在数据处理中的重要作用.测量注入试样的这两种检测器的检测常数,可以同时得到试样的折光指数增量和重均分子量的绝对值.这一方法除了适用于各种均聚物外,还可以应用于高分子混合物的分析.此时,如将混合物看作为单一溶质,从所得折光指数增量和重均分子量,可对它们的组成作出定量分析,还可以判断共混物两个组分之间有无分子缔合等现象的产生.这一方法应用于聚甲基丙烯酸甲酯/聚苯乙烯(PMMA/PS)混合物的溶液,指明在四氢呋喃中两者产生缔合而形成了复合物.     

Development of a liquid chromatography-based screening methodology for proteolytic enzyme activity

A new methodology for the detection and isolation of serine proteases in complex mixtures has been developed. It combines the characterization of crude samples by electrospray tandem mass spectrometry (ESI-MS/MS) in a multi-substrate assay and the differentiated sensitive detection of the responsible enzymes by means of liquid chromatography hyphenated online to biochemical detection (BCD). First, active samples are identified in the multi-substrate assay monitoring the conversion of eight substrates in multiple reaction monitoring in parallel within 60 s. Hereby, the product patterns are investigated and the suitable peptide as substrate for BCD analysis is selected. Subsequently, the active proteases are identified online in the continuous-flow reactor serving as BCD after non-denaturing separation by size-exclusion chromatography and ion-exchange chromatography. For BCD, the selected para-nitroaniline (pNA) labeled peptide is added post-column and is cleaved by eluting proteases under release of the coloured pNA in a reaction coil (reaction time 5 min). The method was optimized and the figures of merit were characterized with trypsin and chymotrypsin serving as the model proteases. For trypsin, a limit of detection in LC–BCD of 0.1 U/mL corresponding to an injected amount of 0.4 ng protein (∼18 fmol) was observed. The BCD signal remained linear for an injected enzyme concentration of 0.3–10 U/mL (1.3–42 ng enzyme). The method was applied to the characterization of the crude venom of the pit viper Bothrops moojeni and the extracellular protease of the pathogenic amoeba Acanthamoeba castellanii. In the two samples, fractions with proteolytic activity potentially interfering with the blood coagulation cascade were identified. The described methodology represents a tool for serine protease screening in complex mixtures by a fast ESI-MS/MS identification of active samples followed by the separation and isolation of active sample constituents in LC–BCD.     

Propagation rate coefficients of isobornyl acrylate,tert‐butyl acrylate and 1‐ethoxyethyl acrylate: A high frequency PLP‐SEC study

Pulsed laser polymerization (PLP) coupled to size exclusion chromatography (SEC) is considered to be the most accurate and reliable technique for the determination of absolute propagation rate coefficients, k_p. Herein, k_p data as a function of temperature were determined via PLP‐SEC for three acrylate monomers that are of particular synthetic interest (e.g., for the generation of amphiphilic block copolymers). The high‐T_g monomer isobornyl acrylate (iBoA) as well as the precursor monomers for the synthesis of hydrophilic poly(acrylic acid), tert‐butyl acrylate (tBuA), and 1‐ethoxyethyl acrylate (EEA) were investigated with respect to their propagation rate coefficient in a wide temperature range. By application of a 500 Hz laser repetition rate, data could be obtained up to a temperature of 80 °C. To arrive at absolute values for k_p, the Mark‐Houwink parameters of the polymers have been determined via on‐line light scattering and viscosimetry measurements. These read: K = 5.00 × 10⁵ dL g⁻¹, a = 0.75 (piBoA), K = 19.7 × 10⁵ dL g⁻¹, a = 0.66 (ptBA) and K = 1.53 × 10⁵ dL g⁻¹, a = 0.85 (pEEA). The bulky iBoA monomer shows the lowest propagation rate coefficient among the three monomers, while EEA is the fastest. The activation energies and Arrhenius factors read: (iBoA): log(A/L mol⁻¹ s⁻¹) = 7.05 and E_A = 17.0 kJ mol⁻¹; (tBuA): log(A/L mol⁻¹ s⁻¹) = 7.28 and E_A = 17.5 kJ mol⁻¹ and (EEA): log(A/L mol⁻¹ s⁻¹) = 6.80 and E_A = 13.8 kJ mol⁻¹. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 6641–6654, 2009     

Photooxidation of poly(N-vinylpyrrolidone) (PVP) in the solid state and in aqueous solution

The photooxidation of poly(N-vinylpyrrolidone) (PVP) in the solid state and in an aqueous solution has been studied under irradiation at long wavelengths (at λ ≥ 300 nm) and in the presence of oxygen, as these conditions of irradiation are those of natural outdoor aging. Infrared spectroscopy was used to follow the photochemical evolution of the polymer either for solid films of PVP or for PVP irradiated in an aqueous solution. Chemical treatments (NH₃, SF₄) were carried out on the photooxidized samples, and aqueous solutions of PVP were characterized by viscometry and size exclusion chromatography (SEC). Based on photooxidation results obtained in both the solid state and in an aqueous solution, a general mechanism that accounts for the main routes of oxidation is proposed. It was shown that the rates of oxidation and the stoichiometries of the reactions were strongly influenced by the physical state of the polymer (solid state or aqueous solution).     

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