Characterization of the Chemical Composition Distribution of Poly(n‐butyl acrylate‐stat‐acrylic acid)s

A size exclusion chromatography (SEC)‐gradient method is developed allowing poly(n‐butyl acrylate‐stat‐acrylic acid)s to be separated with respect to content of acrylic acid over the ­complete composition range. After setting up the chromatographic method, samples that, according to the amounts of charged monomers, are expected to have identical chemical composition are compared. The chromatograms reveal differences in elution volume, which, by ¹H NMR spectroscopy, can be partially traced back to differences in polymer composition. In addition, samples of similar compositions prepared in ­different solvents exhibit differences in chemical composition distribution.

     

Characterization of the Chemical Composition Distribution of Ethylene/1‐Alkene Copolymers with HPLC and CRYSTAF—Comparison of Results

A series of copolymers of ethylene with propene, 1‐hexene, 1‐octene, and 1‐octadecene is characterized by size‐exclusion chromatography (SEC), nuclear magnetic resonance spectroscopy (NMR), crystallization analysis fractionation (CRYSTAF), and high‐temperature interactive liquid chromatography. Four different solvent pairs are used as the mobile phase, while porous graphite is used as the column packing. The elution volumes of the polymer samples do not correlate with their average molar mass (SEC); however, they correlate with the average chemical composition (NMR). High performance liquid chromatography (HPLC) enables separation of the copolymers over the full range of their composition and independent of their crystallinity. Dependence between the elution volume and the average chemical composition distribution (CCD) of the copolymer is linear and it is a function of the length of branches as well as the type of the mobile phase. The CCDs of copolymers derived from HPLC profiles are similar to, yet broader than the CCDs obtained with CRYSTAF.

     

Analysing the Chemical Composition Distribution of Ethylene‐Acrylate Copolymers: Comparison of HT‐HPLC,CRYSTAF and TREF

HT‐HPLC is an attractive technique to analyse CCD of olefin copolymers and offers the possibility to shorten analysis times compared to fractionation techniques based on crystallisation. We have found that HT‐HPLC enables the selective elution of EMA and EBA copolymers according to their content of the polar co‐monomer. This fractionation could be confirmed by coupling the gradient HPLC system with FT‐IR spectroscopy. The CCDs obtained by this new method were then compared to the results from CRYSTAF. Both methods, HT‐HPLC and CRYSTAF, can discriminate between sets of samples having a narrow or a broad CCD. They can also prove the presence of acrylate‐poor fractions.

     

Simultaneous Deconvolution of the Bivariate Molecular Weight and Chemical Composition Distribution of Ethylene/1‐Hexene Copolymers

The bivariate molecular weight and chemical composition distribution (MWD×CCD) of ethylene/1‐hexene copolymers can be measured using TREF×GPC cross fractionation characterization (CFC). In this work, the experimental MWD×CCD of ethylene/1‐hexene copolymers made with a Ziegler–Natta catalyst under different polymerization conditions are measured by CFC and deconvoluted to identify the minimum number of site types present in the catalyst. Blends of ethylene/1‐hexene copolymers produced with a metallocene catalyst with known MWD×CCD are used to validate the proposed technique. This is a powerful methodology to better understand the nature of active sites on multisite catalysts, and can be beneficial for the development of copolymers with precisely controlled microstructures.     

Characterization of Ethylene/α‐Olefin Copolymers Using High‐Temperature Thermal Gradient Interaction Chromatography

Several crystallization‐based techniques are used to measure the chemical‐composition distribution of polyolefins, but they are limited to semicrystalline polyolefins. Recently, high‐temperature thermal gradient interaction chromatography (HT‐TGIC) has been developed to quantify the chemical‐composition distribution of semicrystalline and amorphous polyolefins, thus broadening the range of techniques available for the analysis of polyolefin chemical‐composition distribution. In HT‐TGIC, the fractionation mechanism relies on the interaction of polyolefin chains with a graphite surface upon temperature change in an isocratic solvent. In the present investigation, a series of ethylene/1‐octene copolymers having approximately the same molecular weight average and different comonomer fractions (up to 25% of 1‐octene) is synthesized using a metallocene catalyst to investigate the fractionation mechanism of HT‐TGIC. Three copolymer samples and their blends are also studied to determine which operation parameters influence the HT‐TGIC peak shape and position. The cooling rate has no significant effect on the desorption temperature and the broadness of the HT‐TGIC chromatograms. On the other hand, the heating rate and the elution flow rate substantially influence the peak temperature and breadth.

     

Separation of High‐Impact Polypropylene Using Interactive Liquid Chromatography

Fractionation techniques such as temperature rising elution fractionation or crystallization analysis fractionation fail to fractionate the ethylene–propylene (EP) copolymers, which are a component of high‐impact polypropylene (hiPP), according to their chemical composition. High‐temperature high‐performance liquid chromatography separates blends of EP‐copolymers and polypropylene. The elution volume of the EP‐copolymers depends linearly on the average content of ethylene. The separation according to the chemical composition was hyphenated with size exclusion chromatography. In this way, the relationship between the distribution with regard to chemical composition and molar mass, that is, the full chemical heterogeneity of hiPP, was revealed for the first time.     

Comparison of High‐Temperature HPLC,CRYSTAF and TREF for the Analysis of the Chemical Composition Distribution of Ethylene‐Vinyl Acetate Copolymers

The chemical composition distribution (CCD) is a fundamental molecular parameter of copolymers. High‐temperature interactive liquid chromatography (HT‐HPLC) has recently emerged as a new analytical technique for determination of the CCD of semicrystalline copolymers of ethylene and polar comonomers. With the aim of comparing the results of HT‐HPLC with those from the traditionally used temperature rising elution fractionation (TREF) and crystallization analysis fractionation (CRYSTAF) techniques, three ethylene‐vinyl acetate (EVA) copolymers were fractionated by TREF and the fractions were analyzed by HT‐HPLC. HT‐HPLC‐Fourier transform‐infrared (FT‐IR) spectroscopy showed that individual fractions of different VA‐content coelute in the HPLC. While the separation in TREF and CRYSTAF is mainly the result of the overall effect of alkyl branches and VA‐comonomer units, in HT‐HPLC it is the polar comonomer that selectively contributes to the adsorption. Thus, HT‐HPLC leads to a much more detailed knowledge of the distribution of the structured units; in addition, it saves time.

     

Rapid Determination of the Chemical Composition of Ethylene/Butadiene Copolymers Using FTIR Spectroscopy and Chemometrics

Fourier transform infrared spectroscopy by attenuated total reflection (ATR‐FTIR), combined with the partial least square (PLS) method provides a fast characterization of ethylene/butadiene copolymers' intricate composition. The PLS regression method is constructed to quantify ethylene, 1,2‐butadiene (vinyl), trans‐1,4‐butadiene, and 1,2‐cyclohexane units in the copolymer. These rings are formed by intramolecular cyclization during polymerization. The performance of PLS models is evaluated by comparing the result obtained by ¹³C NMR and the model for three unknown samples. It is shown that the proposed method allows to accurately estimate the chemical composition of ethylene/butadiene copolymers in a much shorter time than NMR.     

Effect of Solvent Type on High‐Temperature Thermal Gradient Interaction Chromatography of Polyethylene and Ethylene–1‐Octene Copolymers

The effects of the solvent type and operation conditions on the high‐temperature thermal gradient interaction chromatography (HT‐TGIC) of ethylene homopolymers, ethylene–1‐octene copolymers, and their blends are investigated. While the HT‐TGIC profiles of single polymers measured with 1,2,4‐trichlorobenzene (TCB) and chloronaphthalene (CN) are similar, they are always narrower when o‐dichlorobenzene (ODCB) is used, particularly for samples with lower 1‐octene fractions. Significant differences between the experimental and the calculated profiles of binary blends are observed with all three solvents, but better peak separation is seen when the ODCB is used. Having higher fractions of a 1‐octene‐poor component in the blend causes a more significant distortion of the shape expected for the peak from the component with the higher 1‐octene fraction. The effect of the molecular weight on HT‐TGIC profiles is also studied using samples with the same comonomer content and different molecular weights. Samples with low molecular weight have broader distributions and significant lower‐temperature tails, particularly when TCB is used. Chain crystallization after adsorption effects may also play a minor role for low‐comonomer samples. Finally, HT‐TGIC profiles are compared with their equivalent crystallization elution fractionation (CEF) profiles. The HT‐TGIC curves are broader than the equivalent CEF profiles, but these differences decrease as the comonomer content increases.

     

高效液相色谱法测定人红细胞膜脂肪酸含量及组成

本文采用高效液相色谱法测定了４２例正常成人红细胞膜脂肪酸（ＦＡ）含量及组成。结果表明：该法分离效果好、定量准确。重复性变异系数平均５．５％，回收率平均９４．７％。人红细胞膜主要由廿二碳六烯酸（Ｃ２２６）、花生四烯酸（Ｃ２０４）、亚油酸（Ｃ１８２）、软脂酸（Ｃ１６０）、油酸（Ｃ１８１）和硬脂酸（Ｃ１８０）等六种ＦＡ组成，其中花生四烯酸含量最高，其次为硬脂酸。不饱和脂肪酸占７１．６％。     

Cocrystallization of Blends of Ethylene/1‐Olefin Copolymers: An Investigation with Crystallization Analysis Fractionation (Crystaf)

Summary: Crystallization analysis fractionation (Crystaf) is a technique for estimating the chemical composition distribution (CCD) of semi‐crystalline copolymers. Cocrystallization may happen during Crystaf analysis, affecting Crystaf profiles and leading to misinterpretation of the CCD. This study investigates this phenomenon and determines the main factors leading to cocrystallization by analyzing a series of ethylene/1‐olefin copolymers. We considered three factors affecting cocrystallization: comonomer type, cooling rate and chain crystallizability. The results showed that cooling rate and similarity in chain crystallizability are the key factors regulating cocrystallization during Crystaf analysis.

Crystaf analysis of blends of copolymers.     

Addition Polymers of Strained Cyclic Olefins – Transition Metal Catalysed Polymerisations of the Cyclobutene Derivative Bicyclo[3.2.0]hept‐6‐ene

Bicyclo[3.2.0]hept‐6‐ene was converted into the corresponding addition polymer poly(6,7‐bicyclo[3.2.0]heptylene) with the aid of early and late transition metal based olefin polymerisation catalysts. Moderate to very good yields (42–99%) of polymer were obtained with [Pd(NCEt)₄][BF₄]₂, [(η³‐allyl)Pd(solv)₂][SbF₆], [(2,9‐dimethyl‐1,10‐phenanthroline)Pd(CH₃)(NC(CH₂)₆CH₃)][SbF₆], and Cp₂ZrCl₂/MAO, using monomer to transition metal ratios between 50/1 and 250/1. Reaction occurs at the olefin π‐bond, and the four‐membered ring of the monomer is retained during polymerisation which differs from ring‐opening olefin metathesis polymerisation in which the four‐membered ring is opened. The nearly exclusively saturated structure of the polymer was confirmed by ¹H and ¹³C NMR spectroscopy. It is proposed that the polymers consist of repeating units that are predominantly cis‐exo‐enchained. GPC analysis of the soluble polymers prepared with [Pd(NCEt)₄][BF₄]₂ showed that the molecular mass values (GPC) were in the range of 3 700 to 22 600.

     

Mathematical Modeling of Crystallization Elution Fractionation of Ethylene/1‐Octene Copolymers

Crystallization elution fractionation (CEF) is a relatively new polyolefin characterization technique used to estimate the chemical composition distribution (CCD) of semicrystalline copolymers. CEF is developed to enhance the resolution and reduce the analysis time of temperature rising elution fractionation (TREF) by separating polymer samples in both the crystallization and elution steps. A model based on the concept of population balance, crystallization/dissolution kinetics, and dispersion model is developed to understand the CEF fractionation mechanisms. The proposed CEF model is found to describe well the experimental CEF profiles of a series of ethylene/1‐octene copolymers with different comonomer contents.

     

“Anatomical” View of the Protein Composition and Protein Characteristics for Gloydius shedaoensis Snake Venom via Proteomics Approach

The bioactive protein components from snake venom complexes have been utilized for studies of enzymology, structural biology, and pharmacology. The Gloydius shedaoensis snake (GSS) is the only snake species found exclusively at the Chinese Shedao (snake) Island in Dalian. To investigate the protein components of Chinese GSS venom (GSSV), we initialized a proteomic assay for GSSV by the combination of sodium dodecyl sulfate‐polyacrylamide gel electrophoresis with high‐performance liquid chromatography (HPLC)‐nanoelectrospray ionization tandem mass spectrometry (nESI‐MS/MS). Thirty gel bands visualized by Coomassie blue staining were excised and digested by trypsin. The tryptic‐digested peptides were separated by HPLC and subsequently sequenced by nESI‐MS/MS. Twenty‐four types of proteins were identified by searching the mass spectrometry data against NCBInr database through TurboSequest Bioworks. The most abundant proteins are phospholipase A₂, metalloproteinase, L ‐amino acid oxidase (LAAO), serine protease/thrombin‐like enzyme. Except for 20 types of known snake venom proteins, the homolog peptides of hypothetical protein PFLC2230, LOC495267 protein, DEAD/DEAH box helicase‐like, and pancreatic trypsin 1 from other organisms are matched for GSSV protein components. Mass spectrometric data also indicated that (i) dimerization happens to PLA₂s as monomer and dimer of PLA₂s coexist in GSSV and (ii) truncation or hydrolysis might happen to LAAOs as three molecular‐weight‐ranged LAAO species are present in GSSV. The results provide an “anatomical” view of the protein composition and important information for protein characteristics of GSSV. Anat Rec, 2011. © 2010 Wiley‐Liss, Inc.     

A Comprehensive Kinetic Model for the Combined Chemical and Thermal Polymerization of Styrene up to High Conversions

In the present study, a comprehensive mathematical model is developed for the free‐radical polymerization of styrene to predict the polymerization rate and the molecular‐weight distribution of the polymer. The kinetic model accounts for both chemical and thermal radical generation and, thus, can be employed over an extended range of polymerization temperatures (e.g., 60–200 °C). The thermal initiation mechanism includes the reversible Diels‐Alder dimerization of styrene, radical formation via the reaction of the Diels‐Alder adduct with monomer, the formation of dead trimers, and the initiation of new polymer chains. Moreover, a comprehensive free‐volume model is employed to describe the variation of termination and propagation rate constants as well as of the initiator efficiency with respect to the monomer conversion. The cumulative molecular‐weight distribution of the polystyrene is calculated by the weighted sum of all the ‘instantaneous’ weight chain‐length distributions formed during the batch run. The capabilities of the present model are demonstrated by a direct comparison of model predictions with experimental data on monomer conversion, number‐ and weight‐average molecular weights, and molecular‐weight distribution. It should be noted that previously published kinetic models cannot describe the combined thermal and chemical free‐radical polymerization of styrene in terms of a unified, fundamental, kinetic model, which further underlines the significance of this study.

Predicted and experimental weight‐average molecular weights with respect to monomer conversion (experimental conditions same as in Figure 1 ).     

A Simple Access to the (Log/Normal) Molecular Weight Distribution Parameters of Polymers Using PGSTE NMR

A log/normal MWD is characterized by two parameters, its mean molecular weight M₀ and width σ. It is demonstrated how these parameters can be obtained by model fitting a stretched exponential function (SEF), as characterized by two parameters β and D_S, to the PGSTE response curve. Based on simulations, two general empirical equations relating β and D_S to M₀ and σ are found. The model enables the MWD characteristics to be determined if the scaling law between diffusivity and molecular weight is known. The sensitivity and relative error of σ and M₀ are discussed and the applicability of the model is illustrated by analyzing experimental NMR response curve of some PEO samples. The key advantages of this technique are its simplicity, numerical robustness, and reliability.

     

Effect of a Polymeric Additive on the Pore‐Size Distribution and Shrinking Process of a Hydrogel Network

A systematic comparison of the effect of architectural modifications to the network structure on the internal microstructure of N‐isopropylacrylamide (NIPA) based hydrogels showed that the addition of a second component to the network significantly increased the proportion of macropores in the network. The second components considered were short poly(N‐isopropylacrylamide) (PNIPAM) chains grafted to the network backbone, high‐molecular‐weight polyacrylamide (PAM) chains, or microsphere particles of PNIPAM. Structures are proposed for each of the modified gel networks taking into account the new structural information. Through a combination of the pore size and network structure data reported here, and with the shrinking data obtained previously, shrinking mechanisms are proposed for each of the modified network structures. In all cases, the enhanced shrinking rates were directly caused by the presence of the second component, which acted as nuclei for shrinking (graft‐PNIPAM and PNIPAM microspheres) or as water‐release channels (PAM gel), and indirectly caused by the second components via their affect on the network microstructure.

Proposed structures for the architecturally modified gels based on the pore‐size information. Graft‐PNIPAM gel. The freely mobile graft chains prevent chains from meeting resulting in larger pores.     

Comparative Study of Distribution of Active Sites According to Their Stereospecificity in Propylene Polymerization over the Traditional TiCl3 and Supported Titanium–Magnesium Catalysts with Different Composition

The preparative‐temperature rising elution fractionation method is used to obtain comparative data on contents of fractions with different microtacticities for polypropylene (PP) samples prepared using three catalytic systems: the traditional Ziegler–Natta (Z–N) catalyst δ‐TiCl₃ and two types of supported titanium–magnesium catalysts: the “donor‐free” TiCl₄/MgCl₂ catalyst and TiCl₄/MgCl₂·nDBP catalyst (DBP – dibutylphthalate used as an internal donor) at polymerization with the same cocatalyst (AlEt₃) in the absence and presence of an external donor (propyltrimetoxy silane). The separated individual PP fractions are also studied by gel permeation chromatography (molecular weight and molecular weight distribution) and differential scanning calorimetry. The results demonstrate general regularities and differences in the formation of active sites having different isospecificities for the traditional TiCl₃‐based Z–N catalyst and highly active supported titanium–magnesium catalysts.     

A New Method for the Analysis of the Substitution Pattern of Hydroxyethyl(methyl)‐Celluloses Along the Polysaccharide Chain

Hydroxyethylmethyl celluloses (MS_HE 0.15–0.26, DS_Me 1.49–1.82) and hydroxyethyl celluloses (MS_HE 1.89–3.03) are analyzed with respect to their substituent distribution in the polymer chains. The cellulose ethers are peralkylated and partially hydrolyzed, and are analyzed by electrospray ionization‐ion trap‐mass spectrometry (ESI‐IT‐MS). The randomness of the partial hydrolysis is proven. Quantitative evaluation of their mass spectra becomes possible after labeling the oligosaccharides at the reducing end. Reductive amination with o‐aminobenzoic acid gives better results than hydrazone formation with cationic Girard's T reagent. Syringe pump infusion gives more‐accurate results compared with liquid chromatography (LC)‐ESI‐MS. Profiles of the substituent distribution in the oligosaccharide fractions of DP 2–DP 7 are compared with the theoretical random distribution of glucosyl units in the chain.

     

Monitoring the Chemical Heterogeneity and the Crystallization Behavior of PP‐g‐PS Graft Copolymers Using SEC‐FTIR and CRYSTAF

Graft copolymers of propene with styrene were analyzed with regard to their chemical heterogeneity using both SEC coupled to FT‐IR spectroscopy and CRYSTAF. The SEC‐FTIR indicates chemical homogeneity of the copolymer samples. The decrease in crystallization temperature in CRYSTAF does not correlate with the concentration of PS in the samples but it correlates decisively with the branching frequency. The length of the PS branches does not influence the crystallization temperature in CRYSTAF, although the longest branches in the individual samples were 44 times longer than the shortest ones.