Size Exclusion Chromatography of Polymers With Random Tetrafunctional Branching

Abstract

The behaviour of polydisperse branched copolymers of methyl methacrylate with a small amount of randomly situated tetrafunctional ethylenedimethacrylate units was investigated by means of size exclusion chromatography (SEC). A procedure has been suggested for the conversion of apparent values of molecular parameters of real polymer branched systems (M_{n, app}; M_{w, app} obtained from SEC data by calibration of the separation system using a linear polymer) into actual values. This was made possible by off-line coupling of SEC and viscometry. The branching was characterized by the weight average number of branching sites in the macro-molecule, m_w, and the branching index, y.     

Comprehensive two-dimensional liquid chromatography for the characterization of functional acrylate polymers

Comprehensive two-dimensional liquid chromatography-size-exclusion chromatography (LC x SEC) was investigated as a tool for the characterization of functional poly(methyl methacrylate) (PMMA) polymers. Ultraviolet-absorbance and evaporative light-scattering detection (ELSD) were used. A simple method to quantify ELSD data is presented. Each data point from the ELSD chromatogram can be converted into a mass concentration using experimental calibration curves. The qualitative and quantitative information obtained on two representative samples is used to demonstrate the applicability of LC x SEC for determining the mutually dependent molar-mass distributions (MMD) and functionality-type distributions (FTD) of functional polymers. The influence of the molar mass on the retention behavior in LC was investigated using LC x SEC for hydroxyl-functional PMMA polymers. The critical conditions, at which retention is--by definition--independent of molar mass, were not exactly the same for PMMA series with different end-groups. Our observations are in close agreement with theoretical curves reported in the literature. However, for practical applications of LC x SEC it is not strictly necessary to work at the exact critical solvent composition. Near-critical conditions are often sufficient to determine the mutually dependent distributions (MMD and FTD) of functional polymers.     

Characterization of low-density polyethylene by gel permeation chromatography—II. Study on the Drott method using fractions

Polyethylenes of different structures were fractionated and the fractions characterized by light scattering, gel permeation chromatography and viscometry. Intrinsic viscosities were measured in solvents of different thermodynamical quality including a θ-solvent (diphenyl at 118° for low-density polyethylene and at 130° for high-density polyethylene and ethylene-butene-1 copolymer). The results were used for examining two aspects of the Drott iterative procedure: (a) the relationship between thermodynamical quality of the solvent and depression in the intrinsic viscosity due to branching; and (b) analytical form of expression relating the so-called g-factor to the number of long-chain branches. The ratio of intrinsic viscosities of branched and linear species at a given weight-average molecular weight has been clearly proved to be solvent independent, and the equation relating the g-factor to the number of branches for polymer monodisperse with respect to molecular weights appears to be a fair representation of long-chain branching in low-density polyethylene. For the polymers examined, the branching frequency λ is not independent of molecular weight.     

Polymerization of vinyl chloride at reduced monomer accessibility. II. Polymerization at subsaturation pressure with emulsion PVC as seed

Vinyl chloride was polymerized at 59–92% of saturation pressure in a water-suspended system at 45–65°C with an emulsion poly(vinyl chloride) (PVC) latex as a seed. A water-soluble initiator was used in various concentrations. The monomer was continuously charged as vapor from a storage vessel kept at lower temperature. Characterization included determination of molecular-weight distribution and degree of long-chain branching by gel permeation chromatography (GPC) and viscometry, thermal dehydrochlorination, and microscopy. The polymerization rate decreases with decreasing pressure but is reasonable even at the lowest pressure. The molecular weight decreases with decreasing pressure and increasing initiator concentration and also with increasing polymerization temperature, if the initiator concentrations are chosen to give a constant initiator radical concentration. The degree of long-chain branching increases with increasing initiator concentration and decreasing monomer pressure but is unaffected by the polymerization temperature, if the initiator radical concentration is kept constant. The thermal stability decreases with decreasing M _n, while the degree of long-chain branching has only a minor influence. The most important factor in the system influencing the molecular parameter is the monomer accessibility.     

Effect of molecular structure on rheological and crystallization properties of polyethylenes

This article describes the development of reliable techniques to measure the isothermal crystallization rates (ICR) under quiescent as well as under small amplitude, oscillatory shear conditions. Quiescent crystallization rates were obtained using a differential scanning calorimeter. Those under small amplitude shear were obtained using Rheometrics rheometers. It is shown how a small amount of long-chain branching in high-density polyethylene homopolymer (HDPE) dramatically influences rheological properties and enhances ICR. For these HDPEs, the rate increases with the increase in long-chain branching. The general application of isothermal crystallization studies, however, should be done with great caution. This is because the fundamentals of isothermal crystallization require that it be done on the basis of a fixed undercooling with respect to the equilibrium melting temperature. Such a temperature is ill-defined for the commercial polymers having broad molecular weight distribution (MWD). Nonetheless, a practical procedure is outlined wherein the melting curve of a previously isothermally crystallized sample is used as a substitute for judging the equilibrium melting point and in deciding the selection of a proper crystallization temperature. Even this new procedure may not be applicable for polymers having heterogeneous short-chain branching distribution. © 1996 John Wiley & Sons, Inc.     

Distribution of molar mass and branching index of natural rubber from hevea brasiliensis trees of different age by size exclusion chromatography coupled with online viscometry

Natural rubber from hevea brasiliensis trees (Thailand, RRIM 600 clone) of different age (8, 20, and 35 years) were characterized by size exclusion chromatography (SEC) coupled with online viscometry with respect to their distribution of molar mass and branching index at a temperature of 70°C using cyclohexane as solvent. The natural rubber samples were purified by washing with an aqueous solution of sodium dodecylsulfate and subsequent saponification. With this procedure physical branching points caused by phospholipids, proteins and hydrophobic terminal units, mainly fatty acids, of the natural rubber (cis-1,4-polyisoprene) molecule, could be removed leading to completely soluble polymer samples. All samples investigated possess a very broad (10 to 50,000 kg/mol) and distinct bimodal molar mass distribution. With increasing age of the trees the peak area in the low molar mass region decreases favoring the peak area in the high molar mass region. By plotting the branching index as a function of the molar mass it could be shown that branching of the natural rubber increases with both, the molar mass and the age of the trees.     

用GPC-级分特性粘数法表征高顺式-1,4聚丁二烯的长链支化

本文在Ambler方法和kraus方法的基础上,用GPC-级分特性粘数法来测定聚合物的长链支化度,能同时以g_i、λ_i、G_i、m_i、支化重量百分数等支化参数来表征聚合物的支化分布、支化程度和支化含量等;得到了相应的计算gi、λi、[η]_i等有关的计算公式和计算方法;还研制成了以光导纤维为冷光源的高精度光电自动计时毛细管粘度计和60小时内恒温精度优于±5×10~(-4)℃的超级恒温水浴,使计时精度达到≤±4×10~(-3)秒;并以国产和进口的镍系顺丁橡胶为例,讨论了分子量和支化度多分散性之间的某些关系;从而确定了该法比较合理地、全面地相对比较聚合物的长链支化度。     

Size Exclusion Chromatography of Polyamides

Abstract

We report here a new chromatographic method for characterization of polyamides and polyether-block-amide copolymers by Size Exclusion Chromatography. First, it concerns absolute characterization of polyamide probes by classical light scattering and Ubbelohde viscometry measurements and the choice of narrow distribution standards to calibrate the GPC system. The GPC analysis of polyamides 6, 11, 12 and copolymers is based upon the dual detection refractometer/on-line continuous viscometer at 130°C using columns packed with cross-linked polystyrene gels, benzyl alcohol as mobile phase and polytetrahydrofuran standards for calibration. The main results are absolute average molecular weights and distribution curve, intrinsic viscosity and viscosity law. In addition, viscometric data produced evidence of long-chain branching occuring beyond a limiting molecular weight in some polyamide 12 samples.     

Characterization of branched ultrahigh molar mass polymers by asymmetrical flow field-flow fractionation and size exclusion chromatography

The molar mass distribution (MMD) of synthetic polymers is frequently analyzed by size exclusion chromatography (SEC) coupled to multi angle light scattering (MALS) detection. For ultrahigh molar mass (UHM) or branched polymers this method is not sufficient, because shear degradation and abnormal elution effects falsify the calculated molar mass distribution and information on branching. High temperatures above 130 °C have to be applied for dissolution and separation of semi-crystalline materials like polyolefins which requires special hardware setups. Asymmetrical flow field-flow fractionation (AF4) offers the possibility to overcome some of the main problems of SEC due to the absence of an obstructing porous stationary phase. The SEC-separation mainly depends on the pore size distribution of the used column set. The analyte molecules can enter the pores of the stationary phase in dependence on their hydrodynamic volume. The archived separation is a result of the retention time of the analyte species inside SEC-column which depends on the accessibility of the pores, the residence time inside the pores and the diffusion ability of the analyte molecules. The elution order in SEC is typically from low to high hydrodynamic volume. On the contrary AF4 separates according to the diffusion coefficient of the analyte molecules as long as the chosen conditions support the normal FFF-separation mechanism. The separation takes place in an empty channel and is caused by a cross-flow field perpendicular to the solvent flow. The analyte molecules will arrange in different channel heights depending on the diffusion coefficients. The parabolic-shaped flow profile inside the channel leads to different elution velocities. The species with low hydrodynamic volume will elute first while the species with high hydrodynamic volume elute later. The AF4 can be performed at ambient or high temperature (AT-/HT-AF4). We have analyzed one low molar mass polyethylene sample and a number of narrow distributed polystyrene standards as reference materials with known structure by AT/HT-SEC and AT/HT-AF4. Low density polyethylenes as well as polypropylene and polybutadiene, containing high degrees of branching and high molar masses, have been analyzed with both methods. As in SEC the relationship between the radius of gyration (R(g)) or the molar mass and the elution volume is curved up towards high elution volumes, a correct calculation of the MMD and the molar mass average or branching ratio is not possible using the data from the SEC measurements. In contrast to SEC, AF4 allows the precise determination of the MMD, the molar mass averages as well as the degree of branching because the molar mass vs. elution volume curve and the conformation plot is not falsified in this technique. In addition, higher molar masses can be detected using HT-AF4 due to the absence of significant shear degradation in the channel. As a result the average molar masses obtained from AF4 are higher compared to SEC. The analysis time in AF4 is comparable to that of SEC but the adjustable cross-flow program allows the user to influence the separation efficiency which is not possible in SEC without a costly change of the whole column combination.     

Band broadening in size-exclusion chromatography of polydisperse samples

Understanding and controlling the band broadening is essential to obtain accurate molar-mass distributions by size-exclusion chromatography (SEC). In this paper, band broadening in SEC is reviewed from a contemporary perspective. The observed band broadening is due to dispersion inside and outside the chromatographic column (undesirable band broadening) and to the polydispersity of the sample (desirable SEC selectivity). The various contributors to band broadening are discussed. Integrity plots are introduced as a tool to evaluate the performance of specific SEC columns at given experimental conditions. For narrow polymer standards on single SEC columns the observed peak width is dominated by the chromatographic dispersion. MALDI-ToF-MS is demonstrated as an alternative to determine the PDI of narrowly distributed samples. The plate heights encountered at very high reduced velocities are found to be lower than expected. This is advantageous for fast separations by SEC.     

1H NMR Analysis of Long-Chain-Branched Strong Polyelectrolytes Obtained by Vinyl/Divinyl Monomer Copolymerization in Aqueous Medium

Statistical long-chain branching occurring during the free-radical polymerization of the system sodium 4-vinylbenzenesulfonate (SSNa) and N, N′-methylene-bis(acrylamide) (MBAA) in aqueous medium was studied by ¹H NMR spectroscopy and SEC. The former method yielded the degree of conversion and the content of the three monomer units in the chain, i.e., SSNa, MBAA with pendant vinyl groups, and MBAA as branching points. It was found that the number of individual monomer units per a total of 1000 monomer units does not perceivably change with the degree of conversion and only slightly increases with increasing ratio MBAA/SSNa in the feed.     

Comparative evaluation of size-exclusion chromatography and viscometry for the characterisation of cellulose

The analysis using size-exclusion chromatography (SEC) with multi-angle light scattering (MALS) and differential refractive index (DRI) detection of cellulose dissolved in lithium chloride/N,N-dimethylacetamide (LiCI/DMAc) is evaluated and compared to two other methods currently used for cellulose analysis. These are SEC with low-angle light scattering (LALS) and ultra-violet detection of cellulose derivatised to tricarbanilates (CTC), and viscometry in cadmium triethylene diamine dihydroxide (cadoxen). The cellulose source is Whatman No. 1 paper, unaged or artificially aged with a combination of heat and humidity. The values of the molar mass (Mr) averages of cellulose obtained with the different methods resulted quite different for both aged and unaged paper. SEC of cellulose in LiCl/DMAc provided the highest Mr averages values, followed by SEC of CTC, while viscometry yielded the lowest values. These differences were more or less pronounced depending on the initial degradation state of the paper. Several hypotheses are presented in order to explain these discrepancies and each method is discussed on the basis of its suitability to characterise the aging-induced degradation.     

High pressure radical polymerization of ethylene with water dilution

The radical polymerization of ethylene has been performed in the presence of water. The structural characteristics of polymers prepared with 0-60% wt of water at 1400 atm and various temperatures (140–260°) were determined by the usual solution methods (viscometry, GPC), by density and by infrared spectroscopy. The experimental results show that, when water content increases, long chain branching (LCB) increases and molecular weight distribution broadens.     

Size-exclusion chromatography (SEC) of branched polymers and polysaccharides

Branched polymers are among the most important polymers, ranging from polyolefins to polysaccharides. Branching plays a key role in the chain dynamics. It is thus very important for application properties such as mechanical and adhesive properties and digestibility. It also plays a key role in viscous properties, and thus in the mechanism of the separation of these polymers in size-exclusion chromatography (SEC). Critically reviewing the literature, particularly on SEC of polyolefins, polyacrylates and starch, we discuss common pitfalls but also highlight some unexplored possibilities to characterize branched polymers. The presence of a few long-chain branches has been shown to lead to a poor separation in SEC, as evidenced by multiple-detection SEC or multidimensional liquid chromatography. The local dispersity can be large in that case, and the accuracy of molecular weight determination achieved by current methods is poor, although hydrodynamic volume distributions offer alternatives. In contrast, highly branched polymers do not suffer from this extensive incomplete separation in terms of molecular weight.     

Long-chain branching in low-density polyethylene

A method is given for the analysis of long-chain branching in polymers by using combined GPC and intrinsic viscosity measurements. A computer program was written to evaluate branching indices by a tabular, iterative method. The method was applied to the evaluation of long-chain branching in low-density polyethylene.     

Size Exclusion Chromatography (SEC) of Complex Polymers-Methods of Correction for Imperfect Resolution

Abstract

Herein is reported a review and extension of recently published methods of correction for imperfect resolution (inadequate peak separation and or excessive peak broadening) for the SEC of linear homo and uniform copolymers and complex polymers such as polymers with long chain branching and nonuniform copolymers. Emphasis Is placed on analytical correction methods and absolute detector systems such as the low angle laser light scattering photometer and viscometer in series with a mass detector. Analytical correction methods and absolute detector systems play a vital role in the SEC characterization of complex polymers.     

Viscoelastic properties of branched polyethylene melts

The dynamic mechanical properties of branched polyethylenes in the molten state were determined in the frequency range 10^?3–10 radians/sec. The materials tested have remarkably similar rheological properties even though they vary greatly in molecular weight and molecular weight distribution. The similarity in properties is attributed to the influence of long chain branching on the relaxation spectra. A mechanistic argument is proposed to relate the observed behavior to molecular entanglement coupling. The concept of entanglement coupling involving long-chain branching leads to the expectation that the quasi-Newtonian and non-Newtonian viscosities of branched polymers may be either greater or less than those of linear polymers of the same species, which have comparable molecular weights. This is borne out by experiment.     

Radical polymerization in the presence of peroxide and reducing agent monomer for branched polymers

In this article, we report the radical polymerization in the presence of peroxide and commercially available or designed reducing agent monomer (RAM) for the preparation of branched poly(methyl methacrylate)s (PMMAs). The reaction behavior of the RAM was studied by NMR. Triple‐detection SEC (TD‐SEC) analysis was used to confirm the branching structure of the prepared PMMAs and to investigate the influence of peroxide concentration and RAM concentration on molecular weight and branched structure. The obtained branched PMMAs exhibited high molecular weights and relatively narrow polydispersities at high conversion of MMA. Interestingly, a significant increase in molecular weight and degree of branching of the obtained polymers are observed in higher BPO concentration, these results are quite different from that reported in the literature. The unique radical polymerization mechanism in the RAM/BPO redox‐initiated radical polymerization system resulted in branched PMMAs with high molecular weights at relatively high RAM and BPO concentrations. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2019 , 57, 833–840     

在四官能团引发剂存在下的自缩合乙烯基聚合反应制备丙烯酸酯类超支化共聚物

超支化聚合物具有特殊的结构和性能 ,可通过一步法聚合直接制得 ,具有大规模工业应用前景 .近年来 ,超支化聚合物的研究已成为高分子科学的热门课题之一[1～ 3 ] .超支化聚合物的一个主要缺点是它的分子量分布比较宽 .Ｍ櫣ｌｌｅｒ[4] 等通过理论计算指出 ,在聚合体系中加入ｆ个功能基团的分子Ｂｆ[对自缩合乙烯基聚合反应 (ＳＣＶＰ) ,Ｂｆ为ｆ个引发基的引发剂 ;对ＡＢｘ 型单体的缩聚反应 ,为有ｆ个Ｂ官能团的分子 ],可以降低超支化聚合物的分子量分布 ,这一结果已被实验证实[5～ 7] .我们用ＭｏｎｔｅＣａｒｌｏ方法模拟了在多官能团引…     

Determination of chemical composition distributions in synthetic polymers

A characteristic feature of synthetic polymers is their dispersity in molar mass and, in many cases, chemical composition. Since dispersity is highly relevant in relation to polymer properties, ongoing efforts are being put in the development of appropriate analysis methods. In this respect, size-exclusion chromatography (SEC) is well known for the determination of molar mass distributions. Methods for chemical composition distributions are less mature than SEC and mainly include liquid chromatography and mass spectrometry and the combination of these techniques. The term chemical composition distribution is considered broad in this paper, i.e. for the chemical composition distribution of a (co)polymer backbone, for the functionality type distribution of a polymers' functional end groups, for the block length distribution of a block copolymer, for the branching distribution and for the tacticity distribution. In this paper, analysis methods for all types of chemical composition distributions are reviewed. Special attention is paid to practical requirements and common misconceptions that sometimes arise. Applications within the last 5 years are summarized.