The determination of copolymer composition as a function of molecular weight by preparative gel permeation chromatography and comparison to the rapid stop-and-go GPC/IR method

The determination of the copolymer composition as a function of molecular weight by preparative gel permeation chromatography (GPC) for a poly(styrene-co-vinyl stearate) sample is described. These results were compared to data obtained on the same copolymer by the previously described rapid stop-and-go GPC/IR method of analysis of copolymer composition as a function of molecular weight and found to be in good agreement.     

Functionality distribution of hydroxyl-terminated polybutadienes using gel permeation chromatography. I. The method and calibration procedure

A method for simultaneously determining the molecular weight averages, molecular weight distribution, hydroxyl equivalent weight, functionality averages, and functionality distribution of hydroxyl-terminated polybutadienes using GPC has been developed. The method is based on the preparation of a UV absorbing derivative of the hydroxyl group and GPC analysis using dual differential refractive index and UV detectors. In order to determine the hydroxyl equivalent weight, quantitative derivatization of the hydroxyl group is required. If the equivalent weight can be determined by an independent method, the derivatization reaction can be less than quantitative if sufficient UV absorptivity can be obtained. The procedure used for calibrating the GPC columns and UV detector are presented. Equations for calculating number- and weight-average functionalities from GPC data were also developed. The number-average functionality is independent of the functionality distribution, but the weight-average functionality is dependent upon the distribution of functionality. The ratio of the weight-average to number-average functionality is indicative of how the functionality is skewed as a function of molecular weight.     

Multiple detectors for molecular weight and composition analysis of copolymers by gel permeation chromatography

The use of a single detector in gel permeation chromatography (GPC) for samples of varying composition leads to erroneous conclusions. With certain simplifying assumptions, a gel permeation chromatograph equipped with properly selected dual detectors yields composition and molecular weight distribution information that is meaningful. Examples discussed are a mixture of homopolymers and a sample supposed to have been a styrene–butadiene block copolymer. The ultraviolet absorption is used in conjunction with the refractive index trace to give qualitative information that is much more informative than could be obtained with one detector. Calibration of the relative responses of the detectors to each of the components of the mixture is described, and these calibrations are used to calculate point-by-point composition, molecular weights, and molecular weight averages.     

GPC-messungen von polymeren an oberflächenmodifizierten silikagelen

The fractionation of homo- and copolymers by GPC-experiments was investigated, using surface modified silica gels as porous supports. Linear polystyrenes, poly-α-methyl-styrenes, and polybutadienes have been analysed. Methods are shown which consider the hydrodynamic broadening effects due to GPC. A computer program of PROVDER and ROSEN has been improved by a subsequentiteration method. With this program good results for molecular weightdistributionscould be obtained. “True” molecular weight averages and polydispersities have been measured with a recycle method of WATERS and with extrapolation by HAMIELEC. By comparison with results from sedimentation transport runs and ?-fractionations a good agreement has been achieved within the limits of error of these methods. The (α-methyl styrene methacrylonitrile)-copolymers have been analysed fortheir heter-ogeneity of chemical composition. These polymers show an unusual elution behaviour,and exhibit more chemical heterogeneity than is computed by kinetic data.     

Method for correcting molecular weight from gel-permeation chromatography. I. Skewing and concentration corrections

The purpose of this paper is to present a metod to calculate real molecular weight averages of polymer samples from GPC chromatograms where the instrumental spreading functions are skewed and the concentration effect exists. In this method, it is assumed that (1) the skewed chromatograms of monodisperse polymer samples can be represented as resultant of halves of two different Gaussians, (2) the resolution factors are regarded as constant in the case of low sample loading, and (3) the peak elution volume is independent of the presence of other components in the case of low sample loading. Adequate monodisperse polystyrenes and the mixtures (binary, seven and ten components) were examined for this purpose; and the molecular weight averages calculated by this method were compared with the ones obtained by Rosen and Provder's method. From the results in our study, it is found that this method can be available for correcting molecular weight from GPC chromatograms except for very narrow high molecular weight samples.     

Functionality distribution of hydroxyl-terminated polybutadienes using gel permeation chromatography. II. Measurements for commercial polymers

The functionality averages, functionality distribution, hydroxyl equivalent weight, molecular weight averages, and molecular weight distribution of three commercial hydroxyl terminated polybutadienes have been determined using a dual-detector GPC method used to analyze the polymers before and after derivatization with phenyl isocyanate. The values of these parameters are compared with existing literature data. The determined number-average functionalities were in reasonable agreement with previously published values. However, the distribution of functionality as a function of molecular weight differs from distribution data obtained by column fractionation techniques. Our distribution data appears to be generally consistent with the distribution expected from the polymerization mechanisms. The differences in the variation of hydroxyl content with molecular weight obtained from the dual-detector GPC method and the column fractionation procedures should be resolved since a combination of these procedures could provide additional information regarding the actual amounts of mono-, di-, and polyfunctional polymer and their molecular weight distributions. The dual-detector GPC method should be applicable for the determination of the distribution of a variety of functional groups provided a selective derivatization reaction is available or a second detector which can directly and accurately determine the concentration of the functional group is available.     

Dispersion in gel permeation chromatography. A rapid numerical solution to Tung's integral equation

A rapid iteration method has been developed to correct the molecular weight averages calculated from raw GPC data for dispersion. Though simple in its performance, it covers the general case that the instrumental spreading characteristics (Tung's resolution factor h) depend on the elution volume. Moreover, it is irrelevant whether the calibration curve, being the logarithmic plot of the molecular weight versus the elution volume, is linear or not. The method has been applied to a number of well-characterized polystyrene mixtures and yields molecular weight averages which agree with those predicted theoretically. The effect of asymmetry exerted by the dispersion on both molecular weight averages M?_n and M?_w is also discussed.     

聚合条件对P（AN-co—IA）分子质量分布影响的研究

采用凝胶色谱（GPC）法测定了丙烯腈与衣康酸共聚物P（AN—co—IA）的重均分子质量和数均分子质量,并通过已知聚丙烯腈的重均分子质量数据和数均分子质量数据对所测的分子质量进行校正,进一步计算得到共聚物的多分散系数。同时研究了引发剂用量、单体浓度、聚合温度、聚合时间对P（AN—co—IA）分子质量分布的影响。研究结果表明,P（AN-co-IA）分子质量分布随引发剂用量的增大、聚合单体浓度的增加而变宽,与聚合反应温度、聚合反应时间无明显的变化趋势。     

Synthesis and characterization of styrene‐butyl acrylate polymers,varying feed composition in a semicontinuous emulsion process

Two‐stage polymerization has been used to improve properties of two‐component polymers. In this work, a semicontinuous emulsion process varying feed composition along the reaction is used to produce copolymer chains of different composition as conversion proceeds. Polymer composition and evidence of branching were determined by ¹H‐NMR. Polymer molecular weight values determined by GPC are beyond the range where mechanical properties depend on molecular weight. Mechanodynamic properties show a copolymer type behavior with a synergistic effect around the 50/50 styrene/butyl acrylate composition ratio. For such composition, mechanical performance superiority of variable composition copolymer with respect to two‐stage polymer was confirmed with stress–strain tests carried out at several temperatures. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 3964–3971, 2007     

Synthesis and characterization of well-defined hydrophilic block copolymer brushes by aqueous ATRP

Homopolymer brushes of poly(N,N-dimethylacrylamide) (PDMA), poly(methoxyethylacrylamide) (PMEA) and poly(N-isopropylacrylamide)(PNIPAM) grown on atom transfer radical polymerization (ATRP) initiator functionalized latex particles were used as macroinitiators for the synthesis of PDMA-b-PNIPAM/PMEA, PMEA-b-PDMA/PNIPAM and PNIPAM-b-PDMA block copolymer brushes by surface initiated aqueous ATRP. The grafted homopolymer and block copolymer brushes were analyzed for molecular weight, molecular weight distribution, chain grafting density, composition and hydrodynamic thickness (HT) using gel permeation chromatography-multi-angle laser light scattering, ¹H NMR, particle size analysis and atomic force microscopy (AFM) techniques. The measured graft molecular weight increased following the second ATRP reaction in all cases, indicating the second block had been added. Chain growth depended on the nature of the monomer used for block copolymerization and its concentration. Unimodal distribution of polymer chains in GPC with non-overlap of molar mass-elution volume curves implied an efficient block copolymerization. This was supported by the increase in HT measured by particle size analysis, equilibrium thickness observed by AFM and the composition of the block copolymer layer by ¹H NMR analysis, both in situ and on cleaved chains in solution. ¹H NMR analysis of the grafted latex and cleaved polymers from the surface demonstrated that accurate determination of the copolymer composition by this method is possible without detaching polymer chains from surface. Block copolymer brushes obey the same power law dependence of HT on molecular weight as homopolymer brushes in good solvent conditions. The NIPAM-containing block copolymer brushes were sensitive to changes in the environment as shown by a decrease in HT with increase in the temperature of the medium.     

苯乙烯与N,N-二异丙基丙烯酰胺共聚物分散剂的合成及性能

以聚乙烯（Ｍ１）和Ｎ,Ｎ－二聚丙基丙烯酰胺（Ｍ２）为单体,在甲苯溶液中共聚制得一种新的反相悬浮分散剂,并用此分散剂制得具有较大粒径的高吸水性树脂。共聚物的组成由元素分析法和紫外光谱法测定,聚合物的分子量由ＧＰＣ测定。研究了多种因素对聚合物分子量、转化率及特性粘度的影响,并由此得出如下结论：共聚物分子量随引发剂用量的增大而下降,当共聚物的分子量为３万￣４万且Ｆ２〉１６％时,分散剂具有较好的稳定性且合     

Correction method for a concentration effect in the calculation of molecular weight averages from GPC chromatograms

In the calculation of molecular weight averages by GPC, the traditional method uses the calibration curve obtained at the same concentration as the samples, which results in a large degree of disagreement between molecular weight averages at several concentrations. Because of the concentration dependence of peak elution position in gel permeation chromatography of polymers, correct molecular weight averages cannot be obtained if calibration concentrations are the same as sample concentrations. A computation approach which uses calibration curves at finite and zero concentrations and can correct concentration effects is shown. The concentration used varied from 0.1% up to 0.4%. The elution chromatogram was divided into several parts, and concentration of species at each elution point was obtained from a concentration–peak height calibration curve. Molecular weight at the point was obtained from a molecular weight–elution volume calibration curve corresponding to a concentration of species at the point, and molecular weight averages were calculated by using the usual method. Nearly identical values for molecular weight averages could be obtained at different concentrations, and additional support for this approach is that these values for molecular weight averages were in fair agreement with NBS data.     

甲基丙烯酸甲酯-甲基丙烯酸三氟乙酯共聚物细乳液的合成及其表征

以甲基丙烯酸甲酯(MMA)和甲基丙烯酸三氟乙酯(TFEMA)为反应单体进行细乳液聚合,制得了MMA-co-TFEMA共聚物乳液。利用FTIR和GPC表征了共聚物的结构和分子量,采用激光光散射法及透射电镜对乳胶粒子的粒径大小及形貌进行了表征,并通过接触角法对共聚物膜的表面性能进行了研究。结果表明,与常规乳液相比,以细乳液方法制得的MMA-co-TFEMA共聚物乳液稳定性好,粒径分布窄,聚合物的分子量分布窄,并且共聚物膜随着氟含量的增加疏水疏油性增强,表面能降低。     

Calibration of GPC with polydisperse standards

An iteration method has been developed to prepare a calibration curve for gel permeation chromatography (GPC). It requires a number of samples of the same polymer which may have broad molecular weight distributions (MWD) of which two molecular weight averages must be known previously. The method has been applied to dextran standards with known M _w and M _n. Modifications involving the use of branched polymers are discussed.     

The Instrument Spreading Correction in GPC. I. The General Shape Function Using a Linear Calibration Curve

Abstract

A general shape function is proposed for describing the instrumental spreading behavior in gel permeation chromatography (GPC) columns due to axial dispersion and skewing effects. The general shape function contains statistical coefficients which describe the axial dispersion, skewing, and flattening of ideal monodisperse standards. A method denoted as the “method of molecular weight averages” is used to derive equations to correct GPC number- and weight-average molecular weights and intrinsic viscosities calculated from linear molecular weight calibration curves. The validity of these equations is experimentally verified with data for polystyrene, polybutadiene, and polyvinyl chloride polymers in tetrahydrofuran. The physical significance of the correction equations and their statistical coefficients is discussed in relation to the observed GPC chromatograms. Application of this shape function to the numerical Fourier analysis method for correcting differential molecular weight distribution (DMWD) curves is outlined. Also, a method is presented for obtaining corrected DMWD curves from a fitted molecular weight calibration curve corrected for instrument spreading by use of the hydrodynamic volume concept.     

Change of molecular weight distribution of statistical poly(styrene-co-acrylonitriles) with compositio of copolymer

Statistical poly(styrene-co-acrylonitrile) (SAN) copolymes with varying mole fractions of comonomer units have been synthesized in a batch reactor. The intrinsic viscosity and gel permeation chromatography (GPC) patterns of model copolymer samples were the basic experimental results. Chromatographic patterns of SAN copolymer samples were converted into molecular weight distributions and afterwards fitted to the theoretical distribution functions. The correlation between the composition of copolymers and the best fitted model distribution (Schulz's two parameters distribution in this case) was established. The treatment of data shows that parameter α is inversely proportional to the content of acrylonitrile units in the sample and indicates the molecular weight interval. Parameter b shows the invariability of the molecular weight distribution shape.     

Molecular Characterization of Styrene-Butadiene-Styrene Block Copolymers (SBS) by GPC, NMR, and FTIR

Summary This paper deals with the characterization of styrene-butadiene-styrene (SBS) block copolymers at molecular level through different techniques. SBS molecular weight distributions (MWD) were measured by Gel Permeation chromatography (GPC) in tetrahydrofuran (THF) solvent and using a calibration curve based on mono-dispersed polystyrene standards; afterwards, the relative molecular weights obtained by GPC were adjusted using a correction factor based on Mark-Houwink-Sakurada parameters for SBS in THF. Quantitative characterization of polybutadiene (PB) structures in SBS was made by solid-state ¹³C Nuclear Magnetic Resonance (NMR). A novel method using Fourier transform infrared spectroscopy (FTIR) has been developed for characterizing the SBS composition. This method covers the determination of composition in SBS ranging from 20 to 75 wt% of polybutadiene (PB) and was performed based on a FTIR calibration curve, which was prepared using mixtures of polystyrene (PS) and polybutadiene (PB) of known compositions.     

Simple and facile synthesis of aryl benzoates from stabilized arenediazonium tetrafluoroborate using a recyclable polymer-supported benzoate ion

Temperature-responsive P(NIPAM-co-HMAM)-b-PEO-b-P(NIPAM-co-HMAM) triblock copolymers were synthesized by an atomic transfer radical polymerization (ATRP) method without freeze?Cpump?Cthaw cycles. The composition, structure, and molecular weight of the synthesized block copolymer were characterized by ¹?H NMR and GPC. The phase transitions induced by temperature for different copolymers in dilute aqueous solutions have been studied using transmittance measurements, laser particle size measurements, viscosity analysis, and surface tension measurement, which showed that the HMAM content and the PEO (or PEG) chain length in the synthesized triblock copolymer affects the copolymer??s lower critical solution temperature (LCST). The micellization behavior of each temperature-responsive triblock copolymer was investigated by fluorescence probe measurements and transmission electron microscopy (TEM), which showed that the triblock copolymers form stable micelles above the LCST. The introduction of the HMAM component and the formation of micelles represent the first steps in the development of an injectable gel that forms in situ through chemical and physical crosslinking.     

Preparation and characterization of the molecular weight controllable poly(lactide-<Emphasis Type="Italic">co</Emphasis>-glycolide)

A series of poly(d,l-lactide-co-glycolide) (PLGA) polymers with various molecular weight were synthesized by a ring-opening polymerization method using stannous 2-ethyl hexanoate (Sn(Oct)₂) as the catalyst. The molecular weight of these polymers was controlled in a novel way, using t-butyldimethylsilanol (TBDS) or triphenylsilanol (TPS). The silicon-end group attached to the PLGA copolymer was removed at room temperature using either hydrochloric acid (HCl) or trifluoroacetic acid (TFA). The structures of these polymers before and after end group removal were characterized by ¹HNMR spectroscopy, while the molecular weight and polydispersity index (PDI) were determined by viscosity method and gel permeation chromatography (GPC). The residual amounts of stannum in PLGA and the glass transition temperature (T _g) of copolymer before and after end group removal were determined by the atomic absorption spectrum (AAS) and differential scanning calorimetry (DSC), respectively. The results showed that the removal method was effective. This study demonstrated that the molecular weight of PLGA could be easily controlled by altering the monomers/silanol molar ratio and the molecular weight and the purity of PLGA copolymer materials after silicon-end group removal could meet the demand of drug release.     

Styrene-butadiene branched star-shaped asphalt modifiers: Synthesis and mechanical characterization

Abstract

The synthesis and the corresponding characterization of styrene-butadiene (SB), branched, star-shaped copolymers was investigated as part of a research project on asphalt modification using polymers with precise molecular structures. The method of anionic polymerization was followed to prepare samples of block copolymers of SB, a synthesis method that controls chain-architecture, molecular weight distribution, monomer distribution, and the average molecular weight. The research studies are the synthesis of block copolymers including linear, three- and four-arms constructs, depending on the coupling agent used. The techniques of nuclear magnetic resonance (1NMR), differential scanning calorimetry (DSC), gel permeation chromatography (GPC), and rheology were carried out to characterize the copolymers. From the results of the 1NMR, DSC, and GPC analyses, all star-shaped copolymers investigated showed a similar block copolymer composition. Furthermore, the rheological behavior of one of the synthesized star-shaped copolymers was nearly the same as a four-branched commercial copolymer. Rheologically, the four-arm block copolymer sample had the largest storage modulus (G′) among the branched copolymers synthetized, indicating that such architecture produces a highly structured material. In regard to polymer-modified asphalt formulations, the three-branched copolymer architecture yielded better elastic behavior than the four-branch version. In summary, the findings of this investigation provide new insight about a polymer system that may offer advantages in industrial asphalt paving applications.