Characterization of Branched Poly (vinyl Acetate) by GPC and Low Angle Laser Light Scattering Photometry

Abstract

Poly (vinyl acetate), PVAC, synthesized by bulk polymerization over a range of initiator concentrations ([AIBN] = 10^?5 to 4 × 10^?3 g-mole/1), temperatures (50°C, 60°C, 70°C, and 80°C) and conversion levels (3 to > 90%) were characterized using low angle laser light scattering (LALLS) photometry to measure M_w of the whole polymers. A number of these samples were characterized using GPC with a differential refractive index (DRI) and LALLS detector to measure the molecular weight distribution (weight fraction versus M_w). M_w for PVAC samples synthesized at suitably low initiator levels at various conversions were found to agree with classical light scattering measurements after Graessley.

An electronic device and a technique which optimizes the sensitivity and the signal-to-noise ratio of the LALLS photometer throughout the molecular weight distribution (MWD) of the GPC chromatogram were devised. These considerably simplify the operation of the LALLS for both offline and online operation with GPC.

Most importantly it was unambiguously shown that the commonly used universal calibration parameter (UCP) with GPC, [n]M_w, is incorrect for polymers with molecules having the same hydrodynamic volume but different molecular weights, i. e., those with only chain branching (LCB), copolymers with compositional drift, and polymer blends. The correct UCP was found to     

GPC-LALLS研究各类顺丁橡胶的分子量分布

凝胶色谱与激光小角光散射(GPC-LALLS)联用是高聚物表征的有效手段,但将它用来研究橡胶的报导还很少见,这是由于实践中存在着一定的团难。对顺丁橡胶的表征国外曾有一些报导^[1-3]。GPC-LALLS法不仅可以测定试样的几种平均分子量,更有意义的是可以直接测得谱图各区间的分子量,而且溶质的分子量越大,散射光强越高,因此光散射法对大分子特别敏感,本工作利用这方法的特点,克服了技术上的困难,对国内外不同催化体系合成的顺丁胶进行了对比表征,得到了满意的结果。     

Characterization of Nylons by Gel Permeation Chromatography and Low Angle Laser Light Scattering in 2,2,2-Trifluoroethanol

Abstract

A GPC method was developed for the analysis of several commercial nylons in trifluoroethanol + 0.05M LiBr using a styrene-divinylbenzene column custom-packed by Jordi Associates.

A broad molecular weight standard method was developed by interfacing GPC with LALLS to give the absolute molecular weight for each data point or elution volume along the chromatographic peak from a nylon sample of known molecular weight. The integrity of the interface was verified by static LALLS measurements; no loss or adsorption of solute was found in the chromatographic system.

A strong ionic effect was observed for nylon samples and the method to alleviate it was described. The molecular weights and distribution of the following nylons were determined by this method: nylon 6, nylon 4,6, and nylon 6,6. Much higher than quoted molecular weights were obtained for nylons when polymethyl methacrylates and ethylene glycols were used as standards; this necessitated the use of this broad molecular weight method for column calibration. The ambient operating conditions offered several advantages over the conventional m-cresol solvent which required operation at higher than 100 C in order to reduce the viscosity, possessed a strong odor, and occasionally resulted in degradation of polyamides.     

Solution characterization of the novel organometallic polymer poly(ferrocenyldimethylsilane)

A series of four well‐defined poly(ferrocenyldimethylsilane) (PFS) samples spanning a molecular weight range of approximately 10,000–100,000 g mol⁻¹ was synthesized by the living anionic polymerization of dimethyl[1]silaferrocenophane initiated with n‐BuLi. The polymers possessed narrow polydispersities and were used to characterize the solution behavior of PFS in tetrahydrofuran (THF). The weight‐average molecular weights (M_w ) of the polymers were determined by low‐angle laser light scattering (LALLS), conventional gel permeation chromatography (GPC), and GPC equipped with a triple detector (refractive index, light scattering, and viscosity). The molecular weight calculated by conventional GPC, with polystyrene standards, underestimated the true value in comparison with LALLS and GPC with the triple detection system. The Mark–Houwink parameter a for PFS in THF was 0.62 (k = 2.5 × 10⁻⁴), which is indicative of fairly marginal polymer–solvent interactions. The scaling exponent between the radius of gyration and M_w was 0.54, also consistent with marginal polymer–solvent interactions for PFS in THF. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 3032–3041, 2000     

Size Exclusion Chromatography with Low Angle Laser Light Scattering Detection

Abstract

A review is given of the use of low angle laser light scattering (LALLS) detection in conjunction with size exclusion chromatography (SEC) to measure polymer molecular weight distributions without conventional SEC column calibration methods. A summary of light scattering theory is presented, and instrument configurations and principles of operation are described for two LALLS photometers. Also discussed are the overall performance of the SEC/LALLS technique and data from selected applications.     

Determination of persistence lengths and mark-houwink constants of aromatic polyesters from GPC-differential viscometric coupling

The introduction of lateral substituents and/or twisted biphenylylene units increase the solubility of aromatic para-linked polyesters. Two polyesters of this type of structure were characterized by gel permeation chromatography (GPC), low angle laser light scattering (LALLS) and viscometry. From the molecular weights and limiting viscosity numbers obtained by universal calibration and LALLS/viscometry the Mark-Houwink constants and persistence lengths were determined. The values of these parameters indicated that the polyesters can be described as wormlike chains in dilute solution.     

Size Exclusion Chromatography of Poly(vinylpyrrolidone)

Abstract

Poly(vinylpyrrolidone) and poly(ethylene oxide) separate by hydrodynamic volume on Toyo Soda TSK-PW columns in a mixed solvent mobile phase of 50:50 (v/v) MeOH/H₂O containing 0.1M LiNO₃. From this separation a single universal calibration curve based on hydrodynamic volume [η]M can be obtained. Accurate weight average molecular weights of PVP were obtained by both SEC/LALLS and universal calibration showing good agreement between the two methods. SEC/LALLS overestimates the number average molecular weight for broad distribution polymers due largely to the lack of sensitivity of the LALLS detector to the low molecular weight portion of the polymers, while the universal calibration method slightly underestimates the number average molecular weight as compared to osmometric values.     

Evaluation of a Commercial Differential Viscometer as a GPC Detector and Its Application to Polymer Characterization

Abstract

When used as a GPC detector, Viscotek's differential viscometer (DV) measures specific viscosities at each elution volume across the chromatogram. With the addition of a concentration detector, intrinsic viscosities may be calculated. As a result, true molecular weights can be calculated via the universal calibration method.

It was found that true molecular weights and branching analysis obtained using DV for acrylate polymers initiated by VAZO and benzoyl peroxide show excellent agreement with those from low angle laser light scattering (LALLS) measurement. Moreover, comparison of intrinsic viscosities for different polymers at the same molecular weights can be made from the DV technique. In general, linear polymers will have a higher IV than branches ones and the concept has been verified for acrylate polymers in this work.

A comparison between DV and LALLS in terms of capabilities, ease of use, and maintenance is also included.     

聚乙酸乙烯酯的溶液性质及长链支化度

用粘度法,GPC和LALLS测定了线型及不同转化率的PVAc分级级份的粘度与分子量。提出了以线型和支化聚合物的K,α计算临界分子量的方法。讨论了表征PVAc长链支化的各种参数与分子量和转化率之间的关系以及不同条件下迭代法计算的支化频率λ的差异。实验结果表明,特性粘数和数均分子量乘积所表示的流体力学体积更适合GPC的普适标定概念。     

Overloading and Degradation Study in GPC Using Low Angle Laser Light Scattering Detector (LALLS)

Abstract

The unique macromolecular compression effect or delayed GPC elution of high M.W. material was observed using the GPC + LALLS technique for a polystyrene standard of M.W. 5.0 E5. Further overloading which resulted in nonlinear fractionation is also described. The degradation of a 4.2 E6 standard after elution was detected by LALLS with calculated M.W. of 1.0-1.1 E6 but not by GPC, as indicated by normal GPC retention time and the shape of the chromatogram. This degradation was further verified by reinjection of the collected fractions into the GPC which showed a bimodal distribution with calculated M.W. of ca. 1.0 E6 via GPC calibration and LALLS. The source of degradation was attributed to the 2 micron exit frit in the single Jordi mixed bed column. Similar degradation of 2.3 E6 standard to same M.W. of ca. 1.0 E6 was also observed. The use of these standards as GPC calibrants should not be affected by this “post column” degradation.     

Effects of dextran polydispersity on red blood cell aggregation

B 512 F dextran fractions of different polydispersities were prepared by fractionnal precipitation and preparative elution chromatography. By combination of low angle laser light scattering (LALLS) and gel permeation chromatography (GPC), absolute average molecular weights (MWs) and molecular weight distribution functions (MWDs) were determined. Static and thermodynamical properties in terms of polymer dimensions and second virial coefficient of dilute solutions of dextran in water have been investigated. The results indicate that dextran macromolecules in water are rather compact and impenetrable coils. Measuring the disaggregation shear stress of dextran-induced red blood cell aggregates by laser light reflectometry, the macromolecular bridging energy was shown to depend upon dextran sample polydispersity. This reflects the weak and reversible character of red blood cell aggregation by dextran chains in physiological saline solution.     

Gel-permeation chromatography: X. Molecular weight detection by low-angle laser light scattering

Effluent from a gel-permeation chromatographic column has been simultaneously and continuously monitored with a differential refractometer and a low-angle laser light-scattering (LALLS) photometer. This provides a true and direct determination of molecular weight distribution rather than through a calibration method as obtained by conventional GPC techniques. Computer assisted data reduction provides a rapid determination of M?_w, M?_n, M?_z, M?_w/M?_n, as well as a plot of molecular weight distribution. Samples of very narrow molecular weight distribution (MWD) polystyrene from Pressure Chemicals Co. and relatively wide MWD samples of poly(methyl methacrylate) in chloroform have been characterized.     

Data Treatment in Aqueous GPC with On-Line Viscometer and Light Scattering Detectors

Abstract

Gel Permeation Chromatography (GPC) is becoming a very powerful tool for polymer characterization with the coupling of mass detectors using viscometry and light scattering techniques. The triple coupling seems to be the best way since the light scattering detector gives absolute molecular weights and viscometric detection provides intrinsic viscosity, leading to absolute molecular weights through universal calibration and information on long-chain branching. However, instrumentation becomes more sophisticated, expensive and, simultaneously, very sensitive to several parameters which are not critical in classical GPC. Moreover, an on-line computer is required for data acquisition and appropriate software for reliable interpretation of chromatograms.

Our experiments were performed with a Waters Associates room temperature instrument in which a home-made continuous viscometer, using pressure transducers, and a light scattering detector (LALLS Chromatix-CMX 100) were inserted on-line between the column set and the refractometer. Data were interpreted through personal software written on HP9836 and PC-AT computers.

We describe, here, the behavior of some polymers in aqueous solutions, mainly those that are commonly used as calibration standards (polyethylene oxides, pullulans). Experiments were run using two different sets of columns (‘Ultrahydrogel’ from Waters Associates and ‘Shodex OH-Pak’ from Showa Denko K.K.) in several aqueous solvents, pure water or water with various salts (LiNO₃, NaNO₃, LiCl, NaCl, Na₂SO₄) at different concentrations. Intrinsic viscosities were determined through viscometric detection and weight average molecular weights through the LALLS detector, leading to a plot of universal calibration curves Log([ηl.M) versus elution volumes.     

Size Exclusion Chromatography (SEC) of Complex Polymers - Generalized Analytical Corrections for Imperfect Resolution

Abstract

Herein is reported generalized analytical solutions which permit correction for imperfect resolution when the molecular weight calibration curve is nonlinear and the variance of single-species chromatograms changes significantly with molecular size of the polymer solute. Two kinds of generalized analytical solutions have been obtained. One is a solution of Tung's integral equation for the corrected chromatogram or the molecular weight distribution and the other is a solution for the corrected molecular weight averages of the whole polymer. Also discussed is the use of local corrections for imperfect resolution across the chromatogram with detectors such as the low angle laser light scattering spectrophotometer (LALLS) when used with micro and macropackings.     

Light scattering detection in aqueous high-performance gel permeation chromatography (HPGPC): Relative molecular mass distribution of eye lens proteins

Summary Light scattering techniques have been greatly improved since laser light sources, enabling dynamic light scattering and measurements at low angles have been available. Relative molecular mass determinations can be performed at low solute concentration, extrapolations to zero-angle are no longer required and, because of the low scattering volume, a flow-through cell construction has become possible where dust particles only interfere as spikes [1]. For HPLC detection the low-angle laser light scattering (LALLS) signal corresponds to the product of relative molecular mass and concentration; combination with a concentration detector (for example, differential refractometer, UV absorbance) enables calculation of relative molecular mass [2]. The sensitivities of LALLS and the usual concentration detectors are comparable for (bio)polymers with relative molecular masses near 100,000. The minimum relative molecular mass to be determined in this way is near 10,000 and, therefore, the only mode of HPLC using the LALLS detector to date is gel permeation (size exclusion) chromatography.     

Synthesis and solution properties of star‐shaped poly(tert‐butyl acrylate)

A series of star polymers consisting of poly(tert‐butyl acrylate) arms and an ethyleneglycol dimethacrylate (EGDMA) microgel core were synthesized using anionic polymerization. The effect of various parameters (precursor length, ratio [[EGDMA]/[Initiator], reaction time, and overall concentrations) on the average number of arms was investigated. Molecular weights were determined using GPC coupled with an online viscometer and MALLS. The exponents for the relation between intrinsic viscosity or radius of gyration and molecular weight, respectively, are extremely low, indicating that the dimensions of the star polymers only slightly increase with the number of arms. After a certain number of arms is reached the intrinsic viscosity even decreases with molecular weight. Computer simulations for star polymers were carried out where the radius of gyration was calculated as a function of the number of arms. The results are in good agreement with the experimental data.     

A study of aqueous solutions of dextrans by gel permeation chromatography using a multiple detection system

We studied the elution of dextrans in gel permeation chromatography (GPC) using a low-angle laser light-scattering (LALLS) system to monitor the molecular weight and the standard refractive index (RI) detector to measure the concentration. In pure water the dextrans show bimodal chromatograms of the RI response as well as of the LALLS response. The first eluted peak reflects the macroion exclusion due to the repulsion between negatively charged macromolecules and equally charged gel. In spite of the resulting distortion of the chromatograms, correct values of the weight-average molecular weights (M?_w) are obtained from them. If instead of pure water a salt solution (0.1 M KNO₃) is used as eluant, the charge effect is completely suppressed and single-peak chromatograms are found. Again correct values of M?_w are obtained, but number-average molecular weights turn out to be too large owing to axial column dispersion in the coupling arrangement. By introducing a spreading factor, values of M?_n could be corrected. Investigations of the charge effect were also carried out by monitoring the electric conductivity of the eluted dextran zone. In this way, the phenomenon of ion inclusion, evidently provoked by charged dextran molecules, was observed.     

Synthesis and Characterization of Monodisperse α,ω-Divinylpolydimethylsiloxane and ω-Vinylpolydimethylsiloxane

Abstract

ω-Vinylpolydimethylsiloxanes (ω-PDMS) and α,ω-divynilpolydimethylsiloxanes (α,ω-PDMS) have been synthesized by anionic polymerization of hexamethylcyclotrisiloxane (D3). The reactions were carried out in n-hexane and tetrahydrofuran (THF), respectively. The initiator was n-butyl-lithium (n-BuLi); tetrahydrofuran was used as an electron donor compound to promote the polymerization of D3. The synthesized polymers have been characterized by infrared (FTIR), proton nuclear magnetic resonance spectroscopy (NMR), light scattering (LALLS), and gel permeation chromatography (GPC). Molecular weights ranging from 20,000 to 100,000 were obtained with relatively narrow molecular weight distributions; Mw/Mn < 1.25.     

Study on the determination of the molecular weight of polyethylene with ultrahigh temperature GPC

Ultrahigh or high molecular weights of polyethylenes (PE) and their distributions are for the first time determined at 160° or 170°C by gel permeation chromatography (GPC). The thermostability of PE at high temperatures is discussed. In order to calculate the real molecular weight of PE, a new calibration curve is established. For PE with high molecular weight more reliable and accurate results can be obtained by GPC measurements at these temperatures. The application of ultrahigh temperature GPC for polymer characterization is demonstrated in this paper.