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     

Characterization of Nonionic Polyacrylamides by Aqueous Size Exclusion Chromatography Using a DRI/LALLSP Detector System

Abstract

Herein is reported an experimental investigation of the molecular weight characterization of nonionic polyacrylamides by aqueous SEC with a DRI/LALLSP detector system. Methodology for the use of the DRI/LALLSP detector responses to determine the molecular weight calibration curve and the peak broadening parameter, [sgrave]² (variance of a Gaussian instrumental spreading function) over a wide molecular weight range has been developed. The method is based on the use of a broad MWD standard made by blending Polysciences broad MWD standards and a generalized analytical solution of Tung's integral equation for the detector response corrected for peak broadening. Molecular weight averages measured by SEC/DRI/LALLSP are in excellent agreement with those measured offline by LALLSP.     

Anomalous density and refractive index variation of a nematic liquid crystal

Abstract

This paper reports the results of the measurement of refractive indices and densities of p-ethoxyphenyl trans-4-butyl cyclohexane carboxylate at different temperatures. The molecular polarizabilities have been calculated from refractive indices using Vuks' formula and orientational order parameters are determined from the polarizability values. The order parameter values have been compared with those obtained from Maier-Saupe theory. The compound shows anomalous behaviour regarding variation of density, ordinary refractive index and order parameter values with temperature. This is consistent with our previous X-ray study of this compound. The possible reason for this peculiar behaviour has been discussed.     

Linearization of evaporative light scattering detector signal

Recent advances in nebulizer technology of the evaporative light scattering detector (ELSD) allow the evaporation of trichlorobenzene (TCB) at much lower temperatures than the previous instruments, thus avoiding the sample loss in the lower molecular weight domain. Therefore, the new ELSD opens the possibility to correctly evaluate the molecular weight distribution (MWD) of polymers by gel permeation chromatography, after linearizing the ELSD signal intensity in function of concentration. To find the correct exponent parameter for linearization, it is necessary to take into account not only the peak area, but each point of the chromatogram. The evaluation method for this exponent parameter, found to be 1.61 for the analysis in TCB of polyolefin and polystyrene samples, is presented in this study. This value was verified by the excellent correlation found between the obtained MWD of a high-density polyethylene both with the ELSD and with the traditional differential refractive index detector.     

Synthesis and Characterization of Star Polymer with Comb-like Poly(lauryl methacrylate) Arms by Atom Transfer Radical Polymerization via One-pot ‘Arm-First’ Method

Atom transfer radical polymerization (ATRP) was used to prepare core crosslinked star polymers with comb-like poly (lauryl methacrylate) (LMA) arms by one-pot “arm-first” method, involving the synthesis of comb-like PLMA arms, followed by their crosslinking, using a mixture of LMA monomer and ethylene glycol dimethacrylate (EGDMA) crosslinker. By adjusting the feeding time and level of EGDMA, a series of star-like polymers with various comb-like arms length and number can be obtained. The molecular architecture including radius of gyration (Rg), hydrodynamic radius (Rh) and intrinsic viscosity (η_i) etc. were characterized by a triple-detector gel permeation chromatography (GPC) equipped with a refractive index detector, viscometer detector and a multi-angle static laser light scattering (MALLS) detector. The thermal property and shearing stability of these star-like polymers were also investigated.     

Controlling the evolution of polypropylene microstructure during melt free radical modification using zinc dithiocarbamate with different N-substituted groups

The effects of zinc dithiocarbamates on degradation and branching of polypropylene (PP) were studied during melt radical modification using a tri-functional monomer (trimethylol propane triacrylate (TMPTA)). High-temperature size-exclusion chromatography (HT-SEC) coupled with differential refractive index detector (DRI), light scattering detector (LSD) and viscometer detector (VD) and rotational rheometry were used to analyse the microstructure of modified PP samples. The chemical structure of the N-substituted group showed an important influence in controlling the evolution of PP microstructure during melt radical reaction. The chain cleavage of PP was controlled in the presence of zinc N, N-dimethyldithiocarbamate (ZDMC), and a substantial long chain branched (LCB) fraction was formed. Without co-agent, the molecular weight of PP decreased measurably, and only a minor LCB fraction was formed. Importantly, considerable amounts of highly branched (microgel and hyperbranched) structures were formed in this case.     

The High Performance Liquid Chromatography and Detection of Phospholipids and Triglycerides. III. Response of the Differential Refractive Index and Ultraviolet Absorption Detector

Abstract

A liquid chromatographic differential refractive index detector (RI) and an ultraviolet absorption (at 195 nm) detector (UV) were studied for detection of triglyceride (TG) and phospholipid (PL) molecular species. It was found that the log UV/RI detector response ratio was linearly related to the log of the number of conjugated double bonds (degree of unsaturation) of the lipid in a predictable fashion, indicating the usefulness of the combination of both detectors in TG and PL analysis. The detection limit of the RI detector for TG and PL was found to be 5 × 10 ^?7 M or as sensitive as the UV detector for saturated TG and PL.     

On-Stream HPLC Determination of Residual Ethylene Oxide and Propylene Oxide in Glycerol Based Polyol Synthesis

Abstract

A simple automated HPLC scheme was developed to monitor synthetic polymerization reaction on-stream. Chromatographic conditions that affect the separation of the reaction species from the reaction product and base catalyst using high-performance aqueous gel permeation chromatography were also studied. Reactor samples are automatically drawn from the reaction vessel through a micro-loop sampling valve/actuator assembly and transferred to the chromatographic system via stainless steel tubing without interruption of the mobile phase flow. The resulting chromatograms, monitored by a refractive index detector, of reactants and products are continuously measured at intervals during the reaction automatically and unattended. Application of this system for the reaction of propylene oxide and ethylene oxide to high molecular weight polyols is presented.     

Characterization of polysaccharide solutions by means of chromatography-multidetection

Size exclusion chromatography (SEC) combined with double detection, utilizing a differential refractive index (DRI)- and a low angle laser light scattering (LALLS) - detector represents a powerful experimental set-up in the field of chromatography-multidetection (C-MD). By means of these techniques high-quality information for profound polymer characterization is provided in a fast and semi-automatical (autosampler/PC-controlled) way. Molecular characteristics such as molecular weight distributions, molecular weight averages, tendencies for intermolecular interactions, can be obtained by these techniques. Successful handling of data from C-MD-techniques within reasonable time ranges requires adequate hardware and software. This is especially true if advanced data processing is applied, e.g. to yield polymer particle size/shape characteristics in terms of Staudinger/Mark/Houwink constants (K,a), distributions of sphere equivalent particle radii (R_cD)-, sphere equivalent mass density of solved polymer coils (ρ_cD)- and intrinsic viscosity ([η]D). For aqueous solutions of polysaccharide samples (waxy maize starch hydrolyzate, hydroxyethyl-amylopectin from waxy maize hydrolyzate, dextran) data from SEC-DRI/LALLS and universal calibration experiments are utilized for a comprehensive physico-chemical characterization of these polymers.     

Assessment of ethanol and acetonitrile in 18F-FDG preparations by means of liquid chromatography

Introduction Acetonitrile (ACN) and ethanol (EtOH) are common solvents used in radiopharmaceutical production. In accordance to official compendia, the concentration of these solvents should be assessed by gas chromatography. In the present paper, an optimized method, based on Koziorowski (2010), is validated. Methods ACN and EtOH concentrations and retention times (Rt) were obtained by a HPLC system equipped with a refractive index detector (RID), an ion exclusion column and ultrapure water as mobile phase. The methodology was validated following the ICH Q2(R1) requirements. Results The solvents EtOH and ACN were eluted at 23.22 and 26.32 minutes, respectively, with a final run time of 30 minutes. The validation parameters (accuracy, precision, linearity, specificity, robustness, detection and quantification limits) were obtained. Conclusions A reproducible HPLC method for the quantification of residual solvents in preparations of 2-deoxy-2-[fluorine-18]fluoro-D-glucose (¹⁸F-FDG) was described and validated. The method was precise, accurate, selective, robust and linear over a wide range. In addition, this method showed a high sensitivity, with limits of detection and quantitation comparable to the usual methods by gas chromatography.     

An Analysis of Imperfect Resolution in the Chromatography of Particle Suspensions

Abstract

Here-in is reported a general method of correction for imperfect resolution in the chromatography of particle suspensions. It overcomes most of the limitations of previously reported methods. A non-linear particle diameter - retention volume calibration curve and a generalised spreading function are considered. Moment equations are developed for two types of general detectors; the first type includes a refractive index detector and a turbidity detector with Rayleigh scattering while the second type includes a tubidity detector with Mie scattering. The moment equations were applied to the analysis of chromatograms of narrow Dow polystyrene latices measured by size exclusion chromatography.     

Polyolefin characterization in dibutoxymethane by high temperature gel permeation chromatography with a new evaporative light scattering detector

A new evaporative light scattering detector (ELSD) for the analysis of polyolefins by high temperature gel permeation chromatography (GPC) was recently introduced by Agilent Technologies. For the first time, we investigated the possibility to use this detector to measure the molecular weight distributions (MWD) of different types of polyolefins (polypropylene, linear and low-density polyethylene) in dibutoxymethane (DBM, butylal). These samples were previously characterized by GPC in trichlorobenzene (TCB) with a differential refractive index (DRI) detector in an interlaboratory study conducted by the International Union of Pure and Applied Chemistry (IUPAC) [1], and in a recent publication by GPC with the new ELSD in TCB [2]. The signal to noise of ELSD using DBM is about 10 times lower than that for TCB. However, the ELSD signal power exponent for DBM was measured as 1.35, which is much closer to unity than the value of 1.61 for TCB. After applying the required corrections to linearize the response of the ELSD signal as a function of concentration, similar average molecular weights to those measured in the interlaboratory study using DRI, were obtained for the analyzed resins.     

Semipreparative High-Pressure Liquid Chromatography of Synthetic Carbohydrates

Abstract

A rapid and effective method has been developed for the purification of hundred-milligram quantities of water-soluble synthetic carbohydrates. The method utilizes a 30 cm x 7.8 mm i.d. column packed with Waters Associates carbohydrate analysis packing in conjunction with isocratic water-acetonitrile elution and refractive index detection. The generality of this method is illustrated by its application to 13 sucrose derivatives and one derivative each of D-fructose and α,α-trehalose.     

Determination of molecular weight of polyethylene glycol using size-exclusion chromatography with multi-angle laser light scattering and acid–base titration

Size-exclusion chromatography with multi-angle laser light scattering (SEC-MALLS) and acid–base titration were used to determine the molecular weight of a polyethylene glycol with low molecular weight. All potential uncertainty factors for each measurement were evaluated using cause-effect diagrams. Weight analysis was applied to harmonize the two different measurement results. It was found that the main uncertainty sources of SEC-MALLS measurement arose from the dn/dc value, the calibration constant of the differential refractive index (DRI) detector, and the intermediate precision of the instrument, while the sample mass, the titration volume and the concentration of titrant contributed to the uncertainty of titration measurement. The weighted mean value of the two measurement results was taken as the molecular weight of the polyethylene glycol.     

Effect of dopant structure on refractive index and glass transition temperature of polymeric fiber‐optic materials

Graded‐index plastic optical fibers, composed of doped polymers, have advantages over conventional glass optical fibers, but need to be developed further for practical application. Here, a variety of aromatic sulfide dopants were synthesized, and their effects on the refractive indexes and glass transition temperatures (T_g) of poly(methyl methacrylate) and methyl 2‐chloroacrylate/2,2,2‐trichloroethyl methacrylate copolymers were studied. While polymers containing large dopants exhibited relatively high refractive indices, their T_g values were low, making these materials unsuitable for graded‐index plastic optical fiber applications. Six dopants yielded polymers that exhibited higher T_g values than the conventionally used (diphenyl sulfide)‐doped polymer. The dopant dibenzothiophene, in particular, yielded polymers with the highest refractive indexes and T_g values, and polymers containing (phenylthio)benzene dopants also performed well. Copyright © 2013 John Wiley & Sons, Ltd.     

High Refractive Index Polymers

Rodlike polymers with repeat units composed of groups with high π-electron density directly on the backbone, such as linearly conjugated double bonds and aromatic heterocyclic rings, exhibit high isotropic refractive indexes and high birefringence values when oriented. Typical polyamide birefringence values for oriented films far exceed 0.5 and several are as high as 0.85; the corresponding parallel and perpendicular indexes for these polymers are in the 2.2-2.4 and 1.5-1.7 range, respectively, depending on the molecular structure and degree of orientation. The isotropic index values may be as high as 1.8-2.0.

In order to make optical devices utilizing these highly birefringent films, it is frequently necessary to bond them to films or glass, which necessitates the use of index-matching, optical-quality bonding agents. We devised two synthetic strategies to obtain polymers that exhibit these properties. In one approach, we synthesized a series of colorless, nonbirefringent, polyacrylates (and methacry-lates) containing halogenated carbazole rings; these results will be reported in a forthcoming paper that is currently being prepared. We have also modified rodlike polyamides by substituting index-enhancing groups directly on the amide nitrogen; the refractive index values of the resulting materials are in the 1.60-1.67 range. The most important finding of the latter research was the realization that rodlike polyamides not only exhibit unusually high birefringence, but also greatly enhanced isotropic refractive indexes, which is directly related to their rodlike conformation.     

Determination of Compositional Heterogeneity of Polyamide Copolymers

Abstract

A gel permeation chromatograph equipped with dual detectors provides very useful information on compositional and molecular weight distributions. One copolymer composed of nylon 12 and polytetramethylene ether glycol, and the other of nylon 6 and natural rubber were discussed in this study. By trifluoroacetylation of the amide group, these polymers became soluble in common solvents such as dichlcromethane and tetrachloroethane. Good chromatograms were obtained using these solvents for the above copolymers. At the same time, the compositional heterogeneity was determined from the chromatograms obtained with refractive index and ultraviolet detectors.     

New evaporative light scattering detector for high temperature gel permeation chromatography

A new evaporative light scattering detector (ELSD) for the analysis of polyolefins by high temperature gel permeation chromatography (GPC) was recently introduced by Agilent Technologies. For the first time, we investigated the possibility to use this detector to measure the molecular weight distributions (MWD) of different type of polyolefines (polypropylene, linear, and low-density polyethylene). These samples were previously characterized by GPC with a differential refractive index (DRI) detector by several companies, in an interlaboratory study conducted by International Union of Pure and Applied Chemistry.^[1 Luruli, N. 2010. PHASE 1: IUPAC SEC/GPC Round Robin Project Report: Repeatability and Reproducibility of Sample Preparation and Analysis in High-Temperature SEC, http://media.iupac.org/projects/2005/2005-011-3-400_rpt-phase1_110510.pdf [Google Scholar]^] The excellent baseline stability of ELSD as compared with DRI was reflected in a better reproducibility of the measured average molecular weights. More importantly, after applying required corrections to linearize the response of the ELSD as a function of concentration, we obtained similar results as previously obtained with DRI for the MWD of analyzed resins, covering typical applications of polyolefins.     

Preparation of 3‐arm star polymers (A3) via Diels–Alder click reaction

Diels–Alder click reaction was successfully applied for the preparation of 3‐arm star polymers (A₃) using furan protected maleimide end‐functionalized polymers and trianthracene functional linking agent (2) at reflux temperature of toluene for 48 h. Well‐defined furan protected maleimide end‐functionalized polymers, poly (ethylene glycol), poly(methyl methacrylate), and poly(tert‐butyl acrylate) were obtained by esterification or atom transfer radical polymerization. Obtained star polymers were characterized via NMR and GPC (refractive index and triple detector detection). Splitting of GPC traces of the resulting polymer mixture notably displayed that Diels–Alder click reaction was a versatile and a reliable route for the preparation of A₃ star polymer. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 302–313, 2008