Mark Houwink Sakurada Parameters Research Articles

Thickening Castor Oil with a Lignin-Enriched Fraction from Sugarcane Bagasse Waste via Epoxidation: A Rheological and Hydrodynamic Approach

Thickening vegetable oils to different extents is of great interest in the design and development of new bio-based lubricant formulations, as achieving a wide range of rheological properties is crucial to the successful replacement of petroleum-based traditional counterparts. With this aim, the influence of epoxidation degree, modified by altering the reaction conditions, on the viscous flow properties of epoxidized castor oil was investigated together with the incorporation of a lignin-enriched fraction from sugarcane bagasse waste to more extensively modify the rheological properties, thereby valorizing this waste fraction. Oil thickening was achieved by promoting the cross-linking between the epoxidized oil and the lignin-enriched fraction that enables the compatibilization of both components. Castor oil epoxidation was assessed by means of standard volumetric titration methods and infrared spectroscopy. In addition, a fully rheological characterization of both epoxidized and lignin-thickened castor oils was carried out. A hydrodynamic approach was also followed, aiming to provide an estimation of the Mark–Houwink–Sakurada parameters and relate the intrinsic viscosity with the average molecular weight of the resulting epoxidized castor oil/lignocellulose macromolecular compounds. The chemical interaction between castor oil and the lignocellulosic material increased as the extent of epoxidation was increased, yielding a variety of rheological responses from Newtonian liquids of increasing viscosities (from around 1 to 500 Pa·s) to viscoelastic liquids.

Universal calibration of gel permeation chromatography using evaporative light scattering detector coupled with viscometer

The linearized evaporative light scattering detector (ELSD) allows the evaluation of molecular weight distributions (MWD) of a range of polymers using conventional gel permeation chromatography (GPC), and is a suitable replacement for the differential refractive index (DRI) detector in applications which will benefit from fast equilibration, solvent gradients or when working with low polymer concentrations. Further, when DRI is coupled with a viscometer, the Universal Calibration GPC method also allows the evaluation of Mark–Houwink–Sakurada parameters K and alpha, which provides valuable information on the chemical structure of polymer chains. Therefore, for a wider acceptance of ELSD in GPC, we investigated the possibility of coupling the ELSD with the viscometer. Recommendations are provided for successfully coupling the ELSD and viscometer, as well as on software adjustments to calculate K and alpha parameters. For linear polyethylene, a good correlation was found between the measured and the expected K and alpha values.

Characterization of chain dimensions of poly(ε-caprolactone) diols in THF by size-exclusion chromatography coupled with multi-angle light scattering (SEC-MALS)

In this work, we studied the chain dimensions, shape, and thermodynamic characteristics of poly(e-caprolactone) diols (HO-PCL-OH) in solution. PCL diol samples of different molecular weights and architectures were synthesized using immobilized Yarrowia lipolytica lipase as catalyst. Gel permeation chromatography (GPC) with online right-angle laser-light scattering (RALLS), differential viscometer (DV), and interferometric refractometer IRS detectors offered a proper way to obtain information on thermodynamic characteristics and chain flexibility. The weight-average molecular weights of the PCL diol samples (M w ) ranged from 2,750 to 13,120 uma. The z-average radius of hydrodynamic volume (<R h 2 > z 1/2 ) vs. z-average molecular weight curve (M z ) could be satisfactorily fitted to a power-law equation. Mark–Houwink–Sakurada parameters (K = 2.74 × 10−3 dL/g and a = 0.64) were derived from the plots of [η] w against M w . The overall results clearly suggest that a flexible geometry is present in tetrahydrofuran (THF) solution of PCL at 33 °C. Unlike other PCL systems, PCL diols are more hydrophilic and expected to form associated species. They behave differently from common hydrophobic polymers and do not strictly conform to thermodynamic relationships generally used in Polymer Science. A more compact geometry is present for Mn lower than 4,000 Da. For higher molecular weights, the chain expands and become more elongated. Plots of ln [η] w against ln M w (MHS equation) and of log R hz against log M z suggest that PCL diols behave as flexible chains in a good solvent.

A re-investigation of the Mark–Houwink–Sakurada parameters for cellulose in Cuen: A study based on size-exclusion chromatography combined with multi-angle light scattering and viscometry

The MHS parameters for cellulose in Cuen (0.5M) were calculated by determining the weight (DPw), number (DPn), and the viscosity average (DPv) of partially hydrolysed celluloses using SEC-MALLS in DMAc containing 0.5% LiCl, combined with intrinsic viscosity measurements in Cuen. The modified MHS equation is: η=2.45DPv0.70=0.070Mv0.70. Application of the equation provides the true viscosity average DP (DPv) for any type of distribution. In contrast, the apparent ‘DPv’ referred to in standard methods (ASTM, SCAN) is an undefined type of average DP which depends on the chain length distribution, and may differ considerably from both DPv and DPw. The DP values obtained by SEC-MALLS depend on the quality of the data, in particular the specific refractive index increment at constant chemical potential (dn/dc)μ, which was found to be 0.117ml/g (at λ0=633nm). Further analysis of the SEC-MALLS and viscometry data in terms of the wormlike chain model provided estimates of the persistence length, obtaining 4.7nm in Cuen and 8.2nm in 0.5% DMAc/LiCl, illustrating the more expanded structure in the latter solvent.

Using apparent molecular weight from SEC in controlled/living polymerization and kinetics of polymerization

AbstractApparent molecular weights from size exclusion chromatography, that is molecular weights relative to standards of a nature different to that of the polymer sample being studied, are frequently used. We use calculations corresponding to realistic cases to provide guidelines for situations when, and to what extent, apparent molecular weights (MWs) can be meaningful. In controlled polymerization, we show how, without due care, use of apparent MW, could lead to the incorrect conclusion that the reaction was not controlled, whereas the true MWs would be close to theoretical values. We show here that the quality of the eluent as a solvent for the standard and the polymer sample is a good indication of the accuracy and the significance of the apparent polydispersity index. Accurate Mark–Houwink–Sakurada parameters are of limited availability, but the data about solvent quality available in handbooks or available from static light scattering measurements. Apparent Mn is of no use in controlled polymerization if simple simulations as performed in this work do not validate their use. The determination of transfer constants by the Mayo plot can be performed using apparent Mn without introducing any significant error, contrary to apparent weight‐average molecular weight Mw or apparent ln number distribution. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 897–911, 2008

Guar gum methyl ethers. Part I. Synthesis and macromolecular characterization

Guar gum (GG) has been partially methyl-etherified under heterogeneous reaction conditions. The resulting products, (methyl ether guar: MG) with different degrees of substitution, have been characterized by means of viscosity, 1H NMR, and FTIR measurements. The introduction of methoxyl groups along the polysaccharidic chains reduces the hydrogen bonding sites on the guar backbone reducing primarely the extent of hydrogen bonding between guar macromolecules, hence their aggregation tendency. A comparative analysis of Mark–Houwink–Sakurada parameters and of the characteristic ratio ( C ∞) of GG and MG samples in aqueous solution has been carried out using the Burchard–Stockmayer–Fixman method for flexible and semiflexible chains. The MG chains exhibit more flexibility than those of native guar gum which is traceable to a disruption of intrachain hydrogen bonds.

Controlled radical polymerization of a trialkylsilyl methacrylate by reversible addition–fragmentation chain transfer polymerization

AbstractThe reversible addition–fragmentation chain transfer (RAFT) polymerization of a hydrolyzable monomer (tert‐butyldimethylsilyl methacrylate) with cumyl dithiobenzoate and 2‐cyanoprop‐2‐yl dithiobenzoate as chain‐transfer agents was studied in toluene solutions at 70 °C. The resulting homopolymers had low polydispersity (polydispersity index &lt; 1.3) up to 96% monomer conversion with molecular weights at high conversions close to the theoretical prediction. The profiles of the number‐average molecular weight versus the conversion revealed controlled polymerization features with chain‐transfer constants expected between 1.0 and 10. A series of poly(tert‐butyldimethylsilyl methacrylate)s were synthesized over the molecular weight range of 1.0 × 104 to 3.0 × 104, as determined by size exclusion chromatography. As strong differences of hydrodynamic volumes in tetrahydrofuran between poly(methyl methacrylate), polystyrene standards, and poly(tert‐butyldimethylsilyl methacrylate) were observed, true molecular weights were obtained from a light scattering detector equipped in a triple‐detector size exclusion chromatograph. The Mark–Houwink–Sakurada parameters for poly(tert‐butyldimethylsilyl methacrylate) were assessed to obtain directly true molecular weight values from size exclusion chromatography with universal calibration. In addition, a RAFT agent efficiency above 94% was confirmed at high conversions by both light scattering detection and 1H NMR spectroscopy. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 5680–5689, 2005

Comparative studies on solution characteristics of mannuronan epimerized by C-5 epimerases

Both dilute and concentrated solutions of bacterial Mannuronan (MANNA) and its epimerized products by AlgE1 at 5 and 24 h, named MANNAEp1t5h and MANNAEp1t24h, respectively, and AlgE4 (MANNAEp4) have been studied as a function of variables such as polymer concentration and ionic strength (NaCl) in order to investigate the macromolecular solution properties of these innovative polyuronic acids having the same charge density but different composition and sequence of β- d-mannuronic acid (-M-), α- l-guluronic acid (-G-) or MG-blocks. Measurements of intrinsic viscosity [ η] as a function of ionic strength, I, by capillary viscometry has led to an estimate of the Smidsrød-Haug parameter B, an index useful to characterize the stiffness of polymeric chains. The results are largely consistent with much of the published data relative to chain extension and conformational freedom around the torsional angles of the glycosidic linkages occurring in alginates. Steady shear rheometry provided information about the coil-overlapping parameter c*, which marks the transition from dilute to concentrated solution. The slopes of the double logarithmic plots of η sp vs. c[ η] both at low and high degrees of coil overlap suggest that all samples solutions behave like linear polymer entangled network systems. The value of c* is strictly influenced by the stiffness of the chains, and hence by the primary structure. Dynamic shear rheometry shows that the frequency dependence of dynamic viscosity is only partially superimposable to the shear rate dependence of viscosity. Such behaviour may be ascribed to the presence of semiflexible polymeric coils in a non-totally destructured entangled state. By solvent/non-solvent (H 2O/isopropanol) fractionation carried out on mannuronan, a set of samples with different average molecular weights and narrow polydispersities were obtained. Triple detection GPC allowed the evalutation of the Mark–Houwink–Sakurada parameters as well as of the characteristic ratio C ∞ for one of the fractionated MANNA samples. The chain persistence length was estimated by the wormlike chain model.

Matrix-assisted laser desorption/ionization (MALDI) mass spectrometry: determining Mark–Houwink–Sakurada parameters and analyzing the breadth of polymer molecular weight distributions

Polystyrene, poly(methyl methacrylate), and poly(ethylene glycol) standards were characterized via matrix-assisted laser desorption/ionization (MALDI) mass spectrometry. This study develops two new contributions to the rapidly growing body of data appearing in recent literature. First, MALDI was found to be an optimum absolute molecular weight technique accompanying viscosity measurements for determining Mark–Houwink–Sakurada parameters. Second, since MALDI provides the mass spectra of polymer molecules without fragmentation, a new method of describing the breadth of the distribution of polymer standards is presented. The ratio of the distribution breadth at half-height to the molecular weight of the monomer unit, polymer spread, is shown to more clearly represent the molecular weight distribution than the customary ratio, Mw/Mn.

Anionic polymerization of octamethylcyclotetrasiloxane in miniemulsion II. Molar mass analyses and mechanism scheme

Hydroxyl α,ω-functionalized polydimethylsiloxane (PDMS) standards have been synthesized by ring-opening anionic polymerization of octamethylcyclotetrasiloxane (D4)11The notation for the siloxane oligomers throughout the paper is the following: M holds for (CH3)3SiO1/2–, Mv for CH2CHSi(CH3)2O1/2–, MOH for HOSi(CH3)2O1/2– and D for –Si(CH3)2O–. in miniemulsion. Their absolute molar masses as well as Mark–Houwink–Sakurada parameters were then estimated in toluene at 30°C by triple detection size exclusion chromatography (SEC3). MALDI-TOF confirmed the SEC3 results in addition to providing several clues on chain microstructure and evidence of redistribution reactions. Trimethyl and vinyl α,ω-terminated PDMS oligomers were similarly synthesized in miniemulsion in the presence of functional transfer agents and used together with small dihydroxylated PDMS standards to compare the effect of substituents on the SEC calibration curve. Precise measurement of average molecular weights showed that the existing kinetics model could not account solely for mass control below 70% conversion. A thermodynamic explanation is then proposed where the molar mass control is exerted by the surface activity of the chains which drives their reactivity. Small chains rapidly propagate and backbite at the interface. Once the chains reach a critical DP corresponding to their loss of surface tension activity, they penetrate into the particles where side reactions such as redistribution and condensation hardly occur.

Temperature dependence of chain dimensions for highly syndiotactic poly(methyl methacrylate)

The Mark houwink Sakurada parameters and the unperturbed dimensions of highly syndiotactic in ketone solvents are determined at the θ temperatures by viscometry. The results are compared with predictions of RIS models

Cellulose molecular weights determined by viscometry

AbstractThe equation suggested in the standard method SCAN C15:62 for the estimation of the degree of polymerization (DP) of a cellulose sample from its intrinsic viscosity ([η]) in cupriethylenediamine hydroxide (cuene) solution, P0.905 = 0.75 [η]/mL g−1, where P is an indeterminate average DP, is incorrect. Although differences between the experimental results from several laboratories need to be resolved, a tentative replacement (PV = 1.65 [η]) is suggested, based upon the pooled data and a conversion from the intrinsic viscosity of cellulose tricarbanilate (CTC) in tetrahydrofuran (THF) to that of cellulose in cuene. The treatment of statistical errors in Mark–Houwink–Sakurada parameters, and the nonlinearity of the log[η]−log Pv correlation are discussed.

The Mark–Houwink–Sakurada Equation for the Viscosity of Atactic Polystyrene

In this review, the second in a series, the viscosity–molecular weight (Mark–Houwink–Sakurada) relationships have been critically evaluated for atactic polystyrene for a variety of solvents often used for viscosity measurements. These are benzene, toluene, 1,2,4-trichlorobenzene, tetrahydrofuran, o-dichlorobenzene, 2-butanone, and two theta solvents, cyclohexane and decalin. In addition, the Mark–Houwink–Sakurada parameters for several other solvents, not used as frequently, are provided.