Incorporation of C60 into Poly(methyl methacrylate) and Polystyrene by Radical Chain Polymerization Produces Branched Structures
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Abstract:
Polymerizations of styrene and methyl methacrylate (MMA) containing 1 wt % C60 initiated by 5 or 10 mol of azobis(isobutyronitrile)/mol of C60 in 1,2-dichlorobenzene solution produce brown polymers in 53−97% yield with all of the C60 incorporated, linear polymer equivalent molecular weights of Pn = 19 000−31 000, and Pw/Pn < 2. There are short induction periods before polymerization begins. All of the C60 is incorporated into the polymer after low conversion of the monomer. Multidetector size exclusion chromatography analyses measured polymer mass by differential refractive index, Mw by two-angle laser light scattering, intrinsic viscosity by differential viscometry, and mass of only C60 derivatives by UV. Molar chromatograms show that all of the polymer at the high end of the molecular weight distributions contains C60, and there are sizeable amounts of a lower molecular weight linear polymer. The high molecular weight polystyrene contains as many as 10−100 C60 units, but the high molecular weight PMMA contains an average of one C60 unit per macromolecule. All of the polymers have lower intrinsic viscosities and higher Mw than linear standards of the same retention volume due to branched or star structures. Calculations from a random branching model of Zimm and Stockmayer indicate that the PMMAs have an average branch number of five over the entire molecular weight distribution and systematically increasing average branch lengths with an increasing degree of conversion.Keywords:
Polystyrene
Molar mass distribution
Branching (polymer chemistry)
Molecular mass
Molar mass
Gel permeation chromatography
Degree of polymerization
Dispersity
Molar mass
Molar mass distribution
Molar ratio
Molar concentration
Throughflow
Molecular mass
Mass distribution
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Chemically modified starches are commonly used for various purposes. Depending on the type of derivatization, a chemical degradation of the original polymeric structure may occur, resulting in a change of molar mass. It is therefore always of interest to know the molar mass and possibly the conformation of the derivative. Four commercially available hydroxypropyl and hydroxyethyl modified starches were examined by asymmetrical flow field-flow fractionation combined with multiangle laser light scattering. The weight-average molar mass and the molar mass distribution were determined, with emphasis put on the rapid analysis and studies of the suitable experimental conditions regarding flow rates so that accurate data were obtained. The molar mass distribution determinations showed good reproducibility and repeatability and were fast. Efforts to obtain conformational information are described.
Molar mass
Multiangle light scattering
Molar mass distribution
Repeatability
Field-Flow Fractionation
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Degree of polymerization
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Molar mass distribution
Multiangle light scattering
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Abstract Commercially available, blended methylhydroxyethyl celluloses with similar weight-average molar masses but varying molar mass distributions were characterized by different techniques like steady shear flow and uniaxial elongation in capillary breakup experiments. The determined relaxation times t were then correlated with the absolute molar mass distribution acquired via SEC/MALLS/DRI (combined methods of size-exclusion-chromatography, multi angle laser light scattering and differential refractometer). In order to describe the longest relaxation time of the polymers in uniaxial elongation via integral mean values of the molar mass distribution, defined blends of polystyrene standards with varying molar mass distributions were characterized. The obtained data was scaled via different moments of the molecular weight distribution and could be correlated with the results obtained for the methylhydroxyethyl celluloses.
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Polystyrene
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Abstract The refractive indices of poly(β‐hydroxybutyric acid) (PHB) at four wavelengths have been determined via different procedures. Viscometric and light scattering measurements have been made on solutions of eight samples of PHB ( M w = 20·9 × 10 3 −929 × 10 3 g mol −1 ) in 2,2,2‐trifluoroethanol. From the dependences of intrinsic viscosity and of radius of gyration on molar mass, the conformation of PHB in dilute solution is shown to be that of a random coil. The findings are discussed in relation to existing conflicting evidence on the conformation of this polymer.
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Radius of gyration
Random coil
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Molar mass distribution
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Gel permeation chromatography
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ABSTRACT Series of polymers of various molar mass, chemical composition, and molecular architecture was analyzed by size exclusion chromatography (SEC) coupled with a multi‐angle light scattering (MALS) photometer and an online viscometer. The molar mass averages were determined from the signal of MALS or calculated from the intrinsic viscosity and universal calibration. The comparison of the obtained results showed significant differences between the two methods. The MALS detection was shown to be more accurate for the determination of the weight‐average molar mass and less vulnerable to the spreading of polymer peak by band broadening. The universal calibration can yield more accurate estimation of the number‐average molar mass of branched polymers. It is also significantly more accurate for the characterization of fluorescent polymers than MALS with a regular laser of 660 nm. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136 , 47561.
Molar mass
Molar mass distribution
Gel permeation chromatography
Multiangle light scattering
Refractometry
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Understanding of the physical characteristics of a polymer requires molar mass determination. For the commercially available polymers, having average molar mass below 1 000 000 g/mol, chromatography is the method that is often applied to determine the molar mass and molar mass distribution. However, the application of conventional chromatography techniques for polymers having molar mass >1 000 000 g/mol becomes very challenging, and often the results are disputed. In this article, melt rheometry based on the "modulus model" is utilized to measure the molar mass and polydispersity of ultra high-molecular-weight polyethylenes (UHMWPEs) having molar mass >1 000 000 g/mol. Results are compared with the chromatography data of the same polymer samples and the boundary conditions where the chromatography technique fails, whereas the rheometry provides the desired information is discussed. The rheological method is based on converting the relaxation spectrum from the time domain to the molecular weight domain and then using a regularized integral inversion to recover the molecular weight distribution curve. The method is of relevance in determining very high molar masses (exceeding 3 000 000 g/mol) that cannot be ascertained conclusively with the existing chromatography techniques. For this study, UHMWPEs with various weight-average molar masses, where the number-average molar mass exceeds >1 000 000 g/mol, are synthesized. Catalyst used for the synthesis is a living homogeneous catalyst system: MAO-activated bis(phenoxy imine) titanium dichloride. The rheological behavior of the thus synthesized nascent reactor powders confirms the disentangled state of the polymer that tends to entangle with time in melt.
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Molar mass distribution
Dispersity
Rheometry
Gel permeation chromatography
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In synthesizing polymers in vivo and in vitro, molecular homogenous ("monodisperse") polymers (i.e., those in which every macromolecule has the same molar mass or "molecular weight") occur only under quite specific conditions. The overwhelming majority of polymer syntheses proceed more or less randomly, and the resulting macromolecular substances have more or less broad molar mass distributions. The kind of molar mass distribution obtained depends on the nature of the polymerization, which may be either thermodynamically or kinetically controlled. Each kind of distribution is characterized by a definite relationship between the mole fraction x and the degree of polymerization X. Consequently, it is possible in many cases to deduce the kind of polymerization involved from the type of distribution function obtained.
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