Laser light scattering as GPC detector

Hjertberg, Thomas; Kulin, Lars‐Inge; Sörvik, Erling M.

doi:10.1016/0142-9418(83)90013-2

Cited by 21 publications

(3 citation statements)

References 29 publications

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“…In previous work on the same polymer, size‐exclusion chromatography showed a progressive decrease in the low molecular weight portion of the distribution at a temperature of 86°C . However, size‐exclusion chromatography is not used in this work because of the very broad molecular weight distribution observed for this polymer that exceeded the ideal range of the differential reflective index detector and laser light scattering detector individually . Using a single detector with such a broadly distributed and highly branched polymer can introduce significant errors in the tails of the distributions, reconciling the 2 detector responses is nontrivial and has been the subject of research that goes beyond the focus of the work …”

Section: Introductionmentioning

confidence: 96%

“…19 However, size-exclusion chromatography is not used in this work because of the very broad molecular weight distribution observed for this polymer that exceeded the ideal range of the differential reflective index detector and laser light scattering detector individually. 20,21 Using a single detector with such a broadly distributed and highly branched polymer can introduce significant errors in the tails of the distributions, reconciling the 2 detector responses is nontrivial and has been the subject of research that goes beyond the focus of the work. [21][22][23][24][25] This work presents a mathematical formalism to account for the weight loss of polycarbosilane as a function of temperature and time, which is dominated by the volatilization of the low molecular weight fraction.…”

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confidence: 99%

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Process modeling of the low‐temperature evolution and yield of polycarbosilanes for ceramic matrix composites

et al. 2018

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The volatilization of polycarbosilanes is important to the processing and performance of polymer infiltration and pyrolysis‐based ceramic matrix composites. Low molecular weight (MW) polycarbosilane is often present in preceramic polymers and enhances viscosity for the purpose of composite infiltration. Due to the volatility of low MW chains, a model was developed to semi‐empirically determine the MW distribution and then predict the mass yield and evolution of the MW distribution as a function of temperature and time for StarPCS™ SMP‐10. The enthalpy of vaporization, the temperature dependence of the enthalpy of vaporization, the temperature dependence of the normal boiling point and a representation of the molecular weight distribution were fit using a series of thermogravimetric measurements, involving isothermal holds on a particular batch of SMP‐10. Once calibrated for SMP‐10 in this fashion, the molecular weight distribution of different batches of SMP‐10 could be fit using a thermogravimetric measurement involving a reduced temperature‐time series. The model was then predictive of mass loss over time for temperatures below the onset of curing (>90°C). Understanding this volatilization enables improved SiC yield, reduced processing time and minimizing void/bubble formation.

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Section: Introductionmentioning

confidence: 96%

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Process modeling of the low‐temperature evolution and yield of polycarbosilanes for ceramic matrix composites

et al. 2018

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“…At points along the chain, neutral sugars, predominantly rhamnose, are attached to form T-junctions (2). The number average degree of polymerization of unaggregated citrus pectins is 50-85 galacturonic units (3). Differences in DM are caused by natural variations in the methyl ester content of pectins as they occur in nature and by the extent of demethylation induced during extraction and purification (4).…”

Section: Instrumentationmentioning

confidence: 99%

Rejection of spike noise from size exclusion chromatography/low-angle laser light scattering experiments

Berkowitz¹

1986

Anal. Chem.

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2571 Brass Perspex P T F E r t z (luartz Windows IQ15x21 Calibration RI \Inlet Figure 1. A diagram of variable path length flow-through spectrophotometer cell.is fabricated so that the quartz windows just about touch when the drum is set to reading zero, resulting in a very small difference between the drum reading and the actual path length. Calibration is therefore necessary for measurements at very short path lengths and, depending on the degree of accuracy required, also at longer path lengths. One calibration method is to measure absorbances of an aqueous solution (e.g., KNOB or K2Cr04) of suitable concentration against air at a number of short path settings and at any convenient wavelength. The stray light error of the spectrophotometer should of course be negligible at the chosen wavelength (4). The procedure is then repeated with distilled water to obtain the correct absorbance of the solution by subtraction of the blank values. An illustrative set of absorbance values measured at two wavelengths for each of four different path length settings is given in Table I. These values were used to calibrate the cell for a titration where a path length of 0.2 mm was required. The true path length, b, is deduced as follows from the data: If the reading on the drum is denoted by L, then the path length is given by b = L + 6 (1) where 6 is the path length correction. From Beer's law A = ecb one obtains A = EC(L + 6 ) = tcL + ec6Table I. Absorbance Values at Various Path Lengths Used to Calibrate the Cell drum (L)/mm A (220 nm) A (230 nm) 0.05 0.3489 0.2351 0.10 0.5840 0.3926 0.15 0.8212 0.5492 0.20 1.053 0.7080 6 = 0.0243 mm 6 = 0.0246 inmValues for cc and ec6 can be readily obtained as the slope and intercept of the straight line plot of A against L, or by fitting eq 3 to the data by least-squares analysis. The quotient of tc6/cc then gives the path length correction. The agreement between the two 6 values, 0.0246 and 0.0243 mm, calculated from the two sets of independent measurements is satisfactory and implies an uncertainty of less than 0.1% at path length 0.2 mm. The path length to be used and the accuracy required should dictate the range and number of path length settings chosen for calibration purposes. Since aging of the O-ring can have a measurable effect on the value of 6, occasional calibration is recommended. In fact, calibration can be most conveniently carried out as part of a titration experiment by using the reaction mixture and its blank as described above. CONCLUSIONThe variable short path capability of the cell offers advantages in cases where a titration procedure can be utilized to vary conditions of a reaction mixture to be investigated by spectrophotometry (e.g., ref 5). Examples are, end-point determinations in volumetric analysis, the determination of complex stoichiometry by the slope ratio or molar ratio methods, and especially equilibrium investigations in which the concentration of a strongly absorbing component has to be varied over a wide range. LITERATURE CITED(1) Llnge, H. G.; Jones,...

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