Analysis of the Molecular Weight Distribution

Gel permeation chromatography (GPC) is a convenient and reliable method to determine the entire molecular weight distribution (mwd) of a polymer. In general, the resulting elution curve D(V ), where is the elution volume is related to the mwd by Tung s integral equation 

G(V — V) is the spending function of the GPC apparatus. The inversion of Eq. (12) is till-conditioned which leads in practice to oscillating solutions for 0(Vj). If the standard deviation of the kernel G(V ), which may be approximated by a Gauss function, is small as compared to the width of the mwd 0(V ), Eq. (12) reduces to  

The primary goal of the present work is the demonstration of the paramount influence of solvent power on the shear degradation in solution. The solvent/polymer systems used for this purpose should be well-defined with regard to solution thermodynamics as well as to flow behavior at different solvent power. The molecular weight distribution must not be too broad because of the strong rise in viscoelasticity if a high molecular weight tad is present (see above). 

Themodynamically induced shear degradation also has been investigated using solutions of anionically polymerized poly(n-alkyl methacrylate)s in poor solvents Three different lengths of the alkyl substituents (methyl PMMA n-butyl PBMA -decyl PDMA) were used in the course of the study. As an example for the thermodynamic characterization of these systems, Fig. 6 shows the cloud point curves of PDMA dissolved in -butanol 

---

In PLP the sample is subjected to a series of short (<30 ns) laser pulses at intervals t. Analysis of the molecular weight distribution gives the length of chain formed between successive pulses (v) and this yields a value for kp (eq. 13). 

Additional analysis of the molecular weight distribution of the polyethylene layer in the "good" versus "bad" packages was performed using high-temperature GPC. 

Gel permeation chromatographic (GPC) analysis of the molecular weight distribution of the polymers was performed with a Perkin-Elmer series 10 liquid chromatograph equipped with an LC-25 RI detector (25 °C), a 3600 data station, and a 660 printer. A Perkin-Elmer PL 10- xm particle mixed-pore-size cross-linked polystyrene gel column (32 cm by 7.7 mm) was used for the separation. The eluting solvent was reagent-grade tetrahydrofuran (THF) at a flow rate of 0.7 mL/min. The retention times were calibrated against known monodispersed polystyrene standards with MpS of 194,000, 87,000, or 10,200 and for which the ratio Mw/M is less than 1.09. 

A method for the gel permeation chromatographic analysis of the molecular weight distribution of wood pulp holocellulose as the carbanilate derivative has been applied to red maple Acer rubrum) and loblolly pine Pinus taeda). Either the chlorine-ethanolamine or acid-chlorite method could be used to prepare the holocellulose and the derivative was obtained by heating at 80 with phenylisocyanate in pyridine. Higher temperatures caused depolymerization. 

A more recent analysis of the molecular weight distribution by SEC using a triple detection (viscosity, concentration, molecular weight) has been described [51-53]. It was performed on heterogeneous chitosans, obtained from commercial sources after solid state treatment and... 

Here cm is monomer concentration, t time, kp propagation rate coefficient, f inu rate of initiation, and ki termination rate coefficient. Measurement of initiator decomposition rates, and thus specification of has never been a problem. However for much of the history of RP, the disentangling of kp and ki was a problem. This was solved in 1987 when it was shown that by relatively simple analysis of the molecular weight distribution from a pulsed-laser polymerization (PLP), the value of kp could be obtained without requirement for any knowledge of ki (or So enthusias-... 

Tanaka, R., Sato, S., Takanohashi, T., Hunt, J.E., Winans, R.E. (2004) Analysis of the molecular weight distribution of petroleum asphaltenes using laser desorption-mass spectrometry. Energy Fuels, 18,1405-1413. 

G. Wenz, G. Wegner. Kinetics of Radiation Induced Polymerization of a Diacetylene Studied by Analysis of the Molecular Weight Distribution. Mol. Cryst. Liq. Cryst. 9i (1983) 99... 

Similar observations of PDMS-hydrophobed silica antifoam deactivation on inorganic carrier materials have been reported in a pharmaceutical context. The antifoam performance of antiflatulent preparations with PDMS-hydrophobed silica mixed with basic antacid carriers, such as aluminum hydroxide and magnesium carbonate, has been shown to deactivate after the ingredients were either granulated or compressed into tablets [81, 82]. Analysis of the molecular weight distribution of... 

---