Characterisation methods molecular weights

This also means that calibration is required in methods based on viscosity measurements before the method can be applied to characterise the molecular weight of a given polymer. Such calibration is tedious and requires that the molecular weights of a series of the polymer have been characterised by another technique in order to establish the relationship with the intrinsic viscosity. At present, this can be performed using the SEC method coupled with triple detection. It is noteworthy that calibration of the Mark-Houwink-Sakurada equation is valid only for one couple including a polymer and a solvent at a given temperature. 

Siddiqu and Wu [31] used a dynamic laser light scattering method to characterise an unfractionated PI in chloroform at 25 °C. The relatively small angular and concentration dependencies and translational diffusion coefficients measured by this technique enabled the PI to be characterised from only one measurement at a finite concentration and small scattering angle. Thus, this method could be used to characterise the molecular weight distribution of PI from the measured line-width distribution. 

In random degradation molecular mass decreases early, while in chain degradation the molecular mass of the polymer remains almost constant. Characterisation methods for molecular mass are thus very sensitive methods to follow random degradation. In contrast, as monomer is produced in chain depolymerisation, weight loss measurement techniques are the best methods to follow this kind of degradation. (Chapters 10-12, in Section IV, of this book focus on the methods used in the molecular characterisation and analysis of polymer degradation and polymer degradation mechanisms.)... 

An attractive route to dialkoxy PTV derivatives has recently been reported by Elsenbaumer and co-workers [131, 132], The method employs the thermal elimination of a sulfmyl group from a soluble sulfoxide precursor polymer (Scheme 1-31). In addition, the authors claim the first isolation of the quinomethide intermediate and characterised it by NMR and mass spectrometry. Dibutoxy-PTV produced by this methodology exhibits a significantly smaller band gap (1.2 eV) and higher molecular weight (M =8700) than the same material obtained by other methods. Poly(3,4-dimethoxy-2,5-thienylene vinylene) PDMoxTV was deep blue in color... 

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