Polymer molecular mass, changes intrinsic viscosity

Additionally, online monitoring methods have been developed to adapt off-line characterization methods into in situ (i.e., in-reactor) probes for determination of kinetics and monomer conversion with optical methods such as mass spectroscopy (MS), ESR, FTIR, near IR, and Raman spectroscopy. However, frequently, due to high turbidity and viscosity of the polymer reaction milieu, the optical surfaces are easily fouled, leading to frequent sensor failure. Furthermore, data acquired with these probes are model dependent the empirical and inferential calibration schemes used can be expensive and time consuming to develop and can drift and become unreliable as reactor conditions change and as sensors become fouled. Another limiting feature of these methods is that they usually measure only one characteristic of the reaction, such as monomer conversion and are not directly sensitive to polymer molecular mass and intrinsic viscosity. More detailed discussion of these techniques can be found in Chapters 6-10 of this book. 

Matsuoka and Cowman [32] proposed the consideration of two simple models to study the hydrodynamic properties of hyaluronan on the basis of inherent viscosity. The first model of the not freely-jointed or non-ideal coil is based on the statistical conformations of polymer chains. Under this model, the intrinsic viscosity [ /] is directly proportional to the volume occupied by mass units of the polymer segments. The volume is filled mainly with solvent and has low density of polymer segments. The second model is the freely-jointed chain model. It is assumed that the chain is more extended and its viscosity corresponds to that of the worm-like chains. The intrinsic viscosity changes as a square of the mean-squared end-to-end distance. Experimental studies of intrinsic viscosity of hyaluronan indicate that short chains act as freely-jointed chains and long chain of hyaluronan behave like the not freely-jointed chains. The molecular weight, at which these two types of behaviour co-exist, is approximately 3.75xl(yDa. The size of the polymer corresponds to a smallest coil of hyaluronan (Figure 4.6). 

As a model liquid three different polymers polyvinylpyrrolidone (PVP) of different molecular weights are used. These polymers are made available by BASF SE. Luvitec K17 has a mean molecular weight of 9000 Da, Luvitec K30 has 49,000 Da and Luvitec K90 has 1,250,000 Da. The letter K is an abbreviation for the fsT-value, a value that is proportional to the intrinsic viscosity and therefore proportional to the mean molecular weight. Applications of these polymers are found in pharmaceutical and cosmetic industry, because they are not toxic and have a universal solubility, ranged from hydrophilic solvent to hydrophobic solvents [1]. The effect on surface tension is described as low and measurements show a variation between 63 and 67 mN/m, changing with the fsT-value of the polymer. In addition to these solutions glycerin-water mixtures of different mass fractions are used to compare the effect of higher viscosities. 

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