Polymer experimental methods

For both copolymers and stereoregular polymers, experimental methods for characterizing the products often involve spectroscopy. We shall see that nuclear magnetic resonance (NMR) spectra are particularly well suited for the study of tacticity. This method is also used for the analysis of copolymers. 

Number average molecular weight of the polymer Weight average molecular weight of the polymer Experimental method used... 

Although the emphasis in these last chapters is certainly on the polymeric solute, the experimental methods described herein also measure the interactions of these solutes with various solvents. Such interactions include the hydration of proteins at one extreme and the exclusion of poor solvents from random coils at the other. In between, good solvents are imbibed into the polymer domain to various degrees to expand coil dimensions. Such quantities as the Flory-Huggins interaction parameter, the 0 temperature, and the coil expansion factor are among the ways such interactions are quantified in the following chapters. 

In addition to an array of experimental methods, we also consider a more diverse assortment of polymeric systems than has been true in other chapters. Besides synthetic polymer solutions, we also consider aqueous protein solutions. The former polymers are well represented by the random coil model the latter are approximated by rigid ellipsoids or spheres. For random coils changes in the goodness of the solvent affects coil dimensions. For aqueous proteins the solvent-solute interaction results in various degrees of hydration, which also changes the size of the molecules. Hence the methods we discuss are all potential sources of information about these interactions between polymers and their solvent environments. 

J. E. Rabek, Polymer Degradation Mechanisms and Experimental Methods, Chapman and HaU, London, 1995, pp. 296—306. 

J. E. Rabek, Experimental Methods in Polymer Chemisty, Wiley-Interscience, New York, 1980. 

Thus electrical conductivity is commonly measured in units of S/cm (0 cm ). Various experimental methods have been used to measure the electrical conductivity of conductive polymers, eg, 4-probe method. Van der Pauw method, etc, and are well documented in the Hterature. 

Data on a large range of polymers obtained by experimental methods have indicated the approximate general validity of the equation... 

The classical representation of a homopolymer chain, in which the end groups are disregarded and only one monomer residue is considered, allows no possibility for structural variation. However, possibilities for stercoscqucnce isomerism arise as soon as the monomer residue is considered in relation to its neighbors and the substituents X and Y are different. The chains have tacticity (Section 4,2.1). Experimental methods for tacticity determination are summarized in 4.2.2 and the tacticity of some common polymers is considered in 4.2.3. 

Although R2 is the easiest quantity to be obtained theoretically, there is no straigthforward experimental method for its determination. For this reason, two other quantities are widely in use to characterize the dimensions of a randomly coiled polymer molecule ... 

The existence of the mesophase layer has been proved by infra-red spectroscopy, ESP, NMR, electron microscopy and other experimental methods. Moreover, it has been also proved that the thickness of this layer depends on the polymer cohesion energy, free surface energy of the solid, and on the flexibility of the polymer chains. 

Table 6.1 Experimental methods for determining different types of average relative molar mass of polymers...

Electric-field-driven transport in media made of hydrophilic polymers with nanometer-size pores is of much current interest for applications in separation processes. Recent advances in the synthesis of novel media, in experimental methods to study electrophoresis, and in theoretical methodology to study electrophoretic transport lead to the possibility for improvement of our understanding of the fundamentals of macromolecular transport in gels and gel-like media and to the development of new materials and applications for electric-field-driven macromolecular transport. Specific conclusions concerning electrodiffusive transport in polymer hydrogels include the following. 

Table 1 summarizes several of the experimental methods discussed in this chapter. A need exists for new or revised methods for transport experimentation, particularly for therapeutic proteins or peptides in polymeric systems. An important criterion for the new or revised methods includes in situ sampling using micro techniques which simultaneously sample, separate, and analyze the sample. For example, capillary zone electrophoresis provides a micro technique with high separation resolution and the potential to measure the mobilities and diffusion coefficients of the diffusant in the presence of a polymer. Combining the separation and analytical components adds considerable power and versatility to the method. In addition, up-to-date separation instrumentation is computer-driven, so that methods development is optimized, data are acquired according to a predetermined program, and data analysis is facilitated. 

In the case of heterogeneous polymers the experimental methods need to be refined. In order to analyze those polymers it is necessary to determine a set of functions / (M), which describe the distribution for each kind of heterogeneity i This could be the mass distributions of the blocks in a diblock copolymer. The standard SEC methods fail here and one needs to refine the method, e.g., by performing liquid chromatography at the critical point of adsorption [59] or combine SEC with methods, which are, for instance, sensitive to the chemical structure, e.g., high-pressure liquid chromatography (HPLC), infrared (IR), or nuclear magnetic resonance spectroscopy (NMR) [57],... 

We hope that this chapter on the molecular weight determination of synthetic polymers has illustrated that in the case of a complex polymer it is preferable to use several experimental methods for the molecular weight determination to obtain a full picture. Owing to the different sensitivity of the various methods some are blind for low molar masses while others are blind at low concentrations. As exemplified, often scaling laws can be utilized to compare results of different methods and different sensitivities. 

Volume and mass-based expressions for the degree of crystallinity are easily derived from the experimentally measured density (p) of a semi-crystalline polymer. The method is based on an ideal crystalline and liquid-like two-phase model and assumes additivity of the volume corresponding to each phase... 

The general experimental methods of analysis and materials used in this study have been previously described(l,2) with the exception of the ionic hydroxyethyl cellulose polymers. 

In our previous paper (H), we introduced a novel experimental method to study the mechanistic details of solvent permeation into thin polymer films. This method incorporates a fluorescence quenching technique (19-20) and laser interferometry ( ). The former, in effect, monitors the movement of vanguard solvent molecules the latter monitors the dissolution process. We took the time differences between these two techniques to estimate both the nascent and the steady-state transition layer thicknesses of PMMA film undergoing dissolution in 1 1 MEK-isoproanol solution. The steady-state thickness was in good agreement with the estimate of Krasicky et al. (IS.). ... 

There has been extensive effort in recent years to use coordinated experimental and simulation studies of polymer melts to better understand the connection between polymer motion and conformational dynamics. Although no experimental method directly measures conformational dynamics, several experimental probes of molecular motion are spatially local or are sensitive to local motions in polymers. Coordinated simulation and experimental studies of local motion in polymers have been conducted for dielectric relaxation,152-158 dynamic neutron scattering,157,159-164 and NMR spin-lattice relaxation.17,152,165-168 A particularly important outcome of these studies is the improved understanding of the relationship between the probed motions of the polymer chains and the underlying conformational dynamics that leads to observed motions. In the following discussion, we will focus on the... 

Nonpolar Systems. Most of the early theoretical studies on radiation action were carried out on water and aqueous solutions. This was a consequence not only of Its Importance In radiation biology but also of the greater amount of experimental data and the simplicity of Its radiation chemical reactions as compared with organic systems. Recently, however, more studies on non-polar systems such as alkanes have appeared (24). It Is a long step to solid polymers but methods are being continually refined. 

See for example (a) Pospisil, J. and Klemchuk, P. P., Oxidation Inhibition in Organic Materials, Vol II, CRC Press, New York, 1990 (b) Rabek, J. F Polymer Photodegradation, Mechanisms and Experimental Methods, Chapman Hall, London, 1995 (c) Wypych, G., Handbook of Material Weathering, 2nd Edn, ChemTec Publishing, Ontario, Canada, 1995. 

Fig. 6. Determination of the critical protein concentration. (A) Plot of protein in the supernatant fluid after quantitatively sedimenting polymer from a polymerized solution of tubules and tubulin at steady state. The critical concentration, Ko, is determined from the value of the y axis intercept, and the fraction of active protein, y, from the slope. (B) The conventionally used experimental method for estimating the critical concentration. Note that the x axis intercept is actually Ko/y, instead of Kj,. Interpretation of the slope from such plots requires knowledge of the ratio of polymer weight concentradon to turbidity (given here as a). Data from experiments such as those in A may be used in conjunction with this plot to obtain the cridcal concentration, and this can serve as an internal test for self-consistency of the data.

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