Characterisation of polymers

In general, polymers for biomedical and pharmaceutical applications are characterised in order to determine their molecular weight, composition and thermal properties. All of these characteristics may influence the properties of the final device or medicine. 

In the case of copolymers, the composition is also a mean composition that generally reflects the composition of the different co-monomers used in the polymerisation medium after total conversion of the monomers into polymers. However, because the reactivity of monomers between each other can be quite different, the composition of the different molecules of copolymers in a single preparation can vary. Indeed, composition in monomer units of the copolymers formed at the beginning of the polymerisation reaction is not necessarily the same as composition of the copolymers formed at the end of the polymerisation reaction. This effect adds heterogeneity to chemically synthesised copolymers, and the only way to appreciate this effect is to analyse the composition of the polymers at low conversion degree during polymer synthesis. 

The distribution in molecular weight of each population of macromolecules appears as a Gaussian curve. Mathematical analysis of such a distribution curve can provide different average values that can be used to characterise the molecular weight of the polymer and the distribution of the molecular weights in the population. 

For instance, the first moment gives the number-average molecular weight, M . This corresponds to the total weight of the sample, W, divided by the number of molecules included in this amount of sample, N as shown 

The third moment of the distribution, which can be calculated from Equation 2.3, gives the z-average molecular weight, which is highly affected by the heaviest macromolecules. 

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Whereas SEC is the dominant technique for the characterisation of polymers, various nonexclusion liquid chromatographic (NELC) methods, such as GPEC and LACCC offer equally valid possibilities for deformulation of complex polymer systems. In fact, molecular characterisation of polymers in the precip-itation/adsorption mode (gradient HPLC) enables differences in chemical structure and composition to be... 

Applications Rather intractable samples, such as organic polymers, are well suited to FD, which avoids the need for volatilisation of the sample. Since molecular ions are normally the only prominent ions formed in the FD mode of analysis, FD-MS can be a very powerful tool for the characterisation of polymer chemical mixtures. Application areas in which FD-MS has played a role in the characterisation of polymer chemicals in industry include chemical identification (molecular weight and structure determination) direct detection of components in mixtures off-line identification of LC effluents characterisation of polymer blooms and extracts and identification of polymer chemical degradation products. For many of these applications, the samples to be analysed are very complex... 

Applications Applications of SEC-FTIR include quantitative analysis of copolymers [701] product deformulation of hot melt adhesives characterisation of polymer compositional heterogeneity analysis of complex mixtures of urethane oligomers and eventually also the identification and quantitative analysis of polymer additives... 

In this chapter we illustrate a direct method of characterisation of polymer/additive dissolutions by means of (500 MHz) NMR, which takes advantage of selective signal suppression allowing elimination of unwanted signals, such as the ca. 105 x more intensive PE signal. The most effective approach to solvent suppression is the destruction of the net solvent magnetisation by pulsed... 

Having said this, it was felt therefore that there is a need for a book addressing analysis and characterisation of polymers from the point of view of what we wish to call the primary analytical question. Many excellent textbooks and reference works exist which address one or more individual analytical techniques, see, for example, references [1-10]. These books form the basis of the knowledge of the technique expert. They also contain many excellent and varied examples on successful applications of analytical techniques to polymer analysis and characterisation. There are also books which address the multitude of analytical techniques applied in polymer analysis, see, for example, references [11-24], However, a synthetic chemist may wish to know the constitution of his/her polymer chain, a material scientist may want to find out the reasons why a fabricated sample had failed. What technique is best or optimal to study chain constitution will depend on the situation. Polymer failure may result from morphological features, which needs to be avoided, a contaminant, a surface property degradation, etc. When a sample has been processed, e.g., a film blown, molecular orientation may be the key parameter to be studied. A formulation scientist may wish to know why an additive from a different supplier performs differently. It is from such points of view that polymer analysis and characterisation is addressed in this book. 

W.M. Groenewoud (Ed.), Characterisation of Polymers by Thermal Analysis, Elsevier, Amsterdam,... 

Another polymer symposia was organised by IUPAC in 1947 in Liege. At this conference, the discussion included synthesis and technology of polymers like polyethylene, nylon, polyester. New characterisation methods such as x-ray scattering, x-rays, electron microscope, osmometry, nmr, IR, Raman spectroscopy, etc. were now available for characterisation of polymers. These methods become essential because of increasing complexity of new polymers. 

The characterisation of polymers is very difficult because of various inherent weaknesses observed in case of various polymers. The difficulty in characterisation can be well grasped from the fact that unlike low Molecular weight compounds, like benzene (M=78), methacrylate (M =100.12), vinyl chloride (M=62.5), etc. which have a fixed value o/Molecular weight, the polymers which are macromolecules, do not have a certain definite and permanent Molecular weight. For example, the Molecular weights of polystyrene varies between 50,000 to 10 million. 

The usefulness of viscosity as a measure of polymer Molecular weight was recognised in the early work of Staudinger (1930). Solution viscosity is a measure of the size or extension in space of polymer molecules. It is empirically related to Molecular weight for linear polymers the simplicity of the measurement and the usefulness of the viscosity-Molecular weight correlation are so great that viscosity measurement constitutes an extremely valuable and simple tool for the molecular characterisation of polymer. 

Since the technique was introduced (JJ in 1964, gel permeation chromatography (GPC), or size exclusion chromatography (SEC), has played an increasingly important role for the characterisation of polymers. The theory and practice of this chromatographic method have been extensively reported and a comprehensive text has recently been published on modern size exclusion chromatography (2). 

A particularly important application of NMR spectroscopy is the structural characterisation of polymers. While initial attempts were made using NMR, the wide... 

Since its discovery in 1959 (1) and first application to synthetic organic polymers in 1964 (2), SEC has become the most widely used technique for routine characterisation of polymer molecular weights (MW) and molecular-weight distributions (MWD), as attested... 

Recent examples of the application of three-dimensional H/13C/Y correlation spectroscopy for the characterisation of polymers included studies of polystyrene samples obtained by diphenylphosphinyl radical initiated polymerisation of styrene (Y = 31P),38,39,86 and the characterisation of Sn-containing polybutadiene that was prepared by anionic polymerisation... 

D. R. Lloyd, T. C. Ward, H. Schrieber, eds., Inverse Gas Chromatography Characterisation of Polymers and Other Materials, American Chemical Society, Washington, D.C., 1989. 

The mean distance between the centres of adjacent macromolecular coils d ss n /3 can be compared with the mean squared radius of gyration of the macromolecular coil (S2), which presents the mean dimension of the coil. Taking the definition (1.21) into account, one can see, that a non-dimensional parameter n R2)3/2 is important for characterisation of polymer solutions. The condition... 

M.N. Bikales in Characterisation of Polymers, Wiley Interscience, New York, 1971, 129. 

Samyn, F., Bourbigot, S., Jama, C., Bellayer, S., Nazare, S., Hull, R., Castrovinci, A., and Camino, G. (2008) Crossed characterisation of polymer-layered silicate (PLS) nanocomposite morphology TEM, x-ray diffraction, rheology and solid-state nuclear magnetic resonance measurements, European Polymer Journal 44(6) 1642-1653. 

Structural characterisation of polymer supported complexes using EXAFS... 

S. W. Shalaby, Thermoplastic polymers. In Thermal Characterisation of Polymer Materials, Turin E. A. (ed.). Academic Press New York, 237-264, 1981. 

A paper on new developments in the characterisation of polymers in the solid state must include a discussion of the possibilities offered by scanning electron transmission and the ancillary detection devices EDX (energy dispersive analysis of X-rays) and EELS (electron energy loss spectroscopy). 

Kavanagh, G. M. and Ross-Murphy, S. B. 1998. Rheological characterisation of polymer gels. Prog. Polym. Sci. 23 533-562. 

Thorough colloidal/surface characterisation is fundamental to the success of research on polymer colloids. A wide range of complementary techniques are available for colloidal/surface characterisation of polymer colloids and access to several is necessary since no single technique can provide full characterisation. There is an ongoing need for experimental and theoretical work on improvements to existing methods and on development of new techniques to support the needs of research. Additionally, the necessary improvements in process modelling will naturally lead to a demand for advances in on-line analysis to support feedback loops for process control and manufacturing. Thus, further developments in on-line methods for measurement of particle... 

In the last twenty years, major advances in the characterisation of polymer melt viscoelasticity has taken place and in addition applied mathematicians have produced numerical codes that enable viscoelastic fluids to be modelled for processing conditions. Within the last few years it has become possible to reasonably accurately predict the way in which a viscoelastic polymer will flow into, within and out of an extrusion die. The accurate prediction of die swell is nearly possible and advances are being made to predict the onset of extrusion instabilities. 

Molecular weightjmass detectors include light scattering detectors and viscosity detectors. When SEC is used in the characterisation of polymer systems, its main aim will be the production of a molecular mass/weight distribution and where possible absolute molecular weights. Mass calibration is a complicated matter (section 9.3.5.1) in that calibration curves differ for different polymer types, and for many commercial polymers, direct molar mass calibration is not possible because of the lack of suitable, known molecular weight standards. 

Jones, C.E., Preparation and Characterisation of Polymer Films for the Release of Metronidazole, Ph.D. thesis, School of Pharmacy, University of London, 1990. 

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