Characterisation of commercial polymers

For commercial purposes the molecular weight is usually characterised from measurements of the viscosity of dilute solutions. It has been shown that, for dilute solutions, the relation between the viscosity and the molecular weight (in this case the viscosity average molecular weight) may be given by the relationship 

T-value is, however, rather dependent on the method of measurement and in the past different suppliers have used difficult solvents and different polymer concentrations. For this reason it is now becoming more common to quote the 

ISO viscosity number. Table 12.1 compares typical correlations between number and weight average molecular weights with ISO numbers, AT-values and ASTM viscosity measurements. 

The properties of PVC may also he expected to depend on the molecular weight distribu n. Most commercial polymers, however, appear to have similar values for MJM and in any case there is little published information on effects of altering the parameter. It is perhaps rather surprising that there appears to be little work reported on the effect of blends of polymers of differing molecular weight on mechanical and rheological properties. 

With commercial polymers the major differences are, perhaps, not differences in molecular structure hut in the characteristics of the particle, i.e. its shape, size distribution and porosity. Such differences will considerably affect the processing behaviour of a polymer. 

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Polymers have inherently high hydrocarbon ratios, making liquefaction of waste plastics into liquid fuel feedstocks a potentially viable commercial process. The objective is to characterise the thermal degradation of polymers during hydrogenation. LDPE is studied due to its simple strueture. Isothermal and non-isothermal TGA were used to obtain degradation kinetics. Systems of homopolymer, polymer mixtures, and solvent-swollen polymer are studied. The significant variables for... 

An important aspect relating to the ability to predict extrusion behaviour is the recognition that all commercial polymers must be characterised by a spectrum of relaxation times. A single relaxation time constitutive equation is inadequate to capture all necessary features. The detailed form of the nonlinear component within the constitutive equation is also important and decisive in terms of accurate prediction and again much work has been done refining these parameters. ... 

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. 

There is an enormous body of work on quasielastic neutron scattering from polymers [1,2]. There is a smaller literature on neutron vibrational spectroscopy of polymers but this has had a significant impact on the characterisation of these materials. Crystalline or semi-crystalline polymers are the most important class of polymers commercially. The most-studied and technologically most important of these is polyethylene and this will be considered in some depth and we will highlight the use of the n-alkanes as model compounds ( 10.1.2). We will then see how these concepts can be transferred to polypropylene ( 10.1.3), nylon ( 10.1.4), and conducting polymers ( 10.1.5). Non-crystalline polymers ( 10.2) have been much-less studied by INS. As examples, we will consider polydimethylsiloxane ( 10.2.1) and advanced composites ( 10.2.2). 

It was exciting to follow the development of this polymer from the very first beginning on the laboratory bench up to a product ready to enter the engineering polymers market. This commercial significance also makes it a nice example to illustrate how different TA techniques (DSC, DMA, TMA and thermo electrometric analysis) focussed on one product contribute to the characterisation of such a new polymeric system. All data given are measured on non-stabilised, development phase PK co- and terpolymer samples made more than five years ago. Hence, these data can be different compared with those of the present, further developed, commercial grades. 

Pfannkoch, E., Lu, K.C., Regnier, F.E. and Barth, H.G. (1980). Characterisation of some Commercial High Performance Size-Exclusion Chromatography Columns for Water-Soluble Polymers. J. Chromatogr. Sci., 18, 430. 

Some polymer systems of both academic and commercial interest are derived from chemical modification of preformed polymers. For example, poly (vinyl alcohol) is prepared by hydrolysis of poly (vinyl acetate) because vinyl alcohol monomer does not exist. NMR spectroscopy again plays an important role in characterising such materials. In cases where chemical modification is incomplete, these systems fall into the category of copolymers comprising modified and unmodified monomer repeat units. Statistical analyses of the... 

Several examples of NMR studies of copolymers that exhibit Bernoullian sequence distributions but arise from non-Bernoullian mechanisms have been reported. Komoroski and Schockcor [11], for example, have characterised a range of commercial vinyl chloride (VC)/vinylidene chloride (VDC) copolymers using carbon-13 NMR spectroscopy. Although these polymers were prepared to high conversion, the monomer feed was continuously adjusted to maintain a constant comonomer composition. Full triad sequence distributions were determined for each sample. These were then compared with distributions calculated using Bernoullian and first-order Markov statistics the better match was observed with the former. Independent studies on the variation of copolymer composition with feed composition have indicated that the VDC/VC system exhibits terminal model behaviour, with reactivity ratios = 3.2 and = 0.3 [12]. As the product of these reactivity ratios is close to unity, sequence distributions that are approximately Bernoullian are expected. 

Grechanovskii, V.A. Dmitrieva, I.P. Zaitsev, N.B. Separation and preliminary characterisation of the protein component from commercial varieties of hevea rubber. Int. Polym. Sci. Technol. 1987,14, 1. ... 

This article will provide a general overview of the emulsion polymerisation process and explain how the resulting latexes are used in industrial applications. An introduction to the basic concepts of emulsion polymers will be given, followed by a description of the various production processes and characterisation methods. The classes of emulsion polymers will be surveyed, and the commercial technologies and potential future uses discussed. A number of comprehensive texts on emulsion polymers are available for more in-depth study (60, 89, 94,95, 364, a.l-a.ll). 

Potassium ionisation of desorbed species (K IDS) with mass spectrometric detection is an extremely useful tool for the characterisation of high performance organic coatings. K IDS uses a commercial rapid heating probe to desorb intact molecules which are then ionised by potassium cation attachment. Based upon the molecular ions, which appear as [M]K, coatings components can be qualitatively and quantitatively analysed. In this work K IDS was selected as a method of soft ionisation, (i.e., producing molecular ions) because of its simplicity, wide applicability, low cost and compatibility with the quadrupole mass spectrometer. Simonsick [76] reports the application of K IDS to polymer additives (UV stabilisers and antioxidants), catalysts (organotin), reactive diluents (vernonia oil and aliphatic epoxides) and polyurethane precursors (polyesters and isocyanates). Tikuisis and co-workers [77] also discussed this technique. 

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