Data acquisition, experimental difficulties

Field desorption (FD), pioneered by Beckey in 1969 [4], was the first and clearly the most successful of the early desorption ionization techniques. In the FD experiment, very high electric fields were used to extract ions from sample-coated thin wire emitters. FD spectra normally contained molecular weight information however, structural fragments were often absent and signal inslability resulted in data acquisition difficulties. As an added complication, FD was experimentally difficult and the method by which ions were formed was not well understood. 

It is evident that, in order to elucidate the copolymerization kinetics, extensive and systematic experimentation is required to provide data on the initiation, termination and propagation rates. The major stumbling block in the acquisition of experimental data has been, besides the normal difficulties associated with polymer experimentation, the lack of efficient characterization techniques which can yield reliable quantitative information on the MWD, CCD, and SLD or at least some of their leading moments. Such information is of primary importance in the elucidation of copolymerization kinetics. It is, therefore, felt that a major effort aimed at the study of copolymerization kinetics and at the development of characterization techniques is clearly justified. 

In dilute solutions the problem may be attacked by light scattering. X-ray scattering, or hydrodynamic measurements. In solution, the acquisition of experimental data is relatively easy, but the interpretation presents formidable problems which have not yet been solved completely satisfactorily. The main trouble arises from the fact that models are required to interpret data on dilute solutions, and it is difficult to assess how applicable the models are to molecularly dispersed species. Very often dubious assumptions are introduced which tend to render the results meaningless. Our first task, therefore, shall be to examine a variety of hydrodynamic experiments and see to what extent the data from such experiments can be interpreted in terms of size and shape. We shall not discuss scattering measurements here, except to mention that they too involve difficulties of the same kind in the interpretation of the data. 

The second cause is related to the first. Even where the value of theory for the prediction and control of the behaviour of these materials has been recognised, the utility of these approaches has often been greatly reduced because of the experimental methods which have been employed or by the poor experimental data which have been available, or both. Indeed, it is only comparatively recently that a proper recognition has arisen concerning the number of potential pitfalls and difficulties that can militate against the acquisition of meaningful and accurate experimental data. 

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