Triad fractions, development

The development of the triad fractions as observed by NMR during the course of a polymerization of a 75/25 ethyl acrylate styrene copolymer is shown in Figure 10. Over the course of the feed, the ethyl acrylate content dropped from 100% to 50% linearly. The increase in styrene containing triads is evident from the NMR spectra and is predicted by the model. Figure 11 shows the correspondence between calculated and measured triad fractions for this system. 

Figure 10. Development of triad fractions as observed by NMR for a model 25/75—styrene/ethyl acrylate copolymer prepared with a linear power feed profile in which ethyl acrylate decreased 1.0 -> 0.50 and styrene increased 0 — 0.50...

To be useful for risk assessment, the answers from all tests in a WOE approach should be made comparable, e.g. by a uniform scaling method, preferably without losing quantitative information (Burton et al., 2002 Schmidt et al., 2002). A continuous effect scale running from 0 to 1 (representing a quantitative measure for the fraction of effect on an ecosystem) seems to fulfil quantitative requirements. For this part, many methods are still in development and answers rely heavily on the experts using these methods. In addition, non-objective choices must be made because there is no comprehensive ecosystem theory available. Fortunately, because the Triad approach is based on a WOE procedure, mismatches can be picked up as results that are obviously out of the range, making evaluation and correction conceivable. 

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