Changes during cross-linking

Figure 4.19 Fractional velocity shift and change in attenuation as a function of time, measured during cross-linking of HR-100 negative photoresist film. (Reprinted with pennission. See Ref. [195].)...

Crosslinking polymerization of comonomers in a diluent diiiers from the above model in that the monomers themselves represent a good solvent for the emerging polymer, but their concentration, as well as that of the polymer and of the crosslinks, steadily changes with monomer conversion and remains unknown. These factors dramatically limit the practical usefulness of Eq. [3.6]. Still, it is worthwhile to analyze which of these four parameters are really critical for the phase separation to occur during cross-linking copolymerization. 

Many studies have been devoted to the determination of the structures of radicals and to the changes in their concentrations during cross-linking photopolymerizations. Most of these studies focused on the structures of the trapped radicals. In the case of multiacrylates, generally a 3-line spectrum was observed, which was consistent both with the chain-end structure (II) as well as with a mid-ehain structure (III) obtained after tertiary hydrogen abstraction from the polymer chain ... 

Fig. 6-4 Viscosity changes during the processing of TS. The B-stage represents the start of the heating cycle followed by a chemical reaction (cross-linking) and solidification of the plastic.

Expansion and contraction can be controlled in plastic by its orientation, cross-linking, adding fillers or reinforcements, and so on. With certain additives the CLTE value could be zero or near zero. For example, plastic with a graphite filler contracts rather than expands during a temperature rise. RPs with only glass fiber reinforcement can be used to match those of metal and other materials. In fact, TSs can be specifically compounded to have little or no change. 

The chemical changes that can occur during processing and effect product performances include (1) continued polymerization and cross-linking, which increases viscosity (2) depolymerization or damaging of molecules, which reduces viscosity and (3)... 

In a film, the cooperative effort of the different molecular motors, between consecutive cross-linked points, promotes film swelling and shrinking during oxidation or reduction, respectively, producing a macroscopic change in volume (Fig. 18). In order to translate these electrochemically controlled molecular movements into macroscopic and controlled movements able to produce mechanical work, our laboratory designed, constructed, and in 1992 patented bilayer and multilayer103-114 polymeric... 

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