Gelation and Associating Polymers
The static theories of equilibrium gelation (percolation theory) and vulcanization (Flory-Stockmayer theory) are well known. But many of the interesting experiments on polymer sols and gels concern dynamics (e.g., viscoelasticity), which are less universal and more difficult to describe theoretically than static properties. The dynamical response of a polymer sol near its gel-point obviously depends on whether (i) the reaction process has been quenched, or (ii) reversible exchange between one sol-molecule and another is taking place. For associating polymer systems, such as solutions of ionomers close to the overlap threshold, case (ii) is of interest. However, if the rates of exchange are not too large, clusters can move a certain amount before losing their identity: at short time-scales the system is effectively quenched. This means that case (i) must be understood first. Some old and some new ideas concerning the quenched problem are reviewed below, followed by a few comments on future prospects for understanding case (ii).
KeywordsFractal Dimension Longe Relaxation Time Exclude Volume Interaction Rouse Model Entanglement Effect
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