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In their experiment "An Interferometric Study of Epoxy Polymerization" (J. Chem. Educ. 1999, 76, 666-668), Melissa Page and W. Tandy Grubbs describe an apparatus and method to monitor the polymerization of household epoxies. Their data yield a plot from which the gel point of the polymer formed can be identified. It is possible to obtain similar information with only a multimeter by following the resistance of a mixed sample with time. Components of Devcon five-minute epoxy were mixed for one minute and then squeezed between two plates held 0.013 cm apart by spacers. Data were collected, yielding Figure 1. The small current flowing through the sample as a result of the applied voltage of the meter is choked off between 500 and 600 seconds as the polymer gels. This result is comprehensible to introductory students and goes some way toward bringing to life the invisible cross-linked network being formed. Tested separately, the resistivity of the epoxy monomer is beyond the meter's range and the initiator has approximately half the resistivity of the initial mixture.
Figure 1. Curing of five-minute epoxy. Zero time was taken as the moment of mixing of components. The initial dip in the plot is due to compression of the blob of glue. The irregularities in the steep region are due to loss of precision at high resistivity.
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