Using a tensile testing machine we perform mechanical testing to quantify the impact of changing stoichiometry on mechanical behavior for thiol-ene based polymeric materials. These thiol-ene polymers are unique because of their ability to be used in "click" chemistry reactions which in turn allow for many possibilities in terms of developing novel materials by choice of crosslinking moeieties and ene groups containing C-C double bonds. In our study we synthesize polymer specimens using poly[(3-mercaptopropyl)methylsiloxane] (PMMS) with 2,4,6-Trialloyloxy-1,3,5-triazine (TAC) and ethoxylated(2) Bisphenol-A Dimethacrylate (BPADMA) used as crosslinking agents. By varying the crosslinker-thiol ratio from approximately 0.25 to 1.5 we realize almost a five-fold change in stiffness. Increasing crosslinker-thiol ratio to unity also results in greater strength, and greater ability to dissipate strain energy.

We explain the decrease in stiffness when the crosslinker-thiol ratio is increased past unity by hypothesizing that due to excess crosslinkers present that there are thiol groups on monomer chains that form links with thiol groups on the same chain and not on different chains, which leads to a decrease in crosslinking and therefore a decrease in stiffness. We also realize an increase in stiffness in aged specimens for unity crosslinker-thiol ratio specimens where the stiffness is highest, as expected, which gives evidence to support the hypothesis that crosslinks can form even after the energy source needed to drive free radical propagation is removed. We also perform exploratory tests on aged specimens to test the effects of strain rate as well as to understand phenomena such as increased stiffness at low displacements, self-healing in certain classes of specimens, and viscoelastic effects occurring during testing.

Finally, we present some tests done to measure the load-time decay behavior of certain specimens and provide a possible explanation of behavior seen in earlier force-displacement curves due to the dependence of material properties on previous loading history.