| Affiliation: | 1. Department of Chemical Engineering, Texas Tech University, Lubbock, Texas 79409 State Key Laboratory of Polymer Material Engineering, Department of Polymer Science and Materials, College of Polymer Science and Engineering, Sichuan University, Chengdu 610065, China;2. Department of Chemical Engineering, Texas Tech University, Lubbock, Texas 79409 |
| Abstract: | Building on previous observations of anomalous melting behavior of solvents in polyisoprene, we have expanded our insight into the melting behavior of organic solvents in polymers and polymer networks through a calorimetric investigation of cylcohexane and cyclooctane in poly(dimethyl siloxane) (PDMS) precursors and model networks. The results are contrary to general expectations. Besides deviations between the predictions of the Flory-Huggins model and observed melting point depression of the small molecule organics, it is found that the melting point depression of cyclohexane in model networks is lower than that in the uncrosslinked precursors and unaffected by the molecular weight between crosslinks, which is not consistent with the general observation that higher crosslinking density leads to greater melting point depression. We interpret the observed phenomenon in terms of phase separation. In the case of cyclooctane, it exhibits a double melting peak in the model networks with high molecular weight between crosslinks. Furthermore, the heats of fusion of both cyclohexane and cyclooctane decrease with increasing polymer volume fraction which violates the underlying assumption that the heat of fusion of solvent in the polymer is the same as that in the bulk for both the Flory-Huggins model and the Gibbs-Thomson equation. © 2008 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 46: 2779–2791, 2008 |
