10.1021/am800197j.s001 Markus Klinger Markus Klinger Lars Poulsen Tolbod Lars Poulsen Tolbod Kurt V. Gothelf Kurt V. Gothelf Peter R. Ogilby Peter R. Ogilby Effect of Polymer Cross-Links on Oxygen Diffusion in Glassy PMMA Films American Chemical Society 2009 UV polymer cinnamic acid film Glassy PMMA FilmsOxygen diffusion coefficients 2009-03-25 00:00:00 Journal contribution https://acs.figshare.com/articles/journal_contribution/Effect_of_Polymer_Cross_Links_on_Oxygen_Diffusion_in_Glassy_PMMA_Films/2868766 Oxygen diffusion coefficients, <i>D</i>, have been measured in poly(methyl methacrylate) (PMMA) films containing small amounts of a cinnamic acid derived cross-linker. In the technique employed, the time evolution of oxygen sorption into the film was monitored using the phosphorescence of singlet oxygen as a spectroscopic probe. Although the effect of adding up to 1 mol % of the cross-linker is clearly manifested in the molecular weight and <i>T</i><sub>g</sub> of these samples, values of <i>D</i> are only moderately influenced. Nevertheless, a systematic decrease in the value of <i>D</i> is discernible as the extent of cross-linking is increased. Although it is reasonable to expect that, in a glassy polymer, cross-linking should not significantly perturb the local motions and confined changes in free volume that influence the translational motion of a small penetrant such as oxygen, our data indicate that even small amounts of a cross-linker can, nevertheless, have a noticeable and potentially meaningful effect. Although UV irradiation of the polymer films disrupts the cinnamic acid derived cross-linker via a [2 + 2] cycloreversion reaction, the photoinduced changes observed in <i>D</i> appear, rather, to reflect degradation reactions in the PMMA-based polymer.