Klinger, M.; Tolbod, L. P.; Gothelf, K. V.; Ogilby, P. R.
ACS Appl. Mater. Interfaces 2009, 1, 661–667, doi: 10.1021/am800197j
Center for Oxygen Microscopy and Imaging and Centre for DNA Nanotechnology, Department of Chemistry, University of Aarhus, Langelandsgade 140, Arhus, Denmark
Oxygen diffusion coefficients, D, 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 T(g) of these samples, values of D are only moderately influenced. Nevertheless, a systematic decrease in the value of D 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 D appear, rather, to reflect degradation reactions in the PMMA-based polymer.