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This paper presents the use of phosphorescence spectroscopy to reveal the molecular mobility of polyepoxide networks. The polyepoxides are prepared by a photoinitiated cationic polymerization and cross-linking of (cyc1o)aliphatic bisepoxides. These networks emit fluorescence (Amu = 340 nm) and phos- phorescence (Amm = 480 nm) originating from intermediates in the photolysis of the initiator bis(4-tert-b~- tylpheny1)iodonium hexatluoroarsenate. The emission properties have been studied as a function of temperature. Both phosphorescence intensity and triplet excited state half-life show a discontinuity in their Arrhenius plots. For all networks this discontinuity is situated around 260 K and is due to the onset of quenching of the triplet excited state. The activation energy above the transition point is characteristic of the individual networks and is an indication of the increase in motion as the temperature is raised, ultimately leading to a simultaneous motion of large parts of the network. From these emission data the glass transition temperature and the width of the glass transition region have been estimated. The mechanical properties of the network are established with dynamic mechanical thermal analysis (DMTA) measuremenb. A striking correlation between molecular mobility (from emission data) and mechanical properties (from DMTA) is observed.

Molecular mobility of polyepoxide networks as revealed by emission spectroscopy and mechanical analysis