Positron annihilation studies of nanoholes and microphase formation control of a PMMA+MMA+TEGDMA system

Positron annihilation lifetime spectroscopy (PALS) was applied for the study of a set of PMMA (polimethyl-methacrylate)+MMA (methyl-methacrylate)+TEGDMA (triethyleneglycol-dimethacrylate) blends prepared by two synthesis routes (standard and phase separation methods). The aim was to investigate the correlation between free volume and miscibility of the compounds. PALS measurements were performed in order to determine contents and sizes of free volume on the 'standard' and 'phase-separation' polymers; important differences in the behavior of the free volume composition curves were found, which are explained in terms of the formation of microregions in the phase separation material. When considering simple binary interchain interaction, the mean free volume hole fraction in a blend was computed in terms of an interaction parameter (β) that might be correlated to the Flory-Huggins interaction parameter (χ). This suggests that local free volume properties of polymer in blends are very important for local packing and segmental arrangements. We have re-encountered the task of defining miscibility depending upon the scale of observation: we observed distinct phases in the micrometer scale while still nothing can be discerned in the nanometer scale. We conclude that it is possible to produce a PMMA+TEGDMA blend with the presence of a low fraction of MMA/TEGDMA copolymer situated at the interphase between the PMMA and TEGDMA regions allowing a higher degree of compatibility of the components.