Investigation of the micro-morphology of polyethylene and polypropylene films: The type and distribution of sites as assessed by the accessibility of small organic molecules

Five polyolefins in film form have been derivatized at interior sites with 9-anthrylmethyl (9-AnCH₂) lumophoric groups. Their static and dynamic photophysical properties in the absence and presence of two small diffusing molecules that quench the excited singlet states of the lumophores, N,N-dimethylaniline (DMA) and N,N-didodecylaniline (DODA), have been used to investigate polymer micro-morphology, especially the number and distribution of site types where the 9-AnCH ₂ reside and the ease of access to them by DMA and DODA. The polymers are polyethylenes of varying crystallinities and polypropylenes with different tacticities. The influence of different chain lengths and molecular weights of the N,N-dialkylanilines on their accessibility rates of diffusion to the lumophore-occupied sites have been assessed. Correlations between the accessibilities of the N,N-dialkylanilines to the lumophore-occupied sites and the structures of the polymers have been made. From the temperature dependence of the diffusion coefficients, the activation energies for diffusion have been calculated. In some films, more than one diffusion coefficient is needed to fit satisfactorily the diffusion data. In the polyethylenes, crystallinity is found to be a major factor in influencing the accessibilities; in the polypropylenes, tacticity (which is related to crystallinity) is an important factor. The long alkyl chains of DODA induce favorable interactions with the polymer chains, increasing the rates of diffusion and the accessibilities to lumophore-occupied sites. Comparisons of these results with those from other related systems are made.