Tensile Orientation Behavior of Alkoxy-Substituted Bis(phenylethynyl)benzene Derivatives in Polyolefin Blend Films

A series of new dichroic, photoluminescent alkoxy-substituted bis(phenylethynyl)benzene derivatives 1a − e, have been synthesized and characterized. All dyes are highly emissive and show bright-blue photoluminescence with quantum yields in solution ranging from 0.63 to 0.72. Oriented blend films comprising these dyes were prepared with ultrahigh-molecular-weight polyethylene (UHMW PE) as the matrix material by solution-casting, and with linear low-density polyethylene (LLDPE) by melt-processing as well as guest diffusion. Despite the introduction of alkoxy substituents, not all dyes are compatible with UHMW PE and large-scale phase segregation was observed during the preparation of a number of UHMW PE blend films. In the case of the latter, films with relatively good dichroic properties are only obtained if the melting point of the dye is lower than or equal to the deformation temperature. On the other hand, melt-processing of 1a − e with LLDPE produces homogeneous blends that, after tensile deformation, give rise to highly dichroic photoluminescent films. In this case, the melting temperature of the dye was found to be less relevant for the orientation process. In view of a future application of these PL blends as photoluminescent polarizer, melt-processed blends based on octyloxy- and dodecyloxy-substituted bis(phenylethynyl)benzene derivatives ( 1c, d ) and LLDPE embody the optimal combination of good accessibility, excellent luminescence characteristics and high polarization of the emitted light.