Factors Influencing Orientations of Covalently-Attached and Doped Aromatic Groups in Stretched Polyethylene Films

Abstract

Linear polarizations have been measured for covalently attached and doped 9-anthryl and 1-pyrenyl groups residing in interior sites of stretched polyolefinic films. The influences of polymer crystallinity, the concentration of aromatic groups, and the length of the substituents attached to doped molecules or of the tethers to polymer chains of covalently attached species on the degree of polarization have been explored. The results demonstrate the utility of comparing orientational parameters from doped and covalently attached groups in analyzing the factors responsible for stretch-induced orientation. The anthryl and pyrenyl groups prefer to reside in interfacial regions more than amorphous regions even before film stretching, and the specificity of their orientations is determined by the nature of interactions with surrounding polymer chains. The magnitudes of orientation factors are dependent on polymer crystallinity and substituent or tether length, but are independent of aromatic group concentrations as long as they are low. There are significant differences between the orientations of doped and covalently attached groups of the same type due to the inability of the latter to translocate between site types during film stretching. The results, as interpreted in the context of current theories, demonstrate the necessity of crystallite surfaces (i.e., interfacial sites), but not stretching-induced translocation, for selective orientation of aromatic groups along the axis of stretching.

Stretched Polyethylene Films Probed by Single Molecules

“…[7] The microfibrillar structure of drawn polyethylene possesses a rather large lateral surface area, which may stimulate solute translocation from the amorphous regions to the interfacial phase. [11] Optical spectroscopy on doped and stretched PE films has usually involved linear dichroism or comparable methods. Aligned dopant molecules in stretched PE have mostly been studied in order to determine the directions of transitiondipole moments of various electronic transitions.…”

Comparisons of Photo-Fries Rearrangements of 4-Dodecylphenyl Phenylacetate and Two Structurally Related Esters in Hexane and Polyethylene Cages. How Important Are Anchoring Chains?†

“…4-Dodecylphenyl phenylacetate (DPPA) was synthesized in four steps (see SUPPLEMENTAL MATERIALS). After the crude product was purified by HPLC with the use of a semipreparative C8 reverse-phase column from IBM Instruments Inc. Polyethylene films are designated by their degrees of crystallinity: PE0 (0% crystallinity 137-391; Nordel 3430, DuPont-Dow Elastomers, Murray, KY; 42.5 wt% ethylene, 57 wt% propylene, 0.5 wt% ethylidenenorbomene; thickness 1.0-2.0 mm); PE42 (42% crystallinity [37]; Sclair type from Dupont of Canada, Ontario, Canada; thickness 83 pm); and PE71 (71% crystallinity [37]; type ES-300 from Polialden Petroquimica of Brazil, Camacari, Bahia, Brazil; thickness 20 pm).…”

“…Furthermore, aryl esters reside both within the amorphous part and at interfacial sites (along the interfaces between crystallites and amorphous regions) of partkdlly crystalline PE films; they do not enter the crystalline portions (30)(31)(32)(33). The distribution of guests between these two site types varies with the specific PE film, but the interfacial concentration usually increases with increasing degree of crystallinity or after a film is stretched (30)(31)(32)(33)37). The distribution is important because molecules in the two site types can behave differently.…”

Time-resolved fluorescence of cationic dyes covalently bound to poly(methacrylic acid) in rigid media

“…In particular, the higher solubility of the dye in the solvent should drag it toward the surface, arranging a fraction of the chromophores in a spatial pattern proper for bimolecular interaction and excited state energy migration. Orientation of aromatic probes covalently attached to polymer has been clearly demonstrated in the study of stretched films [36,37]. Here, the external force is related to the solvent flow and bubbles during film forming.…”