Orientation and In-Situ Photopolymerization of a Diacetylene Monomer in Gel-Processed Ultra-High Molecular Weight Polyethylene: Films with Several Optical Security Features

• Published in: Advanced functional materials 2002-06, Vol.12 (6-7), p.441-446
• Main Authors: Uhm, J.S., Giesa, R., Schmidt, H.-W.
• Format: Article
• Language: English
• Subjects: Diacetylenes; Optical dichroism; Optical security devices; Photopatterning; Photopolymerization; Polyethylene
• ISSN: 1616-301X; 1616-3028
• DOI: 10.1002/1616-3028(20020618)12:6/7<441::AID-ADFM441>3.0.CO;2-1

Highly transparent and oriented films of the diacetylene monomer, 5,7‐dodecadiyne‐1,12‐bis(n‐butoxycarbonylmethylurethane) (4BCMU) in ultra‐high molecular weight polyethylene (UHMW PE) were prepared utilizing the gel‐processing technique with subsequent tensile drawing. After UV radiation the films yield highly absorbing and oriented poly‐4BMCU. The orientation of the polymerized 4BCMU form was investigated using polarized UV‐vis spectroscopy and wide‐angle X‐ray diffraction. Morphology studies showed that 4BCMU crystallized from the melt within the microchannels, with the monomer long axis perpendicular to the internal surfaces and therefore with the polymer axis parallel to the drawing direction. Thermal annealing and the transition to the red form of the films results in a five‐ to six‐fold increase in optical anisotropy. The described system combines several useful security features such as photopatterning, easily detectable optical anisotropy, and irreversible color change upon heating, which could be utilized in optical security devices. Useful optical security features such as photopatterning (see Figure), easily detectable optical anisotropy, and irreversible color change are displayed by the polymer films presented here, i.e., oriented polydiacetylene incorporated in a polyethylene matrix. The optical anisotropy of these films—prepared via gel processing and subsequent tensile drawing—is demonstrated to be dependent on the draw ratio and concentration and form of polydiacetylene in the matrix.