ISSN:
0887-6266
Keywords:
liquid crystals
;
acrylate
;
photopolymer network
;
dynamic mechanical analysis
;
infrared dichroism
;
Physics
;
Polymer and Materials Science
Source:
Wiley InterScience Backfile Collection 1832-2000
Topics:
Chemistry and Pharmacology
,
Physics
Notes:
This article is concerned with molecular orientation in liquid crystal (LC) monomers and the retention of orientation in crosslinked network polymers formed from them by photopolymerization. This is of importance because anisotropic mechanical and physical properties can be beneficial in certain structural applications. To this end, linear viscoelastic behavior of liquid crystal photo-monomers was investigated with dynamic mechanical analysis, and molecular order was studied by infrared dichroism measured with Fourier transform infrared spectroscopy. Although the order parameter of the monomer could vary from 0.45 to 0.70, depending on temperature, the order parameters of the polymer samples varied only from 0.50 to 0.62 and depended on polymerization temperature and extent of cure. The mechanical anisotropy was found to be a complicated phenomenon that depended not only on the molecular order, but also on other factors such as free volume and network structure. The difference in the elastic modulus parallel and perpendicular to the alignment direction was as high as a factor of two in the glassy state, and a factor of three above Tg. In addition, different amounts of mechanical anisotropy could be induced by varying the cure conditions. Finally, different postcuring schemes could cause variations in mechanical behavior by advancing cure or by inducing secondary reactions. © 1998 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 36: 1081-1089, 1998
Additional Material:
10 Ill.
Type of Medium:
Electronic Resource
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