Modern Polymer Spect..

74 2 Seyrneiitiil Mobility qf' Liquid Cvj~stul~ iiizd Liquid-Cryrtulliiie Polyriievs
L)FFORRl.AI~ION
-%I {E".l
CROSSLlhKING UNDER -
STRESS
.Y LSCE
\
CROSSLINKING WITHOUT
DEFORMATION
I>F.I'ORMATION
- =
1 REFERENCE ELASTOMER
CH3 4
g,n 3°C n,i 83OC LSCE
g,n 2 OC n.i 81 'C REFERENCE ELASTOMER
Figure 2-43. Cheinical structure, transition temperatures and schematic presentation of the crosslinking
processes involved in the synthesis of the investigated LSCE and reference elastomer [l 1 11.
(compound 3) and a vinyl- and niethacryloyl-substituted derivative (compound 4).
which has also liquid-crystalline properties, The key point of the crosslinking reactions
is the fact that, under the experimental conditions, the addition of the vinyl
group is faster by approximately two orders of magnitude [ll 11. Thus, in the first
step, a network with a low crosslink-density is synthesized because predominantly
compound 3 becomes active. In the second reaction step, the mesogens of this
network are macroscopically oriented by application of a stress at elevated temperature
and the induced anisotropy is fixed in the system by crosslinking via the
niethacryloyl groups. The crosslinking reactions were performed in the nematic
phase of the system. Part of the methoxy functionalities in compound 2 have been
replaced by nitrile groups to provide an IR-active probe for the Orientation measurements.
Additionally to the LSCE system, a structurally identical reference
elastomer was investigated, which had not been subjected to a mechanical deformation
during the second crosslinking step (Figure 2-43). In the reference polymer
the mesogens do not exhibit a macroscopic orientation and, contrary to the LSCE,
this material is opaque.
2.7.2.2 Rheo-Optical FTIR Spectroscopy
The increased need for more detailed data and a better understanding of the mechanisms
involved in polymer deformation and relaxation has led to the search