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Two new ferroelectric oligosiloxanes, a cyclic tetramer and a twin, have been synthesized. By a comparative study with their corresponding monomer and side chain polysiloxanes, the influence of oligo-and polymerization on the liquid crystalline and ferroelectric properties have been investigated. Polymerization leads to a stabilization of LC phases through increase of the clearing temperatures and suppression of crystallization. Oligomerization also leads to mesophase broadening, but, due to the low degree of polymerization, the effect is inferior to the linear polysiloxanes. The low viscosity of the oligosiloxanes ensures response times in the microsecond region, thus being comparable with their monomer and conventional LMWFLCs.It is Pound that polymerization increases the spontaneous polarization P,. This is attributed to the density increase after polymerization, enhancing the inter-mesogenic interactions. The collective and local dynamics of the OFLCs are influenced differently with respect to their molecular structures. Each oligomer is already a good model for its corresponding polymer concerning the soft mode dynamics. For the local p-relaxation a similar temperature dependence of the relaxation times z for the cyclic tetramer and for the side chain polysiloxanes is observed. The long axial rotation of the twin, having a very efficient decoupling, is significantly faster, thus resembling the monomer.

Communications ADVANCED MATERIALSobserved at high temperatures. The experimental values of i(, at high temperatures are not reproduced well by the two models mentioned above. Above 180 K the measured susceptibility is larger than the calculated one. The mechanism of the spin-spin coupling in the dimer 1 in this temperature range remains to be discussed. Further studies are necessary before this system can be understood completely. E.xperimental4-amino-4-carboxyl-2,2,6,6-tetramethylp1peridine-l-oxyl(2) and the dinitroxylamide (2) were prepared from 4-0~0-2.2,6,6-tetramethylpiperidine as described in our previous work [lo]. The magnetic susceptibilities were determined with an AC Susceptometer Model 7000 in an external field of 5.027 Oe. The measurements were carried out with about 100 mg of the powder samples over a temperature range from 4.2 K to 300 K for the dimer 1 and 4.3 K to 150 K for the monomer 2. The diamagnetic contributions of the radicals xd = -1 . 4~ (emulmol) for the monomer 2 and xd = -2.6 x (emuimol) for the dimer 1, which are calculaled using Pascal's constants (1 I] and the values from Yamanchi [12], are used to correct the measured susceptibilities to obtain the paramagnetic susceptibilities xg.