  We report the first study to characterise intranight variability of the
blazar class from the perspective of (rest-frame) UV emission. For this, we
carried out intranight optical monitoring of 14 flat-spectrum radio quasars
(FSRQs) located at high redshifts (1.5 < $z$ < 3.7), in 42 sessions of median
duration $\sim$ 5.4 hr. These sources were grouped into two samples
distinguished by published fractional optical polarisation: (i) nine
low-polarisation sources with $p_{opt} < 3\%$ and (ii) five high-polarisation
sources. Unexpectedly, a high duty cycle (DC $\sim$ 30$\%$) is found for
intranight variability (with amplitude $\psi > 3\%$) of the low-polarisation
sources. This DC is a few times higher than that reported for low-polarisation
FSRQs located at moderate redshifts ($z$ $\sim$ 0.7) and hence typically
monitored in the rest-frame blue-optical. Further, we found no evidence for an
increased intranight variability of UV emission with polarisation, in contrast
to the strong correlation found for intranight variability of optical emission.
We briefly discuss this in the context of an existing scenario which posits
that the nonthermal UV emission of blazars arises from a relativistic particle
population different from that radiating up to near-infrared/optical
frequencies.
