  We present measurements of rotations of the optical polarization of blazars
during the second year of operation of RoboPol, a monitoring programme of an
unbiased sample of gamma-ray bright blazars specially designed for effective
detection of such events, and we analyse the large set of rotation events
discovered in two years of observation. We investigate patterns of variability
in the polarization parameters and total flux density during the rotation
events and compare them to the behaviour in a non-rotating state. We have
searched for possible correlations between average parameters of the
polarization-plane rotations and average parameters of polarization, with the
following results: (1) there is no statistical association of the rotations
with contemporaneous optical flares; (2) the average fractional polarization
during the rotations tends to be lower than that in a non-rotating state; (3)
the average fractional polarization during rotations is correlated with the
rotation rate of the polarization plane in the jet rest frame; (4) it is likely
that distributions of amplitudes and durations of the rotations have physical
upper bounds, so arbitrarily long rotations are not realised in nature.
