  Poly(N-isopropylacrylamide) (PNIPAM) is a synthetic polymer that is widely
studied for its thermoresponsive character. However, recent works also reported
evidence of a low temperature (protein-like) dynamical transition around 225 K
in concentrated PNIPAM suspensions, independently of the polymer architecture,
i.e., both for linear chains and for microgels. In this work, we investigate
water-polymer interactions by extensive differential scanning calorimetry (DSC)
measurements of both systems, in order to understand the effect of the
different topological structures on the solution behaviour, in particular
regarding crystallization and melting processes. In addition, we compare
protiated and deuterated microgels, in both water and deuterated water. The DSC
results are complemented by dynamic light scattering experiments, which confirm
that the selective isotopic substitution differently affects the solution
behaviour. Our findings highlight the important role played by the polymer
architecture on the solution behaviour: indeed, microgels turn out to be more
efficient confining agents, able to avoid water crystallization in a wider
concentration range with respect to linear chains. Altogether, the present data
will be valuable to interpret future low-temperature investigations of PNIPAM
dispersions, particularly by neutron scattering experiments.
