Crosslinked poly(methyl methacrylate) (PMMA‐c), poly(carbonate‐urethane) (PCU‐c), poly(vinyl pyridine) (PVP‐c), and full, simultaneous interpenetrating polymer networks (IPNs) based on the above polymers were characterized by precise heat capacity (Cp) measurements in the temperature interval 4.2–450 K. The raw values of Cp scaled with temperature (T) as Cp ∼ Td with d = 2 and 5/3, as expected for a fracton‐like vibration regime, in the temperature intervals 8–10 and 10–30 K, respectively. A single glass transition temperature (Tg) and two Tg's were observed for apparently homogeneous and microphase‐separated IPNs, respectively. Judged by the positive sign of the excess Gibbs free energy, the apparently single‐phase state of homogeneous IPNs is thermodynamically unstable; however, its kinetic stability is ensured by permanent topological constraints (network junctions) prohibiting the incipient phase separation.
SYNOPSISCrosslinked poly (methyl methacrylate) and poly (carbonate-urethane) as well as full interpenetrating network on their base (IPN) were characterized by precise heat capacity measurements in the temperature interval 4.2-450 K. As judged by the positive sign of the excess Gibbs free energy in the whole temperature interval above 30 K, the apparently single-phase state of IPN is thermodynamically unstable; however, its kinetic stability is ensured by permanent chamical crosslinks prohibiting the incipient phase separation.
Unfilled and carbon black-filled samples of synthetic isoprene-and butadiene-methylstyrenebased rubbers were characterized by precise heat capacity measurements in the temperature interval 4.2-300 K. Both unfilled samples proved to behave in an essentially fraeton-like way in the temperature interval 6-30 K. The excess thermodynamic quantities derived from the smoothed data suggested that the thermodynamic state of the elastomeric phase in the filled rubbers was intrinsically unstable.
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