Polymers, inorganic thermal transitions

Table 8.1 Thermal transitions for selected inorganic polymers.

Differential scanning calorimetry (DSC) is a calorimetric method that finds widespread use in many fields, including protein dynamics, polymers, pharmaceuticals, and inorganic materials. DSC measures energy (heat) flow into a sample and a reference substance as a function of controlled increase or decrease of temperature. In a typical power-compensated DSC (Fig. 3.2), the sample and reference are placed on metal pans in identical furnaces each containing a platinum resistance thermometer (thermocouple) and heater. During a thermal transition (e.g., when a physical change in the sample occurs),... 

Considering, for instance, a system containing 1 nm thick plates, Ipm in diameter, the distance between plates would approach 10 nm at only 7 vol% of plates [217]. The behavior of PNCs can be rationalized as follows. The proliferation of internal inorganic-polymer interfaces means the majority of polymer chains reside near an inorganic surface. Since an interface restricts the conformations that polymer molecules can adopt, and since in PNCs with only a few volume percent of dispersed nanoparticles the entire matrix polymer may be considered as nanoscopically confined interfacial polymer, the restrictions in chain conformations will alter molecular mobility, relaxation behavior, and the consequent thermal transitions such as glass transition temperature of the composites [217]. 

In our work, we have used thermal analysis and have confirmed that the transition temperatures of NIPA gels are very close to the cloud points of aqueous solutions of NIPA polymers [5]. This can be seen in Figs. 2 and 3 which compare the phase transitions in the presence of an inorganic salt and in the presence of a cosolvent such as DMSO [5, 6]. Clearly, the transition temperature of the gel shows the same tendency as that of the polymer. 

Polyvinylidene fluoride (PVDF) is considerably less thermally stable than PTFE but much more stable than polyvinyl fluoride (PVF) or polychlorotrifluoroethylene (PCTFE). Certain inorganic compounds (silica, titanium dioxide, and antimony oxide) can catalyze its decomposition at temperatures above 375°C (707°F) [10], ETFE degradation is autocatalytic and similar to that of PVDF and is accompanied by the evolution of hydrogen fluoride (HF). Iron and transition metal salts can accelerate the degradation of ETFE by dehydrofluorination and oligomer formation [10], Copper salts have been found to stabilize the polymer [11], ETFE decomposes rapidly at temperatures above 380°C (716°F) [11],... 

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