Polymerization-induced phase separation decomposition

The Spinodal Decomposition, also named reaction-induced [29] and also polymerization-induced phase separation [30], is the phase separation mechanism most observed on thermoset/thermoplastic blends, commonly initially miscible. In this mechanism the second-phase grows spontaneously, without a thermodynamic or energetic barrier, leading the blend to a immiscible region [27]. 

Spinodal decomposition is of fundamental importance in processes involving phase separation of polymers in near- and supercritical fluids [145]. Pressure-induced phase separation (PIPS) has recently been used [4], with a novel experimental apparatus [146] that permits the imposition of rapid and controlled multiple pressure quenches, to study spinodal decomposition of near- and off-critical mixtures of a polymer and a compressed solvent following deep quenches into the unstable region. Spinodal decomposition is also important in SAS, in situations where the mass transfer pathway leads to penetration into the unstable region [76,147,148]. It can also be important in RESS involving polymeric solutes [35]. Experimental aspects of spinodal decomposition and the kinetics of phase separation in polymer solutions in near-critical fluids are discussed in the chapter by E. Kiran in this volume. 

Under the DSC conditions (N, scanning rate = 10°C/min), it is apparent that the decomposition processes are occurring at a much faster rate at or near the temperature at which cure is taking place in all the pure dlcyanate samples. Both BADCy and THIOCy showed small exotherms (onset at 277°C and 226°C and peak at 308°C and 289°C, respectively). Their major decompositions began about 251°C and 246°C, respectively, as observed by TGA. On the contrary, all the 1 1 BCB/dlcyanate blends displayed the expected thermal transitions. Besides initial Tg s (20-28°C) and Tm s (171-183°C), all samples showed small exotherms in their DSC scans with maxima at 147-151°C. This is attributable to the thermally-induced crystallization in the mixtures, which also led to some initial phase separation. The polymerization exotherms are consistent with the typical temperature ranges for the known benzocyclobutene-based systems (onset 229-233°C max. 259-266°C). 

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