Phase separation functional/reactive

Riccardi et al. (1996) focussed on the modelling of phase separation in reactive thermoset-solvent-high-performance-polymer mixtures by characterizing the interaction parameter as a function of conversion in a thermodynamic model. The reaction-induced... 

Porous materials used for chromatography result from a chemically induced phase separation using chain-wise polymerization of vinyl-containing monomers crosslinked with a portion of divinyl functional monomers. Frechet has improved this technique for the preparation of porous PS beads [48]. In this approach the inner phase consists of a mixture containing the reactive styrene and divinylbenzene monomers as well as an unreactive polymeric porogen. After polymerization, the soluble polymeric porogen is removed, leaving behind ma-croporous beads with pore sizes of around 100-500 nm. 

In copolycondensation for example, the more reactive monomer is expected to become exhausted more rapidly than the less reactive one. If the functionalities of the polyfunctional crosslinker are more reactive, short chains are formed in the beginning of the reaction and long chains in the end. If we assume equilibrium conditions throughout the reaction, the unreacted functionalities of the crosslinker on different growing trees, with short links in the beginning, are expected to react more likely with each other and as a result a part of the final network may be more crosslinked than the other part. This may eventually lead to phase separation. If the reaction is diffusion-controlled (177), cores with higher crosslinking density may be formed. 

In this case of three-monomer polyurethane synthesis, there is no thermodynamic driving force for phase separation. The formation of clusters is fully controlled by the initial composition of the system, the reactivity of functional groups, and the network formation history (one or two stages, macrodiol or triol reacted with diisocyanate first, etc.). 

In summary, the results show that a small variation in the nature (i.e., polarity and functionality) of the diamine or the epoxidized triglyceride oil leads to a big difference in thermoset morphology in terms of particle-size distribution (Table V) and phase inversion (Table VI). In addition to the nature of the diamines and the oils, other factors, such as their reactivity, are expected to influence the phase-separation process. Although we do not have data, a small difference in the cure rates of the DDM formulations at 75 °C and the DDS formulations at 150 °C might affect both the particle-size distribution and phase inversion. 

The thermoregulated phase-transfer function of nonionic phosphines has been proved by means of the aqueous-phase hydrogenation of sodium cinnamate in the presence of Rh/6 (N =32, R = n-CsHu) complex as the catalyst [16]. As outlined in Figure 2, an unusual inversely temperature-dependent catalytic behavior has been observed. Such an anti-Arrhenius kinetic behavior could only be attributed to the loss of catalytic activity of the rhodium complex when it precipitates from the aqueous phase on heating to its cloud point. Moreover, the reactivity of the catalyst could be restored since the phase separation process is reversible on cooling to a temperature lower than the cloud point. 

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