Interfacial processes prepared from

Unsaturated polyesters (UPs), 4, 18, 19 from PET waste, 560-561 Unsaturated polyester/styrene resin, preparation and cure of, 101 Unsaturated polyester thermosetting resins, syntheses of, 101-103 Unstirred interfacial process, 155 U-Polymer, 77... 

Emulsions are two-phase systems formed from oil and water by the dispersion of one liquid (the internal phase) into the other (the external phase) and stabilized by at least one surfactant. Microemulsion, contrary to submicron emulsion (SME) or nanoemulsion, is a term used for a thermodynamically stable system characterized by a droplet size in the low nanorange (generally less than 30 nm). Microemulsions are also two-phase systems prepared from water, oil, and surfactant, but a cosurfactant is usually needed. These systems are prepared by a spontaneous process of self-emulsification with no input of external energy. Microemulsions are better described by the bicontinuous model consisting of a system in which water and oil are separated by an interfacial layer with significantly increased interface area. Consequently, more surfactant is needed for the preparation of microemulsion (around 10% compared with 0.1% for emulsions). Therefore, the nonionic-surfactants are preferred over the more toxic ionic surfactants. Cosurfactants in microemulsions are required to achieve very low interfacial tensions that allow self-emulsification and thermodynamic stability. Moreover, cosurfactants are essential for lowering the rigidity and the viscosity of the interfacial film and are responsible for the optical transparency of microemulsions [136]. 

When the polycarbonate of bisphenol A was made interfacially in a non-solvent for the polymer the distribution of molecular weights showed two clear maxima and was unusually broad [40]. This was probably a consequence of the two-step process often employed in the preparation of polycarbonates here, the first step yields low-molecular-weight polymer from phosgene and the aqueous alkaline solution of the aromatic diol, then an accelerator salt and more alkali and phosgene are added in the second step. Polycarbonates prepared in the melt and in solution show the expected essentially statistical distribution of molecular weights [40]. Polycarbonates have also been prepared from bisphenols and bisphenol bischloroformates studies of this reaction in nitrobenzene solution have shown it to be second order [79]. 

The process has been extensively explored by Barbe and coworkers in Australia (where the same scientists established the spin-off company Ceramisphere), and can be viewed as an emulsification of a sol-gel solution in which gelation takes place concomitantly. Depending on the order of addition of the different chemicals, furthermore, the porous microparticles prepared from interfacial hydrolysis and condensation of TEOS in W/0 emulsion will be full porous matrix particles or core-shell capsules. Normally, if the emulsification of the sol-gel solution takes place concomitantly with gelation, full microparticles are formed with the dopant molecules homogeneously distributed within the inner huge porosity of the particles (Figure 18.3). 

Often, in bench studies aimed at understanding emulsion-stabilization mechanisms, a hypothesis is devised. Most often the components of crudes are first separated, and a model emulsion is prepared from various combinations of the components in a model oil and in water of quality similar to that of formation or process water. The stability or instability is traced either by water resolution or by observing flie interfacial film properties under some form of externally applied stress over time. The stress may include temperature increases or solvent changes. The system may then be modified by the demulsifier and the changes in behavior are compared to that without the demulsifier. Deductions are then made about the film mechanics of the system in response to the variables. 

From a manufacturing standpoint, the interfacial process is capital-intensive to purify the resin solution, isolate and dry the resin, and recycle solvents and brine. With melt transesterification, because it is a solventless process, the only recycle streams that must be dealt with are those related to the recovery of phenol for reuse in the production of DPC. Hence, there is no need to invest in solvent recovery infrastructure with the melt process, and polymer purification units and dryers can likewise be avoided. However, these investments are somewhat diminished by the investment required for the preparation and purification of DPC. 

The copolymer (Fig. 14.4) is prepared from l,l-bis(4-hydroxyphenyl)-3,3, 5-trimethylcyclohexane (1) and bisphenol A. The cyclohexane containing bisphenol (1) is prepared by the condensation of phenol with 3,3,5-trimethylcyclohexanone and an acidic catalyst. The cyclohexanone can be prepared by the selective hydrogenation of isophorone [113, 114]. The Tg of the copolymers can be varied from 150°C (e.g., BPAhomopolymer) to 240°C [e.g., homopolymer of l,l-bis(4-hydroxyphenyl)-3,3,5-trimethylcydohexane]. And the resins can be prepared by either melt or interfacial processes. For increased ductility, terpolymers have been reported with a sUoxane block [115]. For applications requiring low moisture absorption, the bisphenol (1) has been polymerized with bisphenol M (see the section New Copolymers for Optical Storage Media ). 

Aromatic polycarbonates are prepared from various bisphenols, the most widely used being bisphenol A. The synthesis of aromatic polycarbonates is based on the reaction of bisphenol with carbonic acid derivatives such as phosgene, diphosgene, carbonic acid esters and chloroformic acid esters. The most important process for production of aromatic polycarbonate is the so-called interfacial process , first developed by Bayer. In this process, bisphenol A is phosgenated in the presence of methylene chloride in controlled conditions. 

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