Polymerizations interfacial

Polycarbonates are manufactured via interfacial polymerization or through a melt esterification process. The properties of polycarbonate can differ greatly based on the method of polymerization. Specifically, the molecular weight distributions created by the two methods differ because of kinetic effects. Polycarbonates manufactured via interfacial polymerization tend to be less stable at high temperatures and less stiff than those produced via melt esterification, unless proper manufacturing precautions are taken. Therefore, when choosing a polycarbonate resin grade for a specific application, it is important to know the method by which it was produced. Either polymerization method can be performed as a continuous or batch process. 

At the start of interfacial polymerization, bisphenol A is dissolved in methylene chloride, then introduced into a reactor. Phosgene is injected into the reactor as a liquefied gas together with an aqueous solution of sodium hydroxide. The methylene chloride and the aqueous solutions are immiscible polymerization occurs at the interface between them. The reactants are combined in a rapidly stirred reactor as shown in Fig. 20.7. The sodium hydroxide neutralizes the hydrochloric acid that is generated by polymerization, while the organic phase serves as a solvent for the polymer. The organic phase is separated and washed to remove traces of the base or salts after which the solvent is removed. 

Polymerization occurs very quickly and the process is controlled via kinetic effects rather than thermodynamic ones. The net result is that the molecular weight distribution of the product does not match the thermodynamically stable one. If the chains were not capped with monofunctional phenols, the polymer chains would depolymerize, allowing the monomers to rearrange themselves at elevated temperature to approach the thermodynamically stable 

This class of polymerization type is similar to an emulsion and suspension polymerization, however, it is mostly commonly employed for polycondensation reactions. An interfacial polymerization reaction occurs at or near the interfacial boundary of two immiscible solutions. The two reagents meet at the interface and react rapidly. The basis for this method is from the Schotten-Baumann reaction between an acid chloride and a compound containing an active hydrogen atom. Under the right conditions thin flexible walls of alternating copolymer form rapidly at the interface to form liquid-filled capsules (Scott et al, 2005. These capsules (about 210 nm) have been explored as direct and efficient encapsulation devices, given that their nanometer thick shells (about lOnm) and confined liquid-core domain, offer unique sequestration potential compared to conventional polymer nanoparticles. It has been proposed that 

Interfacial polymerization techniques can be used to prepare robust microcapsules (about 4 pm) that have selectively incorporated functionality such as catalytic groups in their liquid-core domains. The synthesis of these particles is achieved via an oil-in-oil emulsion in combination with interfacial polymerization methods and allows for the encapsulation of substrates not compatible with water-in-oil or oil-in-water emulsion systems (Kobalija and McQuade, 2006). Often these capsules have polyurea shells that can be formed from w/o emulsions containing reactive polyols and isocyanates. This has been very elegantly demonstrated by McQuade and coworkers for the DMAP-catalyzed acylation transformation of an alcohol within the protected environment of polyurea microcapsules formed from reaction of a polyisocyanate and a poly(vinyl alcohol) in the presence of an amine catalyst (Price et ah, 2006 Poe et al, 2007). 

There are few other examples of the application of interfacial polymerizations for the synthesis of encapsulated polymer materials. There is one notable example from the group of Tanaka, in which microcapsules were formed by interfacial polymerization using an oil-inwater emulsions with limonene oil (Mizuno et al, 2004). This was achieved by dispersing 

Many of the polymers that are produced by the usual high-temperature reactions could be produced at lower temperatures by using the faster Schotten Baumann reactions of acid chlorides. Thus polyesters and polyamides could he produced by replacing the diacid or di-eser reactant by the corresponding diacyl chloride 

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As with polyesters, the amidation reaction of acid chlorides may be carried out in solution because of the enhanced reactivity of acid chlorides compared with carboxylic acids. A technique known as interfacial polymerization has been employed for the formation of polyamides and other step-growth polymers, including polyesters, polyurethanes, and polycarbonates. In this method the polymerization is carried out at the interface between two immiscible solutions, one of which contains one of the dissolved reactants, while the second monomer is dissolved in the other. Figure 5.7 shows a polyamide film forming at the interface between an aqueous solution of a diamine layered on a solution of a diacid chloride in an organic solvent. In this form interfacial polymerization is part of the standard repertoire of chemical demonstrations. It is sometimes called the nylon rope trick because of the filament of nylon produced by withdrawing the collapsed film. 

The HCl by-product of the amidation reaction is neutralized by also dissolving an inorganic base in the aqueous layer in interfacial polymerization. The choice of the organic solvent plays a role in determining the properties of the polymer produced, probably because of differences in solvent goodness for the resulting polymer. Since this reaction is carried out at low temperatures, the complications associated with side reactions can be kept to a minimum. 

Figure 5.7 Sketch of an interfacial polymerization with the collapsed polymer film being withdrawn from the surface between the immiscible phases. [Redrawn with permission from P. W, Morgan and S. L. Kwolek, J. Chem. Educ. 36 182 (1959) copyright by the American Chemical Society.]...

A brief review has appeared covering the use of metal-free initiators in living anionic polymerizations of acrylates and a comparison with Du Font s group-transfer polymerization method (149). Tetrabutylammonium thiolates mn room temperature polymerizations to quantitative conversions yielding polymers of narrow molecular weight distributions in dipolar aprotic solvents. Block copolymers are accessible through sequential monomer additions (149—151) and interfacial polymerizations (152,153). 

Interfdci l Composite Membra.nes, A method of making asymmetric membranes involving interfacial polymerization was developed in the 1960s. This technique was used to produce reverse osmosis membranes with dramatically improved salt rejections and water fluxes compared to those prepared by the Loeb-Sourirajan process (28). In the interfacial polymerization method, an aqueous solution of a reactive prepolymer, such as polyamine, is first deposited in the pores of a microporous support membrane, typically a polysulfone ultrafUtration membrane. The amine-loaded support is then immersed in a water-immiscible solvent solution containing a reactant, for example, a diacid chloride in hexane. The amine and acid chloride then react at the interface of the two solutions to form a densely cross-linked, extremely thin membrane layer. This preparation method is shown schematically in Figure 15. The first membrane made was based on polyethylenimine cross-linked with toluene-2,4-diisocyanate (28). The process was later refined at FilmTec Corporation (29,30) and at UOP (31) in the United States, and at Nitto (32) in Japan. 

Fig. 15. Schematic of the interfacial polymerization process. The microporous film is first impregnated with an aqueous amine solution. The film is then treated with a multivalent cross-linking agent dissolved in a water-immiscible organic fluid, such as hexane or Freon-113. An extremely thin polymer film...

Membranes made by interfacial polymerization have a dense, highly cross-linked interfacial polymer layer formed on the surface of the support membrane at the interface of the two solutions. A less cross-linked, more permeable hydrogel layer forms under this surface layer and fills the pores of the support membrane. Because the dense cross-linked polymer layer can only form at the interface, it is extremely thin, on the order of 0.1 p.m or less, and the permeation flux is high. Because the polymer is highly cross-linked, its selectivity is also high. The first reverse osmosis membranes made this way were 5—10 times less salt-permeable than the best membranes with comparable water fluxes made by other techniques. 

Interfacial polymerization membranes are less appHcable to gas separation because of the water swollen hydrogel that fills the pores of the support membrane. In reverse osmosis, this layer is highly water swollen and offers Httle resistance to water flow, but when the membrane is dried and used in gas separations the gel becomes a rigid glass with very low gas permeabiUty. This glassy polymer fills the membrane pores and, as a result, defect-free interfacial composite membranes usually have low gas fluxes, although their selectivities can be good. 

Interfacial Polymerization. Many types of polymerization reactions can be made to occur at interfaces or produce polymers that concentrate at interfaces thereby producing microcapsules. Accordingly, this approach to encapsulation has steadily developed into a versatile family of encapsulation processes. Figure 4 schematically illustrates five types of encapsulation processes that utilize these types of reactions. 

Fig. 4. Schematic diagrams that illustrate the different types of interfacial polymerization reactions used to form microcapsules. Reactants X, Y polymerization product (X — Y)—n or —(X—See text for descriptions of cases (a)—(e).

Because almost any diacid can be leaddy converted to the acid chloride, this reaction is quite versatile and several variations have been developed. In the interfacial polymerization method the reaction occurs at the boundary of two phases one contains a solution of the acid chloride in a water-immiscible solvent and the other is a solution of the diamine in water with an inorganic base and a surfactant (48). In the solution method, only one phase is present, which contains a solution of the diamine and diacid chloride. An organic base is added as an acceptor for the hydrogen chloride produced in the reaction (49). Following any of these methods of preparation, the polymer is exposed to water and the acid chloride end is converted to a carboxyhc acid end. However, it is very difficult to remove all traces of chloride from the polymer, even with repeated washings with a strong base. 

An excellent review of composite RO and nanofiltration (NE) membranes is available (8). These thin-fHm, composite membranes consist of a thin polymer barrier layer formed on one or more porous support layers, which is almost always a different polymer from the surface layer. The surface layer determines the flux and separation characteristics of the membrane. The porous backing serves only as a support for the barrier layer and so has almost no effect on membrane transport properties. The barrier layer is extremely thin, thus allowing high water fluxes. The most important thin-fHm composite membranes are made by interfacial polymerization, a process in which a highly porous membrane, usually polysulfone, is coated with an aqueous solution of a polymer or monomer and then reacts with a cross-linking agent in a water-kniniscible solvent. 

Bisphenol A Polycarbonate Resins. These resins are manufactured by interfacial polymerization (84,85). A small amount of resin is produced by melt-polymerization of bisphenol with diphenyl carbonate in Russia and the People s RepubHc of China. Melt technology continues to be developmental in Japan and the West, but no commercial activities have started-up to date, although some were active in the late 1960s. No reports of solvent-based PC manufacture have been received. 

UF Membranes as a Substrate for RO An important use of UF membranes is as a substrate for composite reverse-osmosis membranes. After the UF membrane (usually polysulfone) is prepared, it is coated with an aqueous solution of an amine, then dipped in an organic solution of an acid chloride to produce an interfacially polymerized membrane coating. 

Polymerization reactions can occur in bulk (without solvent), in solution, in emulsion, in suspension, or in a gas-phase process. Interfacial polymerization is also used with reactive monomers, such as acid chlorides. 

Interfacial polymerization is mainly used in polycondensation reactions with very reactive monomers. One of the reactants, usually an acid... 

Figure 3.17 Setup for interfacial polymerization with pulling a rope.34...

Acid chlorides are very reactive and at room temperature react readily with amines. Synthesis by interfacial and solution methods is possible. However, care should be taken that the hydrochloric acid produced does not react with unreacted amine groups. With the strong basic aliphatic diamines, the acid binder must preferably be even more basic. The attainable molecular weights are strongly dependent on the concentrations this is particularly the case for easily precipitated terephthalamide polymers. Possible problems with the acid binder can be overcome by starting with silylated diamines.33,34 A typical example for interfacial polymerization of terephthalamides is PA-2,T.66... 

This polymer can be synthesized from m-phenylenediamine and isophthaloyl chloride. It can be prepared by interfacial polymerization or solution polymerization.4,7 9 14... 

Preparation of siloxane-carbonate segmented copolymers by interfacial polymerization involves the reaction of carboxypropyl-terminated siloxane oligomers with bisphenol-A and phosgene, in the presence of a strong base and a phase transfer catalyst, in water/methylene chloride solvent system l50 192), as shown in Reaction Scheme XIV. 

Poly(arylester)-polysiloxane multiblock copolymers have also been synthesized by the interfacial polymerization of aminopropyl terminated polysiloxane oligomers with bisphenol-A and a mixture of isophthaloyl and terephthaloyl chlorides117, 193-1951 as illustrated in Reaction Scheme XV. In these reactions the poly(arylester) blocks are formed in situ during the copolymerization, so the control of their block sizes is not very precise. It is also important to note that since aminopropyl terminated siloxane oligomers are employed, the linkages which connect the arylester and siloxane blocks are amide linkages. 

Perhaps the most interesting finding of our synthetic studies was that the interfacial preparation of poly(iminocarbonates) is possible in spite of the pronounced hydrolytic instability of the cyanate moiety (see Illustrative Procedure 3). Hydrolysis of the chemically reactive monomer is usually a highly undesirable side reaction during interfacial polymerizations. During the preparation of nylons, for example, the hydrolysis of the acid chloride component to an inert carboxylic acid represents a wasteful loss. 

Illustrative Procedure 3 Poly(iminocarbonates) by Interfacial Polymerization (46) 4.5 mmol of a diphenol was dissolved in... 

The structure of poly(iminocarbonates) synthesized by the direct interfacial polymerization of BPA and cyanogen bromide was analyzed by NMR, Fourier transform infrared spectroscopy and elemental analysis and found to be identical in all aspects to authentic poly(imino-carbonates) obtained by solution polymerization (46). 

Hollow and porous polymer capsules of micrometer size have been fabricated by using emulsion polymerization or through interfacial polymerization strategies [79,83-84, 88-90], Micron-size, hollow cross-linked polymer capsules were prepared by suspension polymerization of emulsion droplets with polystyrene dissolved in an aqueous solution of poly(vinyl alcohol) [88], while latex capsules with a multihollow structure were processed by seeded emulsion polymerization [89], Ceramic hollow capsules have also been prepared by emulsion/phase-separation procedures [14,91-96] For example, hollow silica capsules with diameters of 1-100 micrometers were obtained by interfacial reactions conducted in oil/water emulsions [91],... 

The second general method, IMPR, for the preparation of polymer supported metal catalysts is much less popular. In spite of this, microencapsulation of palladium in a polyurea matrix, generated by interfacial polymerization of isocyanate oligomers in the presence of palladium acetate [128], proved to be very effective in the production of the EnCat catalysts (Scheme 3). In this case, the formation of the polymer matrix implies only hydrolysis-condensation processes, and is therefore much more compatible with the presence of a transition metal compound. That is why palladium(II) survives the microencapsulation reaction... 

The predominant RO membranes used in water applications include cellulose polymers, thin film oomposites (TFCs) consisting of aromatic polyamides, and crosslinked polyetherurea. Cellulosic membranes are formed by immersion casting of 30 to 40 percent polymer lacquers on a web immersed in water. These lacquers include cellulose acetate, triacetate, and acetate-butyrate. TFCs are formed by interfacial polymerization that involves coating a microporous membrane substrate with an aqueous prepolymer solution and immersing in a water-immiscible solvent containing a reactant [Petersen, J. Memhr. Sol., 83, 81 (1993)]. The Dow FilmTec FT-30 membrane developed by Cadotte uses 1-3 diaminobenzene prepolymer crosslinked with 1-3 and 1-4 benzenedicarboxylic acid chlorides. These membranes have NaCl retention and water permeability claims. 

Recently, many synthetic polymers such as urea/formalin resin, melamine/formalin resin, polyester, and polyurethane have been widely used as the wall material for the microcapsule, though the gelatin microcapsule is still used. Microcapsules using a synthetic polymer wall have several advantages over those using a gelatin wall (1) the preparation process is simple, (2) the size of the microcapsules is well balanced, (3) the microcapsule concentration can be increased twofold or more and (4) the microcapsules have a high resistance to water and many chemicals. Synthetic microcapsules are prepared by interfacial polymerization or in situ polymerization. 

Preparation of nanoparticles can be by a variety of different ways. The most important and frequently used is emulsion polymerization others include interfacial polymerization, solvent evaporation, and desolvation of natural proteins. The materials used to prepare nanoparticles are also numerous, but most commonly they are polymers such as poly-alklcyanoacrylate, polymethylmethacrylate, poly-butylcyanoacrylate, or are albumin or gelatin. Distribution patterns of the particles in the body can vary depending on their size, composition, and surface charge [83-85]. In particular, nanoparticles of polycyanoacrylate have been found to accumulate in certain tumors [86,87]. 

In interfacial polymerization, monomers react at the interface of two immiscible liquid phases to produce a film that encapsulates the dispersed phase. The process involves an initial emulsification step in which an aqueous phase, containing a reactive monomer and a core material, is dispersed in a nonaqueous continuous phase. This is then followed by the addition of a second monomer to the continuous phase. Monomers in the two phases then diffuse and polymerize at the interface to form a thin film. The degree of polymerization depends on the concentration of monomers, the temperature of the system, and the composition of the liquid phases. 

Many polymers can be produced via interfacial polymerization. These multiphase reactions occur in emulsions, suspensions, slurries, or at the interface between a gas and a solid. 

When the reactants involved in a step growth polymerization process are mutually immiscible, we can employ an interfacial polymerization method. Two solutions, each containing one of the monomers, are layered one on top of the other. This creates a phase boundary that forms wth the least dense liquid on top. The different monomers can then meet and polymerize at the interface. A commonly demonstrated example of this is the manufacture of nylon 610 by the interfacial reaction between an aqueous solution of hexamethylenediamine with sebacoyl chloride dissolved in carbon tetrachloride. Because the reaction only occurs at the interface, it is possible to pull the products from this interface to isolate the final product. 

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