Step polymerization interfacial process

Solid-state polymerization involves first-step production of low molecular weight polymer or oligomer via melt or interfacial process. The low molecular weight material is then crystallized in acetone. Basic catalyst is added and the material is heated above Tg but below crystalline melting temperature (Tm) to polymerize, and phenol is removed. The resulting polymer is melt-processed to remove crystallinity and form amorphous... 

Interfacial coacervation has been successfully used for many types of microcapsules. Stabilization of the emulsion phase with surfactant is an important step in this process. The surfactants used have included lignin sulfonates, other sulfonated polymeric surfactants, and vinylpyrrolidone co-and terpolymers. Increased photo stabilization of the AI, apparently due to light-absorbing properties of the polymers used, has been an added benefit observed for some encapsulated formulations. 

In the case of aliphatic diols, and for interfacial polymerizations, typically the diol is first prereacted with phosgene to form chloroformates [126,127]. The chloroformates are then condensed with BPAin a standard interfacial process to yield the copolymer with a reduced T and increased melt flow (Fig. 14.5). Selection of the diol in the process is important. Diols containing beta hydrogens, which often readily crack at elevated processing temperatures, lead to melt instabilities. This potential for poor melt stability, coupled with complications of a two-step process, has limited commercial interest in this approach. 

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. 

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. 

Polymerization of coniferyl alcohol is attempted at the air/water interface. The polymerization process was monitored by surface tension, ellipsometry and neutron reflectivity. The formation of the interfacial layer was found to proceed according to two steps formation of a dilute layer and then densification. 

The first step in all interfacial polymerization processes for encapsulation is to form an emulsion. This is followed by initiation of a polymerization process to form the capsule wall. Most commercial products based on interfacial or in situ polymerization employ water-immiscible liquids. For encapsulation of a water-immiscible oil, an oil-in-water emulsion is first formed. Four processes are schematically illustrated in Figure 5.82. In Figure 5.82(a), reactants in two immiscible phases react at the interface forming the polymer capsule wall. For example, to encapsulate a water-immiscible solvent, multifunctional acid chlorides or isocyanates are dissolved in the solvent and the solution is dispersed in water with the aid of a polymeric emulsifier, e.g., poly(vinyl alcohol). When a polyfunctional water-soluble amine is then added with stirring to the aqueous phase, it diffuses to the solvent-water interfece where it reacts with acid chlorides or isocyanates forming the insoluble polymer capsule wall. Normally some reactants with more than two functional groups are used to minimize a regation due to the formation of sticky walls. 

The formation of a microcapsule wall through interfacial polycondensation/addition takes place in two steps. First step is the deposit of the oligomer (initial wall) at the oil droplet, and the second step is the wall thickness builds up. As described earlier, the polymerization occurs in oil phase, and the formed initial wall can limit the diffusion of the reactants. This reduces the polymerization rate that has great impact on the surface morphology and thickness of the microcapsule wall. - - Polycondensation by which polyamide, polyester, and polycarbonate microcapsules are prepared can generate acid byproduct during the process therefore, a base is needed to neutralize the acid and drive the reaction to complete. ... 

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