Polymerization of Monomers Containing Other Dissolved Polymers

Polymerization of Monomers Containing Other Dissolved Polymers 

Styrene as matrix and polybutadiene as dispersed phase. During this phase inversion the above-mentioned graft copolymers act as polymeric emulsifiers and determine, inter alia, the particle size and particle size distribution of the dispersed polybutadiene phase. This morphology is fixed through another chemical reaction, that is the crosslinking of the polybutadiene phase. Therefore, the reaction mixture at the end of the prepolymerization period (at 30% conversion) does scarcely alter its morphology when it is polymerized to complete conversion, which is done without stirring mostly in bulk in a separate vessel. 

Grafting of styrene (ST) onto polybutadiene (PB) can occur in two ways Via a chain-transfer reaction with an allylic hydrogen of the 1,4- and the 1,2-units (Case 1) via copolymerization with C=C-double bounds of polybutadiene, in particular with the vinyl groups of the 1,2-units (Case 2)  

Under the conditions of Example 5-23 the rubber phase of the end product shows an interesting micro-morphology. It consists of particles of 1-3 microns diameter into which polystyrene spheres with much lower diameters are dispersed. These included polystyrene spheres act as hard fillers and raise the elastic modulus of polybutadiene. As a consequence, HIPS with this micro-morphology has a higher impact resistance without loosing too much in stiffness and hardness. This special morphology can be visualized with transmission electron microscopy. A relevant TEM-picture obtained from a thin cut after straining with osmium tetroxide is shown in Sect. 2.3.4.14. 

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S.5.2.4 Polymerization of Monomers Containing Other Dissolved Polymers... 

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. 

Monomer Droplets. The monomer droplets serve primarily as reservoirs that supply monomer to the reaction sites in the polymer particles. These droplets can also contain a variety of other oil-soluble ingredients including dissolved polymer, chain transfer agents, and in unusual cases oil-soluble initiator. The monomer and other ingredients, if they have the requisite water solubility, are transported to the primary polymerization locus in the polymer particles. Reaction phenomena that can occur in the monomer droplets include the following ... 

Have you ever seen the example of forming nylon rope in a chemistry demonstration, where the polymer magically appears between two immiscible phases This is an example of a variation of solution polymerization known as interfacial polycondensation. Besides being used for a wow experiment in demonstrations, it has been used in the laboratory for a long time [9], and is also applicable in industrial polymerizations. One monomer of a condensation pair is dissolved in one solvent and the other member of the pair in another solvent note this applies to AA and BB monomers, but does not work for AB-type monomers). The two solvents must be insoluble in each other. The polymer is soluble in neither and forms at the interface between them. One of the phases, generally, also contains an agent that reacts with the molecule of condensation to drive the reaction to completion. 

The mechanism proposed by Kennedy requires that allylic or tertiary chlorines be attached to the first polymer chain. Chlorobutyl rubber, PVC, and other chlorine-containing polymers usually have 1-2% of mers with chlorines in the required reactive positions. The halogen-containing polymer is dissolved in an inert but polar solvent in the presence of an organoaluminum catalyst and a cationically polymerizable monomer, such as styrene, and polymerization is effected, usually at about — 50 C. The major point is that the second component chains can be initiated only at an active chlorine site on the first polymer. 

Nytril fibers are made up of polymers containing at least 85% vinyli-dene dinitrile units, which appear at least every other unit in the polymer chain. The comonomer used in Nytril synthesis is vinyl acetate. The two monomers are polymerized in benzene using peroxide catalyst. The polymer is precipitated, washed, and dissolved in ], ] -dimethyl formamide and then passed through a spinneret into an aqueous coagulating bath to form Nytril fibers. The properties of the Nytril fiber are similar to the other acrylic fibers. The fiber possesses moderate tensile, regain, and thermal properties. The fiber is chemical and sunlight resistant but is as flammable as cellulosic fibers. Darvan Nytril fibers were produced in the U.S. until 1961. 

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