Step polymers

As mentioned a moment ago, nylons are condensation or step polymers and, because of this, they are different from all of the other commercially important polymers described so far. The nylons are distinguished from each other by a numbering system based on the number of carbon atoms in the starting materials. Thus, nylon 6,6, which was first prepared in 1935 and is still the major... 

Here the polymer grows by successive esterification with elimination of water and no termination step. Polymers formed by linking monomers with carboxylic acid groups and those that have alcohol groups are known as polyesters. Polymers of this type are widely used for the manufacture of artificial fibers. For example, the esterification of terephthalic acid with ethylene glycol produces polyethylene terephthalate. 

Equilibrium molecular mass distribution in step polymers. 

In the case of random degradation, the molecular mass drop due to chemical reaction with a contaminant (e.g., H20, alcohol, acid, for a polyester) can easily be calculated. Consider the example of hydrolysis of a step polymer. 

Some polymers can be decomposed directly, e.g. by photolysis or by irradiation, giving macroradicals which are new centers for monomer addition. More often however, active centers are built into a preformed first-step polymer which can be isolated, purified and characterized it is then used as initiator for a foreign monomer in a second step of the synthesis. We will consider both possibilities successively. 

One difficulty of this method is the unstability of the hydroperoxide groups in the direct neighbourhood of acid groups therefore the application of the same technique to copolymers containing neutral units is more attractive and much easier for the isolation and characterization of the first-step polymer (43). 

A sample polymerization reaction, showing the synthesis of a polyurethane, is shown equation 3. Using similar synthetic strategies, various polyurethanes, polyureas (eq. 4), and polyamides (eq. 5) have been synthesized.14-17 Note that the step polymers in these reactions have a metal-metal bond in every repeat unit. Copolymers are straightforwardly synthesized by adding appropriate difunctional organic molecules into the reaction mixture (e.g., eq. 6). 

The related polymer-supported reagents field affords useful if lesser advantages than polymer-supported synthesis in that the polymer support allows the ready removal of a reagent promoting only a single reaction step. Polymer-supported reagents, and especially catalysts, have nevertheless become very important in numerous chemical manufacturing situations. 

In the next step, polymer films (thickness 200 nm) of PS-COOH or FPS-COOH were spin coated on the top of the GPS layer from 2% toluene solutions. After casting, the films were annealed in a vacuum oven at 150 °C for 15 h. Non-grafted polymer was removed by Soxhlet extraction in toluene for 6 h. The thickness of PS and FPS grafted layers was determined using null ellipsometiy. 

Fig. 7.2 The principles of the two-step process suitable to control several parameters of an USCA independently. In the first step, polymer nanoparticles are synthesized via emulsion polymerization. The size of the resulting nanoparticles can be tuned by a simple process parameter and covers a range of about 30-400 nm. In the second step, these nanoparticles are used to coat microbubbles in a controlled bubble formation process. Consequently, the size of the nanoparticles deter-...

Solid-phase synthesis by the cyclization of polymer-bound hydrazones of [1-keto esters. Jung and co-workers (99JOC1362) (Scheme 24) have reported the synthesis of pyrazol-3-one 102 from polymer-bound /1-keto ester 100 and phenyl hydrazine. In the first step, polymer-bound 3-hydroxy-2-methylidenepropionic acid 99 is derived from a Baylis-Hillman reaction between polymer-bound allylic alcohol... 

Interesting hexafluorocarbinol-functionalized block copolymers were prepared by a three-step polymer modification process (Fig. 88) [296]. The fluo-rocarbinol functional group was incorporated into the polymer backbone... 

Preparation of ultrafine monodisperse hybride particles, dispersible in low polar organic solvent, from monodisperse colloidal silica by two-step polymer modification was studied. Bindings of the secondary polymer to monodisperse poly(maleic anhydride-styrene)-modified colloidal silica particles (120 nm) have made the composites in low polar solvent dispersible. The dispersion of the particles in good solvent for the secondary polymer is due to the steric repulsion of solvated polymer chains. The dispersibility of the hybrid particles in poor solvent-rich solution was controlled by delicate balance between nonpolar-nonpolar interaction and electrostatic repusion among the particles. 

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