Step-growth copolymerization

Average Values of Distributions for Homogeneous Step Growth AA,BB,CC Copolymerization... 

Appendix 1 Toward a Model for Step-Growth Copolymerization w ith Phase Separation... 

A detailed description of AA, BB, CC step-growth copolymerization with phase separation is an involved task. Generally, the system we are attempting to model is a polymerization which proceeds homogeneously until some critical point when phase separation occurs into what we will call hard and soft domains. Each chemical species present is assumed to distribute itself between the two phases at the instant of phase separation as dictated by equilibrium thermodynamics. The polymerization proceeds now in the separate domains, perhaps at differen-rates. The monomers continue to distribute themselves between the phases, according to thermodynamic dictates, insofar as the time scales of diffusion and reaction will allow. Newly-formed polymer goes to one or the other phase, also dictated by the thermodynamic preference of its built-in chain micro — architecture. 

Step-growth condensation reactions, for water- soluble polymers, 20 441 Step-growth copolymerization, 7 611, 632-635... 

Siloxane containing block or segmented copolymers can be synthesized either by living anionic polymerization of the cyclic organosiloxane trimers with appropriate vinyl monomer(, 4 ) or by step-growth or condensation copolymerization of preformed a,w-difunctional siloxane oligomers with conventional difunctional... 

The next step concerned the synthesis of the polyester-polyimide copolymers. Triblock copolymers have been prepared by a step-growth copolymerization of stoichiometric amounts of an aromatic diamine and dianhydride (e.g., PMDA and 3FDA, as depicted in Scheme 41a) added with the single oo-amino polyesters as chain end-cappers. Graft copolymers can be prepared as well. In this case, the diamine end-functionalized oligomeric macromonomers are copolymerized with the polyimide condensation comonomers (Scheme 41b). 

Hence, cation-radical copolymerization leads to the formation of a polymer having a lower molecular weight and polydispersity index than the polymer got by cation-radical polymerization— homocyclobutanation. Nevertheless, copolymerization occnrs nnder very mild conditions and is regio-and stereospecihc (Bauld et al. 1998a). This reaction appears to occnr by a step-growth mechanism, rather than the more efficient cation-radical chain mechanism proposed for poly(cyclobutanation). As the authors concluded, the apparent suppression of the chain mechanism is viewed as an inherent problem with the copolymerization format of cation-radical Diels-Alder polymerization. ... 

An unsaturated polyester resin consists of a linear polyester whose chain contains double bonds and an unsaturated monomer such as styrene that copolymerizes with the polyester to provide a cross-linked product. The most common unsaturated polyester is made by step growth polymerization of propylene glycol with phthalic and maleic anhydrides. Subsequent treatment with styrene and a peroxide catalyst leads to a solid, infusible thermoset. 

This reaction can also be applied to achieve step-growth copolymerization of aromatic ketone with a, >-dienes and to synthesize high molecular weight copolymers (equation 135)242,243. 

An example of multicomponent system that can be dealt with by using kinetics equations of the Smoluchowski type is provided by a step growth alternating copolymerization of two bifunctional monomers [16]. This system requires fit-tie more laborious, but quite straightforward algebra. 

Table 2. The list of reactions taking place during step growth alternating copolymerization of two bifunctional monomers...

Table 3. Explicit solutions of the sets of equations (Eqs. 56-58) and the distribution functions of polymer species for the step growth alternating copolymerization of two bi-functional monomers [16] with the stoichiometric monomer mixture, c c (q) L...

In polymer chemistry, there are two known CDSD techniques (i) the chemical modification (polymer-analogous transformation) of homopolymers and (ii) the step-growth copolymerization of monomers with different properties under special conditions. We will address both these techniques. 

A macromonomer is a macromolecule with a reactive end group that can be homopolymerized or copolymerized with a small monomer by cationic, anionic, free-radical, or coordination polymerization (macromonomers for step-growth polymerization will not be considered here). The resulting species may be a star-like polymer (homopolymerization of the macromonomer), a comblike polymer (copolymerization with the same monomer), or a graft polymer (copolymerization with a different monomer) in which the branches are the macromonomer chains. 

Comparison of the Two Reactions Step-Growth Polymerization in More Detail Making PET in the Melt Interfacial Poly condensation Chain-Growth Polymerization in More Detail Free Radical Chain Polymerization Going One Step Better Emulsion Polymerization Copolymerization Ionic Chain Polymerization It Lives ... 

Woodgate et al. [51] applied the C-H/acetylene coupling to the ortho-selective alkenylation of terpene derivatives (Eq. 27). The basic feature of this reaction is the same as the alkenylation reaction of Murai et al. The combination of acetophenone and diynes provides a new entry for the copolymerization of aromatic ketones with acetylenes. Weber et al. [50] studied extensive reactions of ruthenium-catalyzed C-H/acetylene coupling with respect to the step-growth copolymerization of aromatic ketones and acetylenes (Eq. 28). These coupling reactions provide a new route to the preparation of trisubstituted styrene derivatives. 

We recently have reported our initial studies on step-growth block copolymers containing segments of poly (aryl ethers) and poly (aryl carbonates) (9,10). The multiblock [ A-B ]n block copolymers were prepared by phosgenation in methylene chloride/pyridine solution either by what was termed an in situ or by a coupled oligomer technique (JO). The choice of polycarbonates and poly (aryl ethers) for initial studies was based on the several considerations. Copolymerization is feasible since the end groups in the two oligomers can be identical, as shown in Structures 1 and 2. Considerable information is available in the... 

C with two feed compositions are shown in Tables I and II. Surface tension has been measured as a function of time, and the viscosity of the solutions are shown along with surface tension. The data clearly show that as the viscosity increases with time, surface tension increases, and the higher the rate of increase of viscosity, the higher the rate of increase of surface tension. It has been shown for silicone polymers that as the viscosity increases from an increase in molecular weight, the surface tension increases (27). A step growth copolymerization mechanism, as mentioned earlier for the sulfur-DCP solutions, will have an increase of molecular weight with time, and the surface tension behavior appears to support this mechanism. 

Kinetic aspects of step-growth copolymerization have been examined in Section 10.2.2. The principal features of chain-growth copolymerization are very different, but are alike for all types of chain growth, that is, for free-radical, anionic, cationic, and coordination polymerization. 

Step-growth copolymerization involves the use of three or more monomers which do not ordinarily all react with each other. Examples include mixtures of acids and polyols in the synthesis of alkyds, as illustrated in the recipes in Table 5-1. Such polymers will contain a random distribution of monomer residues if they are synthesized under conditions in which the polymerization is reversible and the molecular weight distribution is random. Polymers like alkyds are intended to be homogeneous products with properties which represent an average of those of all the component monomers. The copolymerization of linolcic acid in the recipe in Table 5-1 would confer air-drying properties on all the macromolccules in which it is incorporated. 

In the copolymerization chain-growth reaction, we shall concentrate only on the propagation step in which a monomer adds to an active site at the end of a macromolecular species and the active site is transferred to the new terminal unit created by this addition. 

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