Step-growth polymerization copolymerizations

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. 

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 ... 

The versatility of polymerization resides not only in the different types of polymerization reactions and types of reactants that can be polymerized, but also in variations allowed by step-growth synthesis, copolymerization, and stereospecific polymerization. Chain polymerization is the most important kind of copolymerization process and is considered separately in Chapter 7, while Chapter 9 describes the stereochemistry of polymerization with emphasis on the synthesis of polymers with stereoregular structures by the appropriate choice of polymerization conditions, including the more recent metallocene-based Ziegler-Natta systems. Synthetic approaches to starburst and hyperbranched polymers which promise to open up new applications in the future are considered in an earlier chapter dealing with step-growth polymerization. 

As a last point, let us consider how copolymerization relates to the polymer growth mechanism. Eirst, most step-growth polymerizations (e.g., the production of nylon 6/6 by the reaction of hexamethylene diamine with adipic acid) use two monomers to produce the final polymer. One can say that these are inherently copolymerizations. Considering... 

This type of copolymerization results from spontaneous interactions of nucleophilic and electrophilic ihonomers (Mn and Me, respectively) without any additions of catalysts. Zwitterions form in the process that subsequently leads to formation of polymers. The mechanism is a step-growth polymerization. It can be illustrated as follows ... 

A number of different methods have been used to synthesize polymers from suitable monomers, such as condensation or step-growth polymerization, addition polymerization, copolymerization, and insertion polymerization (Fig. 6). 

Unsaturated Polyester Systems. Coatings in the furniture industry rely heavily upon resin formulations containing unsaturated polyesters, styrene, and photoinitiator (3,4,13,43,44). The imsaturated polyesters are synthesized using step-growth polymerization (see Polyesters, Unsaturated). Upon illumination, the carbon-carbon double bond in the imsaturated polyester and st5Tene copolymerize to form a cross-linked network (eq. 6). Equation 6 shows a generalized reaction scheme for an imsaturated polyester system. 

Free-radical polymerization is the most widely used process for polymer synthesis. It is much less sensitive to the effects of adventitious impurities than ionic chain-growth reactions. Free-radical polymerizations are usually much faster than those in step-growth syntheses, which use different monomers in any case. Chapter 7 covers emulsion polymerization, which is a special technique of free-radical chain-growth polymerizations. Copolymerizations are considered separately in Chapter 8. This chapter focuses on the polymerization reactions in which only one monomer is involved. 

For copolymerization of monomer A-B with A -B, the sequence distribution may be analyzed in a manner similar to that in Section 16.2.3.1, although the analysis will be more difficult since step-growth polymerization proceeds by the combination to two existing chains. 

---