Step-growth polymerization polycondensation

Table 2.3. Synthesis of macromolecules by step growth polymerization (polycondensation)...

Because it is the extraordinarily large size of the macromolecules which leads to their unusual properties, it would be most sensible to classify polymerization reactions in accordance with the way in which they affect the molecular size and size distribution of the final product, i.e., in terms of the mechanism of polymerization. On this basis, there appear to be only two basic processes whereby macromolecules are synthesized (Zhang et al., 2012 Penczek and Premia, 2012 Moore, 1978 Saunders and Dobinson, 1976 Odian, 2004b Penczek, 2002 Jenkins et al., 1996) (1) step-growth polymerization (polycondensation and polyaddition) and (2) chain-growth (chain) polymerization. 

Zhang, M., June, S.M., Long, T.E., 2012. Principles of step-growth polymerization (polycondensation and polyaddition). In Matyjaszewski, K., Moller, M. (Eds.), Polymer Science A Comprehensive Reference, vol. 5. Elsevier, Amsterdam, pp. 7-47. 

Lactic acid (LA 2-hydroxypropanoic acid) is an organic acid and the simplest hydroxycarboxylic acid. It is soluble in water and exists in two enantiomeric forms l-(+)-LA and d-( )-LA. Even though both forms are used in industry, l-LA is the preferred isomer for medical applications because only this form is suitable to be assimilated by the human body. A qualifying feature of this component is its bifunctional reactivity imparted by its carboxyl and hydroxyl groups, which makes it ideal for step-growth polymerization (polycondensation). The annual production of LA is... 

A polymer formed by a step-growth polymerization (polycondensation or polyaddition) is a homopolymer, even if it was formed by reaction of two compounds. These polymers are formed by mutual reaction of complementary monomers. These monomers can be easily visualized as an implicit monomer . Its homopolymerizatiOTi gives the actual product. In this sense, it can be regarded as a homopolymer. 

Step-growth polymerization (polycondensation) Step reaction of bi-functional monomers 2... 

Several polymer types and classes are known to exhibit photoconductivity. Consequently no preferred method of synthesis exists. The known photoconductive polymers are prepared by almost all common methods like free-radical, cationic, anionic, coordination, and ringopening polymerization, step-growth polymerization (polycondensation and polyaddition), and polyanalo-gous reactions. The only common requirement for all photoconductive materials is that they have to be of extreme purity. It is well known [37-39] that even traces of impurities act as traps and have a drastic influence on both quantum yield and carrier mobility. From the structural point of view the photoconductive polymers described in this chapter can be divided into three groups ... 

Step-growth polymerization is characterized by the fact that chains always maintain their terminal reactivity and continue to react together to form longer chains as the reaction proceeds, ie, a -mer + -mer — (a + )-mer. Because there are reactions that foUow this mechanism but do not produce a molecule of condensation, eg, the formation of polyurethanes from diols and diisocyanates (eq. 6), the terms step-growth and polycondensation are not exactly synonymous (6,18,19). 

Another factor in step-growth polymerizations is cyclization versus linear polymerization.1516 Since ADMET is a step-growth polymerization, most reactions are carried out in the bulk using high concentrations of the reactant in order to suppress most cyclic formation. A small percentage of cyclic species is always present but is dependent upon thermodynamic factors, typical of any polycondensation reaction. 

Step-growth polymerization, 22, 24-25, 23, 84-86, 86,90-92,114-115, 261 compared with chain-growth polymerization, 88-89, 88-89 interfacial polymerization, 91-92 laboratory activities on synthesis of nylon, 228-230 synthesis of polyesters in the melt, 231-233 synthesis of polyurethane foam, 234-237 molar mass and, 86, 86 polycondensation of poly ethylene terephthalate), 90-91 polymers produced by, 86 types of monomers for, 90 Stereochemistry, 28, 37-39,41-42, 70 tacticity, 103-105 Stereoisomers, 41 Stereoregularity, 70 Stiffness, 142, 261 Strain, 142-143, 261 Strength... 

Step-growth polymerizations at high temperatures produce nearly random copolymers because of end-group interchange reactions like (5-14) between macromolecules. Interfacial and low-temperature solution polycondensations are conducted under essentially irreversible conditions, by contrast. In these cases the average copolymer composition and blocklike character of the product may depend on the reaction conditions and relative reactivity of the functional groups involved in the polymerization. 

ADMET has been shown to be a step-growth polycondensation reaction [31[. The kinetics of step-growth polymerization and consequences thereof are completely different than those of chain polymerizations. Since ROMP and many other single-site transition metal-catalyzed polymerizations discussed in this book proceed... 

Many methods have been reported to synthesize hyperbranched polymers. These materials were first reported in the late 1980s and early 1990s by Odian and Tomalia [9], Kim and Webster [10], and Hawker and Frechet [11]. As early as 1952, Hory actually developed a model for the polymerization of AB -type monomers and the branched structures that would result, identified as random AB polycondensates [46], Condensation step-growth polymerization is likely the most commonly used approach however, it is not the only method reported for the synthesis of statistically branched dendritic polymers chain growth and ringopening polymerization methods have also been applied. 

Ziegler -Natta complex as active site. The formation of the polycondensate does not proceed in one stroke. Rather each potential functionality can start to be active at a certain time and react with another monomer or likewise with an already formed polymer to form a polymer with a still higher degree of polymerization. After such a reaction step, the functionalities may be dormant for a certain time and after the dormant period again a reaction step will occur. For this reason, polycondensation is also addressed as step growth polymerization. 

Step-growth polymerizations can be divided into two main categories polycondensation, in which a small molecule is eliminated at each step, as discussed above and polyaddition, in which, as the name suggests, monomers react without the elimination of a small molecule. These are shown in Equations 2.27 and 2.28, respectively, where R and R are the nonreactive portions of the molecules. 

---