Chain-growth Polycondensation

All reactions involved in polymer chain growth are equilibrium reactions and consequently, their reverse reactions lead to chain degradation. The equilibrium constants are rather small and thus, the low-molecular-weight by-products have to be removed efficiently to shift the reaction to the product side. In industrial reactors, the overall esterification, as well as the polycondensation rate, is controlled by mass transport. Limitations of the latter arise mainly from the low solubility of TPA in EG, the diffusion of EG and water in the molten polymer and the mass transfer at the phase boundary between molten polymer and the gas phase. The importance of diffusion for the overall reaction rate has been demonstrated in experiments with thin polymer films [10]. 

Yokozawa, T. Yokoyama, A. Chain-growth polycondensation The living polymerization process in polycondensation. Prog. Polym. Sci. 2007, 32, 147-172. 

Interfacially formed condensation polymers such as polyesters, polycarbonates, nylons, and PUs are typically formed on a microscopic level in a chain-growth manner largely because of the highly reactive nature of the reactants employed for such interfadal polycondensations. 

A very promising variant on this type of condensation polymerisation is to use monomers that possess groups X and Y which can be eliminated from the same molecule (Scheme 8.1, Route C). This circumvents the need for careful control of reaction stoichiometry as an equal number of the different functional groups are built in to the monomer. Furthermore, in certain cases, polymerisation of monomers of this type can follow a chain-growth polycondensation type of... 

Keywords Chain-growth polymerization Condensation polymers Cyclic polymers jt-Conjugated polymers Polycondensation... 

A quite different approach to chain-growth condensation polymerization is phase-transfer-catalyzed polycondensation of solid monomer dispersed in an... 

Heck-type step-growth condensation polymerisation involves mainly palladium-based catalysts, although nickel-based catalysts are also effective. It is worth noting that this polycondensation requires a change in the oxidation state of the metal (e.g. Pd) [schemes (30) and (31)] [71], which is in contrast to chain growth polymerisation, such as ethylene/carbon monoxide alternating copolymerisation promoted by Pd-based catalysts [schemes (82) and (83) in Chapter 3], for which the preservation of the oxidation state of palladium, Pd(II), is typical [83-85] ... 

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... 

There are many other ways by means of which polyamides have been synthesized, not all of them polycondensation reactions. Thus the ringopening polymerization of e-caprolactam produces nylon-6 by a chain-growth [1] process... 

FIGURE 22.1 Relationship of the product number average molecular weight, Mn, to the percent monomer conversion for (a) a step-growth, polycondensation versus (b) a chain growth (vinyl-type) polymerization. 

The ROP of lactide affords high molecular weight PLA polymers with better control of the polymerization process relative to polycondensation. These advantages can be directly attributed to the fact that ROP can be a living polymerization process. Living polymerization is a chain-growth polymerization where chain termination is absent and is characterized by a linear relationship between the monomer to initiator ratio and the experimental molecular weight, and narrow dispersity indicates the... 

Once the aminoacid is formed polycondensation can contribute to chain growth ... 

Thus, the proposed mechanisms of chain growth, i.e. one polycondensation and three polymerization mechanisms (activated monomer, oxonium ion and activated ester) may proceed in various proportions, as dictated by conditions. To determine the relative extent of these contributions conditions have to be devised under which this multiplicity is reduced. The use of an acid like HMtX + 1 (HX MtXJ that has a complex anion and is unable to form coValent bonds will simplify the system by excluding ester formation. Another simplification would be to use TfOH in a nonpolar solvent (e.g. CCI4) this should highly decrease the concentration of ions. 

Hilker et al (44) combined dynamic kinetic resolution with enzymatic polycondensation reactions to synthesize chiral polyesters from dimethyl adipate and racemic secondary diols. The concept offered an efficient route for the one-pot synthesis of chiral polymers from racemic monomers. Palmans at al (18,43) generalized the approach to Iterative Tandem Catalysis (ITC), in which chain growth during polymerization was effected by two or more intrinsically different catalytic processes that were compatible and complementary. 

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. 

The dominant contribution of simultaneous chain growth from all the chain ends, controlled by the deprotonation level of the initiator, leads to relatively narrow MWD B 1.1-1.4) while maintaining branching levels typical of random polycondensation reactions (degree of branching a 0.5, Eq. 30.7) [70]. The SCROP technique has also been used to synthesize hyperbranched polyglycerols [70], polyethers [71], and polyamines [72]. 

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. 

The synthesis and the modification techniques concerning PES have been reviewed by Kricheldorf. Poly(ethersulfone)s can be obtained either by a conventional step-growth polycondensation, or by a chain-growth polycondensation, which is in fact a living polycondensation. ... 

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