Polycondensation condensation chain growth

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] ... 

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. 

A well-defined poly(ether sulfone) can be synthesized from 4-flu-oro-4 -hydroxydiphenyl sulfone, with (fluorophenyl)(trifluorophenyl) sulfone as an initiator, as shown in Figure 7.4. The condensation is performed with 18-crown-6 ether in sulfolane at 120°C. Flowever, when the polymerization is conducted at a higher feed ratio of monomer to initiator, both chain-growth and step-growth polycondensation occurs. 

Polymerization is a chemical reaction in which the molecules of monomers are linked together to form polymers. The two principle kinds of polymerization are addition and condensation polymerization. Addition polymerization has two subgroups chain propagation polymerization and stepwise chain growth. (It should be noted that much of the literature, especially in Emope, uses polymerization only for the chain propagation process. Stepwise growing is referred to as polyaddition, condensation polymerization is named polycondensation.)... 

The recently developed living polymerization in polycondensation is reviewed by Yokozawa T, Yokoyama A (2004) Chain-growth Poly condensation Living Polymerization Nature in Polycondensation and Approach to Condensation Polymer Architecture. Polymer J (Japan) 36 65-83 (in English). Examples are found for polyamides (2000) JAmChemSoc 122 8313-2314. Polyesters (2003) Macromolecules 36 4328 336. Polyethers (2001) J Am Chem Soc 123 9902-9903. Polythiophenes (2004) Macromolecules 37 1169-1171. Several block copolymers can be found in the publications (2002) J Am Chem Soc 124 15158-15159 and (2003) J Polymer Sci, Part A Polymer Chem 41 1341-1346. 

When Si alkoxides are used, a stoichiometric amount of water and a catalyst are normally required to ensure the hydrolysis of Si(OR)4 in Si(OH)4 and high yield of Si02 in the final material. Acid catalysis results in fast hydrolysis and slow condensation, which leads to linear chain growth of the organic phase. In contrast, slower hydrolysis and faster polycondensation were observed in the case of base catalysis, leading to spherical colloidal particles. 

Carothers, in 1929, classified synthetic polymers into two classes, according to the method of their preparation, i.e., condensation polymers and addition polymers. In polycondensation, or step-growth polymerization, polymers are obtained by reaction between two polyfunctional molecules and elimination of a small molecule, for example water. Typical condensation polymers are shown in Figure 2. Addition (or chain reaction) polymers are formed from unsaturated monomers in a chain reaction. Examples of addition polymers are shown in Figure 2. 

Yokozawa, T. and Yokoyama, A. (2004) Chain-growth polycondensation Living polymerization nature in polycondensation and approach to condensation polymer architecture. Polymer Journal, 36,65-83. 

An important conclusion reached in the work of Suzuki and co-workers [83] is that by using initiators chain growth polycondensation polymers can control the topology of condensation polymers obtained by conventional polycondensation, that is, chain growth polycondensation yields only linear polymers, whereas conventional polycondensation yields linear and cyclic polymers. 

Keywords Catalyst-transfer Chain-growth condensation polymerization Living polymerizatiOTi Polycondensation jr-Conjugated polymers... 

Yokozawa, T., Yokoyama, A., Chain-growth polycondensation for well-defined condensation polymers and polymer architecture. The Chemical Record 2005, 5 (1), 47 57. 

Finally, it should be emphasized that all the theoretical considerations presented above also apply to syntheses of hyper branched polymers as discussed in Chap. 11. Cyclization limits the chain growth according to Eqs. (7.13) or (7.14), it reduces the dispersity compared to Flory s calculations (see Sect. 4.3) and the law of self-dilution (Eq. (7.11)) is also valid together with the RZDP. Furthermore, the existence of a permanent competition of cyclization and chain growth in KC polycondensations is decisive for a proper understanding of non-stoichiometric poly condensations as discussed in Chap. 8. 

In summary, two conclusions may be drawn. First, non-stoichiometric polycondensations of class ni may give much higher molar masses than polycondensations of a-b monomers. Second, the kinetic course of the polymerizations deviate largely from that of a normal step-growth polymerization, and the term non-stoichiometric polycondensation is rather a formal label than a correct terminology. In the extreme case, when cyclization is totally suppressed, class III polymerization exactly obeys the definition of an aa + condensative chain polymerizaion . This term was proposed by lUPAC, and numerous condensative chain polymerizations are known from a-b monomers as discussed in Chap. 16. 

The term solid state polycondensation (SSP) simply says that chain growth by condensation steps occur under conditions, where at least one reaction partner exists in the solid state. As discussed below, SSP encompasses a broad variety of condensation reactions and substrates. Seemingly, the first example of a SSP (but not recognized as such) was the synthesis of poly(4-hydroxybenzoic acid), poly(4-oxybenzoate) by dry distillation of 4-hydroxybenzoic acid (see Chap. 2, Refs. [64—66]). A more detailed discussion of syntheses of poly(4-hydroxybenzoic acid) will we presented in Sect. 14.3. The first section is dedicated to SSPs of peptide esters which were also described for the first time before World War 1. 

Regardless of the scenario it must be kept in mind that a ROP plus polycondensation process needs two different definitions of conversion for its proper description. For the ROP part the conversion is defined by the consumption of monomers as usual for a chain-growth polymerization. Yet, for polycondensations the conversion is defined by the consumption of functional (end) groups regardless, if inter- or intramolecular condensation steps take place. 

The temi condensative chain polymerization (CCP) was coined and approved by the lUPAC. It defines polymerizations which show all the typical kinetic features of a chain growth polymerization, whereas the individual growing steps involve an elimination (condensation) reaction quite analogous to a tme polycondensation. The typical features of a CCP are the following ones ... 

The second category of polymerization reactions does not involve a chain reaction and is divided into two groups poly addition and poly condensation [4]. In botli reactions, tire growth of a polymer chains proceeds by reactions between molecules of all degrees of polymerization. In polycondensations a low-molecular-weight product L is eliminated, while polyadditions occur witliout elimination ... 

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). 

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