Polycondensation condensation step-growth

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. 

HMF is a suitable precursor for the synthesis of bifunctional furan monomers as summarized in Scheme 4. All these monomers can be used to prepare polycondensates by step-growth reactions with the other corresponding bifunc-tional monomers derived either from petrochemical precursors or from renewable resources. The polycondensates obtained, such as polyesters, polyamides, and polyurethanes, etc. have been characterized [107-113]. Scheme 5 shows another approach for the synthesis of bifunctional monomers through acid-catalyzed condensation of the corresponding mono-functional furan derivatives with an aldehyde... 

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. 

Polycondensation. The step-growth polymerization of ABj -monomers is by far the most utilized synthetic pathway to hyperbranched polymers. A number of AB2-monomers, suitable for step-growth polymerizations, are commercially available. This has, of course, sparked off the interest for hyperbranched condensation polymers, and a wide variety has been presented in the literature (11,25,33,34). 

The industrial process (Figure 1) consists of a reactor (acting as the reboiler), a packed column, a total condenser and two distillate vessels. The polymer is manufactured through reversible linear polycondensation or step-growth polymerisation. The overall reaction can be characterised by the following scheme ... 

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). 

A second example of step-growth polycondensations with formation of the ole-finic double-bond are Wittig- and Wittig-Horner-type condensations. The Wittig-type polycondensations involve AA/BB-type reactions of aromatic bisal-dehydes with bisphosphonium ylides [99,100] with formation of PPV derivatives (75) and lead to products of only moderate molecular weight (DP 10-20). 

Step-growth condensation polymers, such as polyesters and polyamides, are formed by reversible reactions. In the case of PET, the commercial synthesis is essentially carried out by two reactions. The first is the formation of bishydroxyethyl terephthalate by esterification of a diacid with a glycol or by transesterification of a diester with a glycol. The second is the formation of the polymer by a polycondensation reaction. 

Let us emphasise that the driving force for acyclic diene metathesis, which is a step-growth condensation polymerisation, is the release and removal of a small condensate molecule. The polycondensation is performed preferably under bulk conditions (no solvent used), since acyclic diene metathesis is thermally neutral and there is no need to remove the heat of the reaction, in contrast to exothermic cyclic olefin ring-opening metathesis polymerisation. 

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] ... 

A characteristic common to the monomers of all condensation, or step-growth, polymers is that they possess two (or more than two) more-or-less reactive functional groups. The functional groups of a single monomer may be different, in which case the polymer may be produced by reaction of the single monomer with itself (Table 20.1, first two examples) or the functional groups required for condensation reactions may be on different monomers, in which case two monomers are required (Table 20.1, last three examples). Examples 1, 2, and 4 from this table are also typical of polycondensations in which a small molecule is split out, water in the first two cases and alcohol in... 

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. 

As a consequence of the lack of special active centers, the chain formation in step growth polymerizations occurs via a sequence of accidental and independent reaction events. It proceeds via dimers, short and longer oligomers until, finally, at conversions higher than 99% long chains are formed which are called condensation polymers (polycondensates) or addition polymers, respectively. Apart from high... 

Most natural polymers are condensation polymers. Condensation polymerization is a commonly used polymerization technique for preparing various biomedical polymers. The majority of these are step-growth polymerizations, which involve the stepwise condensation of bifimctional monomers with the elimination of small molecules such as water and HCl. A generalized equation for the linear polycondensation reaction involving two bifunctional monomers A and B can be given as ... 

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