Polycondensation reaction Subject

Imbalance in the stoichiometry of polycondensation reactions of AA-BB-type monomers can be overcome by changing to heterofunctional AB-type monomers. Indeed, IIMU has been subjected to bulk polycondensation using lipases as catalyst in the presence of 4 A molecular sieves. At 70 °C, CALB showed 84% monomer conversion and a low molecular weight polymer (Mn 1.1 kDa, PDI 1.9). No significant polymerization was observed with other lipases (except R cepacia lipase, 47% conversion, oligomers only) and in reference reactions with thermally deactivated CALB or in the absence of enzyme. Further optimization of the reaction conditions (60wt% CALB, II0°C, 3 days, 4 A molecular sieves) gave a polymer with Mn of 14.8 kDa (PDI 2.3) in 86% yield after precipitation [42]. 

Monomer XIV was introduced into the polycondensation reaction. The reaction was performed in CI C solution in the presence of 10 mol. Z of tritylium perchlorate at room temperature, the removal of traces of moisture being essential. The latter was most conveniently achieved by using a high-vacuum technique although, for larger runs, it is also possible to use standard equipment. The reaction practically came to an end after 50-60 h it was then finally terminated by the addition of CF CO H and, after neutralization and solvent removal, the polymer obtained, without purification, was subjected to de-acetylation. The free polysaccharide XV was isolated by precipitation. 

The presence of these cyclic esters in the crude polycondensation reaction product was found to be unavoidable indeed some evidence was developed that the polycondensation at least in part proceeds via these cyclic esters. Considerable effort was expended to find means for eliminating these cyclic five-membered esters from our polycondensation products. The cyclic esters can be eliminated by either inducing them to polymerize by use of Lewis acid catalysts such as stannous octoate, or by subjecting them to ring opening by means of an alcohol or water (7). 

This chapter will attempt to survey critically the major areas of experimentally determined kinetic data which are available on polycondensation reactions and their mechanisms, and to emphasize the mechanistic similarities of many of the reactions. The statistics of polycondensation reactions will be touched on only to the extent that it helps understand the reactions and their kinetics. The general approach to the subject of kinetics is designed to be of primary use and interest to those polymer chemists who are concerned with the synthesis of products having desired properties, and with the understanding of their synthetic processes. 

Emulsion systems, while widely used in the polymerization of unsaturated monomers, are used rarely for polycondensation. The emulsion system is one in which two (or more) liquid phases are present, md in which polymerization occurs entirely in the bulk of one of the phases and is almost exclusively kinetically controlled. It thus represents a transition from solution polymerization to interfacial polymerizations. In the case of polycondensation reactions, emulsion polymerization has not been studied in detail. Results thus far indicate that molecular weight and molecular weight distribution are subject to the same statistical considerations as apply to solution and melt polymerizations. 

This section focuses on polycondensation reactions to synthesize thermoset polymers. Specific condensation chemistries are studied here a more extensive treatment of the subject of thermoset polymers can be found in Chapter 28 of this handbook. 

Conjugated polymers remain prime candidates for use as semiconductors in the emergent field of organic electronics [40-43]. Such materials are typically synthesized via polycondensation reactions, using a variety of aryl cross-coupling reactions. These methods are subject to problems that relate to, for example, the elimination of precursor functional groups. Unfortunately, the polymers produced via these methods often contain defects and unwanted branching, that may have deleterious effects on the conductive properties of the resultant material. 

PFK (polyetherketone) and PSU (polysulfone) polymers can be easily prepared by the mentioned polycondensation methods, furnishing polymers with controllable end groups (either —OH, or fluorine (—F)) (Figure 3.14). These polymers can then be subjected to further polycondensation reactions to attach appropriate end-group moieties (such as 2,6-diamino-triazine (Figure 3.14a) or barbituric acid (such as in Figure 3.14b) (Kunz et al, 2004a Petraru et al, 2004). 

Lipase-catalyzed polycondensation and transesterification reactions are the subjects of intensive research activities but polyesters of low molecular weight are obtained by this technique [45-52]. 

The crosslinking of polymeric materials by Mannich reaction includes the polycondensation of acetone with oligomeric polyalkyleneamines and aldehydes (see also 480, Chap. IV) and, more relevantly, polyamides (430, Chap. Ill) crosslinked with benzidine and formaldehyde. Macromolecular materials such as cellophane and polyglucosamine (Fig. 183), deriving from natural substances, are also subjected to the reaction. 

By suitable activation, relatively stable compounds, e.g methane or benzene, can be made to polymerize. However, the term monomer is usually used to designate unsaturated compounds or molecules with reactive groups, but always those that predominantly react by addition to an active centre and give rise to the same kind of centre in the reaction. The subject of interest in this volume are polymerizing, not polycondensing, monomers. Even so, there are very many of them. An overwhelming majority of these monomers are organic compounds composed of C, H, O, N, S, P and also Si. 

The hydrolysis of (EtO)4Si (and the subsequent polycondensation of Si-OH containing molecules) has been the subject of considerable investigation because of its importance in the fabrication of glasses and colloidal silica via the sol-gel process see Sol-Gel Synthesis of Solids). Hydrolysis of the Si-0 bond in alkoxysilanes is also very widely used to attach silicon compounds to surfaces and in coupling reactions. The fundamental reaction types involved in the formation of polymeric silica materials (via, for example, cyclic oligomers similar to those shown in Figures 4 and 5) from monomeric (RO)4Si compounds are shown in Scheme 43. 

Hence, fraction of macromolecular coil p, subjecting to evolution (chemical reaction in polycondensation process) can be defined as follows [76] Eq. (46) ... 

According to DIN 60001-T4, the synthetic fibers are divided into materials synthesized by different chain building processes polymerization, polycondensation, and polyaddition. Polymerization is subjected to monomers containing a vinyl group (double bond) in the molecular structure. The chain reaction will be induced by radical reaction. Polycondensation... 

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