Bifunctional monomers, synthesis

Later, Kricheldorf and coworkers [93,94] extensively demonstrated the use of 0-silylated bifunctional monomers, such as diphenols, for synthesis of a wide variety of polycondensation polymers. The silylated oxygen of difunctional phenols may be condensed with activated... 

The synthetic strategy towards the copolymers is shown in Figure 16-3. The use of bifunctional monomers in a Heck reaction allows the synthesis of polymers, and the great potential of this approach has been demonstrated previously [53-55]. The syntheses have been described in detail by Hilberer el al. [16],... 

The chemical and physical properties of the polymers obtained by these alternate methods are identical, except insofar as they are affected by differences in molecular weight. In order to avoid the confusion which would result if classification of the products were to be based on the method of synthesis actually employed in each case, it has been proposed that the substance be referred to as a condensation polymer in such instances, irrespective of whether a condensation or an addition polymerization process was used in its preparation. The cyclic compound is after all a condensation product of one or more bifunctional compounds, and in this sense the linear polymer obtained from the cyclic intermediate can be regarded as the polymeric derivative of the bifunctional monomer(s). Furthermore, each of the polymers listed in Table III may be degraded to bifunctional monomers differing in composition from the structural unit, although such degradation of polyethylene oxide and the polythioether may be difficult. Apart from the demands of any particular definition, it is clearly desirable to include all of these substances among the condensation... 

Chemical Crosslinking. Only linear polymers are produced from bifunctional monomers. The reaction system must include a polyfunctional monomer, i.e., a monomer containing 3 or more functional groups per molecule, in order to produce a crosslinked polymer. However, the polyfunctional reactant and/or reaction conditions must be chosen such that crosslinking does not occur during polymerization but is delayed until the fabrication step. This objective is met differently depending on whether the synthesis involves a chain or step polymerization. In the typical... 

In the early days of polymer science, when polystyrene became a commercial product, insolubility was sometimes observed which was not expected from the functionality of this monomer. Staudinger and Heuer [2] could show that this insolubility was due to small amounts of tetrafunctional divinylbenzene present in styrene as an impurity from its synthesis. As little as 0.02 mass % is sufficient to make polystyrene of a molecular mass of 2001000 insoluble [3]. This knowledge and the limitations of the technical processing of insoluble and non-fusible polymers as compared with linear or branched polymers explains why, over many years, research on the polymerization of crosslinking monomers alone or the copolymerization of bifunctional monomers with large fractions of crosslinking monomers was scarcely studied. 

Another method of achieving the desired molecular weight is by addition of a small amount of a monofunctional monomer, a monomer with only one functional group. Acetic acid or lauric acid, for example, are often used to achieve molecular weight stabilization of polyamides. The monofunctional monomer, often referred to as a chain stopper, controls and limits the polymerization of bifunctional monomers because the growing polymer yields chain ends devoid of functional groups and therefore incapable of further reaction. Thus, the use of benzoic acid in the polyamide synthesis yields a polyamide (XI) with phenyl end groups that are unreactive toward polymerization. 

Starting from monomers Monomers in bulk or in solution are irradiated. Polymerization takes place as the first stage of reaction. The polymer chains are then cross-linked. It is frequent practice to add bifunctional monomers to increase the efficiency of cross-linking. Typically, this procedure is used for synthesis of wall-to-wall hydrogels or microspheres. For biomedical use of the formed gels, all non-reacted monomers and residues have to be extracted. 

So far, we have only considered linear polymerization reactions, as in condensation reactions involving bifunctional monomers (A-B or A-A/B-B pairs). Obviously, incorporating multifunctional monomers into this type of polymerization results in the synthesis of highly branched polymers and can lead to the formation of very large interconnected molecules. These can have macroscopic dimensions and are considered to be infinite networks . The formation of such gels does not follow automatically from the incorporation of multifunctional monomers into the reaction pot, however. So, keeping in mind that an A can only react with a B and vice-versa, which of the reactions in Figure 5-11 do you think would lead to network formation ... 

Figure 2 The structure of a tripeptide and the corresponding monomer for solid-phase synthesis, contrasted with trimers and monomers for three other oligomer libraries prepared from bifunctional monomers...

As mentioned in the introduction, the synthesis of low molecular N202-chelates as Co(sa-len) (6) is rather easy when starting from salicylaldehyde, diamines and a metal salt. For the polymer synthesis only bifunctional o-hydroxyaldehydes must be used. The limiting factor for practical use of polymers may be the price of the bifunctional monomer. The difficulty in preparation is to get a structurally pure polymer and to reach quantitative metallization. 

Fig. 9.11. Reaciion scheme for the synthesis of network-polymeric CSPs and representative chromatograms, (a) Derivatization of A, A -diallyl-(R.R)-tartaric acid diamide (DATD) to give the bifunctional monomers used as chiral SO units, (b) Cross-linking and immobilization by hydrosilylation with multifunctional hydrosilane (alternatively, cross-linking and immobilization can be performed first with DATD followed by O-derivatization). (c) Enantioseparation of 2-(octylsulphinyl)benzoic acid. The chromatograms illustrate the column performance under non-overloadcd (left) and overloaded conditions (right). CSP network polymer from /V. -diallyl-i/il.Rl-tartaric acid diamide fc/.s-. i.S-dimethylbenzoatc bound to. ) pm 1.50 A Kromasil. Mobile phase hexane-THF (80 20 v/v) with 0.0.55 - of TFA (reprinted with permission from Ref. [194]).

One possibility for the synthesis of such polymers is the reaction of a bifunctional Schiff-base ligand or chelate with another bifunctional monomer [1]. The advantage is that side-reactions, which may occur during ligand formation, are avoided because the ligand moiety is employed in the polymerization reaction. An example of the reaction of a substituted low... 

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... 

SCHEME 12.1 Synthesis of the bifunctional monomer, 2-methacryloyloxyethyl-3-pyrrolyl butyrate, via esterification reaction between 2-hydroxyethyl methacrylate and lH-pyrrole-3-butyric acid. (Brahim, S., A.M. Wilson, D. Narinesingh, E. Iwuoha, and A. Guiseppi-Elie. 2003. Chemical and biological sensors based on electrochemical election using conducting electroactive polymers. Microchim Acta 143 (2-3) 123. 

Anotha- approach to the synthesis of bifunctional monomers which has also been widely explored, calls upon the acid-catalyzed condensation of the corresponding monofunctional furan derivatives with an aldehyde or a ketone, as shown in Scheme 6.13 [4]. 

The LSCEs represent a new class of macromolecular systems distinguished by macroscopically uniform anisotropy. The concept of LSCE can be furthermore extended to other synthesis routes and to the densely crosslinked systems. Macroscopic uniaxially oriented films can be formed by mechanical force, alignment surface [30], magnetic and electric fields [31], polarized light [32], etc., and then crosslinked to form an anisotropic network (LC network is abbreviated as LCN) if the mixture components contain polymerizable or crosslink-able bifunctional monomers (Figure 9.13). Alternatively, amorphous or liquid crystalline side-group and/or main-chain polymers incorporating additional... 

The free-radical copolymerization of electron-donor olefinic monomers, including commercial allyl and vinyl ethers, was quite frequently reported and studied during last years and seems to present interesting potentialities for the synthesis of new bio-sourced polymers. However the only publication devoted to donor-acceptor copolymerization of monomers from biomass was focused on the photopolymerization of divi-nylfumarate, a bifunctional monomer bearing both type of double... 

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