Active polycondensation

Activating agents, such as trifluoroacetic anhydride 1,1 -carbonyldiimidazolc carbodiimides sulfonyl, tosyl, and picryl chlorides and a range of phosphorus derivatives can promote direct solution reactions between dicarboxylic acids and diols or diphenols in mild conditions. The activating agents are consumed during the reaction and, therefore, do not act as catalysts. These so-called direct polycondensation or activation polycondensation reactions proceed via the in situ transformation of one of the reactants, generally the carboxylic acid, into a more... 

This review summarizes the recent results in the preparation of well-defined chiral polymers from optically inactive monomers. To date, optically active polycondensates based on non-natural monomers are still a curiosity in polymer chemistry. Expanding the catalytic toolbox in polymer chemistry by adopting methods from chemo-enzymatic synthesis may enable easy access to chiral polymers and allow the exploration of the added value of chirality in materials. Moreover, chemo-enzymatic approaches have the potential to further enhance macromolecular complexity and hence allow to access new materials with applications envisaged in nanomaterials and biomedical materials. 

R. Katsarava, Active polycondensation from peptide chemistry to amino acid based biodegradable polymers, Macromol. Symp. 199 (2003) 419-429. 

PAIs with the electroactive triphenylamine were then prepared by the triphenyl phosphite activated polycondensation of the diimide-diacid with various aromatic diamines [106]. Also 2,4-dimethoxytriphe-nylamine and A,A-diphenyl-A, A -di-4-tert-butyl-phenyl-l,4-phenylenediamine may be used as chro-mophores [107,108]. 

With regards to new polymeric biomaterial, Gomurashvilli and co-workers (2) have developed new biodegradable and tissue-resorbable co-poly(ester amides) (PEAs) using a versatile Active PolyCondensation (APC) method which involves di-p-toluenesulfonic acid salts of bis-(L-a-amino acid)-a,(o-alkylene diesters and active diesters of dicarboxylic acids as monomers. A wide range of... 

The PEAs reported in this work were prepared in a simple way by solution or interfacial polycondensation, where di-p-toluenesulfonic acid salts of bis-(a-amino acid)-a,co-alkylene diesters react with chlorides of dicarboxylic acids (interfacial polycondensation) or their active diesters (Active Polycondensation, APC). The APC method involves the condensation of two partners (I) bis-electrophilic, activated dicarboxylic acids, and (II) bis-nucleophilic, acid salts of bis-(a-amino acid)-a,(0-alkylene diesters in combination with di-p-toluenesulfonic acid salts of L-lysine benzyl ester. This reaction proceeds under mild conditions in common organic solvents and leads to polymer of high molecular weight (up to 300 KDa). A detailed review of the APC method has been recently summarized by Katsarava (7). 

Polydispersity indices estimated by GPC ranged from 1.24 to 1.9, which is typical for PEAs prepared by active polycondensation (1,2). Sample copolymer structures are depicted in scheme 3. 

However, side reactions, such as formation of ether groups or cychzation, were not investigated. Turner et al. [11] reported on the Bu2Sn(OAc)2-catalyzed polycondensation of 5-(2 -hydroxyethoxy) isophthalic acid in bulk at 190 °C. Dimethyl isophthalate served as core monomer in several experiments. Polycondensation promoted by bis(cyclohexyl)carbodiimide (DCC) were reported for the aromatic monomer (f), Formula 11.1 [35]. The mild reaction conditions prevented transesterification, but only low molar mass polyesters (Mw < 17 kDa) were obtained. Similar molar masses were achieved by Voit et al. [36] for carbodiimide promoted polycondensations of the triazene monomers (b) and (c), Formula 11.4. Somewhat more successful were DCC-activated polycondensations of trifunctional oligo(e-caprolactone)s such as (d), Formula 11.4, reported by Hedrick et al. [37, 38]. Syntheses of LC polyesters from monomers (e), Formula 11.4, and isomers were achieved by means of thionyl chloride and pyridine [39]. 

As a variation on the base-catalyzed nucleopbilic displacement chemistry described, polysulfones and other polyarylethers have been prepared by cuprous chloride-catalyzed polycondensation of aromatic dihydroxy compounds with aromatic dibromo compounds. The advantage of this route is that it does not require that the aromatic dibromo compound be activated by an electron-withdrawing group such as the sulfone group. Details of this polymerization method, known as the Ullmaim synthesis, have been described (8). 

There are two very active special fields of phase-transfer appHcations that transcend classes (/) and 2) metal—organic reactions both with and without added bases, and polymer chemistry. Certain chemical modifications of side groups, polycondensations, and radical polymerizations can be influenced favorably by PTC. 

Material produced by the reaction of relatively simple molecules with functional groups that allow their combination to proceed to high-molecular weights under suitable conditions formed by polymerization or polycondensation. Chemical reaction that takes place when a resin is activated. 

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... 

To incorporate a labile azo group as the essential active site to MAI, a series of azo compounds such as 2,2 azobisisobutyronitrile (AIBN), 4,4 -azobis(4-cyanopen-tanoyl chloride) (ACPC), 2,2 azobis (2-cyanopropanol) (ACPO), 2,2 azobis [2-methyl-N-(2-hydroxyethyl)prop-ionamide] (AHPA), etc., were used as starting materials for polycondensation with various diols, diamines, diacids, or diisocyanates. 

The ring is in the chain backbone as a 2,5-disubstituted moiety. In these situations the polymer is more resistant to side reactions but some substituents are more susceptible than others to activation by the presence of the ring and promote branching and degradation under the influence of air, particularly at high temperature. This particular behaviour is encountered in some polycondensates as discussed in Section Il-A. 

A general step ahead in polycondensation was achieved by the application of the active ester method by DeTar et al.19) and Kovacs et al.291 Very soon, the nitrophenyl ester, the pentachlorophenyl ester, or the hydroxysucdnimido ester were used exclusively. The esters of the protected tripeptides could be purified by crystallization, then the N-protecting group was split off and the free peptide esters were purified again. Addition of base starts the polycondensation, resulting quickly in the formation of a viscous solution at low temperature. 

Now, it is widely known that proline at the N-terminal position causes problems of steric hindrance by using active ester couplings in the polycondensation step as well as in the synthesis of the tri- or hexapeptides. This is often a stringent restriction also if proline or glycine are intended to be in the C-terminal position. 

Table 2 shows a list of collagen model peptides which have teen prepared. Many efforts have been made to prevent racemization. The polycondensation reaction seemed to be more sensitive to racemization than the coupling steps preparing the monomeric tripeptide. Therefore, the sequence of the monomer was selected with Gly or Pro at the C-terminal chain end, because racemization is mostly favored at the carboxy-activated amino acid, and these amino acids cannot racemize. 

Difficulties due to side reactions (cyclization) and a broad molecular weight distribution accompanying the polycondensation of active esters led to the application of methods wherein the polymers are built up stepwise. In 1968, Sakakibara et al.31) introduced the solid-phase technique using Merrifield s resin. By stepwise addition of tert-pentyloxycar-bonyl tripeptides, they have synthesized (Pro-Pro-Gly)n with n = 5, 10, 15 and 20. 

On the other hand, Sb203 and metal oxides such as Ge02 exhibit a good catalytic activity for the polycondensation step. This explains why the associations of metal acetates with Sb203 are often reported catalytic systems. The following order in catalytic activity was found for the PEN polycondensation step Ti(IV)... 

Tractable polymers can be prepared when amino and anhydride functions are not located on the same aromatic ring, and different strategies were employed to obtain soluble polymer. AB benzhydrol imide was prepared by polycondensation of 4-(3-amino-l-hydroxymethylene) phtlialic acid monomethyl ester in NMP. The polymer soluble in NMP has been used as adhesive and coating.56 A second approach was based on an ether imide structure. AB aminophenylether phthalic acids (Fig. 5.34) were prepared by a multistep synthesis from bisphenols.155 The products are stable as hydrochloride, and the polycondensation takes place by activation with triphenylphosphite. The polymers are soluble in an aprotic polar... 

In the AA-BB type of sulfonylation, two or more activated aromatic hydrogen atoms are commonly present in the reacting molecules. Therefore, this polycondensation process may result in different repeating units. Structural irregularities... 

This value is similar to that obtained in the polycondensation of AB2 monomers (M, /Mn=Pn/2) [5]. This can be explained by the fact that large molecules have a higher probability of reacting with vinyl groups than smaller ones since they have more active centers. In fact, even at high conversion there is still a consid-... 

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