Hyperbranched polyesters synthesis

Polyester chemistry is the same as studied by Carothers long ago, but polyester synthesis is still a very active field. New polymers have been very recently or will be soon commercially introduced PTT for fiber applications poly(ethylene naph-thalate) (PEN) for packaging and fiber applications and poly(lactic acid) (PLA), a biopolymer synthesized from renewable resources (corn syrup) introduced by Dow-Cargill for large-scale applications in textile industry and solid-state molding resins. Polyesters with unusual hyperbranched architecture also recently appeared and are claimed to find applications as crosstinkers, surfactants, or processing additives. 

TABLE 2.18 Monomers Used for Synthesis of Hyperbranched Polyesters... 

Although low-molar-mass aliphatic polyesters and unsaturated polyesters can be synthesized without added catalyst (see Sections 2.4.1.1.1 and 2.4.2.1), the presence of a catalyst is generally required for the preparation of high-molar-mass polyesters. Strong acids are very efficient polyesterification catalysts but also catalyze a number of side reactions at elevated temperature (>160°C), leading to polymers of inferior quality. Acid catalysts are, therefore, not much used. An exception is the bulk synthesis of hyperbranched polyesters reported in Section 2.4.5.1, which is carried out at moderate temperature (140°C) under vacuum in the presence of p-toluene sulfonic acid catalyst. The use of strongly acidic oil-soluble catalysts has also been reported for the low-temperature synthesis of polyester oligomers in water-in-oil emulsions.216... 

The use of silylated monomers is an interesting alternative method of aromatic polyester synthesis since the silylated gaseous by-products cannot participate in the reverse reaction, shifting polyesterification toward polymer formation. Reactions between silyl esters and acetates (Scheme 2.23) and reactions between silyl ethers and acid chlorides (Scheme 2.24) have been applied to the synthesis of linear265-267 and hyperbranched wholly aromatic polyesters202,268 269 (see Section 2.4.5.2.2). 

Hydroxyphenylimide, polybenzoxazole synthesis via, 318 Hydroxy-terminated hyperbranched polyesters, 32... 

Hyperbranched aromatic polyesters, synthesis of, 116-118 Hyperbranched aromatic polymers, 286 Hyperbranched polyamine, synthesis of, 519-520... 

Hyperbranched polyesters, 18, 32, 55-58 bulk synthesis of, 64 synthesis of, 114-118 Hyperbranched polyimides, 307-309 Hyperbranched polymers, 8-10, 348-350, 475-476, 481, 519-520 degree of branching in, 57 Hyperbranched polyphenylquinoxalines, 312-314... 

Several applications of hyperbranched polymers as precursors for synthesis of crosslinked materials have been reported [91-97] but systematic studies of crosslinking kinetics, gelation, network formation and network properties are still missing. These studies include application of hyperbranched aliphatic polyesters as hydroxy group containing precursors in alkyd resins by which the hardness of alkyd films was improved [94], Several studies involved the modification of hyperbranched polyesters to introduce polymerizable unsaturated C=C double bonds (maleate or acrylic groups). A crosslinked network was formed by free-radical homopolymerization or copolymerization. 

Considerable attention has been paid to aromatic hyperbranched polyesters synthesized from monomers derived from 3,5-dihydroxybenzoic acid (DBA). The thermal stability of DBA is not good enough to allow direct esterification of DBA, and therefore chemical modifications are necessary. Some aromatic monomers used for the synthesis of hyperbranched aromatic polyesters are presented in Fig. 6. 

Feast and Stainton [63] reported on the synthesis of aromatic hyperbranched polyesters from 5-(2-hydroxyethoxy)isophthalate copolymerized with 1,3,5-benzenetricarboxylate (core molecule) as a moderator of the molecular weight. The degree of branching was found to be 0.60-0.67 as determined by C-NMR. Apparent molecular weights (M ) were found to be 5-36 kDa according to SEC characterization using linear polystyrene standards. 

Hawker et al. report on the synthesis of a similar hyperbranched polyester based on the corresponding AB4-monomer that is, the preformed dendron of the second generation was used in the condensation reaction [79]. 

In this chapter we describe the synthesis of new hyperbranched polyester-amides carried out with standard melt condensation technology as well as the properties of these new structures. 

Parquette et al. reported on a disaccharide synthesis on a hyperbranched polyester support (Boltorn hyperbranched polymer) (16) (Fig. 7.9) [44]. This polymer was obtained in a one-step synthesis and offers low cost, high-loading capacities (8.8 mmol OH-groups g ), and the intermediates were soluble in most aprotic solvents. 

Parzuchowski PG, Grabowska M, Tryznowski M, Rokicki G (2006) Synthesis of glycerol based hyperbranched polyesters with primary hydroxyl groups. Macromolecules 39 7181-7186... 

In the second part of this review, we report the synthesis of dendrimers and hyperbranched polyesters based on 2,2-bis(methylol)-propionic acid. An extensive study has also been made on the material properties of the hyperbranched polyesters both as thermoplastics and as cross-linkable resins. All characterization techniques and apparatus that have been used throughout this work are described in the Appendix. An outline of the material covered is shown in Figure 2. 

To avoid some limitations of PEGs, as for instance low loading, hyperbranched polyester such as Boltorn H40 and H50 have been successfully investigated in glycosylation reactions with 0-glycosyl trichloroacetimidates [121]. For simple mono- and disaccharide synthesis optimization of the reaction conditions led to practically quantitative transformations. 

Nonlinear, dendritic or hyperbranched polymers have received considerable attention in recent years. These polymers have seen little use as supports for oligosaccharide synthesis compared to Merrifield or soluble MPEG resins. Nevertheless, some interesting applications of hyperbranched polymers such as hyperbranched polyester and poly(amidoamine) to oligsaccharide synthesis have been reported. 

Zhao, Y, Zou, J., and Shi, W. 2005. In situ synthesis and characterization of lead sulfide nanocrystallites in the modified hyperbranched polyester by gartuna-ray irradiation. Mater. Sci. Eng. B 121(l-2) 20-24. 

Bao, He and Li [14] also prepared the AB2 monomer illustrated in Scheme 6.4, and undertook a systematic study on the synthesis of hyperbranched polyesters using Ti(OBu)4, Sb203 and Zn(OAc)2 as transesterification catalysts. The final materials had Mn values of 11-60 kDa. 

Pig. 3. Aromatic monomers used for the synthesis of hyperbranched polyesters (3—5). OH HO... 

Marija Pergal, MSc, works at the Department for Polymeric Materials, Institute for Chemistry, Technology and Metallurgy since 2003 as Research Scientist. Since 2007 she is also Teaching Assistant for the course Chemistry of Macromolecules at Department of Chemistry, University of Belgrade. Her research interests are focused on synthesis and characterization of siloxane homopolymers and copolymers, especially thermoplastic elastomers based on poly(butylene terephthalate) and polyurethanes, as well as polyurethane networks based on hyperbranched polyester. In addition to physico-chemical, mechanical and surface properties of polymers, her particular interest is directed towards the study of biocompatibility of polymer materials. 

Drug delivery Synthesis of water-soluble and degradable hyperbranched polyesters for drug delivery [48]... 

Metal ion extractant Synthesis and application of new nitrogen centered hyperbranched polyesters [52]... 

Goswami, A., and Singh, A. K., Hyperbranched polyester having nitrogen core synthesis and applications as metal ion extractant Reactive Functional Polymers, 61 255-263 (2004). 

Hyperbranched Macromolecules. Because of their close structural and synthetic similarities to dendrimers, the comparison of hyperbranched macromolecules with their dendritic analogs has been studied by a number of groups. Ihre and Hult(7i) have recently reported the synthesis and characterization of the dendritic analogs of the commercially available hyperbranched polyesters, Boltron(D(7, based on 2,2-bis(hydroxymethyl)propionic acid, while Moor iJ) has reported a novel solid-supported synthesis of hyperbranched poly(phenylacetylenes) which are the hyperbranched analogs of Moore s well studied phaiylacetylene dendrimers(id). An intriguing study was also reported by Feast into the synthesis and physical properties of hyperbranched analogues of Tomalia s poly(amidoamine) dendrimers (77). 

One of the recent advancements and interests in alkyd resin technology is hyperbranched alkyd resins, which, due to their unique highly branched polymer architecture, have low viscosities at higher MWs. An important characteristic of these alkyds is rapid drying. Generally they are prepared by reacting hyperbranched polyester polyols with fatty acids. The main limitation of such alkyds, however, is higher cost, due to the need for unique, more expensive raw materials in their synthesis. 

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