Hyperbranched aliphatic polyesters

Characterization of Aliphatic Hyperbranched Polyesters Molar Mass 

The architecture of hypeibranched polymers and dendrimers is connected with difficulties in determining molar mass. Many of the common characterization techniques—e.g. size exclusion chromatography (SEC)—used for polymers are relative methods where polymer standards of known molar mass and dispersity are needed for calibration. Highly branched polymers exhibit a different relationship between molar mass and hydrodynamic radius than their linear counterparts. 

Polymer No. Ratio Core bis-MPA Core Molecule No. of Terminal Groups Terminal Groups 

Note Abbreviations 2-elhyl-2-(hydroxyinethylH,3-propanediol (TMP), 2 -bis(hydroxymeihyl) propionic acid (bis-MPA). 

Because there are no appropriate calibration standards for hyperbranched polymers, the results from SEC-measurements are difficult to interpret. The hydrodynamic radius is also strongly affected by the solvent used in the analyses, and this can further complicate the results. Another problem with SEC-measurements is that the 

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This aliphatic hyperbranched polyester is prepared by the bulk polycondensation of 2,2-bis(hydroxymethyl)propionic acid (bis-MPA) as AB2 monomer and 1,1,1-tris(hydroxymethyl)propane (TMP) as B3 core molecule, according to a procedure... 

Aliphatic hyperbranched polyesters, 56 Aliphatic isocyanate adducts, 202 Aliphatic isocyanates, 210, 225 Aliphatic polyamides, 138 Aliphatic polyesteramides, 56 Aliphatic polyesters, 18, 20, 29, 32, 87 degradable, 85 hyperbranched, 114-116 melting points of, 33, 36 structure and properties of, 40-44 syntheses of, 95-101 thermal degradation of, 38 unsubstituted and methyl-substituted, 36-38... 

Fig. 10. Complex dynamic viscosity as function of temperature for three different aliphatic hyperbranched polyesters based on bismethylol propionic acid and having different end-group structure - (O) propionate end-groups, ( ) benzoate end-groups, ( ) hydroxyl end-groups [118]...

B. Characterization of Aliphatic Hyperbranched Polyesters Molar Mass... 

Zagar E, Huskic M, Grdadolnik J, Zigrai M, Zupancic-Valant A (2005) Effect of annealing on the theological and thermal properties of aliphatic hyperbranched polyester based on 2,2-bis (methylol)propionic acid. Macromolecules 38 3933-3942... 

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... 

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. 

The use of aliphatic monomers for hyperbranched polyesters has been debated because aliphatic monomers are said to be prone to thermal degradation reactions such as decarboxylation, cyclization, or dehydration [77]. The only commercial hyperbranched polymer is a hydroxy-functional aliphatic polyester, Boltorn, available from Perstorp AB, Sweden. 

Hult et al. [36] have described semi-crystalline hyperbranched aliphatic polyesters where the crystallinity was induced by attachment of long alkyl chains as end groups. The crystallization was affected by several factors such as length of the end groups and the molecular weight of the hyperbranched polyester. The crystallization was proposed as being either intra- or intermolecular depending on the size of the hyperbranched polyester onto which the alkyl chains were attached. 

Caprolactone was grafted on hydroxy-functional hyperbranched aliphatic polyesters forming semicrystalline copolymers (Fig. 15). The crystallinity and rheological properties were found to be tailorable by means of the appropriate choice of hyperbranched polyester and the degree of polymerization of the crystalline... 

The use of epoxidized hyperbranched polyesters as toughening additives in carbon-liber reinforced epoxy composites has been demonstrated [191]. The use of hyperbranched polymers as the base for various coating resins has been described in the literature. For example, a comparative study [192] between an alkyd resin based on a hyperbranched aliphatic polyester and a conventional (less branched) high-solid alkyd showed that the former had a substantially lower viscosity and much shorter drying time than the conventional resin of comparable molecular weight. 

Schallausky F, Erber M, Komber H, Lederer A (2008) An easy strategy for the synthesis of well-defined aliphatic-aromatic hyperbranched polyesters. Macromol Chem Phys 209 2331-2338... 

Concerted efforts to examine the synthesis and polymerization of such ABx monomers was however not attempted until 1989 when Kim and Webster (17) reported their preparation of hyperbranched polyphenylenes fi-om the AB2 monomers, 3,5-dibromophenyl boronic acid, 7, or 3,5-dibromophenyl magnesium bromide, 8 (Figure 1). In a similar way to dendrimers, the field of hyperbranched macromolecules has been extended considerably since this initial report. Hyperbranched polyesters based on fully aromatic, fiilly aliphatic, or partially aliphatic/aromatic systems have been extensively studied by a number of groups (18-20). Similarly, hyperbranched poly(etherketones) (21), poly(ethers) (22), poly(urethanes) (23), poly(siloxanes) (24), etc. have been prepared using classical step growth chemistry. 

Hyperbranched Aliphatic Polyester Based on 2,2-Bis(hydroxymethyl) Propionic Acid... 

A key monomer, namely, 2,2-bis(methylol)propionic acid (bis-MPA) has been used extensively for the preparation of hyperbranched aliphatic polyesters. Hult... 

Fig. 7. Examples of A B monomers used for the preparation of hyperbranched aliphatic and aromatic-aliphatic polyesters [56,62,78]...

The dilution properties of hyperbranched polymers also differ from those of linear polymers. In a comparison between two alkyd resin systems, where one was a conventional high solid alkyd and the other based on a hyperbranched aliphatic polyester, the conventional high solid alkyd was seen to exhibit a higher viscosity [113]. A more rapid decrease in viscosity with solvent content was noted for the hyperbranched alkyd when the polymers were diluted. 

A study of the PVT properties of hyperbranched aliphatic polyesters by Hult et al. [ 117] showed that these polyesters were dense structures with smaller thermal expansion coefficients and lower compressibility compared to some linear polymers. 

Fig. 11. Melt viscosity at 85 °C vs molar mass for hydroxy-functional hyperbranched aliphatic polyesters based on bismethylol propionic acid. Theoretical molar mass based on core bis-MPA ratio ( ) and Mn determined with SEC relative to linear polystyrene standards (O) [117]...

Fig.12. Comparison between a conventional high solid alkyd coating ( ) and an alkyd based on a hyperbranched aliphatic polyester ( ). Drying time as a function of molar mass [123]...

Pettersson and Sorensen have described a number of different thermoset resin structures based on hyperbranched aliphatic polyesters [123]. Their results can best be exemplified by a study on hyperbranched alkyd coating resins. A comparative study was performed between an alkyd resin based on a hyperbranched aliphatic polyester and a conventional high solid alkyd, which is a less branched structure. The hyperbranched resin had a substantially lower viscosity than the conventional resin of comparable molecular weight, that is, less solvent was needed to obtain a suitable application viscosity. The hyperbranched resin also exhibited much shorter drying times than the conventional resin, although the oil content was similar. These achievements would not have been possible without a change in architecture of the backbone structure of the resins (Figs. 12,13). 

Studies on acrylate resins [82, 124, 125] based on hyperbranched aliphatic polyesters have shown that it is possible to vary both the polarity (wetting be-... 

Commercially available hyperbranched polymers are Polyglycerol (aliphatic polyether polyol) and Polyethylenimine (aliphatic polyamine) both from Hyperpolymers, Boltom (aliphatic polyesters) from Perstorp and Hybrane (aromatic polyester amide) from DSM. 

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