Hyperbranched alkyd

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. 

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). 

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. 

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. 

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]...

A combination of enhanced reactivity and reduced viscosity for alkyd resins has been achieved by using hyperbranched polyester structures as discussed in Sect. 4.2.3 [ 123]. This study clearly showed the benefits of using highly branched structures in coating applications to obtain improved properties. 

Another resin application based on the same hyperbranched polyester structure described herein is low-VOC alkyds, which have very low viscosity and high reactivity compared to conventional high-solid alkyds. Other resin structures are unsaturated polyesters, polyurethane dispersions, and epoxides. ... 

Polymers are normally classified into four main architectural types linear (which includes rigid rod, flexible coil, cyclic, and polyrotaxane structures) branched (including random, regular comb-like, and star shaped) cross-linked (which includes the interpenetrating networks (IPNs)) and fairly recently the dendritic or hyperbranched polymers. I shall cover in some detail the first three types, but as we went to press very little DM work has been performed yet on the hyperbranched ones, which show some interesting properties. (Compared to linear polymers, solutions show a much lower viscosity and appear to be Newtonian rather than shear thinning [134].) Johansson [135] compares DM properties of some hyperbranched acrylates, alkyds. and unsaturated polyesters and notes that the properties of his cured resins so far are rather similar to conventional polyester systems. 

Fig. 13. Hyperbranched resins have a substantially lower viscosity than conventional resins with comparable molar mass (alkyd resin made from Boltom). 1 Reference alkyds and -Q- dendritic alkyds.

Fig. 14. Hyperbranched resins have much shorter drying times than conventional resins (alkyd resin made from Boltorn). Reference alkyds and -B- dendritic alkyds.

Fatty acids and glycerol are products in hydrolysis reaction of triglycerides. Glycerol is a trifunctional polyol obtained as a by-product of soap production (nowadays it is also known as a by-product of biodiesel production). It has been used in the food industry, the pharmaceutical industry, and the cosmetics industry, and especially used as a monomer for alkyd resin and polyurethane in the polymer industry. More recently, hyperbranched polymers are synthesized on the basis of trifunctional reactivity of glycerol. ... 

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. 

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