https://doi.org/10.15255/KUI.2005.019
Published: Kem. Ind. 55 (9) (2006) 365–372
Paper reference number: KUI-19/2005
Paper type: Original scientific paper
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Carboxylated Polyurethanes Containing Hyperbranched Polyester Soft Segments

G. Prevec, E. Žagar and M. Žigon

Abstract

In this contribution we focus on the synthesis and characterization of polyurethanes containing hyperbranched polyester soft segments (HB PU) with functional carboxylic groups in order to enable the preparation of stable HB PU dispersions. Carboxylated hyperbranched polyurethanes were synthesized using a hyperbranched polyester based on 2,2-bis(methylol)propionic acid of the fourth pseudo-generation (Boltorn® H40) and hexamethylene (HDI) or isophorone diisocyanate (IPDI). The reactivity of hyperbranched polyester with HDI was lower than expected, possibly due to the presence of less reactive hydroxyl groups in the linear repeat units. A gel was formed at mole ratios rNCO/OH = 1:2 or 1:4. The synthesis of HB PU was performed with partly esterified hyperbranched polyester with lowered hydroxyl functionality. The carboxyl groups were incorporated in the HB PU backbone by reaction of residual hydroxyl groups with cis-1,2-cyclohexanedicarboxylic anhydride. HB PU aqueous dispersions were stable at least for two months, although their films were brittle. The tensile strength and Young’s modulus of blends of linear and HB PU decreased with increasing content of HB PU whereas elongation at break remained nearly constant, which was explained in terms of looser chain packing due to more open tree-like hyperbranched structures.

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Keywords

polyurethanes, polyurethane anionomers, hyperbranched polymers, aqueous dispersions