Molecular weight distribution polyester polyols

Similar materials, hyperbranched polyesters based on bis-MPA and a polyol are now commercially available [11] from Perstorp AB under the trade name Boltorn [12], Figure 8.1. The average number of hydroxyl groups per molecule can be tailored between 8 and 64 and molecular weight can be varied between c. 2000 and 11 000. The co-polymerization of bis-MPA and a polyol core keeps the molecular weight distribution fairly low, typically below 2. 

The molecular weight distribution (MWD) of polyester polyols is broader than that of polyether polyols. The polydispersity index (PDI) of high MW polyester polyols (e.g., 2000 daltons) is around 2.8. 

Calculation according to the Eq. (1) gives for A. = 2.648 (T = 443 K) the value = 0.918 and for = 2.693 (T = 473 K) = 0.954. These both values correspond well to the estimation according to the Eq. (1) of Chapter 5 (the discrepancy makes up less than 8%). This circumstance confirms, that in melts of synthesized polyester polyols macromolecnlar coils of different sizes are formed, i.e., certain molecular weight distribution takes place. 

Most hydroxy-terminated polyesters are made by coesterifying two polyols (a diol and a triol) and two diacids (an aliphatic dibasic acid and an aromatic dicarboxylic acid or its anhydride). The ratio of moles of dibasic acid to polyol must be less than 1 so as to give terminal hydroxyl groups and avoid gelation. Molecular weight is controlled by this ratio the smaller the ratio, the lower the molecular weight. The molecular weight distribution Mn, and /n are all controlled by the diol-to-triol ratio. The ratio of aromatic to aliphatic dibasic acids controls Tg of the resin. 

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