Lewis Acid‐Catalyzed Synthesis of Hyperbranched Polymers Based on Glycerol and Diacids in Toluene

Abstract

Examples of monomeric glycerol-derived hyperbranched polyesters produced in a nonpolar solvent system are reported here. The polymers were made by the Lewis acid [dibutyltin(IV) oxide]-catalyzed polycondensation of glycerol with either succinic acid [n (aliphatic chain length) = 2], glutaric acid (n = 3), or azelaic acid (n = 7) in toluene. Poly(glycerol-diacid)s were recovered in yields as low as 65% and as high as 95%. The polyesters were characterized by gas chromatography to determine the extent of reaction and by gel permeation chromatography to determine molecular weight, polydispersity index, and degree of polymerization. None of the conditions explored gave 100% conversion but products could be recovered in greater than 97.8% purity. Gelation and low conversion were observed, respectively, for 24-and 10-h polyesterifications of glutaric acid and glycerol (2:1 molar ratio) performed at 155°C when the standard (neat) synthetic protocol was employed. Gelation was avoided and conversion improved when esterifications were performed in quasi-melt solutions with toluene. The optimal reaction conditions to produce polymers with high conversion and high molecular weight before the onset of gelation were observed for 24-h esterifications in toluene at 155°C (2:1 molar ratio of glutaric acid/glycerol) and 135°C (1:1 molar ratio of reactants). Expanding on the success of those findings, it was determined that gelation could be avoided for each of the three diacids studied. When all other conditions were held constant, in the absence of gelation, degree of polymerization increased with decreasing aliphatic chain length of the diacid.

Degree of Branching in Hyperbranched Poly(glycerol-co-diacid)s Synthesized in Toluene

“…We have synthesized hyperbranched poly(diacid-glycerol)s in nonpolar media [16] and in aprotic polar media [17]. In dilute solutions, decreased interactions between propagating chains decrease crosslinking and increase the degree of polymerization when compared to neat polymerizations.…”

“…Poly(diacid-glycerol)s were synthesized as previously described [16]. A 2:1 molar ratio of diacid (0.02 mol) and glycerol (0.0105 mol) or a 1:1 molar ratio of diacid (0.015 mol) and glycerol (0.0155 mol) were reacted in the presence of 0.15% w/w (catalyst/reactants) dibutyltin(IV)oxide in a single-neck 50 mL round bottom flask with 28 mL of toluene.…”

“…Poly(diacid-glycerol)s were synthesized as previously described [16]. The diacid (0.20 mol), glycerol (0.105 mol) and 0.15% w/w dibutyltin(IV)oxide (catalyst/reactants), were placed in a 100 mL two-neck round bottom flask and heated to 60 °C under reduced pressure (~150 Pa) for one hour.…”

“…The synthesis and analytical charaterization of these polymers have been previously reported [16]. Therefore, information regarding yields, solubilities, and molecular weights is available.…”

The Enzymatic Synthesis and Characterization of Disolketal Iminodiacetic Acid (DSIDA)

“…Polyester synthesis is among the most facile chemical reactions. However, when making polyesters from glycerol and diacids, branching can be controlled by many factors such as solvent type, reaction time, temperature, and molar ratio of the reactants [8][9][10]. Such control is not trivial and must be meticulously monitored.…”