Intramolecular cyclization in hyperbranched polyesters

Abstract

The effect of monomer structure and catalyst on the synthesis of hyperbranched polyesters based on 4,4‐(4′‐hydroxyphenyl)pentanoic acid has been examined. The nature of the ester group and the catalyst have a significant effect on the molecular weight of the hyperbranched polyester but do not effect the degree of branching for these materials. The fate of the single ester group at the focal point of these hyperbranched macromolecules is probed by the synthesis and polymerization of 13C labeled methyl 4,4‐(4′‐hydroxyphenyl)pentanoate. Comparison of the molecular weights determined by 1H‐ or 13C‐NMR spectra with those determined by osmometry suggest that intramolecular cyclization does not occur to a significant extent in these systems. © 1997 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 35: 1627–1633, 1997

Cyclic hyperbranched polyesters derived from 4,4-bis(4′-hydroxyphenyl)valeric acid

“…In agreement with the report of Chu et al [22], no cyclization was observed for polycondensations of monomer 1a (BHVAM). However, very low conversions were found to be responsible for the absence of cycles.…”

“…The SEC elution curve shows well resolved peaks of oligomers, but no fraction of high molar mass polymers. Therefore, these findings agree with the conclusion of Chu et al [22] in that no cyclization was indeed detectable, but this result is a necessary consequence of the low conversion (75 -80%). Chu et al [22] reported high weight average molecular weights, M w s, (typically 18,000 -128,000 Da), but unfortunately, they did not give viscosity values, number average molecular weights (M n s) or polydispersities.…”

Cycle Formation in the Polycondensation of Potassium 3‐Bromomethyl‐5‐methylbenzoate

“…In the synthesis of hyperbranched polyesters, as the reaction was usually carried out in bulk or in the melt at elevated temperatures, cyclization can occur according to the two above mentioned ways. If it was claimed from 13 C NMR analyses that cyclization was negligible in the polycondensation of 13 C methyl 4,4-bis(4 0 -hydroxyphenyl)pentanoate, [2] large amounts of cyclic molecules were detected by MALDI-TOF MS in the polycondensation of dimethyl 5-(2-hydroxyalkoxy)isophthalates [3][4][5] and 2,2-bis(hydroxymethyl)propanoic acid, [6,7] in agreement with recent theoretical calculations. [6][7][8] The presence of cycles was also demonstrated in hyperbranched polyethers prepared at low or moderate temperatures.…”

Branched poly(arylene ether ketone)s with tailored thermal properties: Effects of AB/AB2 ratio, core (B3) percentage, and reaction temperature

“…First, while the presence of intramolecular cyclization reactions would lead to a broadening in the PDI values of linear polymers, it has actually been shown to provide hyperbranched polymers with PDI values considerably lower than those predicted by theory [17][18][19][20]. Second, the presence of a highly reactive core molecule should eliminate, or at the very least, limit the ability of a system to form macrocyclic species.…”