Response surface analysis for understanding the effects of synthesis parameters on the microstructure of hyperbranched polyesters

Synthesis parameters including the time of condensation reaction, the monomer-to-core ratio (2, 2-bis (hydroxymethyl) propionic acid) (pseudo-generation) and the type of catalyst were changed methodically to investigate their effects on the microstructure of resulting hyperbranched polyesters (HBPEs). Response surface methodology (RSM) was utilized to uncover the relationship between changing variables and the number of terminal hydroxyl groups of HBPSs by which the individual and interactive effects of the aforementioned synthesis parameters were explored. The degree of branching and molecular weight of the HBPEs were evaluated by titration of hydroxyl number and gel permeation chromatography, respectively. Fourier transform infrared spectroscopy and nuclear magnetic resonance analyses confirmed attachment of functional groups to the molecules. Interpretations based on RSM showed that increase of the number of the core molecules, which is equivalent To reduction of the pseudo-generation, narrows the molecular weight distribution of the prepared hyperbranched polyester; so that the lowest molecular weight distribution is obtained for the first pseudo-generation HBPEs with the monomer-to-core ratio of 3:1 and the average number of the terminal hydroxyl groups in between 6 and 8. The samples prepared by the sulfuric acid catalyst had the highest average number of terminal hydroxyl groups, at the same time narrowest molecular weight distribution.