Synthesis and molecular structure investigation of aliphatic hyperbranched polyesters

Abstract

The results obtained by investigation of the influence of synthesis procedure on the molecular structure of aliphatic hyperbranched polyesters (AHBP) are presented in this work. Different pseudo generations of these three-dimensional polymers were synthesized via an acid-catalyzed polyesterification of 2,2-bis(hydroxymethyl)propionic acid (bis-MPA) and di-trimethylolpropane (DiTMP) using two different procedures: pseudo one-step (samples of the series I) and one-step (samples of the series II). In pseudo one-step procedure the sample of certain pseudo generation was obtained starting from the sample of previous pseudo generation and adequate amount of monomer, while in simple one-step procedure polymer of the wanted pseudo generation was synthesized by mixing the stoichometric amount of all necessary reactants at once. Beside these samples, three commercial Boltorn® AHBP synthesized by pseudo one-step procedure were also investigated. Results obtained by NMR, MALDI-TOF MS and VPO show that formation of poly(bis-MPA) and cyclization through the ester and ether bonds (intramolecular) occurred as side reactions during the both procedures for the synthesis. With increasing degree of polymerization, the extent of these unwanted reactions increased and it was slightly higher when one-step procedure was applied for the preparation of AHBP samples. During the synthesis of AHBP from second till fifth pseudo generation, cyclization occurred through ester and ether bonds (intramolecular), while in the case of the higher generation samples, cycles were formed due to the intramolecular esterification. Furthermore, –OH groups belonging to the terminal units had better reactivity than linear ones. Consequently, the degree of branching for all investigated samples is lower than 0.50. Due to the side reactions occurrence, molar mass increases only up to the sixth pseudo generation and values of the molar masses are much lower than theoretical. From the obtained results it was also possible to calculate the percentage of deviation from the perfect dendrimer structure for AHBP samples of the series I and II.