The chemical structure of the galactan and the regioselectivity and stereoselectivity of the polymerization were discussed with the aid of phosphoric acid catalysis and microwave-assisted synthesis of galactan as the research object. The relative molecular weight of the galactan, the three-dimensional configuration and the attachment site were characterized by high-efficient gel permeation chromatography, infrared spectroscopy, methylation analysis and one-dimensional, two-dimensional nuclear magnetic resonance spectroscopy (1HNMR, 13CNMR, 1H-1HCOSY, TOCSY, HSQC, HMBC).
The results showed that the synthesized galactosans were multibranched, with a relative molecular weight of 2657 and a weight average polymerization degree of 16. The sugar residues were mainly α-galactopyranose. The main fragments were →4 (- α-D-Galp) 1→ and →2 (- α-D-Galp) 1→. The results of structure analysis further showed that the hydroxyl groups at different sites had different reactivity in the process of microwave assisted phosphoric acid catalyzed galactose condensation, and the reaction activity of 4 hydroxyl groups was the strongest.