Acylation of pullulan by ring-opening of lactones

In this paper, we report on the production of modified pullulan derivatives that have been produced in solution by ring-opening epsilon-caprolactone and [L]-lactide using a tin octanoate [Sn(Oct)(2)] catalyst system in DMSO. These derivatives designated as hexanoates (1 and 2) and dilactates (4-7) have been characterized and have varying degrees of substitution (DS). 1 and 2 were characterized by interesting thermal properties as well as crystalline morphology. From DSC analysis, 2, unlike the parent polysaccharide, appears to melt at 114 degrees C. The crystalline morphology of this polymer was characterized by X-ray powder diffraction and d spacings were calculated. This pullulan derivative possessed new crystallographic reflections not seen in either pullulan or poly (epsilon-caprolactone). The pullulan-6 dilactate samples (4-7), produced had DS values ranging from 0.1 to 0.75. Depending upon the DS, these samples were soluble in a wide range of organic solvents including acetone and methanol. Although these materials did not exhibit any observable melting transitions from inspection of DSC, glass transition temperatures were detected for 5 [DS = 0.21], 6 [DS = 0.44], and 7 [DS = 0.80], at 130, 120, and 90 degrees C, respectively. As confirmed by C-13 NMR, the ring-opening process for all of these pullulan derivatives appears to be taking place through an acyl-oxygen cleavage, producing an ester linkage to the backbone with a hydroxy terminus.