Self-healing disulfide-containing polyester-urethane networks composed of 6-armed star-shaped oligolactide and oligocaprolactone segments

Abstract

The ring opening polymerization reactions of e-caprolactone and L-lactide in the presence of the initiator dipentaerythritol, generated the hydroxy-terminated 6-armed star-shaped e-caprolactone and L-lactide oligomers (H6CLO and H6LAO), respectively. The disulfide-containing polyester-urethane networks (PN-LCxy-DSz, weight ratios of H6LAO/H6CLO: x/y = 1/0, 3/1, 1/1, 1/3, and 0/1, BHEDS/(H6LAO + H6CLO) molar ratios: z = 0, 1, and 3) were produced by reacting H6LAO, H6CLO and bis(2-hydroxyethyl)disulfide (BHEDS) with hexamethylene diisocyanate (HDI). Fourier-transform infrared (FT-IR) spectroscopy and gel fraction analyses were conducted, which revealed that the urethanization reaction proceeded smoothly to generate the polymer networks. The differential scanning calorimetry (DSC) experiments with the PN-LCxy-DSz networks revealed that the oligocaprolactone (CLO) segments were crystallized, while the oligolactide (LAO) segments were not. The dynamic mechanical analysis (DMA) and scanning electron microscopy (SEM) techniques were used to reveal the high compatibility of the LAO and CLO segments in the PN-LC31-DS1 network. The compatibility of the co-networks decreased with increasing CLO fraction. The cut lines in the PN-LCxy-DS1 (xy = 10, 31, 11, and 31) films self-healed at room temperature within 24 h. The PN-LC31-DS1 film exhibited the highest healing efficiency on the tensile strength (98.5%). In contrast, the cut lines in the PN-LC10-DS0 and PN-LC01-DS0 films, devoid of disulfide bonds, did not exhibit the self-healing property.