Synthesis of poly(ε-caprolactone)-grafted guar gum by surface-initiated ring-opening polymerization

This study reports the grafting of poly(ε-caprolactone) (PCL) on guar gum (GG) by in-situ ring-opening polymerization using tetra(phenylethynyl)tin (Sn(C≡CPh)₄) as catalyst. The hydroxyl groups of guar gum act as initiators for ε-caprolactone ring-opening polymerization and the resulting poly(ε-caprolactone) binds covalently to the polysaccharide. The highest stability of Sn(C≡CPh)₄ allows the reaction in open-air, thereby reducing the cost of the synthesis and provides polymers with high molar mass. Fourier transform infrared (FTIR) and the long-term stability of the suspension PCL-g-GG in dichloromethane confirmed the effectiveness of grafting of PCL into GG. The size exclusion chromatography (SEC) results show that the molar masse of grafted PCL could be modulated by varying the amount of guar gum. From thermogravimetric analysis and differential scanning calorimetry results the thermal stability of PCL-g-GG is greatly improved with different content of guar gum, also the melting temperature and crystallinity increased by increasing the GG content. The scanning electron microscopy (SEM) analyses showed the good adhesion between GG and PCL with 5% of GG contents. It was also revealed by contact angle measurements that the grafting of PCL to GG leads to a decrease of hydrophobicity of PCL. The micro-indentation hardness properties of the prepared PCL-g-GG were significantly improved, as compared to neat PCL.