Synthesis and characterization of thermoresponsive-co-biodegradable linear-dendritic copolymers

A novel linear-dendritic copolymer containing thermoresponsive poly(N-isopropylacrylamide) (PNIPAAM), hydrophobic and biodegradable poly(L-lactic acid) ( PLLA), and hydrophilic poly(L-lysine) (PLL) dendrons was designed, synthesized and characterized. The thermoresponsive-co-biodegradable linear-dendritic copolymer was synthesized by 1,3-dicyclohexylcarbodiimide (DCC) coupling reaction of three generation PLL dendron and PNIPAAM grafted with PLLA. UV-vis spectroscopy and dynamic light scattering measurements demonstrated that the linear-dendritic copolymer was thermoresponsive by showing a lower critical solution temperature whose value depended on the linear-dendritic copolymer concentrations. The viscosity and molar mass of the linear-dendritic copolymer decreased with time in PBS (pH=7.4) solutions indicating that the linear-dendritic copolymer is degradable. FTIR measurements further revealed that the degradation of the linear-dendritic copolymer was due to the hydrolytic degradation of the ester bonds of the PLLA component.