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.