Abstract
Abstract A series of poly(4-vinyl pyridine)-b-poly(ε-caprolactone) diblock copolymers, P4VP-PCL, has been synthesized through sequential living ring-opening polymerization and atom transfer radical polymerization. In the P4VP-PCL diblock copolymers, a hybridization of inorganic and organic components can be achieved by coordination of P4VP block with inorganic elements whereas PCL block can be degraded by hydrolysis. Consequently, the self-assembly P4VP-PCL/inorganic materials hybrid system gives rise to a promising and convenient way for the manufacturing of mesoporous and nanoarrayed hybrid materials. A variety of self-assembly nanostructures including P4VP-rich cylinder, lamellae and PCL-rich cylinder has been obtained by simply varying the constituted volume fraction as evidenced by transmission electron microscopy and small-angle X-ray scattering. In-situ creation of gold (Au) nanoparticles in the phase-separated P4VP microdomains was formed by reduction of Au metal ions in the presence of N2H4 in dichloromethane as evidenced by Fourier transform infrared and ultraviolet experiments. Interesting phase-separated morphological evolution was observed by introducing various amounts of gold metal ions with P4VP-PCL. For instance, a significant phase transformation from cylindrical to lamellar nanostructure can be identified for diblock copolymer of VP32CL46 (fPVPv=40%) blended with Au metal ion at the molar ratio of nitrogen to gold around 5. By contrast, phase-separated nanostructure of P4VP-PCL might be destructed by strong coordination of P4VP block and Au metal ions. At the same gold content, the ratio of nitrogen to gold around 5, the lamellar nanostructure of VP146CL91 (fPVPv=61%) became disordered. As expected, the hybrid morphology is strongly dependent upon the content of Au metal ions and the original nanostructure of block copolymers. The observed morphological evolution for the hybrid system of P4VP-PCL/Au blends is consistent to the theoretical prediction on the basis of thermodynamics. Owing to the interaction of Au metal ion and the P4VP block, the introduction of Au nanoparticles having size below nanometer for the formed hybrid system is similar to the mixture of low molecular weight P4VP homopolymers and P4VP-PCL. As a result, the effected volume fraction of P4VP-rich phase is constantly increased with the added amount of reduction gold nanoparticles so as to induce phase transformation. On the other hand, the ordered self-assembly morphology might be destructed by the overdose of gold content due to overstretched P4VP chains within phase-separated microdomains. It is also interesting to find that the introduction of inorganic materials to block copolymers might promote the thermal properties of self-assembly system. As observed, the glass transition temperature of P4VP block can be significantly increased by coordinating reduction gold nanoparticles due to the crosslinking-like effect for the P4VP chains