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. A hybridization of inorganic and organic components can be achieved by protonation of P4VP block with gold precursor (HAuCl4). In-situ growth of gold (Au) nanoparticles in the phase-separated P4VP microdomains was formed by reduction of Au metal ions. The reduction as traced by Fourier transform infrared and ultraviolet analyses was carried out in dichloromethane solution by using hydrazine (N2H4) as reduction agent. Interesting morphological evolution was observed by introducing various amounts of gold precursors to P4VP-PCL system. For instance, a significant phase transformation from cylindrical to lamellar nanostructure can be identified for diblock copolymer of VP27CL46 (fPVPv=37%) blended with gold precursors (as small particles) at the molar ratio of nitrogen to gold around 7. By contrast, phase-separated nanostructure of P4VP-PCL might be destructed by strong coordination (equimolar addition of gold precursor). The hybrid morphology is strongly dependent upon the added amount of inorganic materials in hybrid system. The observed morphological evolution in the hybrid system of P4VP-PCL/Au hybrid system is consistent to that of theoretical prediction on the basis of mean-field calculation. Owing to the interaction of Au precursors and the P4VP block, the introduction of Au precursors (i.e., Au ions), having size much smaller than the radius of gyration of the P4VP chains, in the hybrid system is similar to the mixing of low-molecular-weight P4VP homopolymers with P4VP-PCL. As a result, the effective volume fraction of P4VP-rich phase is constantly increased with the added amounts of gold ions so as to induce phase transformation. Eventually, the ordered self-assembly morphology might be destructed without the appearance of ordered microphase separation. By contrast, we speculate that the reduction of Au precursors may lead to the localization behavior at which the formed Au nanoparticles might be too large to be accommodated by P4VP chains, finally forming the self-assembled ordered arrays of Au nanoparticles. Detailed studies with respect to the size effect of reductive Au nanoparticles on morphological evolution in the hybrid system will be systematically examined.