Comparative Study of Linear Poly(alkylarylsilane)s as Reducing Agents toward Ag(I) and Pd(II) Ions−Synthesis of Polymer−Metal Nanocomposites with Variable Size Domains of Metal Nanoparticles

摘要

Several new poly(alkylarylsilane)s, [Et₃Si(CH₂)₂Si(C₆H₄R)]_n [R = H (1), p-Me (2), p-OMe (3), p-NMe₂ (4)] with M_w = 2.9−4.6 × 103 and PDI = 1.41−1.64, have been synthesized by dehalocondensation of appropriate dichlorodiorganosilanes using Na dispersion in refluxing toluene. The σ−σ* electronic transitions associated with the silicon backbone of 1−4 exhibit a progressive red shift (λ_max: 320−342 nm) as a result of increasing electron donating ability of the substituent on the phenyl ring. This intrinsic optimization of band gap energy has been considered as a measure of oxidation potential of these polysilanes which varies in the following order: 1 > 2 > 3 > 4. The result obtained from electronic spectra is further confirmed by electrochemical studies using cyclic voltammetry which reveals a lowering of the oxidation potential (V_peak) from 0.95 to 0.49 V in the polysilanes 1−4. These polysilanes act as reducing agents of variable strengths toward Ag(I) and Pd(II) ions and afford the formation of metal nanoparticles with optimized size domains [21.0−4.8 nm for Ag; 31.6−16.6 nm for Pd], the smaller size nanoparticles being formed by the use of polysilanes with lower oxidation potential (or higher λ_max). The polymer−metal nanocomposites have been characterized by NMR and UV−vis spectroscopy as well as powder X-ray diffraction, TEM, and DLS studies.