Synthesis and characterization of model diblock copolymers of poly(dimethylsiloxane) with poly(1,4-butadiene) or poly(ethylene)

Model diblock copolymers of poly(1,4-butadiene) (PB) and poly(dimethylsiloxane) (PDMS), PB-b-PDMS, were synthesized by the sequential anionic polymerization (high vacuum techniques) of butadiene and hexamethylciclotrisiloxane (D₃) in the presence of sec-BuLi. By homogeneous hydrogenation of PB-b-PDMS, the corresponding poly(ethylene) and poly(dimethylsiloxane) block copolymers, PE-b-PDMS, were obtained. The synthesized block copolymers were characterized by nuclear magnetic resonance (¹H and ¹³C NMR), size-exclusion chromatography (SEC), Fourier transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), transmission electron microscopy (TEM), and rheology. SEC combined with ¹H NMR analysis indicates that the polydispersity index of the samples (M_w/M_n) is low, and that the chemical composition of the copolymers varies from low to medium PDMS content. According to DSC and TGA experiments, the thermal stability of these block copolymers depends on the PDMS content, whereas TEM analysis reveals ordered arrangements of the microphases. The morphologies observed vary from spherical and cylindrical to lamellar domains. This ordered state (even at high temperatures) was further confirmed by small-amplitude oscillatory shear flow tests.