Molecular dynamics in homo, diblock and triblock polymers studied by dielectric relaxation spectroscopy

The dynamics of poly(oxybutylene) chains was investigated in comparison to that of poly(oxybutylene) blocks in solid semicrystalline poly(oxyethylene)-poly(oxybutylene) (EB) diblock copolymers and poly(oxyethylene)-poly(oxybutylene)-poly(oxyethylene) (EBE) triblock copolymers, using broadband dielectric relaxation spectroscopy (10^-2 to 10⁹ Hz). The B homopolymers and the B blocks of the triblocks were dipole-inverted, whereas no dipole inversion occurred in the B blocks of the diblocks. For B blocks longer than a critical value B_cr, the main relaxation, which is related to the glass transition, exhibits similar characteristics in all three systems. The normal mode relaxation process due to chain motions of larger length scales than that of segmental motion, also was studied for the homopolymers and the copolymers. The results also imply that B blocks of triblock copolymers exhibit normal mode relaxation, where mainly normal eigenmodes of relatively high orders contribute. The mobility of the global chain motion is determined by the order of the normal eigenmodes with the highest intensities, whereas the whole chain conformations are mainly determined by the spatial confinement in the solid copolymers and the effects of fixed chain ends, irrespectively of the order of the most intensive eigenmodes. For very short B blocks, fixed chain end effects affect significantly the dynamics of both, main and normal mode relaxation