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(oxybu tylene)-poly (EBE) triblock copolymers, using broadband dielectric relaxati on spectroscopy (10(-2) to 10(9) Hz). The B homopolymers and the B blocks o f 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, exhibi ts similar characteristics in all three systems. The normal mode relaxation process due to chain motions of larger length scales than that of segmenta l motion, also was studied for the homopolymers and the copolymers. The res ults also imply that B blocks of triblock copolymers exhibit normal mode re laxation, where mainly normal eigenmodes of relatively high orders contribu te. The mobility of the global chain motion is determined by the order of t he 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 orde r of the most intensive eigenmodes. For very short B blocks, fixed chain en d effects affect significantly the dynamics of both, main and normal mode r elaxation.