Molecular Dynamics Study of Polystyrene-b-poly(ethylene oxide) Asymmetric Diblock Copolymer Systems

Abstract

Two polystyrene-b-poly(ethylene oxide) (PS-b-PEO) diblock copolymers differing in molecular mass (49 and 78 kDa) but possessing the same PEO cylindrical morphology are examined to elucidate their molecular dynamics. Of particular interest here is the molecular motion of the PEO blocks involved in the rigid amorphous fraction (RAF). An analysis of complementary thermal calorimetry and X-ray scattering data confirms the presence of microphase-separated morphology as well as semicrystalline structure in each copolymer. Molecular motion within the copolymer systems is monitored by dielectric and nuclear magnetic resonance spectroscopies. The results reported herein reveal the existence of two local Arrhenius-type processes attributed to the noncooperative local motion of PEO segments involved in fully amorphous and rigid amorphous PEO microphases. In both systems, two structural relaxations governed by glass-transition phenomena are identified and assigned to cooperative segmental motion in the fully amorphous phase (the α process) and the RAF (the α process). We measure the temperature dependence of the dynamics associated with all of the processes mentioned above and propose that these local processes are associated with corresponding cooperative segmental motion in both copolymer systems. In marked contrast to the thermal activation of the α process as discerned in both copolymers, the α process appears to be a sensitive probe of the copolymer nanostructure. That is, the copolymer with shorter PEO blocks exhibits more highly restricted cooperative dynamics of PEO segments in the RAF, which can be explained in terms of the greater constraint imposed by the glassy PS matrix on the PEO blocks comprising smaller cylindrical microdomains.

Solvent-Induced Swelling Behaviors of Microphase-Separated Polystyrene-block-Poly(ethylene oxide) Thin Films Investigated Using In Situ Spectroscopic Ellipsometry and Single-Molecule Fluorescence Microscopy

“…Similar observations were reported for polymers in nanoconfined systems, including polymers incorporated into rigid nanopores and ultrathin polymer layers sandwiched between solids. , In particular, polystyrene- block -poly­(ethylene oxide) (PS- b -PEO) electrolytes exhibited a unique dependence of Li + conductivity on PEO molecular weight, , which could be associated with the preferential Li + distribution to the middle of the PEO microdomains and low ionic permeability of the PS–PEO interfacial regions . These observations could be explained by enhanced interfacial interactions and geometric restriction that manipulate the dynamics and packing/entanglement of the polymer chains. − ,− Indeed, enhanced chain dynamics in BCP microdomains were shown using dielectric spectroscopy , and neutron scattering . The dynamic properties of polymer chains should have a significant influence on polymer–solvent interactions and associated phenomena such as solvent permeation and swelling .…”

“…25 These observations could be explained by enhanced interfacial interactions and geometric restriction that manipulate the dynamics and packing/entanglement of the polymer chains. 21−23,25−27 Indeed, enhanced chain dynamics in BCP microdomains were shown using dielectric spectroscopy 26,28 and neutron scattering. 27 The dynamic properties of polymer chains should have a significant influence on polymer−solvent interactions and associated phenomena such as solvent permeation and swelling.…”

Effect of Composition on the Molecular Dynamics of Biodegradable Isotactic Polypropylene/Thermoplastic Starch Blends

“…Independent results obtained from 1 H NMR investigations of the internal motion in neat iPP have been reported elsewhere. − Corresponding measurements of spin–lattice relaxation times ( T 1 ) have been analyzed adopting one or two magnetization fractions with different relaxation times. These prior studies presume that the heterogeneous nature of iPP, which exhibits crystalline, rigid amorphous, and disordered amorphous spatial regions in the same fashion as poly­(ethylene oxide), is primarily responsible for promoting nonexponential magnetization recovery. The dependence of T 1 on reciprocal temperature for virgin iPP and TPS is displayed in Figure a, whereas that for several iPP/TPS blends is presented in Figure b.…”