Dynamic Heterogeneity in Interfacial Region of Microphase-Separated Polystyrene-block-poly(methyl acrylate) Studied by the ESR Spin-Label Technique

Abstract

Molecular motion in an interfacial region of microdomains of polystyrene-block-poly(methyl acrylate) (PS-block-PMA) was studied by electron spin resonance (ESR) technique. The junction points between the blocks, which are located in the interfacial region, were labeled with stable nitroxide radicals. Mobility of the spin-labels reflected the dynamic environments in the interfacial region. The transition temperature of the motion of the spin-labels, T 5.0mT, at which the extreme separation width due to 14N anisotropic hyperfine splitting is 5.0 mT, was estimated, and it reflects a glass transition of the region around the labels. The T 5.0mT of the PS-block-PMA labeled at the junction point was almost the mean value of those of the spin-labeled PS and PMA homopolymers, and the distribution of the motional correlation times (τc) in the interfacial region was much broader than that in the homopolymers. These results are considered to be caused by the heterogeneous mixture of the each segment in the interfacial region at a certain length scale. The molecular weight strongly influenced the interfacial thickness and the segmental mobility and the width of the distribution of the τc in the interfacial region as well as on the glass transition temperatures (T g's) of the microdomains. It was revealed that the width of the distribution of the τc depended on not the interfacial thickness so much as the difference between the mobilities of the block chains in the microdomains. On the other hand, extremely small effects of the overall composition and the morphology of the PS-block-PMA on the segmental mobility in the interfacial region were observed. From these results, it was considered that the dynamic environment in the interfacial region was strongly affected by the gradient of the segmental concentration in the interfacial region and the mobility of the block chains in the microdomains.

Cyclic Macromolecules: Dynamics and Nonlinear Rheology, Final Report DOE Award # DE-FG02-05ER46218, Texas Tech University

“…This indicates that the domain spacing in this ultrahigh MW sample is large enough to reflect green light. 48 On the other hand, highly asymmetric block copolymers, , it is clear that the backbone is not fully extended in its highly asymmetric polymer. In addition, both polymers show oscillations at higher q that originate from the form factor of the block copolymer aggregates.…”

“…In addition, both polymers show oscillations at higher q that originate from the form factor of the block copolymer aggregates. 49 Although the quality of fits is not sufficient to identify the specific shape of the aggregates, the period of the oscillations allows us to identify the characteristic size of the presumably spherical or cylindrical PLA domains with sizes of 38 and 67 nm in diameter, respectively, (48) The wavelength of the reflected light at the interfaces of multilayer lamellae is governed by:…”

“…The two plateau region phenomenon is referred to as a double relaxation mechanism which is typical for brush, comb, or star polymers with long side chains. 1À12 To clarify the attribution of the two plateaus in the dynamic spectrum for the brush polymers with different side chain molecular weight, the dynamic master curves were plotted following the van GurpÀPalmen method 48 by plotting the phase angle (δ o ) vs the logarithm of the complex modulus |G*|. The van GurpÀPalmen plot is sensitive to the molecular weight and molecular architectures of the materials and provides an excellent tool to estimate the value of the plateau modulus.…”

ESR Spectroscopy of Multiphase Polymer Systems

“…An existence of the heterogeneous mixture of each segment in the interfacial region at a certain length scale was found. It was concluded that the dynamic heterogeneities in the interfacial region were due to the gradient of the segmental concentration in the interfacial region, and the dynamic environment in the interfacial region was strongly influenced by the mobility of the block chains within microdomains [41]. Molecular mobility in the interfacial region of a microphase-separated structure was studied in binary mixtures of AB-type diblock copolymers and homopolymers (miscible with only A).…”

One-step synthesis to photoelectric hybrid composite of N-vinylcarbazole–methyl acrylate copolymer and ZnO nanocrystals via nanocrystals-initiated polymerization

“…Further, in this study we design a copolymerization, in which ZnO nanocrystals initiate a copolymerization of NVK and methyl acrylate (MA), to resolve the crucial issue of film-forming ability about PVK-contained nanocomposites. One reason for selecting MA is that its homopolymer (PMA) is a typical flexible polymer having T g of 8°C [17]. It should be mentioned that a copolymerization initiated by nanocrystals has not been reported as yet.…”