Dielectric relaxation block copolymers

Various experimental techniques (dielectric relaxation, dynamic mechanical analysis, 1H, 2H and 13C solid-state NMR) have been used for investigating the secondary transitions of BPA-PC, and the block copolymers of BPA and TMBPA carbonates as well as compatible blends of BPA-PC and TMBPA-PC. They have provided lots of information on the motions of methyl, phenyl ring and carbonate units in bulk BPA-PC. The effect of intermolecular packing has also been clearly evidenced. 

Polystyrene and polybutadiene homopolymers as well as random and block copolymers of these mers have been studied via dielectric relaxation spectroscopy and tensile stress-strain measurements. The results suggest that some block copolymer systems studied have styrene rich surfaces which appear to partially crosslink upon initial exposure to ozone even though surface oxygen concentrations are not significantly affected. After continued exposure these samples appear to then undergo chain scission. Complex plane analysis implies that after degradation... 

The dielectric spectra were obtained using the samples with thicknesses ranging between 80 and 150 pm, and in the temperature -130°C to 150°C range, except for the PVDF-h-PVCN block copolymer (-130°C to 100°C) [89]. The values of the dielectric permittivities versus temperature (Figure 20.19) show the existence of two relaxations. At room temperature (100 Hz), the values for PVDF homopolymer, PVDF-h-PAN, PVDF-h-MAN, and PVDF-h-PVCN block copolymers are 6.3, 3.9, 5.0, and 5.5 respectively. 

Dielectric relaxation thus resembles self-diffusion. Both processes observe the motion of single macromolecules through a uniform albeit fluctuating background. In a two-component polymer-solvent system, dielectric spectroscopy reveals the effect of intermacromolecular interactions on single-molecule size and reorientation. Dielectric measurements on a three-component polymer-polymer-solvent mixture, in which a tracer polymer has a nonzero type-A dipole and a potentially nondilute matrix polymer has none, can be used for example to separate the effects of probe and matrix molecular weights on dielectric relaxation. This motif in the comparative study of binary and ternary solutions appears repeatedly below. Finally, dielectric measurements on block copolymers in which some copolymer subchains have been inverted end-to-end or have no dipole moment allow one to observe internal motions and dynamic cross-correlations of subchains. 

The next section of this chapter treats the use of dielectric spectroscopy to determine polymer mean-square end-to-end distances and principal relaxation times, and the correlation between these variables. Further sections treat static scattering determinations of Rg c), the detailed forms for dielectric relaxation spectra, and the use of block copolymers with inverted monomer sequences to infer internal mode relaxations. The chapter closes with a discussion of major results. 

Adachi, Watanabe, and their collaborators have ingeniously used type-A block copolymers to study aspects of subchain motion. The experimental approach is of enormous potential significance, because it offers one of the few possibilities as of this writing for measuring motional correlations between two identifiable, large parts of a polymer coil. The general approach is to examine dielectric relaxation of... 

Finally, this chapter discussed the use of block copolymers to examine local relaxations. Relationships between polymer motion, polymer dynamic modes, and paths for extracting regiospecific dynamic information by use of dielectric relaxation spectroscopy were considered. Quantitative applications of the block copolymer approach presented in this chapter are very demanding on the calibration, accuracy, and sensitivity of the dielectric apparatus and on the synthetic precision of the polymer chemist. 

K. Adachi, H. Hirano, and J. J. Freire. Dielectric study of dynamics of subchains and distribution of normal mode relaxation times in dilute and semidilute solutions of miscible block copolymers. Polymer, 40 (1999), 2271-2279. 

Block copolymers with dielectrically active segments can provide insight into more local chain motions. A block polymer with a central active segment and dielectrically-silent wings shows relaxations in two frequency domains the relaxations are plausibly interpreted as local segmental motion and whole-body reorientation. 

Szymczyk A, Ezquerra T A and Roslaniec Z J (2001) Poly(ether-block-sulfonated ester) copolymers. 2. Mechanical and dielectrical relaxation, J Macromol Sci-Phys 840 685-708. 

Examples of various correlation functions for the diblock copolymer system at high and at low temperatures are shown in Fig. 7. It has been observed that at high temperatures TjN = I), the systems behave like a homogeneous melt. All correlation functions show a single step relaxation. The fastest is the bond relaxation and the slowest is the chain relaxation described by the end-to-end vector autocorrelation function. The relaxation of the block is faster than the whole chain relaxation by a factor of approximately two. Such relations between various relaxation times in the disordered state of the copolymer can be regarded as confirmed experimentally for some real systems, in which the dielectric spectroscopy allows distinction of the different relaxation modes [41]. At low temperatures, drastic changes... 

Suzuki T, Kotaka T (1980) Dielectric and mechanical relaxations in randomly coupled multiblock copolymers with varying block lengths bisphenol-A polycarbonate-poly (oxyethylene) systems. Macromolecules 13 1495-1501... 

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