These studies suggest that knowledge of the initial depth distribution of fallout radionuclides is important for future decontamination work and countermeasures to reduce the transfer of radionuclides to agricultural products. In order to determine how the initial depth distribution of the radioactive substances varies depending on field type, such as wheat fields, rice paddies, orchards, and forestland, we need to take measurements at locations with different land-use patterns but with nearly equal exposure to radioactive fallout. The Fukushima Agricultural Technology Centre has wheat fields, rice paddies, orchards, and forestland all enclosed within a 500 × 500 m test site. At this test site, we sampled and determined the depth profiles of radiocesium and radioiodine for each type of land use. On the basis of these depth profiles, we derived an estimate of the deposition density to clarify the influence that land use has on the distribution pattern of radionuclides in soils. Several other studies have been also conducted in this issue for the distribution of the radionuclides on land and mechanism of retention of radiocesium at soil surface (
The dipole moment of poly(ethylene oxide) (PEO) and its dependence on molecular weight and temperature have been investigated by measuring the dielectric constant and the density of dilute PEO-benzene solutions in the temperature range from 25 to 55 C. The dipole moments of the polymers h molecule 2 i 1=2 , increased linearly with respect to the square root of the degree of polymerization n, which confirms the theoretical prediction that the long-range excluded volume interactions have little effect on the dipole moment of polymers such as PEO. The estimated value for diethyl ether DE is 1.20 D, according to the relationship between h molecule 2 i 1=2 and n 1=2 for PEO oligomers, 10,17 which leads to a C-O bond moment, m C{O , of 1.07 D. The averaged dipole moment per constitutional repeating unit h 2 i 1=2 for PEO polymers is 1:040 AE 0:002 [D] at 25 C. The following dipole moment ratio and the temperature coefficient were obtained for PEO in benzene: h 2 i=m 2 ¼ 0:472 AE 0:002 (at 25 C) and d lnh 2 i=dT ¼ ð2:11 AE 0:28Þ Â 10 À3 K À1 (25-45 C). The experimental results are compared with the conformational characteristics of PEO investigated by the rotational isomeric state (RIS) analyses by Abe et al. and Sasanuma et al.
ABSTRACT:Dipole moments of isotactic (iso) and syndiotactic (syn) poly(methyl methacrylate) (PMMA) samples were determined from measurements of dielectric constants and densities in dilute benzene solution over the temperature range from 25 to 55°C. The dipole moments and their temperature coefficients showed marked tacticity dependence. It was found that the iso-PMMA gives greater values of the dipole moment than those for the syn-PMMA; e.g., 1.457D ( = µ, dipole moment per constitutional repeating unit) was obtained for the iso-PMMA, and 1.323 D for the syn-PMMA at 25°C. With increasing temperature, the dipole moment of the iso-PMMA showed little change and remained nearly constant, while that of the syn-PMMA increased continuously, giving 1.399 D at 55°C. Experimental dipole moment ratios, D, = (m 2 )/nµJ = (µ 2 )/µJ, (m, dipole moment of polymer; µ0 , dipole moment of the constitutional unit; n, the number of units;) were compared with the calculated ones, which leads to the conclusion that rotational conditions regarding the orientation of polar side groups in the PMMA chains are highly restricted.KEY WORDS Poly(methyl methacrylate) / Tacticity / Dipole Moment Ratio / Temperature Coefficient / Conformation / Dilute Solution / The mean square dipole moment (m 2 ) of polymers having polar groups in their constitutional units is a conformation-dependent property like as the unperturbed chain dimension (rJ). Experimental values of the dipole moment can be determined from dielectric constant measurements in solution while theoretical values of (m 2 ) may be calculated using the "rotational isomeric state" model from structural information and conformational energies. Thus, study of dipole moments should provide information regarding the spatial configuration of polymers having polar groups.Dipole moments of poly(methyl methacrylate) (PMMA) have long been studied, and the results of experimental studies have been reported numerously. 1 -6 The value of (m 2 ) of isotactic (iso) PMMA may be different from that of syndiotactic (syn) PMMA, because the conformation of chain molecules should depend on stereochemical constitution of the chain. The dependence of (m 2 ) of PMMA on tacticity was studied experimentally, in the 1960s, by Pohl et al.,4 Salovey, 5 and Roig et al. 6 • More recently, theoretical studies on conformational statistics of iso-and syn-PMMA chains were reported by Flory, Sundararajan, and coworker. 8 -10 The dipole moments of iso-and syn-PMMAs were calculated by Birshtein et al. 11 . However, the reliability of experimental values of the dipole moments previously reported is apparently not 579
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