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
Two series of well-characterized (styrene-p-chlorostyrene) tri-block copolymers of B,,,A,B,-and A,B,A,-types (A : styrene monomeric unit, B: p-chlorostyrene monomeric unit. n = 2m denotes the number of units) were synthesized by anionic polymerization technique. Their intrinsic viscosities in toluene, 2-butanone, and cumene were studied over a wide range of molecular weights. The data were analyzed on the basis of two-parameter theories. The unperturbed dimensions of the block copolymers are expressed by those of the parent homopolymers and the composition. The conformational behaviours of the B,,,AnB, and A,B,,A, copolymers are similar in the non-selective solvents, toluene and 2-butanone, whereas in the selective solvent, cumene, which is a O solvent for poly-p-chlorostyrene and a good solvent for polystyrene, a molecule of the A,B,,A, copolymers takes a more extended chain conformation and a greater value of the longrange interaction parameter than the B,,,AA,B, copolymers of the same composition. However, an anomaly which suggests "intrachain phase separation" wqs not observed in the viscosity behaviours of the block copolymers in cumene as well as in toluene and 2-butanone. ZUSAMMENFASSUNG :Zwei Reihen gut definierter Dreiblock-Copolymerer aus Styrol (A) und p-Chlorstyrol (B) wurden durch anionische Polymerisation hergestellt. Sie haben die Formen B,-A,-B, und A,-B,-A,, wobei n = 2 m die Anzahl der Monomereinheiten bezeichnet. Ihre Viskositatszahlen in Toluol, 2-Butanon und Cumol wurden in einem groBen Molekulargewichtsbereich untersucht und aufgrund der Zweiparameter-Theorien ausgewertet. Die ungestorten Dimensionen der Blockcopolymeren lassen sich durch die der Homopolymeren und die Zusammensetzung ausdrucken. Das Konformationsverhalten beider Copolymertypen in den nicht selektiven Losungsmitteln Toluol und 2-Butanon ist ahnlich. Im selektiven Cumol, das fur Poly-p-chlorstyrol ein 0-Losungsmittel und fur Polystyrol ein gutes Losungsmittel ist, werden die Knaueldimension und der Parameter fur die weitreichende Wechselwirkung fur die A,-B,-A,-Copolymere groBer als fur die B,-A,-B,-Typen gleicher Zusammensetzung. Es ergaben sich jedoch weder in Cumol noch in Toluol oder 2-Butanon Anomalien im Viskositatsverhalten beider Blockcopolymeren, die auf eine innere Phasentrennung hinweisen.
ABSTRACT:A three-terminal cell for the dielectric measurement of liquid was made and the cell capacitance was determined using a capacitance bridge. The accuracy of the dielectric constant measurement with the apparatus was examined by measuring standard materials such as benzene and cyclohexane. The mean square dipole moments of poly(p-methoxystyrene) in benzene were determined by accurate measurements of dielectric constants on the polymer dilute solutions and the values were estimated according to two procedures, i.e., one based on Debye and HalverstadtKumler equations (DHK method) and the other on Guggenheim and Smith equations (G-S method). The average dipole moments per repeat unitµ were obtained as 1.214 (25°C) and 1.221 (40°C) by the DHK method and 1.204 (25°C) and 1.209 (40°C) by the G-S method (in debye unit). The slight disagreement in µ values obtained by two different procedures was interpreted as arising from differences in assumptions used in the DHK method and the G-S method.KEY WORDS Dipole Moment / Dielectric Constant / Molecular Polarization / Electronic Polarization / Atomic Polarization / Molecular Refraction / Poly(p-methoxystyrene) / Dielectric Cell / Dilute Solution / Dipole moment is a configurationdependent property of polymer chains carrying polar groups in their monomer units and the observed dipole moment is the statistical average of molecular conformations. Theory predicts that the dipole moments of polymer molecules cannot be affected greatly by longrange excluded volume interactions when the molecules have the dipole components perpendicularly attaching to the chain axis. 1 • 2 The probable absence of the effect of the excluded volume on dipole moments, in contrast with its pronounced effect on chain dimensions, is of great advantage in investigating the influence of intramolecular interactions on the conformation of polar polymers.We have been studying since early in the 1960's the dipole moments µ of polar vinyl polymers to investigate configurational properties such as the stereochemical structure of the vinyl chains and the monomer sequence distribution in the copolymers.
The infrared absorption spectra of polymers and copolymers of methyl acrylate and methyl methacrylate have been measured, and then used as the basis of a spectrophotometric method for the analysis of the copolymers. The 6.73 μ band, which may be due to methyl (–C–CH3) vibration, was selected as the key band for measuring the methyl methacrylate component, while the 6.89 μ band was used as the standard. The monomer reactivity ratios for copolymerization of methyl acrylate-methyl methacrylate system have been determined to be r1=0.5±0.1, and r2=2.3±0.4 (M1 methyl acrylate, M2; methyl methacrylate) at 130°C. These values are in good agreement with those previously obtained by the deuterium tracer method. It has also been shown that the procedure used in this study is appropriate for the analyses of methyl acrylate-methyl methacrylate copolymers.
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