Isotactic and syndiotactic poly(alky1 methacry1ate)s (R=CH3, C2H5, isoC3H7, n-C4H9 and t G H 9 ) were prepared by anionic mechanism and the spin-lattice relaxation times TI of individual carbons and protons were measured mainly in toluene-& by the inversion-recovery Fourier transform (IRFT) method. The Tl's of the carbons in the isotactic polymers were consistently longer than those of the comparable carbons in the syndiotactic polymers. The ratios of "C-TI'S for syndiotactic and isotactic polymers were always in the range of ca. 0,44,6 for all types of carbons. The '3C-T1's decreased with an increase in the bulkiness of the ester gfoup in both polymers. From the measurements of the nuclear Overhauser enhancement (NOE) it was found that the spin-lattice relaxations of carbons in polymethacrylates are dominated by 13C-'H dipolar interactions and;that the extreme narrowing condition is satisfied at least above 70°C. The effect of solvent on I3C-T1 was also studied. The results of the measurements of 'H-Tl's were parallel to those in the carbons' case. It was concluded that the dependence of TI upon the configuration of the polymer is mainly caused by the configurational dependence of the segmental mobility of the polymer. P W m

No abstract

ABSTRACT:Polymerizations of ethyl methacrylate were carried out in toluene with butyllithium at various temperatures. The polymer obtained at -78°C could be fractionated into methanol-insoluble and methanol-soluble fractions. The former was rather syndiotactic. The latter was found by gel-permeation chromatography and 1 H NMR spectroscopy to be composed of highly isotactic polymer and isotactic oligomer. These three fractions were formed simultaneously at the beginning of the polymerization and the amounts and molecular weights of the isotactic and syndiotactic fractions increased during the polymerization, while the amount of oligomeric fraction remained almost constant after the initial rapid increase. These results indicate the coexistence of three different active species for isotactic and syndiotactic polymers and isotactic oligomer, respectively, at the initial stage of the polymerization and two propagating species during the polymerization. The amounts of syndiotactic fraction and oligomeric fraction decreased with an increase in the polymerization temperature and only the isotactic polymer was obtained above -20°C. When the polymerization was initiated with 1,1-diphenylhexyllithium, only an isotactic polymer was produced. In the polymerization initiated with butyllithium, an appreciable amount of lithium ethoxide formed at the initial stage of the reaction, but no formation of the ethoxide was observed in the case of I, 1-diphenylhexyllithium. This indicates that the multiplicity of the active species in the polymerization with butyllithium is strongly related to the lithium ethoxide formed.

It is well known that the results in anionic polymerization of r-substituted acrylates are not the same and that yield, stereoregularity and molecular weight of the polymer strongly depend on the reaction conditions. Even if the reaction conditions are the same, the results are sometimes very different and depend on the research group or time and person even in the same group','). One of the important reasons of disagreement may be the purity of the reagents used. It is extremely difficult to attain the same degree of purity in different groups, at different times o r by different persons. Among various kinds of impurities moisture is the most probable one. In our previous paper it was revealed that the addition of a small amount of water enhanced the isotacticity of the polymer in the polymerization of methyl r-ethylacrylate (MEA) in toluene by butyllithium (~-B u L~)~) .In this work we studied the influence of water on the anionic polymerization of several r-substituted acrylates and found that the presence of a small amount of water generally increased the isotacticity of the polymer owing to the preferential deterioration of syndiotactic site.Polymerization was carried out in a glass ampoule in toluene under dry nitrogen. Toluene containing a known amount of water was mixed with completely dried toluene in various amounts and the mixture was used as a solvent in order to introduce water into the polymerization agents. 'H NMR spectra of the polymers were taken on a 1215

NMR relaxation studies of chemically shifted nuclei give valuable information about the local molecular motion of polymer in solution. In our previous it was found that the spin-lattice relaxation times (T1) of the protons in isotactic poly(x-substituted acry1ate)s were always longer than that of the comparable protons in the syndiotactic polymers. On the other hand, the equality of the relaxation time for comparable carbons in different steric configurations was reported on the solutions of polystyrene3', poly(viny1 chloride)4) and polya~rylonitrile~.~'. Recently Heutley et al." reported that in s~w / i otactic poly(methy1 methacrylate) the T1 of z-methyl carbon in heterotactic triad was greater than that in syndiotactic triad, although the Tl of backbone methylene carbon was independent on the steric configuration of the polymer. In this work 13C spin-lattice relaxation times were measured on the solutions of various polymethacrylates in isotactic and syndiotactic configurations and a strong dependence of Tl was found on the tacticity of the polymer. TI was measured by the inversion-recovery method on a JNM-FX-100 Fourier Transform Spectrometer (JEOL) operating at 25 MHz. The precision of the measurement was within f 10%. The solution of the polymer in toluene-d8 (1 mol/l) was degassed and sealed in an NMR sample tube (10 mm 0.d.) under N2 pressure.The polymers employed for the measurements were poly(methy1 methacrylate) [PMMA], poly(ethy1 methacrylate) [PEMA], poly(isopropy1 methacry-61 7