Carbon‐13 spin lattice relaxation times of polymethacrylates of various tacticities in solution

Abstract

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

Comparison of molecular motions detected by the spin label technique and carbon-13 nuclear magnetic resonance in benzene solution of poly(methyl methacrylate)

“…Hatada and co-workers have recently reported that 13C nuclear Overhauser enhancements (NOE) for isotactic and syndiotactic PMMAs is very LI NEW1DTH , gauss close to the theoretical maximum value derived from the dipolar mechanism. 13 Their NOE results indicate that the spin-lattice relaxation time of 13C is mostly governed by the dipolar interactions with the directly attached protons. 14 In the extreme narrowing case ( « 1), Tx is inversely proportional to the number of attached protons, N, and expressed by the following equation:…”

Selektive NMR T1‐ und NOE‐Messungen zur Untersuchung lokaler Molekülbewegungen in gelösten Vinylchlorid/Vinylacetat‐Copolymeren

“…Literatur [l] ANDERS, €I., BEHNISCH, J., und ZIMMERMANN, H.: hcta [2] T U D~S , F., und KELES, T.: Macromol. Chem.…”