Two-Dimensional NMR Spectra of Isotactic Poly(methyl methacrylate) Prepared with t-C4H9MgBr and Detailed Examination of Tacticity

Tanaka

et al. 1987

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KEY WORDSStereochemistry I Oligomer I Methyl Methacrylate I t-C4 H9MgBr I HPLC I 2D NMR I End Group I Living Polymerization I Tacticity I Molecular Weight Distribution IInvestigations on the oligomerizations of vinyl monomers provide useful and important information on the corresponding vinyl polymerization. Yoshino et al. studied the structures of the oligomers of isopropyl acrylate formed with phenylmagnesium bromide to elucidate the stereoregulation in the polymerization.1·2 Hogen-Esch and his coworkers have extensively studied the stereochemistry of anionic oligomerizations of vinylpyridines3 -9 and vinyl phenyl sulfoxide 10 · 11 using chromatographic and NMR spectroscopic techniques. However, little has been reported on the stereoregular oligomerization of acrylate 12 or methacrylate 13 -ts monomer. Wulff et al.U and Okamoto et a/. 14 studied asymmetric oligomerizations of triphenylmethyl methacrylate with 1, 1-diphenylhexyllithium-and fluorenyllithium-(-)-sparteine complexes, respectively, in toluene at -78oC. Hogen-Esch and his coworkers carried out the anionic oligomerization of methyl methacrylate (MMA) in tetrahydrofuran (THF) by lithio or sodio salt of methyl isobutyrate followed by termination with CH 3 I or 13 CH 3 I and determined the structure of the symmetrical oligomers by gas chromatography and 13 C NMR spectroscopy. 15Recently, we found that the polymerization of MMA by t-C 4 H 9 MgBr in toluene at -78°C was a completely living and highly isotacticspecific system. 16 · 17 The a-and w-end tacticities of the PMMA were studied by 2D NMR techniques. 18 OCH3In this work, isotactic oligo(MMA)s were prepared by the polymerization of MMA with tC4H9MgBr in toluene at -78oC and their configurational sequences were investigated in detail by chromatography and 2D NMR spectroscopy to gain a more detailed understanding of stereoregulation in polymerization. The oligomers were isolated as reaction products from the early stage of the polymerization. The crude oligomers were fractionated into dimer to octamer by gel permeation chromatography. Each fraction was further separated into stereoisomers by HPLC on a silica gel column (Develosil 100-5) with mixtures of n-C 4 H 9 Cl and CH 3 CN as eluent. The stereosequence of each stereoisomer was eluc-1325

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Section: Stereochemistry Of the Oligomn Of Mma By T-bumgbr 100r------mentioning

confidence: 90%

Stereochemistry of the Oligomerization of Methyl Methacrylate by t-C4H9MgBr in Toluene at −78°C

Hatäda

Tanaka

et al. 1987

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“…Chemical shifts were referred to hexamethyldisiloxane (HMDS) added as an internal standard and given in the HMDS scale. 9 Molecular mass of the uniform l 5mer (C76-H124O30 = 1516) and 18mer (C91H 148 0 36 = 1816) of 2 were determined clearly using a JEOL JMS-DX303HF spectrometer operated Polym. J., Vol.…”

Section: Measurementsmentioning

confidence: 99%

“…The isotacticity of the parent PMMA 1 is 96-97% in triads, and thus the isolated 50mer, for example, should contain statistically one racemo (r) oiad somewhere in its configurational sequence. Moreover, the uniform PMMAs have configurational disorder at the chain-end diads (the a-band y-z diads in eq 1) because the stereospecificity in the initiation 9 and termination processes 10 of the polymerization was found to be 90 and 94% in mesa (m) diad, respectively. In the present paper, we report the synthesis and SFC fractionation of an isotactic and symmetrical PMMA (2) containing very few r diads throughout the whole polymer chain.…”

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confidence: 99%

Controlled Synthesis of Isotactic and Symmetrical Poly(methyl methacrylate) Directed toward Uniform Polymers with High Crystallinity

Yamasaki

Naito

et al. 1995

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ABSTRACT:The synthesis and fractionation by supercritical fluid chromatography (SFC) of an isotactic and symmetrical poly(methyl methacrylate) (PMMA) containing very few configurational defects, H+MMA+.-CH 3 (2), are described. Detailed analysis by 1 H NMR spectroscopy showed that the PMMA 2 was almost perfectly isotactic ( -100%) except a small amount (11 % ) of racemo sequence at the first tactic diad from the initiating chain-end. The uniform PMMAs 2 with 31, 36, 41, and 44 repeating units (n) had melting points higher by 4.5-12.2°C than those of the uniform PMMAs prepared in a previous work, t-C4 H 9 +MMA+.-H (1) with a triad isotacticity of 96.1 %. The degrees of crystallinity of the uniform PMMA 2 samples were determined to be 92-97%, also high as compared with those of uniform PMMA 1 samples. Single crystals were grown from a solution of the 7mer of 2 (n = 7), and the crystal structure was determined by X-ray analysis.KEY WORDS Uniform Polymer / Supercritical Fluid Chromatography / Living Polymerization / Tacticity / End-Group / Melting Temperature / Degree of Crystallinity / X-Ray Crystallographic Analysis/ Polymerization of methyl methacrylate (MMA) initiated with t-C 4 H 9 MgBr in toluene at -78°C proceeds in a living manner to yield a highly isotactic PMMA with a well-defined chain structure ( Recently, we have succeeded in fractionating this PMMA into the individual homologues from 3mer (C 19 H 34 0 6 =358.5) to lOOmer (C 504 H 810 0 200 = 10069.9) by means of supercritical fluid chromatography (SFC). 2 -6 A series of the uniform isotactic PMMAs was subjected to investigations of its glass transition temperature (Tg), 3 • 5 • 7 crystalline melting ternperature (Tm), 5 • 7 and of the stereocomplexation with uniform syndiotactic PMMAs. 3 • 4 Usefulness of the uniform PMMAs as a standard material for molecular weight determinations has also been demonstrated. 4 • 5 Although the purity of the uniform PMMAs with respect to degree of polymerization (DP) was proved to be higher than 99% by SFC 3 • 4 and mass spectrometry, 8 there still remains a purity problem at the stereochemical level. The isotacticity of the parent PMMA 1 is 96-97% in triads, and thus the isolated 50mer, for example, should contain statistically one racemo (r) oiad somewhere in its configurational sequence. Moreover, the uniform PMMAs have configurational disorder at the chain-end diads (the a-band y-z diads in eq 1) because the stereospecificity in the initiation 9 and termination processes 10 of the polymerization was found to be 90 and 94% in mesa (m) 951

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“…In addition, we reported the structural analysis of the oligomeric products [I] (n = 0 -6) by HPLC and 1 H NMR spectroscopy. 4 In the literatures mentioned above, 3 .4 the mesa/ racema assignments for the monomeric sequences in the PMMA and the oligomeric products were made on the basis of the nonequivalency of methylene protons; 5 · 6 the chemical shift difference between the 1 H NMR signals of two methylene protons in a given monomeric unit should be larger for a mesa dyad sequence than for a racema dyad sequence. Very recently, X-ray analysis of a crystallized MMA trimer was carried out, and the stereostructure of the trimer was found to be mesa-mesa.…”

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confidence: 99%

The NMR Chemical Shifts between the Nonequivalent Methylene Protons of Polymer and Oligomers of Methyl Methacrylate: The Revised meso/racemo Assignments for the ω-End Dyad Sequences

Hatäda

Kitayama

et al. 1989

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