Polymerization of tert ‐butyl crotonate

ABSTRACT:Stereospecific living polymerization of methyl crotonate was achieved by using ketene trialkylsilyl acetals as initiators in the presence of Hgl 2 and iodotrialkylsi1anes as catalyst and co-catalysts, respectively. Znl 2 and Cdl2 also catalyzed the polymerization_ Disyndiotactic polymers with narrow molecular weight distribution were obtained quantitatively, Livingness and stereospecificity of this polymerization were sensitive to the structure of tria1kylsilyl groups in the initiator and co-catalyst; (C 2 H 5 hSi-and (n-C 3 H 7 lJSi-systems gave the active species with higher thermal stability and higher stereospecificity than (CH 3hSi-system. Configurational determination of the disyndiotactic poly( methyl crotonate)s was made by chromatographic separation of their low molecular weight homologs (tetramer and hexamer), followed by X-ray single crystal analysis. The results of oligomer analysis led to the conclusion that the disyndiotactic polymer chains are formed by the threo addition of monomers to propagating chain-ends and trans opening of monomer C = C double bonds.KEY Two useful pieces of information led to this finding; (1) the GTP of acry1ates using Hgl 2 as a catalyst in toluene gives a good control of molecular weight, 2 • 3 and (2) the use of (CH 3 hSil as a co-catalyst and CH 2Cl 2 /toluene mixture as a solvent drastically accelerates the Hgl 2 -catalyzed GTP of n-butyl acrylate. 4 • 5 Before this finding, direct preparation of poly( methyl crotonate) from its monomer had been considered to be difficult. As a commonly observed feature of crotonates, methyl crotonate gives no polymer by a free radical mechanism. 6 • 7 Typical anionic initiators such as alkyllithiums or Grignard reagents are ineffective for the polymerization of methyl crotonate, 6 -9 whereas branched alkyl crotonates including t-butyl and triphenylmethyl crotonates are polymerized in good yields 6 -16 and in a living manner 17 · 18 by these initiators. The only compound that had been known to polymerize methyl crotonate in a substantial yield was CaZn(C 2 H 5 )4 complex. The polymerization of methyl crotonate with t To whom correspondence should be addressed. tt Present address: Fukui University of Technology, Japan. this complex in toluene at -78oC for 96 h affords a polymer in 28% yield. 8In spite of the difficulty of methyl crotonate polymerization, several kinds of poly(methyl crotonate)s with various stereoregularities have been prepared and identified in the last five years. These poly(methyl crotonate)s were derived from threodiisotactic poly(triphenylmethyl crotonate), 13 diheterotactic poly(t-butyl crotonate),15 and atactic-like poly(t-butyl crotonate) 12 by means of hydrolytic cleavage of the ester functions and subsequent methylation with CH 2 N 2 . The previous paper 1 reported that the poly(methyl crotonate) formed by GTP showed 1 H NMR spectra quite different from those of threodiisotactic, diheterotactic, and atactic-like poly(methyl crotonate)s.The present paper provides details of our studies on the GTP o...

“…CH 3 and oc 6 -CH 2 resonances were made by 1 H COSY and HMQC experiments. All f3-CH 3 groups except for that of the sixth monomer unit showed NMR signals at 0.90 to 0.95 ppm.…”

Section: Etet Sequencementioning

confidence: 99%

mentioning

confidence: 99%

Preparation of Disyndiotactic Poly(methyl crotonate) by Stereospecific Group Transfer Polymerization

Ute

Tarao

Hongo

et al. 1999

“…8 On the contrary, high molecular weight poly-(RCr) was obtained in polymerization of RCr with bulky sec-and tert-alkyl esters. 9 • 10 Nagasawa and coworkers studied on the synthesis of poly(tert-butyl crotonate) with a semiflexible backbone and a narrow molecular weight distribution by anionic polymerization with very careful procedures for purification and polymerization, 11 and they examined as to the rigidity of the polymer chain from molecular characteristics in dilute solution or in bulk. 12 However, polymerizations of other tert-alkyl esters of RCr have not been ever reported.…”

Section: Or Ormentioning

confidence: 99%

Synthesis and Characterization of Thermally Stable Polymers through Anionic Polymerization of tert-Alkyl Crotonates

Horie

Otsu

1991

ABSTRACT:Some alkyl crotonates bearing tert-alkyl groups, i.e., lert-butyl, tert-amyl, 1-adamantyl and 3,5-dimethyl-1-adamantyl crotonates were prepared and polymerized with sec-butyllithium as an anionic catalyst in toluene or THF. The resulting polymers were confirmed to consist of poly(substituted methylene) structure by IR and NMR spectroscopies. The polymers bearing adamantyl groups had more resistance to hydrolysis, whereas the tert-butyl and amyl esters were readily hydrolyzed. The introduction of the adamantyl groups also increased glass transition temperature and decomposition temperature of the polymer. It was revealed that the polymers bearing the tert-butyl and amyl esters decomposed via a two-step mechanism, resulting in the formation of poly(crotonic acid) accompanied with elimination of corresponding olefins from the ester groups, but the polymers containing adamantyl groups showed excellent thermal stability.

“…The reason for the disagreement may be clarified when the molecular structures and molecular weights of two samples used are carefully compared. It is generally believed 16 that crotonic acid cannot be radically homopolymerized, and the acidity of polyacids markedly varies with molecular weight if the molecular weight of the polyacid is not above a certain value.…”

Section: Samplesmentioning

confidence: 99%

Potentiometric Titration Behavior of Poly(crotonic acid)

Muroga

Nagasawa

1986

The potentiometric titration curve of poly(crotonic acid) was compared with that of poly(methacrylic acid). Poly(crotonic acid) is a far weaker acid than poly(methacrylic acid), despite the fact that the conformation of poly(crotonic acid) is a random coil, similar to that of poly(methacrylic acid). This difference is ascribed to their difference in the relative position of the methyl group to the carboxyl group. The methyl group in poly(crotonic acid) intervenes between two adjacent carboxyl groups, leading to the decrease in the local dielectric constant effective for ionization of carboxyl groups.