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

Abstract

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...

Polymer Structure Control Based on Crystal Engineering for Materials Design

“…Historically, syndiotactic and disyndiotactic polymerizations of olefins and polar vinyl monomers have followed isotactic and diisotactic polymerizations, as seen in the polymerizations of styrene, propylene, methacrylates, and crotonates, because well-designed and more sophisticated catalysts are required for the control of syndiotactic propagation. [106][107][108][109][110][111] The synthesis of cis-1,4 polymers was tried by the use of monomers with an s-cis conformation. Odani et al attempted the solid-state photopolymerization of pyridone derivatives, which is a six-membered cyclic diene amide and is a tautomer of 2-hydroxypyridine.…”

Stereospecific Group Transfer Polymerization of Methyl Methacrylate with Lewis-Acid Catalysis—Formation of Highly Syndiotactic Poly(methyl methacrylate)

“…However, there had been no distinctive evidence of any special stereocontrol responsible to ''group transfer'', 4-7 until we have reported a Lewisacid catalyzed GTP of methyl crotonate with HgI 2 -iodotrialkylsilanes (R 3 SiI) as catalysts, which produces disyndiotactic poly(methyl crotonate) (Scheme 1); the stereoregularity of the polymer depends on the structure of trialkylsilyl transferring groups. [8][9][10][11] During the investigation of Lewis-acid mediated stereoregulation of GTP, we found a stereospecific GTP of MMA catalyzed by aluminum phenoxide with R 3 SiI as a co-catalyst, which gives PMMA with a bimodal distribution of molecular weight (MW), the high MW fraction of which had high syndiotacticity (Scheme 2). Though the overall products had a lower syndiotacticity, it is evident that there exists highly syndiotactic-specific and highly active species in this GTP system.…”

Synthesis of a polyester macromonomer via the cobalt‐catalyzed alternating copolymerization of propylene oxide and carbon monoxide

“…Although the reaction mechanism is unclear, the combination of NaCo(CO) 4 and amine realized the selective synthesis of the oligoester with a crotonate end group. Because anionic or group‐transfer polymerization has been reported for alkyl crotonate,19–22 the macromonomers produced in this work have potential applications as comblike polymers and graft copolymers. Furthermore, because the ring opening of propylene oxide selectively proceeds at the unsubstituted carbon, the use of a single enantiomer of propylene oxide should enable the production of an optically active macromonomer 11…”