Metathesis Polymerization
Pauson-Khand reaction yields monomers
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Powerful technique for controlled polymerization yields unique structures with desirable properties
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Stephen C. Stinson C&EN Northeast News Bureau
From the ACS meeting
O
lefin metathesis has emerged as a powerful technique for polymerization, and several groups reported innovative, potentially useful applications in sessions sponsored by the Division of Polymer Chemistry. Metathesis yields types of structures that would be hard to obtain by other methods. In addition, the number of polymer chains in the products is often almost exactly equal to the number of initiator molecules. This results in narrow molecular-weight distributions, which, in turn, lead to desirable properties. Mechanistically, olefin metathesis is a chain reaction, with initiation, propagation, and sometimes termination steps. But it may be visualized for simplicity as a twostep process in which two olefin molecules come together to make a cyclobutane ring, which then splits apart into two different olefin molecules. Metathesis of propylene, for example, yields 2-butene and ethylene. For many kinds of reactions throughout organic chemistry, monofunctional compounds yield small-molecule products on reacting, while difunctional compounds often yield polymers. In the case
Metathesis yields silane-olefin resins
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of olefin metathesis, dienes tend to polymerize and cyclic monoolefins can polymerize with ring opening. In acyclic diene metathesis (ADMET), lecular weight. Numbers close to 1.00 indithe polymerization is often driven by cate narrow molecular-weight distributions, splitting out a small molecule such as which are often desirable for enhanced ethylene. In ring-opening metathesis po- physical properties.) lymerization (ROMP), the driving force Also, the polymerization catalyst acts can be relief of strain in the ring. One only on the norbornene double bond such strained ring is norbornene. and leaves the cyclopentenone portion But as chemist Tom Yamanaka of Ja- of the monomer unmolested. Thus the pan's Toray Industries pointed out, only cyclopentenone repeating groups are a limited number of norbornene deriva- available in the resin for reactions such tives work well. Diels-Alder reactions as cross-linking. with cyclopentadiene produce endo-subNorbornene-type and other cyclic monostituted norbornenes, which are inert to mers also were reported by the research ROMP. group of organic chemistry professor T. So Yamanaka is visiting the laboratory Randall Lee of the University of Houston. of polymer chemistry professor Bruce He and his students described resins analM. Novak at the University of Massachu- ogous to polysaccharides, semiconducting setts, Amherst, to further the effort there ferrocene-containing polymers, and hybrid to develop new cyclic olefins. Novak and polysilane-polyacetylenes. Yamanaka have applied a catalytic verHouston graduate student Michael B. sion of the Pauson-Khand reaction to the Clark said that furan undergoes a Dielstask. Alder reaction with vinylene carbonate The Pauson-Khand is a one-pot reaction to give an exo-substituted norborneneof an olefin, an acetylene derivative, and carbon monoxide Pseudopolysaccharides from furan that forms a cyclopentenone. For exo o o-^ c ample, norbornadiene, phenylacetyo o lene, and carbon W monoxide give a norbornene derivaO R A tive with a five-memCatalyst H2 bered ring fused on in the exo orientation. Subjecting this monomer to ROMP results in a resin of O3SO OSO3 1.H 2 0 molecular weight • 2.CISO3H about 23,000 and opolydispersity index of 1.05. (Polydispersity is the ratio of Catalyst = [(C 6 H 11 ) 3 P] 2 CI 2 Ru: weight-average molecular weight to R = acetate or acetonide number-average mo
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APRIL 20, 1998 C&EN 63
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science/technoloey Hybrid ferrocenepolyacetylene resins
type product. Hydrolysis of the carbonate group and protection of the diol as a diacetate or acetonide affords a monomer that polymerizes to a resin with repeating dihydroxytetrahydrofuran groups. Varying the monomer-to-catalyst ratio controls molecular weights between about
20,000 and 75,000, with polydispersities Cross-linkable groups cap polymer from 1.3 to 1.8. ReChL CH, action of that polyI mer with chlorosul+ H X = CCO„ O.CC = C H , fonic acid sulfates the hydroxyl groups. Lee is seeking collaborators at Houston CHo who might evaluate hLC = CCO> the pseudopolysaccharide sulfate for antiviral properties. Graduate student And graduate student Lei Zhang reportRichard W. Heo of Houston sketched synthesis of a monomer consisting of ferrocene ed a silicon analog of a^cv'^-l^-cyclooctawhose two cyclopentadienyl rings are diene consisting of two carbon-carbon linked by a butadiene bridge. Metathesis double bonds and four dimethylsilyl polymerization leads to ferrocene repeat- groups. Ring-opening metathesis gives a ing groups that are linked by such conju- polymer chain with conjugated carbongated diene bridges. Depending on the carbon 7T-bonds and silicon a-bonds. Momonomer-to-catalyst ratio, molecular lecular weights are 120,000 to 140,000 weights range b e t w e e n 25,000 and and polydispersities 1.6 to 1.8. 310,000 and polydispersities between 1.6 Takeharu Morita of California Institute and 2.3. Conductivity of the undoped res- of Technology reported use of ring-openin is 10"9 Siemens per cm, which rises to ing metathesis to make polymers with the 10"1 to 10"2 Siemens per cm on doping structure of polybutadiene and capped with iodine. with methacrylatc ester groups. Such end
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APRIL 20, 1998 C&LN
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