Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Polymers from only ethylenic monomers or processes of...
Reexamination Certificate
1999-04-16
2001-09-18
Zitomer, Fred (Department: 1713)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Polymers from only ethylenic monomers or processes of...
C526S091000, C526S170000, C526S171000, C526S285000, C526S902000
Reexamination Certificate
active
06291606
ABSTRACT:
FIELD OF THE INVENTION
The present invention provides a rapid and low cost method for obtaining highly stereoregular polyacetylenes, particularly poly(phenylacetylenes) (also referred to herein as “PPAs”), from aqueous media.
BACKGROUND
Polyacetylenes are structurally simple polymers having alternating double bonds along the main chain (i.e., —(CR═CR′)
n
—). Polyacetylenes are of interest due to the fact that they often possess the following properties: i) electrical conductivity (semiconductivity), ii) paramagnetism, iii) chain stiffness, iv) geometrical isomerism, and v) color.
Shirakawa and co-workers stimulated interest in polyacetylenes in the 1970 s when they reported a 10
11
-fold increase in electrical conductivity of polyacetylene film upon doping. That finding stimulated interest in conjugated polymers. Researchers sought to improve their understanding of such polymers and explored new synthetic routes.
Driven by a vision of doped polymers as versatile, abundant and lightweight “plastic metals”, researchers originally focused on increased electrical conductivity. More recently, conjugated polymers have been shown to have a wider range of uses, e.g., non-linear optical waveguides, light-emitting diodes, gas separation membranes, chiral separation membranes, and cell growth media.
Polymerization of substituted acetylenes has been attempted using radical initiators (e.g. 2,2′-azobisisobutyronitrile, [“AIBN”]) and ionic initiators (e.g., n-BuLi). In most cases, however, linear oligomers with low molecular weight (i.e., M.W. of about several thousand) are produced and cyclotrimers are often formed as by-products. Thus, the selective synthesis of polymers having M.W.s higher than about ten thousand proved difficult.
Ziegler-Natta catalysts (typically obtained by mixing an alkyl or aryl of a metal from Group I-IV of the Periodic Table with a compound, commonly a halide, of a transition metal of Group IV-VII) have been used for the polymerization of substituted acetylenes. In fact, prim- or sec-alkylacetylenes yield high molecular weight polymers in the presence of Ziegler-Natta catalysts such as a mixture of iron trisacetylacetonate and triethylaluminum [Fe(acac)
3
-Et
3
Al(1:3)]. However, insoluble polymers and/or oligomers are produced from aromatic or heteroatom-containing monosubstituted acetylenes; and no disubstituted acetylenes are known to polymerize with Ziegler-Natta catalysts.
TABLE 1
Polymerization of HC≡CR
by Ziegler-Natta catalysts.
a
HC≡CR
R
Product
Aliphatic
Et, n-Bu, sec-Bu
Soluble high
polymer
Aromatic Heteroatom-containing
insoluble polymer + oligomer
a
RC≡CR′: no polymerization.
The results of the polymerization of phenylacetylene (PA) by the use of conventional radical, cationic, anionic and Ziegler-Natta initiators are distinct and are summarized below.
TABLE 2
Polymerization of HC≡CPh
by conventional initiators
Initiator
Example
M
n
Radical
Heat
500-2000
Cationic
AlCl
3
500-1500
Anionic
n-BuLi
−1000
Ziegler-Natta
TiCl
4
-Et
3
-Al
400
catalyst
VO(sal)
2
-Et
3
-Al
7500
a
Fe(acac)
3
-Et
3
Al
4060
a
a
Mostly insoluble
Recently, metathesis catalysts have been used in polymerizing alkynes. The metathesis catalysts polymerize a wider range of monomers. Masuda and co-workers reported that while Ziegler-Natta catalysts can only produce high polymers from sterically undemanding acetylene or n-alkyl terminal alkynes, no soluble high polymer would be produced from alkyl alkynes with a tertiary substituent, aryl alkynes, and disubstituted alkynes. In contrast, Group V and VI metathesis catalysts polymerize more sterically demanding alkynes, such as tert-butylacetylene.
The polymerization of substituted acetylenes initiated by group V, VI and VIII transition metal complexes has also attracted a great deal of attention. In particular, Rh(I) complexes exhibit high reactivity with alkynes and have an ability to effect stereocontrolled polymerization.
A stereoregular polymer, according to the International Union of Pure and Applied Chemistry (IUPAC) definition, is a “macromolecule that can be described in terms of only one species of stereorepeating unit, in a single sequential arrangement.” A stereorepeating unit is a configurational unit having a defined configuration at all sites of isomerism in the main chain of a polymer molecule.
Some Rh(I) complexes polymerize PA and its derivatives to achieve highly stereoregular substituted polyacetylenes. These include [Rh(diene)Cl]
2
, [Rh(diene)(N—N) ]X, Rh(cod) [C
5
H
4
N-2-(CH
2
)
2
P(C
6
H
5
)(CH
2
)
3
ZR]PF
6
, and Rh(C
6
H
5
)(nbd)[P(C
6
H
5
)
3
]
2
, where the term “diene” includes 1,5-cyclooctadiene (“cod”) and 2,5-norbornadiene (“nbd”); “N—N” includes nitrogen-based bidentate ligand; “X” includes PF
6
, ClO
4
, and B(C
6
H
5
)
4
); and “ZR” includes —OC
2
H
5
, —OC
6
H
5
, —NH(C
6
H
5
), and —NH(cycloC
6
H
11
)).
Stereoregular PPA and derivatives are considered important as model compounds of ferromagnetic polymers, non-linear optical materials, and oxygen permeable materials where the geometrical structure of the main chain has to be controlled in order to draw useful properties from them.
Configuration of Monosubstituted Polyacetylenes
A monosubstituted polyacetylene can exist in the following four configurations: cis-cisoidal, cis-transoidal, trans-cisoidal and trans-transoidal. PPA also exhibits those four configurations.
Some research groups have studied the identification of these configurations by using IR and NMR. They report that the cis-cisoidal and cis-transoidal configuration can be distinguished from the two trans configurations by the appearance of an absorption peak at 740 cm
−1
in the IR spectra of the two cis configurations. The cis-transoidal configuration can also be distinguished by the singlet or any multiplicity at &dgr; 5.82 ppm in the
1
H—NMR spectrum
Configuration of Monosubstituted Polyacetylenes.
Correlations between Spectral Properties and Chain Structures of PPA
The cis-content can indicate the degree of the stereoregularity of PPA. The higher the cis-content, the higher the stereoregularity of the polymer. Simionescu C. I. & Percec V. analyzed the chain conformation of PPA. They reported that the cis-transoidal species has characteristic signals at &dgr; 5.82 ppm, which is due to the olefinic proton, and two others at &dgr; 6.7 and &dgr; 6.85 ppm; while according to the theoretical calculations, the
1
H-NMR spectrum of the cis-cisoidal PPA must be different. The olefinic protons of trans-cisoidal and trans-transoidal structure appear at &dgr; 7.0 ppm.
1
H-NMR spectra of cis-cisoidal species were not reported because of its insolubility.
Since the signal corresponding to the olefin protons (&dgr; 5.82 ppm) of the cis-transoidal structure of PPA is separated from other peaks, the percentage (cis-content) of this cis structure can be calculated from the
1
H-NMR spectrum according to Eq. 1.
% cis=A
5.82
[10
4
/A
t
×16.66.] Eq. 1
where:
%
cis
=
cis-content of PPA
A
5.82
=
area of the 5.82 ppm signal
A
t
=
total area of the signals in the
1
H
-
NMR
spectrum
The signal at &dgr; 5.82 ppm of the olefin proton, which is characteristic of the cis-transoidal configuration, is useful in calculating cis-content. In each repeating unit, there are six protons (five aromatic protons and one olefin proton). Hence, the above equation can be reconstructed as:
% cis=A
5.82
/A
t
(6×100%)
When the polymer is entirely in cis-transoidal configuration, all the olefin protons on the chain give signal at &dgr; 5.82 ppm; and hence it has a % cis value of 100 (i.e., A
5.82
/A
t
=⅙). If some olefinic protons are not in cis-transoidal configuration, the ratio of A
5.82
/A
t
decreases; and the % cis value decreases.
However, this equation is only applicable to the cis-transoidal PPA with high stereoregularity. This is because
Poon Wa Hong
Tang Ben Zhong
Burns Doane Swecker & Mathis L.L.P.
The Hong Kong University of Science and Technology
Zitomer Fred
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