Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Polymers from only ethylenic monomers or processes of...
Reexamination Certificate
1999-10-06
2003-01-21
Pezzuto, Helen L. (Department: 1713)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Polymers from only ethylenic monomers or processes of...
C526S219200, C526S317100, C526S328000, C526S329200, C526S346000, C526S347000
Reexamination Certificate
active
06509428
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to a process for radical polymerization in the presence of several stable free radicals.
BACKGROUND OF THE INVENTION
Radical polymerization in the presence of a stable free radical results in a polymer of narrow polydispersity and makes possible the preparation of block polymers by a living polymerization mechanism.
The presence of a stable free radical during a polymerization is generally reflected, however, by a slowing down of the rate of polymerization.
The scale of this slowing down depends on the nature of the stable free radical.
Some stable free radicals have a lesser effect in slowing down the polymerization but, on the other hand, provide poorer control of the said polymerization and/or are expensive and/or decompose during the polymerization. It is therefore useful to have access to systems for controlled radical polymerization which is simultaneously fast, inexpensive and well-controlled by the stable free radical for as long as possible during the polymerization.
A radical polymerization becomes better controlled by virtue of the presence of a stable free radical in proportion as the curve representing the change in the number-average molecular mass as a function of the conversion of monomer to polymer approaches linearity. It is by virtue of the fact that a radical polymerization process is controlled by a stable free radical that the said process makes possible the preparation of sequential (that is to say, block) polymers by successive introduction of different monomers into the polymerization medium.
It will be recalled that the notion of a stable free radical is known to a person skilled in the art to denote a radical which is so persistent and unreactive with respect to air and moisture in the surrounding air that the pure radical can be handled and stored without more precautions at room temperature than are the majority of commercial chemicals (see, in this respect, D. Griller and K. Ingold, Accounts of Chemical Research, 1976, 9, 13-19, or Organic Chemistry of Stable Free Radicals, A. Forrester et al., Academic Press, 1968).
Definition of Stable Free Radical
A stable free radical must not be confused with free radicals with a transitory life time (a few milliseconds), such as the free radicals resulting from the usual polymerization initiators, such as peroxides, hydroperoxides and initiators of azo type. Polymerization initiator free radicals tend to accelerate the polymerization. In contrast, stable free radicals generally tend to slow down the polymerization. It can generally be said that a free radical is stable within the meaning of the present invention if it is not a polymerization initiator and if, under the conditions of use of the present invention, the mean lifetime of the radical is at least five minutes. During this mean lifetime, the molecules of the stable free radical continuously alternate the radical state and the state of a group bonded via a covalent bond to a polymer chain. Of course, it is preferable for the stable free radical to exhibit good stability throughout the duration of its use in the context of the present invention. A stable free radical c an generally be isolated in the radical state at room temperature. A stable free radical is sufficiently stable for its free radical state to be able to be characterized by spectoscopic methods.
Mechanism of Stable Free Radical
The stable free radical forms, during the polymerization, a reversible bond with the growing polymer chain. The stable free radical continuously alternates, at the end of the polymer chain, the state of a group bonded via a covalent bond to the said chain and the state of a stable free radical detached from the said chain in order to allow the insertion of a monomer unit, according to the following process,
—M−Y⇄—M
•
+Y
•
1)
—M
•
+M+Y
•
→—M−M−Y 2)
in which —M represents a monomer unit of the growing chain, M represents a monomer unit and Y
•
represents the stable free radical, for the case where the latter is monofunctional, that is to say that its molecule only carries a single site exhibiting the radical state. This process is repeated in order for the polymer chain to grow by insertion of monomer between the growing chain and the stable free radical.
In the case where a radical polymerization initiator has been introduced into the polymerization medium, another means for describing the degree of control of the polymerization is to compare the number-average molecular mass observed (experimental Mn) with the theoretical number-average molecular mass (theoretical Mn), such as is calculated by the equation:
Theoretical
Mn
=
(
M
)
×
C
×
Mo
F
INI
(
INI
)
in which
(M) represents the number of moles of monomer,
C represents the conversion of the monomer to polymer (which can range from 0 for no conversion to 1 for total conversion) equal to the ratio:
mass
of
polymer
formed
remaining
mass
of
monomer
+
mass
of
polymer
formed
F
INI
represents the functionality of the initiator, that is to say the number of sites exhibiting the free radical state which each initiator molecule is capable of generating,
(INI) represents the number of moles of initiator,
Mo represents the molar mass of the monomer.
The control of the polymerization becomes better in proportion as experimental Mn becomes closer to theoretical Mn.
Mention may be made, as an example of an initiator for which the functionality F
IN
, is 2, of dicumyl peroxide.
Mention may be made, as an example of an initiator for which the functionality F
INI
is 4, of ethyl 3,3-di(tert-amylperoxy)butyrate, which can be represented by:
as it comprises two —O—O— linkages each capable of generating two sites exhibiting the free radical state, namely —O
•
.
SUMMARY OF THE INVENTION
The invention responds to the abovementioned problems. The invention relates to a process for the radical polymerization of at least one monomer in the presence of at least two stable free radicals of different natures. The two stable free radicals are chosen so that they exhibit different equilibrium constants, taking into account the polymer to be polymerized and the polymerization temperature.
This equilibrium constant of a stable free radical with respect to a monomer characterizes the equilibrium of the reaction:
(—M)
F
Y
−Y⇄F
Y
(—M
•
)+Y
F
Y
•
in which
M represents a monomer unit, which is bonded to another monomer unit or to an initiator residue,
M
•
represents a monomer unit in radical form,
Y
F
Y
•
represents the stable free radical for which the functionality is equal to F
Y
, which means that the stable free radical molecule exhibits a number of sites exhibiting the radical state equal to F
Y
,
Y represents the group resulting from the stable free radical when the latter is connected to as many monomer units as its functionality, for this reason making it lose its radical state.
For a given monomer and a given polymerization temperature, at least two of the stable free radicals preferably exhibit equilibrium constants such that their ratio is greater than 5, more preferably greater than 10 and more preferably greater than 100.
Mention may be made, as an example of a stable free radical for which the functionality is equal to 1, of a molecule represented by:
the R
1
, R
2
, R
3
, R
4
, R
5
, R
6
, R
7
and R
8
groups of which represent alkyl radicals.
Mention may be made, as an example of a stable free radical for which the functionality is equal to 2, of a molecule represented by:
the R
1
, R
2
, R
3
, R
4
, R
5
, R
6
, R
7
and R
8
groups of which represent alkyl radicals and n of which represents a non-zero integer, for example ranging from 1 to 20.
The equilibrium constant K is such that
K
=
[
—M
•
]
×
[
Y
F
Y
•
]
[
(
—M
)
F
Y
—Y
]
in which:
Gnanou Yves
Robin Sophie
Senninger Thierry
Atofina
Millen White Zelano & Branigan P.C.
Pezzuto Helen L.
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