Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Polymers from only ethylenic monomers or processes of...
Reexamination Certificate
2002-04-08
2004-08-17
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...
C526S204000, C526S329200, C526S330000, C526S335000, C526S342000, C526S347000
Reexamination Certificate
active
06777513
ABSTRACT:
The present invention relates to a novel process for “controlled” or “living” free-radical polymerization, giving access to block copolymers.
Block polymers are usually prepared by ionic polymerization. A disadvantage of this type of polymerization is that it permits the polymerization only of certain types of non-polar monomers, particularly styrene and butadiene, and that it requires a particularly pure reaction environment, and temperatures often lower than ambient, in order to minimize side reactions, and the result is severe operational constraints.
An advantage of free-radical polymerization is that it is easy to implement without adhering to excessive purity requirements, and at temperatures of ambient or above. However, until recently there was no free-radical polymerization process which could give block polymers.
A novel process for free-radical polymerization has now been developed: this is what is known as “controlled” or “living” free-radical polymerization. Controlled free-radical polymerization proceeds by growth through propagation of macroradicals. These macroradicals have a very short lifetime and recombine irreversibly via coupling or dismutation. When the polymerization proceeds in the presence of a number of comonomers, the variation in the composition of the mixture is infinitely slow compared with the lifetime of the macroradical, and therefore the chains have a random sequence of monomer units, rather than a block-type sequence.
In recently developed techniques for controlled free-radical polymerization, the extremities of polymer chains can be reactivated as a radical by homolytic cleavage of a bond (for example C—O or C-halogen).
Controlled free-radical polymerization therefore has the following distinctive aspects:
1. the number of chains is fixed for the entire duration of the reaction,
2. all the chains grow at the same rate, resulting in:
linear increase in molecular mass with conversion,
a narrow distribution of masses,
3. the average molecular mass is controlled by the molar ratio monomer/chain precursor,
4. the possibility of preparing block copolymers.
The controlled character is all the more pronounced if the rate of reactivation of the free-radical chains is very great compared with the rate of growth of the chains (propagation). There are cases where this does not always apply (i.e. the reactivation rate of the free-radical chains is greater than or equal to the rate of propagation) and conditions 1 and 2 are not complied with, but it is nevertheless still possible to prepare block copolymers.
The publication WO 98/58974 describes a living free-radical polymerization process giving access to block copolymers by a process without UV irradiation, by using xanthate compounds, i.e. compounds having the function:
This free-radical polymerization allows preparation of block polymers with the aid of any kind of monomer, without any UV source. The polymers obtained do not contain any metallic impurities detrimental to their use. They have chain-end functionalization and a low polydispersity index, lower than 2, or even lower than 1.5.
It is an object of the present invention to propose a novel procedure for polymerization with the aid of new precursors of xanthate type.
Another object is to propose a polymerization process which uses precursors of xanthate type and during the course of which the number-average molar masses M
n
of the resultant polymers are well controlled, i.e. close to the theoretical values M
n th
, especially at the start of the polymerization reaction.
Another object is to propose a polymerization process which uses precursors of xanthate type to synthesize polymers and block copolymers whose index of polydispersity (M
w
/M
n
) is low, i.e. close to 1.
With this object in mind, the invention provides a process for preparing polymers, characterized by bringing into contact:
at least one ethylenically unsaturated monomer,
at least one source of free radicals, and
at least one compound (I) of general formula (IA), (IB), or (IC)
in which:
R
2
and R
2
, represent:
an alkyl, acyl, aryl, alkene, or alkyne group (i), or
a carbocyclic system (ii), saturated or unsaturated, optionally aromatic, or
a heterocyclic system (iii), saturated or unsaturated,
these groups and cyclic systems (i), (ii), and (iii) being substituted by at least one fluorine atom, chlorine atom, and/or bromine atom,
R
1
and R
1
′ represent:
an alkyl, acyl, aryl, alkene, or alkyne group (i), optionally substituted, or
a carbocyclic system (ii), saturated or unsaturated, optionally substituted or aromatic, or
a heterocyclic system (iii), saturated or unsaturated, optionally substituted, where these groups and cyclic systems (i), (ii) and (iii) may be substituted by substituted phenyl groups, substituted aromatic groups, or: alkoxycarbonyl or aryloxycarbonyl (—COOR), carboxy (—COOH), acyloxy (—O
2
CR), carbamoyl (—CONR
2
), cyano (—CN), alkylcarbonyl, alkylarylcarbonyl, arylcarbonyl, arylalkylcarbonyl, phthalimido, maleimido, succinimido, amidino, guanidimo, hydroxyl (—OH), amino (—NR
2
), halogen, allyl, epoxy, alkoxy (—OR), S-alkyl, or S-aryl groups, groups having hydrophilic or ionic character, for example the alkali metal salts of carboxylic acids, the alkali metal salts of a sulfonic acid, polyalkylene oxide chains (PEO, PPO), or cationic substituents (quaternary ammonium salts), R representing an alkyl or aryl group, or
a polymer chain,
is between 2 and 10.
The process according to the invention therefore consists in bringing into contact a source of free radicals, an ethylenically unsaturated monomer, and a compound (I) of formula (IA), (IB), or (IC).
This compound (I) bears a xanthate functionality. According to the essential characteristic of the invention, the xanthate functionality bears a group R
2
or R
2′
which has to be substituted by at least one fluorine atom, chlorine atom, and/or bromine atom. R
2
and R
2′
are preferably substituted by at least one fluorine atom, and still more preferably only by fluorine atoms.
According to one preferred version, R
2
represents a group of formula: —CH
2
R′
5
, in which R′
5
represents an alkyl group substituted by at least one fluorine atom, chlorine atom, and/or bromine atom. According to this embodiment, preferred groups R
2
are the following:
—CH
2
CF
3
,
—CH
2
CF
2
CF
2
CF
3
—CH
2
CH
2
C
6
F
13
,
According to another preferred version, R
2
represents the group CH(CF
3
)
2
.
R
1
in the formulae (IA) and (IB) preferably represents:
a group of formula CR′
1
R′
2
R′
3
, in which:.
a R′
1
, R
2
and R′
3
represent the groups (i), (ii), or (iii) as defined above, or
R′
1
=R=
2
=H and R′
3
is an aryl, alkene, or alkyne group,
or a group of formula —COR′
4
in which R′
4
represents a group (i), (ii), or (iii) as defined above.
The most interesting results have been obtained for the compound (I) when R
1
is a group selected among:
—CH(CH
3
) (CO
2
Et)
—CH(CH
3
) (C
6
H
5
)
—CH(CO
2
Et)
2
—C(CH
3
) (CO
2
Et) (S—C
6
H
5
)
—C(CH
3
)
2
(C
6
H
5
)
in which Et represents an ethyl group and Ph represents a phenyl group.
The groups R
1
and R
1′
may also represent a polymer chain from a free-radical or ionic polymerization, or from a polycondensation. Preferred compounds of formula (IC) are those for which R
1′
is the group —CH
2
— phenyl —CH
2
— or the group —CHCH
3
CO
2
CH
2
CH
2
CO
2
CHCH
3
—.
In the preferred embodiment of the invention, the polymerization process uses a compound (I) formula (IA). Preferred compounds of formula (IA) are ethyl a-(O-heptafluorobutylxanthyl)propionate (R
1
═CHCH
3
(CO
2
Et), R
2
═CH
2
CF
2
CF
2
CF
3
), ethyl a-(O-trifluoroethylxanthyl)propionate (R
1
═CHCH
3
(CO
2
Et), R
2
═CH
2
CF
3
), and ethyl ethyl a-(O-tridecafluorooctanylxanthyl)propionate (R
1
═CHCH
3
(CO
2
Et), R
2
═CH
2
CH
2
C
6
F
13
)
The compounds of formulae (IA), (IB), and (IC) are easily accessible. They may particularly be obtained by reacting an alcohol R
2
OH w
Charmot Dominique
Destarac Mathias
Franck Xavier
Zard Samir
Pezzuto Helen L.
Rhodia Chimie
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