Polymerization process in suspension

Details Polymerization process in suspension Polymerization process in suspension

1999-11-08

2002-07-09

Lipman, Bernard (Department: 1713)

Organic compounds -- part of the class 532-570 series

Organic compounds

Carboxylic acid esters

C564S191000

Reexamination Certificate

active

06417390

ABSTRACT:

The present invention relates to a (co)polymerization process in suspension for preparing thermoplastic fluoropolymers containing hydrogen.
Various kinds of fluorinated polymers containing hydrogen having thermoplastic properties are known in the art. A first class is formed by copolymers of per(halo)fluoroolefins with non halogenated olefins, such as for instance tetrafluoroethylene (TFE) or chlorotrifluoroethylene (CTFE) copolymers with ethylene, optionally containing a third fluorinated comonomer in amounts comprised between 0.1 and 10% by moles (see for instance U.S. Pat. No. 3,624,250). The preparation of such copolymers is generally carried out in suspension and, especially in the case of CTFE/ethylene copolymers, is preferably carried out at low temperature.
Another class of thermoplastic fluoropolymers containing hydrogen is formed by polyvinylidenfluoride (PVDF) and by modified PVDF with small amounts (0.1-10% by moles) of other fluorinated comonomers.
The use of suspending and/or wetting agents (both indicated herein generically as wetting agents) is known in the suspension polymerization, especially in the VDF copolymerization. See for instance Encyclopedia of Polymer Science and Engineering, p. 534, vol. 17, 1985, II Edition.
Polyvinylic alcohols, alkyl-alkylhydroxyalkyl-cellulose, for instance methylcellulose, hydroxypropylcellulose are for instance utilized. See U.S. Pat. Nos. 4,524,194 and 5,087,679. The drawback of the wetting agents utilized in the art resides in that they remain in the polymer particles and give rise during the polymer processing to discoloration phenomena and/or starting of decay. See Vol. 16, pag. 444 of the Encyclopedia mentioned above.
On the other hand, wetting agents are used in general to reduce the polymer buildup in the reactor.
The utilization of wetting agents allows the polymerization in organic suspension in totally or partially metal reactors. In these cases in absence of wetting agents it is very difficult to control the polymerization owing to the formation of buildup in the autoclave.
The use of alcohols as wetting agents, for instance methanol and terbutanol, is known in the art. However tests carried out by the Applicant have shown that these can decrease the polymerization yield, (see the examples). Moreover the alcohols, in the case of recovery of the unreacted monomers in the industrial plants, can interact with these by forming azeotropes, thus making it difficult the monomer recovery.
In addition it was felt the need to have available polymerization processes allowing to limit the amount of fines (fine polymer powder) to very low extent for better handling and buildup in the reactor. Further the polymer so produced must not discolour and/or degrade during the successive processing steps at high temperatures for sufficiently long times and even longer than those of the art.
The Applicant has surprisingly and unexpectedly found that the above technical problem has found the solution by utilizing a specific family of non-ionic surfactants, defined hereinafter, which allows to reduce to a minimum the amount of fines and buildup in the polymerization of fluorinated polymers containing hydrogen, as defined above, without giving rise to discoloration processes and/or starting degradation in the extruded product at high temperature. Moreover, the use of a non-ionic surfactant allows, if desired, to recover it from the polymerization phase on the basis of the cloud point of the surfactant.
An object of the present invention is therefore the use of surfactants in the suspension polymerization of fluorinated monomers for preparing fluoropolymers containing hydrogen, said surfactants having the general formula:
 R
f
—[L—(OCHR
1
—CHR
2
)
m
—OZ)]
wherein:
i is equal to 1 or 2, preferably 1;
m is an integer comprised between 4 and 60 preferably between 8 and 30
L can be selected from: —(CFY—CO—O)
p
R′— and —(CFY—CO—NH)
p
R′—
wherein p is an integer equal to 0 or to 1;
Y═F, CF
3
; R′=alkyl radical C
1
-C
5
, linear or branched when possible;
R
1
, R
2
can be both H or the former H and the latter CH
3
; both preferably H.
Z can be H, alkyl radical C
1
-C
3
, linear or branched when possible, or (CH
2
)
n
OH with n an integer from 1 to 6;
R
f
is a perfluoroalkyl radical or a perfluoropolyether radical, having a number average molecular weight comprised between 250 and 1500, preferably between 400 and 1000. When The R
f
radical is of perlfuoropolyether type, comprises repeating units statistically distributed along the polymer chain selected from:
(CF
2
CF
2
O), (CFXO) wherein X is equal to F or CF
3
, (C
3
F
6
O),
(CF
2
(CF
2
)
2
O ) wherein z is an integer equal to 2 or 3,
(CF
2
CF(OR
f′
)O), (CF(OR
f′
)O) wherein R
f′
is equal to —CF
3
, —C
2
F
5
, —C
3
F
7
.
When the R
f
radical is monovalent, the terminal (T) of the perfluoropolyethereal radical is chosen from —CF
3
, —C
2
F
5
, —C
3
F
7
, ClCF
2
CF(CF
3
)—, CF
3
CFClCF
2
—, ClCF
2
CF
2
—, ClCF
2
—.
The following perfluoropolyether R
f
can in particular be mentioned as preferred:
T—O(CF
2
CF(CF
3
)O)
a
(CFXO)
b
—  (a)
wherein
X is F or CF
3
; a and b are such integers that the molecular weight is comprised in the range indicated above; a/b is comprised between 10 and 100;
or the repeating units indicated in (a) can be linked as follows to give a bivalent R
f:
—O(CF
2
CF(CF
3
)
a
(CFXO)
b
—O—CF
2
(R′
f
)
x
CF
2
—O—(CF
2
CF(CF
3
)O)
a
(CFXO)
b
—
wherein R′
f
is a fluoroalkylenic group, for instance from 1 to 4 carbon atoms;
T—O(CF
2
CF
2
O)
c
(CF
2
O)
d
(CF
2
(CF
2
)
z
CF
2
O)
h
—  (b)
wherein c, d and h are such numbers that the molecular weight is comprised in the range indicated above; c/d is comprised between 0.1 and 10; h/(c+d) is comprised between 0 and 0.05, z has the value indicated above,
—O(CF
2
CF
2
O)
c
(CF
2
O)
d
(CF
2
(CF
2
)
z
CF
2
O)
h
—  (b′)
wherein c, d and h are such numbers that the molecular weight is comprised in the range indicated above; c/d is comprised between 0.1 and 10; h/(c+d) is comprised between 0 and 0.05, z has the value indicated above,
T—O(CF
2
CF(CF
3
)O)
e
(CF
2
CF
2
O)
f
(CFXO)
g
—  (c)
wherein
X is F or CF
3
; e, f, g are numbers such that the molecular weight is comprised in the range indicated above; e/(f+g) is comprised between 0.1 and 10, f/g is comprised between 2 and 10,
—O(CF
2
CF(CF
3
)O)
e
(CF
2
CF
2
O)
f
(CFXO)
g
—  (c′)
wherein
X is F or CF
3
; e, f, g are such numbers that the molecular weight is comprised in the range indicated above; e/(f+g) is comprised between 0.1 and 10, f/g is comprised between 2 and 10,
T—O(CF
2
O)
j
(CF
2
CF(OR
f″
)O)
k
(CF(OR
f″
)O)
1
—  (d)
wherein R
f″
is —CF
3
, —C
2
F
5
, —C
3
F
7
; j,k,l are such numbers that the molecular weight is comprised in the range indicated above; k+l and j+k+l are at least equal to 2, k/(j+l) is comprised between 0.01 and 1000, l/j is comprised between 0.01 and 100;
T—O(CF
2
(CF
2
)
z
CF
2
O)
s
—  (e)
wherein s an integer such as to give the molecular weight indicated above, z has the meaning already defined;
—O(CF
2
(CF
2
)
z
CF
2
O)
s
—  (e′)
wherein s is an integer such as to give the molecular weight indicated above, z has the meaning already defined.
T—O(CR
4
R
5
CF
2
CF
2
O)
j′
—  (f)
wherein R
4
and R
5
are equal to or different from each other and chosen between H, Cl or perfluoroalkyl, for instance with 1-4 carbon atoms, j′ being an integer such that the molecular weight is that indicated above; said unit inside the fluoropolyoxy-alkylenic chain being linked each other as follows to have a bivalent radical:
—(OCR
4
R
5
CF
2
CF
2
)
p′
—O—R′
f
—O—(CR
4
R
5
CF
2
CF
2
O)
q′
—
wherein R′
f
is a fluoroalkylenic group, for instance with 1 to 4 carbon atoms, p′ and q′ are integers from 0 to 200, and p′+q′ is at least 1 and such that the molecular weight is that ind

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