Fluoromonomer polymerization

Details Fluoromonomer polymerization Fluoromonomer polymerization

1999-11-29

2002-06-04

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...

C526S206000, C526S209000, C526S250000

Reexamination Certificate

active

06399729

ABSTRACT:

FIELD OF THE INVENTION
This invention is in the field of fluoromonomer polymerization using chain transfer agents.
BACKGROUND OF THE INVENTION
In its simplest form, free-radical polymerization begins with the reaction of a free radical, generated by an initiator, with an olefin molecule to form a new free radical. This adds in turn to another olefin molecule in a polymerization cycle which continues until the growing radical chain is terminated by coupling or disproportionation with another radical chain, or by reaction with an initiator-generated radical. The rate of termination compared with the rate of polymerization affects the molecular weight and molecular weight distribution of the polymer, both critical properties. Because these termination mechanisms do not always give desirable molecular weights or molecular weight distributions and sometimes produce polymer molecules with unstable endgroups or bonds, chain transfer agents are often included in polymerization recipes. See for example U.S. Pat. Nos. 3,636,926 and 5,700,889. Chain transfer agents are molecules with labile atoms, often hydrogen. They give up the labile atom to a growing polymer chain, terminating it. In the process the chain transfer agent is converted to a free radical which initiates a new polymer chain by reacting with an olefin molecule, starting a new polymerization cycle. Chloroform is an example:
 (polymer)·+HCCl
3
→(polymer)—H+·CCl
3
growing chain terminated ·CCl
3
+olefin→Cl
3
C-monomer·
Though effective in fluoromonomer polymerization, chloroform has undesirable health and environmental effects. Hydrocarbons, such as ethane, are also used as chain transfer agents, and are free of the problems of chloroform. However, ethane is a gas. Many fluoromonomers are also gases, and polymerizations often include the recycling of monomers. The presence of chain transfer agents such as ethane in monomer recycle streams presents problems of analysis and purification that increase costs and the probability of contamination. Liquid hydrocarbons are unsuitable because to achieve low enough volatility so that they do not have-a significant concentration in the gas phase, their molecular weights must be high. Fluoropolymers made with high molecular weight hydrocarbon chain transfer agents would have hydrocarbon end groups that would affect their properties and stability.
New chain transfer agents are needed that do not contain chlorine, are liquid at room temperature, and do not significantly affect the character of the polymer being made.
SUMMARY OF THE INVENTION
The present invention provides a chain transfer agent that is chlorine-free, liquid at room temperature, and similar in chemical composition to fluoropolymers made with them, that the fluoropolymer properties are not adversely affected. Thus the invention is a process comprising the polymerizing of fluoromonomer in the presence of initiator and chain transfer agent, said chain transfer agent having the formula
R
1
—O—R
2
  (1)
wherein R
1
is a straight chain or branched saturated hydrocarbon group of 1 to 6 carbon atoms with the proviso that there is at least one hydrogen atom attached to the carbon next to oxygen, and R
2
is a straight chain or branched fluorocarbon group or hydrofluorocarbon group of formula C
a
H
b
F
c
wherein a is 2 to 6, b is 0 to 2a−1 and c is 2 to 2a+1 with the proviso that b+c=2a+1.
Another aspect of the invention is polymer containing endgroups characteristic of chain transfer agent having the formula (1)
R
1
—O—R
2
  (1)
wherein R
1
and R
2
are as defined above.
DETAILED DESCRIPTION
Olefins are molecules containing a carbon-carbon double bond (>C═C<). The vinyl group (CH
2
═CH—) is a member of the class of olefins. “Fluoromonomers” is used in this application to mean olefins that can be free-radically polymerized and that contain at least one fluorine atom, fluoroalkyl group, or fluoroalkoxy group attached to the vinyl group that undergoes polymerization. Useful fluoromonomers include, but are not limited to, vinyl fluoride; vinylidene fluoride; trifluoroethylene; chlorotrifluoroethylene (CTFE); 1,2-difluoroethylene; tetrafluoroethylene. (TFE); hexafluoropropylene (HFP); perfluoro(alkyl vinyl ethers). such as perfluoro(methyl vinyl ether)(PMVE), perfluoro(ethyl vinyl ether)(PEVE), and perfluoro(propyl vinyl ether)(PPVE); perfluoro(1,3-dioxole); perfluoro(2,2-dimethyl-1,3-dioxole) (PDD); CF
2
═CFOCF
2
CF(CF
3
)OCF
2
CF
2
X wherein X is SO
2
F, CO
2
H, CO
2
CH
3
, CH
2
OH, CH
2
OCN or CH
2
OPO
3
H; CF
2
═CFOCF
2
CF
2
SO
2
F; F(CF
2
)
n
CH
2
OCF═CF
2
wherein n is 1, 2, 3, 4, or 5; R
4
CH
2
OCF=CF
2
wherein R
4
is hydrogen or F(CF
2
)
m
— and m is 1, 2 or 3; and R
5
OCF═CH
2
wherein R
5
is F(CF
2
)
z
— and z is 1, 2, 3, or 4; perfluorobutyl ethylene (PFBE); 3,3,3-trifluoropropene and 2-trifluoromethyl-3,3,3-trifluoro-1-propene. Preferred fluoromonomers include 2-trifluoromethyl-3,3,3-trifluoro-1-propene, PFBE, vinyl fluoride, vinylidene fluoride, TFE, HFP, PMVE, PEVE, PPVE, CTFE, and PDD.
The fluoromonomer may be polymerized alone to form a homopolymer if the fluoromonomer can be homopolymerized, or may be polymerized with one or more other fluoromonomers or other monomers, such as hydrocarbon monomers that are not fluoromonomers, to form a copolymer. If a copolymer is to be formed, the monomers chosen must be able to copolymerize. Fluorine-free monomers that copolymerize with some combinations of fluoromonomers include propylene and ethylene. Examples of useful homopolymers from fluoropolymers include polytetrafluoroethylene (PTFE) and polyvinylidene fluoride. Also usually classed with homopolymer PTFE are the modified PTFE polymers containing fluoromonomers other than TFE in such minor amounts that the modified polymers retain the non-melt-fabricable character of PTFE. Examples of useful copolymers include the copolymers of TFE with HFP and/or perfluoro(alkyl vinyl ethers) such as PPVE or PEVE, copolymers of TFE with PMVE, copolymers of TFE with PDD, and copolymers of TFE or CTFE with ethylene. Further examples include the copolymers of vinylidene fluoride with HFP, or with HFP and TFE. As implied above, copolymers may contain additional monomers beyond those named. TFE/ethylene copolymers, for example, are most useful if they include additional monomers that introduce bulky side groups such as PFBE, HFP, PPVE or 2-trifluoromethyl-3,3,3-trifluoro-1-propene, and elastomeric polymers frequently include low concentrations of cure site moieties derived from a cure site monomer.
The polymers of this invention include TFE and CTFE homopolymers; TFE or CTFE polymerized with one or more other fluoromonomers described above such that said other fluoromonomers are <1% by weight of the total polymer (wt. %); TFE or CTFE polymerized with 1 to 99 wt. % of one or more other fluoromonomers, preferably 1 to 50 wt. % of one or more other fluoromonomers, more preferably 1 to 20 wt. % of one or more other fluoromonomers, and most preferably 1 to 10 wt. % of one or more other fluoromonomers. In all cases, the wt. % values refer to the amount of comonomer incorporated in the polymer.
The TFE homopolymers of this invention are not melt fabricable. The copolymers of this invention are melt processible with melt viscosities, determined as described below, of up to 10
6
Pa·s, preferably in the range 10
2
to 10
6
Pa·s, and most preferably in the range 10
3
to 10
5
Pa·s. Such fluoropolymers can be glassy, plastic, or elastomeric. They can be amorphous or partially crystalline, melt-fabricable or non-melt-fabricable. The fluoropolymers made by the process of this invention are normally solid at 15°-20° C. and can have any molecular weight (MW) suitable for the intended use. Generally, the weight average MW is at least 50,000 and can range up to much higher values, such as 1,000,000 and even higher.
The identity and proportion in the polymer of units derived from other monomers, fluorinated and fluorine-free, can have

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