Grafting of polyolefins

Details Grafting of polyolefins Grafting of polyolefins

2001-07-26

2003-05-06

Seidleck, James J. (Department: 1711)

Synthetic resins or natural rubbers -- part of the class 520 ser

Synthetic resins

Mixing of two or more solid polymers; mixing of solid...

C525S193000, C525S240000, C525S243000, C525S273000, C525S301000, C525S326500

Reexamination Certificate

active

06559235

ABSTRACT:

FIELD OF THE INVENTION
Porous polyolefin particles are particularly efficiently grafted using free radical grafting techniques when the grafting compounds are non-homopolymerizable fluoroolefins, vinyl silanes or selected carboxylic acids or their derivatives.
TECHNICAL BACKGROUND
Grafting of various monomeric compounds or polymers onto already existing polymers is a well-known technique in the art for modifying the properties of existing polymers. These modifications may change the properties of the grafted polymer so that it may, for example, be used as an adhesive between a polymer and other materials, as a compatibilizing agent between polymers, for modifying a polymer surface for example making it hydrophilic or hydrophobic, and for other purposes. The grafted compound may also provide a crosslinking site for the polymer. Grafting allows the production of polymers having certain groups chemically attached to those polymers without having to copolymerize monomers containing those groups when the polymer was originally formed.
Some of the monomeric compounds that may be grafted onto polymers contain olefinic groups. Most often these olefinic group containing compounds are grafted onto the polymer using a process involving free radicals. Usually these free radicals are generated by using ionizing radiation, or a chemical free radical generator such as a peroxide. The monomeric compounds may be divided into two types, those that themselves may be free radically homopolymerized, and those that don't so homopolymerize (to any appreciable extent) in the presence of free radicals. Such homopolymerizable vinyl compounds when so grafted often form grafted polymeric chains and ungrafted homopolymer, so the resulting product is usually a mixture of grafted original polymer and ungrafted homopolymer derived from the monomeric grafting compound. Vinyl compounds that do not appreciably homopolymerize free radically under such circumstances usually graft onto the original polymer as single molecules, sometimes a few molecules (a short oligomeric branch), at a time, and usually there is little or no homopolymer of the nonhomopolymerizable compound in the product. However non-homopolymerizable vinyl compounds are often more difficult to graft than the homopolymerizable compounds.
With solid polymers there is often difficulty in obtaining reasonably uniform grafting of the monomeric compound onto the polymer, since the monomeric compound and chemical free radical generator, if used, cannot contact all of the polymer to be grafted. This has been solved in the art by dissolving the polymer in a solvent and then carrying out the grafting in solution, or by melting the polymer and mixing it while molten with the grafting compound and free radical source. However these methods are relatively expensive to carry out. It has been reported in U.S. Pat. No. 5,140,074 and U.S. Pat. No. 5,411,994 (both incorporated by reference herein for all purposes as if fully set forth) that porous particles of polyolefins may be reasonably uniformly grafted with homopolymerizable vinyl compounds, without the need to melt or dissolve the polyolefin.
It has also been reported in EP-A-0519341 (also incorporated by reference herein for all purposes as if fully set forth) that porous particles of polyolefins may be reasonably uniformly grafted by certain non-homopolymerizable vinyl compounds, especially unsaturated cyclic anhydrides and their diacid and diester derivatives, without the need to melt or dissolve the polyolefin. However the grafting efficiency of these types of non-homopolymerizable grafting agents has been found to be poor, while the grafting compounds reported herein generally graft much more easily to polyolefins.
U.S. Pat. No. 6,191,231 and U.S. Pat. No. 6,100,324 report the free radical grafting of certain fluorinated olefins to polyolefins. The use of porous polyolefins is not mentioned.
SUMMARY OF THE INVENTION
This invention concerns an improved process for the free radical grafting of vinyl compounds onto a porous polyolefin having a pore volume fraction of at least 0.07, by contacting said porous polyolefin with a grafting agent in the presence of free radicals, wherein the improvement comprises using as a grafting agent a non-homopolymerizable monomer selected from the group consisting of a vinyl silane, a compound of the formula H
2
C═CH(CH
2
)
n
R
f
, and a compound of the formula R
1
CO
2
R
2
, wherein:
R
f
is a fluoroalkyl group having more fluorine atoms than carbon atoms;
n is 0 or 1;
R
1
is hydrocarbyl or substituted hydrocarbyl having 4 or more carbon atoms, and containing an olefinic double bond, provided that said olefinic double bond is not part of a ring; and
R
2
is hydrogen, hydrocarbyl or substituted hydrocarbyl.
This invention also concerns a process for the grafting of a polyolefin polymer, comprising the step of contacting a porous polyolefin polymer having a pore volume fraction of at least 0.07, a free radical generator, and a non-homopolymerizable grafting monomer selected from the group consisting of a vinyl silane, a compound of the formula H
2
C═CH(CH
2
)
n
R
f
, and compound of the formula R
1
CO
2
R
2
, wherein:
R
f
is a fluoroalkyl group having more fluorine atoms than carbon atoms;
n is 0 or 1;
R
1
is hydrocarbyl or substituted hydrocarbyl having 4 or more carbon atoms, and containing an olefinic double bond, provided that said olefinic double bond is not part of a ring; and
R
2
is hydrogen, hydrocarbyl or substituted hydrocarbyl;
wherein said grafting monomer is contacted with said porous polyolefin either simultaneously with said free radical generator, or after contacting said porous polyolefin with said free radical generator,
and provided that if said free radical generator is a chemical free radical generator said contacting of said porous polyolefin and said chemical free radical generator is done at a temperature at which said chemical free radical generator generates free radicals.
These and other features and advantages of the present invention will be more readily understood by those of ordinary skill in the art from a reading of the following detailed description. It is to be appreciated that certain features of the invention which are, for clarity, described below in the context of separate embodiments, may also be provided in combination in a single embodiment. Conversely, various features of the invention which are, for brevity, described in the context of a single embodiment, may also be provided separately or in any subcombination.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
It is preferred that the porous polyolefin polymer used in the present process is a polymer or copolymer of one or more hydrocarbon olefins, and more preferably that it is:
(a) a homopolymer of ethylene or a linear or branched C
3
-C
8
1-olefin;
(b) a random copolymer of ethylene or a linear or branched C
3
-C
8
1-olefin with a second olefin selected from the group consisting of ethylene and C
3
-C
10
1-olefins, provided that, when the second olefin is ethylene the maximum polymerized ethylene content is about 10%, more preferably about 4%, when the olefin is propylene and the second olefin is a C
4
-C
10
1-olefin the maximum polymerized content of said second olefin is about 20%, more preferably about 16%, and when the olefin is ethylene and the second olefin is a C
3
-C
10
1-olefin the maximum polymerized content of said second olefin is about 10%, more preferably about 5%;
(c) a terpolymer of a linear or branched C
3
-C
8
1-olefin and two different olefins selected from the group consisting of ethylene and C
4
-C
8
1-olefins, provided that, when ethylene is one of the two different olefins the maximum polymerized ethylene content is about 5%, more preferably about 4%, and when each of the two different olefins is a C
4
-C
10
1-olefin, the maximum polymerized content of the two different C
4
-C
10
1-olefins is about 20%, more preferably about 16%; or
(d) a homopolymer of (a) or a random copolymer of (b), impact modified with about 10 to 60% o

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