Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Mixing of two or more solid polymers; mixing of solid...
Reexamination Certificate
1997-10-27
2001-07-10
Cain, Edward J. (Department: 1714)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Mixing of two or more solid polymers; mixing of solid...
Reexamination Certificate
active
06258894
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to methods for curing unsaturated polymer resins, and more particularly to curing such resins with a peroxide initiator in the presence of a cure promoter.
BACKGROUND OF THE INVENTION
The term polyester refers generally to the group of synthetic resins that are polycondensation products of dicarboxylic acids with dihydroxy alcohols. The term unsaturated polyester resin, as used herein, designates a linear-type alkyd possessing carbon-to-carbon double bond unsaturation in the polymer chain. These unsaturated polyesters may be crosslinked and thus cured by reaction with monomers such as styrene or diallyl-phthalate, usually in the presence of a peroxide to form insoluble and infusible resins without the formation of a by-product during the curing reaction. Other types of polymer resins are also known which include carbon-to-carbon double bond unsaturation in the polymer chain, and which can also be crosslinked and cured, such as urethane acrylates, epoxy acrylates, and the like.
Because of their versatility and cost effectiveness, these resins possess broad commercial utility. Such utilities include, but are not limited to, low-pressure laminating; attractive and durable coatings for concrete, masonry, wood, plastic, wallboard, and metal; specialty resins targeted for synthetic marble, boat hulls, polymer concrete, mine-bolt resins, transfer molding, restorative dentistry, automotive body repair, and the like.
Tertiary aromatic amines are widely used as cure promoters or accelerators for unsaturated resins in the presence of peroxide initiators. Exemplary tertiary amines useful as cure promoters include, for example, N,N-dimethylaniline (DMA), N,N-diethylaniline (DEA), N-(2-hydroxyethyl)-N-methyl aniline, N-(2-hydroxyethyl)-N-ethyl aniline, N,N-bis-(2-hydroxyethyl)-m-toluidine, N-(2-hydroxyethyl)-N-[2-(2-hydroxyethoxy)ethylaniline, N,N-bis-(2-hydroxyethyl)-p-toluidine (HEPT), and N,N-dimethyl-p-toluidine (DMPT). However, cure rates for these types of compounds could be improved.
Further, as such uses demonstrate, polyester resins and other crosslinkable resins are often used in environments, i.e., outdoors, where temperatures cannot be easily controlled. Accordingly, it has become increasingly important to increase the cure rate of such polymer resins at low temperatures without detracting from the physical properties of the resins. The effectiveness of tertiary amine cure promoters such as those listed above, however, can fall off dramatically at low temperatures. Further, while the N,N-dimethyltoluidines are known as effective cure promoters at temperatures as low as 10° C. to 15° C., these compounds become much less effective at temperatures approaching or below 0° C.
In addition, the lower dialkylanilines and toluidines can be toxic and can produce irritating and offensive odors; can be corrosive; and cannot sufficiently cure the polymer surface.
OBJECTS AND SUMMARY OF THE INVENTION
It is accordingly an object of the present invention to provide a method for curing unsaturated polymer resins in the presence of a peroxide initiator using a cure promoter which will provide a fast cure without adversely affecting the physical properties of the resins.
It is another object of the present invention to provide a method for curing unsaturated polymer resins in the presence of a peroxide initiator using a cure promoter which will provide a fast cure at low temperatures.
It is another object of the present invention to provide a method for curing unsaturated polymer resins in the presence of a peroxide initiator using a cure promoter which is essentially odorless.
It is yet another object of the present invention to provide a method for curing unsaturated polymer resins in the presence of a peroxide initiator using a cure promoter which is less toxic than lower dialkylanilines and toluidines.
It is yet another object of the present invention to provide a method for curing unsaturated polymer resins in the presence of a peroxide initiator using a cure promoter which is substantially non-corrosive.
It is yet another object of the present invention to provide a method for curing unsaturated polymer resins in the presence of a peroxide initiator using a cure promoter which can provide a more complete surface cure.
It is yet another object of the present invention to provide a method for curing unsaturated polymer resins in the presence of a peroxide initiator using a cure promoter which can be incorporated into the polymer backbone.
It is yet another object of the present invention to provide a method for curing unsaturated polymer resins in the presence of a peroxide initiator using a cure promoter which is relatively inexpensive and thus cost effective.
These and other objects of the present invention will become apparent from the following general and detailed description of the invention. The objects of the present invention are accomplished based on the discovery that compounds according to Formula (I) below can be very effective cure promoters. In the invention, an unsaturated polymer is cured with a peroxide initiator in the presence of a promoter according to Formula I:
wherein:
R
1
is linear or branched C1 to C6 alkyl or C3 to C6 cycloalkyl;
R
2
is H, linear or branched C1 to C6 alkyl or C3 to C6 cycloalkyl, wherein said C1 to C6 alkyl or C3 to C6 cycloalkyl is optionally substituted at the C1 or C3 position, respectively, by X as defined below;
R
3
and R
4
are each independently selected from the group consisting of H, linear or branched C1 to C6 alkyl, and C3 to C6 cycloalkyl;
R
5
, R
6
, R
7
, R
8
, and R
9
are each independently selected from the group consisting of H, linear or branched C1 to C6 alkyl, C3 to C6 cycloalkyl, and C1 to C6 alkoxy; and
X is OH, OR
1
, CN, OC(O)R
1
, O[(CH
2
)
m
O]
n
H or O[(CH
2
)
m
O]
n
R
1
, wherein m=1 to 6 and n=1 to 6, and wherein R
1
is as defined above.
Currently preferred are compounds of Formula (I) wherein:
R
1
is methyl or ethyl;
R
2
is H or hydroxymethyl;
R
3
or R
4
are each independently selected from the group consisting of H, methyl and ethyl;
R
5
, R
6
, R
7
, R
8
, and R
9
are each independently selected from the group consisting of H and methyl; and
X is OH or O[(CH
2
)
m
O]
n
H, wherein m=2 and n=1 to 6.
Exemplary compounds of Formula I in accordance with the invention include, but are not limited to, N-methyl-N-(2-hydroxyethyl)-p-toluidine (MHPT); N-ethyl-N-(2-hydroxyethyl)-p-toluidine (EHPT); and N-methyl-N-(2-hydroxypropyl)-p-toluidine (2HPMT).
In the invention, the promoter is present in an amount sufficient to increase the cure rate of the unsaturated resin to about 75%, preferably about 60%, and more preferably about 50%, of the cure time of the unsaturated resin measured using N,N-dimethyl-p-toluidine. The cure promoter can be present, for example, in an amount between about 0.01 and about 5 percent by weight based on the weight of unsaturated resin, and preferably in an amount between about 0.1 and about 0.5 percent by weight. The cure promoters are particularly effective for use with unsaturated polyester resins as known in the art, but are also useful as cure promoters for other unsaturated polymer resins, such as polyurethane acrylates, epoxy acrylates, and the like.
The use of the cure promoters of Formula I provides a substantial increase in gel and cure rates of polymerizable unsaturated polymers, as compared to conventional tertiary amine cure promoters, such as DMA, DMPT, and the like. Further, the use of these cure promoters provides advantages in terms of gel and cure rates at a wide range of temperatures. The cure promoters can be very effective cure promoters at ambient temperatures, i.e., about 20-25° C., and can also be effective at low temperatures, i.e., as low as 15° C., 0° C. and lower. Promoters of Formula I gradually lose effectiveness at decreasing temperatures. In contrast, various other tertiary amines, such as DMA, DEA, HEPT and DMPT, dramatically lose their effectiven
Bowers, Jr. Joseph Stanton
Geiger Carey Cecil
Santobianco John Gabriel
Alston & Bird LLP
Cain Edward J.
First Chemical Corporation
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