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
1993-12-16
2001-02-13
Wu, David W. (Department: 1713)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Mixing of two or more solid polymers; mixing of solid...
C525S301000, C525S308000, C525S309000
Reexamination Certificate
active
06187870
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to the production of low molecular weight, low viscosity grafted polyolefins by reactive processing in a screw extruder. The present invention also relates to a screw extruder having a chamber or barrel that is capable of maintaining an elevated pressure while extruding a low viscosity material.
BACKGROUND OF THE INVENTION
Grafting of high and low molecular weight polymers has been reported often in the literature, see for example, the polymer text book “Polymer Chemistry” by M. P. Stevens (Addison-Wesley), 1975, PP196-202. Maleation is one type of grafting. For example, maleation of polypropylenes progresses easily to higher acid numbers with free radical initiation (see U.S. Pat. Nos. 3,414,551, 3,480,580, 3,481,910, 3,642,722, 3,746,676, 3,932,368 and 4,613,679). The molecular weight of the products of such reactions are lower than that of the starting polypropylene due to accompanying degradation reactions. On the other hand, direct maleation of polyethylenes results in cross-linking which increases the molecular weight of the polymer, see for example, “Journal of Applied Polymer Science”, 44, 1941, N. G. Gaylord et al (1992); and U.S. Pat. Nos. 4,026,967, 4,028,436, 4,031,062, 4,071,494, 4,218,263, 4,315,863, 4,347,341, 4,358,564, 4,376,855, 4,506,056, 4,632,962, 4,780,228, 4,987,190, and 5,021,510]. Free radical initiated maleation of polypropylenes and polyethylenes in continuous processes is limited to very low levels of grafting and low acid numbers such as below 4percent grafting. Grafted polyolefins are very suitable for use as compatibilizing agents and adhesion promoters between polymers and fillers. An increased acid number and percent grafting of the polyolefins would provide polyolefins with improved properties such as substrate wetting and adhesion and would even make some polyolefins emulsifiable, rendering them useful in emulsions. However, the higher levels of grafting is difficult to achieve due to the flashing of some of the components and/or crosslinking of the polyolefin in the extruder.
U.S. Pat. No. 4,762,890 discloses the grafting of polymers in a twin screw extruder. This technique is effective for high molecular weight polymers; however, the grafting is only up to 2 weight percent. U.S. Pat. No. 4,639,495 discloses the grafting using peroxide initiators however, the percent grafting is only obtainable up to 3 weight percent.
Efficiently grafting high amounts of comonomer onto polyolefins, producing higher acid numbers, have been attempted but only in batch processes with less than perfect results. Conversion of the batchwise process to a commercial continuous extruder based process has not, heretofore, been practical. However, for a polyolefin grafting process to be commercial and cost effective the process should be continuous. It would, therefore, be very desirable to be able to continuously and efficiently produce highly grafted polyolefins of high acid number.
SUMMARY OF THE INVENTION
The process for the production of low molecular weight grafted polyolefins comprises:
(a) mixing, at an elevated temperature of about 160 to 300° C., in an extruder equipped with an outlet pressure control device about 0.1 to 20 weight percent of a free radical initiator, about 0.1 to 30 weight percent of an ethylenically unsaturated polycarboxylic acid, anhydride, or ester thereof, and the remainder of a polyolefin containing at least 93 weight percent C
3
-C
10
olefins, wherein said elevated temperature is higher than the atmospheric boiling point of at least one of the components thereby producing an elevated pressure in said extruder of at least 30 psig, and
(b) extruding the resulting molten grafted polyolefin having a viscosity of less than 3,000 cP at 190° C.
The apparatus according to the present invention comprises a screw extruder having a heated elongated chamber containing a screw feed means, a feed opening at the first end of said chamber, and a pressure control valve at the second end of said chamber having a means to maintain the pressure within said chamber at about 30 to 400 psig, and a means to permit molten polymer to exit the chamber, wherein said screw means operates so as to feed material from said feed opening to said pressure control valve and wherein said chamber has a plurality of injection ports along said chamber for injecting material into said chamber.
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Ford Randal R.
Stuart, Jr. Richard K.
Boshears B. J.
Eastman Chemical Company
Gwinnell Harry J.
Wu David W.
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