Chemistry of hydrocarbon compounds – Aromatic compound synthesis – By condensation of entire cyclic molecules or entire...
Reexamination Certificate
2000-06-01
2002-08-27
Dang, Thuan D. (Department: 1764)
Chemistry of hydrocarbon compounds
Aromatic compound synthesis
By condensation of entire cyclic molecules or entire...
Reexamination Certificate
active
06441260
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Technical Field
The present invention relates to a process for oligomerizing alpha-methylstyrene and an initiator therefor. More particularly, the invention is directed to preparing oligomers of alpha-methylstyrene having a number-average molecular weight (M
n
) of about 5,000 and below.
2. Background
Alpha-methylstyrene (&agr;-methylstyrene) has been utilized as a monomer and comonomer in many polymerization processes. The polymerization products of such processes have been put to use as adjuvants in polymeric compositions, improving the impact and heat-resistant properties of polymers. When admixed with polyvinyl chloride (PVC) low molecular weight poly(&agr;-methylstyrene) reduces the fusion time and melt viscosity of the PVC composition and improves its heat stability. Low molecular weight &agr;-methylstyrene oligomers also improve the melt fracture and shear burning resistance of PVC at high shear processing rates (Wilson A. P.; Raimondi, V. V.; Polym. Eng. Sci. (1978). 18(11), 887-92).
Oligomers of &agr;-methylstyrene have also been employed as processing aids for chlorinated polyvinyl chloride (CPVC). Incorporation of poly(&agr;-methylstyrene) into CPVC reduces fusion time and melt viscosity and improves fusion, melt flow, and stability, without deleteriously affecting the desirable properties of the polymer composition (Raimondi, V.; Wilson, Alfred P.; Soc. Plast. Eng. Tech. Pap. (1978), 24, 747-9).
Heretofore, low molecular weight poly(&agr;-methylstyrene) has been produced by polymerizing &agr;-methylstyrene in the presence of Lewis acid initiators such as BF
3
, BCl
3
, and SbCl
5
in combination with an aluminum halides and the like. In commercial practice, low molecular weight poly(&agr;-methylstyrene) has been provided by polymerizing &agr;-methylstyrene in the presence of a BF
3
/water mixture. However, such catalyst systems have been demonstrated to be highly corrosive, resulting in many engineering problems leading to eventual shut down of the manufacturing plant. The corrosive nature of the BF
3
/water and aluminum halide mixtures have necessitated the use of expensive metal alloys in manufacturing plant design. Even when such measures have been employed, the corrosive nature of the residual catalyst system dictated that the spent catalyst system had to be neutralized and removed from the obtained product. What is desired is an oligomerization process involving mild reaction conditions and a simple initiator system.
SUMMARY OF THE INVENTION
Accordingly, it is a general object of the present invention to provide a process for the oligomerization of &agr;-methylstyrene.
It is another object of the invention to provide a process for &agr;-methylstyrene oligomerization utilizing inert reaction media.
It is yet another object of the invention to provide an initiator system that does not need to be neutralized or removed from the oligomerized product.
It is still another object of the invention to provide a poly(&agr;-methylstyrene) product having a number average molecular weight of about 5000 and below.
It is another object of the invention to provide an oligomerized &agr;-methylstyrene product having a number average molecular weight of about 500 to 5000.
In accordance with the present invention, it has been discovered that &agr;-methylstyrene can be oligomerized when contacted with a catalytic amount of a single component initiator comprising a cation and a weakly coordinating anion (WCA) at a temperature ranging from about −15° C. to about 40° C. By weakly coordinating anion is meant that the anion is only weakly coordinated to the cation complex. The anion is sufficiently labile to be displaced by monomer. The WCA functions as a stabilizing anion to the cation complex and does not transfer to the cation complex to form a neutral product. The WCA is relatively inert in that it is non-oxidative, non-reducing, and non-nucleophilic.
The cation portion of the single component initiator useful in the process of the invention is selected from lithium or a carbocation of the formula:
C
+
(R
1
)(R
2
)(R
3
)
wherein R
1
, R
2
, and R
3
, independently represent hydrocarbyl and substituted hydrocarbyl radicals.
The WCA portion of the single component initiator useful in the process of the present invention is selected from a borate of the formula:
B(R
4
)
3
(R
5
)
wherein R
4
, independently represents a fluorinated aryl radical and R
5
represents a radical selected from hydrocarbyl, fluorinated hydrocarbyl or fluorinated aryl.
International Published Patent Application No. WO 95/29940 discloses a cationic catalyst system for polymerizing olefinic and styrenic monomers to high polymers having molecular weights above 10,000 M
n
, and most preferably above 100,000 M
n
. The catalyst system includes a cationic component selected from a hydrocarbyl substituted carbocation or a cyclopentadienyl transition metal cations and a non-coordinating anionic complex including hydrocarbyl substituted borates. The catalyst system is combined with the monomer in slurry or solution and the polymerization reaction is conducted at temperatures below about 20° C., and more preferably between −150 and −20°. There is no disclosure of a process for making oligomers of &agr;-methylstyrene.
T. D. Shaffer and J. R. Ashbaugh, J. Poly. Sci., Part A, Vol. 35, 329-344 (1997) (Table IX), have reported polymerizing (&agr;-methylstyrene) to a M
n
of 6400 in the presence of a multicomponent catalyst system consisting of lithium n-butyltrispentafluorophenylboron and the initiator 1,3-bis(1-chloro-1-methylethyl)-5-tert-butylbenzene. However, there is no disclosure of a single component catalyst system capable of producing poly(&agr;-methylstyrene) oligomers having molecular weights of 5000 or below (M
n
)
DETAILED DESCRIPTION
The present invention is directed to a non-corrosive initiator system and process for oligomerizing (&agr;-methylstyrene) to low molecular weight poly(&agr;-methylstyrene). By low molecular weight is meant that the &agr;-methylstyrene oligomer has a number average molecular weight (M
n
) of 5000 and below (relative to a polystyrene standard). In one aspect of the invention the molecular weight of the oligomerized &agr;-methylstyrene ranges between 500 and 4500 M
n
. In another aspect of the invention the molecular weight of the oligomerized &agr;-methylstyrene ranges between 1000 and 4000 M
n
. The desired oligomers are made in inert (non-corrosive) media in the absence of water and the corrosive compounds of the prior art, obviating the need for the use of expensive alloys in the physical plant and by-passing the necessity to neutralize and remove catalyst components from the resulting product.
In one embodiment of the invention the polydispersity (Mw/Mn) is 10 or less. In another embodiment the polydispersity is 5 or less. In still another embodiment it ranges from 1.5 to 4, and in another embodiment it ranges from 2 to 3.5.
The single component catalyst system of the invention is represented by the formula:
[M
+
][WCA
−
]
In the formula above, M represents lithium or a carbocation of the formula:
wherein R
1
, R
2
, and R
3
, independently represent hydrocarbyl and substituted hydrocarbyl radicals. In one aspect of the invention, the hydrocarbyl and substituted hydrocarbyl radicals are independently selected from hydrogen, linear or branched (C
1
to C
20
) alkyl, (C
5
to C
10
) cycloalkyl, (C
6
to C
14
) aryl, and (C
7
to C
24
) aralkyl, provided that only one of R
1
, R
2
, and R
3
can be hydrogen at any one time. By substituted is meant that the hydrocarbyl radical can be substituted with a halide selected from chlorine, fluorine, bromine, and iodine, or with another hydrocarbyl group selected from (C
1
to C
10
) alkyl, (C
5
to C
10
) cycloalkyl, (C
6
to C
14
) aryl, and (C
7
to C
24
) aralkyl. In another aspect, the carbocations of the invention contain aryl radicals wherein R
1
, R
2
, and R
3
are selected from phenyl, tolyl, xylyl, and biphenyl. In still another aspect, the carbo
Goodall Brian Leslie
King Brian Michael
Dang Thuan D.
Dunlap Thoburn T.
Hudak & Shunk Co. LPA
The B.F. Goodrich Company
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