Syndiotactic polypropylene

Details Syndiotactic polypropylene Syndiotactic polypropylene

1995-06-02

2001-02-06

Wu, David W. (Department: 1713)

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

Synthetic resins

Polymers from only ethylenic monomers or processes of...

C526S160000

Reexamination Certificate

active

06184326

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to highly crystalline syndiotactic polypropylene and, particularly, to syndiotactic polypropylene having a syndiotactic index of greater than 75%.
2. Description of the Prior Art
As known in the art, syndiotactic polymers have a unique stereochemical structure in which monomeric units having enantiomorphic configuration of the asymmetrical carbon atoms follow each other alternately and regularly in the macromolecular main chain. Syndiotactic polypropylene was first disclosed by Natta et al, in U.S. Pat. No. 3,258,455. The Natta group obtained syndiotactic polypropylene by using a catalyst prepared from titanium trichloride and diethyl aluminum monochloride. A later patent to Natta et al, U.S. Pat. No. 3,305,538, discloses the use of vanadium triacetylacetonate or halogenated vanadium compounds in combination with organic aluminum compounds for producing syndiotactic polypropylene. U.S. Pat. No. 3,364,190 to Emrick discloses a catalyst system composed of finely divided titanium or vanadium trichloride, aluminum chloride, a trialkyl aluminum and a phosphorus-containing Lewis base as producing syndiotactic polypropylene.
As disclosed in these patent references and as known in the art, the structure and properties of syndiotactic polypropylene differ significantly from those of isotactic polypropylene. The isotactic structure is typically described as having long sequences of monomer units with the same relative configuration of the tertiary carbon atoms. Using the Fischer projection formula, the stereochemical sequence of isotactic polypropylene is described as follows:
The methyl groups attached to the tertiary carbon atoms of successive monomeric units on the same side of a hypothetical plane through the main chain of the polymer, e.g., the methyl groups are all above or below the plane.
Another way of describing the structure is through the use of NMR. Bovey's NMR nomenclature for an isotactic pentad is . . . mmmm . . . with each “m” representing a “meso” dyad or successive methyl groups on the same side in the plane. As known in the art, any deviation or inversion in the structure of the chain lowers the degree of isotacticity and crystallinity of the polymer.
In contrast to the isotactic structure, syndiotactic polymers are those in which long sequences of monomer units have an alternating relative configuration of the tertiary carbon atoms. Using the Fischer projection formula, the structure of a syndiotactic polymer is designated as:
The methyl groups attached to the tertiary carbon atoms of successive monomeric units in the chain lie on alternate sides of the plane of the polymer.
In NMR nomenclature, this pentad is described as . . . rrrr . . . in which each “r” represents a “racemic” dyad, i.e., successive methyl groups on alternate side of the plane. The percentage of r dyads in the chain determines the degree of syndiotacticity of the polymer. Syndiotactic polymers are crystalline and like the isotactic polymers are insoluble in xylene. This crystallinity distinguishes both syndiotactic and isotactic polymers from atactic polymer that is soluble in xylene. Atactic polymer exhibits no regular order of repeating unit configurations in the polymer chain and forms essentially a waxy product.
While it is possible for a catalyst to produce all three types of polymer, it is desirable to produce predominantly isotactic or syndiotactic polymer with very little atactic formed. Catalysts that produce isotactic polyolefins are disclosed in European Patent Application No. 87870132.5 (Publication No. 0 284 308) published Oct. 5, 1988 and U.S. Pat. Nos. 4,794,096 issued Dec. 27, 1988 and 4,975,405 issued Dec. 4, 1990. These applications disclosed chiral, stereorigid metallocene catalysts that polymerize olefins to form isotactic polymers and are especially useful in the polymerization of a highly isotactic polypropylene. The present invention, however, utilize a different class of metallocene catalyst that are useful in the polymerization of syndiotactic polyolefins, and more particularly syndiotactic polypropylene.
The present invention provides highly crystalline syndiotactic polypropylene. It was discovered that the catalyst structure affected the formation of a syndiotactic polymer as opposed to an isotactic polymer. One theory, without limiting the scope of the claims of the present invention, is that the catalyst structure appears to affect the type and number of deviations in the chain from the principally repeating units in the polymer. Previously, the catalyst used to produce syndiotactic polypropylene were believed to exercise chain-end control over the polymerization mechanism. These previously known catalysts, such as the ones disclosed by Natta et al in the references cited above, produce syndiotactic polymers which primarily have the following structure:
or in NMR nomenclature . . . rrrmrrr . . . The NMR analysis for this structure of syndiotactic polypropylene is shown in Zambelli, et al., Macromolecules, Vol. 13, pp 267-270 (1980). Zambelli's analysis shows the predominance of the single meso dyad over any other deviations in the chain.
SUMMARY OF THE INVENTION
The present invention provides syndiotactic polypropylene having a high syndiotactic index. The highly crystalline syndiotactic polypropylene is obtained through use of a stereorigid metallocene compound described by the formula
R″(C
5
R
4
)(C
4
R′
4
C
5
C
4
R′
4
)MeQ
p
wherein (C
5
R
4
) is a cyclopentadienyl ring or substituted cyclopentadienyl ring; (C
4
R′
m
C
5
C
4
R′
n
) is a substituted cyclopentadienyl ring, preferably a fluorenyl radical; each R and R′ is hydrogen or hydrocarbyl radical having from 1-20 carbon atoms, a halogen, an alkoxy, and alkoxy alkyl or an alkylamino radical, each R and R′ may be the same or different; (C
5
R
4
) has bi-lateral or pseudo bi-lateral symmetry for the proximal carbon atoms and bi-lateral symmetry only for the distal carbon atoms, “proximal” referring to position 2 or 5 of the cyclopentadienyl rings and “distal” referring to position 3 or 4 of the cyclopentadienyl ring relative to the carbon attached to R″ (position 1), i.e., proximal being near the bridgehead carbon and distal being away from the bridgehead carbon; R″ is a structural bridge between the (C
5
R
4
) and (C
4
R′
4
C
5
C
4
R′
4
) rings to impart stereorigidity and, preferably, is a hydrocarbyl radical having 1-4 carbon atoms, a silicon hydrocarbyl compound, a germanium hydrocarbyl compound, an alkyl phosphine, an alkyl amine, a boron compound or an aluminum compound and may be unsubstituted or substituted with hydrocarbyl groups, such as an alkyl, aryl, alkylaryl or arylalkyl radical, to form the bridge; Q is a hydrocarbyl radical, such as an alkyl, aryl, alkenyl, alkylaryl or arylalkyl radical having 1-20 carbon atoms or is a halogen; Me is a Group IIIB, IVB, VB, or VIB metal as positioned in the Periodic Table of Elements; and p is the valence of Me minus 2. It was discovered that the use of a metallocene catalyst as described above product highly crystalline syndiotactic polypropylene.
The highly crystalline syndiotactic polypropylene is obtained by introducing at least one of the compounds described by the above formula with a cocatalyst or ionizing agent, such as alumoxane, into a polymerization reaction zone containing propylene monomer. In addition, an electron donor compound, such as an organosilicon compound and/or a scavenging agent, such as an aluminum alkyl, may be introduced into the reaction zone. Further, the catalyst may also be pre-polymerized prior to introducing it into the reaction zone and/or prior to the stabilization of reaction conditions in the reactor. The prepolymerization of the catalyst system can occur by contacting the metallocene compound with a small amount of the cocatalyst or ionizing agent and an olefin monomer at a temperature below that at which polymerization occurs in the reaction zone.


REFERENCES:
patent: 325

Affiliated with

Also associated with

Rating

Syndiotactic polypropylene does not yet have a rating. At this time, there are no reviews or comments for this patent.

If you have personal experience with Syndiotactic polypropylene, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Syndiotactic polypropylene will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFUS-PAI-O-2589030