Syndio-isoblock polymer and process for its preparation

Details Syndio-isoblock polymer and process for its preparation Syndio-isoblock polymer and process for its preparation

1995-06-06

2001-03-06

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...

C502S117000, C502S103000, C502S152000, C526S348000, C526S943000, C556S053000, C556S058000

Reexamination Certificate

active

06197902

ABSTRACT:

The invention relates to a syndio-isoblock polymer having long isotactic and syndiotactic sequences and to a process for its preparation.
It is known that polypropylene exists in various structural isomers:
(a) highly isotactic polypropylene in whose molecular chains almost all of the tertiary carbon atoms have the same configuration,
(b) isotactic stereoblock PP in whose molecular chains isotactic blocks of opposite configuration alternate with each other in a regular manner,
(c) syndiotactic polypropylene in whose molecular chains every second tertiary carton atom has the same configuration,
(d) atactic polypropylene in whose molecular chains the tertiary carbon atoms have a random configuration
(e) atactic-isotactic stereoblock PP in whose molecular chains isotactic and atactic blocks alternate with each other, and
(f) isoblock PP whose molecular chains contain isotactic blocks which are separated from one another by a tertiary carbon atom having, in each case, the opposite configuration relative to the isotactic blocks.
A process for the preparation of isotactic stereoblock polymers is known in which propylene is polymerized using a metallocene of a metal from group IVb, Vb or VIb of the Periodic Table (cf. U.S. Pat. No. 4,522,982). This metallocene is a mono-, di- or tricyclopentadienyl or substituted cyclopentadienyl metal compound, in particular of titanium.
The cocatalyst used is an aluminoxane.
However, in dilute solution the titanocenes which are preferably used are insufficiently heat-stable for use in an industrial process. Moreover, in this process, products having a relatively long run of isotactic sequences (n greater than 6) are only obtained at very low temperatures (−60° C.). Finally, the cocatalysts must be used in relatively high concentrations to achieve an adequate catalyst yield, with the consequence that the catalyst residues contained in the polymer product must be removed in a separate purification step.
Furthermore, it is known that stereoblock polymers of 1-olefins having long isotactic sequences can be obtained at industrially appropriate polymerization temperatures by means of a catalyst which is composed of a metallocene compound containing cyclopentadienyl radicals which are substituted by chiral groups, and an aluminoxane (cf. EP 269,987).
Moreover, it is known that stereoblock polymers of 1-olefins having a broad uni-or multi-modal molecular weight distribution can be obtained if the polymerization of the 1-olefins is carried out using a catalyst which is composed of a bridged chiral metallocene and an aluminoxane (cf. EP 269,986). These polymers are particularly suitable for the preparation of transparent films.
It is also known that the use of a catalyst based on biscyclopentadienyl compounds of zirconium and an aluminoxane in the polymerization of propylene gives only atactic polymer (cf. EP 69,951).
Moreover, using soluble stereorigid chiral zirconium compounds, it is possible to prepare highly isotactic polypropylene (cf. EP 185,918).
Finally, isoblock polymers have been proposed.
A polymerization process has been found in which a polymer having a regular molecular structure and a high molecular weight is obtained at industrially appropriate process temperatures in a high yield.


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