Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Mixing of two or more solid polymers; mixing of solid...
Patent
1996-09-12
1998-05-26
Nagumo, Mark
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Mixing of two or more solid polymers; mixing of solid...
525268, 525314, C08F29708
Patent
active
057565872
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The present invention relates to propylene block copolymers containing a non-conjugated .alpha.,.omega.-diene. It more particularly relates to propylene block copolymers containing a non-conjugated .alpha.,.omega.-diene in at least one of the blocks and to a process for the production of these copolymers.
TECHNOLOGY REVIEW
It is known to increase the impact strength of polypropylene by mixing it with ethylene-propylene elastomers. Nevertheless, as such mixtures are not perfectly homogeneous, they do not exhibit all the desired properties.
Attempts have been made to overcome this problem by copolymerizing propylene with another alpha-olefin, such as, for example, ethylene.
Among propylene copolymers, those which exhibit the best impact strength/stiffness compromise are the copolymers, known as block copolymers, prepared in two-stage processes comprising a first stage of homopolymerization of the propylene or of copolymerization of the propylene with a maximum of 6 molar % of another alpha-olefin, such as ethylene, followed by a second stage of polymerization of ethylene or of copolymerization of ethylene with propylene and optionally another alpha-olefin in proportions such that the amount of ethylene is greater than 10 molar % (see, for example, EP-0,202,946).
The rheological properties of these block copolymers and in particular their melt strength remain unsatisfactory however for specific applications, such as thermoforming or the production of foams.
In addition, when the block copolymers are obtained by polymerization in a diluent, such as a hydrocarbon or one of the monomers maintained in the liquid state, the formation of a significant amount of diluent-soluble polymer is observed in the second polymerization stage, which results in an increase in the viscosity of the polymerization mixture, a deterioration in heat exchanges and agglomeration of the polymer particles with each other or on the walls of the reactor. Under these conditions, it is necessary to limit the amount of polymer produced during this stage, which results in a limitation on the impact strength of the final copolymers. The loss of polymer by solubilization is also responsible for a substantial increase in production costs.
Moreover, the document JP 59/155416 discloses propylene block copolymers in which each of the blocks contains from 1 to 30% by weight of 4- or 5-methyl-1,4-hexadiene. These copolymers exhibit good impact strength and are chemically reactive.
SUMMARY OF THE INVENTION
The present invention relates to propylene block copolymers which are different from those described in the prior art and which exhibit many advantages with respect to the latter.
To this end, the present invention relates to a propylene block copolymer containing per: and copolymers of propylene not containing more than 6% by weight of ethylene and/or of an alpha-olefin having from 4 to 6 carbon atoms, homopolymers and copolymers of ethylene not containing more than 90% by weight of propylene and/or of another alpha-olefin having from 4 to 6 carbon atoms, to approximately 20% by weight of .alpha.,.omega.-diene-derived monomer units with respect to the total weight of the block copolymer.
BRIEF DESCRIPTION OF THE DRAWING
The FIGURE illustrates the variation in the elongational viscosity in the molten state (expressed in Pa.s) as a function of the elongation time (expressed in s) for elongation rate gradients of 0.1 s.sup.-1.
DETAILED DESCRIPTION OF THE INVENTION
The propylene block copolymers according to the present invention most often contain at least 5 parts by weight and preferably at least 10 parts by weight of polymer (b) per 100 parts by weight of polymer (a). The copolymers according to the invention which contain at least 20 parts by weight of polymer (b) per 100 parts by weight of polymer (a) give good results. The amount of polymer (b) is in addition not generally greater than 90 parts by weight. Good results are obtained when the amount of polymer (b) is less than or equal to 80 parts by weight per 100
REFERENCES:
patent: 4210736 (1980-07-01), Baekelmans et al.
patent: 4210738 (1980-07-01), Hermans et al.
patent: 4987193 (1991-01-01), Gotoh
patent: 5206198 (1993-04-01), Costa et al.
patent: 5438100 (1995-08-01), Shinozaki et al.
Derwent Abstracts, Abstract No. 84-254528.
Chemical Abstracts, Abstract No. 125417p, vol. 71, No. 13, Dec. 29, 1969.
Bettonville Serge
De Rop Philippe
Franquinet Claude
Nagumo Mark
Solvay Polyolefins Europe -- Belgium (Societe Anonyme
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