Monomodal propylene random copolymer with high impact strength
AssigneeW.R. Grace & Co.-Conn.
InventorsZhiru Ma, John K. Kaarto
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Abstract
Visbroken and monomodal random polypropylene copolymers are disclosed that have excellent impact resistance properties. Because the polymers are monomodal, the polymers also have excellent optical characteristics. In order to produce the polymers, a high molecular weight and low melt flow rate polypropylene polymer is combined with a visbreaking agent under molten conditions that has been found to dramatically improve impact resistance.
Claims20
A polymer composition comprising:
- a monomodal, visbroken polypropylene polymer, the visbroken polypropylene polymer comprising a random propylene and alpha-olefin copolymer, the visbroken polypropylene polymer having a melt flow rate of less than about 10 g/10 min at 230° C. and at a load of 2.16 kg and a polydispersity index of from about 2.5 to about 4, the visbroken polypropylene polymer displays an Izod impact resistance at 23° C. of greater than about 400 J/m, the polymer composition optionally contains a nucleating agent.
A method of preparing a visbroken polypropylene polymer comprising visbreaking a monomodal polypropylene polymer, the monomodal polypropylene polymer comprising a random propylene and alpha-olefin copolymer, wherein the monomodal polypropylene polymer has an initial melt flow rate of less than about 0.5 g/10 min at 230° C. and at a load of 2.16 kg, the random propylene and alpha-olefin copolymer contains the alpha-olefin in an amount of from about 2.5% to about 5.7% by weight, the visbroken polypropylene polymer has a xylene soluble content of from about 6% to about 20% by weight, and wherein the monomodal polypropylene polymer is visbroken so as to achieve a cracking ratio of greater than 3, the visbroken polypropylene polymer has an Izod impact resistance at 23° C. of greater than about 400 J/m.
Dependencies are inferred from the claim text.