Method for preparing molded articles of syndiotactic polypropylene

• US 5,759,469 A
• Filed: 09/25/1996
• Issued: 06/02/1998
• Est. Priority Date: 11/20/1989
• Status: Expired due to Term

• Current Assignee: Mitsui Chemicals Incorporated (Mitsui Chemicals)
• Original Assignee: Mitsui Toatsu Chemicals Incorporated (Mitsui Chemicals)
• Inventors: Ito, Mitsuru, Sasaki, Tateyo, Shiomura, Tetusnosuke, Asanuma, Tadashi
• Primary Examiner(s): HEITBRINK, JILL LYNNE
• Application Number:
  US08/719,514
• Time in Patent Office: 615 Days
• Field of Search: 264/235-237, 264/348, 264/331.17
• US Class Current: 264/235
• CPC Class Codes: B29C 67/24 characterised by the choice of material
• CPC Class Codes: B29K 2023/12 PP, i.e. polypropylene
• CPC Class Codes: B29K 2995/0026 Transparent
• CPC Class Codes: C08F 110/06 Propene
• CPC Class Codes: C08F 2500/03 Narrow molecular weight distribution, i.e. Mw/Mn < 3
• CPC Class Codes: C08F 2500/16 Syndiotactic
• CPC Class Codes: Y10T 428/26 Web or sheet containing structurally defined element or component, the element or component having a specified physical dimension

Abstract

A molded article of a syndiotactic polypropylene having excellent transparency in which a melting point attributed to the polypropylene having the syndiotactic structure measured at a heating rate of 10° C./minute by differential scanning thermal analysis is represented by a substantially single peak, the aforesaid molded article being prepared by heating, melting and then hot-molding a homopolymer of propylene or a copolymer of propylene and a small amount of another olefin, which have a substantially syndiotactic structure, or a mixture of the homopolymer or the copolymer and a small amount of a polypropylene having a substantially isotactic structure, followed by quenching, or, after these steps, additionally subjecting the above molded article to a heat treatment at a temperature of less than its melting point. A method for preparing the above molded article is also disclosed here.

Claims

1. A method for preparing a molded article of a syndiotactic polypropylene having excellent transparency which comprises the steps of heating, melting and then hot-molding (a) a homopolymer of propylene which has a syndiotactic structure such that the syndiotactic pentad fraction is 0.7 or more, (b) a copolymer of propylene and a small amount of another olefin, which has a substantially syndiotactic structure, such that, in a ¹³ C-NMR spectrum of the copolymer, a peak intensity at 20.2 ppm occupies 0.5 or more of the total intensity of all the peaks attributed to the methyl groups of propylene units, or (c) a mixture of said homopolymer or said copolymer and less than 50% by weight of the mixture of a polypropylene having a substantially isotactic structure;

and then quenching the resulting molded article at 100°

C./minutes or more to obtain a molded article in which the melting point attributed to the polypropylene having a syndiotactic structure measured at a heating rate of 10°

C./minute by differential scanning thermal analysis is represented by a substantially single peak.

2. A method for preparing a molded article of a syndiotactic polypropylene having excellent transparency which comprises the steps of heating, melting and then hot-molding (a) a homopolymer of propylene which has a syndiotactic structure such that the syndiotactic pentad fraction is 0.7 or more, (b) a copolymer of propylene and a small amount of another olefin, which has a substantially syndiotactic structure, such that, in a ¹³ C-NMR spectrum of the copolymer, a peak intensity at 20.2 ppm occupies 0.5 or more of the total intensity of all the peaks attributed to the methyl groups of propylene units, or (c) a mixture of said homopolymer or said copolymer and less than 50% by weight of the mixture of a polypropylene having a substantially isotactic structure;

quenching the resulting molded article at 100°

C./minutes or more, to obtain a molded article in which the melting point attributed to the polypropylene having a syndiotactic structure measured at a heating rate of 10°

C./minute by differential scanning thermal analysis is represented by a substantially single peak; and

then subjecting said molded article to a heat treatment at a temperature of less than its melting point.

3. A method for preparing a molded article of a syndiotactic polypropylene having excellent transparency which comprises the steps of heating, melting and then hot-molding (a) a homopolymer of propylene which has a syndiotactic structure such that the syndiotactic pentad fraction is 0.7 or more, (b) a copolymer of propylene and a small amount of another olefin, which has a substantially syndiotactic structure, such that, in a ¹³ C-NMR spectrum of the copolymer, a peak intensity at 20.2 ppm occupies 0.5 or more of the total intensity of all the peaks attributed to the methyl groups of propylene units, the ratio between the weight average molecular weight and the number average molecular weight of said polymer being from 1.5 to 3.5;

and then quenching the resulting molded article at 100°

C./minute or more, to obtain a molded article in which the melting point attributed to the polypropylene having a syndiotactic structure measured at a heating rate of 10°

C./minute by differential scanning thermal analysis is represented by a substantially single peak.

4. A method for preparing a molded article of a syndiotactic polypropylene having excellent transparency which comprises the steps of heating, melting and then hot-molding (a) a homopolymer of propylene which has a syndiotactic structure such that the syndiotactic pentad fraction is 0.7 or more, (b) a copolymer of propylene and a small amount of another olefin, which has a substantially syndiotactic structure, such that, in a ¹³ C-NMR spectrum of the copolymer, a peak intensity at 20.2 ppm occupies 0.5 or more of the total intensity of all the peaks attributed to the methyl groups of propylene units, the ratio between the weight average molecular weight and the number average molecular weight of said polymer being from 1.5 to 3.5;

quenching the resulting molded article at 100°

C./minute or more, to obtain a molded article in which the melting point attributed to the polypropylene having a syndiotactic structure measured at a heating rate of 10°

C./minute by differential scanning thermal analysis is represented by a substantially single peak; and

then subjecting said molded article to a heat treatment at a temperature of less than its melting point.