US-12624136-B2 - Phthalate-free polypropylene homopolymer having high stiffness properties

Abstract

Phthalate-free polypropylene homopolymers and compositions incorporating the homopolymers are described. The phthalate-free polypropylene homopolymers exhibit high molecular weight as well as low XS content. Composition incorporating the phthalate-free polypropylene homopolymer can have relatively high stiffness properties. In addition, the polypropylene compositions can have good melt flow characteristics. Phthalate-free compositions including the homopolymers can be advantageously utilized in forming containers and other articles in food contacting, medical, and personal care applications.

Inventors

• Zhiru MA

Assignees

• W.R. GRACE & CO.-CONN.

Dates

Publication Date

20260512

Application Date

20210629

Claims (19)

1. 1 . A polypropylene homopolymer, wherein the polypropylene homopolymer has a weight average molecular weight of 150,000 or greater, a melting temperature of about 160° C. or greater, a molecular weight distribution of 5 or greater, and a xylene soluble content of 1.8% by weight or less, and wherein the polypropylene homopolymer is produced with a Ziegler-Natta catalyst and is phthalate-free.
2. 2 . The polypropylene homopolymer of claim 1 , wherein the polypropylene homopolymer has an XS content of from 0.5% by weight to 1.5% by weight.
3. 3 . The polypropylene homopolymer of claim 1 , wherein the polypropylene homopolymer has a weight average molecular weight of 200000 or greater.
4. 4 . The polypropylene homopolymer of claim 1 , wherein the polypropylene homopolymer has a weight average molecular weight of 350000 or greater.
5. 5 . The polypropylene homopolymer of claim 1 , wherein the polypropylene homopolymer has a molecular weight distribution of 5.5 or greater.
6. 6 . The polypropylene homopolymer of claim 1 , wherein the polypropylene homopolymer has one or more of an isotactic pentad content of 95% or greater, an isotactic triad content of 97% or greater, an isotactic block length of 150 or greater, and a meso run length of 100 or greater.
7. 7 . The polypropylene homopolymer of claim 1 , wherein the polypropylene homopolymer has a melting temperature of 164° C. or greater.
8. 8 . The polypropylene homopolymer of claim 1 , wherein the polypropylene homopolymer has a crystallization temperature of 120° C.
9. 9 . The polypropylene homopolymer of claim 1 , wherein the polypropylene homopolymer is formed in a gas phase reactor.
10. 10 . A composition comprising the phthalate-free polypropylene homopolymer of claim 1 , wherein the composition has a flexural modulus of about 1700 MPa or greater, and a melt flow rate of about 1 g/10 min or greater and about 10 g/10 min or less.
11. 11 . The composition of claim 10 , wherein the composition has an Izod impact strength of 10 J/m or greater.
12. 12 . The composition of claim 10 , wherein the composition has a tensile strength at yield of 20 MPa or greater.
13. 13 . The composition of claim 10 , wherein the composition comprises a nucleating agent.
14. 14 . The composition of claim 10 , wherein the composition does not include a nucleating agent.
15. 15 . The composition of claim 10 , wherein the composition comprises one or more of a mold release agent, a slip agent, an antiblock, a UV stabilizer, a heat stabilizer, a clarifying agent, an antioxidant, an acid scavenger, or a colorant.
16. 16 . The composition of claim 10 , wherein the composition comprises a second polymer.
17. 17 . A molded article comprising the composition of claim 10 .
18. 18 . The molded article of claim 17 , wherein the molded article is a container.
19. 19 . The molded article of claim 17 , wherein the molded article is a food contact article, a medical care article, or a personal care article.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS This application is a U.S. National Phase Application under 35 U.S.C. § 371 of International Application No. PCT/US2021/039558, filed Jun. 29, 2021, which claims priority to and the benefit of U.S. Provisional Patent application Ser. No. 63/045,348, filed on Jun. 29, 2020, both of which are hereby incorporated by reference in their entireties. BACKGROUND Polypropylene exhibits mechanical and thermal properties useful in a wide variety of applications. One significant mechanical property of polypropylene is stiffness. Stiffness refers to the rigidity characteristics of a material and can be measured by determining the flexural modulus of the material. Flexural modulus relates to the ability of the material to bend or, in other words, its resistance to bending when a force is applied perpendicular to a structure formed from the polymer. High stiffness polymers will resist deformation when subjected to exterior forces and thus are often utilized in forming freestanding and shape-retaining products. In recent years, improvements in polymer formation techniques have been achieved that decrease the environmental impact of both the formation techniques and the polymers formed by the techniques. For instance, phthalate-free catalysts have been developed that can be used to produce phthalate-free polymers, i.e., polymers that carry with them no vestige of a phthalate-containing catalyst. Unfortunately, polymers, and particularly polypropylenes, that exhibit multiple different beneficial qualities, e.g., desirable mechanical characteristics such as stiffness in conjunction with desirable environmental qualities such as being phthalate-free while also maintaining desirable processability characteristics, have proven elusive. In view of the above, a need exists for a phthalate-free polypropylene homopolymer that has relatively high stiffness properties and good processability characteristics. A need also exists for polypropylene polymer compositions incorporating such a polypropylene homopolymer. SUMMARY In general, the present disclosure is directed to a polypropylene homopolymer having desirable characteristics. In particular, the polypropylene homopolymer can be phthalate-free. In addition, the polypropylene homopolymer can exhibit both a high molecular weight and a low xylene solubles (XS) content. For instance, a polypropylene homopolymer can have a molecular weight of greater than about 150,000, such as greater than about 200,000, such as greater than about 250,000, such as greater than about 300,000, such as greater than about 350,000. A polypropylene homopolymer can have a xylene soluble content (XS) of about 1.8% by weight or less, such as about 1.5% by weight or less, such as about 1.3% by weight or less, or about 1% by weight or less. Also disclosed is a composition including the phthalate-free polypropylene homopolymer having high stiffness and good processability properties. For instance, a composition including the phthalate-free polypropylene homopolymer as described herein can have a flexural modulus of about 1700 MPa or greater, for instance from about 1700 MPa to about 2100 MPa. A composition as described can have a melt flow rate of about 1 g/10 min or greater and about 10 g/10 min or less, for instance about 5 g/10 min or less, about 4.5 g/10 min or less, or about 4 g/10 min or less. A composition including the polypropylene homopolymer can be used to form all different types of molded articles using any suitable thermoforming process or molding process. For example, articles can be produced using extrusion blow molding, injection molding, rotational molding, extrusion, and the like. The polypropylene homopolymer can also be used to produce biaxially oriented polypropylene films. Articles that may be made in accordance with the present disclosure include food contact articles, medical care articles, and personal care articles. Other features and aspects of the present disclosure are discussed in greater detail below. DEFINITIONS AND TESTING PROCEDURES The term “phthalate-free propylene,” as used herein, is a propylene polymer (either a homopolymer or a copolymer) that carries with it no vestige of a phthalate catalyst system, including any phthalate-containing components of a catalyst system and any phthalate decomposition products of a phthalate catalyst system. Similarly, a composition including a phthalate-free polypropylene can be a phthalate-free composition and can be free of phthalate-containing components and phthalate decomposition products. The term “polypropylene homopolymer,” as used herein, is a homopolymer containing propylene monomer units. The term “propylene copolymer”, as used herein, is a copolymer containing a weight percent propylene monomer with a different monomer, e.g., an ethylene monomer, as a secondary constituent. A “propylene-ethylene copolymer” (also sometimes referred to as a polypropylene random copolymer, PPR, PP-R, RCP or RACO