Elastomers polypropylene-based

Table 15.13. Key properties of commercial thermoplastic elastomer blends based on polypropylene/elastomer dynamic vulcanizates...

A most significant example, which was also provided by the Symyx team, deployed the same methodology to uncover an entirely new family of isospecific propylene polymerization catalysts. The Symyx team, in collaboration with Dow Chemical, discovered and developed a new catalyst class, and a new commercial solution process for the production of isotactic polypropylene-based elastomers and plastomers. " ... 

Bokobza, L. Burr, A. Garnaud, G. Perrin, M. Pagnotta, S. (2004) Fibre Reinforcement of Elastomers Nanocomposites Based on Sepiolite and Poly(hydroxyethyl acrylate). Polym. Int. Vol.53, N0.8, pp.1060-1065, ISSN 0959-810 Bonduel, D. Mainil, M. Alexandre, M. Monteverde, F. Dubois, P. (2005) Supvported Coordination Polymerisation A Unique Way to Potent Polyolefin Carbon Nanotube Nanocomposites. Chem. Commun. Vol.l4, No.6, pp.781-783 Bruckner, S. Meille, S. Petraccone, V. Pirozzi, B. (1991) Polymorphism in Isotactic Polypropylene. Prog. Polym. Sci. 16, No.2-3, pp.361-404 Bryning, M. Islam, M Kikkawa, J. Yodh, A. (2005) Very Low Conductivity Threshold in Bulk Isotropic Single-Walled Carbon Nanotube-Epoxy Composites. Ado. Mater. Vol.17, N0.9, pp.1186-1191... 

Table 4.5 Typical Properties of Polypropylene-based Elastomers...

The most important commercial thermoplastic elastomers are based on polypropylene (PP) and ethylene-propylene-diene monomer (EPDM) elastomer (see Ethylene-Propylene Elastomers). The diene portion of the elastomer is cross-linked, frequently by dynamic vulcanization, ie, chemical cross-linking during melt shearing. 

All commercial polymers are compounds that have additives primarily intended as stabilizers. These additives protect the polymer from oxygen, heat, and other aspects of the environment. Many available polymer products are compounds that involve a wide range of ingredients, including commercial products such as polypropylene-based thermoplastic elastomers, polyvinyl chloride pipes, mineral-filled polypropylene, and pneumatic tire components. These compounds contain not only stabilizers but also other polymers, fillers, oils, curatives, accelerators (for curatives), and other ingredients. 

A manufacturer considering using a thermoplastic elastomer would probably first consider one of the thermoplastic polyolefin rubbers or TPOs, since these tend to have the lowest raw polymer price. These are mainly based on blends of polypropylene and an ethylene-propylene rubber (either EPM or EPDM) although some of the polypropylene may be replaeed by polyethylene. A wide range of blends are possible which may also contain some filler, oil and flame retardant in addition to the polymers. The blends are usually subject to dynamic vulcanisation as described in Section 11.9.1. 

Antony P., Bandyopadhyay S., and De S.K., Thermoplastic elastomers based on ionomeric polyblends of zinc salts of maleated polypropylene and maleated EPDM rubber, Polym. Eng. Sci., 39, 963, 1999. Weiss R.A., Sen A., Pottick L.A., and Willis C.L. Block copolymer ionomers. Thermoplastic elastomers possessing two distinct physical networks, Polym. Commun., 31, 220, 1990. 

Tullock C.W. et al.. Polyethylene and elastomeric polypropylene using alumina-supported bis(arene) titanium, zirconium, and hafnium catalysts, J. Polym. Sci, Part A, Polym. Chem., 27, 3063, 1989. Mueller G. and Rieger R., Propene based thermoplastic elastomers by early and late transition metal catalysis. Prog. Polym. Sci., 27, 815, 2002. 

Medintseva, T.I., Dreval, V.E., Erina, N.A., and Prut, E.V., Rheological properties thermoplastic elastomers based on isotactic polypropylene with an ethylene-propylene-diene terpolymer, Polym. Sci. A, 45, 2032, 2003. 

Ismail, H. and Suryadiansyah, S., Thermoplastic elastomers based on polypropylene/natural rubber and polypropylene/recycle rubber blends. Polymer Test., 21, 389, 2002. 

Microstructure-property correlations in dynamically vulcanized thermoplastic elastomers based on polypropylene (PP)/EPDM have shown that clay was nearly exfoliated and randomly distributed into the continuous polypropylene phase [23]. SEM photomicrographs revealed that the size of rubber particles increased with clay incorporation. Also, the clay layers act as nucleating agents, resulting in higher crystallization temperature and reduced degree of crystallinity. 

The Ziegler-Natta catalysts have acquired practical importance particularly as heterogeneous systems, mostly owing to the commercial production of linear high- and low-density polyethylenes and isotactic polypropylene. Elastomers based on ethylene-propylene copolymers (with the use of vanadium-based catalysts) as well as 1,4-cz s-and 1,4-tran.y-poly(l, 3-butadiene) and polyisoprene are also produced. These catalysts are extremely versatile and can be used in many other polymerisations of various hydrocarbon monomers, leading very often to polymers of different stereoregularity. In 1963, both Ziegler and Natta were awarded the Nobel Prize in chemistry. 

On the other hand, it is not always necessary that an interfacial agent be present. Polypropylene is available in impact-modified grades which are made by simply blending polypropylene with suitable olefin-based elastomers. Most often the elastomer is a suitably chosen ethylene-propylene-based rubber. Evidently, the required adhesion develops naturally in these systems without the need for an interfacial agent. However, proper control of phase morphology during mixing is essential. 

They are based on various metals. Such as zirconium, complexed with cyclopentadienide anions. This type of compound is called a zirconocene and is used with organoalu-minum to make highly regular polymers. The catalyst has the ability to flip back and forth from making atactic to isotactic polypropylene in the same polymerization. The alternating tacticity of the polymer breaks up the crystallinity of the chains and yields an elastomer. Metallocene catalysts are currently very expensive and cannot yet polymerize dienes such as butadiene, so they have only enjoyed limited commercial success in elastomers. However, this is one of the most intense fields of polymer research and many new product breakthroughs are expected in the near future. 

Polyolefin based thermoplastic elastomers are either made by reactor copolymerization or physical blending of crystalline polypropylene with EPDM in an extruder under conditions where the optimum level of chemical crosslinking of the EPDM phases could be promoted. 

IPDI-based prepolymer. This is an aliphatic prepolymer formed by the reaction of IPDI with polyether polyol (3000 molecular weight PPO-based triol) (PPG = polypropylene oxide). The NCO group content of such systems is about 3.4%, and the viscosity about 15 000 CP at 20°C. Solid content is typically 98%-100%. The general reaction is given in Figure 2.22. This prepolymer may typically be used in two-part elastomer systems. 

Composition (type of polymeric components). The base polymer (which is to be modified) may be an amorphous polymer [e.g., polystyrene (PS), styrene-acrylonitrile copolymer, polycarbonate, or poly(vinyl chloride)], a semicrystalline polymer [e.g., polyamide (PA) or polypropylene (PP)], or a thermoset resin (e.g., epoxy resin). The modifier may be a rubber-like elastomer (e.g., polybutadiene, ethylene-vinyl acetate copolymer, ethylene-propylene copolymer, or ethylene-propylene-diene copolymer), a core-shell modifier, or another polymer. Even smaller amounts of a compatibilizer, such as a copolymer, are sometimes added as a third component to control the morphology. 

The abrasion loss of PU elastomers is markedly improved with the MW increase of the oligo-glycol. PU elastomers based on polytetramethylene glycols and on polyfethylene adipate) glycols have the lowest abrasion loss. Polypropylene glycols (obtained in anionic catalysis) lead to PU elastomers with poorer abrasion resistance [2],... 

Polypropylene Blends The majority of papers related to the crystallization of isotactic polypropylene, PP, based blends concern those where the PP matrix crystallizes in the presence of a molten dispersed phase of polyethylenes and olefinic elastomers. As a result, crystallization of a PP matrix in the presence of a solidified dispersed polymer has seldom been reported [Nadkarni and Jog, 1991]. 

The choice of date range is arbitrary. The number of journal articles for each year was obtained from a search of electronic version of English-based polymer and polymer-related journals using the keywords polyolefin and blends. Within polyolefin keyword, the subkeywords used in the search were polyethylene (PE, LLDPE, LDPE, HDPE, UHMWPE, PE, etc.), polypropylene (PP, iPP, sPP, aPP, etc.), polybutene-1, poly-4-methylpentene-l, ethylene-diene monomer, ethylene-propylene-diene terpolymer, ethylene propylene rubber, thermoplastic olefins, natural rubber (NR), polybutadiene, polyisobutylene (PIB), polyisoprene, and polyolefin elastomer. For the polyolefin blends patent search, polymer indexing codes and manual codes were used to search for the patents in Derwent World Patent Index based on the above keywords listed in the search strategy. 

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