Polyolefins isotactic polypropylene

Polyolefins. The most common polyolefin used to prepare composites is polypropylene [9003-07-0] a commodity polymer that has been in commercial production for almost 40 years following its controlled polymerisation by Natta in 1954 (5). Natta used a Ziegler catalyst (6) consisting of titanium tetrachloride and an aluminum alkyl to produce isotactic polypropylene directly from propylene ... 

Blends of isobutylene polymers with thermoplastic resins are used for toughening these compounds. High density polyethylene and isotactic polypropylene are often modified with 5 to 30 wt % polyisobutylene. At higher elastomer concentration the blends of butyl-type polymers with polyolefins become more mbbery in nature, and these compositions are used as thermoplastic elastomers (98). In some cases, a halobutyl phase is cross-linked as it is dispersed in the polyolefin to produce a highly elastic compound that is processible in thermoplastic mol ding equipment (99) (see Elastomers, synthetic-thermoplastic). ... 

Aliphatic Polyolefins other than Polyethylene, and Diene Rubbers 11.1.4 Additives for isotactic polypropylene... 

Polypropylene block and graft copolymers are efficient blend compatibilizers. These materials allow the formation of alloys, for example, isotactic polypropylene with styrene-acrylonitrile polymer or polyamides, by enhancing the dispersion of incompatible polymers and improving their interfacial adhesion. Polyolefinic materials of such types afford property synergisms such as improved stiffness combined with greater toughness. 

Brosse et al. [41] modified isotactic polypropylene and other polyolefins by a cold plasma. In isotactic polypropylene, plasma treatment results in a polypropylene crystallization of paracrystalline or smectic form into a a-crystalline form. Further, the active films are susceptible to react with monomers in a postgrafting reaction. 

Similarly large anisotropies were later reported for highly emissive blends of alkoxy-substituted bis(phenylethynyl)benzene derivatives and polyolefins such as linear low-density polyethylene (LLDPE) and isotactic polypropylene (z-PP) [8,9]. The latter systems reach high levels of anisotropy at very low draw ratios, which is advantageous from a processing point of view. 

Abstract The fracture properties and microdeformation behaviour and their correlation with structure in commercial bulk polyolefins are reviewed. Emphasis is on crack-tip deformation mechanisms and on regimes of direct practical interest, namely slow crack growth in polyethylene and high-speed ductile-brittle transitions in isotactic polypropylene. Recent fracture studies of reaction-bonded interfaces are also briefly considered, these representing promising model systems for the investigation of the relationship between the fundamental mechanisms of crack-tip deformation and fracture and molecular structure. 

Table I shows the production of different kinds of polyolefins [high-density polyethylene (HDPE), low-density polyethylene (LDPE), isotactic polypropylene (PP), and linear low-density polyethylene (LLDPE)] (6). Apart from LDPE (discovered by workers at ICI), which has a highly branched structure and is produced in free radical reactions at ethylene pressures of 1000-3000 bar (1 bar = 105 Pa), the other polyolefins are synthesized at far lower pressures and in the presence of catalysts (7).

This is often conducted to make impact-resistant polyolefin blends. For this purpose, isotactic polypropylene, which is tough but somewhat brittle, is produced on the catalyst pellet in a first reaction step, using highly active stereospecific... 

A further breakthrough was the synthesis of enantiomeric sterorigid ansa-metallocenes by Brintzinger and co-workers [33] and the discovery by Ewen [34] that such racemic metallocene/methylalumoxane systems generate isotactic polypropylene. It was further found that the metallocene structure determines the polymer structure [35-37]. Again, with these compounds polyolefins such as syndiotactic polypropylene become available on a large scale [38]. Indeed, metallocene/methylalumoxane catalysts offer new prospects for olefin oligomers and polymers [39 2],... 

The phase diagram of polyolefins and hydrocarbon diluents is exemplified for high-density polyethylene in Figure 1. When the polymer-diluent mixture is heated, dissolution of the semicrystalline polymer takes place along the borderline 1 (turbidity curve) [43, 44], This line depends on the polymer (e. g., polyethylene, isotactic polypropylene), average chain length, and copolymer composition. 

Fig. 4.8 (a) Histograms of pull-off force values obtained with an unmodified Si3N4 tip on untreated and oxyfluorinated iPP films in ethanol. The total surface free energy y of the polymer film is shown, (b) Mean values of pull-off force measured with COOH-terminated tips on modified polyolefin surfaces (iPP, isotactic polypropylene LDPE, low-density polyethylene) in ethanol (top) and with OH-terminated tips on oxyfluorinated iPP in water (pH 3.8, bottom) as a function of cos 0 (contact angle measured with water). (Reprinted in part/adapted with permission from [26, 27]. Copyright 1998, 2000, American Chemical Society.)... 

Piperazine HALS 2 is a colorless crystalline solid which melts at 134-6°C. It is a powerful UV stabilizer for polyolefins as illustrated in the outdoor aging data in isotactic polypropylene tapes. 

Polypropylene is a polyolefin found in high concentrations in the plastic waste stream. Of the different types of PP, isotactic polypropylene is the one most widely used on a commercial scale and so is the type predominant in plastic wastes. Compared to PE, the backbone of the PP molecule is characterized by the presence of a side methyl group at every second carbon. This fact implies that half of the carbons in a PP chain are tertiary carbons and so, as a consequence of their higher reactivity, PP is thermally degraded at a faster rate than PE. Thus, as can be seen in Figure 4.7, the PP weight loss in TGA measurements starts at a lower temperature compared to both HDPE and LDPE. 

There have been extensive applications of isotactic polypropylene (iPP)/EPM blends. These were used to produce rubber toughened polypropylene blends and subsequently polyolefin thermoplastic elastomers (88,89). Most commercial EPMs contain more than 50 mol% of ethylene, and these are elastomers. The solubility parameter of EPM should be intermediate to those of polyethylene and polypropylene dependent on ethylene content. Thus, it is often used to compatibilize PE/PP blends (90,91). 

BLENDS OF POLYOLEFINS (HIGH DENSITY POLYETHYLENE AND ISOTACTIC POLYPROPYLENE) WITH A SEMIFLEXIBLE LIQUID CRYSTALLINE POLYMER... 

Processes of ethene/a-olefin copolymerization are of great practical importance. Copolymerization of ethene with small amounts of highest a-olefins (1-butene, 1 -hexene, 1 -octene) allows one to produce linear low density polyethylene (LLDPE), which is one of the most widely used large-scale polyolefin products. Polypropylene, modified with small amounts of ethene, exhibits higher impact strength compared to isotactic homopolypropylene. Copolymerization of propene with large amounts of ethene and terpolymerization of ethene/propene/diene result in amorphous elastomer materials (rubbers) [103]. 

Wong WS (2012) Application of high temperature chromatographic and viscometric techniques for the characterization of highly isotactic polypropylene samples. In Proceedings 4th international conference on polyolefin characterization, Houston, October 2012... 

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... 

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