Semicrystalline PP

With MAO activation, Zr- and Hf-FI catalysts 1 and 3 exhibit fairly high reactivity toward propylene and produce propylene oligomers [64, 65], Conversely, the corresponding Ti-FI catalyst/MAO 2 forms semicrystalline PP (1 °C polymerization), which displays a peak melting temperature of 97 °C, indicative of the formation of a stereoregular polymer. To our surprise, microstructural analysis by 13C NMR indicates that the resultant polymer is syndiotactic (rr 19%), and that a chain-end control mechanism is responsible for the observed stereocontrol, regardless of the C2 symmetric catalyst ([28] for the first report on syndiospecific propylene... 

Fig. 39 a. Schematic comparison of the deformation processes in crazes and shear bands. Corresponding fracture surfaces are shown in b for amorphous PS and in c for semicrystalline PP (craze) and PB-1 (shear band)... 

PSF with 25-45 wt% semicrystalline PPS and 0-10 wt% MBS resistance to impact, high temperatures, and adverse enviromnental crmditions Golovoy and Cheung 1994... 

Polypropylene (PP) is a thermoplastic material that is produced by polymerizing propylene molecules, which are the monomer units, into very long polymer molecules or chains. There are a number of different ways to link the monomers together, but PP as a commercially used material in its most widely used form is made with catalysts that produce crystallizable polymer chains. These give rise to a product that is a semicrystalline solid with good physical, mechanical, and thermal properties. Another form of PP, produced in much lower volumes as a byproduct of semicrystalline PP production and having very poor mechanical and thermal properties, is a soft, tacky material used in adhesives, sealants, and caulk products. The above two products are often referred to as isotactic (crystallizable) PP (i-PP) and atactic (noncrystallizable) PP (a-PP), respectively. 

Semicrystalline PP is a thermoplastic material containing both crystalline and amorphous phases. The relative amount of each phase depends on structural and stereochemical characteristics of the polymer chains and the conditions under... 

El-Naggar et al. [84] have studied the effect of electron-beam irradiation on the thermal and mechanical properties of PPS. The dose rate was 50Mrads/sec and the maximum dose was 4000Mrads. They observed a decrease in crystallinity of PPS with increasing dose. Also, it was observed that the effect was more pronounced for the initially amorphous PPS than initially semicrystalline PPS, suggesting a lower radiation resistance of the amorphous phase. 

Impact copolymers, also known as heterophasic copolymers or rTPOs, usually contain up to about 40% ethylene-propylene rubber (EPR), distributed inside the semicrystalline PP homopolymer matrix. This copolymer phase is added to increase the impact strength of the product at low temperatures. As a result of its glass transition temperature the impact strength of polypropylene homopolymer is often unacceptable for use in low temperature applications, such as packaging or automotive applications. 

The conclusions drawn by Maiti and Okamoto (2003) are reminiscent of the conclusions drawn from Figure 12.22 in that use of CaC03 treated with silane or titanate coupling agents as a filler in PP affected the morphology and crystallization rate of semicrystalline PP during melt blending and consequently enhanced the mechanical properties of the composites (Han et al. 1981). 

Some peaks in Fig. 5.4 are difficult to analyze. They are encircled by dotted lines. These peaks result from sandwich domain size distributions hcac (r lz, ) that overlap severely with the strong and narrow meridional disffibutions. Therefore an analysis would require to separate these peaks from the meridional disffibutions by fitting the complete CDF patterns with a three-dimensional model of the semicrystalline PP nanostracture. The CDFs exhibit that such a model would have to be rather complex. 

Figure 5.7 shows the evolution of the scattering power Q of the semicrystalline PP as a function of strain. The curves are normalized to constant irradiated volume and constant flux. Thus... 

Poly(phenylene sulfide) (PPS) is another semicrystalline polymer used in the composites industry. PPS-based composites are generally processed at 330°C and subsequently cooled rapidly in order to avoid excessive crystallisation and reduced toughness. The superior fire-retardant characteristics of PPS-based composites result in appHcations where fire resistance is an important design consideration. Laminated composites based on this material have shown poor resistance to transverse impact as a result of the poor adhesion of the fibers to the semicrystalline matrix. A PPS material more recently developed by Phillips Petroleum, AVTEL, has improved fiber—matrix interfacial properties, and promises, therefore, an enhanced resistance to transverse impact (see PoLYAffiRS containing sulfur). 

Poly(phenylene sulfide). Poly(phenylene sulfide) (PPS) is a semicrystalline thermoplastic with a T of 85°C and a of 285°C. The nominal... 

Drbscher, M. Solid State Extrusion of Semicrystalline Copolymers. Vol. 47, pp. 120-138. 

Drobnik, J. and Rypalek, F. Soluble Synthetic Polymers in Biological Systems. Vol. 57, pp. 1-50. Droscher, M. Solid State Extrusion of Semicrystalline Copolymers. Vol. 47, pp. 120-138. 

This equation is not particularly useful in practice, smce it is difficult to quantify the relationship between concentration and activity. The Elory-Huggins theory does not work well with the crosslinked semicrystalline polymers that comprise an important class of pervaporation membranes. Neel (in Noble and Stern, op. cit., pp. 169-176) reviews modifications of the Stefan-Maxwell approach and other equations of state appropriate for the process. 

RF Ofstead, Cl Posner. Semicrystalline poly(vinyl alcohol) hydrogels. In J Glass, ed. Polymers in Aqueous Media. Washington, DC American Chemical Society, 1989, pp 61-72. 

Anantawaraskul, S., Soares,. B. P. and Wood-Adams, P. M. Fractionation of Semicrystalline Polymers by Crystallization Analysis Fractionation and Temperature Rising Elution Fractionation. Vol. 182, pp. 1-54. 

Auriemma, F., deRosa, C. and Corradini, P. SolidMesophases in Semicrystalline Polymers Structural Analysis by Diffraction Techniques. Vol. 181, pp. 1-74. 

Graphite/ Thermo- plastic AS4/PPS Phillips Petroleum Phillips Petroleum Polyphenylene sulfide, semicrystalline thermoplastic... 

As discussed above, many polymers contain some crystalline structures when they are solidified. These polymers are referred to as semicrystalline resins. These crystalline structures can be observed using microscopy as shown in Fig. 2.12 for PP and sPS resins. As shown schematically in Fig. 2.13 and discussed above, not all portions of the polymer chains are incorporated into the crystalline structure. Instead, the portions of the chains that are not crystallized make up the amorphous phase. Solid density is the most commonly used method for measuring the... 

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