Isotactic propylene-hexene

Isotactic propylene/1-hexene co-polymers have received the most attention 1-hexene has been found to be more efficient than butene in lowering the melting point of the co-polymer840,847 (see Figure 35), and their structure and physical properties have been investigated.8... 

The crystallinity of propylene-1-butene copolymers changes to a much smaller extent with an increase in the amount of the comonomer relative to the copolymers of another type (propylene-ethylene, propylene-hexene, propylene-octene). This tendency is consistent with the published data, which shows that 1-butene slightly affects the crystallization of the isotactic PP owing to its cocrystallization with propylene in a wide range of copol5mier compositions.The incorporation of 1-pentene entails a more efficient reduction in the degree of crystallinity than the incorporation of 1-butene. 1-pentene, like 1-butene, may undergo cocrystallization with propylene molecules in PP chains. At the same time, 1-hexene and 1-octene are incorporated into pol mier chains in the form of lattice defects, and thus ensure disorder that causes more distinct decreases in T and crystallinity of pol miers. ... 

Figure 2.16 X-ray powder diffraction profiles of samples of isotactic propylene-pentene (a) [105] and propylene-hexene (b) [103,104] random copolymers with the indicated concentration of comonomeric units in comparison with those of the a form of iPP and form I of iPB. The 110, 040, and 130 reflection of the a form of iPP and the (llO)i, (300)i, and (220 -H 211)i reflections of the form I of iPB are indicated. Reproduced from References [105] (a) and [103] (b) with permission from American Chemical Society, Copyright 2007 (a) and 2006 (b).

A scandium complex, Cp ScH, also polymerizes ethylene, but does not polymerize propylene and isobutene [125]. On the other hand, a linked amidocyclo-pentadienyl complex [ Me2Si( / 5-C5 Me4)( /1 -NCMe3) Sc(H)(PMe3)] 2 slowly polymerizes propylene, 1-butene, and 1-pentene to yield atactic polymers with low molecular weight (Mn = 3000-7000) [126, 115]. A chiral, C2-symmetric ansa-metallocene complex of yttrium, [rac-Me2Si(C5H2SiMe3-2-Buf-4)2YH]2, polymerizes propylene, 1-butene, 1-pentene, and 1-hexene slowly over a period of several days at 25°C to afford isotactic polymers with modest molecular weight [114]. 

Propylene has been co-polymerized with a broad set of higher olefins to isotactic co-polymers, including 1-pen-tene, 4-methyl-1-pentene, 1-hexene, 1-heptene, 1-octene,... 

As discussed earlier, ethylene propylene rubber (EPR or EPM) has been blended with PP and PE to improve the impact strength and to render the materials softer. Recently, metallocene catalysts or postmetallocene catalysts provide new pathways to generate elastic copolymers that can replace EPR. These pathways possess cheaper manufacturing cost and generate new materials with better compatibility to PP or PE. Such new materials included ethylene-propylene random copolymers with dominant ethylene component (33-34) or propylene-dominant component (35 1), propylene-ethylene block copolymer (42), ethylene-octene copolymer (43), poly(propylene-co-ethylene) (44), ethylene-hexene copolymer (45), ethylene-butene copolymer (46), low isotactic PP (47), and stereoblock PP (48). These materials are generally compatible with PP or PE, thus can be used to tailor the toughness (or the softness) of... 

Thermoplastic olefin (TPO) compositions typically consist of an immiscible blend of an isotactic polypropylene mixed with a polyolefin elastomer that acts as an impact modifier. It is possible to toughen these compositions further by using ethylene-propylene, ethylene-octene or ethylene-hexene impact modifiers. 

Coordination polymerization also produces high sterospecificity in the polymerization of alkenes. Isotactic and syndiotactic polymers can be obtained by appropriate choice of the catalyst components although such polymers are not useful as elastomers. However, Ziegler-Natta catalysts are used to produce EPR and EPDM rubbers. (Coordination polymerization is important for the synthesis of linear polyethylene and isotactic polypropylene which find extensive utility as plastics.) The Symposium paper by Su and Shih describes the synthesis of propylene-l-hexene block copolymers using several catalysts based on titanium and aluminum components. 

Similarly, in statistical isotactic polypropylene copolymers containing ethylene or butene counits, a mixture of a monoclinic and y orthorhombic [52-54] crystal phases was observed, and the proportion of the /form increased with increasing counit concentration [25, 47, 55, 56]. The /form is typically observed in propylene homopolymers when crystallized under high pressure [57,58]. In the case of copolymers, the presence of non-crystallizable counits disrupts the development of polypropylene helices, resulting in an increase in the / phase content [25, 47, 55, 56]. The /phase was also observed in isotactic copolymers of propylene and 1-hexene [59]. Additionally, propylene copolymers that contain 10-25 mol% hexene units were found to crystallize in a crystal form having a trigonal unit cell [60, 61]. This structure is isomorphous to that of poly(l-butene), which. 

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