Isotactic propylene-pentene

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).

Isotactic poly(4-methyl-l -pentene) Ethylene/isotactic propylene block (compact) copolymers (polyallomers)... 

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,... 

Kiang et al.44 have studied the thermal cracking of both isotactic and atactic propylene, observing that isotactic PP degrades faster than atactic PP. Conversions of the isotactic PP of over 80% were obtained at 414 °C in less than 20 min, which leads to the formation of gases and liquids in an approximate ratio of 30/70 wt%. Whereas the gases contained a high proportion of propylene, the liquid fraction consisted mainly of branched olefins such as 2-methyl- 1-pentene, 2,4-dimethyl-1-heptene and 2,4,6-trimethyl-1-nonene. 

As noted above, even if monomer addition to the growing species is highly enantioface-selective in an isotactic-spedfic polymerization, the resulting isotaaic polymer is configurationally achiral except for the chirality of the stereocenters in the vicinity of the chain terminal. Related examples have been reported for coordination oligomerization and polymerization of propylene, f-pentene, and 4-methyl-f-pentene with optically active zirconocene catalysts and for radical... 

Polymer tacticity was also assayed by using compound 43 as a precatalyst for polymerization. The prediction for 43 was that it would behave like an achiral, Ci-symmetric system (vide supra). This prediction was borne out by using 43 as a precatalyst for polymerization of neat propylene a predominately syndiotactic polymer was formed with [r] = 91.5%. Pertinent tacticity data appears in Table 4.2. However, when 43 is used to polymerize 3-methyl-1-pentene, the resulting polymer is predominantly isotactic (similar to the results from precatalyst 41a). Quantitative tacticity data was not given. 

When propylene or another prochiral 1-olefin is replaced by a chiral 1-olefin such as 3-methyl-1-pentene the stereochemical analysis becomes more complicated. However, when starting with a pure enantiomer the same definition of an isotactic polymer can be valid as for polypropylene, with the additional restriction that all monomeric units have in the side chain an asymmetric carbon atom of a single absolute configuration (Fig. 3). 

This parameter characterizes the fraction of propylene links in isotactic sequences with a length of 11-13 monomer units. The content of 1-butene was estimated from the ratio of bands at 760 and 1460 cm" the content of 1-pentene, from the band at 740 cm". ... 

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. ... 

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