Ethylene-hexene statistical copolymer

Figure 1L8 Weight fraction crystallinity Wc) as a function of time (t) for isothermal crystallization at various temperatures indicated (in °C), for an ethylene-hexene statistical copolymer (a), and hydrogenated polybutadienes of varying branch content (b-d). Lines at left in each panel reflect Avrami exponents, n = 2 or 3. Reprinted with permission from Reference [69]. Copyright 1991 American Chemical Society.

In a similar study by Cheng [32] on ethylene/1-butene copolymers, a two-site model was also invoked. In contrast, he found that the microstructure of ethylene/1-hexene copolymers could be described adequately using a one-site first-order Markov model [33]. Regio-irregularity in polypropylene has also been treated by Cheng using Markov statistics (see [5] and references therein). 

Using Table 2.6, calculate the run numbers and average sequence lengths for the two poly(ethylene-.stflt-l-hexene) copolymers. Do they indeed appear to be statistical copolymers ... 

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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