Copolymers Containing Ethylene

In terms of processing there is no need for pre-drying PCHE granules, a standard extruder screw as used for polycarbonate may be used and discs are said to release well from the mould. Question marks remain on the oxidative stability of the polymer and on the quality of adhesion of the reflective layer but Dow claim that metallising is possible. 

Many monomers have been copolymerised with ethylene using a variety of polymerisation systems, in some cases leading to commercial products. Copolymerisation of ethylene with other olefins leads to hydrocarbon polymers with reduced regularity and hence lower density, inferior mechanical properties, lower softening point and lower brittle point. 

Two random copolymers of this type are of importance, ethylene-propylene copolymers and ethylene-but-l-ene copolymers. The use and properties of polypropylene containing a small quantity of ethylene in stereoblocks within the molecule has already been discussed. Although referred to commercially as ethylene-propylene copolymers these materials are essentially slightly modified polypropylene. The random ethylene-propylene polymers are rubbery and are discussed further in Section 11.9. 

The Phillips process for the manufacture of high-density polyethylene may be adapted to produce copolymers of ethylene with small amounts of propylene or but-l-ene and copolymers of this type have been available since 1958. These soon found application in blown containers and for injection moulding. Properties of two grades of such copolymers are compared with two grades of Phillips-type homopolymer in Table 11.11. 

From this table it will be noted that in terms of the mechanical and thermal properties quoted the copolymers are marginally inferior to the homopolymers. They do, however, show a marked improvement in resistance to environmental stress cracking. It has also been shown that the resistance to thermal stress cracking and to creep are better than with the homopolymer.This has led to widespread use in detergent bottles, pipes, monofilaments and cables. 

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Copolymers Containing Ethylene 277 Table 11.12 Typical properties of three olefin-ester copolymers... 

How would you design a copolymer containing ethylene that is more transparent, heat seals better, and is more permeable to water than LDPE ... 

Diamanti, S.J., Khanna, V., Hotta, A. etal. (2006) Tapered block copolymers containing ethylene and a functionalized comonomer. Macromolecules, 39, inQ- illA. 

Another self-assembhng butadiene-based system is the near-random copolymer containing ethylene and butene segments. The crystallinity can be tuned by the number of ethyl branches in the chain. For the series PEB-2 to PEB-12 the samples exhibit decreasing crystallinity while the PEB-13 to PEB-50 materials are wholly amorphous. The random PEB copolymers self-assemble to yield modulated rod-Hke structures. If the self-assembly event... 

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. 

Nguyen, V.P.N., Kuo, N.Y, Loh, X.J. New biocompatible thermogeUing copolymers containing ethylene-butylene segments exhibiting very low gelation concentrations. Soft Matter 7,2150-2159(2011)... 

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