Poly long branched chains

Poly(macromonomers) with moderately long side chains attached to every few (second) atom along the backbone are very densely branched polymers. When the degree of polymerization of the backbone is low then the poly(macromon-mers) tend to resemble star polymers [39, 40]. When the degree of polymerization is very high the poly(macromonomer) acquires a cylindrical conformation (bottlebrush), due to the stretching and linearization of the backbone [40]. 

Chain branching is a common occurrence during radical polymeriza ] tions and is not restricted to poiyethyiene. Polypropylene, polystyrene, andt poly(methyl methacrylate) all contain branched chains. Studies have shown that short-chain branching occurs about 50 times as often as long-chain branching. 

In this chapter the solid state extrusion of different grades of polyethylene is discussed. The term copolyethylene stands as well for short and long branched PE as for the nearly alternating 1 1 copolymer poly(ethylene-co-chlorotrifluoroethylene) (PECTFE). It is well known that even HOPE contains a certain amount of short branches. Therefore, it is of interest to note that already one butyl side group per thousand main chain carbom atoms effects the solid state extrusion properties of PE remarkably. 

Commercially available poly(vinyl chloride) contains small amounts of different abnormal structures (defects) which may originate from synthesis. Such groups are random unsaturation (allylic chlorines) [316, 317,710,956,957] chain end groups [2, 3, 357, 710, 955, 1431, 2052] branch points (tertiary-bonded chlorine atoms) [2,3, 319, 357, 995,1514,2052-2054] head-to-head units [3,309,357,710] and oxidized structures [3,317,357,700]. It has been estimated that the number of defects per 1000 monomer units in commercial poly(vinyl chloride) samples are [357] 4-6 chloromethyl branches, 0.4-2.4 chloroethyl branches, 0.4-1.6 butyl branches (value uncertain), 0.18-2.4 long branches (value uncertain), 6-7 head-to-head structures (values uncertain), 1.4-3 total double bonds and 0.08-0.27 internal double bonds. Labile chloride atoms have been estimated at 0.6-2.5 per 1000 monomer units of which 0.5-2.5 are allylic chlorine or ketochloroallylic chlorine and 0.16-1.0 are chlorine at tertiary carbon (value uncertain). The possible structures of these defects are given in Table 3.12. 

Less commonly used as third monomer is dicyclopentadiene [77-73-6] or DCPD, for which, due to its symmetrical shape, the tendency of the second double bond to take part in the polymeri2ation process is more pronounced than for ENB. This is one of the reasons for the formation of long-chain branches. The resulting product is poly(ethylene- (9-prop54ene- (9-DCPD) [25034-71-3]. 

Poly(olefins), long chain branching 1980s 1990s Elastomers, plastomers ... 

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