Ethylene branching

For certain monomers such as vinyl acetate and ethylene, branching is much more significant. The free-radical (high-pressure) polymerization of low-density polyethylene (LDPE) includes a back-biting internal chain-transfer reaction that results in the formation of a short branch. It is this branching that results in an upper limit for the crystallinity of LDPE of about 60%-70% and a melt temperature of 110 C the backbiting reaction preferentially occurs with the formation of an intramolecular six-membered ring that results in preferential formation of a C4 short-chain branch as shown in Scheme 1.41. 

FIG. 18 Bakhuis-Roozeboom p T) projection for the system ethylene/branched polyethylene. Heavy curves are based on experimental data, light curves are estimations. Triple point polyethylene A three-phase equilibria solid PE/liquid 6/vapor, S2IIIV, liquid a/liquid 6/vapor, Q liquid/vapor (//v) critical point of ethylene C and C" critical end points critical... 

Poly(ethylene) (branched) vs. poly(propylene) (atactic) 1.1 - 17... 

The resonance lines at 39.38 and 37.86 are assigned to ethylene branches CHe and butyl, amyl, long chain branches (CHb + CHa + CHl), and Y-type branches (CHy) respectively. A new resonance line at 42.50 ppm produced by irradiation is assigned to the H-links (CHh). Table 7.4 shows the spectral assignments for the main components of unirradiated and irradiated LDPE samples. 

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