The mechanism for the free-radical polymerization of ethylene shown in Eqs. 5.72a–c (pp. 217–218) is somewhat simplified because it does not account for the observation that low-density polyethylene (LDPE) contains a significant number of branched chains. (The branching accounts for the low density of LDPE.) It is believed that the first step that leads to branching is an internal hydrogen abstraction reaction that occurs within the growing polyethylene chain, shown in Fig. P5.45.

(a) Use bond dissociation energies to show that this process is energetically favorable.

(b) Show how this reaction can lead to a branched polyethylene chain.

Transcribed Image Text:

H SCH -(CH₂CH₂) CH₂ Figure P5.45 H₂C. CH₂ CH₂ -CH₂ -(CH₂CH₂)CH₂ CH H₂C CH₂ CH₂ T CH₂