Chemistry Reference
In-Depth Information
Fig. 6.1
Illustration of a
tubular reactor
Polyethylene prepared in this way may have as many as 20-30 short branches per 10,000 carbon
atoms in the chain [
9
] and one or two long-chain branches per molecule, due to “backbiting” [
10
]
(explained in Chap.
3
):
CH
2
The reaction results in predominantly ethyl and butyl branches. The ratio of ethyl to butyl groups is
roughly 2:1 [
11
,
12
]. Chain transferring to the tertiary hydrogens at the location of the short branches
causes elimination reactions and formation of vinylidene groups [
13
,
14
]. This mechanism also
accounts for formation of low molecular weight species.
+
R
+
RH
C
3
H
7
Commercial grades of low-density polyethylene vary widely in the number of short and
long branches, average molecular weights, and molecular weight distributions.
M
w
/
M
n
is
