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O
O
O
O
O
O
•
H
H
•
O
O
O
O
R
•
O
O
β
-scission
RH
H
•
+
+
Scheme 9.2 Mechanism for formation of the graft 4.
Reproduced from ref. 27 with permission of Elsevier.
and propylene units in the polymer.
28
Notably, only single succinic an-
hydride rings (5) on tertiary carbons are observed in poly(ethylene-alt-pro-
pylene). For poly(ethylene-stat-propylene) with a molar ratio of ethylene/
propylene Z1, the grafts are assigned to the structures of 1 and 5. On the
other hand, poly(ethylene-stat-propylene) with a molar ratio of 1 : 3 has more
variable grafts, and the assigned grafts are the structures 3 and 4 as well as
1 and 5, with the former two being observed for i-PP.
9.4.2 Mechanochemical Grafting of Maleic Anhydride onto
Polypropylene
Free-radical grafting of maleic anhydride (MA) onto polyolefin starts with
formation of macroradicals through hydrogen abstraction by primary rad-
icals. The resultant macroradicals, which are mostly secondary and tertiary
carbon radicals for PE and PP respectively, cause not only reaction with MA
monomers resulting in their grafting but also side reactions. The main side
reaction is a recombination for PE, while for PP b-scission generates frag-
ments with the secondary carbon radical and the terminal isopropenyl
group. Ecient grafting of MA monomers onto polyolefin requires sup-
pression of such side reactions causing changes in the molecular chain
structure from that of the original polymer. Increasing temperature is
favorable not only for formation of macroradicals from PP but also for
b-scission of the macroradicals leading to degradation of the PP. Grafting of
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