Polyacrylamide and its derivatives for oil recovery

Figure 8. 
The sketch of a cross-linked network formation by ionic bonds using the 
multivalent ion Cr (III) as example. 
 
Alternatively, multivalent metal cations of Cr (III), Al(III), Zr(IV), Fe(III), or 
Ti(IV) and similar cations can serve as the central ion of a chelation complex.[198] The 

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40 
inorganic salts of these ions are capable of forming polynuclear olation and coordinate 
covalent complex ions, which can coordinate and crosslink with carboxyl and acylamino 
groups of partially hydrolyzed PAM. Chelation cross-linked gels have the potential to 
develop bulk gels with higher strengths and reduced sensitivities to monovalent ions.
Additionally, to improve the material properties by introducing clay and several 
inorganic is a hot pot in the progress of material science recently. To make hybrid 
polyacrylamide with higher mechanical property, temperature and salt resistance 
becomes a target in gel treatment. Direct covalent bond networks can be formed by 
reacting the –CONH
2
in PAM chains through dehydration. Covalent crosslinking 
monomer molecules must then contain an functional group equivalence of at least two, 
such as formaldehyde (see Figure 9), multifunctional phenolic compounds,[199-201] 
phenol-formaldehyde resin,[202-204] urea-formaldehyde resins,[205, 206] and 
malondialdehyde, etc. These gels have higher thermal and oxidative resistance due to the 
increased stability of the covalent bond in comparison to associative bonding 
arrangements.
PAM chain
PAM chain
C
O
N
H
CH
2
C
O
NH
C
O
N
H
CH
2
C
O
N
H
Figure 9. 
Sketch of a cross-linked network structure formed by covalent bonds using 
formaldehyde as example.
 

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41 
Organic crosslinking can also be obtained by copolymerization with 
multifunctional organic monomers, i.e., with more than a single C=C double bond, such 
as polyethylene glycol diacrylate (see Figure 10),[180] polyethylene glycol 
dimethacrylate, polypropylene glycol diacrylate, ethyleneglycol diacrylate, 
trimethylolpropane trimethacrylate, ethoxylated trimethylolpropane triacrylate, 
ethoxylated pentaerythritol tetraacrylate,N,N’-methylenebisacrylamide[207] and 
analogous derivatives.[208, 209] The multiple telechelic double bonds make them be 
capable to react with the AM monomer and participates the radical polymerization in 
more than one growing polymer chain resulting in the oligomer forming a crosslink 
between two growing chains and, overall, a network structure. Recently, micro-gels as 
products have been applied in the EOR field and cross-linkers appear to be mostly this 
type.[209, 210] 
C
H
2
O
O
CH
2
O
O
n
C
H
2
C
NH
2
O
PAM chain
PAM chain
O
O
O
O
n
O
O
O
O
n
+
small amount(PEGDA)
main monomer(AM)
crosslinked structure