Polyacrylamide and its derivatives for oil recovery

Table I. 
Measured Swelling Properties of Microgels Dispersed in DI water
 
The average molecular weight, 
M
c
between crosslinks calculated according to the 
Flory-Rehner equation from swelling ratios and theoretical 
M
c
*
calculated through 
feeding amount are listed in Table 1. At low temperature, the swelling of microgel is 
controlled by two crosslinkers, MBAM and PEGDA. Through comparing 
M
c
 and M
c
*
, 
the efficiency of crosslinkers was 79.1% of theoretical. After high temperature stimuli, 
the swelling of the microgel was intended to be controlled by the quantity of thermally 
stable crosslinker (MBAM). However, the efficiency of the MBAM crosslinker was 
observed to be only 10.2%.
At high temperature, either only a portion of MBAM crosslinks were effective or 
additional swelling was observed due to polymer chain degradation
50,51
and/or hydrolysis 
of acrylamide groups to acrylic acid, changing 

1
. A six-carbon ring degradation structure 
was detected in polyacrylamide hydrogel exposed to the higher temperature by mass 
spectra, which indicated imidization with breaking of the polymer backbone. It should be 
noted that swelling expansion did not completely stop during the higher temperature 
Microgel Sample 
Swelling 
Ratio (S) 
Mc (g/mol) 
Mc* 
(g/mol) 
Crosslinker 
efficiency 
Aqueous, 40 ºC 
18 
8.24 x 104 
6.69 x 104 
79.1% 
Aqueous, 80 ºC 
150 
4.58 x 106 
4.67 x 105 
10.2% 

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155 
observation. Hydrogels at 80 º
C eventually dissolved as particle-solvent boundaries 
became blurred further supporting polymer chain degradation.