In the aqueous two-phase copolymerization of acrylamide (AM) with quaternary ammonium cationic monomers

such as 2-methylacryloylxyethyl trimethyl ammonium chloride (DMC)

in aqueous poly-(ethylene glycol) (PEG) solution a double phase separation process was observed.In order to fix the critical points

the spectrophotometer was employed to detect the transmittance of the copolymerization system on-line.The transmittance curves showed three intervals.At the first interval

the transmittance keeps constant at the beginning

and then drops off quickly.At the second interval

the transmittance stops dropping and begins to increase.And at the last interval

the transmittance stops to keep constant for a moment

and then drops rapidly to nearly zero.When acrylamide was copolymerized with different monomers

the double phase separation process can be observed only for DMC and acryloylxyethyl trimethyl ammonium chloride (DAC).It confirms that the double phase separation is attributed to the cationic nature of DMC and DAC.Then the mechanism of the double phase separation process of the aqueous two-phase copolymerization system was brought up.At the beginning of the aqueous two-phase copolymerization

the growth of copolymer chains is the key factor

so the 1st phase separation occurs when they achieve a critical length.With the copolymerization progressing

the DMC amount in the chains increases and the electrostatic repulsion effect is strengthened

so the precipitated chains begin to dissolve again.However

when the conversion is too high

the molecular weight of the copolymers becomes large

and then the chains precipitated again

so the 2nd phase separation occurs.To validate the mechanism

different inorganic salts were added into the system respectively

and the transmittance curves were investigated.The results showed that the 2nd phase separation process of the aqueous two-phase system disappeared after added some inorganic salts.Therefore

the electrostatic repulsion effect of cationic monomer species is the true reason for double phase separation process.Lastly

the effect of reaction conditions on the double phase separation process was discussed.With the increase of overall monomers amount or PEG amount

the double phase separation process appeared and became obvious gradually

but it disappeared when the amount was too large.With the increase of PEG molecular weight

the double phase separation process became obvious.Raising the copolymerization temperature from 45℃ to 55℃

the double phase separation process was accelerated only.When the mole fraction of DMC is between 0.25 and 0.60

the double phase separation process can be observed

and the first critical conversions were very small

but the second critical conversions were high.When the mole fraction of DMC is above 0.60

the copolymerization finished mainly at the second interval

and the 2nd phase separation is difficult to be observed.