丙烯酰胺与季铵类阳离子单体双水相共聚的二次相分离

DOUBLE PHASE SEPARATION OF AQUEOUS TWO-PHASE COPOLYMERIZATION OF ACRYLAMIDE WITH QUATERNARY AMMONIUM CATIONIC MONOMERS

以(2-甲基丙烯酰氧乙基)三甲基氯化铵(DMC)为例,用分光光度法研究了丙烯酰胺(AM)与季铵类阳离子单体在聚乙二醇(PEG)水溶液中双水相共聚的二次相分离.提出了二次相分离的机理,认为是阳离子单体单元的电离使得聚合物带上了正电荷,大分子间的静电排斥作用增加了其在PEG相中的溶解性(增容作用).讨论了反应条件对体系二次相分离的影响,发现二次相分离在一定的单体浓度和PEG浓度、以及适当的单体比例和PEG分子量条件下才能发生.总单体用量或PEG用量增加,第二次分相先出现后消失;PEG分子量增大,第二次分相逐渐明显;反应温度升高,两次分相更快完成.DMC摩尔分率为0.25～0.60时,第一次分相的临界转化率很小,第二次分相的临界转化率则随DMC摩尔分率的增加而增大;DMC摩尔分率超过0.60后,聚合反应主要在过渡区完成,第二次分相难以发生.

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 aerylamide 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 2^nd 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 2^nd 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 2^nd phase separation is difficult to be observed.