CO_2/N_2可逆单层囊泡-网状结构转变研究

CO_2/N_2 Switchable Unilamellar Vesicle-Network Structure Transition

以聚乙二醇6000与α-溴代异丁酰溴进行酯化反应得到大分子引发剂PEG6000-Br,使用原子转移自由基聚合(ATRP)法合成了对称三嵌段且聚合度相等的聚甲基丙烯酸二甲胺乙酯-聚乙二醇-聚甲基丙烯酸二甲胺乙酯(PDM_(165)-PEG_(165)-PDM_(165))。利用FTIR和~1HNMR对其结构进行了表征。以p H、电导率测试证明了聚合物溶液的CO_2/N_2循环可逆性,聚合物溶液中通入CO_2后,5 min内,溶液p H值即从7.74下降至5.47,溶液电导率从0.176 m S/cm迅速上升至0.405 m S/cm;继而向溶液中通入N_2,经过30 min后,溶液的p H值和电导率都恢复到初始值。冷冻透射电镜(Cryo-TEM)观察得知,聚合物在水中可自组装形成单层囊泡,通入CO_2后,叔胺被质子化,囊泡解离形成网状结构,导致溶液黏度从3 m Pa·s上升至12 m Pa·s,叔胺质子化由~1HNMR证明,N原子附近的氢位移从δ2.3、2.7、4.1向低场分别移动至δ2.8、3.2、4.3。

A macroinitiator PEG6000-Br,was first synthesized by esterification of polyethylene glycol（PEG）6000 andα-bromoisobutyryl bromide.Then,a symmetrical triblock copolymer with the same degree of polymerization,poly（2-dimethylaminoethyl methacrylate）-PEG-poly（2-dimethylaminoethyl methacrylate）（PDM（165）-PEG（165）-PDM（165））,was synthesized by atom transfer radical polymerization（ATRP）.The copolymer was characterized by means of FTIR and^1HNMR.The p H and conductivity tests showed that the copolymer exhibited switchable responsiveness to CO2/N2,after 5 min of bubbling CO2,the p H value of solution decreased from 7.74 to 5.47 and the conductivity of solution increased rapidly from 0.176 m S/cm to 0.405 m S/cm.Then,after 30 min of bubbling N2,the p H value and conductivity of solution recovered to the initial values.According to the cryogenic transmission electron microscopy（Cryo-TEM）results,the copolymer could form self-assembled unilamellar vesicles in the water.The protonation of tertiary amine groups in copolymer resulted in vesicles dissociation and network structure formation.This vesicle-network aggregate structure transition led to an enhancement of viscosity of solution（from 3 m Pa·s to 12 m Pa·s）after bubbling of CO2.The key mechanism of these changes was proved by^1HNMR.The results showed that the chemical shifts（δ）of H atoms near N atom shifted from 2.3,2.7,4.1 to 2.8,3.2,4.3,respectively.