Zwitterionic microspheres of poly2-(dimethylamino) ethyl methacrylate (PDMAEMA) block polymethacrylic acid (MAA) were prepared by RAFT dispersion polymerization in alcohols. 4-Cyano-4-(phenylcarbonothioylthio) pentanoic acid (CPDB) was used as the RAFT agent. 2,2′-Azobis(2,4-dimethyl) valeronitrile (V65) was used as the initiator, and PDMAEMA-CPDB was used as the macro-chain transfer agent (CTA). 1HNMR was applied to determine the polymerization degrees of both PDMAEMA-CTA and PDMAEMA-b-PMAA. SEM, dynamic light scattering (DLS), and small-angle X-ray diffraction (SAX) were employed to characterize the microspheres. It was observed that the polarity of alcohols impacted the partition of MAA and V65 between the mini-droplets of PDMAEMA-CTA/MAA complexes and the continuous phase, thereby affected on the diameters of microspheres, the total conversion of MAA, and the polymerization degree of PMAA in the copolymers. For example, in methanol, the smallest diameter and polymerization degree of PMAA in the block copolymers were obtained, whereas the total conversion of MAA of the RAFT polymerization system was the highest. Most of RAFT polymerization of MAA occurred nearby PDMAEMA-CTA chains; thus, PDMAEMA-CTA acted as a template to regulate the length of PMAA in the copolymers. pH-sensitive characteristics of microspheres were dependent to the extra length of PDMAEMA-CTA, i.e., the difference of lengths between two blocks. When the length of PMAA was too short, e.g., PDMAEMA600-b-PMAA87, or the length of PMAA was closed to that of PDMAEMA, e.g., PDMAEMA79-b-PMAA93 and PDMAEMA102-b-PMAA131, the amphoteric characteristics of microspheres disappeared. The self-assembly behavior of diblock copolymers in KCl alcohol-water solution was also determined by the extra length of PDMAEMA. Microspheres turned into nanofibers or nano-ribbons, but for PDMAEMA600-b-PMAA87, the microspheres maintained their original spheric morphology. These results indicated that the charge-screening effects of salts played the key roles in the self-assembly. Graphical abstract Graphical abstract

中文翻译：

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醇中RAFT分散聚合制备PDMAEMA-b-PMAA两性离子微球及其在水中的pH敏感性和在KCl溶液中的自组装

聚2-（二甲氨基）甲基丙烯酸乙酯（PDMAEMA）嵌段聚甲基丙烯酸（MAA）的两性离子微球是通过RAFT在醇中分散聚合制备的。4-氰基-4-(苯基碳硫酰硫基)戊酸(CPDB)用作RAFT剂。2,2'-偶氮双（2,4-二甲基）戊腈（V65）用作引发剂，PDMAEMA-CPDB用作大链转移剂（CTA）。1HNMR 用于测定 PDMAEMA-CTA 和 PDMAEMA-b-PMAA 的聚合度。采用扫描电镜、动态光散射 (DLS) 和小角 X 射线衍射 (SAX) 来表征微球。观察到醇的极性影响了 MAA 和 V65 在 PDMAEMA-CTA/MAA 复合物的微液滴和连续相之间的分配，从而影响了微球的直径，MAA 的总转化率和共聚物中 PMAA 的聚合度。例如，在甲醇中，嵌段共聚物中 PMAA 的直径和聚合度最小，而 RAFT 聚合体系的 MAA 总转化率最高。MAA 的大部分 RAFT 聚合发生在 PDMAEMA-CTA 链附近；因此，PDMAEMA-CTA 作为模板来调节共聚物中 PMAA 的长度。微球的 pH 敏感特性取决于 PDMAEMA-CTA 的额外长度，即两个块之间的长度差异。当PMAA长度过短，如PDMAEMA600-b-PMAA87，或PMAA与PDMAEMA的长度接近时，如PDMAEMA79-b-PMAA93和PDMAEMA102-b-PMAA131，微球的两性特性消失。二嵌段共聚物在 KCl 醇-水溶液中的自组装行为也由 PDMAEMA 的额外长度决定。微球变成纳米纤维或纳米带，但对于 PDMAEMA600-b-PMAA87，微球保持其原始球形形态。这些结果表明盐的电荷屏蔽效应在自组装中起关键作用。图形摘要图形摘要