Deane O J, Lovett J R, Musa O M, Fernyhough A, Armes S P
Dainton Building, Department of Chemistry, University of Sheffield, Brook Hill, Sheffield, South Yorkshire S3 7HF, U.K.
Ashland Specialty Ingredients, 1005 US 202/206, Bridgewater, New Jersey 08807, United States.
Macromolecules. 2018 Oct 9;51(19):7756-7766. doi: 10.1021/acs.macromol.8b01627. Epub 2018 Sep 25.
Poly(-vinylpyrrolidone) (PNVP) is a well-known, highly polar, nonionic water-soluble polymer. However, -vinylpyrrolidone (NVP) usually exhibits strongly non-ideal behavior when copolymerized with methacrylic or styrenic monomers. Moreover, NVP is not particularly well-controlled under living radical polymerization conditions. For these reasons, alternative pyrrolidone-based monomers have been investigated. For example, the reversible addition-fragmentation chain transfer (RAFT) polymerization of 2-(-methacryloyloxy)ethylpyrrolidone (NMEP) has been recently investigated using various polymerization formulations. However, PNMEP homopolymers are significantly less hydrophilic than PNVP and exhibit inverse temperature solubility in aqueous solution. In the present work, we studied the RAFT aqueous solution polymerization of 2-(-acryloyloxy)ethylpyrrolidone (NAEP) using either AIBN at 70 °C or a low-temperature redox initiator at 30 °C. PNAEP homopolymers are obtained in high yield (>99%) with good control ( / < 1.20) for target degrees of polymerization (DP) of up to 400 using the latter initiator, which produced relatively fast rates of polymerization. However, targeting DPs above 400 led to lower NAEP conversions and broader molecular weight distributions. 2-Hydroxyethyl acrylate (HEA) and oligo(ethylene glycol) methyl ether acrylate (OEGA) were chain-extended using a PNAEP macro-CTA via RAFT aqueous solution polymerization, yielding double-hydrophilic acrylic diblock copolymers with high conversions (>99%) and good control ( / < 1.31). In addition, a PNAEP macro-CTA was chain-extended via RAFT aqueous solution polymerization of -isopropylacrylamide (NIPAM) at 22 °C. Dynamic light scattering (DLS) analysis indicated that heating above the lower critical solution temperature of PNIPAM led to so-called "anomalous micellization" at 35 °C and the formation of near-monodisperse spherical micelles at 40 °C. Finally, 2-(diethylamino)ethyl methacrylate (DEA) was polymerized using an -morpholine-functionalized trithiocarbonate-based RAFT chain transfer agent and subsequently chain-extended using NAEP to form a novel pH-responsive diblock copolymer. Above the p of PDEA (∼7.3), DLS and H NMR studies indicated the formation of well-defined PDEA-core spherical micelles.
聚（乙烯基吡咯烷酮）（PNVP）是一种著名的、高度极性的非离子水溶性聚合物。然而，乙烯基吡咯烷酮（NVP）在与甲基丙烯酸或苯乙烯类单体共聚时通常表现出强烈的非理想行为。此外，NVP在活性自由基聚合条件下的控制效果不是特别好。由于这些原因，人们研究了替代的基于吡咯烷酮的单体。例如，最近使用各种聚合配方研究了2-（甲基丙烯酰氧基）乙基吡咯烷酮（NMEP）的可逆加成-断裂链转移（RAFT）聚合。然而，PNMEP均聚物的亲水性明显低于PNVP，并且在水溶液中表现出逆温溶解性。在本工作中，我们研究了2-（丙烯酰氧基）乙基吡咯烷酮（NAEP）在70℃下使用AIBN或在30℃下使用低温氧化还原引发剂的RAFT水溶液聚合。使用后一种引发剂，对于高达400的目标聚合度（DP），可以高产率（>99%）且良好控制（Đ/M<1.20）地获得PNAEP均聚物，该引发剂产生相对较快的聚合速率。然而，目标DP高于400会导致NAEP转化率降低和分子量分布变宽。通过RAFT水溶液聚合，使用PNAEP大分子链转移剂对丙烯酸2-羟乙酯（HEA）和聚（乙二醇）甲基醚丙烯酸酯（OEGA）进行扩链，得到转化率高（>99%）且控制良好（Đ/M<1.31）的双亲水性丙烯酸二嵌段共聚物。此外，在22℃下通过RAFT水溶液聚合，使用PNAEP大分子链转移剂对N-异丙基丙烯酰胺（NIPAM）进行扩链。动态光散射（DLS）分析表明，加热至高于PNIPAM的低临界溶液温度会在35℃导致所谓的“异常胶束化”，并在40℃形成近单分散的球形胶束。最后，使用一种N-吗啉官能化的基于三硫代碳酸酯的RAFT链转移剂聚合甲基丙烯酸2-（二乙氨基）乙酯（DEA），随后使用NAEP进行扩链，以形成一种新型的pH响应性二嵌段共聚物。在PDEA的pKa（约7.3）以上，DLS和1H NMR研究表明形成了结构明确的以PDEA为核的球形胶束。
