Cumming Juliana M, Deane Oliver J, Armes Steven P
Dainton Building, Department of Chemistry, University of Sheffield, Brook Hill, Sheffield, South Yorkshire S3 7HF, UK.
Macromolecules. 2022 Feb 8;55(3):788-798. doi: 10.1021/acs.macromol.1c02431. Epub 2022 Jan 19.
The reversible addition-fragmentation chain transfer (RAFT) aqueous dispersion polymerization of 2-hydroxypropyl methacrylate (HPMA) using a poly(glycerol monomethacrylate) (PGMA) precursor is an important prototypical example of polymerization-induced self-assembly. 4-Hydroxybutyl acrylate (HBA) is a structural isomer of HPMA, but the former monomer exhibits appreciably higher aqueous solubility. For the two corresponding homopolymers, PHBA is more weakly hydrophobic than PHPMA. Moreover, PHBA has a significantly lower glass transition temperature ( ) so it exhibits much higher chain mobility than PHPMA at around ambient temperature. In view of these striking differences, we have examined the RAFT aqueous dispersion polymerization of HBA using a PGMA precursor with the aim of producing a series of PGMA-PHBA diblock copolymer nano-objects by systematic variation of the mean degree of polymerization of each block. A pseudo-phase diagram is constructed using transmission electron microscopy to assign the copolymer morphology after employing glutaraldehyde to cross-link the PHBA chains and hence prevent film formation during grid preparation. The thermoresponsive character of the as-synthesized linear nano-objects is explored using dynamic light scattering and temperature-dependent rheological measurements. Comparison with the analogous PGMA -PHPMA formulation is made where appropriate. In particular, we demonstrate that replacing the structure-directing PHPMA block with PHBA leads to significantly greater thermoresponsive behavior over a much wider range of diblock copolymer compositions. Given that PGMA-PHPMA worm gels can induce stasis in human stem cells (see Canton , , 2016, , 65-74), our findings are likely to have implications for the design of next-generation PGMA-PHBA worm gels for cell biology applications.
使用聚（甘油单甲基丙烯酸酯）（PGMA）前体进行甲基丙烯酸2-羟丙酯（HPMA）的可逆加成-断裂链转移（RAFT）水分散聚合是聚合诱导自组装的一个重要典型例子。丙烯酸4-羟丁酯（HBA）是HPMA的结构异构体，但前一种单体在水中的溶解度明显更高。对于两种相应的均聚物，聚（丙烯酸4-羟丁酯）（PHBA）的疏水性比聚（甲基丙烯酸2-羟丙酯）（PHPMA）弱。此外，PHBA的玻璃化转变温度（ ）显著更低，因此在环境温度左右它比PHPMA表现出更高的链流动性。鉴于这些显著差异，我们研究了使用PGMA前体进行HBA的RAFT水分散聚合，目的是通过系统改变每个嵌段的平均聚合度来制备一系列PGMA-PHBA二嵌段共聚物纳米粒子。使用透射电子显微镜构建伪相图，以便在使用戊二醛交联PHBA链从而防止在制样过程中形成薄膜后确定共聚物的形态。使用动态光散射和随温度变化的流变学测量来探索所合成的线性纳米粒子的热响应特性。在适当的地方与类似的PGMA-PHPMA配方进行比较。特别是，我们证明用PHBA取代具有结构导向作用的PHPMA嵌段会在更宽范围的二嵌段共聚物组成中导致显著更强的热响应行为。鉴于PGMA-PHPMA蠕虫凝胶可诱导人类干细胞停滞（见坎顿， ，2016， ，65 - 74），我们的发现可能对用于细胞生物学应用的下一代PGMA-PHBA蠕虫凝胶的设计具有重要意义。
