Lambeth Robert H, Ramakrishnan Subramanian, Mueller Ryan, Poziemski John P, Miguel George S, Markoski Larry J, Zukoski Charles F, Moore Jeffrey S
Department of Chemistry and Beckman Institute for Advanced Science and Technology, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801, USA.
Langmuir. 2006 Jul 4;22(14):6352-60. doi: 10.1021/la060169b.
To mimic the three-dimensional (3-D) globular architecture resulting from the precise positioning of hydrophobic/hydrophilic domains (blocks) of naturally occurring proteins, water-soluble linear and star homopolymers of N,N'-dimethylacrylamide (DMA) were synthesized with prescribed molecular weights via reversible addition-fragmentation chain transfer (RAFT) polymerization and subsequently used as macro chain transfer agents for block copolymerization with N-isopropylacrylamide (NIPAM). For the star block copolymers, the interior block consisted of NIPAM while the exterior block was DMA. Since polyNIPAM thermally switches from hydrophilic to hydrophobic, the 3-D solution conformations of the polymers were studied as a function of temperature using differential scanning calorimetry (DSC), static light scattering (SLS), and dynamic light scattering (DLS). The polymers were observed to form monodisperse aggregates in an aqueous pH 4 buffer solution when heated above the lower critical solution temperature (LCST) of polyNIPAM. The temperature at which the polymers aggregated and the size of the aggregates were dependent on the NIPAM block length and the core architecture. A simple model based on an optimal area per headgroup was used to analyze our experimental findings and was useful for predicting the final size and molecular weight of the aggregates formed.
为了模拟天然蛋白质中疏水/亲水结构域（嵌段）精确定位所产生的三维（3-D）球状结构，通过可逆加成-断裂链转移（RAFT）聚合反应合成了具有规定分子量的N，N'-二甲基丙烯酰胺（DMA）水溶性线性和星形均聚物，随后将其用作与N-异丙基丙烯酰胺（NIPAM）进行嵌段共聚的大分子链转移剂。对于星形嵌段共聚物，内部嵌段由NIPAM组成，而外部嵌段为DMA。由于聚NIPAM会从亲水性热转变为疏水性，因此使用差示扫描量热法（DSC）、静态光散射（SLS）和动态光散射（DLS）研究了聚合物的三维溶液构象随温度的变化。当加热到高于聚NIPAM的低临界溶液温度（LCST）时，观察到聚合物在pH 4的水性缓冲溶液中形成单分散聚集体。聚合物聚集的温度和聚集体的大小取决于NIPAM嵌段长度和核心结构。基于每个头基的最佳面积的简单模型用于分析我们的实验结果，并且有助于预测所形成聚集体的最终尺寸和分子量。
