Kikuchi Mao, Saito Nozomi, Ohke Mizuki, Nagano Shusaku, Nishitsuji Shotaro, Matsui Jun
Graduate School of Science and Engineering, Yamagata University, 1-4-12 Kojirakawa-machi, Yamagata 990-8560, Japan.
Faculty of Science, Yamagata University, 1-4-12 Kojirakawa-machi, Yamagata 990-8560, Japan.
Soft Matter. 2023 May 3;19(17):3058-3068. doi: 10.1039/d3sm00265a.
This study demonstrates that a simple statistical copolymer can form self-assembled lamellae, whose structures depend on both the comonomer composition and the annealing temperature. Statistical copolymers of octadecyl acrylamide and hydroxyethyl acrylamide [p(ODA/HEAm)] were prepared free-radical copolymerization, and their thermal properties were studied by differential scanning calorimetry. Thin films of p(ODA/HEAm) were prepared spin-coating, and their structures were analyzed using X-ray diffraction. It was found that copolymers with HEAm contents between 28 and 50% formed self-assembled lamellae upon annealing at a temperature ∼10 °C above the glass-transition temperature. The self-assembled form was found to possess a "side-chain-mixed" lamellar structure, in which the ODA and HEAm side chains are oriented perpendicular to the lamellar plane composed of the polymer main chain. Interestingly, a copolymer with a HEAm content between 36 and 50% transformed from the side-chain-mixed lamellar structure to generate a "side-chain-segregated" lamellar structure upon annealing at a significantly higher temperature (∼50 °C above ). In this structure, the ODA and HEAm side chains were found to be oriented in opposite directions but perpendicular to the lamellar plane. The packing of the side chains in the lamellar structures was studied using Fourier-transform infrared spectroscopy. It was concluded that the structures of the self-assembled lamellae are determined by the strain forces generated during self-assembly, and by the segregation forces existing between the comonomers.
本研究表明，一种简单的统计共聚物可形成自组装片层，其结构取决于共聚单体组成和退火温度。通过自由基共聚制备了十八烷基丙烯酰胺和羟乙基丙烯酰胺的统计共聚物[p(ODA/HEAm)]，并采用差示扫描量热法研究了它们的热性能。通过旋涂制备了p(ODA/HEAm)薄膜，并利用X射线衍射分析了其结构。研究发现，HEAm含量在28%至50%之间的共聚物在高于玻璃化转变温度约10℃的温度下退火时会形成自组装片层。发现自组装形式具有“侧链混合”的片层结构，其中ODA和HEAm侧链垂直于由聚合物主链组成的片层平面取向。有趣的是，HEAm含量在36%至50%之间的共聚物在显著更高的温度下（高于约50℃）退火时，会从侧链混合片层结构转变为产生“侧链分离”的片层结构。在这种结构中，发现ODA和HEAm侧链取向相反，但垂直于片层平面。利用傅里叶变换红外光谱研究了片层结构中侧链的堆积情况。得出的结论是，自组装片层的结构由自组装过程中产生的应变力以及共聚单体之间存在的分离力决定。
