Biodesign Center for Sustainable Macromolecular Materials and Manufacturing, School of Molecular Sciences, Arizona State University, Tempe, AZ 85281, USA.
Department of Chemistry, Macromolecules Innovation Institute (MII), Virginia Tech, Blacksburg, VA 24061, USA.
Molecules. 2021 Aug 3;26(15):4705. doi: 10.3390/molecules26154705.
This work reveals the influence of pendant hydrogen bonding strength and distribution on self-assembly and the resulting thermomechanical properties of A-AB-A triblock copolymers. Reversible addition-fragmentation chain transfer polymerization afforded a library of A-AB-A acrylic triblock copolymers, wherein the A unit contained cytosine acrylate (CyA) or post-functionalized ureido cytosine acrylate (UCyA) and the B unit consisted of -butyl acrylate (BA). Differential scanning calorimetry revealed two glass transition temperatures, suggesting microphase-separation in the A-AB-A triblock copolymers. Thermomechanical and morphological analysis revealed the effects of hydrogen bonding distribution and strength on the self-assembly and microphase-separated morphology. Dynamic mechanical analysis showed multiple tan delta (δ) transitions that correlated to chain relaxation and hydrogen bonding dissociation, further confirming the microphase-separated structure. In addition, UCyA triblock copolymers possessed an extended modulus plateau versus temperature compared to the CyA analogs due to the stronger association of quadruple hydrogen bonding. CyA triblock copolymers exhibited a cylindrical microphase-separated morphology according to small-angle X-ray scattering. In contrast, UCyA triblock copolymers lacked long-range ordering due to hydrogen bonding induced phase mixing. The incorporation of UCyA into the soft central block resulted in improved tensile strength, extensibility, and toughness compared to the AB random copolymer and A-B-A triblock copolymer comparisons. This study provides insight into the structure-property relationships of A-AB-A supramolecular triblock copolymers that result from tunable association strengths.
这项工作揭示了悬垂氢键强度和分布对自组装以及所得热机械性能的影响 A-AB-A 嵌段共聚物。可逆加成-断裂链转移聚合提供了一系列 A-AB-A 丙烯酸嵌段共聚物，其中 A 单元包含胞嘧啶丙烯酸酯 (CyA) 或后官能化的脲基胞嘧啶丙烯酸酯 (UCyA)，B 单元由 - 丁基丙烯酸酯 (BA) 组成。差示扫描量热法显示出两个玻璃化转变温度，表明 A-AB-A 嵌段共聚物存在微相分离。热机械和形态分析揭示了氢键分布和强度对自组装和微相分离形态的影响。动态力学分析显示出多个 tan δ（δ）转变，与链松弛和氢键解离相关，进一步证实了微相分离结构。此外，由于四重氢键的更强结合，UCyA 嵌段共聚物相对于 CyA 类似物具有扩展的模量平台。根据小角 X 射线散射，CyA 嵌段共聚物表现出圆柱状微相分离形态。相比之下，由于氢键诱导的相混合，UCyA 嵌段共聚物缺乏长程有序性。与 AB 无规共聚物和 A-B-A 嵌段共聚物相比，将 UCyA 掺入软质中心嵌段可提高拉伸强度、延展性和韧性。本研究深入了解了由可调谐的缔合强度引起的 A-AB-A 超分子嵌段共聚物的结构-性能关系。
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