Towards bio-inspired polymer adhesives: Activation assisted via HOBt for grafting of dopamine onto poly(acrylic acid)

The design of bio-inspired polymers has long been an area of intense
study, however applications to the design of concrete admixtures for
improved materials performance have been relatively unexplored. In this
work we functionalized poly(acrylic acid) (PAA), a simple analogue to
polycarboxylate ether admixtures in concrete, with dopamine to form a
catechol-bearing polymer (PAA-g-DA). Synthetic routes utilizing
hydroxybenzotriazole (HOBt) as an activating agent were examined for their
ability in grafting dopamine to the PAA backbone. Previous literature
using the traditional coupling reagent
1-Ethyl-3-(3-dimethylaminopropyl)-carbodiimide (EDC) to graft dopamine to
PAA were found to be inconsistent and the sensitivity of EDC coupling
reactions necessitated a search for an alternative. Additionally, HOBt
allowed for greater control over percent functionalization of the
backbone, is a simple, robust reaction, and showed potential for
scalability. This finding also represents a novel synthetic pathway for
amide bond formation between dopamine and PAA. Finally, we performed
preliminary adhesion studies of our polymer on rose granite specimens and
demonstrated a 56% improvement in the median adhesion strength over
unfunctionalized PAA. These results demonstrate an early study on the
potential of PAA-g-DA to be utilized for improving the bonds within
concrete.

仿生聚合物的设计长期以来一直是研究热点领域，但将其应用于混凝土外加剂以改善材料性能的相关探索却相对匮乏。本研究以混凝土用聚羧酸醚类外加剂的简单类似物聚丙烯酸（poly(acrylic acid), PAA）为基底，通过接枝多巴胺制备得到含儿茶酚结构的聚合物（PAA-g-DA）。我们考察了以羟基苯并三氮唑（hydroxybenzotriazole, HOBt）作为活化剂的合成路径，以实现多巴胺向PAA主链的接枝改性。此前文献中采用传统偶联试剂1-乙基-3-(3-二甲基氨基丙基)碳二亚胺（1-Ethyl-3-(3-dimethylaminopropyl)-carbodiimide, EDC）进行多巴胺接枝PAA的方法存在稳定性欠佳的问题，且EDC偶联反应敏感性较强，因此亟需寻找替代方案。相较之下，HOBt活化体系不仅可精准调控主链的功能化率，反应操作简便、体系稳定，同时具备规模化应用潜力。该发现同时为多巴胺与PAA之间的酰胺键构建提供了一条全新的合成路径。最后，我们对制备得到的聚合物在玫瑰花岗岩试样上开展了初步粘附性能测试，结果显示其粘附强度中位数较未功能化的PAA提升了56%。本研究初步探索了PAA-g-DA用于改善混凝土内部粘结性能的应用潜力。