**4. Conclusions**

A new series of acenaphthene-based α-diimine cobalt complexes were synthesized that can polymerize 1,3-butadiene to access highly *cis*-1,4 selective (up to 98%) polybutadiene in all conditions. Due to the formed intra-ligand π-π stacking interactions, the complexes performed high catalytic activities at elevated temperature, and for complex Co4, the activities were maintained at 7.0 × <sup>10</sup><sup>4</sup> g PBD (mol of Co)−<sup>1</sup> <sup>h</sup>−1, which had not been reported before. Furthermore, all of the obtained polymers possessed a relatively narrow molecular weight distribution as well as high molecular weight (up to 92.2 × <sup>10</sup><sup>4</sup> Dalton). The complexes were also able to promote the copolymerization of 1,3-butadiene with polar 2-MOPB, directly producing functionalized polymers, although their incorporation content was limited. After introducing polar 2-MOPB into the backbone, the surface properties of the polymers significantly improved, and greatly decreased water contact angles were revealed.

**Author Contributions:** B.W. performed the experiments and analyzed the data. H.L. and B.W. contributed to the analysis of the results and the writing of the manuscript. T.T. and X.Z. contributed to the discussion section and revised the paper. H.L. and X.Z. provided the funds. All authors have read and agreed to the published version of the manuscript.

**Funding:** We are grateful for the financial support from the National Natural Sciences Foundation of China (21801236, U1862206).

**Institutional Review Board Statement:** Not applicable.

**Informed Consent Statement:** Not applicable.

**Data Availability Statement:** The data presented in this study are available on request from the corresponding author.

**Conflicts of Interest:** The authors declare no conflict of interest.
