**4. Conclusions**

In summary of the present study, we synthesized linear, 4- and 6-arm star-shaped polymers based on acrylic acid using chain transfer agents with corresponding thiol groups in order to provide insight into the types of polymers that could both bind to HAP and repel bacteria from the surface. We have found that polymer shape was more important to HAP surface binding than polymer composition (hydrophobicity). However, polymer composition played a larger role than polymer shape (linear vs. star-shape) when providing anti-bacterial protection. This information will be important for targeted properties (binding, anti-bacterial attachment, wettability, etc.,) and further design polymers for dental applications. In this study, our focus was the synthesis of star-shaped polymers and initial evaluation of their physical and biological properties in order to test new polymer platforms for dental applications. The oral environment is quite dynamic and subject to continuously changing environments due to salivary flow, food and drink intake, and the resulting fluctuating pH. Therefore, the efficiency of dental materials to provide benefits, as delivered through common oral care products, must be investigated through delivery, substantivity, and efficacy. While limited to very simple systems here, this approach is critical to build an understanding of dental materials as it can more effectively isolate and identify specific modes of action in addition to chemical or physical barriers to the effectiveness of these materials. Our future research will focus on further developing an understanding of star-shaped polymers in reference to artificial-saliva and human-saliva-coated HAP surfaces, including binding activity and bacterial anti-attachment properties.

**Supplementary Materials:** The following are available online at http://www.mdpi.com/2079-4983/10/4/56/s1. Figure S1: Chain transfer process in free-radical polymerization. Figure S2: The relationships of 1/DP (A) and 1/Mn (B) with SH/monomer ratio for RhB-labeled PAA (tBu)-protected polymers. Table S1: Polymerization conditions of tBu PAA polymers. Table S2: Polymerization conditions for hydrophobic random copolymers. Table

*J. Funct. Biomater.* **2019**, *10*, 56

S3: Polymerization conditions for rhodamine-labeled tBu linear polymers. Table S4: Polymerization conditions for rhodamine-labeled tBu 4-arm star-shaped polymers. Table S5: Polymerization conditions for rhodamine-labeled tBu 6-arm star-shaped polymers. Table S6: Polymerization conditions of rhodamine-labeled tBu linear and 4-arm PAA/MA random copolymer. Table S7: Polymer characterization of tBu-protected polymers. Table S8: Polymer characterization of tBuA-MA random copolymers. Table S9: Polymer characterization of F-labeled polymers. Table S10: Polymer characterization and Langmuir constants. Table S11: Chain transfer constants for tBu polymers.

**Author Contributions:** Conceptualization, L.A.Z., C.P.M., and K.K.; investigation, H.M., G.A.P., J.L., and C.P.M.; writing—original draft preparation, C.P.M., and K.K.; writing—review and editing, C.P.M., and K.K.; supervision, C.P.M. and K.K.; project administration, C.P.M. and K.K.; funding acquisition, K.K.

**Funding:** Kenichi Kuroda, Hamid Mortazavian, and Janis Lejnieks acknowledge the funding from Colgate-Palmolive (Star-Shaped Polymer Architecture for Anti-Attachment, Anti-Stain, and Actives Delivery).

**Acknowledgments:** We would like to thank Rehana Begum-Gafur and Mark Vandeven for their help with statistical analysis of anti-attachment microbial data, and Donghui Wu for helpful discussions.

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