Synthesis of Poly(decahydro-2-naphthyl methacrylate)s with Different Geometric Structures and Effects of Side-Group Dynamics on Polymer Properties Investigated by Thermal and Dynamic Mechanical Analyses and DFT Calculations

We prepared the geometric isomers of decahydro-2-naphthols as the source materials for the synthesis of poly(decahydro-2-naphthyl methacrylate)s [poly(DNMA)-I, -II, -III, and -IV] including alicyclic ester groups with different geometric structures. The geometry and conformational dynamics of the decahydro-2-naphthyl moieties were investigated by NMR spectroscopy and DFT calculations. We synthesized each isomer of the methacrylic monomers, polymerized them, and investigated the optical, thermal, and mechanical properties of poly(DNMA)s with different isomer compositions. The T g values of the poly(DNMA)s were in the following order: 139.3 °C for poly(DNMA)-II < 142.7 °C for poly(DNMA)-I < 146.2 °C for poly(DNMA)-III < 152.9 °C for poly(DNMA)-III/IV. On the basis of the dynamic motion of the alicyclic substituents determined by dynamic mechanical analysis, the tan δ peaks due to the β-relaxation for the a conformation change of the side group were observed for poly(DNMA)-I, while no peak was observed for poly(DNMA)-III. The activation energies for the β-relaxation were 65 kJ/mol for poly(DNMA)-I and 56–63 kJ/mol for the poly(DNMA)s including the four isomeric ester groups with various compositions. An increase in the DNMA-II content in the repeating units accelerated a dynamic conformation change, resulting in a decrease in the tan δ peak temperature and the activation energy value, as well as the glass transition temperature of the polymers. The optical property of the resulting polymers as the transparent polymer materials was also investigated. The density, refractive index value, and Abbe number of poly(DNMA)s were 1.04–1.10 cm3/g, 1.489, and 42–44, respectively.