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 Tg 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.