Performance of heat-resisting functional polypropylene/hollow silica substrates for 6th generation wireless communication

Abstract

The effects of density and shape of hollow silica (functionalized silica hollow tubes (FSHT) or hollow glass microspheres (FHGM)) on dielectric constant (ε_r) and dielectric loss (tan δ) of hindered phenol (HP) grafted functional polypropylene (FPP)/FSHT, heat-treated FPP (HTFPP)/FSHT, FPP/FHGM or HTFPP/FHGM substrate films were systematically investigated. The dielectric or free-volume-hole characteristics of FPP/FSHT, FPP/FHGM, HTFPP/FSHT, or HTFPP/FHGM films decrease to a minimum, as FSHT or FHGM contents approach an optimal value of 4wt% or 8wt%, respectively, and their dielectric or free-volume-hole characteristics decrease or increase gradually with increasing HP molar%. The minimum ε_r and tan δ of FPP/FSHT or HTFPP/FSHT films decrease significantly with decreasing FSHT’s densities. By filling with 0.46 g/cm³ identical density of hollow silica fillers, the minimum ε_r or tan δ procured for FPP/FSHT or HTFPP/FSHT films are somewhat smaller than those of corresponding FPP/FHGM or HTFPP/FHGM films. The linear coefficient of thermal expansion (LCTE) or onset degradation temperature (DT_onset) of FPP/FSHT, HTFPP/FSHT, FPP/FHGM or HTFPP/FHGM films reduce or increase visibly with increasing FSHT or FHGM contents, respectively. All DT_onset values of HTFPP/hollow silica films are ~ 150℃ higher than those of conventional PP polymers. Satisfactorily low ε_r/tan δ (1.74/0.0019, 1.83/0.0020, 1.83/0.0024 and 1.92/0.0028 at 1 MHz), LCTE (95 × 10^–6/℃, 89 × 10^–6/℃, 80 × 10^–6/℃ and 74 × 10^–6/℃) and pleasing heat-resisting properties for 6G ultrarapid communication are acquired for properly prepared FPP/FSHT, HTFPP/FSHT FPP/FHGM or HTFPP/FHGM substrate films having 1.2 HP molar% and 0.46 g/cm³ density of FSHT and FHGM fillers. Probable reasons accounting for these reduced dielectric, LCTE and improved heat-resisting characteristics are proposed.