Boldyrev Konstantin, Chernyak Alexander, Meshkov Ivan, Muzafarov Aziz, Tatarinova Elena, Vasil'ev Sergey
N.S. Enikolopov Institute of Synthetic Polymeric Materials of Russian Academy of Sciences, Profsoyuznaya st. 70, 117393 Moscow, Russia.
Soft Matter. 2020 Nov 4;16(42):9712-9725. doi: 10.1039/d0sm01183e.
Recently developed non-functional derivatives of polymethylsilsesquioxane (PMSSO) dendrimers of the first to fifth generation were characterized by 1H, 13C and 29Si NMR spectroscopy. The self-diffusion and NMR relaxation of PMSSO dendrimers in dilute solutions of toluene and melts were investigated in a wide temperature range (-50-80 °C). The hydrodynamic radii of dendrimers were determined from the self-diffusion coefficients measured in diluted solutions according to the Stokes-Einstein equation. The hydrodynamic radius of PMSSO dendrimers as a function of molecular mass follows a power law with the scaling exponent of 0.32 ± 0.02 in the investigated temperature range. The temperature dependences of the self-diffusion coefficients of dendrimers were described by the Arrhenius-type equation. The activation energies of self-diffusion of dendrimers in diluted toluene solutions are identical for different generations while the dependence of activation energy for dendrimers in melts shows a maximum for the third generation (G3) dendrimer. Taking into account the absence of specific interactions in PMSSO dendrimer melts the observed behavior was ascribed to the manifestation of interpenetration of dendrimer molecules. For low generations (G1 and G2) the short length of the branches does not considerably affect the translational diffusion while for higher generations (G4 and G5) the densification of the structure prevents significant interpenetration.
最近合成的第一代至第五代聚甲基倍半硅氧烷（PMSSO）树枝状大分子的非功能性衍生物通过1H、13C和29Si核磁共振光谱进行了表征。在较宽的温度范围（-50-80°C）内，研究了PMSSO树枝状大分子在甲苯稀溶液和熔体中的自扩散及核磁共振弛豫。根据斯托克斯-爱因斯坦方程，由稀溶液中测得的自扩散系数确定树枝状大分子的流体力学半径。在研究的温度范围内，PMSSO树枝状大分子的流体力学半径随分子量的变化遵循幂律，标度指数为0.32±0.02。树枝状大分子自扩散系数的温度依赖性用阿累尼乌斯型方程描述。不同代数的树枝状大分子在稀甲苯溶液中的自扩散活化能相同，而树枝状大分子在熔体中的活化能依赖性在第三代（G3）树枝状大分子处出现最大值。考虑到PMSSO树枝状大分子熔体中不存在特定相互作用，观察到的行为归因于树枝状大分子分子相互渗透的表现。对于低代数（G1和G2），短支链长度对平动扩散影响不大，而对于高代数（G4和G5），结构致密化阻止了显著的相互渗透。
