Molecular Dynamics of PEGylated Multifunctional Polyhedral Oligomeric Silsesquioxane

Here we report a study of molecular dynamics of (1) four different poly(propylene oxide)/poly (ethylene oxide) (PPO/PEO) copolymers, two amorphous and two semicrystalline, and (2) the product of the chemical reaction between these copolymers and a multifunctional polyhedral oligomeric silsesquioxane (POSS). We refer to the latter group of compounds as PEGylated POSS. Experimental results were generated using broadband dielectric relaxation spectroscopy (DRS) and dynamic mechanical spectroscopy (DMS) over a wide range of frequencies and temperatures. Amorphous copolymers exhibit the segmental process (alpha), the normal mode process (alpha(N)), and two local processes (beta and gamma), while semicrystalline copolymers possess segmental (alpha) and two local relaxations (beta and gamma). The beta process is a secondary relaxation and the gamma process is due to the combination of the local motions in PPO and PEO blocks. PEGylated POSS was synthesized by chemical reaction between the functional end groups on the PPO block (amine) and the POSS side chain (epoxy). Dynamics of PEGylated POSS were investigated and contrasted with the dynamics of the corresponding neat copolymers. Covalent bonding between POSS and copolymer slows down the segmental and the normal mode process but does not affect the time scale of the beta the gamma process. A detailed account of the effect of molecular weight, PPO/PEO mole ratio, copolymer morphology and covalent bonding between POSS and copolymer on the molecular origin, temperature dependence, and spectral characteristics of relaxation processes in copolymers and PEGylated POSS is provided.