Adsorption and segmental dynamics of acrylate and methacrylate polymers adsorbed on a silica surface

Poly(isopropyl acrylate)-d₇ (PIPA- d₇) was studied using ²H solid-state NMR and modulated differential scanning calorimetry (MDSC). The polymer was deuterated on the methyl groups and side-chain methine. The PIPA- d₇ was adsorbed onto Cab-O-Sil silica. These two types of deuterons each showed their own characteristic deuterium nuclear magnetic resonance (NMR) spectra for bulk PIPA- d₇. The ²H NMR spectra of adsorbed PIPA- d₇ samples showed the presence of heterogeneity of the segmental dynamics. A residual powder pattern was found in the spectra of the surface samples at higher temperatures, indicating that the segments were tightly attached to the silica. The tightly bound segments were due to the hydrogen bonding between carbonyl groups on the side chains and silanol groups on the silica surface. This resulted in a higher glass transition temperature (Tg) of the PIPA-d₇-silica composite, which was also observed from MDSC experiments. Simulated ²H NMR lineshapes (with different jump rates) were generated based upon two different jump models--a soccer ball model (60-site jump) based on vertices of a truncated icosahedron, and a tetrahedral angle model (2-site hop). The hydrogen bonding interaction at the interface between polymers-containing carbonyl groups and the silica surface was monitored by using FTIR. Methacrylate polymers with different side chain lengths, including poly(ethyl methacrylate) (PEMA), poly(n-butyl methacrylate) (PnBMA), poly(benzyl methacrylate) (PBenzylMA), and poly(lauryl methacrylate) (PLMA), were studied. Two different surface areas of silica were used as the substrates for PEMA for comparison of the effect surface area sizes. Ratios of the absorption coefficients of bound to free carbonyls, and bound fractions of each system were estimated --Abstract, page iv