Segmental Motion of Surface-Bound Swollen Poly(methyl acrylate)-d

Abstract

Poly(methyl acrylate)-d (PMA-d), labeled in the backbone R position, was prepared and adsorbed from toluene on silica at a coverage of 0.38 mg of PMA-d/mg of silica. This coverage was roughly that of the maximum found in the adsorption isotherm. Comparisons of deuterium NMR spin-lattice relaxation time, T1, and spin-spin relaxation time, T2, for the adsorbed, swollen polymer at different temperatures were made to obtain information about the backbone motion of the surface-bound polymer. The results were consistent with a system where the fast local motions were similar to those in solution but the longer range segmental motions were more restricted than those in solution. The log-normal distribution yielded mean correlation times which were 4-10 times slower for the surface-bound species than that in solution. The Hall-Helfand (HH) model with two correlation times yielded slow correlation times more than an order of magnitude slower for the surface species. Compared to previous studies on terminally attached polymers which formed extended brushes, liquid-like segments of randomly attached homopolymers have significantly reduced longer range segmental motions.

Thermoreversible Polymers Adsorbed to Colloidal Silica: A 1H NMR and DSC Study of the Phase Transition in Confined Geometry

“…The dependence of the width of the transition on polymer amount can be understood in a model assuming that the motional heterogeneity is caused by a gradient of mobility in dependence on the distance from the surface. Such models were employed to describe the distribution of mobility in other polymer adsorption layers, where the motional correlation time is generally assumed to decrease with distance from the surface. , If polymer segments, which are located close to the silica surface, exhibit a broader transition due to their stronger immobilization, then the width of the phase transition can be considered dependent on the distance of the segments from the surface. The transition width in our experiments thus appears to scale with the motional correlation time of the segments, since at low coverage the layer is dominated by immobile segments close to the surface, while at higher coverage more mobile segments with a smaller broadening of the transition contribute to the signal.…”

A Soft Hydrogen Storage Material: Poly(Methyl Acrylate)‐Confined Ammonia Borane with Controllable Dehydrogenation

“…Synthesis of PMA: The PMA was synthesized through the free-radical polymerization of methyl acrylate according to a reported method [12]. In a typical synthesis, ammonium persulfate (polymerization initiator, 0.7 g) was dissolved in water (4 mL) at room temperature.…”

13C Spin−Lattice Relaxation Times and NOE Related Studies of Hydroxyl-Terminated Polybutadiene (HTPB)

“…13 C spin−lattice relaxation times, T 1 , and nuclear Overhauser effects, NOE, are often used for studying the molecular dynamics of polymer chains. − These relaxations often arise from intermolecular dipole−dipole interactions. Practically for 13 C relaxations, only 13 C− 1 H nuclear dipoles are considered.…”

“…Hydroxyl-terminated polybutadiene, HTPB, is used extensively as a polymeric binder and is of considerable interest. − Recently, efforts are devoted to the study of dynamics of such polymers. − This is often done through the determination of 13 C NMR relaxation parameters. − The main advantage of this spectroscopic technique is providing a detailed analysis of molecular motions at the atomic levels. Several reviews are available which describe the various models developed for the interpretation of nuclear spin relaxation data of polymers. − As a model for molecular motion, the asymmetric log χ 2 distribution is useful at describing and quantifying the dynamics of polymers and polymer solutions. − The goal of this research is to obtain insights into the chain local motions of HTPB.…”