Deuterium solid-state echo delay line shapes are used to establish the local motions occurring in linear and cross-linked epoxy systems based on Bisphenol A. Four isotopically labeled samples were prepared: linear and cross-linked resins with deuterated methylene units, and linear and cross-linked resins with deuterated phenylene units. Two local motions are observed in all four samples: transgauche isomerization of the methylene units and π flips of the phenylene units. The solid-state echo delay line shapes were simulated to obtain the rates of motion, the amplitudes of motion, and apparent distribution of rates, and the apparent temperature dependence of the rates. The two jump motions differ by about an order of magnitude in rate, with the π flip process being the faster of the two. Both have similar distributions of relaxation times given by a stretched exponential correlation function with an exponent of 0.6-0.7. The apparent activation energy for the π flip process is 50 kJ/mol and for the trans-gauche isomerization, 57 kJ/mol. For a given frequency, the breadth and temperature of the shear loss peak can be calculated from the information determined from the NMR data. Both motional processes lie in the envelope of relaxation referred to as the β process, with the π flips occurring on the lower temperature side of the envelope and the trans-gauche isomerization occurring on the higher temperature side. These two motions do not appear to account for all of the relaxations contributing to the β peak.

Poly(tetramethylene oxide) (PTHF) oligomers, M" = 650-2000, have been capped with phthalate ester (2) and with phthalic half-ester (3). Properties of the latter are strongly influenced by hydrogenbonding association of carboxylic acid termini. DSC revealed new, high-temperature transitions in the carboxylterminated oligomers (3) which decreased in temperature as PTHF molecular weight increased. Esterterminated oligomers 2 have the rheological properties of simple liquids. Oligomers 3 exhibit melt viscosities and dynamic moduli which decrease sharply at the highest DSC transition temperature but nevertheless exceed those of 2 over the entire range studied. These carboxyl-terminated oligomers exhibit elasticitydominated responses to small strains with a linear viscoelastic region and good recovery to large strain amplitude oscillatory shear. All observations are consistent with formation of large crystalline aggregates of carboxyl-terminated chain ends below the high-temperature DSC transition. Solid-state 13C-NMR suggests the presence of phthalic half-ester end groups in both crystalline and amorphous environments.

Two-dimensional (2D) solid-state orientational exchange NMR has been used to investigate the motion of a cross-link unit in a model network. The 31P chemical shift anisotropy provides an orientational probe of the tris(4-isocyanatophenyl) thiophosphate cross-link in the network interconnected with telechelic polypropylene glycol). Two-dimensional spectra were taken at two temperatures near the glass transition and at a series of mix times. From the variation of the 2D-NMR pattern with temperature and mix time, the motion of the cross-link is identified as isotropic Brownian reorientational diffusion. Good simulations of the spectra were obtained using a distribution of Brownian rotational diffusion correlation times corresponding to the Williams-Watts stretched exponential correlation function. The parameters are the mean correlation time r and the exponent a. At 30 °C r = 1.0 s and a = 0.45; at 35 °C r = 0.05 s and a = 0.45. The temperature dependence of the cross-link motion follows the WLF form with Ci = 15 and C2 = 104. The parameters derived from the NMR data are sufficient to describe the temperature dependence and breadth of both the dielectric and mechanical loss associated with the glass transition.

A new ionomer blend of zinc-neutralized sulfonated poly(2,6-dimethyl-1,4-phenylene oxide) and an amino silicone copolymer was prepared. The blend precipitates as a gel from dilute solution and forms a coherent film. Magic angle spinning carbon-13 spectra indicated coordination of the amine of the amino silicone copolymer by the zinc ion. Differential scanning calorimetry and dynamic mechanical spectra show a smearing out of the glass transition over the more than 300 deg temperature separation of the glass transitions of the component polymers. Solid-state proton NMR line shapes indicate narrowing commences at −115 °C, but then the line remains a composite of a narrow Lorentzian line and a broad Gaussian line for at least the next 200 deg, in agreement with the dynamic mechanical data. Goldman−Shen proton spin diffusion measurements give a domain size of the order of 30 Å, corresponding to the more mobile protons contributing to the Lorentzian line shape component. Silicon-29 chemical shift anisotropy line shapes demonstrate the onset of mobility for some of the siloxane units beginning at −115 °C, but complete line shape collapse does not occur even after a 200 deg temperature rise. This again indicates an extended glass transition process even when considering just one component of the blend.

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