Nuclear magnetic resonance and molecular motion in polymethyl acrylate, polymethyl methacrylate, and polyethyl methacrylate

Abstract

The proton magnetic resonance in polymethyl acrylate, polymethyl methacrylate, and polyethyl methacrylate has been studied between 77 and 400°K. The second moments of the absorption lines are compared with the values calculated for some of the modes of molecular motion possible in these polymers. This comparison leads to the conclusion that motion of the ester methyl and ethyl groups in the respective polymers occurs below 77°K. and that motion of the main chain methyl groups in polymethyl methacrylate and polyethyl methacrylate occurs above 130°K. This interpretation of the results is shown to be in agreement with previous measurements of the mechanical and dielectric properties of these polymers. The shape of the absorption line observed in polymethyl methacrylate at 77°K. was reproduced by a suitably weighted superposition of the absorption lines of rigid and rotating methyl groups and a rigid methylene group confirming that motion of one methyl group occurs below 77°K. in polymethyl methacrylate.

Microscopic dynamics of the glass transition investigated by time-resolved fluorescence measurements of doped chromophores

“…Many other studies also support this idea that the side chains are still moving even when the main chain is frozen in below T g . [51][52][53] For each curve in Fig 10, a kink can be seen at T g , although it is not so pronounced as those for the monomeric samples and PB. However, no singular point could be clearly distinguished above T g ; i.e., we could not find the crossover at T c , which, even if it exists, may be masked by the sidechain motions.…”

“…Hindered rotation of ester methyl group in poly͑methyl acrylate͒ and poly͑methyl methacrylate͒ was found even at 77 K by means of nuclear magnetic resonance measurements. 53 In the above we have shown that the dynamics of complex polymers is different from that of the monomers and PB, since the side-chain motion plays an important role in the microscopic dynamics. On the other hand, we found that the dynamics of PB, a polymer without side chains, is similar to that of the monomeric glass-forming solvents.…”

“…The relaxation of polymers due to the local motions of ester side chains has been studied by dynamic mechanical measurements, 51,54,55 dielectric relaxation measurements, 51 and nuclear magnetic resonance measurements. 53 The results of those studies showed that the reorientation of ester side chain occurs even below T g . Therefore, the kink observed in the present study at several tens of degrees below T g may be attributed to the freezing of the rotation of ester groups.…”

Radiation-initiated graft polymerization of methylmethacrylate onto poly(tetrafluoroethylene): Characterization by1H-NMR

“…Sinnott et al reported that the CH 3 group attached to the ester groups in bulk PMMA is freely rotating at even 77 K. 22 However, in the present study, the same CH 3 group in PMMA grafted onto PTFE does not rotate completely freely. That is, the diffusion rate of the CH 3 groups in PMMA grafted onto PTFE is lower than that of the CH 3 groups in bulk PMMA.…”

“…and freely rotating CH 3 group around the C 3 axis (5.4 Gauss 2 ), the CH 3 groups of both components attached to the ester groups in PMMA were concluded to be an intermediate rotational rate between them at this temperature. The same CH 3 group of bulk PMMA has been reported to be freely rotating at even 77 K. 22 This difference of the CH 3 group rotation can be attributed to a stronger interaction between the PTFE and PMMA chains than that between the PMMA chains. The ͗⌬H 2 ͘ values of the L and G components were independent of the grafting amounts, but the L/G ratio depended on the grafting amounts.…”