Comments on a paper by Axelson and Mandelkern concerning ¹³C NMR spectra of polymers

Abstract

SynopsisIt is shown that the 13C NMR spectral collapse temperatures T, reported by Axelson and Mandelkern tend to give a constant ratio of T,/T, averaging 1.21 f 0.05 and independent of T, or of polymer structure. It is further shown that T, is not a high-frequency value for T, because this would require TJT, to decline with increasing T,. T,/T, agrees in numerical value with T[l/T,, where Ti/ is the liquid-liquid transition lying above T,. Direct comparison of T, and Tu for four polymers PIB, PnBA, atactic PP, and isotactic PMMA shows very close agreement. The various results suggest, but do not prove, that T, from NMR spectroscopy may be a new, direct measure for TI[. A measured T, of 233K for linear P E is compatible with a Tg near 195 K (233/195 = 1.191, whereas a Tg of 148 K gives the ratio 233/148 = 1.57, which is outside any value shown in tabulated form.frequency of lo3 Hz. Table I assembles the data and these calculations.The most surprising result is the tendency of T,/Tg to be relatively constant from polymer to polymer with an average value of 1.21 (glycerol omitted) and a range from 1.16 to 1.30.The differences (again omitting glycerol) are more erratic at first glance. The

Dynamics and thermodynamics of the liquid state (T < Tg) of amorphous polymers

“…We note the unusually high ratio, TPn/T = 1.32, for very low frequency o r quasi-static values g 13 of T and TRP . This is consistent with C-NMR data discussed previously [97,98]. Stiffness of the PIB chain may be responsible.…”

“…"C-NMR spectroscopy as a function of temperature in the T > T g region suggests that the sharp 13C spectra for a variety of polymers collapse on cooling below Tpp [97], This conclusion is still tentative but is interesting. Appearance of 13C spectra requires decoupling between motion of the 13C atom and neighboring protons.…”

“…Appearance of 13C spectra requires decoupling between motion of the 13C atom and neighboring protons. In particular, we have found [97] that Tc/T is constant at 1.2, where Tc is g -1 Trans-gauche changes (527 and 566 cm ) a r e PI1 * in the collapse temperature measured by Axelson and Mandelkern 1981. The thermally stimulated current method, TSC, has been employed by Lacabanne et al t o observe both T and Tip in a PMMA [99] and in a PS [91,100]; and by Marchal et al [loll in several types of PS. Lacabanne et al [99,100] have shown for PMMA and PS that T gives Arrhenius-type behavior, whereas T p p follows a Vogel-type of equation as would be expected for the liquid state.…”

“…The first expressed recognition of a numerical relationship between T and TQQ for PS was presented by Stadnicki et al [27,28] [97] that the ratio, T /T encouraged u s to suggest that T is a measure f o r T at which c g' is 1.21, which c g' PP * C One might expect the ratio T /T t o approach unity as Mn+ 0, E 2 g since the distinction between segmental (T ) and macromolecular (Tan) motion should vanish (see Fig. 2).…”

Real time optical and mechano-optical studies during drying and uniaxial stretching of Polyetherimide films from solution

“…The presence of this elastic behavior above T g is attributed to the material having distribution of rigidities and some regions showing stiffer segmental correlations than others in this T g eT ll (liquideliquid transition). The T ll is commonly observed at approximately 1.2 times of T g [50,51]. In the T g eT ll range, the material does not exhibit fluid behavior due to the presence of rigid segmental correlations adding to the entanglement network junctions.…”