Pulsed NMR observation of ultradrawn polypropylene

Abstract

Proton spin‐spin relaxation times have been measured as a function of temperature for ultradrawn polypropylene with draw ratios λ up to 24. The three relaxation times T2a (the longest), T2i (intermediate), and T2c (the shortest), observed for all the samples, have been ascribed to the relaxations of the amorphous, constrained amorphous, and crystalline components, respectively. T2i and T2a, which reflect the changes in structure and mobility in the noncrystalline regions, decrease with increasing λ; T2i becomes saturated at λ > 9, whereas T2a shows a substantial decrease up to λ = 24. The continued decrease in T2a indicates that the constraint on the amorphous segments keeps increasing up to the highest λ. The associated mass fractions Fa, Fi, and Fc also change with λ. At λ < 9, the increasc in Fi with increasing λ is accompanied by a decrease in Fa, with Fc remaining unchanged. At higher λ, however, Fa is almost constant, and stepwise rises in Fc at about λ = 12 and 24 are accompanied by corresponding drops in Fi. It seems that, in this high draw ratio range, some of the taut molecules are fully extended and are in sufficiently good lateral register to transform into crystalline bridges. This conjecture is supported by the similarity in the λ dependence of Fc and the mass‐fraction crystallinity obtained from the heat of fusion.

Study of stretched polypropylene fibres by pulsed and CW NMR spectroscopy

“…These effective interproton distances were calculated according to Eq. (5) with fulfilled condition (6). For relaxation constant C was used the expression for rigid lattice approximation [1, p. 42].…”

“…There are several papers dealing with relaxation properties of the partially crystalline PP by using the pulsed NMR techniques [1][2][3][4][5][6]. A lot of investigators [4,7,8] analysed the broad-line NMR spectrum.…”

“…The estimated values of the parameters obtained by the least-square fit of Eqs. (4)-(6) are given in…”

Effects of uniaxial stretching and shrinkage on proton spin-lattice and spin-spin relaxation times of isotactic polypropylene

“…On oriented isotactic polypropylene films and fibers, several works have already been reported [3][4][5]. There are, however, few investigations of the relaxation effects on the thermally shrunk sample.…”

Rheological studies of moderately concentrated polystyrene solutions. I. A new method for the extrapolation of the zero‐shear viscosity

“…In the second part of this series the form of the master curve is discussed in terms of the modified Graessley theory. [11][12][13][14] The shift parameter TO [cf. eq.…”