NMR Study of β Relaxation in Modified and Blended Isotactic Polypropylene

Abstract

ABSTRACT:Broad line NMR and spin-lattice relaxation times T1 have been used to study glass transition phenomena in isotactic polypropylene modified and blended with an ethylene aminoalkylacrylate copolymer. By means of decomposition of spectra into elementary components corresponding to the chains with different mobility a softening due to the polymer modifier was observed. The modification results in an increase of fractions of amorphous and intermediate chains, respectively, gives rise to the enhancement of the chain mobility in amorphous regions, but the higher amount of the polymer modifier, which was used in the range up to I 5 wt%, the lower chain mobility in intermediate regions was found out. From the temperature dependences of the spin-lattice relaxation times T1 measured over the temperature range 290--430 K, a broadening of correlation time distribution on the side of the shorter correlation times has been found out to be and it was ascribed to overlapping of relaxation processes in amorphous regions. The sample containing the highest amount of the polymer modifier, in contrast to others, was shown to blend not only on the molecular level but also on the overmolecular.KEY WORDS In many of the previous works it was shown that isotactic polypropylene (PP) has a complex structure with regions of the different chain arrangement and different chain mobility. A heterogeneity, which may be studied by means of the broad line NMR spectra 1 -7 (ref I is to see the earlier papers) gives rise to the multiple transitions occuring in the temperature range around and above the glass transition ofPP. 8 Three components of the rotating frame spin-lattice relaxation times T 1 P with several relaxation minima in their temperature dependences also confirmed such relaxation behaviour. 9 · 10 On the other hand, due to spin diffusion only one relaxation time T1, a value of which is obviously determined by the most quickly relaxing, i.e., amorphous chains, may usually be measured. The minimum being appeared in the temperature range above the glass transition of PP corresponds to the f3 relaxation which was assigned to the glass transition phenomena. 9 · 11 -15In the precedent paper a considerable effect of the polymer modifier PFDA 522 on relaxation processes in PP was found out by the rotating frame spin-lattice relaxation times T 1P. 10 By the modification two temperature shifts towards the low temperatures were provoked in the amorphous regions of modified PP. They were the small shift only of the f3 relaxation corresponding to the segmental motion and the marked shift of the a. process, which was ascribed to the motion of the whole amorphous chains. This behaviour produced an overlapping of both discussed relaxations. It is reasonable to expect that this effect will also be observable by the spin-lattice relaxation times T1. But on the score of the spin diffusion only averaged parameters can be drawn from the T 1 measurements, an interpretation of which is not always unambiguos. On the other hand, it turns out that the b...

Study of stretched polypropylene fibres by pulsed and CW NMR spectroscopy

“…Decomposition of the NMR spectra into elementary components is very important for studying both molecular motion and structural heterogeneity of the partially crystalline polymers [8,[10][11][12][13][14]. The parameters characterizing molecular motion can be obtained also from the temperature dependences of the second moment of CW NMR spectra.…”

“…To describe a system with a distribution of correlation times one can use the non-symmetrical modified Fuoss-Kirkwood (mFK) distribution developed by Schneider [24,25]. The mFK distribution, particularly suitable for an account of the temperature dependences of the rate of spin-lattice relaxation 1=T 1 with different slopes on the low and high temperatures sides of the minimum, was considered in our calculation [12,26].…”

NMR and dynamic mechanical studies of drawn polypropylene fibers

“…The fibers investigated were prepared from commercial polymers: PP Mosten D3, which has been studied by NMR only recently [2,7], and PP denoted as Tatren 430. They differ in the number-average molecular weight, flow index and intrinsic viscosity measured at 135 8C.…”

“…The relaxation processes in polypropylene (PP) materials prepared under different conditions have been frequently studied by NMR and to date many papers (most of them cited in [1,2]) have been published on this topic. However, little attention has been paid to the influence of drawing on the relaxation behavior of the PP fibers and films studied by the measurement of the temperature dependence of spin -lattice relaxation times T 1 .…”

“…The temperature dependence of the correlation times s c , in the range from the glass transition T g up to T g + 100 K, is described by the WLF function or its analogous expression [6], but also the Arrhenius relation has been used in the interpretation of the relaxation behavior in this temperature range [2,5].…”