¹³C Nuclear magnetic resonance spectroscopy of polypropylene, 2. ¹³C spin‐lattice relaxation study in solution

Abstract

Proton-decoupled partially relaxed FOURIER transform (PRFT) NMR of 13C in natural abundance was used to determine spin-lattice relaxation times (TI) of individual carbons of polypropylene and polyethylene in o-dichlorobenzene solution and molten polyethylene. It is shown that the relaxation times of polypropylene carbons are independent of the difference in stereochemical configuration. From the values of the nuclear OVERHAUSER enhancement factor it is shown that the excess energy from equilibrium of all 13C in polypropylene and polyethylene are absorbed into lattice mainly through W -l H dipolar interactions. It is shown that the effective rotational motion of the skeletal carbons in polypropylene is isotropic. The activation energies of skeletal and internal methyl motions in polypropylene, separately, and skeletal motion in polyethylen in solutions were estimated from the temperature dependence of the correlation time. The assignment of the two peaks appearing in methine carbon region of polypropylene was briefly discussed. ZUSAMMENFASSUNG:Protonenentkoppelte PRFT-NMR Spektren von naturlich vorkommendem 13C wurden zur Bestimmung von Spin-Gitter-Relaxationszeiten (TI) bestimmter Kohlenstoffatome des Polypropylens und Polyathylens in o-Dichlorbenzol-Losung und in geschmolzenem Polyathylen verwendet. Es wird gezeigt, daB die Relaxationszeiten der Polypropylen-Kohlenstoffe von Konfigurations-Unterschieden unabhangig sind. Mit Hilfe der Werte des OVERHAUSER-VerStarkungSfaktorS wird gezeigt, daB die oberschul3-Energie aus dem Gleichgewicht aller 1% in Polypropylen und Polyathylen vom Gitter aufgenommen wird, und zwar hauptsachlich durch 13C-lH-dipolare Wechselwirkungen. Es wird auoerdem die Isotropie der effektiven Rotations-Schwingung der Kohlenstoff-Skelette im Polypropylen aufgezeigt. Die Aktivierungsenergien der Skelett-und der internen Methyl-Schwingungen im Propylen selbst und die Skelett-Schwingungen im Polyathylen in Losung wurden aus der Temperaturabhangigkeit der Korrelationszeit abgeschatzt. Die Zuordnung der beiden Peaks, die im Bereich des Methin-Kohlenstoffs von Polypropylen erscheinen, wurde kurz diskutiert.*) cf.4); this paper is considered to be Part 1 of this series.

Local dynamics of isotactic and syndiotactic polypropylene in solution

“…[12][13][14][23][24][25][26] The highfield CH 2 lines were assigned to carbons located in mesocentered tetrads, whereas the low-field CH 2 lines corresponded to CH 2 groups in racemic-centered tetrads. The opposite behavior was observed for the CH lines: the lowfield lines correspond to meso sequences whereas the highfield lines belong to racemic-enriched sequences.…”

“…The position and height of the T 1 minimum are independent of the microstructure of the tetrad considered within the accuracy of the experiment. At high temperature, the [12][13][14] The identical values determined for the T 1 minimum of the CH carbons ͑or for the T 1 minimum of the CH 2 carbons͒ in the different stereosequences in the aPP polymer can be interpreted in terms of the DLM motional model as an independence of the fast libration amplitude on the microstructure. Since the contribution of the libration to the 13 C spinlattice relaxation is very similar in all the stereosequences, the higher T 1 values observed at high temperature in the meso-centered sequences indicate that the segmental motions of the chain are somewhat faster in the meso-centered sequences than in the racemic-centered ones.…”

“…͑b͒ Both experiments and simulations indicate a slight but noticeable difference between the local dynamics of meso and racemic microstructures, in agreement with previous experimental indications. [12][13][14] We will use our OACF analysis to pinpoint the microscopic origin of this difference.…”

Application of Catastrophe Theory to Draw Resonance

“…Such a delay is expressed in eq 4 in the form of simple exponential decay. The quantities ri and f3 can be solved as functions Linear differential equations such as eq 2 and 4 can be summarized in the general form of dxfdt= -f(x) (5) where xis the representative of ri and {3, andf(x) is a function of x. The variable x is called a dynamical variable.…”

“…In a trans-decalin solution of a polypropylene the PRFT (partially relaxed Fourier transform) 13 C NMR spectrum, there are many peaks corresponding to chemical groups and stereochemical configurations. 5 The intensity of each peak in the PRFT spectrum recovers exponentially with respect to its thermal equilibrium value with a corresponding discrete time constant. As seen from experimental evidence, no positive proof for the necessity of a relaxation spectrum from NMR experiments could be found.…”