We achieved a thermal sampling scanning of the β-relaxation region of polypropylene (PP) block copolymers together with the β process of isotactic polypropylene, high-density polyethylene, propylene-ethylene rubber, and part of the PP bloc copolymer soluble in xylene and insoluble in ether. The comparison of activation parameters determined in the above relaxations confirmed the hypotheses drawn from complex spectra studies concerning phase separation and the origin of dielectric relaxations in PP block copolymers. One of the dielectric relaxations of the part of PP block copolymer soluble in xylene and insoluble in ether could be attributed to polypropylene blocks. We related the preexponential factor of the relaxation time to chain environment. Then we discussed the compensation phenomenon in distributed relaxations and the relation between the compensation temperature and variation of thermal expansion coefficient through the compensating relaxation.

The thermally stimulated depolarization (TSD) technique was used to observe the amorphous phase separation in polypropylene block copolymers and to attribute its various dielectric relaxations to precise mobile entities. The complex thermostimulated spectra of polypropylene block copolymers were compared to complex spectra of polymers of the same nature as those of its main components, i.e., isotactic polypropylene, high-density polyethylene, and propylene-ethylene rubber. With TSD we then studied a binary blend of polypropylene and high-density polyethylene and another blend of polypropylene and propylene-ethylene rubber and also the various parts of polypropylene block copolymer which were separated by a selective solvent extraction. From peak-position and intensity considerations we suggested the origin of the three relaxations appearing from 90 to 290 K in the TSD complex spectra of polypropylene block copolymer.

A thermally stimulated depolarization current technique has been used to deduce the compensation law in low density polyethylene β and γ relaxations. The linear relationship between the activation energy and the logarithm of the preexponential factor of the relaxation time has been discussed in terms of compensation temperature and variation of the thermal expansion coefficient through the β and γ processes.

We determined the chain segment lengths involved in the γ process of low-density polyethylene by introducing linear alkanes of different chain lengths into the polymer. These alkanes possess at one end of the chain an electric dipole constituted by an ester group. Their influence on the γ relaxation of low-density polyethylene was observed by thermostimulated depolarization measurements. We found a correlation between the γ temperature peak position and the alkane chain length, while the activation parameters distributions determined by the thermal sampling technique were only slightly modified. This was explained by considering that the distribution in activation parameters is partly induced by a distribution in the chain segment length of the relaxing species. Adding a linear alkane to the polyethylene modifies the population of the mobile chain segments of a given length. We deduced that the γ1 subrelaxation is induced by the motion of chain segments having approximately between 10 and 20 carbon atoms. A compensation law was evidenced in the γ process of all samples studied. The slight modifications of the preexponential factor of relaxation time and the variation of compensation temperature with the alkane chain length are discussed considering a local order in the amorphous phase of low-density polyethylene.

The poor im oact strength of isotactic polyprooylene ( P.P) is one of the major deficiencies of this p oly m er for many aonlications. Its toughness can be im proved by incoroorating a propylene-ethylene rubber (EPR) by "in situ" block co polyme ri�ation techniques. A oolypropylene copoly m er is thus obtai ned w hose pro p erties deoend on the molecular motions allo w ed in its phase separated m ophology.W he have studied the chain motions in the amor p hous regions of the polyprooylene cODoly m er using ther m ostim ulated depo larization comDlex soectra (TSD) cou p led with thermal sam pling (T .5) techniques (1, 2). EXPERIMENTALThe experiments have been carried out in a com mon LN2cryostat. The T.S.D cell has been designed to avoid thermal gradients in the sa m pIes and has been described else w hEl't'(3).Sa m pIe preoaration is an im portant sten towards obtaining noiseless and reproducible results. The noly m ers under conside ration have been melt pressed between two stainless steel circular electrodes (28 m m in dia meter) in order to obtain a film of about 220 Ii m thick. To extract all tra p ped charges, the films needed to be melted again between the electrodes.T he crystallization conditions were 10 K / m n cooling rate and have been the sa m e for all sa moles.In T 5 D and T 5 exoeri m ents cooling and heating rates were 10K / m n. 454