Crystallization of the γ form in random propylene‐ethylene copolymers

Abstract

Wide‐angle X‐ray scattering and differential scanning calorimetry measurements have been conducted on seven random copolymers of propylene with ethylene in order to study the γ phase formation as a function of the comonomer content. The lamellar morphology of the samples was also investigated by small‐angle X‐ray scattering. The content of the γ phase was found to go through a maximum with crystallization temperature and to increase with comonomer concentration, up to a point (ethylene ≥6.5 wt%) where the latter parameter became less influential. The multiple melting endotherms behaviour of the samples was studied by DSC and temperature‐controlled diffractometric techniques. The attribution of the DSC peaks to the different isotactic polypropylene polymorphs that form in these conditions was confirmed. The results obtained permitted us to ascertain that, in the experimental conditions chosen, some further formation of crystallites takes place during the quenching to room temperature after the crystallization isotherm. In this phase, the chains organize themselves in stacks with thin lamellae, forming a distinct population with respect to those formed on isothermal crystallization. The melting of the thinner lamellae determines a convergence of the two populations into just one, still retaining an organization in stacks, that gradually disappears until complete melting of the material. Copyright © 2004 Society of Chemical Industry

Thermal Behavior, Structure and Morphology of Propene/Higher 1-Olefin Copolymers

“…This is in full agreement with recent findings by various authors for propene homopolymers [29,36] and copolymers with even 1-olefins. [32,49] The slope of the straight line in Figure 8 is slightly lower than unity because in the evaluation of K gDSC the contribution of the low melting g-form crystals are neglected, as it will be later justified, while in the room temperature WAXD they are fully accounted for.…”

Quantification of organoclay dispersion and lamellar morphology in poly(propylene)–clay nanocomposites with small angle X-ray scattering

“…The crystalline component shows an inverse dependence on number of stacks becoming prominent as the stack dimension becomes smaller and leads to peak broadening. This approach was applied to study broad diffraction patterns from low density polyethylene [41], high density polyethylene [48] polypropylene [38,49,50] and poly(butene) [51], and models consisting of statistically uniform stacks with a finite sizeknown as the finite lamellar stack model -as well as a variable stack model which also takes into account that a spatial variation in local crystallinity was seen to agree better with experimental intensity profiles than a simple stack of infinite width. Lattice model is based on two distributions; one that of a lattice with varying lattice parameters in space, with its lattice points defined as the centre of each stacks.…”

“…This approach was demonstrated by Causin et al for the quantification of organoclay dispersion in polypropylene and poly(butene) [49][50][51]53,54]. Influence of additives and processing conditions on extent of nanoclay dispersion was explained with quantitative data such as the number of clay layers, interlayer spacing and its distributions.…”

“…This effect has been ascribed to decreased chain mobility induced by clay particles, leading to the formation of smaller, less ordered crystallites [65]. In RCP and ICP, the g-fraction is also introduced by ethylene co-monomer [49] and additionally by nanosized filler in the nanocomposites. For the three polymers and their nanocomposites, relative content of g form with respect to a form was estimated from WAXS and is shown in Table 2.…”

Volumetric rheology of polymers

“…The hexagonal b-modification of polypropylene is obtained sporadically at high supercoolings or the presence of selective b-nucleating agents [4,5]. The triclinic c-phase is favored by the presence of structural defects in the polypropylene chain that can be introduced either by incorporating very low molecular weight branches [6,7] or by copolymerization with ethylene co-units of \10% mol [8][9][10][11][12][13]. Moreover, the crystallization of c-phase is enhanced under high pressure [14][15][16][17].…”