Miscibility of Propylene−Ethylene Copolymer Blends

Abstract

Miscibility of homogeneous propylene/ethylene (P/E) copolymers of relatively narrow molecular weight distribution was studied as a function of constituent comonomer content. Polymers with up to 31 mol % ethylene were blended in pairs in order to vary the comonomer content difference. Binary blends were rapidly quenched from the melt to retain the phase morphology, and the phase volume fractions were obtained from AFM images. Copolymers of molecular weight about 200 kg mol-1 were miscible if the difference in ethylene content was less than about 18 mol % and immiscible if the ethylene content difference was greater than about 20 mol %. Blends with constituent composition difference in the range of 18−20 mol % exhibited partial miscibility in the melt as indicated by a phase volume fraction that was different from the blend volume fraction. The temperature dependence of blend morphology confirmed the UCST behavior of P/E copolymer blends. The phase composition and the χ interaction parameter were extracted by using an approach that considered the molecular weight distribution. The compositional dependence of χ conformed to the copolymer equation and depended on comonomer content difference only, not on comonomer content per se.

The chemical structure of the amorphous phase of propylene–ethylene random copolymers in relation to their stress–strain properties

“…In binary blends of polypropylenes with small quantities of ethylene content, the presence of rubbery domains has been previously reported [26,32,58,59]. The situation is probably very similar in the case of PPR.…”

“…From this trend in mobility, it is most likely that chain segments with an amount of ethylene units above a certain concentration aggregate and form small (possibly nanoscopic) rubbery domains. Previously, it has been shown that phase separation can already occur in the molten state for metallocene-derived statistical ethylene e a-olefins copolymers [57,58]. The tendency for phase separation should be even larger for the samples studied here, as they were synthesized using ZN catalysis.…”

“…This type of catalysis causes a more heterogeneous distribution of ethylene units alongand between chains. In addition, crystallization should further increase the tendency for phase separation due to higher concentration of ethylene-rich chain fragments in the amorphous phase [58].…”

Phase Evolution Theory for Polymer Blends with Extreme Chemical Dispersity: Parameterization of DDFT Simulations and Application to Poly(propylene) Impact Copolymers

“…The interaction between neat PE and PP that we will use in the numerical calculations is x 1;0 ¼ x 0;1 ¼ 0:01 (see Introduction and ref. [25][26][27] ). For the coarse-grained chain this is replaced by the interactions between the beads as…”

“…[25][26][27][28] . In our analysis we will assume that all chains have same length of N ¼ 10 4 monomers with a Flory-Huggins parameter x ¼ 0.01 between the E and P monomers (xN ¼ 100); these are typical values that can easily be adjusted to specific samples.…”