Crystal Structure of Alternating Propylene-Carbon Monoxide Copolymers of Different Stereo- and Regioregularities

D. V. Anokhin, V. M. Neverov, S. N. Chvalun, N. P. Bessonova, Yu K. Godovsky, F. Hollmann, U. Meier, B. Rieger

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Abstract

The structure of alternating propylene-carbon monoxide copolymers is studied. The polymers are synthesized either without any regularity control or with the use of an enantioselective catalyst. It turned out that poly(propyleneketone) crystallizes with the formation of two lattice types depending on the conditions of its synthesis. Copolymers that contain one of the enantiomers crystallize into an orthorhombic cell (a = 10.68 Å, b = 6.18 Å, and c = 9.01 Å). Samples consisting of a mixture of two enantiomers form a stereocomplex, which crystallizes with the formation of a triclinic lattice (a = b = 9.45 Å, c = 9.04 Å, α = β = 109.4 °, and γ = 109.0°). The macroscopic properties of these samples significantly differ. Both crystal forms are shown to have identical chain conformations represented by a 31 helix. The cells contain two polymer chains each. The unit cell parameters and the melting point of the triclinic modification significantly depend on the chain regularity. For example, samples containing the stereocomplex of isotactic regioregular L- and D-helices melt at 239°C. As the number of attachment defects increases, the melting point notably decreases and amounts to 68°C for samples synthesized without any regularity control. Nevertheless, the process of stereocomplex formation remains energetically favorable, a fact explained by the existence of a selective interaction between the helices.

Original languageEnglish
Pages (from-to)52-60
Number of pages9
JournalPolymer Science - Series A
Volume46
Issue number1
StatePublished - Jan 2004
Externally publishedYes

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