Scientific Publications of Jos Aerts
Polymorphism in Alternating Polyketones Studied by X-ray Diffraction and Calorimetry
E.A.Klop, B.J.Lommerts, J.Veurink, J.Aerts and R.R. van Puijenbroek
J.Pol.Sci., Pol.Phys., 33, 315-326 (1995)
Differential scanning calorimetry and high-temperature X-ray diffraction were used to study the
perfectly alternating copolymer of ethene and carbon monoxide (polyketone; POK-C2).
It was found that oriented POK-C2 fibers show a crystalline phase transition at a temperature
between 110-125C with a 10% change in crystalline density. At this temperature,
the crystal structure reported recently (POK-alfa) is transformed to a crystal structure
that was reported in the past for room temperature imperfectly alternating polyketone.
The latter will be designated POK-beta. The influence of chain defects on the crystal structure
was studied by synthesizing terpolymers (POK-C2/C3), in which small amounts of propylene-CO
units are incorporated into the polymer backbone. The resulting terpolymers differs from
the copolymer by the presence of methyl groups randomly distributed along the polyketone backbone chain.
Evidence is presented that indicates that the methyl groups are build into the crystal lattice as defects.
With more than 5 mole-% propene the terpolymer fibers crystallize exclusively in the beta-modification.
Below this level the alfa-beta ratio (at room temperature) increases with decreasing amounts of propene.
Both as-synthesized and as-spun POK-C2 were found to consist of POK-alfa and POK-beta;
the alfa-beta ratio depends on the method of preparation.
Because the drawn POK-C2 fibers studied here consist exclusively of POK-alfa,
the process of spinning and drawing leads to the transformation of unoriented beta-rich
material into oriented POK-alfa.