Effects of the chain microstructure on the properties of polyketones terpolymers characterized by scanning force microscopy

Abstract

A new approach is described to tailor properties of polyketones based on the controlled modification of the block structure by varying the polymerization process. Ethylene–propylene–CO (ECOPCO) terblock copolymers with similar composition but different chain microstructures have been synthesized using either preset polymerization (PSP) or pulsed-feed polymerization (PFP), respectively. Whereas by PSP an ABC-triblock structure is obtained, the PFP results in [AB] n -multiblock structure. In this paper we investigate the influence of the chain microstructure on the mechanical behavior and the surface properties. SFM phase images display a phase-separated bulk morphology where triblock polymers due to the larger block lengths form coarser structures than the multiblock samples. If the ECO content is above 50%, partially crystalline lamellar structures can be found, which in case of the multiblock sample form a continuous network of lamellar-like ECO rich domains. All ECOPCO terpolymers reveal elastomeric behavior with an elastic recovery of at least 82% but tensile strength and elongation vary with the block length of the chain microstructures. Differences in elasticity are explained by the formation of different amounts of cross-links consisting of blocks of parallel-aligned ECO chain segments or crystalline lamellae. It can be shown that the surface morphology differs from bulk morphology, mainly by the point that no distinct phase separation appears but ECO rich domains can be detected. Surface tension measurements enable to correlate the surface energy with surface composition and surface morphology.