Improving the high-temperature performance by constructing restricted amorphous regions in PEEK

Abstract

Improving the high-temperature performance of polymers through crosslinking without compromising properties such as ductility and processability remains a significant challenge. In this study, we synthesize a cross-linkable poly (ether ether ketone) end-capped with phenylethynyl groups (PEEK-PEPs) and subsequently melt-blended it with semi-crystalline PEEK to create the PEEK alloy (PEEK/PEEK-PEPs). Under thermal treatment, the curing process of PEEK-PEPs is dominated by the formation of a cross-linked network, accompanied by chain growth reactions. The chain growth reaction will gradually become the dominant reaction as the treatment time increases. These results are validated by successive self-nucleation and annealing, as well as measurements of gel fraction and viscosity before and after thermal treatment. With this approach, the storage modulus (E') of PEEK/PEEK-PEPs is improved by 95 % at 290 °C, and the heat deflection temperature (HDT) is increased by 25 °C. Meanwhile, the tensile strength of PEEK/PEEK-PEPs at room temperature and 150 °C increases to 125 MPa and 72 MPa, respectively, which is 30 % and 31 % higher than that of pristine PEEK resins, while the strain at break remains at the same level as PEEK. These findings potentially provide an advanced polymer alloy preparation method for high-temperature applications, particularly in extreme environments.