Structure-property behaviour of poly(ether ether ketone)-polydimethylsiloxane block copolymers and their ketamine precursors

The influence of changing the block length of the polydimethylsiloxane block on the structure/property behaviour of two poly(ether ether ketone)-polydimethylsiloxane (PEEK-PSX) multiblock copolymers and their amorphous (non-crystallizable) ketamine precursors (PEEKt-PSX) was investigated. In the precursor block copolymer form, as well as the reduced amorphous and its corresponding semicrystalline form, a microphase morphology was noted from transmission electron microscopy (TEM) studies. For the solution cast precursor or the compression moulded reduced amorphous systems, the materials displayed two Tgs at ca. −130 and +145°C, indicating strong phase separation. It was found that the room temperature tensile modulus of the PEEK-PSX multiblock copolymers with amorphous PEEK blocks of M n = 4000 increased by 800% as the PSX block length was decreased from M n = 5000 to M n = 3000 , i.e. the PSX mass fraction was decreased from 56 to 45%. This increase in stiffness resulted from developing a more continuous phase of the PEEK block component. After crystallization of the PEEK blocks, the room temperature modulus of both of the PEEK-PSX copolymers increased by 200–500% in contrast to their amorphous forms. Relative to the PEEK homopolymer of approximately the same molecular weight, the melt crystallization half-times for the multiblock copolymers were increased by a factor of 500 for the PEEK(4K)PSX(3K) system and by a factor of 1000 for the PEEK(4K)PSX(5K) system. A dramatic dependence of crystallization behaviour on thermal history prior to crystallization was observed in both microphase-separated block copolymer systems. Block copolymers thermally crystallized from the glassy state obtained a distinctly higher degree of crystallinity at a much faster rate of crystallization than the same copolymers crystallized from the melt at identical crystallization temperatures. Copolymers crystallized from the glass attained maximum levels of PEEK crystallinity of ~ 40%, while those crystallized from the melt attained a maximum level of crystallinity of only 5–20%. The rate of crystallization for samples crystallized from the glass was ~ 30 times greater than that for samples crystallized from the melt at identical crystallization temperatures. Possible explanations for these observations are presented.