Crystallization control of etherethersulfone copolymers by regular insertion of an allyl functionality†
Acyclic diene metathesis (ADMET) polymerisation and nucleophilic aromatic substitution polycondensation are used to synthesize alternating copolymers based on polyetherethersulfone (PEES) blocks. ADMET results in incorporation of trans-allyl groups with more than 94 to 98% selectivity. The resulting polymers have a Mw of up to 13 600 g mol−1 and low dispersity (Đ = 1.1 to 1.4). Polycondensation, on the other hand, allows incorporation of either cis- or trans-allyl groups depending on the starting monomers. Molecular weights in the same range are obtained, but with much larger dispersity (up to 2.3), as expected. Characterization by differential scanning calorimetry and wide angle X-ray diffraction shows that incorporation of the cis group completely suppresses crystallization, whereas that of the trans group results in semi-crystalline polymers. Crystallinity is lost post-melting, but can be restored using appropriate solvent treatments. The crystal form changes with the length of the etherethersulfone (EES) group indicating that, when the repeat unit is small (containing a 4-ring etherethersulfone (EES) block), the allyl function is incorporated into the crystallographic repeat, whereas when the EES segment increases to eight rings, the allyl group is excluded from the crystal phase. Post-functionalization of the allyl group is demonstrated by using hydrogenation. The resulting polymer adopts a different crystal form for the 4-ring block, but the same crystal form for the 8-ring block, confirming the dependence on the block length for incorporation into the crystallographic repeat unit.