Order-disorder transition in comblike block copolymers obtained by hydrogen bonding between homopolymers and end-functionalized oligomers: Poly(4-vinylpyridine)-pentadecylphenol

Dynamic mechanical spectroscopy (DMS) is used to further investigate the recently observed order-disorder transition (ODT) in comblike block copolymers obtained by hydrogen bonding between poly(4-vinylpyridine) and pentadecylphenol (P4VP-PDPx). For stoichiometric amounts of pyridine and phenol, i.e., z = 1.0, the ODT to a lamellar structure occurs at T similar or equal to 65 degrees C. The dynamic moduli G' and G '' simultaneously show a crossover from a liquidlike behavior (G' similar to omega(1.5) and G '' similar to omega) to a response intermediate between a Newtonian fluid and a solid (G' approximate to G'' similar to omega(1/2)). The behavior above T-ODT differs slightly from a homopolymer melt (G' similar to omega(2.0)) due to composition fluctuations, whereas the behavior below T-ODT is characteristic for quenched block copolymer lamellar phases with local uniaxial order and global isotropy. Near room temperature, a transition to solid behavior (G similar to omega(0)) takes place due to crystallization of the alkyl side chains. Larger amounts of PDP lower the T-ODT temperature, and for x = 2.0 the transition to solid response occurs directly from the disordered state. Small and wide angle X-ray scattering (SAXS and WAXS) experiments and differential scanning calorimetry (DSC) corroborate these findings. Furthermore, SAXS and WAXS demonstrate that the low-temperature state of P4VP-PDP2.0 is not stable and indicate that ultimately macrophase separation into a pure crystalline PDP phase and a microphase separated P4VP-PDP phase occurs.