Specific interaction between poly(styrene-co-4-vinylphenol) and poly(styrene-co-4-vinylpyridine) studied by C-ray photoelectron spectroscopy and time-of-flight secondary ion mass spectrometry

The specific interaction of hydrogen bonding between poly(styrene-co-4-vinylphenol) (STVPh) and poly(styrene-co-4-vinylpyridine) (STVPy) was investigated by X-ray photoelectron spectroscopy (XPS) and time-of-flight secondary ion mass spectrometry (ToF-SIMS). The density of the hydrogen bond was adjusted by varying the 4-vinylphenol (VPh) content in the STVPh copolymers. Immiscible blends were formed when the VPh content was low, and an interpolymeric complex was formed when the VPh content was above a certain value. In addition, an interpolymer complex was formed between poly(4-vinylphenol) (PVPh) and STVPy-72 (containing 72 mol % of Py). For the complexes, XPS results revealed that the intermolecular hydrogen bonds between the hydroxyl and pyridyl units can induce a shift of 0.6-0.7 eV and 0.4-0.5 eV in the N 1s and O 1s binding energies, respectively. Such large shifts in the binding energy may imply that the nitrogen is partially protonated. The XPS results also showed that STVPy-72 was enriched on the surface of immiscible blends of STVPy-72 and STVPh-y (where y is the mol % of VPh, y = 1, 9, and 22). However, surface segregations of STVPh-50 and PVPh were detected respectively for the complex between STVPh-50 and STVPy-72 and the complex between PVPh and STVPy-72. The intensity ratios of the ions for the complexes that were affected by the formation of hydrogen bonding, such as C5H6N+/C5H5N+ and C6H7N+/C6H6N+, were larger than those in the STVPy-72 copolymer. The intensity ratios of these ions for immiscible blends of STVPh and STVPy-72 and for the STVPy-72 copolymer were almost the same. The results indicate that hydrogen bonding plays an important role in the distribution of the peak intensities of the ions that are affected by the formation of hydrogen bonding in a SIMS process.