No abstract

The hydrophilic−hydrophobic diblock copolymer (2-hydroxyethyl methacrylate, HEMA)41-block-(isoprene)84 was synthesized by anionic living polymerization using a protection technique for the hydroxyl group of HEMA. The surface structures of the block copolymer film under dry and wet conditions were analyzed by transmission electron microscopic observation and contact angle and angle-dependent X-ray photoelectron spectroscopic measurements. The top surfaces of the films cast from DMF/THF and THF/methanol are covered with a polyisoprene microdomain. When the as-cast film is exposed to water, the polyisoprene layer at the top surface disappears and is replaced with a PHEMA microdomain. In particular, the hydrated surface clearly emerges under transmission electron microscopy (TEM) by the double-staining method and reverts again to a hydrophobic polyisoprene layer by annealing the film at 52 °C for 1 h. Such surface rearrangement occurs repeatedly by soaking in water and annealing. The short-time-scale reorientation of the surface microdomain of the film under dry to wet conditions is successively observed with TEM. The difference between the surface rearrangements of the PHEMA-block-polyisoprene and PHEMA-block-polystyrene films in response to environmental change is also investigated.

Hydrophilic−hydrophobic diblock copolymers composed of 2-hydroxyethyl methacrylate (HEMA) and 4-(7‘-octenyl)styrene with 26, 47, and 82 wt % of poly[4-(7‘-octenyl)styrene], HO-30, -50, and -80, respectively, were synthesized by anionic living polymerization. The surface structures of their solvent-cast films under dry and wet conditions were analyzed by contact angle measurements, transmission electron microscopic (TEM) observation, and X-ray photoelectron spectroscopic (XPS) measurements. The analytical results of HO-30 and HO-50 substantiate surface restructuring in response to environmental change. When the films were soaked in water, very quick hydration of the surface was observed. However, dehydration of the surface occurred slowly even by annealing in air. TEM observation was successfully performed by staining technique with OsO4 and introduction of a carbon−carbon double bond in the hydrophobic segment. Cross sectional TEM images of near film surfaces suggested that the phase restructuring at the outermost surface corresponding to environmental change occurred at the microdomain scale of the block copolymer. The block copolymer film of HO-80 retained a hydrophobic surface under various conditions and never experienced surface restructuring.