Poly(2-ureidoethyl methacrylate) (PUEM) was prepared via reversible addition-fragmentation chain transfer (RAFT) controlled radical polymerization and a post-modification reaction. PUEM shows upper critical solution temperature (UCST) behavior in aqueous solution. Although PUEM can dissolve in water above the UCST, it cannot dissolve in water below the UCST. Diblock copolymers (MmUn) composed of a biocompatible hydrophilic poly(2-methacryloyloxyethyl phosphorylcholine) (PMPC) block and a PUEM block with different compositions were prepared via RAFT radical polymerization and a post-modification reaction. "M" and "U" represent PMPC and PUEM blocks, respectively, and the subscripts represent the degree of polymerization of each block. M95U149 and M20U163 formed polymer micelles comprising a PUEM core and a PMPC shell below the critical aggregation temperature (Tc) in aqueous solution. Polymer micelles were formed from M20U163 below 32 °C, which can incorporate guest molecules into the core.

Poly(2-ureidoethylmethacrylate) (PUEM n ) was synthesized via reversible addition-fragmentation chain transfer (RAFT) radical polymerization and following polymer reaction. We prepared two PUEM n samples with different degrees of polymerization (n 5 100 and 49). The polymers exhibited upper critical solution temperature (UCST) in phosphate-buffered saline (PBS) solution. The phase separation temperature (T p ) in PBS can be controlled ranging from 17 to 55 8C by changing molecular weight of the polymer, polymer concentration, and adding NaCl concentration. The polymers in PBS formed coacervate drops by liquid-liquid phase separations below T p . Results of the dielectric relaxation measurement, the hydration number per monomeric unit was 5 above T p . Based on a fluorescence study, the polymer formed slightly hydrophobic environments below T p . The liquid-liquid phase separation was occurred presumably because of weak hydrophobic interactions and intermolecularly hydrogen bonding interactions between the pendant ureido groups.

The tribological properties of the dilute solution of an ABA triblock copolymer, poly(11-acrylamidoundecanoic acid)-block-poly(stearyl methacrylate)-block-poly(11-acrylamidoundecanoic acid (A5S992A5), in poly(α-olefin) (PAO) confined between mica surfaces were investigated using the surface forces apparatus (SFA). Friction force was measured as a function of applied load and sliding velocity, and the film thickness and contact geometry during sliding were analyzed using the fringes of equal chromatic order (FECO) in the SFA. The results were contrasted with those of confined PAO films; the effects of the addition of A5S992A5 on the tribological properties were discussed. The thickness of the A5S992A5/PAO system varied with time after surface preparation and with repetitive sliding motions. The thickness was within the range from 40 to 70 nm 1 day after preparation (the Day1 film), and was about 20 nm on the following day (the Day2 film). The thickness of the confined PAO film was thinner than 1.4 nm, indicating that the A5S992A5/PAO system formed thick adsorbed layers on mica surfaces. The friction coefficient was about 0.03 to 0.04 for the Day1 film and well below 0.01 for the Day2 film, which were 1 or 2 orders of magnitude lower than the values for the confined PAO films. The time dependent changes of the adsorbed layer thickness and friction properties should be caused by the relatively low solubility of A5S992A5 in PAO. The detailed analysis of the contact geometry and friction behaviors implies that the particularly low friction of the Day2 film originates from the following factors: (i) shrinkage of the A5S992A5 molecules (mainly the poly(stearyl methacrylate) blocks) that leads to a viscoelastic properties of the adsorbed layers; and (ii) the intervening PAO layer between the adsorbed polymer layers that constitutes a high-fluidity sliding interface. Our results suggest that the block copolymer having relatively low solubility in a lubricant base oil is effective at forming low-friction adsorbed layers in oil-based lubrication.

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