PEO-PLL

The work presented in the next section concerns the immobilization of retinoic acid by three polyamino acids poly(-L-lysine), poly(-L-arginine) and poly(-L-histidine). The mesomorphous structure of these complexes, which are prepared as nano-particles, has been examined. Then we will report on the physicochemical characteristics of water-soluble complexes formed between PEO-PLL block copolymers and retinoic acid. The structure in the solid-state and solution are discussed. Further the dissociation of the complex when changing the pH is reported. Finally, the immobilization of retinoic acid by PEI with different molecular weights is presented. 

This section reports on the physicochemical characteristics of water-soluble complexes formed between PEO-PLL block copolymers and retinoic acid. Two block copolymers were used. The lengths of the PEO blocks in both are identical, the molecular weight was 5000 g/mol (Mw/Mn=l.l). This corresponds to a degree of polymerization of 114. The length of the PLL block varies PEO-PLL18 has 18 L-lysine monomer units and PEO-PLL30 has 30. A sketch of the molecular structures is given in Fig. 17. 

The alcoholate was alternatively reacted with tin octoate to initiate the polymerization of L-lactide (LL) and produce (PS)(PEO)(PLL) star terpolymer. In another application of the method, the 1,1-diphenyl -alkylpotassium intermediate (I) was used to initiate the polymerization of MM A at —78 °C. After de-protecting and activating the hydroxyl group, the polymerization of ethylene oxide was initiated, leading to the formation of the (PS)(PMMA)(PEO) star terpolymer. If e-CL is polymerized instead of EO, then (PS)(PMMA)(Pe-CL) stars are produced. Limited characterization data were given for these stars. In all cases two of the arms grow from the star center and thus cannot be isolated and characterized. However, interesting amphiphilic structures were obtained. 

IPEC-containing micelles based on double-hydrophilic cationic block copolymers, such as PLL [303-306], PEI [307], or PDMAEMA [308] in combination with PEO, have been examined for the complexation of oligonucleotides in order to provide new pharmaceutical forms for gene therapy [309]. 

Poly(ethylene oxide)-b-poly (L-lysine) (PEO-h-PLL) Block copolymer In vitro transfection, systemic administration of plasmids, encapsulation of oligonucleotides (Kataoka et al., 1996 Wolfert et al., 1996)... 

Poly(ethylene oxide )-g-poly (/.-lysine) (PEO-g-PLL) Graft copolymer In vitro and in vivo transfection, delivery of oligonucleotides Choi etal, 1998)... 

Contributions of / -sheet structures to the spectra were not found to be present. It was concluded that the PLL conformation in the PEO-PLL18 retinoate and PEO-PLL30 retinoate micelles adopts an a-helix for pH values higher than 9.0 and a random coil at a pH lower than 3.7, while between these limiting values a mixture of a-helical and random coil structures is present. 

Keywords Aqueous lubrication Poly(dimethylsiloxane) (PDMS) Oxygen-plasma-treatment Hydrophilization Soft EHL PLL-g-PEG PEO-b-PPO-b-PEO... 

Amphiphilic copolymers have also been employed for the hydrophilization of PDMS surfaces. Two types of copolymers have been employed poly(ethylene oxide)-h/ock-poly(propylene oxide)-htock-poly(ethylene oxide) (PEO-h-PPO-h-PEO) and poly(L-lysine)-graft-poly(ethy-lene glycol) (PLL-g-PEG). PEO-h-PPO-I -PEO (Plutonic ) was a commercially available, standard material that was kindly supplied by BASE (Mt Olive, NJ, USA). The molecular weight of the PEG and PPO blocks of the PEO-I -PPO-h-PEO used in this work were ca. 3250 (1625 for each PEO side) and 3250 g/mol, respectively (denoted as P105 according to the manufacmrer [13,14]). The PEO-h-PPO-1)-PEO was dissolved in distilled water at 2 mg/ml concentration and used as an aqueous lubricant. Since PEO-h-PPO-h-PEO is well known to adsorb onto various hydrophobic surfaces through hydrophobic interactions between the PPO block and the surface, no treatment was carried out other than immersing the tribopair into the polymer solution (15 min prior to the friction measurements). 

Fig. 7. A schematic illustration of (a) bare ox-PDMS, (b) PDMS coated with PEO-b-PPO-ft-PEO, (c) PDMS eoated with PLL-g-PEG in water.

Fig. 8. fi vs. speed plots for the water-lubricated sliding of PDMS/PDMS eontaet in the absence of treatment, and hydrophilized by means of oxygen-plasma-treatment, adsorption of PEO-h-PPO-h-PEO eo-polymer, and adsorption of PLL-g-PEG co-polymer (w= 1 N). 

Then, the solution containing lubricant additives was injected into the flow cell. It is emphasised that the change in refractive index at this stage reflects the adsorption of additives, yet includes the contribution from the refractive index change of bulk solution itself as well. Tbe adsorbed mass was thus measmed only after the flow cell was rinsed with buffer solution. The refractive index increment (dn/dc) values of 0.151 and 0.169cm g were used for PEO-b-PPO-fc-PEO and PLL-g-PEG, respectively. 

On the PDMS surface, PEO- -PPO- -PEO showed the highest amount of adsorption, ca. 118ngcm, followed by PLL-g-PEG, ca. 58ngcm, and SDS again showed virtually no adsorption. The adsorption behaviour of PEO-fe-PPO-fe-PEO onto hydrophobic surfaces, including PDMS, from aqueous solution has been extensively investigated in previous studies, " and its driving force is attributed to a hydrophobic interaction between the PPO block and the surface. 

The net effect of adsorbing either PEO-fc-PPO-fc-PEO or PLL-g-PEG onto hydrophobic surfaces is to cover the surface with hydrophilic PEO (or PEG) chains. With respect to aqueous lubrication of the thermoplastics in this work, this PEO (or PEG) layer is expected to make it feasible to form aqueous boimdary lubricant films due to improved affinity with water, as will be shown in the following section. 

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