Surface-active Block Research Articles

Smart Polymer Surfaces

A methodology is demonstrated for creating responsive polymer surfaces that can alter their wetting characteristics when exposed to a humid environment. For this, we take advantage of the surface partitioning of block copolymers at the polymer/air interface and utilize a hydrophilic group at the end of the surface-active block. When exposed to water vapor, the end group, hidden below the surface when in contact with dry air, presents itself to the surface thus significantly reducing the water contact angle. This function can be reversed and repeated again and again by successive exposures of the surface to dry and wet environment, respectively.

Coatings Based on Side-chain Ether-linked Poly(ethylene glycol) and Fluorocarbon Polymers for the Control of Marine Biofouling

The preparation of side group modified polystyrene-based surface-active block copolymers (SABC) for use as marine fouling resistance/release applications is described. Modifying moieties such as poly(ethylene glycol) (PEG) and semifluorinated segments were used. A novel bilayer methodology has been employed that provides both suitable mechanical properties through the use of an elastomeric primer layer of styrene-ethylene/butylene-styrene (SEBS) and control of surface-chemistry through use of the SABCs. This approach has potential as a cost-effective technology for environmentally benign coatings that resist and release marine biofouling. Initial testing of these materials included determination of captive bubble contact angles and protein adsorption. Testing against marine fouling organisms was performed using settlement and adhesion bioassays with zoospores of the green alga Enteromorpha . The results showed that all surfaces had markedly reduced levels of zoospore settlement compared with glass controls and that adhesion strength was strongly affected by the semifluorinated SABC. The results are discussed in terms of surface properties.

Creating Smart Polymer Surfaces with Selective Adhesion Properties

A new concept for polymer surface modification is described that employs surface-active ω-functional block copolymers as additives to create polymers with smart sufaces. The block copolymers are composed of three components: a low surface energy block that causes the copolymer to segregate to the surface of the matrix homopolymer to which it is added, an anchor block that tethers the copolymer into that matrix, and a functional group located at the terminus of the surface-active block. The functional end group is selected to interact selectively with a complementary receptor on the target substrate. When the modified polymer surface and a substrate are placed in contact, adhesion is enhanced only if the functional end group senses an appropriate receptor on that substrate with which it can form the specific interaction. If a receptor is not present, the modified surface exhibits release properties. This class of copolymer additives can thereby be employed to create smart polymer surfaces with selective adhesive properties. We present preliminary results that demonstrate how this new concept can be employed to modify the surface of polystyrene and impart selective adhesion toward either poly(methyl methacrylate) or poly(dimethylsiloxane) substrates.

Polyoxyethylene-polyoxypropylene block copolymer gels as sustained release vehicles for subcutaneous drug administration

Polyoxyethylene-polyoxypropylene surface-active block copolymers (Pluronic®) were evaluated as a vehicle for subcutaneous administration of drugs using a phenolsulfophthalein (PR) as a tracer. The type of Pluronic® copolymer (F108 or F127), and their concentrations, and the effect of solutes (NaOH, NaCl or PR) on gelation properties were studied. Sodium hydroxide and sodium chloride decreased the gel-sol transition temperature, whereas the opposite effect was observed with PR. The ‘in vitro’ release rates obtained for PR were inversely proportional to the concentration of Pluronic used and a zero-order release rate was observed in all preparations assayed. Pluronic® F127/PR preparations were administered subcutaneously (SC) to Wistar rats and PR plasma levels were compared with those reached after SC or intravenous (i.v.) administration of a PR aqueous solution. The gel formulation produced a sustained plateau level within 15 min that lasted 8–9 h. In vivo data analysis was performed with the JANA and PCNONLIN computer programs. The best fittings for experimental data from Pluronic gels were obtained using a zero-order input and first-order output two-compartment model. The results obtained suggest that PF127 aqueous gels may be of practical use as a vehicle for SC administration of drugs.

Low temperature transmission electron microscopy and differential scanning calorimetry characterization of latexes stabilized with surface active block oligomers

The spatial distribution of a short-chain amphiphilic diblock copolymer (i.e. block oligomer), used as an emulsifier during the preparation of a latex, is determined by low temperature transmission electron microscopy and differential scanning calorimetry (d.s.c.). The main question is whether intermixing of the amphiphilic block oligomer and latex core materials actually takes place to a significant extent. Electron microscopy gives a clear indication that a surfactant-rich layer exists in all latex samples examined. At very high surfactant concentration (>6%, not typically used in commercial latexes), electron beam radiation damage reveals the presence of a surfactant gradient from the particle surface to its core. These results are in good agreement with our d.s.c. data.

Low surface energy polymers and surface-active block polymers IV: Monolayers at the air-water interface

The spreading of five block copolymers of 2-( p-( t-butyl)phenyl) oxazoline (hydrophobic block) and 2-ethyl oxazoline (hydrophilic block) at the air-water interface was studied using Langmuir-Blodgett film balance techniques. Three regions of compression were found. At low force, the hydrophilic block was being compressed. This continued until the hydrophobic tails contacted each other. The second region was the compression of the hydrophobic tails lying almost flat on the water surface. As the pressure increased to 40 mN m −1, the hydrophobic tail rotated so that the side chains were perpendicular to the surface. The area of the hydrophobic block in the most compressed state was about equal to its thickness multiplied by its chain length. As chain length increased, packing efficiency decreased slightly. All compressed phases remained liquid like. The films remained as monolayers up to the pressure (about 70mNm −1) permitted by the trough.

Chemical Structure and Surface Activity

In a reaction of bis(2-hydroxyethyl)disulphide with methyl- or ethyloxirane (proylene or α-butylene oxide) carried out in the presence of ternary amine as catalyst, hydrophobic oligomers were obtained. By reacting them with oxirane (ethylene oxide), surface active block copolymers were obtained. The all-block copolymers were characterized and their efficiency of adsorption as well as foaming and wetting properties were measured

Low surface energy polymers and surface-active block polymers: II. Rigid microporous foams by emulsion polymerization

Block polymerization of different weight ratios of 2-( p-t-butylphenyl)-2-oxazoline (B) and 2-ethyl-2-oxazoline (E) with methyl p-nitrobenzenesulfonate as the initiator gave diblock co-oligomers with narrow molecular weight distributions in 100% yields. Co-oligomers with 40–50 wt% of B were excellent inverse emulsifiers for styrene/water ( St W ) polymerization: water-in-oil solid emulsions with internal phase ratios as high as 90% have been obtained using small amounts of the oligomers (⩾1 wt% of the total system). The total surface area of the water droplets is approximately proportional to the number of surfactant molecules, and thus the average pore diameter is proportional to the water volume divided by the surfactant concentration. For any given St W volume ratio, there is a maximum amount of emulsifier which can produce stable solid foams; higher amounts cause the emulsions to break.

Low surface energy polymers and surface active block polymers. I. t‐butylphenyl containing polymers

AbstractTwo new monomers in the 2‐oxazoline series were synthesized and polymerized. These were 2‐[4‐(t‐butyl)phenyl]‐2‐oxazoline (I) and 2‐[(3‐(3,5‐di‐t‐butyl)phenoxy)propyl]‐2‐oxazoline (II). The polymer from I crystallized readily during bulk polymerization and showed Tm at 592 K (319°C). After annealing, the polymer showed a critical surface tension of 23.2 dyn/cm. Polymer from II was amorphous; hence, annealing showed little effect on contact angles. Block polymers were made with I (Xn = 10) and ethyl oxazoline (Xn = 6,20,60). Very sharp molecular weight distributions were obtained. All samples crystallized when annealed. The block polymer was an effective emulsifier for emulsion polymerization of butyl acrylate at 0.1%.

Pluronic F-127 gels as a vehicle for topical administration of anticancer agents.

Pluronic F-127 (a polyoxyethylene-polyoxypropylene surface-active block copolymer) was evaluated as a vehicle substance for topical administration of anticancer agents. 5-Fluorouracil and adriamycin were used in this evaluation. The effects of the concentration of Pluronic F-127, temperature, and the drug concentration on the release were studied by means of an in vitro release method using a cellulose membrane. With increasing concentration of Pluronic F-127 in the vehicle a corresponding decrease in the apparent release rate of the anticancer agents occurred. The apparent release rate increased with increasing temperature from 30 to 44°C. Increase in drug concentration increased the drug release rate. The Pluronic F-127 gels appeared to have good potential for use in topical drug delivery systems since they exhibit reverse thermal gelation behavior and have good drug release characteristics and low toxicity.

In vitro release of lidocaine from pluronic F-127 gels

The release of lidocaine from aqueous, crystal clear and colorless gels of Pluronic F-127 (a polyoxyethylene-polyoxypropylene surface-active block polymer) has been studied in an in vitro release model which did not utilize a membrane. Pluronic F-127 forms micelles in aqueous systems and the gels are believed to be viscous isotropic liquid crystals. Due to their reverse thermal gelation behavior, good solubilization capacity, optical properties and low toxicity, they appear to have potential application as topical drug delivery systems. It has been found that the rate of lidocaine release was inversely proportional to its concentration, the concentration of Pluronic F-127 and electrolyte concentration (sodium chloride). Release of lidocaine was maximal at pH values close to its pK a; however, release of the more water-soluble benzocaine (included for comparison purposes) was relatively pH-independent over the pH range studied. Since the apparent diffusion coefficient of lidocaine increased with increasing temperature, in spite of increasing macro-viscosity of the gel, it is apparent that drug is released by diffusion through the extramicellar aqueous channels of the gel matrix. Hence, the rate of drug release was determined by the micro-viscosity of the extramicellar fluid, the dimensions of the aqueous channels, and the equilibrium relationship of drug between the micelles and the external aqueous phase.

The effect of Pluronic F-38 (Polyoxamer 108) administered intravenously to rats

Soluble surface-active block copolymers of polyoxypropylene and polyoxyethylene have been widely used as suspending or wetting agents in materials for topical or oral administration. One such copolymer, Pluronic F-38 (Polyoxamer 108), has been used experimentally in a new fractionation procedure for plasma proteins. Since residual amounts of this copolymer might be administered intravenously with a plasma fraction, its toxicity was evaluated following intravenous administration. Sprague-Dawley rats were injected intravenously with 0.15, 1, 2, and 4 g/kg of Pluronic F-38 five times a week for 2 weeks. Examination of tissues by light microscopy revealed that Pluronic F-38 caused early and prominent vacuolization of epithelial cells in the proximal renal tubules and of hepatocytes, as well as a gradual accumulation of vacuoles in Type II macrophages in the lung. These alterations in morphology were dose dependent and increased in severity during the period of administration. The lesions were slowly reversible; there was a moderate decrease in vacuolization 14 days after the last injection. Transmission electron microscopy indicated that the vacuoles were probably distended lysosomes. The paucity of additional cellular changes suggests that, although Pluronic F-38 may be rapidly phagocytized, it is well tolerated even when administered intravenously in large doses.

Surface active block copolymers: I. The preparation and some surface active properties of block copolymers of tetrahydrofuran and ethylene oxide

AbstractA new type of surface active block copolymer (TE type) having the general formula HO(C2H4O)x(CH2. CH2CH2CH2O)y‐(C2H4O)zH, was obtained by addition of ethylene oxide to polyoxytetramethylene glycols with molecular weight of 1000‐3400. TE types in which the polyoxyethylene sections comprised more than 20–25% of the total weight are soluble in water, and the relation between cloud point and oxyethylene content for TE types was similar to that for propylene oxide‐ethylene oxide block copolymers (Pluronics). Some surface active properties of TE types were examined in comparison with those of Pluronics and some other surfactants. The surface tension, foaming and antifoaming properties of TE types were comparable to those of Pluronics. Although the wetting power of TE types was poor, their suspending power (for carbon black) was superior to that of Pluronics in both aqueous and nonaqeuous media. The addition of TE types to some conventional detergents enhanced significantly their detergency. TE types showed a remarkable demulsifying action, on addition to some W/O emulsions.