Synthesis of poly(styrene-tetrahydrofuran-2-methyl-2-oxazoline) triblock and graft copolymers

Poly[styrene (ST)-tetrahydrofuran (THF)-2-methyl-2-oxazoline(MeOz)] triblock and graft copolymers were prepared by ionic polymerizations. Poly(ST-THF) graft copolymers were synthesized by coupling of ST-4-vinylpyridine (4VP) copolymer with a large excess of PTHF dication. The ion coupling of PST dianion with PTHF dication was accompanied by the side reaction (abstraction of α proton of oxonium ion). After tosylation of terminal hydroxyl groups of PTHF blocks, cationic copolymerizations of MeOz with poly(ST-THF) block and graft copolymers were carried out, and characteristics of produced copolymers were investigated in some detail.     

Behavior of thermoresponsive ionogenic poly(2-isopropyl-2-oxazoline) stars and their mixture in aqueous solutions

Star-shaped eight-arm poly(2-isopropyl-2-oxazoline)s with basic and acidic groups were synthesized using a “grafting from” approach. Molar masses were 13,700 and 14,900?g mol^?1 for polybase and polyacid, respectively. The aqueous solutions of synthesized polymers and their mixture were investigated by the light scattering and turbidimetry methods within wide range of temperatures and pH values. It was shown that the studied polymers separately do not exhibit pH-sensitivity due to the low content of ionogenic groups. For the solutions of mixture, one phase transition was detected, the onset temperature T₁ of which lies between the phase separation temperatures for polymers. The value of T₁ for mixture decreases with increasing acidity of the medium.     

Preparation and properties of poly(alkyl vinyl ether-2-ethyl-2-oxazoline) diblock copolymers

A method for the synthesis of well-defined poly(alkyl vinyl ether–2-ethyl-2-oxazoline) diblock copolymers with hydrolytically stable block linkages has been developed. Monofunctional poly(alkyl vinyl ether) oligomers with nearly Poisson molecular weight distributions were prepared via a living cationic polymerization method using chloroethyl vinyl ether together with HI/ZnI₂ as the initiating system and lithium borohydride as the termination reagent. Using the resultant chloroethyl ether functional oligomers in combination with sodium iodide as macroinitiators, 2-ethyl-2-oxazoline was polymerized in chlorobenzene/NMP to afford diblock copolymers. A series of poly(methyl vinyl ether–2-ethyl-2-oxazoline) diblock materials were found to have polydispersities of ≈ 1.3–1.4 and are microphase separated as indicated by two T_g's in their DSC thermograms. These copolymers are presently being used as model materials to study fundamental parameters important for steric stabilization of dispersions in polar media. © 1993 John Wiley & Sons, Inc.     

Synthesis and morphology of BAB type poly(styrene-b-2-methyl-2-oxazoline) block copolymers

Well defined BAB-type poly[styrene(ST)-b-2-methyl-2-oxazoline(MeOz)] was prepared by the cationic polymerization of α,ω-p-toluenesulfonic acid ester-terminated PST (PST-BTs) as an initiator. Alkaline hydrolysis of this block copolymer was carried out under various reaction conditions to obtain BAB-type poly[ST-b-ethylene imine(EI)]. Morphologies of these block copolymer specimens cast from several solvents were observed by electron microscope. The results are discussed in some detail.     

Aggregation behavior of thermo-responsive poly(2-oxazoline)s at the cloud point investigated by FCS and SANS

We have studied different thermo-responsive poly(2-oxazoline)s with iso-propyl (iPrOx) and n-propyl (nPrOx) pendant groups in aqueous solutions, where they exhibit lower critical solution temperature behavior. This paper focuses on the effect of the degree of polymerization, n, the concentration, c, in the dilute regime, and the presence of hydrophobic moieties. The cloud points were investigated as a function of the degree of polymerization, n, and of the polymer concentration, c. The aggregation behavior near the cloud point was studied by temperature-resolved small-angle neutron scattering and fluorescence correlation spectroscopy, i.e., a combination of ensemble and single molecule methods. We found that at the cloud points, large aggregates are formed and that the cloud points depend strongly on both, n and c. Diblock copolymers from iPrOx and nPrOx form large aggregates already at the cloud point of PnPrOx, and, unexpectedly, no micelles are observed between the cloud points of the two blocks. Gradient copolymers from iPrOx and n-nonyl-2-oxazoline (NOx) display a complex aggregation behavior resulting from the interplay between intra- and intermolecular association mediated by the hydrophobic NOx blocks. Above the cloud point, an intermediate temperature regime with a width of a few Kelvin was found with small but stable polymer aggregates. Only at higher temperatures, larger aggregates are found in significant number.     

Characterization of poly(2-oxazoline) homo- and copolymers by liquid chromatography at critical conditions

In this study liquid chromatography at critical conditions for poly(2-ethyl-2-oxazoline)s (PEtOx) has been performed for the first time in order to analyze functional PEtOx homopolymers and block copolymers. Besides the verification of the critical point of adsorption with two series of ester end group functionalized PEtOx homopolymers, to evaluate the effect of both the chain length dependence and the end group polarity, using a cyano column with a solvent combination of 2-propanol and water, also two-dimensional liquid chromatography (2D-LC) has been applied for a poly(2-oxazoline) block copolymer. The combined characterization techniques provided further information about the polymerization procedure with regard to the formation of side-products by separation of the block copolymer from the corresponding homopolymer impurities. In addition, hyphenation of LCCC with MALDI-TOF MS and ESI-Q-TOF tandem mass spectrometry verified the obtained results.     

Behavior of aqueous solutions of polymer star with block copolymer poly(2-ethyl-2-oxazoline) and poly(2-isopropyl-2-oxazoline) arms

Eight-arm star-shaped poly(2-alkyl-2-oxazoline) (M?≈?21,000?g?·?mol^?1) was studied by turbidimetry and light scattering in aqueous solutions within concentration ranging from 0.00038 to 0.0276?g?·?cm^?3. The arms were the block copolymers of poly(2-isopropyl-2-oxazoline) (PiPrOx) and poly(2-ethyl-2-oxazoline) (PEtOx). Calix[8]arene core was connected with poly(2-isopropyl-2-oxazoline). The behavior of investigated polymer differed from that of thermosensitive stars with poly(2-alkyl-2-oxazoline) homopolymer arms. At low temperatures, the aggregates were formed due to interaction of hydrophobic cores. The phase separation temperatures T₁ and T₂ of studied star were higher than those for star-shaped poly(2-isopropyl-2-oxazoline) and lower than for poly(2-ethyl-2-oxazoline). T₁ and T₂ increased with dilution.     

Kinetic study of poly(ethylene oxide-b-2-methyl-2-oxazoline) diblocs synthesis from poly(ethylene oxide) macroinitiators

The synthesis of poly(ethylene oxide-b-2-methyl-2-oxazoline) (PEO-POXZ) block copolymers was carried out by the polymerization of 2-methyl-2-oxazoline (MeOXZ) from monomethoxy poly(ethylene oxide) macroinitiator. The initiating functions were 4-chloromethylbenzoate or tosylate groups. The functionalization of α-methoxy-ω-hydroxy PEO was optimized by adjustment of the reaction temperature. The duplication side reaction was investigated in the case of tosylate functionalization. The determination of the propagation rate constants of the MeOXZ polymerization showed that the presence of the PEO chains decreased the propagation rate constant in the case of active species under the form of oxazolinium ions, while it increased the propagation rate constant in the case of covalent active species, most probably by partial ionization.     

Efficient and robust coatings using poly(2-methyl-2-oxazoline) and its copolymers for marine and bacterial fouling prevention

Molecular design, fabrication, and properties of thin-film coatings based on poly(2-methyl-2-oxazoline) (PMOX) and its copolymers were investigated to tackle problem of marine and bacterial fouling prevention. The ultraviolet crosslinkable macromonomer poly(2-methyl-2-oxazoline) dimethylacrylate was synthesized by cationic ring-opening polymerization in a microwave reactor initiated by 1,4-dibromobutane. In order to study the charge effect of the PMOX coatings on the adhesion of fouling organisms, PMOX surfaces with negative, neutral, and positive ζ-potential values were prepared by copolymerization with the positively charged monomer [2-(methacryloyloxy)-ethyl]trimethylammonium chloride. The coatings were stable in sea water for at least 1 month without significant reduction in the film thickness. The marine antifouling activity was evaluated against barnacle cyprids Amphibalanus amphitrite and algae Amphora coffeaeformis. Results showed that PMOX coatings provide effective reduction of the settlement regardless of the molar mass and surface charge of the polymer. Bacterial adhesion test showed that PMOX coatings effectively reduce Staphylococcus aureus and Escherichia coli adhesion. Owing to its good stability and antifouling activity PMOX has a great potential as antifouling coating for marine antifouling applications. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016, 54, 275–283     

The behavior of thermoresponsive star-shaped poly-2-isopropyl-2-oxazoline in saline media

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Synthesis and aggregation of poly(valine)‐poly (ethylene glycol) block copolymers

The solubility nature of many medicines presents a challenge for successful delivery of these drugs to the body. Polymeric carriers are potentially viable as vessels for both the protection and transport of these medicinal substances. In an effort to generate polymeric materials for this desired application, A‐B‐A triblock copolymers have been synthesized with a central block composed of hydrophilic poly (ethylene glycol) (PEG) and flanking hydrophobic sequences composed of five valine units terminated with end groups of varying hydrophobicity. These copolymers were constructed by adding amino acids stepwise to the hydrophilic block using solution phase chemistry. The self‐assembly behavior of all polymers was investigated using fluorimetry with a pyrene probe. In general, copolymers with more hydrophobic end groups exhibited lower critical aggregation concentrations (CACs). Fmoc‐terminated copolymers displayed the lowest CAC of 0.032 mg/mL and demonstrated little cytotoxicity when exposed to SW620 colorectal cancer cells. Transmission electron micrographs show the presence of multiple compartments within these spherical assemblies, which may prove useful in encapsulating medicinal substances. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 5381–5389, 2008     

Synthesis of Y-shaped poly(solketal acrylate)-containing block copolymers and study on the thermoresponsive behavior for micellar aggregates

One novel type of Y-shaped amphiphilic copolymers with two hydrophobic poly(solketal acrylate) (PSA) branches and one hydrophilic monomethoxy poly(ethylene glycol) (MPEG) block was synthesized by atom transfer radical polymerization (ATRP). These Y-shaped polymers can disperse in aqueous media to self-assemble into micellar aggregates with a spherical core-shell structure. The aqueous copolymer solutions exhibited transmittancy transition in the temperature range of 30-60 °C via optical transmittance measurements. An interesting thermo-dependent size of the micellar aggregates was observed by dynamic light scattering techniques and transmission electron microscopy, which showed that the micelle diameters were decreased with temperature increasing. The nile red release from the micelles at 25 °C and 37 °C under various pHs showed that temperature has great influence on release behavior. With good biocompatibility, the micellar aggregates formed from MPEG-block-(PSA)(2) may serve as one promising thermosensitive nanovehicle for targeted drug delivery.     

Aggregation behavior of amphiphilic poly(2-alkyl-2-oxazoline) diblock copolymers in aqueous solution studied by fluorescence correlation spectroscopy

The diffusional behavior of amphiphilic poly(2-oxazoline) diblock copolymers in aqueous solution is studied using photon correlation spectroscopy (PCS) and fluorescence correlation spectroscopy (FCS). The polymers were synthesized by living cationic polymerization and were fluorescence-labeled with tetramethyl rhodamine isothiocyanate either at the end of the hydrophilic or the hydrophobic block. Temperature-resolved PCS showed that, at room temperature, large metastable aggregates are present along with unimers and micelles. An annealing above ~40 °C resulted in stable equilibrium micellar solutions. By means of FCS, the hydrodynamic radii of the unimers and the micelles were measured simultaneously in a broad concentration range, and the critical micelle concentration could be determined. Comparison of the results from conventional PCS measurements with this first FCS study showed excellent agreement and the high potential of the FCS technique.Dedicated to Prof. Dr. Erhard W. Fischer on the occasion of his 75th birthdayAn erratum to this article can be found at     

Influence of arm length and number on star-shaped poly(2-isopropyl-2-oxazoline) aggregation in aqueous solutions near cloud point

Four-arm star-shaped poly(2-isopropyl-2-oxazolines) (PiPrOx₄) are synthesized by cationic polymerization on t-butylcalix[4]arene macroinitiator. The obtained samples differ by polymerization degree of arms N_PiPrOx = 9 and 25 and are characterized in chloroform. The behavior in aqueous solutions is studied by light scattering methods and compared with the results of investigation of eight-arm star with similar structure. Three types of particles are observed in solution of short-arm PiPrOx₄ at room temperature, whereas only two particle types are present in long-arm star solution. Arm shortening leads to widening of the phase transition interval. The arm number decreasing reduces the phase transition temperature by 1°C.     

First aldehyde-functionalized poly(2-oxazoline)s for chemoselective ligation

A protected aldehyde-functionalized 2-oxazoline, 2-[3-(1,3)-dioxolan-2-ylpropyl]-2-oxazoline (DPOx), was synthesized from commercially available compounds in high yields. The polymerization of DPOx with different initiators proceeds via a living ionic mechanism; thus, the polymers were of low polydispersity and the degree of polymerization could be precisely adjusted. Copolymerization with 2-methyl-2-oxazoline gave water-soluble statistical copolymers. Hydrolysis of the homo- and copolymers resulted in well-defined, aldehyde-bearing poly(2-oxazoline)s. The aldehyde side functions reacted quantitatively with an amino-oxy compound to form the corresponding oxime.