Synthesis and microwave assisted polymerization of fluorinated 2-phenyl-2-oxazolines: the fastest 2-oxazoline monomer to date

The living cationic ring-opening polymerization of 2-oxazolines with fluorinated aromatic substituents was found to be strongly accelerated by o-fluoro substituents.     

Chemical Design of Non‐Ionic Polymer Brushes as Biointerfaces: Poly(2‐oxazine)s Outperform Both Poly(2‐oxazoline)s and PEG

The era of poly(ethylene glycol) (PEG) brushes as a universal panacea for preventing non‐specific protein adsorption and providing lubrication to surfaces is coming to an end. In the functionalization of medical devices and implants, in addition to preventing non‐specific protein adsorption and cell adhesion, polymer‐brush formulations are often required to generate highly lubricious films. Poly(2‐alkyl‐2‐oxazoline) (PAOXA) brushes meet these requirements, and depending on their side‐group composition, they can form films that match, and in some cases surpass, the bioinert and lubricious properties of PEG analogues. Poly(2‐methyl‐2‐oxazine) (PMOZI) provides an additional enhancement of brush hydration and main‐chain flexibility, leading to complete bioinertness and a further reduction in friction. These data redefine the combination of structural parameters necessary to design polymer‐brush‐based biointerfaces, identifying a novel, superior polymer formulation.     

Revisiting the crystallization of poly(2‐alkyl‐2‐oxazoline)s

Poly(2‐alkyl‐2‐oxazoline)s (PAOx) exhibit different crystallization behavior depending on the length of the alkyl side chain. PAOx having methyl, ethyl, or propyl side chains do not show any bulk crystallization. Crystallization in the heating cycle, that is, cold crystallization, is observed for PAOx with butyl and pentyl side chains. For PAOx with longer alkyl side chains crystallization occurs in the cooling cycle. The different crystallization behavior is attributed to the different polymer chain mobility in line with the glass transition temperature (T_g) dependency on alkyl side chain length. The decrease in chain mobility with decreasing alkyl side chain length hinders the relaxation of the polymer backbone to the thermodynamic equilibrium crystalline structure. Double melting behavior is observed for PButOx and PiPropOx which is explained by the melt‐recrystallization mechanism. Isothermal crystallization experiments of PButOx between 60 and 90 °C and PiPropOx between 90 and 150 °C show that PAOx can crystallize in bulk when enough time is given. The decrease of T_g and the corresponding increase in chain mobility at T > T_g with increasing alkyl side chain length can be attributed to an increasing distance between the polymer backbones and thus decreasing average strength of amide dipole interactions. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2016 , 54, 721–729     

Design of new amphiphilic triblock copoly(2‐oxazoline)s containing a fluorinated segment

New amphiphilic triblock copoly(2‐oxazoline)s, containing hydrophobic domains with fluorine‐containing blocks, were synthesized. Using microwave radiation as heating source, triblock copolymers with narrow molar mass distributions were obtained by the sequential addition of 2‐ethyl‐2‐oxazoline, 2‐(1‐ethylheptyl)‐2‐oxazoline, and 2‐(2,6‐difluorophenyl)‐2‐oxazoline. The polymers obtained were characterized by size exclusion chromatography, ¹H NMR spectroscopy and matrix‐assisted laser desorption/ionization time‐of‐flight mass spectrometry (MALDI‐TOF MS). To investigate the incorporation of all three monomers into the triblock copolymers, a model polymer was prepared with shorter blocks exhibiting a suitable length to be measured in the reflector mode of a MALDI‐TOF MS. In addition, kinetic investigations on the homopolymerizations of all monomers were performed in nitromethane at 140 °C, yielding the polymerization rates under these conditions. DSC measurements of poly(2‐(1‐ethylheptyl)‐2‐oxazoline) and poly(2‐(2,6‐difluorophenyl)‐2‐oxazoline)) revealing glass transitions at about 33 and 120 °C, respectively. The thermal analysis of a blend of the two polymers showed two glass transitions revealing demixing, which could be an indicating for the immiscibility of the two components in the block copolymers. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2010     

Are o‐nitrobenzyl (meth)acrylate monomers polymerizable by controlled‐radical polymerization?

We report on the controlled‐radical polymerization of the photocleavable o‐nitrobenzyl methacrylate (NBMA) and o‐nitrobenzyl acrylate (NBA) monomers. Atom transfer radical polymerization (ATRP), reversible addition‐fragmentation chain transfer polymerization (RAFT), and nitroxide‐mediated polymerization (NMP) have been evaluated. For all methods used, the acrylate‐type monomer does not polymerize, or polymerizes very slowly in a noncontrolled manner. The methacrylate‐type monomer can be polymerized by RAFT with some degree of control (PDI ∼ 1.5) but leading to molar masses up to 11,000 g/mol only. ATRP proved to be the best method since a controlled‐polymerization was achieved when conversions are limited to 30%. In this case, polymers with molar masses up to 17,000 g/mol and polydispersity index as low as 1.13 have been obtained. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 6504–6513, 2009     

Amphiphilic gradient copolymers containing fluorinated 2‐phenyl‐2‐oxazolines: Microwave‐assisted one‐pot synthesis and self‐assembly in water

Here, we present the one‐step synthesis of 2‐(m‐difluorophenyl)‐2‐oxazoline and its use as a monomer for microwave‐assisted statistical cationic ring‐opening copolymerizations (CROP). Well‐defined amphiphilic gradient copolymers, as evidenced by the polymerization kinetics, were prepared using 2‐ethyl‐2‐oxazoline as comonomer and methyl tosylate as initiator in nitromethane at 140 °C. The resulting gradient copolymers (DP = 60 and 100) were characterized by means of size exclusion chromatography and ¹H NMR spectroscopy. In the second part, we focus on a detailed study of the self‐assembly of the copolymers in aqueous solution using atomic force microscopy and dynamic light scattering. Both methods revealed the self‐assembly of the gradient copolymers into spherical micelles. To quantify the influence of the fluorine atoms and the monomer distribution on the self‐assembly, a comparative study with gradient copolymers of 2‐phenyl‐2‐oxazoline and 2‐ethyl‐2‐oxazoline was performed. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 5859–5868, 2008     

Kinetic study of the polymerization of aromatic polyurethane prepolymers by high‐throughput experimentation

In this contribution, high‐throughput screening experiments are reported to study the polymerization of different aromatic polyurethane (PU) prepolymers. The prepared prepolymers were synthesized from toluene diisocyanate (T80) with different molar mass polyether diols and polyether triols, respectively. The reactions were performed in solution using a Chemspeed Accelerator? SLT106 automated parallel synthesizer as well as in bulk to evaluate the high‐throughput approach for this kind of prepolymers. More than 100 samples were prepared and characterized by GPC within 1 week labor time to investigate the reaction kinetics and to compare the resulting trends obtained by high‐throughput experimentation (HTE) or by conventional, bulk prepolymerization. The synthesis of the prepared prepolymers with a linear (T80‐Diol) or a branched (T80‐Triol) structure followed a second‐order kinetic in solution but showed deviation from this phenomenon in bulk under the selected reaction conditions, although the same trends are observed in both cases. The calculation of the rate constants allowed comparing the reactivity of different prepolymer systems, which could have a significant influence on the industrial application and processing of these materials. As a result, the HTE approach was found to represent a powerful tool for the kinetic studies of PU prepolymers. Moreover, in spite of the complexity of the curing process, the results obtained by high‐throughput solution polymerization can be applied for evaluating the bulk polymerization. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 570–580, 2010     

New terpyridine macroligands as potential synthons for supramolecular assemblies

A Williamson type etherification approach was applied for the reaction of 4′-chloro-2,2′:6′,2′′-terpyridine with a number of well-defined mono- and bis-hydroxy functionalized polymers, namely poly(tetrahydrofuran), poly(2-ethyl-2-oxazoline) and Pluronics®. The resulting terpyridine functionalized polymers were characterized by ¹H NMR spectroscopy and SEC, as well as MALDI-TOF-MS demonstrating the successful functionalization. This type of end-functionalized chelating macromolecules could be considered as key candidates for the preparation of metallo-supramolecular polymers via metallo-terpyridine complexation; the principle feasibility was demonstrated by UV-vis titration of iron(II) chloride to bis-terpyridine functionalized poly(tetrahydrofuran).     

Partial Hydrolysis of Poly(2‐ethyl‐2‐oxazoline) and Potential Implications for Biomedical Applications?

The hydrolysis of PEtOx is studied to evaluate the potential toxicity of partially hydrolyzed polymers that might interfere with its increasing popularity for biomedical applications. The hydrolysis of PEtOx is studied in the presence of digestive enzymes (gastric and intestinal) and at 5.8 M hydrochloric acid as a function of temperature (57, 73, 90, and 100 °C). It is found that PEtOx undergoes negligible hydrolysis at 37 °C and that thermal and solution properties are not altered when up to 10% of the polymer backbone is hydrolyzed. Mucosal irritation and cytotoxicity is also absent up to 10% hydrolysis levels. In conclusion, PEtOx will not decompose at physiological conditions, and partial hydrolysis will not limit its biomedical applications.