Bioinspired polymers, biohybrids, block copolymers, ...

"Living"/controlled ionic and radical polymerizations
Ring-opening polymerization of heterocycles (oxiranes, lactones, oxazolines, amino acid N-carboxyanhydrides)
Metathesis polymerizations, polycondensations, etc.
Post-polymerization reactions, click chemistry, photochemistry

Stimuli-responsive/smart polymers and colloids, polymer-polymer complexes
Aggregates (micelles, vesicles, fibers, etc.), colloids, gels, and films
Bioinspired structures, hierarchically structured materials and composites

Polymer synthesis:

Metal-free ring-opening polymerization of oxiranes

End-functionalized poly(ethylene oxide)s (PEG or PEO) and block copolymers are prepared by living/controlled anionic ring-opening polymerization of ethylene oxide using hydroxyl initiators in the presence of the phosphazene base t-BuP4 (Macromolecules 2001, 34, 4302; Langmuir 2003, 19, 4455; Adv. Mater. 2005, 17, 1158; Polym. Chem. 2012, 3, 1763). The t-BuP4 can also be used for a direct grafting of ethylene oxide from poly(N-isopropylacrylamide) (PNIPAM), using the NIPAM secondary amide units as initiating sites, to yield well-defined thermoresponsive graft copolymers (Macromolecules 2011, 44, 5861).

Ring-opening polymerization of amino acid N-carboxyanhydrides

Block copolymers with a synthetic segment (polystyrene or 1,2-polybutadiene) and a polypeptide segment (poly(Z-L-lysine) or poly(gamma-benzyl-L-glutamate)) are synthesized via the ring-opening polymerization of amino acid N-carboxyanhydrides (NCA) initiated by primary amino-functional polymers. Using amine hydrochlorides instead of free amines yields block copolymers with a near monodisperse (Poisson) molar mass distribution (Chem. Commun. 2003, 2944). Kinetic studies show that the rate of polymerization is vastly determined by the position of the ammonium–amine equilibrium, thus it is higher the more polar is the reaction medium, the softer is the counterion, and the higher is the temperature (PMSE Prepr. 2007, 97, 183). Alternatively, primary amine hydrochlorides can be combined with tertiary amines to initiate the controlled polymerization of NCA (Chem. Commun. 2015, 51, 15645).

Ring-opening metathesis polymerization of amino acid-based macrocycles

Macrocycles based on L-cystine are synthesized by ring-closing metathesis (RCM) and subsequently polymerized by entropy-driven ring-opening metathesis polymerization (ED-ROMP) to yield poly(ester-amine-disulfide-alkene)s with apparent molar masses of up to 80 kDa. The polymers can be further functionalized with acid anhydrides and degraded by reductive cleavage of the main-chain disulfide (Polym. Chem. 2017, 8, 366).

Modification of polymers with thiol-ene (click) chemistry

Series of functionalized polymers, e.g., fluoro polymers, polyelectrolytes and biohybrids (peptide, sugar, and DNA copolymers) can be readily prepared by addition of thiols to 1,2-polybutadiene (homopolymers and block copolymers) (Polymer 2005, 46, 12057; Angew. Chem. Int. Ed. 2006, 45, 7578, J. Am. Chem. Soc. 2006, 128, 13336, J. Phys. Chem. C 2011, 115, 22931). Unsaturated polyamides like poly[2-(3-butenyl)-2-oxazoline], poly(N-allyl glycin), and polyallylglycin can be modified quantitatively and without side reactions by photochemical thiol-ene addition (Macromolecules 2007, 40, 7928; Polymer 2008, 49, 817; Chem. Commun. 2012, 48, 7835; J. Am. Chem. Soc. 2012, 134, 18542; Macromolecules 2014, 47, 2536).

Also polymer colloids and inorganic surfaces (glass fibers and plates) can be functionalized by photochemical addition of thiols (Chem. Eur. J. 2009, 15, 11469; Chem. Mater. 2009, 21, 5698; ACS Appl. Mater. Interfaces, 2012, 4, 3484; ACS Appl. Mater. Interfaces 2013, 5, 2469).

Structure formation:

Polypeptide block copolymers

Polybutadiene-block-poly(L-lysine) can form large vesicles or “peptosomes” with a hydrodynamic radius of a few hundreds of nanometers in dilute aqueous saline solution. Vesicles are observed irrespective of the solution pH (7.0 or 10.3) and the secondary structure of the polypeptide segment (100% random coil conformation or in 80% alpha-helix). At the higher pH, aggregates are smaller in size (hydrodynamic radius: 364 nm → 215 nm) and chains are more densely packed at the core-corona interface (inter-chain distance: 3.2 nm → 2.4 nm) (Langmuir 2007, 23, 7196).

Swelling of thin films of polystyrene-poly(g-benzyl-L-glutamate) heteroarm star block copolymers in chloroform vapour leads to the nucleation of ordered three-dimensional structures of ellipsoidal shape. The nucleation density not only increases with concentration but also sensitively depends on the presence of protic non-solvents, like for instance water, in the surrounding gas phase. An explanation for this behaviour is that the solubility of the polymer (in chloroform) decreases upon hydrogen bonding complexation of water molecules to the polypeptide chains (Soft Matter 2008, 4, 993; Adv. Polym. Sci. 2011, 242, 117).

Amphiphilic glycopolymers

Glycopolymers, made by radical photoaddition of 1-thio-glucose onto 1,2-polybutadiene homopolymers and block copolymers, can self-assemble into vesicles or “glycosomes” in dilute aqueous solution, irrespective of their composition or hydrophilic weight fraction. Vesicles exhibit either a bilayered membrane or, in the case of glucosylated 1,2-polybutadiene-block-poly(ethylene oxide), a monolayered membrane with an asymmetric structure (i.e., glucose coating on the outside and PEO coating on the inside) (J. Am. Chem. Soc. 2006, 128, 13336; Macromolecules 2007, 40, 3901; Chem. Commun. 2009, 1478).

Double hydrophilic block copolymers

Water-soluble block copolymers made of polysaccharide and poly(ethylene oxide) or polysarcosine can self-assemble into vesicles in the nanometer (<500 nm) or micrometer range (>5 μm), depending on polymer concentration and composition. Due to the purely hydrophilic nature of the polymers highly water permeable microcompartments are formed, which should be suitable models for cell mebranes (Angew. Chem. Int. Ed. 2015, 54, 9715).

Crystallizing polymers

The crystallization of poly(2-isopropyl-2-oxazoline) in hot water can produce uniform microparticles with internal fibrous structure with a melting point close to 200 °C (Soft Matter 2007, 3, 430; Angew. Chem. Int. Ed. 2007, 46, 8622). The morphology on the micron length scale can be manipulated through the addition of a co-solvent or surfactant (Macromol. Rapid Commun. 2010, 31, 511).
Kinetic studies indicate that the temperature-induced phase separation of a dilute aqueous poly(2-isopropyl-2-oxazoline) solution produces a bicontinuous network-like structure, which with the onset of crystallization collapses into individual particles composed of a porous fiber mesh. These “premature” particles then act as nucleation sites for secondary crystallization. Nanofibers preferentially form at the particle surface, thus wrapping the microspheres like a ball of wool (Soft Matter 2010, 6, 3784).

Lab equipment:

Several vacuum lines, microwave reactor (CEM),
Turbidity photometer, UV-vis spectrometer, ATR-FTIR spectrometer,
Size exclusion chromatography (GPC/SEC; THF - UV/MALLS/RI, NMP - UV/Viscosity/RI),
Static/dynamic light scattering (ALV / CGS-3 Compact Goniometer System, HeNe @ 632,8 nm).