Block copolymers of polyisoprene and polystyrene are key materials for polymer nanostructures as well as for several commercially established thermoplastic elastomers. In a combined experimental and kinetic Monte Carlo simulation study, the direct (i.e., statistical) living anionic copolymerization of a mixture of isoprene (I) and 4-methylstyrene (4MS) in nonpolar media was investigated on a fundamental level. In situ 1 H NMR spectroscopy enabled to directly monitor gradient formation during the copolymerization and to determine the nature of the gradient. In addition, a precise comparison with the established copolymerization of isoprene and styrene (I/S) was possible. Statistical copolymerization in both systems leads to tapered block copolymers due to an extremely slow crossover from isoprene to the styrenic monomer. For the system I/4MS the determination of the reactivity ratios shows highly disparate values with r I = 25.4 and r 4MS = 0.007, resulting in a steep gradient of the comonomer composition. The rate constants determined from online NMR studies were used for a kinetic Monte Carlo simulation, revealing structural details, such as the distribution of the homopolymer sequences for both blocks, which are a consequence of the peculiar kinetics of the diene/styrene systems. DFT calculations were used to compare the established copolymerization of isoprene and styrene with the isoprene/4-methylstyrene system. A variety of gradient copolymers differing in molecular weight and monomer feed composition were synthesized, confirming strong microphase segregation as a consequence of the blocklike structure. The one-pot synthesis of such tapered block copolymers, avoiding high vacuum or break-seal techniques, is a key advantage for the preparation of ultrahigh molecular weight block copolymers (M n > 1.2 × 10 6 g/mol) in one synthetic step. These materials show microphase-segregated bulk structures like diblock copolymers prepared by sequential block copolymer synthesis. Because of the living nature of the tapered block copolymer structures, a vast variety of complex structures are accessible by the addition of further monomers or monomer mixtures in subsequent steps.

Poly(ethylene glycol) (PEG) is a widely used biocompatible polymer. We describe a novel epoxide monomer with methyl-thioether moiety, 2-(methylthio)ethyl glycidyl ether (MTEGE), which enables the synthesis of well-defined thioether-functional poly(ethylene glycol). Random and block mPEG-b-PMTEGE copolymers (Mw/Mn = 1.05-1.17) were obtained via anionic ring opening polymerization (AROP) with molecular weights ranging from 5 600 to 12 000 g·mol(-1). The statistical copolymerization of MTEGE with ethylene oxide results in a random microstructure (rEO = 0.92 ± 0.02 and rMTEG E = 1.06 ± 0.02), which was confirmed by in situ (1)H NMR kinetic studies. The random copolymers are thermoresponsive in aqueous solution, with a wide range of tunable transition temperatures of 88 to 28 °C. In contrast, mPEG-b-PMTEGE block copolymers formed well-defined micelles (Rh ≈ 9-15 nm) in water, studied by detailed light scattering (DLS and SLS). Intriguingly, the thioether moieties of MTEGE can be selectively oxidized into sulfoxide units, leading to full disassembly of the micelles, as confirmed by detection of pure unimers (DLS and SLS). Oxidation-responsive release of encapsulated Nile Red demonstrates the potential of these micelles as redox-responsive nanocarriers. MTT assays showed only minor effects of the thioethers and their oxidized derivatives on the cellular metabolism of WEHI-164 and HEK-293T cell lines (1-1000 μg·mL(-1)). Further, sulfonium PEG polyelectrolytes can be obtained via alkylation or alkoxylation of MTEGE, providing access to a large variety of functional groups at the charged sulfur atom.

The catechol-containing vinyl monomers 4vinylcatechol acetonide (4-VCA) and 3-vinylcatechol acetonide (3-VCA) are introduced for carbanionic polymerization in THF, using sec-butyllithium as an initiator. Molecular weights (M n ) ranging from 3000 to 80 000 g mol −1 were obtained, with polydispersities (M w /M n ) below 1.10 for 4-VCA and 1.15 for 3-VCA homopolymerization. Furthermore, block copolymers and gradient copolymers with styrene have been prepared via living carbanionic copolymerization. The reactivity of the new monomers 4-VCA and 3-VCA in the copolymerization with styrene and the resulting monomer gradient in the copolymer chains were investigated via in situ 1 H NMR spectroscopic kinetic studies in toluene-d 8 . The results show lower reactivity of the 4-VCA monomer than styrene (r S = 4.0, r 4-VCA = 0.24) and a higher reactivity than styrene for 3-VCA (r 3-VCA = 2.4, r S = 0.48). Well-defined copolymers of styrene and 4-VCA exhibit a strong gradient structure within the polymer chains with the catechol functionalities preferentially incorporated near the chain terminus. However, in the case of 3-VCA, the gradient structure of the copolymers is reversed, and the catechol functionalities are preferentially incorporated in the vicinity of the initiator. The direction of the monomer gradient in the copolymers can be predicted from the difference of the chemical shift of the β-carbon signal of the respective vinyl monomers in 13 C NMR spectra, which has general implications for the copolymerization of vinyl monomers. All polymers were characterized by 1 H NMR spectroscopy, size exclusion chromatography (SEC), MALDI-ToF mass spectrometry, and differential scanning calorimetry (DSC). Quantitative cleavage of the acetonide protecting group under mild acidic conditions rendered well-defined poly(vinyl catechol)s, which were used for pH-sensitive precipitation of iron(III) cations and for surface coating on a variety of materials, showing very stable and permanent catechol-promoted adhesion.

A protected catechol-containing epoxide monomer, catechol acetonide glycidyl ether (CAGE), is introduced. CAGE is conveniently obtained in three steps and enables the incorporation of surface-active catechol moieties into a broad variety of hydrophilic and biocompatible polyether architectures by copolymerization. Via acidic cleavage of the acetal protecting groups, the polymer-attached catechol functionalities are liberated and available for surface attachment or metal complexation. CAGE has been copolymerized with ethylene oxide and glycidol to obtain both linear poly(ethylene glycol) and hyperbranched polyglycerol copolymers, respectively, with multiple surface-adhesive catechol moieties. The CAGE content in the copolymers was varied from 1 to 16%, and all polymers exhibit moderate polydispersity (linear: M w /M n = 1.05−1.33; hyperbranched: M w /M n = 1.44−1.86). In situ kinetic studies of the simultaneous copolymerization of EO and CAGE via NMR spectroscopy have been performed to determine the microstructure of the linear poly(ethylene oxide-co-catechol acetonide glycidyl ether), P(EO-co-CAGE), copolymers. EO shows slightly higher reactivity than CAGE (r EO = 1.14, r CAGE = 0.88), leading to an almost ideally random copolymerization. Because of the catechol units, the copolymers form pH-induced cross-linked networks through metal−ligand interactions. ABA triblock copolymers of the type PCAGE-b-PEG-b-PCAGE formed highly swellable hydrogels upon addition of FeCl 3 . Furthermore, static water contact angle measurements demonstrate an increase in the hydrophilicity of iron, PTFE, and PVC surfaces after coating with catechol-functional mf-PEGs.