Methylenelactide: vinyl polymerization and spatial reactivity effects.

The first detailed study on free-radical polymerization, copolymerization and controlled radical polymerization of the cyclic push-pull-type monomer methylenelactide in comparison to the non-cyclic monomer α-acetoxyacrylate is described. The experimental results revealed that methylenelactide undergoes a self-initiated polymerization. The copolymerization parameters of methylenelactide and styrene as well as methyl methacrylate were determined. To predict the copolymerization behavior with other classes of monomers, Q and e values were calculated. Further, reversible addition fragmentation chain transfer (RAFT)-controlled homopolymerization of methylenelactide and copolymerization with N,N-dimethylacrylamide was performed at 70 °C in 1,4-dioxane using AIBN as initiator and 2-(((ethylthio)carbonothioyl)thio)-2-methylpropanoic acid as a transfer agent.

Amino-functionalized (meth)acryl polymers by use of a solvent-polarity sensitive protecting group (Br-t-BOC).

We describe the synthesis of bromo-tert-butyloxycarbonyl (Br-t-BOC)-amino-protected monomers 2-((1-bromo-2-methylpropan-2-yl)oxycarbonylamino)ethyl (meth)acrylate 3a,b. For this purpose, 2-isocyanatoethyl (meth)acrylate 1a,b was reacted with 1-bromo-2-methylpropan-2-ol (2a). The free radical polymerization of (Br-t-BOC)-aminoethyl (meth)acrylates 3a,b yielded poly((Br-t-BOC)-aminoethyl (meth)acrylate) 6a,b bearing protected amino side groups. The subsequent solvolysis of the Br-t-BOC function led to the new polymers poly(2-aminoethyl (meth)acrylate) 8a,b with protonated free amino groups. The monomers and the resulting polymers were thoroughly characterized by (1)H NMR, IR, GPC and DSC methods. The kinetics of the deprotection step was followed by (1)H NMR spectroscopy. The solvent polarity and neighboring group effects on the kinetics of deprotection are discussed.

From N-vinylpyrrolidone anions to modified paraffin-like oligomers via double alkylation with 1,8-dibromooctane: access to covalent networks and oligomeric amines for dye attachment.

The double alkylation of N-vinylpyrrolidone (N-VP) with 1,8-dibromooctane yields paraffin-like oligomeric chains bearing polymerizable vinyl moieties. These oligomers were radically crosslinked in bulk with N-VP as co-monomer yielding swellable polymer disks. The vinylic side groups of the N-VP oligomers allow thiol-ene click reactions with 2-aminoethanethiol hydrochloride to obtain reactive amino-functionalized oligomers. Further modification of the free amino groups with 1,4-difluoro-9,10-anthraquinone (DFA) yields red-colored oligomeric anthraquinone dyes. The final reaction of DFA-substituted N-VP oligomers with Jeffamine(®) M 600 leads to blue-colored and branched oligomers with poly(ethylene glycol) side chains.

Glucose oxidase and glucose for redox-initiating the free radical copolymerization of N-(ferrocenoylmethyl)acrylamide in aqueous cyclodextrin solution.

The glucose oxidase and glucose mediated formation of amphipilic copolymers of N-(ferrocenoylmethyl)acrylamide (NFMA) and N,N-diethylacrylamide (DEA) in aqueous cyclodextrin solution is presented. Thereby, NFMA is not only a comonomer but also part of the redox initiation system. The obtained copolymers contain NFMA units between 1 and 10 mol%. The molecular masses of the copolymers are dependent on the ferrocene content, whereupon molecular weights between 38,000 and 71,000 g mol(-1) are achieved.

Redox-switchable supramolecular graft polymer formation via ferrocene-cyclodextrin assembly.

The redox switchable formation of very well-defined supramolecular graft polymers in aqueous solution driven by host-guest interactions between ferrocene (Fc) and cyclodextrin (CD) is presented. The Fc-containing acrylic backbone copolymer (PDMA-stat-Fc) is prepared via reversible addition-fragmentation chain transfer (RAFT) copolymerization of N,N-dimethyl-acrylamide (DMA) and the novel monomer N-(ferrocenoylmethyl)acrylamide (NFMA). Via the RAFT process, copolymers containing variable Fc ratios (5-10 mol%) are prepared, affording polymers of molecular masses of close to 11,000 g mol(-1) and molar mass dispersities (D) of 1.2. The ß-cyclodextrin (ß-CD) containing building block is synthesized via RAFT-polymerization, too, in order to afford a polymer with well-defined molecular mass and low dispersity (Mn = 10 300 g mol(-1) , D = 1.1), employing a propargyl-functionalized chain transfer agent for the polymerization of N,N-diethylacrylamide (DEA). The polymerization product is subsequently terminated with ß-CD via the regiospecific copper (I)-catalyzed 1,3-cycloaddition (PDEA-ßCD). Host-guest interactions between Fc and CD lead to the formation of supramolecular graft-polymers, verified via nuclear Overhauser enhancement spectroscopy (NOESY). Importantly, their redox-responsive character is clearly confirmed via cyclic voltammetry (CV). The self-assembly of the statistical Fc-containing lateral polymer chain in aqueous solution leads to mono- and multi-core micelle-aggregates evidenced via TEM. Only diffused cloud-like, non-spherical nanostructures are observed after addition of PDEA-ßCD (TEM).

Influence of cyclodextrin on the UCST- and LCST-behavior of poly(2-methacrylamido-caprolactam)-co-(N,N-dimethylacrylamide).

The monomer 2-methacrylamido-caprolactam (4) was synthesized from methacryloyl chloride (3) and racemic α-amino-ε-caprolactam (2). Copolymerization of 4 with N,N-dimethylacrylamide (5) was carried out by a free-radical mechanism using 2,2'-azobis(2-methylpropionitrile) (AIBN) as an initiator. The new copolymers show a lower critical solution temperature (LCST) in water and an upper critical solution temperature (UCST) in ethanol, 1-propanol, and 1-butanol. The solubility properties of the copolymers can be influenced significantly by the addition of randomly methylated ß-cyclodextrin (CD). The complexation of the copolymers with CD, was confirmed by the use of ROESY-NMR-spectroscopy.

N-Alkylated dinitrones from isosorbide as cross-linkers for unsaturated bio-based polyesters.

Isosorbide was esterified with acryloyl chloride and crotonic acid yielding isosorbide diacrylate (9a) and isosorbide dicrotonate (9b), which were reacted with benzaldehyde oxime in the presence of zinc(II) iodide and boron triflouride etherate as catalysts to obtain N-alkylated dinitrones 10a/b. Poly(isosorbide itaconite -co- succinate) 13 as a bio-based unsaturated polyester was cross-linked by a 1,3-dipolar cycloaddition with the received dinitrones 10a/b. The 1,3-dipolar cycloaddition led to a strong change of the mechanical properties which were investigated by rheological measurements. Nitrones derived from methyl acrylate (3a) and methyl crotonate (3b) were used as model systems and reacted with dimethyl itaconate to further characterize the 1,3-dipolaric cycloaddition.

End group functionalization of poly(ethylene glycol) with phenolphthalein: towards star-shaped polymers based on supramolecular interactions.

The synthesis of a new phenolphthalein azide derivative, which can be easily utilized in polymer analogous reactions, is presented. The subsequent cycloaddition reaction with propargyl-functionalized methoxypoly(ethylene glycol) yielded polymers bearing phenolphthalein as the covalently attached end group. In presence of per-ß-cyclodextrin-dipentaerythritol, the formation of stable inclusion complexes was observed, representing an interesting approach towards the formation of star shaped polymers. The decolorization of a basic polymer solution caused by the complexation was of great advantage since this behavior enabled following the complex formation by UV-vis spectroscopy and even the naked eye.

Oligomerization of optically active N-(4-hydroxyphenyl)mandelamide in the presence of ß-cyclodextrin and the minor role of chirality.

The oxidative oligomerization of a chiral mandelamide derivative (N-(4-hydroxyphenyl)mandelamide, 1) was performed in the presence of horseradish peroxidase, laccase and N,N'-bis(salicylidene)ethylenediamine-iron(II) to obtain chiral oligophenols 2. The low enantioselectivity of the enzymatic catalyzed asymmetric enantiomer-differentiating oligomerizations was investigated. In addition, the poor influence of cyclodextrin on the enantioselectivity of enzymatic catalyzed asymmetric enantiomer-differentiating oligomerizations was studied.

Host-guest-driven color change in water: influence of cyclodextrin on the structure of a copper complex of poly((4-hydroxy-3-(pyridin-3-yldiazenyl)phenethyl)methacrylamide-co-dimethylacrylamide).

In the present work we report the synthesis of poly((4-hydroxy-3-(pyridin-3-yldiazenyl)phenethyl)methacrylamide-co-dimethylacrylamide) and its reversible optical and complex-forming properties due to copper and cyclodextrin (CD) interactions. Color changing effects are characterized by UV-vis spectroscopy and the supramolecular behavior is investigated by dynamic light scattering experiments.

End-group-functionalized poly(N,N-diethylacrylamide) via free-radical chain transfer polymerization: Influence of sulfur oxidation and cyclodextrin on self-organization and cloud points in water.

In this work we report the synthesis of thermo-, oxidation- and cyclodextrin- (CD) responsive end-group-functionalized polymers, based on N,N-diethylacrylamide (DEAAm). In a classical free-radical chain transfer polymerization, using thiol-functionalized 4-alkylphenols, namely 3-(4-(1,1-dimethylethan-1-yl)phenoxy)propane-1-thiol and 3-(4-(2,4,4-trimethylpentan-2-yl)phenoxy)propane-1-thiol, poly(N,N-diethylacrylamide) (PDEAAm) with well-defined hydrophobic end-groups is obtained. These end-group-functionalized polymers show different cloud point values, depending on the degree of polymerization and the presence of randomly methylated ß-cyclodextrin (RAMEB-CD). Additionally, the influence of the oxidation of the incorporated thioether linkages on the cloud point is investigated. The resulting hydrophilic sulfoxides show higher cloud point values for the lower critical solution temperature (LCST). A high degree of functionalization is supported by (1)H NMR-, SEC-, FTIR- and MALDI-TOF measurements.

Investigations of thiol-modified phenol derivatives for the use in thiol-ene photopolymerizations.

Thiol-ene photopolymerizations gain a growing interest in academic research. Coatings and dental restoratives are interesting applications for thiol-ene photopolymerizations due to their unique features. In most studies the relative flexible and hydrophilic ester derivative, namely pentaerythritoltetra(3-mercaptopropionate) (PETMP), is investigated as the thiol component. Thus, in the present study we are encouraged to investigate the performance of more hydrophobic ester-free thiol-modified bis- and trisphenol derivatives in thiol-ene photopolymerizations. For this, six different thiol-modified bis- and trisphenol derivatives exhibiting four to six thiol groups are synthesized via the radical addition of thioacetic acid to suitable allyl-modified precursors and subsequent hydrolysis. Compared to PETMP better flexural strength and modulus of elasticity are achievable in thiol-ene photopolymerizations employing 1,3,5-triallyl-1,3,5-triazine-2,4,6-trione (TATATO) as the ene derivative. Especially, after storage in water, the flexural strength and modulus of elasticity is twice as high compared to the PETMP reference system.

Supramolecular dynamics as origin for thermally induced insoluble-to-soluble-to-insoluble transitions of copolymers in water.

The synthesis of cationic mono-(6-O-(1-vinylimidazolium))-ß-cyclodextrin with toluenesulfonate as the corresponding anion is described. Free-radical copolymerization of the resulting host-guest complex with N-isopropylacrylamide or N,N-diethylacrylamide yielded copolymers showing a temperature-controlled solubility window in water. The impact of different anionic guests and salt concentrations on solubility behavior was investigated via turbidity measurements.

Color indicator for supramolecular polymer chemistry: phenolphthalein-containing thermo- and pH-sensitive N-(Isopropyl)acrylamide copolymers and ß-cyclodextrin complexation.

The copolymerization parameters of N-(isopropyl)acrylamide (1) and N-(2-hydroxy-5-(1-(4-hydroxyphenyl)-3-oxo-1,3-dihydroisobenzofuran-1-yl)benzyl)acrylamide (2) are determined. For both monomers, the homoaddition proceeds slightly faster than the heteroaddition step; however, the polymer formation occurs in a statistic fashion. Copolymers of different compositions are prepared and the cloud points are determined. Thereby, a significant influence of the concentration of monomer 2 and the pH value is found. For the first time, the complexation of polymer attached phenolphthalein by ß-cyclodextrins is shown. Furthermore, it is possible to achieve a decomplexation by the addition of suitable guest molecules. Both procedures can be followed with the naked eye.

A new type of thermoresponsive copolymer with UCST-type transitions in water: poly(N-vinylimidazole-co-1-vinyl-2-(hydroxymethyl)imidazole).

1-Vinyl-2-(hydroxymethyl)imidazole (2) is synthesized by a procedure described in the literature. Corresponding copolymers with upper critical solution temperature (UCST)-type transitions in water and high-glass transition temperatures (Tg ) are prepared by free radical copolymerization with N-vinylimidazole (1). Depending on the copolymer composition, the cloud point can be varied between 19 and 41 °C. As the copolymer composition is identical with the monomer feed ratio, the cloud point can be easily tuned in the desired range. Furthermore, a distinctive pH-dependence and salt effect can be observed.

Macrocyclic and polymeric oxaziridine-derivatives.

Macrocyclic and polymeric imines 5,5' and 6,6' are obtained in excellent yields by template-free polycondensation of 1,6-bis(4-formylbenzoyloxy)hexane (1) with commercially available 4,4'-methylene-bis(cyclohexylamine) (2) and with bis(2-amino-2-methylprop-1-yl)adipate dihydrochloride (4), respectively. The degree of macrocyclization during imine synthesis strongly depends on the diamine. Matrix-assisted laser desorption-ionization time-of-flight (MALDI-TOF) mass spectrometry analysis and gel permeation chromatography (GPC) measurements show that (2) leads to more macrocyclic adducts than (4). The subsequent meta-chloroperoxybenzoic acid oxidation of polyimines 5,5' and 6,6' ($ \bar M_{\rm n} $ = 1650-11 200 g mol(-1) , $ \bar M_{\rm w} $ = 3800-27 350 g mol(-1) ) yields the corresponding polyoxaziridines 7,7' and 8,8' consisting of macrocyclic and linear polymeric structures ($ \bar M_{\rm n} $ = 1750-8050 g mol(-1) , $ \bar M_{\rm w} $ = 3250-15 800 g mol(-1) ). The synthesized polyoxaziridines are relatively stable and storable at room temperature.

Molecular recognition: influence of para-versus-meta-substituted phenyl moieties on the swelling degree of macroscopic polymeric gels in aqueous cyclodextrin solutions.

Free radical terpolymerization of (N,N)-dimethylacrylamide, ethylene-glycol-dimethacrylate and N-(p- or m-ethyl-phenyl)acrylamide leads to para- and meta-ethyl-phenyl-modified hydrophilic polymer networks. Polymeric networks of different molar ratios are prepared in special molds to give water swellable disc- shaped samples. The swelling behavior in water and aqueous cyclodextrin (CD) solution of the obtained samples is described while a distinctive differentiation between the para- and meta-ethyl-phenyl containing networks in CD solution can be found.

Modulation of the thermoresponsive behavior of poly(N,N-diethylacrylamide) via cyclodextrin host/guest interactions.

The modulation of the cloud point of aqueous poly(N,N-diethylacrylamide) solutions via the formation of supramolecular cyclodextrin complexes with hydrophobic end groups, namely adamantyl, tert-butyl phenyl and azobenzene, synthesized via RAFT polymerization is described. The dependence of the apparent cloud points after cyclodextrin complexation is investigated with respect to the type and quantity of the guest end group, the polymer chain length and the cyclodextrin/end group ratio. Furthermore, the effect is reversed via the addition of guest molecules or via biocompatible enzymatic degradation of the cyclodextrins entire.

Oligomeric epoxide-amine adducts based on 2-amino-N-isopropylacetamide and α-amino-ε-caprolactam: Solubility in presence of cyclodextrin and curing properties.

2-Amino-N-isopropylacetamide and α-amino-ε-caprolactam were reacted with glycerol diglycidyl ether to give novel oligomeric thermoresponsive epoxide-amine adducts. These oligomers exhibit a lower critical solution temperature (LCST) behavior in water. The solubility properties were influenced with randomly methylated ß-cyclodextrin (RAMEB-CD) and the curing properties of the amine-epoxide mixtures were analyzed by oscillatory rheology and differential scanning calorimetry, whereby significant differences in setting time, viscosity, and stiffness were observed.

Polymeric redox-responsive delivery systems bearing ammonium salts cross-linked via disulfides.

A redox-responsive polycationic system was synthesized via copolymerization of N,N-diethylacrylamide (DEAAm) and 2-(dimethylamino)ethyl methacrylate (DMAEMA). N,N'-bis(4-chlorobutanoyl)cystamine was used as disulfide-containing cross-linker to form networks by the quaternization of tertiary amine groups. The insoluble cationic hydrogels become soluble by reduction of disulfide to mercaptanes by use of dithiothreitol (DTT), tris(2-carboxyethyl)phosphine (TCEP) or cysteamine, respectively. The soluble polymeric system can be cross-linked again by using oxygen or hydrogen peroxide under basic conditions. The redox-responsive polymer networks can be used for molecular inclusion and controlled release. As an example, phenolphthalein, methylene blue and reactive orange 16 were included into the network. After treatment with DTT a release of the dye could be recognized. Physical properties of the cross-linked materials, e.g., glass transition temperature (T g), swelling behavior and cloud points (T c) were investigated. Redox-responsive behavior was further analyzed by rheological measurements.