Observations on Finger-like Crack Growth at a Urethane Acrylate/Glass Interface

Interfacial crack growth behavior along a urethane acrylate/glass interface is characterized by the development of finger-like perturbations along the advancing crack front. The finger-like perturbations grow from a slightly irregular crack front until they reach a steady-state where the velocity of the finger tips equals the velocity of the finger valleys. Once the fingers reached steady-state, the crack velocity was dependent on the applied strain energy release rate via a power law relationship where the exponent was independent of test humidity; however, the multiplicative constant A decreased by an order of magnitude from 80 to 15% RH. The spacing of the fingers was found to be independent of the crack′s velocity and the relative humidity of the environment.     

Copolyesters as non‐toxic plasticizers

Plasticized polymer materials have taken an enormous role in our everyday life. Most of the common plasticizers are aromatics, esters of phthalic acid. Since they are not chemically bonded to the polymer matrix, they can be released from material while being used. The concerns raised about toxicity led to a large demand for producing biodegradable and non‐toxic plasticizers. We investigated aliphatic copolyesters synthesized via ring opening polymerization of lactones as plasticizers for poly(vinyl chloride). The material properties of the formulations, such as glass transition temperature and mechanical performance, were studied. Copyright © 2011 Society of Chemical Industry     

Thermal diffusivity of nanocarbon composites

This study was performed to measure the thermal diffusivity of different types of nanocarbon composites. Thermoexfoliated graphite (TEG), ultrasonically dispersed TEG, and multiwalled carbon nanotubes were used as fillers in epoxy polymer matrixes. The nanocarbon filler content was 1–10 wt%. The temperature dependence of the thermal conductivity and the heat capacity were extensively characterized in the temperature range between 150 and 425 K. For this purpose, the thermal diffusivity of the composites was investigated by two experimental methods: dynamic λ‐calorimeter and photoacoustic. The comparative analysis of thermal diffusivity of compacted TEG samples with different densities and of nanocarbon‐epoxy with different filler content was carried out. It was found that for the composites with a low distribution of the nanocarbon filler, the thermal diffusivity increases and that the value is determined by the structural and morphological properties of the filler. The orientation function for the TEG‐epoxy composites and the compact TEG samples differs due to the epoxy matrix that reduced anisotropy of the composite. POLYM. COMPOS., 2011. © 2010 Society of Plastics Engineers     

New calix[4]arenedimethacrylate derivatives for dental composites

Calix[4]arenes were double alkylated with various alkylhalogenides and the residual OH functions were subsequently dimethacrylated with methacryloyl chloride. The successful synthesis of polymerizable calixarenes was proved using ¹H NMR spectroscopy, matrix‐assisted laser desorption ionization time‐of‐flight mass spectrometry and differential scanning calorimetry. The polymerization behaviour was confirmed by copolymerization with methacrylic acid methyl ester. Furthermore, the flexural strength, the flexural modulus of elasticity, the exothermic course of the photo‐curing reaction and the polymerization shrinkage of experimental dental filling composites containing the modified calixarenes were evaluated. Copyright © 2012 Society of Chemical Industry     

Methacrylated calix[4]arene phosphonic acids as functionalized crosslinker for radical polymerization

We describe the synthesis of 5,11,17,23‐tetra‐tert‐butyl‐25,27‐dioxypropylphosphonic acid‐26,28‐dimethacryloyloxy‐calix [4]arene and 5,11,17,23‐tetra‐tert‐butyl‐25‐oxypropylphosphonic acid‐27‐hydroxy‐26,28‐dimethacryloyloxy‐calix[4]arene starting from para‐tert‐butyl‐calix[4]arene. The complete reaction was proved by matrix‐assisted laser desorption ionization time of flight mass spectrometry and nuclear magnetic resonance spectroscopy. The influence of these compounds on the kinetics of the radical polymerization of methyl methacrylate was shown by dilatometry. Furthermore, the adhesive properties of dental adhesives containing these calix[4]arene derivatives were investigated. Copyright © 2012 Society of Chemical Industry     

Single‐step synthesis of a radically polymerizable 1,1′‐bi‐2‐naphthol derivative for asymmetric catalysis

A new polymerizable 1,1′‐bi‐2‐naphthol derivative for polymer‐supported catalytic asymmetric synthesis is presented. The synthesis is conducted within a single reaction step, which is a major advantage over other approaches presented in the literature. The ligand‐bearing polymer is prepared through copolymerization with N‐isopropylacrylamide. Preliminary experiments on the utility in catalytic asymmetric alkylation reactions reveal the accessibility and activity of the polymer‐attached catalysts. The stereoselectivity of the reaction is found to be somewhat lower than for reactions performed in the presence of free 1,1′‐bi‐2‐naphthol, and thus requires further optimization. The enantiomeric excess of the reaction products was determined via ¹H NMR spectroscopy after chiral derivatization with (R)‐α‐methylbenzyl isocyanate. © 2015 Society of Chemical Industry     

Forgotten monomers: isotactic polymers from N‐benzyl‐3‐methylenepyrrolidin‐2‐one via free radical polymerization

N‐Benzyl‐3‐methylenepyrrolidin‐2‐one ( 3 ) was synthesized and homopolymerized under free radical conditions. The configurational microstructure of poly(N‐benzyl‐3‐methylenepyrrolidin‐2‐one) ( 4 ) is isotactic with a minor tendency to syndiotacticity. Monomer 3 was also homopolymerized in water in the presence of methylated β‐cyclodextrin. The glass transition temperature of 4 of 124 °C was compared with the lower value of 61 °C of the ring‐opened analogue poly(N‐benzyl‐N‐ethylacrylamide). © 2015 Society of Chemical Industry     

Forgotten monomers: access to α‐modified N‐vinylpyrrolidone polymers via C‐alkylation

Alkylation of N‐vinylpyrrolidone using lithium diisopropylamide and bis(2‐bromoethyl) ether was carried out to obtain 3‐(2‐(2‐bromoethoxy)ethyl)‐1‐vinyl‐2‐pyrrolidone ( 2 ). The derivative 2 represents a versatile starting molecule for further modification via nucleophilic displacement yielding, for example, the bicyclic 2‐vinyl‐8‐oxa‐2‐azaspiro[4.5]decan‐1‐one ( 4 ) or the ammonium salt 3‐diethoxy‐N,N′‐((dimethylbenzyl)ammonium bromide)‐1‐vinyl‐2‐pyrrolidone ( 10 ). Via free radical polymerization of 4 and 10 , the corresponding homopolymers were obtained. Copolymerization of 4 and 10 with N,N′‐diethylacrylamide yielded water‐soluble materials. The thermosensitive solubility of copolymers poly[(2‐vinyl‐8‐oxa‐2‐azaspiro[4.5]decan‐1‐one)‐co‐(N,N′‐diethylacrylamide)] and poly[(3‐diethoxy‐N,N′‐((dimethylbenzyl)ammonium bromide)‐1‐vinyl‐2‐pyrrolidone)‐co‐(N‐vinylpyrrolidone)] in water was investigated. © 2015 Society of Chemical Industry     

Catalytic performance of methacrylate‐based poly‐4‐(dialkylamino)‐pyridines: activity prediction via NMR shifts

The synthesis of the 4‐(dialkylamino)pyridine derivative 3‐(4‐(pyridin‐4‐yl)piperazin‐1‐yl)propyl methacrylate and its copolymerization with n‐butyl methacrylate are presented. The catalytic activity was evaluated in the acylation of tert‐butanol with acetic anhydride yielding tert‐butyl acetate. It is observed that the activity of polymer‐attached 4‐(dimethylamino)pyridine analogues correlates remarkably well with the chemical shift of the β‐pyridyl protons. Differences in catalytic efficiency result from distinct electronic densities of the pyridine ring, while embedding the catalytically active moiety into a polymeric structure has nearly no deleterious effect on the performance. © 2015 Society of Chemical Industry     

Surface Binding of TOTAPOL Assists Structural Investigations of Amyloid Fibrils by Dynamic Nuclear Polarization NMR Spectroscopy

Dynamic nuclear polarization (DNP) NMR can enhance sensitivity but often comes at the price of a substantial loss of resolution. Two major factors affect spectral quality: low‐temperature heterogeneous line broadening and paramagnetic relaxation enhancement (PRE) effects. Investigations by NMR spectroscopy, isothermal titration calorimetry (ITC), and EPR revealed a new substantial affinity of TOTAPOL to amyloid surfaces, very similar to that shown by the fluorescent dye thioflavin‐T (ThT). As a consequence, DNP spectra with remarkably good resolution and still reasonable enhancement could be obtained at very low TOTAPOL concentrations, typically 400 times lower than commonly employed. These spectra yielded several long‐range constraints that were difficult to obtain without DNP. Our findings open up new strategies for structural studies with DNP NMR spectroscopy on amyloids that can bind the biradical with affinity similar to that shown towards ThT.