Photoinitiators with functional groups. VII. Covalently bonded camphorquinone—amines

Camphorquinone (CQ), a widely used photoinitiator (PI) in dental applications, was covalently bonded to aromatic amines to enhance the rate of electron and proton transfer effect due to the close vicinity of the diketone and the amine group. 10‐bromocamphorquinone and 10‐bromomethylcamphorquinone were selected as suitable precursors for esterification with the carboxyl group containing aromatic amines based on 4‐dimethylaminobenzoic acid. Properties of the new photoinitiating systems were investigated by UV spectroscopy and differential scanning photocalorimetry in lauryl acrylate. Compared to physical mixtures, in all cases similar or even better performance was obtained. Surprisingly, 10‐acetyl derivatives 7 – 9 and 18 especially, were found to be highly reactive. Compared to CQ/ethyl 4‐dimethylaminobenzoate, the rate of photopolymerization was increased by a factor of up to 2. Intramolecular reaction was confirmed by photo‐differential scanning calorimetry experiments with varying PI concentrations. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 4948–4963, 2004     

Antimicrobial activity on the copolymers of 2,4‐dichlorophenyl methacrylate with methyl methacrylate: Synthesis and characterization

Copolymers of monomers 2,4‐dichlorophenyl methacrylate (2,4‐DMA) and methyl methacrylate (MMA) were synthesized with different monomer feed ratios using toluene as a solvent and 2,2′‐azobisisobutyronitrile (AIBN) as an initiator at 70 °C. The copolymers were characterized by IR‐spectroscopy, and copolymer composition was determined with UV‐spectroscopy. The linearization method of Fineman–Ross was employed to obtain the monomer reactivity ratios. The molecular weights and polydispersity indexes were determined by gel permeation chromatography (GPC). Thermogravimetric analyses of polymers were carried out in nitrogen atmosphere. The homo‐ and copolymers were tested for their antimicrobial properties against selected microorganisms. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 5227–5234, 2004     

Hollow latex particles as submicrometer reactors for polymerization in confined geometries

A method was developed for free‐radical polymerization in the confines of a hollow latex particle. Hollow particles were prepared via the dynamic swelling method from polystyrene seed and divinylbenzene and had hollows of 500–1000 nm. So that these hollow poly(divinylbenzene) particles could function as submicrometer reactors, the particles were filled with a monomer (N‐isopropylacrylamide) via the dispersion of the dried particles in the molten monomer. The monomer that was not contained in the hollows was removed by washing and gentle abrasion. Free‐radical polymerization was then initiated by γ radiolysis in the solid state. Transmission electron microscopy showed that poly(N‐isopropylacrylamide) formed in the hollow interior of the particles, which functioned as submicrometer reactors. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 5706–5713, 2004     

Proteins Entrapped in Silica Monoliths Prepared from Glyceroxysilanes

The preparation of discrete polyol based silane precursors derived from glycerol by a simple one-pot process is described. These polyol-based silanes could be hydrolyzed under mild pH conditions and upon gelation resulted in the formation of optically clear, monolithic, mesoporous silica. The hydrolysis and condensation reactions lead to cure rates that are very sensitive to ionic strength, but are almost unaffected by pH in contrast to those of alkoxysilanes derived from primary alcohols such as Si(OEt)₄. Residual glycerol in the silica monolith could be removed by washing, or could be left in the silica to reduce the magnitude of shrinkage during long term storage. The biocompatible glyceroxysilane precursors lead to materials that were able to retain the activity of entrapped enzymes over repeated cycles of use for periods of up to several months.     

Control of the Morphology of Organic-Inorganic Hybrid Materials Elaborated by Reactive Processing Without Solvent

We study the synthesis of organic-inorganic hybrids in the molten state of the polymer without solvent, by reactive processing. The synthesis is based in a first step upon the crosslinking of ethylene vinyl acetate copolymer (EVA) through an exchange reaction between the pendant ester groups of EVA and tetrapropoxysilane (TPOS) in presence of dibutyltin oxide (DBTO) as an indispensable catalyst. Then in a second step the hydrolysis-condensation reactions of residual alkoxide groups results in silica network formation, which is covalently bonded with the organic network. An original approach was developed to correlate the evolution of the hydrolysis-condensation reactions through the assessment of propanol by gas chromatography and the evolution of the morphology through SAXS and TEM analysis. Silica-rich domains with a diameter close to 5 nm are obtained.     

Shear banding in strained semicrystalline polyamide 6 films as revealed by atomic force microscopy: Role of the amorphous phase

Atomic force microscopy (AFM) has been used to visualize the plastic deformation mechanisms that are responsible for the yielding of semicrystalline polymers of low degree of crystallinity (<50%). Indeed, AFM, if operated in suitable conditions, is able to image both the amorphous and the crystalline phases. Polyamide 6 films have been drawn at temperatures T < 160 °C. Postmortem AFM observations show that, at yield, shear bands nucleate and propagate in the amorphous phase. They cross the crystalline lamellae and run over the whole surface of the sample. By crossing the lamellae, they form nanoblocks of uniform size. Neither the size of the nanoblocks nor the angle between the tensile axis and the shear bands can be explained in terms of crystal plasticity. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 687–701, 2004     

Physical properties of glycosaminoglycan hydrogels

The chemical composition of glycosaminoglycan (GAG) hydrogels was found to have a profound effect on the physical properties of gels. Hyaluronan (HA) and chondroitin sulfate (CS) were each modified with adipic dihydrazide (ADH) with carbodiimide chemistry. The resulting polymer was crosslinked with various concentrations of poly(ethylene glycol) dialdehyde (PEG‐diald) to produce a series of hydrogels. The physical properties of these GAG hydrogels varied in a concentration‐dependent fashion. Maximal crosslinking was observed at a theoretical crosslinking of 50% for the HA‐ADH‐PEG‐diald hydrogels and 75% for the CS‐ADH‐PEG‐diald hydrogels. Adding PEG‐diald beyond the optimum for crosslinking prolonged the in vitro enzymatic degradation time of the hydrogels. The swelling of the crosslinked GAG hydrogels was correlated with the amount of PEG‐diald used rather than with the crosslinking density. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 4344–4356, 2004     

Permeability of N2, Ar,He, O2, and CO2 through as‐extruded amorphous and biaxially oriented polyester films: Dependence on chain mobility

For as‐extruded amorphous and biaxially orientated polyester films based on poly(ethylene terephthalate), poly(ethylene naphthalate), and copolymers containing poly(ethylene terephthalate) and poly(ethylene naphthalate) moieties, permeability, diffusion, and solubility coefficients are interpreted in terms of chain mobility. The influence of polymer morphology is determined by comparison of the data for as‐extruded amorphous sheets and materials produced with different biaxial draw ratios. The crystallinities of the samples were assessed using differential scanning calorimetry and density measurements. Changes in mobility at a molecular level were investigated using dielectric spectroscopy and dynamic mechanical thermal analysis. The study, in conjunction with our earlier work, leads to the conclusion that the key to understanding differences in gas transport is the difference in local chain motions rather than in free volume. This was illustrated by the permeability results for He, Ar, N₂, and O₂ in the range of polyesters. However, the permeability of CO₂ was found to require alternative explanations because of polymer–penetrant interactions. For biaxially oriented samples, the differences in diffusivity are not only due to differences in local chain motions, but also additional constraints resulting from the increased crystallinity and chain rigidity—which also act to hinder segmental mobility. The effectiveness of the reduction in permeability in the biaxially oriented films is consequently determined by the ability of the polymer chains to effectively align and form crystalline structures. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 2916–2929, 2004     

Resonance-stabilized phenoxy-like radicals formed by NO-mediated mono-nitration of coumarins containing a hydroxy group

Stable aminoxyls and an iminoxyl were observed by spin trapping and EPR techniques during the nitration of coumarins containing a hydroxy group by nitric oxide. The trapped free radicals are deduced to be the resonance stabilized phenoxy-like radicals. The mechanisms for the nitrations are suggested.