Volumetric shrinkage reduction is a constant challenge in the improvement of dental resins. The inclusion of hyperbranched polymers (HBPs) with modified functionalities (hydroxyl, propionate, and methacrylate) instead of conventional dimethacrylate monomers has the potential to reduce shrinkage, but can also affect other properties. The null hypothesis was that the addition of HBPs (from 5 to 40 mass%) to a 50/50 mass% Bis-GMA/TEGDMA mixture reduces shrinkage without affecting degree of conversion, elastic modulus, glass transition temperature, Wallace hardness (before/after ethanol storage), and viscosity. This hypothesis was rejected, since HBP incorporation significantly affected most properties either negatively or positively. When HBP amounts in the resin were increased, the following general trends were observed: Volumetric shrinkage decreased significantly (p < 0.0001), down to about one-third of the control value at 40% HBP; Wallace hardness (both before and after ethanol) and viscosity increased progressively, while elastic modulus showed a parabolic profile, with a maximum at 10% HBP; and finally, degree of conversion and glass transition temperature were relatively stable, regardless of the HBP content. These results indicate that HBPs with modified end groups might be interesting substitutes for Bis-GMA/TEGDMA.

The introduction of new tailor-made (meth)acrylated oligomers has extended the potential use of the radiation curing technology to metal coating applications where adhesion, flexibility and corrosion resistance are of prime importance. In this paper, we discuss the properties of three fairly simple clearcoat systems spanning a range of glass transition temperatures between approximate to 10 and 70 C. The systems were obtained by combination of two original urethane acrylate resins and two reactive diluents.Practical performance tests typically used to establish coating profiles in the metal industry (i.e., mechanical testing, adhesion, salt-spray test, etc.) were performed on ultraviolet (UV)-coated galvanised steel. In addition, the barrier properties of coated steel panels were systematically investigated at different coating thicknesses using electrochemical impedance spectroscopy. These results are analysed in terms of relevant physico-chemical characteristics such as conversion, volume contraction, swelling, viscoelastic and tensile behaviour determined on free-standing coating layers of the three formulations. (C) 2008 Elsevier B.V. All rights reserved.

INTRODUCTION: Linear polymers (BisGMA, TEGDMA, etc.) have been commonly used in the matrix of composites. Recently, new types of polymers, hyperbranched polymers (HBP), have been synthesized. HBP are very large molecules with many branches and a large number of functional groups on each molecule in comparison with traditional linear polymers. In a previous study [1], a linear relationship was found between the volume contraction and the actual number of double bonds converted. A reduction of the polymerization shrinkage may obviously be expected from the addition of molecules allowing the double bond conversion per unit of volume of resin matrix to be decreased. HBP are thus attractive because their functionalities can be modified to obtain molecules with a high volume and few double bonds. The objective of this study was to investigate the potential of HBP to decrease polymerization shrinkage of the composite matrix while maintaining double bond conversion. METHODS: The resins investigated consisted of a conventional mixture, BisGMA/TEGDMA (50/50 wt/wt), used as a reference, in which three HBPs, with different shell chemistry, were added at several weight ratios (5, 10, 20, 30, and 40%). A photoinitiation system was added to each mixture in a proportion of 1%. Degree of conversion (DC) of the polymers was determined by Raman spectroscopy. The volume contraction was measured by pycnometry and by a density column. RESULTS:

An acid-base titration method for an accurate and reproducible quantification of maleic anhydride grafted onto polyolefins is proposed. The use of an organic base (tetra-butylammonium hydroxide) enhances the base solubility in organic solvents and prevents phenomena like coarcervation. The titration goes on until the visual endpoint of a coloured indicator, corresponding to the neutralisation of the grafted functions. Bromothymol blue is chosen as the coloured indicator to determine this equivalence point.It is critically correlated with a Fourier transform-infrared spectroscopy quantification developed previously by De Roovers et al. [J Polym Sci, Part A: Polym Chem 1995;33:829] and with a viscosimetric titration method here-proposed Finally, the titration mechanism is confirmed by the titration of some well-defined amount of anhydride model compounds and by FTIR analyses of their products after titration. (C) 1999 Elsevier Science Ltd. All rights reserved.

This paper reports on the anionic synthesis of poly(methyl methacrylate) chains end-capped by cyclic anhydride. The method is based on the chemical derivatization of a precursor tert-butyl diester end-group. Compared to the thermal modification, which was previously used, this method allows intermolecular coupling and polymer degradation to be avoided. But up to now, the final anhydride content remains moderate and has still to be improved.

A new and very efficient route for the synthesis of aliphatic primary amine terminated polystyrene (PS) is reported. In contrast to most known methods, only traditional commercially available reagents are used. PS is synthesized by anionic polymerization with a lithium counter ion and the living chains are end-capped by a hydroxyl group upon addition of ethylene oxide followed by protonation. The ω-hydroxyl end group is tosylated and the tosylate is then reacted with sodium azide. The azide terminal group is finally reduced into primary amine. The different steps of functionalization have been fully characterized by SEC, ToF-SIMS, FTIR, and 1H NMR. The amine content (= 98%) has been determined by acid-base titration with perchloric acid. It clearly shows the efficiency of the synthetic method reported in this article although it is a multistep method. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 1618–1629, 2000