Assessment of two‐equation turbulence modelling for high Reynolds number hydrofoil flows

This paper presents an evaluation of the capability of turbulence models available in the commercial CFD code FLUENT 6.0 for their application to hydrofoil turbulent boundary layer separation flow at high Reynolds numbers. Four widely applied two‐equation RANS turbulence models were assessed through comparison with experimental data at Reynolds numbers of 8.284×106 and 1.657×107. They were the standard k–εmodel, the realizable k–εmodel, the standard k–ωmodel and the shear‐stress‐transport (SST) k–ωmodel. It has found that the realizable k–εturbulence model used with enhanced wall functions and near‐wall modelling techniques, consistently provides superior performance in predicting the flow characteristics around the hydrofoil. Copyright © 2004 John Wiley & Sons, Ltd.     

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     

Photochemical attachment of polymers on planar surfaces with a covalently anchored monolayer of a novel naphthyl ketone photochemical radical generator

A monolayer of covalently anchored, novel, binaphthyl ketone is used as a surface‐confined photochemical radical generator (PRG) for anchoring a variety of polymers to silicon surfaces. The precursor PRG is synthesized by the application of a facile and novel method for the oxidation of sterically hindered benzylic hydrocarbons to carbonyl compounds. Oxidation was carried out with a stoichiometric amount of potassium peroxydisulfate, in the presence of a catalytic amount of copper sulfate in an acetonitrile/water mixture. The PRG synthesized is characterized by ¹H NMR, UV, and Fourier transform infrared (FTIR). The covalently attached monolayers are characterized by X‐ray photoelectron spectroscopy, ellipsometry, and water contact angle measurements. The method developed is applicable to the preparation of a monolayer of a variety of polymers on a wide range of substrates carrying surface hydroxyl groups. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 5413–5423, 2004     

Functionalization of polyethylene/silane copolymers in posttreatment reactions

7‐Octenyldimethylphenylsilane was copolymerized with ethylene via Et(Ind)₂ZrCl₂ methylaluminoxane catalyst system without loss of catalyst activity or decrease in molar mass. The comonomer contents in the polymer samples were at a level of 0.15–1.0 mol % and the reactive phenylsilane groups were posttreated to different alcoxy‐ and halosilane groups, for example, Si? F, Si? Cl, Si? OCH₃, and Si? OCH₂CH₃. The posttreatment reactions had no major effect on the molar masses or on the thermal properties (measured with differential scanning calorimetry) of the copolymers. The reaction pathways were nearly independent of the comonomer contents and the reactions reached 70–100% conversions. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 1461–1467, 2004     

Novel dinitroxide mediating agent for stable free‐radical polymerization

A novel dinitroxide mediating agent that was suitable for stable free‐radical polymerization was synthesized and used in the block copolymerization of styrene and t‐butyl styrene. Quantitative yields of a novel dinitroxide based on 1,6‐hexamethylene diisocyanate and 4‐hydroxy‐2,2,6,6‐tetramethyl‐1‐piperidinyloxy were obtained. Various experimental parameters, including the nitroxide‐to‐initiator molar ratio, were examined, and it was determined that the polymerization was most controlled under conditions similar to those of conventional 2,2,6,6‐tetramethyl‐1‐piperidinyloxy‐mediated stable free‐radical polymerization. Moreover, the dinitroxide mediator proved to be a viable route for the facile two‐step synthesis of triblock copolymers of styrene and t‐butyl styrene. However, the dinitroxide mediation process resulted in a higher than expected level of nitroxide decomposition, which resulted in polymers possessing a terminal alkoxyamine and an adjacent hydroxylamine rather than a preferred internal bisalkoxyamine. This decomposition resulted in the formation of diblock copolymer species during the triblock copolymer synthesis. Gel permeation chromatography was used to monitor the chain‐end decomposition kinetics, and the determined observed rate constant (5.89 × 10^?5 s^?1) for decomposition agreed well with previous studies for other dinitroxide mediating agents. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 1547–1556, 2004     

Tetrafunctional initiators for cationic polymerization of olefins

3,3′,5,5′‐Tetrakis(2‐chloro‐2‐propyl)biphenyl (biphenyl tetracumyl chloride, BPTCC) and 1,3‐bis[3,5‐bis(2‐chloro‐2‐propyl)phenoxy]propane (diphenoxypropane tetracumyl chloride, DPPTCC) were synthesized as initiators for quasiliving cationic polymerization of isobutylene (IB). In the synthesis of BPTCC, tetrafunctionality was achieved via the coupling of dimethyl 5‐bromoisophthalate (DMBI) using nickel dibromide bis(triphenylphosphine) and zinc in the presence of a base; in the synthesis of DPPTCC, two equivalents of dimethyl 5‐hydroxyisophthalate were linked via reaction with 1,3‐dibromopropane in the presence of potassium carbonate. Both initiators were used to initiate the polymerization of IB under quasiliving cationic polymerization conditions. PIB initiated from BPTCC revealed a chain end/molecule value (as determined by ¹H‐NMR) of 3.85, verifying the nearly exclusive production of 4‐arm polyisobutylene (PIB). GPC analysis revealed a narrow peak representing the target four‐arm PIB, with a slight shoulder at high elution volumes (low molecular weights). GPC analysis of the PIB initiated by DPPTCC revealed multimodal distributions, suggesting the formation of two‐, three‐, and four‐arm star polymers during the polymerization. This behavior was attributed to Friedel–Crafts alkylation of the initiator core after the addition of one IB unit, which was activated by the electron‐donating oxytrimethyleneoxy linking moiety. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 5942–5953, 2004