Fluorescence spectroscopy and solid state NMR methods were used to elucidate the detailed molecular structure of poly(meth)acrylate networks. Both techniques can be employed on identical samples and give complementary information. In this study a series of diacrylates, a series of dimethacrylates, and 1:1 mixtures of the triacrylate TMPTA with diacrylates (DA's) or dimethacrylates (DMA's), respectively, was investigated. Fluorescence spectroscopy was performed, using the shift in the fluorescence maximum of 4-(dimethylamino)-4′-nitrostilbene (1), a charge transfer probe. This probe monitors both the rigidity and the polarity of the medium in which it is incorporated. CPMAS 13 C NMR spectroscopy was employed monitoring the relaxation times, T1, of carbon atoms from the main chains and pendant groups, determining cross-link densities, and measuring T1F( 1 H) values. With these techniques information about the mobility of individual atoms and the homogeneity of the polymeric networks is obtained.

Polymeric photoinitiators bearing benzophenone triphenylbutyl borate salt as the side chain have been synthesized and characterized and their activity measured in the photoinitiated polymerization of a bifunctional monomer, diethylene glycol diacrylate. The results were compared with a low-molecular weight model compound. At lower concentrations of the requisite benzophenone moiety, the highest activity was observed for the model compound, while at higher concentrations the homopolymer was superior. For both cases, the lowest photoinitiation activity was observed with significant induction period for copolymers with methyl methacrylate when compared to the homopolymer. The results are discussed in light of the microenvironment of the initiator fragments in the polymeric systems.

A theoretical analysis of relaxation processes has been used in the qualitative interpretation of carbon-resolved, proton Tlp data obtained at 100.56 MHz for three solid polyacrylate networks made by photopolymerization of the polyol acrylate monomers poly(ethylene glycol) diacrylate (PEGA), trimethylolpropane triacrylate (TMPTA), and dipentaerythritol pentaacrylate (DPHPA). This analysis permits an estimate of the spin diffusion rates between different chemical species. Such rates are strongly dependent on spatial proximity and hence are applicable to the determination of the homogeneity of the networks. Proton Tip's in networks are not quite averaged to a single value by spin diffusion like in polymer blends, indicating there is extensive intermixing of TMPTA and DPHPA in forming the network. Proton Tip experiments are sufficiently sensitive to distinguish between a TMPTADPHPA network and PEGA homopolymer. When glass fibers are present in the network, they act like a spin diffusion medium, producing an increase in the rates of relaxation for all three components of the network.

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Flow modelling is a key issue not only for the correct prediction of hull-propeller interactions, manoeuvring characteristics and the flow field in the stern region of any marine vehicle, but also for the correct estimation of the fuel consumption. The paper describes a thorough investigation of the hydrodynamic performances of the DARPA suboff hull. The flow is numerically simulated by integrating in time the unsteady Navier-Stokes equations in which closure to the turbulence is achieved by means of a modified detached eddy simulation (DES hereafter) technique. The solver used for the purpose is the ISIS-CFD, part of the Numeca FineTM/Marine suite, which employs the finite volume of fluid technique. A comparative analysis between the numerical solutions based on the DES and explicit algebraic stress model (EASM hereafter) are provided in an attempt to sustain the choice for the turbulence model in the present study. Extensive parallel computations are carried out on 120 processors for which comparisons with the experimental data prove the accuracy of the chosen investigation methodology. A grid convergence test is performed for verification and validation purposes.