Preparation of Hydroquinone‐Containing Polymers by ROMP

Polymers containing ortho‐ and para‐hydroquinone moieties 5a,b and 6a are prepared in good yields by ROMP from hydroquinone‐fused norbornadiene derivatives 1a,b and 2a . Oxidation of 5b yielded a quinone derivative 7 , which is evidenced by a strong absorption at 1656 cm^?1 in infrared spectrum.     

Length distribution of stiff, self-assembled polymers at thermal equilibrium

We investigate the length distribution of self-assembled, long and stiff polymers at thermal equilibrium. Our analysis is based on calculating the partition functions of stiff polymers of variable lengths in the elastic regime. Our conclusion is that the length distribution of this self-assembled system follows closely the exponential distribution, except at the short length limit. We then discuss the implications of our results on the experimentally observed length distributions in amyloid fibrils.     

Analysis and measurement of candle flame shapes

A combined analytical and experimental study was performed to determine the length and width of a candle flame. Measurements were made of laminar steady flames from photographs of straight-wick candles composed of n-tetracosane and normal paraffin waxes. The wicks studied ranged in diameter from about 1 to 9 mm, and in height from about 2 to 10 mm, with aspect ratios (diameter to length) of 0.1 to 2. The flame length from the pool surface and the flame width at the top of the wick were found. It was also noted and recorded that the flame attachment point along the vertical wick varied. The attachment point was found to depend on the aspect ratio of the wick. A model based on stagnant layer burning for a finite cylinder was used, along with the Roper laminar burner model for flame height. With slight adjustment to a constant, the width of the flame was well predicted, and the prediction for the flame height was about 60% too high and offset. In addition, the model gave insight to produce an accurate simple correlation for flame height in terms of wick aspect ratio and Rayleigh number.     

Synthesis of diphosphite ligands derived from glucopyranoside and their application in the Cu-catalyzed asymmetric 1,4-addition of organozinc to enones

Novel chiral diphosphite ligands derived from glucopyranoside and H₈-binaphthol were synthesized, and successfully employed in the Cu-catalyzed asymmetric 1,4-addition of organozinc reagents dimethylzinc, diethylzinc, and diphenylzinc to cyclic and acyclic enones with up to 96% ee. The stereochemically matched combination of d-glucopyranoside backbone and (R)-H₈-binaphthyl in the ligand 2,4-bis{[(R)-1,1′-H₈-binaphthyl-2,2′-diyl] phosphite}-phenyl 3,6-anhydro-β-d-glucopyranoside was essential for inducing high enantioselectivity. A significant dependence of stereoselectivity on the type of enones and the ring size of cyclic enones was observed. Moreover, the sense of the enantiodiscrimination of the products was mainly determined by the configuration of the H₈-binaphthyl moieties.     

Synthesis and characterization of donor–bridge–acceptor alternating copolymers containing perylene diimide units and their application to photovoltaic cells

We have used Suzuki coupling to prepare a series of alternating copolymers featuring coplanar cyclopentadithiophene and hole‐transporting carbazole units. We observed quenching in the photoluminescence spectra of our polymers after incorporating pendent electron‐deficient perylene diimide ( PDI ) moieties on the side chains, indicating more efficient photoinduced electron transfer. Electrochemical measurements revealed that the PDI ‐containing copolymers displayed reasonable and sufficient offsets of the energy levels of their lowest unoccupied molecular orbitals for efficient charge dissociation. The performance of bulk heterojunction photovoltaic cells incorporating the copolymer/[6,6]‐phenyl‐C₆₁‐butyric acid methyl ester blends (1:4, w/w) was optimized when the active layer had a thickness of 70 nm. The photocurrents of the devices were enhanced as a result of the presence of the PDI moieties, thereby leading to improved power conversion efficiencies. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 1298–1309, 2010     

Alternating copolymers incorporating cyclopenta[2,1‐b:3,4‐b′]dithiophene unit and organic dyes for photovoltaic applications

We have synthesized six p‐type copolymers, CPDT ‐ co ‐ TPADCN , CPDT ‐ co ‐ TPADTA , CPDT ‐ co ‐ TPATCN , CPDT ‐ co ‐ DFADCN , CPDT ‐ co ‐ DFADTA , and CPDT ‐ co ‐ DFATCN , consisting of a cyclopenta[2,1‐b:3,4‐b′]dithiophene (CPDT) unit and an organic dye in an alternating arrangement. Triphenylamine (TPA) or difluorenylphenyl amine (DFA) units serve as the electron donors, whereas dicyanovinyl (DCN), 1,3‐diethyl‐2‐thiobarbituric acid, or tricyanovinyl (TCN) units act as the electron acceptors in the dyes. The target polymers were prepared via Stille coupling, followed by postfunctionalization to introduce the electron acceptors to the side chains. Because of the strongest withdrawing ability of TCN acceptor to induce efficient intramolecular charge transfer, CPDT ‐ co ‐ TPATCN and CPDT ‐ co ‐ DFATCN exhibit the broader absorption spectra covering from 400 to 900 nm and the narrower optical band gaps of 1.34 eV. However, the CPDT ‐ co ‐ TPATCN :PC₇₁BM and CPDT ‐ co ‐ DFATCN :PC₇₁BM based solar cells showed the power conversion efficiencies (PCEs) of 0.22 and 0.31%, respectively, due to the inefficient exciton dissociation. The DFA‐based polymers possess deeper‐lying HOMO energy levels than the TPA‐based polymer analogues, leading to the higher V_oc values and better efficiencies. The device based on CPDT ‐ co ‐ DFADTA :PC₇₁BM blend achieved the best PCE of 1.38% with a V_oc of 0.7 V, a J_sc of 4.57 mA/cm², and a fill factor of 0.43. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Development of level set method with good area preservation to predict interface in two‐phase flows

A two‐step conservative level set method is proposed in this study to simulate the gas/water two‐phase flow. For the sake of accuracy, the spatial derivative terms in the equations of motion for an incompressible fluid flow are approximated by the coupled compact scheme. For accurately predicting the modified level set function, the dispersion‐relation‐preserving advection scheme is developed to preserve the theoretical dispersion relation for the first‐order derivative terms shown in the pure advection equation cast in conservative form. For the purpose of retaining its long‐time accurate Casimir functionals and Hamiltonian in the transport equation for the level set function, the time derivative term is discretized by the sixth‐order accurate symplectic Runge–Kutta scheme. To resolve contact discontinuity oscillations near interface, nonlinear compression flux term and artificial damping term are properly added to the second‐step equation of the modified level set method. For the verification of the proposed dispersion‐relation‐preserving scheme applied in non‐staggered grids for solving the incompressible flow equations, three benchmark problems have been chosen in this study. The conservative level set method with area‐preserving property proposed for capturing the interface in incompressible fluid flows is also verified by solving the dam‐break, Rayleigh–Taylor instability, bubble rising in water, and droplet falling in water problems. Good agreements with the referenced solutions are demonstrated in all the investigated problems. Copyright © 2010 John Wiley & Sons, Ltd.