Specific interaction between fluorine atoms and thiol groups accounting for higher domain purity and photostability in narrowband BHJ systems

In order to explore the role of fluorine atoms on photostability as well as morphology control of active layer in the presence of 1,4‐butanedithiol (BT), the four polymers with or without fluorine atoms in the backbones including polythieno[3,4‐b]thiophene/benzodithiophene, poly[(4,8‐bis‐(2‐ethylhexyloxy)‐benzo(1,2‐b:4,5‐b9)dithiophene)‐2,6‐diyl‐alt‐(4‐(2‐ethylhexanoyl)‐thieno[3,4‐b]thiophene‐)‐2‐6‐diyl)], poly[4,8‐bis(5‐(2‐ethylhexyl)thiophen‐2‐yl)benzo[1,2‐b;4,5‐b′]dithiophene‐2,6‐diyl‐alt‐(4‐(2‐ethylhexyl)‐3‐fluorothieno[3,4‐b]thiophene‐)‐2‐carboxylate‐2‐6‐diyl)], and poly[4,8‐bis‐(2‐ethyl‐hexyl‐thiophene‐5‐yl)‐benzo[1,2‐b:4,5‐b0]dithiophene‐2,6‐diyl]‐alt‐[2‐(20‐ethyl‐hexanoyl)‐thieno [3,4‐b]thiophen‐4,6‐diyl] were selected for comparison. It is found that the specimens containing fluorine atoms in polymer backbones showed of higher stability after illumination for 1 h in the presence of BT additive, contributing to the higher domain purity. The specific interaction between fluorine atoms and thiol groups was demonstrated by the appearance of novel absorption peak at 2663.1 cm^?1, in addition to the broadening of peak at 2556.2 cm^?1 ascribing to S? H stretching vibration as confirmed by Fourier transform infrared (FTIR) spectroscopy. The finding may guide the accurate use of thiols as effective solvent additive in morphology and stability optimization. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2019 , 57, 941–951     

Photovoltaic polymers based on difluoroqinoxaline units with deep HOMO levels

We report the synthesis of low bandgap polymers with a difluoroquinoxaline unit by Stille polymerization for use in polymer solar cells (PSCs). A new series of copolymers with 2,3‐didodecyl‐6,7‐difluoro quinoxaline as the electron‐deficient unit and alkyloxybenzo[1,2‐b:4,5‐b′]dithiophene and thiophene as the electron‐rich unit were synthesized. The photovoltaic properties of the devices based on the synthesized polymers revealed that the fluorine atoms at the quinoxaline units aid in decreasing the highest occupied molecular orbital (HOMO) energy levels; this in turn increased the open circuit voltage of the devices. The polymers with long alkyl chains exhibited good solubility that increased their molecular weight, but the power conversion efficiency was low. Efficient polymer solar cells were fabricated by blending the synthesized copolymers with PC₇₁BM, and the PCE increased up to 5.11% under 100 mW cm⁻² AM 1.5 illumination. These results demonstrate that the importance of having a control polymer to be synthesized and characterized side by side with the fluorine analogues. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2018 , 56, 1489–1497     

Strain-dependent electronic and magnetic of Co-doped monolayer of WSe2

We perform first-principles calculation to investigate electronic and magnetic properties of Co-doped WSe₂ monolayer with strains from −10% to 10%. We find that Co can induce magnetic moment about 0.894 μ_B, the Co-doped WSe₂ monolayer is a magnetic semiconductor material without strain. The doped system shows half-metallic properties under tensile strain, and the largest half-metal gap is 0.147 eV at 8% strain. The magnetic moment (0.894 μ_B) increases slightly from 0% to 6%, and jumps into about 3 μ_B at 8% and 10%, which presents high-spin state configurations. When we applied compressive strain, the doped system shows a half-metallic feature at −2% strain, and the magnetic moment jumps into 1.623 μ_B at −4% strain, almost two times as the original moment 0.894 μ_B at 0% strain. The magnetic moment vanishes at −7% strain. The Co-doped WSe₂ can endure strain from −6% to 10%. Strain changes the redistribution of charges and magnetic moment. Our calculation results show that the Co-doped WSe₂ monolayer can transform from magnetic semiconductor to half-metallic material under strain.     

Solution behavior of polyimide‐graft‐polystyrene copolymers in selective solvents

A polyimide‐graft‐polystyrene (PI‐g‐PS) copolymer with a polyimide backbone and polystyrene side chains was synthesized by the “grafting from” method using styrene polymerization on a polyimide multicenter macroinitiator via ATRP mechanism. The side chain grafting density z = 0.86 of PI‐g‐PS is rather high for graft‐copolymers synthesized by the ATRP method. Molecular characteristics and solution behavior of PI‐g‐PS were studied in selective solvents using light scattering and viscometry methods. In all solvents, the backbone tends to avoid contact with a poor solvent. To describe the conformation and hydrodynamic properties of PI‐g‐PS macromolecules in thermodynamically good solvents for side chains and PI‐g‐PS, the wormlike spherocylinder model is used. Macromolecules of the studied graft‐copolymer are characterized by high equilibrium rigidities (Kuhn segment length >20 nm). In Θ‐conditions, PI‐g‐PS macromolecules may be modeled by a rigid prolate ellipsoid of revolution with a low asymmetry form and a collapsed backbone as the ellipsoid core. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2014 , 52, 1539–1546     

Attapulgite grafted with polystyrene via a simultaneous reverse and normal initiation atom transfer radical polymerization

The surface grafting of attapulgite (ATP) with polystyrene (PS) was established via a simultaneous reverse and normal initiation atom transfer radical polymerization (SR&NIATRP). 4‐(chloromethyl)phenyltrimethoxysilane (CMPTMS) chemical bounded on the surface of ATP (ATP‐Cl, Cl‐I) was prepared via one‐step self‐assembly. SR&NI ATRP of styrene was conducted using CuCl₂ complex tris(2‐(dimethylamino)ethyl)amine (Me₆‐TREN) as the catalytic system, initiated by 2,2‐azobis(isobutyronitrile) (AIBN) and ATP‐Cl. FT‐IR, XRD, XPS, TGA and TEM data were consistent with the grafting of benzyl chloride groups and PS chains on ATP surface. The controllability of polymerization was investigated by the kinetics behavior under different molar ratio of AIBN and CuCl₂. The obtained polymer possessed a uniform distribution of molecular weights with a lower polydispersity index of 1.2～1.4. The relationship between polymerization on the surface of ATP and in solution was discussed in detail based on TGA data of hybrid particles and GPC trace of free polymer in solution. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016 , 54, 1508–1516     

AGET ATRP of water‐soluble PEGMA: Fast living radical polymerization mediated by iron catalyst

In this work, living radical polymerizations of a water‐soluble monomer poly(ethylene glycol) monomethyl ether methacylate (PEGMA) in bulk with low‐toxic iron catalyst system, including iron chloride hexahydrate and triphenylphosphine, were carried out successfully. Effect of reaction temperature and catalyst concentration on the polymerization of PEGMA was investigated. The polymerization kinetics showed the features of “living”/controlled radical polymerization. For example, M_n,GPC values of the resultant polymers increased linearly with monomer conversion. A faster polymerization of PEGMA could be obtained in the presence of a reducing agent Fe(0) wire or ascorbic acid. In the case of Fe(0) wire as the reducing agent, a monomer conversion of 80% was obtained in 80 min of reaction time at 90 °C, yielding a water‐soluble poly(PEGMA) with M_n = 65,500 g mol^?1 and M_w/M_n = 1.39. The features of “living”/controlled radical polymerization of PEGMA were verified by analysis of chain‐end and chain‐extension experiments. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

Three‐arm star block copolymers of aromatic polyether and polystyrene from chain‐growth condensation polymerization,atom transfer radical polymerization,and click reaction

Well‐defined (AB)₃ type star block copolymer consisting of aromatic polyether arms as the A segment and polystyrene (PSt) arms as the B segment was prepared using atom transfer radical polymerization (ATRP), chain‐growth condensation polymerization (CGCP), and click reaction. ATRP of styrene was carried out in the presence of 2,4,6‐tris(bromomethyl)mesitylene as a trifunctional initiator, and then the terminal bromines of the polymer were transformed to azide groups with NaN₃. The azide groups were converted to 4‐fluorobenzophenone moieties as CGCP initiator units by click reaction. However, when CGCP was attempted, a small amount of unreacted initiator units remained. Therefore, the azide‐terminated PSt was then used for click reaction with alkyne‐terminated aromatic polyether, obtained by CGCP with an initiator bearing an acetylene unit. Excess alkyne‐terminated aromatic polyether was removed from the crude product by means of preparative high performance liquid chromatography (HPLC) to yield the (AB)₃ type star block copolymer (M_n = 9910, M_w/M_n = 1.10). This star block copolymer, which contains aromatic polyether segments with low solubility in the shell unit, exhibited lower solubility than A₂B or AB₂ type miktoarm star copolymers. In addition, the obtained star block copolymer self‐assembled to form spherical aggregates in solution and plate‐like structures in film. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

Synthesis,purification, and characterization of “perfect” star polymers via “Click” coupling

The copper (I)‐catalyzed azide‐alkyne cycloaddition “click” reaction was successfully applied to prepare well‐defined 3, 6, and 12‐arms polystyrene and polyethylene glycol stars. This study focused particularly on making “perfect” star polymers with an exact number of arms, as well as developing techniques for their purification. Various methods of characterization confirmed the star polymers high purity, and the structural uniformity of the generated star polymers. In particular, matrix‐assisted laser desorption ionization‐time‐of‐flight mass spectrometry revealed the quantitative transformation of the end groups on the linear polymer precursors and confirmed their quantitative coupling to the dendritic cores to yield star polymers with an exact number of arms. In addition to preparing well‐defined polystyrene and poly(ethylene glycol)homopolymer stars, this technique was also successfully applied to amphiphilic, PCL‐b‐PEG star polymers. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

Molecular dynamics simulations of displacement cascades in Fe-10%Cr systems

Molecular dynamics simulations of the displacement cascades in Fe-10%Cr systems are used to simulate the primary knocked-on atom events of the irradiation damage at temperatures 300,600,and 750 K with primary knockedon atom energies between 1 and 15 keV.The results indicate that the vacancies produced by the cascade are all in the central region of the displacement cascade.During the cascade,all recoil Fe and Cr atoms combine with each other to form Fe-Cr or Fe-Fe interstitial dumbbells as well as interstitial clusters.The number and the size of interstitial clusters increase with the energy of the primary knocked-on atom and the temperature.A few large clusters consist of a large number of Fe interstitials with a few Cr atoms,the rest are Fe-Cr clusters with small and medium sizes.The interstitial dumbbells of Fe-Fe and Fe-Cr are in the 111 and 110 series directions,respectively.