Nano‐adhesion and friction of multi‐asperity contact: a molecular dynamics simulation study

In our study, the contact and sliding processes between a flat plate and a substrate with multiple asperities are studied by molecular dynamics (MD) simulations, and how the number of asperities and asperity height influence the adhesion force and friction force are investigated thoroughly. The normal force versus the separation distance curve during contact processes is analyzed completely and from which the van der Waals (vdW) force (F_vdW) and the adhesion force (F_adh) are obtained and compared with the Katainen model. The adhesion force and the friction force increase linearly as the increase of the number of asperities (i.e. real contact area) with same asperity height. With the identical number of asperities, the adhesion force and the friction force decrease with the increase of the asperity height at first. However the reductions of the adhesion force and the friction force become less obvious, when the asperity height is larger than a critical value (20 Å for our simulation parameters). Copyright © 2015 John Wiley & Sons, Ltd.     

Blue light‐emitting hyperbranched polymers using fluorene‐co‐dibenzothiophene‐S,S‐dioxide as branches

A series of blue light‐emitting hyperbranched polymers comprising poly(fluorene‐co‐dibenzothiophene‐S,S‐dioxide) as the branch and benzene, triphenylamine, or triphenyltriazine as the core were synthesized by an “A₂ + A₂' + B₃” approach of Suzuki polymerization, respectively. All resulted copolymers exhibited quite comparable thermal properties with the glass transition temperatures in the range of 59–68 °C and relatively high decomposition temperatures over 420 °C. Photoluminescent spectra exhibited slight variation with the molar ratio of the dibenzothiophene‐S,S‐dioxide unit and the size of the core units. Polymer light‐emitting devices demonstrated blue emission with excellent stability of electroluminescence. Copolymers based on smaller core units of benzene and triphenylamine exhibited enhanced device performances regarding to that of triphenyltriazine. With the device configuration of ITO/PEDOT:PSS/polymer/CsF/Al, a maximum luminous efficiency of 4.5 cd A^?1 was obtained with Commission Internationale de L'.Eclairage (CIE) coordinates of (0.16, 0.19) for the copolymer PFSO15B. These results indicated that hyperbranched structure can be a promising strategy to attain spectrally stable blue‐light‐emitting polymers with high efficiency. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2015 , 53, 1043–1051     

Controllable ring‐opening copolymerization of L‐lactide and (3S)‐benzyloxymethyl‐(6S)‐methyl‐morpholine‐2,5‐dione initiated by a biogenic compound creatinine acetate

Ring‐opening copolymerization (ROCP) of L ‐lactide (L ‐LA) and (3S)‐benzyloxymethyl‐(6S)‐methyl‐morpholine‐2,5‐dione [(3S, 6S)‐BMMD] initiated by creatinine acetate, a biogenic organic compound, was performed in the bulk at 130 °C. The copolymerization was well controlled as evidenced by that both the measured values of number‐average molecular weight (M_n,NMR(OH) and M_n,NMR(COOH)) and serine molar fraction (F_Bz.ser) of synthesized copolymers were close to the corresponding theoretical values; and that the higher isotacticity of synthesized copolymers (85–86%) and lower racemization degree of the ROCP. After removing O‐benzyls of the copolymers with Et₃SiH/Et₃N/CH₂Cl₂ under catalysis of PdCl₂, functional biodegradable copolymers of L ‐lactic acid (L ‐Lac) and L ‐Ser with designed molar fraction of serine (F_ser 1.35%, 3.57%, 5.41%), narrow molecular weight distribution (polydispersity index 1.10–1.36), and improved hydrophilicity (θ_stat 82.3–89.6°) were finally obtained. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

Tuning block copolymer phase behavior with a selectively associating homopolymer additive

We use polymer random phase approximation (RPA) theory to calculate the microphase separation transition (MST) spinodal for an AB + C diblock copolymer–homopolymer blend where the C homopolymers are strongly attracted to the A segment of the copolymers. Our calculations indicate that one can shift the MST spinodal value of the A ? B segmental interaction parameter (χ_ABN)_S to significantly lower values [i.e., (χ_ABN)_S < 10.5] upon the addition of a selectively attractive C homopolymer. For a sufficiently attractive C homopolymer, (χ_ABN)_S can be pushed to negative values, indicating microphase separation in what would appear to be a completely miscible diblock copolymer. Furthermore, we show that microphase separation can occur in diblock copolymer–homopolymer blends where the segmental interactions between all polymer constituents are attractive. By tuning the value of (χ_ABN)_S with a homopolymer additive, one is therefore able to tune the effective copolymer segregation strength and thus dramatically affect the blend phase behavior. © 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47: 2083–2090, 2009     

Phase separation of off‐critical polymer blends of poly(styrene‐co‐maleic anhydride) and poly(methyl methacrylate). I. Kinetics of spinodal decomposition

The kinetics of phase separation via the spinodal decomposition of poly(styrene‐co‐maleic anhydride)/poly(methyl methacrylate) from a delay time period to late stages were investigated with a light scattering technique. The standard procedure for identifying four stages of spinodal decomposition, based on the characteristics of concentration fluctuations, was clearly introduced with the light scattering method. The spinodal limits were divided into four stages: the delay time, the early stage, the intermediate stage, and the late stage. The validity of the linearized theory was reviewed because it was used as an indicator of the limit of the early stage of spinodal decomposition, which divided the delay time period from the early stage and the early stage from the intermediate stage. The linearized theory fit the experimental results very well after the delay time. The scaled structure function of the melt‐mixed blend was analyzed. The universality of the scale structure function, F(x) = S(q,t)q_m³(t) (where S is the structure function, x is equal to q/q_m, q is the scattering wave vector, q_m is the maximum wave vector, and t is the time in seconds), indicated the late stage of phase separation and divided the late stage from the intermediate stage. The simple normalized scaling function profile for the cluster region proposed by Furukawa described the experimental data very well, whereas the profile for deep quenching, which was recently suggested, showed some discrepancies. As a result of the phase separation, the processing of this blend may be able to be developed to provide the most suitable morphology. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 871–885, 2004     

Solvation effect in the thermal decomposition of 2,2′‐azoisobutyronitrile in the three‐component system

The thermal decomposition rate constant (k_d ) of 2,2′‐azoisobutyronitrile in acrylonitrile (AN; monomer A)–methyl methacrylate (MM; monomer B) comonomer mixtures in N,N‐dimethylformamide (DMF) as a function of the comonomer mixture composition and its concentration in the solvent at 60 °C was studied. The dependences k_d = f(x_A ,C) [x_A (mole fraction of A in the comonomer mixture) = A/(A + B) = A/C, where C is the comonomer mixture concentration] have a different course as a function of C: from a curve k_d = f(x_A ) approaching the straight line (C = 2 mol · dm⁻³) to a convex curve possessing a maximum at a point x_A = 0.7 (C = 4 mol · dm⁻³) to a curve with a flattened wide maximum within the range of x_A = 0.2–0.8 (C = 7 mol · dm⁻³) to a curve with the shape of a lying s (C = 9 mol · dm⁻³). All the courses of the experimental dependences k_d = f(x_A ,C) can be explained with a hypothesis of initiator solvation by the comonomers AN and MM and the solvent DMF. The existing solvated forms, their relative stability constants, the thermal decomposition rate constants, and the relative contents in the system were determined. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 2156–2166, 2000     

Synthesis and properties of through‐space conjugated polymers based on cyano‐substituted poly(p‐arylenevinylene)s

New through‐space cyano‐substituted poly(p‐arylenevinylene)s containing a [2.2]paracyclophane unit were synthesized by the Knoevenagel reaction. Polymers 5 and 7 have cyano groups at α‐positions and β‐positions from the dialkoxyphenylene unit, respectively. Their optical and electrochemical behaviors were investigated in detail in comparison with their model compounds. Polymers 5 and 7 exhibited through‐space conjugation via the cyclophane units. Polymer 5 showed greenish blue emission (λ_max = 477 nm) in diluted solution with fluorescence quantum efficiency (?_F) of only 0.007, whereas polymer 7 emitted in the bluish green region (λ_max = 510 nm) with ?_F of 0.32. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 5979–5988, 2009     

Chiral recognition in molecular and macromolecular pairs of (S)‐ and (R)‐1‐cyano‐2‐methylpropyl‐4′‐ {[4‐(8‐vinyloxyoctyloxy)benzoyl]oxy}biphenyl‐4‐ carboxylate enantiomers

(S)‐1‐Cyano‐2‐methylpropyl‐4′‐{[4‐(8‐vinyloxyoctyloxy)benzoyl]oxy}biphenyl‐ 4‐carboxylate [ (S)‐11 ] and (R)‐1‐cyano‐2‐methylpropyl‐4′‐{[4‐(8‐vinyloxyoctyloxy)benzoyl]oxy}biphenyl‐4‐carboxylate [( R)‐11 ] enantiomers, both greater than 99% enantiomeric excess, and their corresponding homopolymers, poly[ (S)‐11 ] and poly[ (R)‐11 ], with well‐defined molecular weights and narrow molecular weight distributions were synthesized and characterized. The mesomorphic behaviors of (S)‐11 and poly[ (S)‐11 ] are identical to those of (R)‐11 and poly[ (R)‐11 ], respectively. Both (S)‐11 and (R)‐11 exhibit enantiotropic S_A, S, and S_X (unidentified smectic) phases. The corresponding homopolymers exhibit S_A and S phases. The homopolymers with a degree of polymerization (DP) less than 6 also show a crystalline phase, whereas those with a DP greater than 10 exhibit a second S_X phase. Phase diagrams were investigated for four different pairs of enantiomers, (S)‐11 /( R)‐11 , (S)‐11 /poly[ (R)‐11 ], and poly[ (S)‐11 ]/poly[ (R)‐11 ], with similar and dissimilar molecular weights. In all cases, the structural units derived from the enantiomeric components are miscible and, therefore, isomorphic in the S_A and S phases over the entire range of enantiomeric composition. Chiral molecular recognition was observed in the S_A and S_X phases of the monomers but not in the S_A phase of the polymers. In addition, a very unusual chiral molecular recognition effect was detected in the S phase of the monomers below their crystallization temperature and in the S phase of the polymers below their glass‐transition temperature. In the S phase of the monomers above the melting temperature and of the polymers above the glass‐transition temperature, nonideal solution behavior was observed. However, in the S_A phase the monomer–polymer and polymer–polymer mixtures behave as an ideal solution. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 3631–3655, 2000     

Influence of alkoxy tail length and unbalanced mesogenic core on phase behavior of mesogen‐jacketed liquid crystalline polymers

When the flexible terminal substituent changes from butoxy to hexyloxy or longer, smectic C (S_C) liquid crystalline phase was firstly reported to develop from a kind of mesogen‐jacketed liquid crystalline polymer (MJLCP) whose mesogenic side groups are unbalancedly bonded to the main chain without spacers. A series of MJLCPs, poly[4,4′‐bis(4‐alkoxyphenyl)‐2‐vinylbiphenyl(carboxide)] (nC2Vp, n is the number of the carbons in the alkoxy groups, n = 2, 4, 6, 8, 10, and 12) were designed and synthesized successfully via free radical polymerization. The molecular weights of the polymers were characterized with gel permeation chromatography, and the liquid crystalline properties were investigated by differential scanning calorimetry, polarized light microscopy experiments, and 1D, 2D wide‐angle X‐ray diffraction. Comparing with the butoxy analog, the polymer with unbalanced mesogenic core and shorter flexible substituents (n = 2, 4) keeps the same smectic A (S_A) phase, but other polymers with longer terminal flexible substituents (n = 6, 8, 10, and 12) can develop into a well‐defined S_C phase instead of S_A phase. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 505–514, 2009     

Synthesis of magnetic,reactive, and thermoresponsive Fe3O4 nanoparticles via surface‐initiated RAFT copolymerization of N‐isopropylacrylamide and acrolein

A reversible addition‐fragmentation chain transfer (RAFT) agent was directly anchored onto Fe₃O₄ nanoparticles in a simple procedure using a ligand exchange reaction of S‐1‐dodecyl‐S′‐(α,α′‐dimethyl‐α″‐acetic acid)trithiocarbonate with oleic acid initially present on the surface of pristine Fe₃O₄ nanoparticles. The RAFT agent‐functionalized Fe₃O₄ nanoparticles were then used for the surface‐initiated RAFT copolymerization of N‐isopropylacrylamide and acrolein to fabricate structurally well‐defined hybrid nanoparticles with reactive and thermoresponsive poly(N‐isopropylacrylamide‐co‐acrolein) shell and magnetic Fe₃O₄ core. Evidence of a well‐controlled surface‐initiated RAFT copolymerization was gained from a linear increase of number‐average molecular weight with overall monomer conversions and relatively narrow molecular weight distributions of the copolymers grown from the nanoparticles. The resulting novel magnetic, reactive, and thermoresponsive core‐shell nanoparticles exhibited temperature‐trigged magnetic separation behavior and high ability to immobilize model protein BSA. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 542–550, 2010     

Bis‐tert‐Alcohol‐Functionalized Crown‐6‐Calix[4]arene: An Organic Promoter for Nucleophilic Fluorination

A bis‐tert‐alcohol‐functionalized crown‐6‐calix[4]arene (BACCA) was designed and prepared as a multifunctional organic promoter for nucleophilic fluorinations with CsF. By formation of a CsF/BACCA complex, BACCA could release a significantly active and selective fluoride source for S_N2 fluorination reactions. The origin of the promoting effects of BACCA was studied by quantum chemical methods. The role of BACCA was revealed to be separation of the metal fluoride to a large distance (>8 Å), thereby producing an essentially “free” F^?. The synergistic actions of the crown‐6‐calix[4]arene subunit (whose O atoms coordinate the counter‐cation Cs⁺) and the terminal tert‐alcohol OH groups (forming controlled hydrogen bonds with F^?) of BACCA led to tremendous efficiency in S_N2 fluorination of base‐sensitive substrates.     

Highly efficient catalysts‐acetylacetonato complexes of transition metals in the 4th period for ring‐opening polymerization of 1,3‐benzoxazine

Acetylacetonato (acac) complexes of transition metals in the 4th period were examined as catalysts for the ring‐opening polymerization of benzoxazine. This examination revealed that acac complexes of manganese, iron, and cobalt exhibited the highest activity, which was comparable or slightly higher than that exhibited by p‐toluenesulfonic acid. By replacing acac ligand by hexafluoroacetylacetonato (F₆‐acac) ligand, the activity of manganese and iron complexes was remarkably enhanced. These metal F₆‐acac complexes were tolerant to moisture to allow their use under air without special caution. Another advantage was their negligible effect to promote unfavorable weight loss during the polymerization. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 479–484, 2010     

Nanoparticle‐enhanced bamboo‐like tubular nanofibers for active capture of particulate matter

We proposed a thought of active capture of particles by improving the interaction force between fibers and particles. Nanoparticle‐enhanced tubular nanofibers (Ag‐SPNTs) were prepared by template‐free cationic polymerization followed by surface modification. Ag‐SPNTs have coarse surface and bamboo‐like tubular structure with a diameter of approximately 80‐150 nm. Ag nanoparticles were embedded on the nanofibers surface, and the content of Ag nanoparticles in the nanofibers could be tuned by changing the concentration of [Ag(NH₃)₂]⁺ in the preparation process. f‐d curve measured by AFM showed that increasing the content of Ag nanoparticles in the nanofibers resulted in the enhanced interaction force between the nanofiber surface and particles. Particle matter capture test showed that the number of captured microscaled/naonoscaled particles on the fiber surface increased obviously for the nanoparticle‐enhanced tubular nanofibers (Ag‐SPNTs) compared to the nanofibers without nanoparticle (SPNTs), probably due to the increased interaction force and adhesion energy between fiber surface and particles. Filtration property test showed that the Ag‐SPNTs fiber films had a better filtration performance with a higher filter efficiency and QF value than that of SPNTs. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2019     

Aminated PCL‐based copolymers by chemical modification of poly(α‐iodo‐ε‐caprolactone‐co‐ε‐caprolactone)

A novel method is proposed to access to new poly(α‐amino‐ε‐caprolactone‐co‐ε‐caprolactone) using poly(α‐iodo‐ε‐caprolactone‐co‐ε‐caprolactone) as polymeric substrate. First, ring‐opening (co)polymerizations of α‐iodo‐ε‐caprolactone (αIεCL) with ε‐caprolactone (εCL) are performed using tin 2‐ethylhexanoate (Sn(Oct)₂) as catalyst. (Co)polymers are fully characterized by ¹H NMR, ¹³C NMR, FTIR, SEC, DSC, and TGA. Then, these iodinated polyesters are used as polymeric substrates to access to poly(α‐amino‐ε‐caprolactone‐co‐ε‐caprolactone) by two different strategies. The first one is the reaction of poly(αIεCL‐co‐εCL) with ammonia, the second one is the reduction of poly(αN₃εCL‐co‐εCL) by hydrogenolysis. This poly(α‐amino‐ε‐caprolactone‐co‐ε‐caprolactone) (F_αNH2εCL < 0.1) opens the way to new cationic and water‐soluble PCL‐based degradable polyesters. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 6104–6115, 2009     

Propagation rate coefficients of isobornyl acrylate,tert‐butyl acrylate and 1‐ethoxyethyl acrylate: A high frequency PLP‐SEC study

Pulsed laser polymerization (PLP) coupled to size exclusion chromatography (SEC) is considered to be the most accurate and reliable technique for the determination of absolute propagation rate coefficients, k_p. Herein, k_p data as a function of temperature were determined via PLP‐SEC for three acrylate monomers that are of particular synthetic interest (e.g., for the generation of amphiphilic block copolymers). The high‐T_g monomer isobornyl acrylate (iBoA) as well as the precursor monomers for the synthesis of hydrophilic poly(acrylic acid), tert‐butyl acrylate (tBuA), and 1‐ethoxyethyl acrylate (EEA) were investigated with respect to their propagation rate coefficient in a wide temperature range. By application of a 500 Hz laser repetition rate, data could be obtained up to a temperature of 80 °C. To arrive at absolute values for k_p, the Mark‐Houwink parameters of the polymers have been determined via on‐line light scattering and viscosimetry measurements. These read: K = 5.00 × 10⁵ dL g⁻¹, a = 0.75 (piBoA), K = 19.7 × 10⁵ dL g⁻¹, a = 0.66 (ptBA) and K = 1.53 × 10⁵ dL g⁻¹, a = 0.85 (pEEA). The bulky iBoA monomer shows the lowest propagation rate coefficient among the three monomers, while EEA is the fastest. The activation energies and Arrhenius factors read: (iBoA): log(A/L mol⁻¹ s⁻¹) = 7.05 and E_A = 17.0 kJ mol⁻¹; (tBuA): log(A/L mol⁻¹ s⁻¹) = 7.28 and E_A = 17.5 kJ mol⁻¹ and (EEA): log(A/L mol⁻¹ s⁻¹) = 6.80 and E_A = 13.8 kJ mol⁻¹. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 6641–6654, 2009     

Hydrophilic CO2‐based biodegradable polycarbonates: Synthesis and rapid thermo‐responsive behavior

Common CO₂‐based biodegradable polycarbonates like poly(propylene carbonate) or poly(cyclohexene carbonate) are generally hydrophobic, leading to slow biodegradation rate and poor cell adhesion, which limit their applications in the biomedical field. Here hydrophilic polycarbonates were prepared by one‐pot terpolymerization of CO₂, propylene oxide (PO), and 2‐((2‐(2‐(2‐methoxyethoxy)ethoxy)ethoxy)methyl)oxirane (ME₃MO) using binary Salen Co(III)‐Cl/PPNCl catalyst system. The resultant terpolymers showed one glass transition temperature (T_g), which decreased with the increase of ME₃MO units in the terpolymers (F_ME3MO). Water contact angles of the resultant terpolymers with F_ME3MO of 4.2?23.6% were 68?25°, while that of poly(propylene carbonate) was 90°, indicating that the terpolymers became hydrophlilic. Furthermore, the terpolymers with F_ME3MO more than 25.8% exhibited reversible and rapid thermo‐responsive property in water, and the lower critical solution temperature (LCST) was highly sensitive to F_ME3MO. In particular, aqueous solution of the terpolymer with F_ME3MO of 72.6% showed a LCST around 35.2 °C, close to body temperature, which was promising for biomedical applications, especially for in vivo applications. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013, 51, 2834–2840.     

Simulation of phase‐separated structures of liquid‐crystalline polymer/flexible polymer blends

The phase‐separation kinetics of liquid‐crystalline polymer/flexible polymer blends was studied by the coupled time‐dependent Ginzberg–Landau equations for compositional order parameter ? and orientational order parameter S_ij. The computer simulations of phase‐separated structures of the blends were performed by means of the cell dynamical system in two dimensions. The compositional ordering processes of phase separation are demonstrated by the time evolution of ?. The influence of orientational ordering on compositional ordering is discussed. The small‐angle light scattering patterns are numerically reproduced by means of the optical Fourier transformation of spatial variation of the polarizability tensor α_ij, and the azimuthal dependence of the scattering intensity distribution is interpreted. © 2001 John Wiley & Sons, Inc. J Polym Sci Part B: Polym Phys 39: 2915–2921, 2001     

Three‐arm star ring opening metathesis polymers via alkyne‐azide click reaction

The click chemistry strategy is successfully applied for the preparation of three‐arm star (A₃) ring opening metathesis polymers. A well‐defined monoazide end‐functionalized poly(N‐ethyl oxanorbornene) and a poly(N‐butyl oxanorbornene) obtained via ring opening metathesis polymerization using first generation Grubbs' catalyst are simply clicked with the trisalkyne core affording the synthesis of target star polymers. The obtained star polymers are characterized via nuclear magnetic resonance spectroscopy and gel permeation chromatography (GPC). The deconvolution analyses of GPC traces reveal that the click reaction efficiency for the star formation strongly depends on the chemical nature and the molecular weight of ROM polymers. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 2344–2351, 2009     

Chiral polyamides consisting of N‐α‐benzoyl‐L‐glutamic acid as a diacid component

Novel polyamide with chiral environment was obtained from aromatic diamine, 4,4′‐diaminodiphenylmethane (DADPM), and N‐α‐protected L ‐glutamic acid, N‐α‐benzoyl‐L ‐glutamic acid (Benzoyl‐L ‐Glu‐OH). The optical rotation ([α]_D ) of the polyamide was determined to be 3.6° (c = 1.00 g/dL in DMF), implying that the optically active polyamide was obtained. The present polyamide gave a durable self‐standing membrane. The membrane selectively incorporated the D ‐isomer of Ac‐Trp from racemic mixture of Ac‐Trp. The adsorption selectivity toward Ac‐D ‐Trp was determined to be 1.95. It showed chiral separation ability by adopting potential difference as a driving force for membrane transport. The permselectivity was dependent on the potential difference, and at the applied potential difference of 3.0 V, the membrane selectively transported Ac‐D ‐Trp and the permselectivity toward Ac‐D ‐Trp was determined to be 1.84, which was close to the adsorption selectivity of 1.95. Contrary to this, the membrane showed opposite permselectivity at the applied potential difference of 2.0 V and the permselectivity toward the L ‐isomer reached 2.48. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 2530–2538, 2009     

A local spin evaluation into the active site models of [2Fe2S] ferrodoxin [Fe<Subscript>2</Subscript>S<Subscript>2</Subscript>(SR)<Subscript>4</Subscript>]<Superscript>2−</Superscript> (R=—H, —CH<Subscript>3</Subscript>)

To test the feasibility of local spin theory of Davidson and Clark for ferrodoxin clusters, the models [Fe₂S₂(SR)₄]²⁻ (R=—H, —CH₃) are chosen for evaluation. This purpose is realized by calculating the local spin expectation values 〈S _A·S _B〉, 〈S _A ² 〉, and m _A and discussing the connection between these expected values and the Heisenberg spin model (HSM) and the Noodleman broken-symmetry approach. In practical calculation, the spin-unrestricted Hartree-Fock (UHF) and spin-polarized density functional theory (DFT) are used and the calculational qualities of these two methods are also discussed. In addition, the theoretical magnetic coupling constants J _AB of these models are calculated by various computational schemes for comparison with both theoretical and experimental results previously reported. Supported by the Doctorial Initial Foundations of Hainan Normal University (Grant No. 13140252)