Lateral thermal expansion of cellulose Iβ and IIII polymorphs

Measurements of the thermal expansion coefficients (TECs) of cellulose crystals in the lateral direction are reported. Oriented films of highly crystalline cellulose I_β and III_I were prepared and then investigated with X‐ray diffraction at specific temperatures from room temperature to 250 °C during the heating process. Cellulose I_β underwent a transition into the high‐temperature phase with the temperature increasing above 220–230 °C; cellulose III_I was transformed into cellulose I_β when the sample was heated above 200 °C. Therefore, the TECs of I_β and III_I below 200 °C were measured. For cellulose I_β, the TEC of the a axis increased linearly from room temperature at α_a = 4.3 × 10^?5 °C^?1 to 200 °C at α_a = 17.0 × 10^?5 °C^?1, but the TEC of the b axis was constant at α_b = 0.5 × 10^?5 °C^?1. Like cellulose I_β, cellulose III_I also showed an anisotropic thermal expansion in the lateral direction. The TECs of the a and b axes were α_a = 7.6 × 10^?5 °C^?1 and α_b = 0.8 × 10^?5 °C^?1. The anisotropic thermal expansion behaviors in the lateral direction for I_β and III_I were closely related to the intermolecular hydrogen‐bonding systems. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 40: 1095–1102, 2002     

Lateral thermal expansion of chitin crystals

Measurements of the thermal expansion coefficients (TECs) of chitin crystals in the lateral direction are reported. We investigated highly crystalline α chitin from the Paralithodes tendon and an anhydrous form of β chitin from a Lamellibrachia tube from room temperature to 250 °C, using X‐ray diffraction at selected temperatures in the heating process. For α chitin, the TECs of the a and b axes were α_a = 6.0 × 10⁻⁵ °C⁻¹ and α_b = 5.7 × 10⁻⁵ °C⁻¹, indicating an isotropic thermal expansion in the lateral direction. However, the anhydrous β chitin exhibited an anisotropic thermal expansion in the lateral direction. The TEC of the a axis was constant at α_a = 4.0 × 10⁻⁵ °C⁻¹, but the TEC of the b axis increased linearly from room temperature to 250 °C, with α_b = 3.0–14.6 × 10⁻⁵ °C⁻¹. These differences in the lateral thermal expansion behaviors of the α chitin and the anhydrous β chitin are due to their different intermolecular hydrogen bonding systems. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 39: 168–174, 2001     

The Thermal Expansion of Wood Cellulose Crystals

We have investigated tension wood cellulose obtained from Populus maximowiczii using X-ray diffraction at temperatures from room temperature to 250 °C. Three equatorial and one meridional d-spacings showed a gradual linear increase with increasing temperature. For temperatures above 180 °C, however, the equatorial d-spacing increased dramatically. Thus, the linear and volume thermal expansion coefficients (TECs) below 180 °C were determined from the d-spacings. The linear TECs of the a-, b-, and c-axes were: α _a = 13.6 × 10⁻⁵ °C⁻¹, α _b = −3.0× 10⁻⁵ °C⁻¹, and α _c =0.6× 10⁻⁵ °C⁻¹, respectively, and the volume TEC was β = 11.1× 10⁻⁵ °C⁻¹. The anisotropic thermal expansion in the three coordinate directions was closely related to the crystal structure of the wood cellulose, and it governed the macroscopic thermal behavior of solid wood.     

Thermally activated transformations in stable and metastable copper(II) pyrovanadate polymorphs

The structural transformations of α- and β′-Cu₂V₂O₇ phases over the entire temperature range of their existence and α → β′-Cu₂V₂O₇ and β′ → β-Cu₂V₂O₇ polymorphic transitions in α-Cu₂V₂O₇ are described from the crystal-chemical standpoint. Variations in the parameters of the polyhedral blocks of the α-Cu₂V₂O₇ structure implies that the greatest deformations occur with a negative and near-zero bulk thermal expansion in the range from room temperature to 400°C. The compression and rotation of vanadium-oxygen diortho groups is accompanied by unbending of zigzag copper-oxygen chains, with the distances between them unchanged, which is the reason for the anomalous volume expansion of the structure. Thermal distortion of β′-Cu₂V₂O₇ is insignificant. The thermal expansion coefficients (TECs) of unit cell parameters are as follows: α _a = ?1.36 × 10^?5 1/K, α _b = 1.95 × 10^?5 1/K, α _c = 1.37 × 10^?5 1/K, α_β = ?0.18 × 10^?5 1/K, and α _V = 1.93 × 10^?5 1/K. We demonstrate that the low-temperature Cu₂V₂O₇ phase can be formed without admixtures of metastable β-Cu₂V₂O₇ upon slow cooling (at about 1 K/min) of the high-temperature phase.     

X-ray diffraction study on the thermal expansion behavior of cellulose Iβ and its high-temperature phase

Oriented films of cellulose prepared from algal cellulose were hydrothermally treated to convert them into highly crystalline cellulose Iβ. The lateral thermal expansion behavior of the prepared cellulose Iβ films was investigated using X-ray diffraction at temperatures from 20 to 300 °C. Cellulose Iβ was transformed into the high-temperature phase when the temperature was above 230 °C, allowing the lateral thermal expansion coefficient of cellulose Iβ and its high-temperature phase to be measured. For cellulose Iβ, the thermal expansion coefficients (TECs) of the a- and b-axes were α_a = 9.8 × 10⁻⁵ °C⁻¹ and α_b = 1.2 × 10⁻⁵ °C⁻¹, respectively. This anisotropic thermal expansion behavior in the lateral direction is ascribed to the crystal structure and to the hydrogen-bonding system of cellulose Iβ. For the high-temperature phase, the anisotropy was more conspicuous, and the TECs of the a- and b-axes were α_a = 19.8 × 10⁻⁵ °C⁻¹ and α_b = −1.6 × 10⁻⁵ °C⁻¹, respectively. Synchrotron X-ray fiber diffraction diagrams of the high-temperature phase were also recorded at 250 °C. The cellulose high-temperature phase is composed of a two-chain monoclinic unit cell, a = 0.819 nm, b = 0.818 nm, c (fiber repeat) = 1.037 nm, and γ = 96.4°, with space group = P2₁. The volume of this cell is 4.6% larger than that of cellulose Iβ at 30 °C.     

Negative thermal expansion of a polydiacetylene single crystal

Macroscopic thermal expansion in the chain direction has been measured for the first time on organic polymeric single crystals. Negative linear thermal expansion coefficients αM are reported and related to chain torsional motion and equilibrium point-defect formation for a solid-state polymerized phase of 2,4-hexadiyne-1,6-diol bisphenylurethane (HDU) which contains crystallographically located interstitial dioxane and for a dioxanefree phase obtained by thermal annealing. Data for as-polymerized single crystals (which are probably of extended chain morphology) between ?50 and 100°C give αM = ?(1.686 ± 0.039) × 10^?5 ? (1.35 ± 0.18) × 10^?7 t with t in °C. During volatilization of 11.7 ± 1.0 wt-% interstitial dioxane and a resulting crystal structure change, the as-polymerized fibers fibrillate and shrink irreversibly by 0.16 ± 0.04%. Although dichroism and diffraction measurements indicate both a high degree of crystallinity and chain alignment for the dioxane-free phase, the average thermal expansion coefficient, (?3.0 ± 1.0) × 10^?6 °C^?1 between ?50 and 150°C, is about an order of magnitude less than for the as-polymerized single crystals.     

Long branching in poly(vinyl acetate) and poly(vinyl alcohol). III. Kinetic study of the branching reaction in the radical polymerization of vinyl acetate

The branching reaction in the radical polymerization of vinyl acetate was studied kinetically. Branching occurs by polymer transfer as well as terminal double-bond copolymerization. The chain-transfer constants to the main chain (C_p,2) and to the acetoxy methyl group (C_p,1) on the polymer were calculated on the basis of the experimental data described in the preceding paper giving C_p,2 = 3.03 × 10^?4, C_p,1 = 1.27 × 10^?4 at 60°C, and C_p,2 = 2.48 × 10^?4, C_p,1 = 0.52 × 10^?4 at 0°C. Chain transfer to monomer is important with respect to the formation of the terminal double bond. The total values of transfer constants to the α- or β-position in the vinyl group and the acetoxymethyl group in vinyl acetate was determined to be 2.15 × 10^?4 at 60°C. The transfer constant to the acetyl group in the monomer (C_m,1) was also evaluated to be 2.26 × 10^?4 at 60°C from the quantitative determination of the carboxyl terminals in PVA. These facts suggest that the chain-transfer constant to the α- or β-position in the monomer (C_m,2) is nearly equal to zero within experimental error. Copolymerization reactivity parameters of the terminal double bond were also estimated. In conclusion, it has become clear that the formation of nonhydrolyzable branching by the terminal double-bond reaction can be almost neglected, and hence that the long branching in PVA is formed only by the polymer transfer mechanism. On the other hand, a large number of hydrolyzable branches in PVAc are prepared by the terminal double-bond reaction rather than by polymer transfer.     

Synthesis of 1‐Methyl‐3‐aryl‐substituted Titanocene and Zirconocene Dichlorides and Crystal Structure of Bis[η5‐1‐methyl‐3‐(α, α‐dimethylbenzyl) cyclopentadienyl] titanium Dichloride

The syntheses of a series of l‐methyl‐3‐aryl‐substituted titanocene and zirconocene dichlorides are reported. These complexes are synthesized by the reaction of 2‐ and 3‐methyl‐6, 6‐dimethylfulvenes (1:4) with aryllithium, followed by the reaction with TiCl₄·2THF, ZrCl₄ and (CpTiCl₂)₂O respectively, to give complexes 1–5. The complex [η⁵‐1‐methyl‐3‐(α, α‐dimethylbenzyl) cyclopentadienyl] titanium dichloride has been studied by X‐ray diffraction. The red crystal of this complex is monoclinic, space group P2_t/C with unit cell parameters: a =6.973(6) × 10^?1 nm, b =36.91(2) × 10^?1 nm, c = 10.063(4) × 10^?1 nm, α=β= γ = 93.35(5)°, V = 2584(5) × 10^?3 nm³ and Z = 4. Refinement for 1004 observed reflections gives the final R of 0.088. There are four independent molecules per unit cell.     

Behavior of cellulose in NaOH/Urea aqueous solution characterized by light scattering and viscometry

Cellulose was dissolved in 6 wt % NaOH/4 wt % urea aqueous solution, which was proven by a ¹³C NMR spectrum to be a direct solvent of cellulose rather than a derivative aqueous solution system. Dilute solution behavior of cellulose in a NaOH/urea aqueous solution system was examined by laser light scattering and viscometry. The Mark–Houwink equation for cellulose in 6 wt % NaOH/4 wt % urea aqueous solution at 25 °C was [η] = 2.45 × 10^?2 weight‐average molecular weight (M_w)^0.815 (mL g^?1) in the M_w region from 3.2 × 10⁴ to 12.9 × 10⁴. The persistence length (q), molar mass per unit contour length (M_L), and characteristic ratio (C_∞) of cellulose in the dilute solution were 6.0 nm, 350 nm^?1, and 20.9, respectively, which agreed with the Yamakawa–Fujii theory of the wormlike chain. The results indicated that the cellulose molecules exist as semiflexible chains in the aqueous solution and were more extended than in cadoxen. This work provided a novel, simple, and nonpollution solvent system that can be used to investigate the dilute solution properties and molecular weight of cellulose. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 347–353, 2004     

Structure of bismuth oxoborate Bi<Subscript>4</Subscript>B<Subscript>2</Subscript>O<Subscript>9</Subscript> at 20, 200, and 450°C

Single crystals of bismuth oxoborate Bi₄B₂O₉ have been grown by slowly cooling the melt of a stoichiometric Bi₂O₃ + H₃BO₃ mixture. The structure of the borate (monoclinic space group P2₁/c, a = 11.107 Å, b = 6.629 Å, c = 11.044 Å, β = 91.04°, Z = 4) has been studied at 20, 200, and 450°C. The structure is described not only in terms of full BiO₆ ^? and BiO₇ polyhedra but also in terms of truncated BiO₃ ^? and BiO₄ ^? polyhedra and BO₃ triangles, as well as oxo-centered OBi₃ triangles and OBi₄ tetrahedra. It is shown that both the B-O and Bi-O bond lengths are practically unaffected by temperature. Only the angles between polyhedra change with temperature, being responsible for the strong anisotropy of Bi₄B₂O₆ thermal expansion, which was measured by high-temperature powder X-ray diffraction: α₁₁ = 20, α₂₂ = 15, α₃₃ = 6 × 10^?6 °C^?1, and μ = (c, α₃₃) = ?19°.     

Seltenerdhalogenide Ln4X5Z. Teil 1: C und/oder C2 in Ln4X5Z

Rare Earth Halides Ln₄X₅Z. Part 1: C and/or C₂ in Ln₄X₅Z The compounds Ln₄X₅C_n (Ln = La, Ce, Pr; X = Br, I and 1.0 < n < 2.0) are prepared by the reaction of LnX₃, Ln metal and graphite in sealed Ta‐ampoules at temperatures 850 °C < T < 1050 °C. They crystallize in the monoclinic space group C2/m. La₄I₅C_1.5: a = 19.849(4) Å, b = 4.1410(8) Å, c = 8.956(2) Å, β = 103.86(3)°, La₄I₅C_2.0: a = 19.907(4) Å, b = 4.1482(8) Å, c = 8.963(2) Å, β = 104.36(3)°, Ce₄Br₅C_1.0: a = 18.306(5) Å, b = 3.9735(6) Å, c = 8.378(2) Å, β=104.91(2)°, Ce₄Br₅C_1.5: a = 18.996(2) Å, b = 3.9310(3) Å, c = 8.282(7) Å, β = 106.74(1)°, Pr₄Br₅C_1.3: a = 18.467(2) Å, b = 3.911(1) Å, c = 8.258(7) Å, β = 105.25(1)° and Pr₄Br₅C_1.5: a = 19.044(2) Å, b = 3.9368(1) Å, c = 8.254(7) Å, β = 106.48(1)°. In the crystal structure the lanthanide metals are connected to Ln₆‐octahedra centered by carbon atoms or C₂‐groups. The Ln₆‐octahedra are condensed via opposite edges to chains and surrounded by X atoms which interconnect the chains. A part n of isolated C‐atoms is substituted by 1‐n C₂‐groups. The C‐C distances range between 1.26 and 1.40Å. In the ionic formulation (Ln³⁺)₄(X^?)₅(C^4?)_n(C₂^m?)_1?n·e^? with 0 < n < 1 and m = 2, 4, 6 (C₂^2?, C₂^4? C₂^6?), there are 1 < e^? < 5 electrons centered in metal‐metal bonds.     

Complexation with diol host compounds. 13. Crystal structures and thermal analyses of inclusion compounds of 1,1,6,6-tetraphenylhexa-2,4-diyne-1,6-diol with cyclohexane,O-xylene,m-xylene and p-xylene

Abstract

It has been shown that host compound 1,1,6,6-tetraphenylhexa-2,4-diyne-1,6-diol is able to include polar guests and now we report on its ability to form clathrate compounds with apolar guests. The structures of this host with cyclohexane (1) and the ortho (2), meta (3) and para (4) xylenes have been determined and are discussed. Crystal data: (1) 2C₃₀H₂₂O₂C₆H₁₂, M _r = 913.20 g mol^?1, mono-clinic, C2/c, a = 22.851(6), b = 14.010(2), c = 17.076(6) Å, β = 108.71(3)°, V = 5178(2) ų, Z = 4, D _c = 1.17g cm^?3, N = 3326, R = 0.092. (2) 2C₃₀H₂₂O₂1 ½C₈H₁₀, M _r = 1976.5 g mol^?1, triclinic, P 1, a = 13.185(3), b = 15.466(3), c = 16.573(2) Å, α = 96.39(13)°, β = 106.96(15)°, γ = 114.94(18)°, V = 2822(2) ų, Z = 2, D _c = 1.16 g cm^?3, N = 6152, R = 0.075. (3) 2C₃₀H₂₂O₂1 ½C₈H₁₀, M _r = 1976.5 g mol^?1, triclinic, P 1, a = 13.267(5), b = 15.453(3), c = 16.654(5) Å, α = 97.12(2)°, β = 107.09(3)°, γ = 114.68(3)°, V = 2843(2) ų, Z = 2, D _c = 1.15 g cm^?3, N = 6505, R = 0.083. (4) 2C₃₀H₂₂O₂1 ½C₈H₁₀, M _r = 1976.5 g mol^?1, triclinic, P 1, α = 13.070(2), b = 15.348(3), c = 16.776(3) Å, α = 67.88<2)°, β = 74.27(1)°, γ = 65.29(1)°, V = 2817(1) ų, Z = 2, D _c = 1.15 g cm^?3, N = 6711, R = 0.050. Thermal analysis studies were also performed in order to examine their stability and the strength with which the guest species are held in the crystal lattice.     

Preparation and X-Ray structural analysis of the remarkably stable Bis(triphenylmethyl)trisulfane-2-oxide R2S3O

Triphenylmethylthiol reacts with thionylchloride in the presence of amines to give [(C₆H₅)₃CS]₂SO which crystallizes with one mole of CS₂ in the triclinic space group P1 with a = 1 193.4(4), b = 1 266.8(5), c = 1 421.6(7) pm, α = 63.79(2)°, β = 65.25(2)°, γ = 63.18(2)°, π = 1.354 g cm^?3 at ?80°C. The R₂S₃O molecules are of C₁ symmetry containing an almost planar CSSSC backbone with d_ss = 212.7(1) and 211.4(1) pm, d_cs = 188.0(2) and 188.2(2) pm, d_so = 146.9(1) pm, α_SSS = 83.8°, α_SSO = 112.0° and 112.2°, τ_CSSS = 160.7° and ?172.3°.     

Relaxation of DF(v = 1) by various polyatomic molecules

By means of the technique of laser-induced fluorescence, the room-temperature vibrational relaxation of DF(v = 1) has been studied in the presence of several polyatomic chaperones. The rate coefficients obtained [in units of (μ;sec·torr)^?1] are CH₄, 0.22; C₂H₆, 0.61; C₄H₁₀, 1.26; C₂H₂, 4.0 × 10^?2; C₂H₂F₂, 1.86 × 10^?2; C₂H₄, 0.175; CH₃F, 0.36; CF₃H, 1.95 × 10^?2; CF₄, 1.0 × 10^?3; CBrF₃, 5.6 × 10^?4; NF₃, 5.1 × 10^?4; SO₂, 1.27 × 10^?2; and BF₃, 7.1 × 10^?3. Results are also reported for vibrational relaxation rate coefficients for HF(v = 1) in the presence of the following chaperones: CH₄, 2.6 × 10^?2; C₂H₆, 5.9 × 10^?2; C₃H₈, 8.4 × 10^?2; and C₄H₁₀, 0.128. A comparison of DF and HF results indicates that for deactivation by C_nH_n+2, rate coefficients for DF are approximately an order of magnitude larger than for HF. The deactivation rate coefficient of DF(v = 1) by CH₄ was found to decrease with increasing temperature between 300 and 740°K.     

一种新型氧离子导体：La3GaMo2O12

A new oxide ion conductor,La_3GaMo_2O_(12),with a bulk conductivity of 2.7×10~(-2)S·cm~(-1) at 800 ℃ in air at-mosphere was prepared by the traditional solid-state reaction.The room temperature X-ray diffraction data could beindexed on a monoclinic cell with lattice parameters of a=0.5602(2) nm,b=0.3224(1) nm,c=1.5741(1) nm,β=102.555(0)°,V= 0.2775(2) nm~3 and space group Pc(7).Ac impedance measurements in various atmospheres furthersupport that it is an oxide ion conductor.This material was stable in various atmospheres with oxygen partial pres-sure p(O_2)ranging from 1.0×10~5 to 1.0×10~(-7) Pa at 800 ℃.A reversible polymorphic phase transition occurred atelevated temperatures as confirmed by the differential thermal analysis and dilatometric measurement.     

Transfer reactions in radical polymerization of styrene in acetone–chloroform mixture

The study of chain-transfer reactions in thermal and AIBN-initiated polymerization of styrene is aimed at the determination of transfer constants to the solvents at 60°C. For thermal polymerization the transfer constants C_s to acetone, chloroform, and chloroform mixed with acetone are 3.2 × 10^?5, 4.1 × 10^?5, and 4.4 × 10^?5, respectively. In the case of AIBN-initiated polymerization, the transfer constant of chloroform in the mixture acetone–chloroform is C_s = 3.3 × 10^?4. All these transfer constants are average values. It has been found that neither acetone nor chloroform satisfies the Mayo equation in the presence of transfer agent very well. These anomalies can be explained by assuming a complexation phenomenon. The changes in the polarity and resonance are taken into account. It is considered that in the chain-transfer reactions under investigation, the association or complex-forming ability of solvent and monomer or polymer play a role. In studying the chain-transfer reaction in the acetone–chloroform solvent mixture another phenomenon affecting the determination of the chain transfer constant is assumed. This phenomenon consists in formation of associates in which both solvents participate.     

Synthesis,Structure and Magnetism of Bis[1,2,4‐tris(trimethylsilyl)cyclopentadienyl]europium

Bis[tris(trimethylsilyl)cyclopentadienyl]europium, Eu{C₅H₂[Si(CH₃)₃]₃}₂ (1) , has been synthesized by a modified transmetallation route between Tl{C₅H₂[Si(CH₃)₃]₃} and europium powder in toluene. 1 crystallizes in the monoclinic space group C2/c (No. 15) with a = 20.293(5) Å, b = 20.221(5) Å, c = 9.654(2) Å, β = 106.412(5)°, V = 3800.1(15) ų, Z = 4. The unit cell contains monomeric molecules that adopt a bent metallocene conformation with two partially staggered Cp? ligands. Magnetic susceptibility measurements in the temperature range 2–300 K display ideal Curie paramagnetic behaviour of the 4f⁷ system with Curie constant C = 9.6 × 10^?5 m³ K mol^?1 corresponding to temperature independent μ_eff = 7.8.     

New Phosphate-Sulfates with NZP Structure

NaZr_2–xB_x(PO₄)_3–2x(SO₄)_2x (0 ≤ x ≤ 1.25, B = Mg, Co, Ni, Cu, Zn), and NaZr_2–xR_x(PO₄)_3–x(SO₄)_x (0 ≤ x ≤ 1.25, R = Al, Fe) phosphate-sulfates series have been prepared by a sol–gel process. These compounds belong to the NaZr₂(PO₄)₃ (NZP) structure family and crystallize in hexagonal crystal system, space group R\(\bar 3\)c. Limited solid solution series were found to exist; their formation temperatures and thermal stability limits were determined. Particle sizes as determined by microstructure observation were 50–200 nm, and for Cu- and Zn-containing samples, 200–500 nm. The thermal expansion of phosphate-sulfate NaZr_1.25Cu_0.75(PO₄)_1.5(SO₄)_1.5 was studied in the range 25–700°C. Thermal expansion coefficients and thermal expansion anisotropy were found to be α_a =–5.40 × 10^–6 °C^–1, α_с = 18.88 × 10^–6 °C^–1, α_avg = 2.69 × 10^–6 °C^–1, and Δα = 24.28 × 10^–6 °C^–1.     

Dilute solution properties of cellulose in LiOH/urea aqueous system

Cellulose was dissolved rapidly in 4.6 wt % LiOH/15 wt % urea aqueous solution and precooled to –10 °C to create a colorless transparent solution. ¹³C‐NMR spectrum proved that it is a direct solvent for cellulose rather than a derivative aqueous solution system. The result from transmission electron microscope showed a good dispersion of the cellulose molecules in the dilute solution at molecular level. Weight‐average molecular weight (M_w), root mean square radius of gyration (〈s²〉_z^1/2), and intrinsic viscosity ([η]) of cellulose in LiOH/urea aqueous solution were examined with laser light scattering and viscometry. The Mark–Houwink equation for cellulose in 4.6 wt % LiOH/15 wt % urea aqueous solution was established to be [η] = 3.72 × 10^?2 M in the M_w region from 2.7 × 10⁴ to 4.12 × 10⁵. The persistence length (q), molar mass per unit contour length (M_L), and characteristic ratio (C_∞) of cellulose in the dilute solution were given as 6.1 nm, 358 nm^?1, and 20.8, respectively. The experimental data of the molecular parameters of cellulose agreed with the Yamakawa–Fujii theory of the worm‐like chain, indicating that the LiOH/urea aqueous solution was a desirable solvent system of cellulose. The results revealed that the cellulose exists as semistiff‐chains in the LiOH/urea aqueous solution. The cellulose solution was stable during measurement and storage stage. This work provided a new colorless, easy‐to‐prepare, and nontoxic solvent system that can be used with facilities to investigate the chain conformation and molecular weight of cellulose. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 3093–3101, 2006     

Kinetics and mechanism of the aquation of pentaaqua (trichloroacetato-O)-chromium(2+) ion

The kinetics of the aquation of (H₂O)₅Cr(O₂CCCl₃)²⁺ have been examined at 35–55°C and 1.00M ionic strength with [H⁺] = 0.01?1.00M. The reaction follows the rate equation -d ln [Cr_total]/dt = (a[H⁺]^?1 + b + c[H⁺])/(1 + d[H⁺]), where [Cr_total] is the stoichiometric concentration of the complex. At 45°C a = (1.41 ± 0.03) × 10^?7M/s, b = (1.66 ± 0.02) × 10^?5 s^?1, c = (7.0 ± 0.8) × 10^?5M^?1·S^?1 and d = 2.3 ± 0.3M^?1. Two mechanisms consistent with this rate law are discussed, with evidence being presented in favor of an ester hydrolysis mechanism involving steady-state intermediates. Equilibrium and activation parameters were determined.