Mesomorphic solutions of cellulose triacetate in trifluoroacetic acid halogenated solvent mixtures: Phase separations and factors affecting the cholesteric pitch

Cellulose triacetate (CTA) forms cholesteric mesophases in trifluoroacetic acetic acid (TFA) and mixtures of TFA and CH₂Cl₂, 1,2-dichloroethane (1,2-DCE), and CHCl₃. Cholesteric pitches and solution flow times indicate that the order of solvent powers is TFA-CH₂Cl₂ > TFA-1,2-DCE > TFA > TFA-CHCl₃, which is the order of decreasing acidity of the solvent systems. With TFA-CH₂Cl₂ as solvent, the one-fourth power of the pitch varies inversely with the CTA concentration, and increases linearly with temperature. The pitch increases exponentially with time and increases faster the more acidic the solvent. In a magnetic field a cholesteric to nematic transition occurs. A minimum in solution viscosity occurs at 34% w/v of CH₂Cl₂ for solutions in TFA-CH₂Cl₂. The miscibility gap as a function of molecular weight depends on the solvent composition and is smaller the higher the acidity of the solvent. Agreement between the experimentally observed A and B points and the theoretical points is better for the Khokhlov and Semenov theory for semiflexible chains than for the original Flory theory or the Flory-Ronca modification.     

Lyotropic mesomorphic formation of cellulose in trifluoroacetic acid-chlorinated-alkane solvent mixtures at room temperature

Mixtures of trifluoroacetic acid (TFA)-1,2-dichloroethane (1,2-DCE); TFA-dichloromethane (CH₂Cl₂); and TFA-trichloromethane (CHCl₃) are excellent cellulose solvents at room temperature. TFA-1,2-DCE and TFA-CH₂Cl₂ are superior to pure TFA. Lyotropic cellulose mesophases were obtained in (20% w/v) solutions of cellulose in these solvent mixtures. The optical and optical rotatory powers of the solutions suggest that the lyotropic mesophase of cellulose is cholesteric. This implies that cellulose molecules are arranged in helical form in these solvent systems.     

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     

Investigation of molecular order in liquid-crystalline solutions of cellulose triacetate using PMR spectroscopy

Liquid-crystalline solutions of cellulose triacetate (CTA) in trifluoroacetic acid (TFA)–CH₂Cl₂, TFA–1.2-dichloroethane (1,2-DCE) solvent mixtures were examined by means of PMR spectroscopy. CTA forms both cholesteric and nematic phases in these solvents depending on the CTA concentration. In cholesteric solutions the CH₂Cl₂ signal is initially a singlet and then splits into a doublet. The time dependence of the splitting and the effect of CTA concentration are reported. The results suggest that the cholesteric phase slowly changes into a nematic phase in the magnetic field. The splitting of the CH₂Cl₂ proton signal into a doublet and the 1,2-DCE signal into a quartet are due to direct magnetic dipole-dipole interactions. Rotation of the sample in the magnetic field results in the disappearance of the doublet or quartet and suggests that the solvent molecules are originally oriented in the direction of the magnetic field. In the biphasic region, immediate splitting of the CH₂Cl₂ proton signal suggests that the anisotropic phase is nematic.     

Benzylation of cellulose in the solvent dimethylsulfoxide/tetrabutylammonium fluoride trihydrate

The cellulose solvent dimethylsulfoxide/tetrabutylammonium fluoride trihydrate (TBAF·3 H₂O) was studied as reaction medium for the synthesis of benzyl cellulose (BC) by treating the dissolved polymer with benzyl chloride in the presence of solid NaOH or aqueous NaOH solution. BC samples with degree of substitution (DS) between 0.40 and 2.85 were accessible applying different molar ratios. The studies show that both the TBAF·3 H₂O concentration and the molar ratio of the reagents to repeating unit influence the DS. The solubility of the BC synthesized in a different way, however, of comparable DS is different. Structural analyses were carried out by means of FTIR-, ¹H- and ¹³C NMR spectroscopy. SEC measurements revealed polymer aggregation in samples of low DS synthesized in a solvent containing 9.0% TBAF·3 H₂O. At higher concentration of TBAF·3 H₂O in the solvent, the BC samples obtained do not form aggregates. BC of high DS is crystalline and shows thermotropic liquid crystalline behavior as analyzed by means of DSC. Melting point and degradation temperature are not related to the DS.     

Dissolution and regeneration of cellulose in NaOH/thiourea aqueous solution

A novel cellulose solvent, 1.5 M NaOH/0.65 M thiourea aqueous solution, was used to dissolve cotton linters having a molecular weight of 10.1 × 10⁴ to prepare cellulose solution. Regenerated cellulose (RC) films were obtained from the cellulose solution by coagulating with sulfuric acid (H₂SO₄) aqueous solution with a concentration from 2 to 30 wt %. Solubility of cellulose, structure, and mechanical properties of the RC films were examined by infrared spectroscopy, X‐ray diffraction, scanning electron microscopy, ¹³C NMR, and tensile tests. ¹³C NMR analysis indicated that the novel solvent of cellulose is a nonderivative aqueous solution system. The presence of thiourea enhanced significantly the solubility of cellulose in NaOH aqueous solution and reduced the formation of cellulose gel; as a result, thiourea prevented the association between cellulose molecules, leading to the solvation of cellulose. The RC film obtained by coagulating with 5 wt % H₂SO₄ aqueous solution for 5 min exhibited higher mechanical properties than that with other H₂SO₄ concentrations and a homogenous porous structure with a mean pore size of 186 nm for free surface in the wet state. The RC film plasticized with 10% glycerin for 5 min had a tensile strength of 107 MPa and breaking elongation of 10%, and about 1% glycerin in the RC film plays an important role in the enhancement of the mechanical properties. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 40: 1521–1529, 2002     

New solvents for cellulose: Hydrazine/thiocyanate salt system

The hydrazine/thiocyanate system was found to be an excellent solvent for cellulose. The solubility and solution properties were investigated. Even at room temperature, the combinations of hydrazine and lithium, sodium, and potassium thiocyanate had high dissolution power for cellulose, up to an 18% (w/w) maximum, unrelated to the polymorph, whereas a combination with ammonium thiocyanate exhibited a solubility difference among celluloses I, II, and III. The effect of the temperature cycling of the system for the rapid dissolution of cellulose was investigated thermodynamically. In these systems, a high concentration of salts was necessary to effect the cellulose dissolution; this suggested that an undissociated salt–solvent complex played an important role in the cellulose dissolution as implied by electroconductivity measurements of the hydrazine/salt system. Gel and liquid‐crystal formation was observed in all systems above 4 and 6% (w/w) cellulose concentrations, respectively. The values of both critical concentrations were quite similar to those observed in the ammonia/ammonium thiocyanate system studied earlier in our laboratories. The gelation temperature was between approximately 10 and 50 °C, depending on the salt and cellulose concentration. The dependence of the cellulose solubility on the degree of polymerization was also examined. It is suggested that these solvent systems have great potential for the fiber and film formation of cellulose. © 2002 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 40: 601–611, 2002; DOI 10.1002/pola.10135     

X‐ray diffraction study of the thermal expansion behavior of cellulose triacetate I

Highly crystalline samples of cellulose triacetate I (CTA I) were prepared from highly crystalline algal cellulose by heterogeneous acetylation. X‐ray diffraction of the prepared samples was carried out in a helium atmosphere at temperatures ranging from 20 to 250 °C. Changes in seven d‐spacings were observed with increasing temperature due to thermal expansion of the CTA I crystals. Unit cell parameters at specific temperatures were determined from these d‐spacings by the least squares method, and then thermal expansion coefficients (TECs) were calculated. The linear TECs of the a, b, and c axes were α_a = 19.3 × 10^?5 °C^?1, α_b = 0.3 × 10^?5 °C^?1 (T < 130 °C), α_b = ?2.5 × 10^?5 °C^?1 (T > 130 °C), and α_c = ?1.9 × 10^?5 °C^?1, respectively. The volume TEC was β = 15.6 × 10^?5 °C^?1, which is about 1.4 and 2.2 times greater than that of cellulose I_β and cellulose III_I, respectively. This large thermal expansion could occur because no hydrogen bonding exists in CTA I. © 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47: 517–523, 2009     

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     

纤维素/聚硅氧烷离子液体混合气相色谱固定相的制备

纤维素是液相色谱中应用十分广泛的一类固定相,可是由于涂渍性能不佳,纤维素在气相色谱中的应用鲜有报道。本论文首先通过酯化反应合成了脂溶性较好的三醋酸纤维素（CTA）,然后与自制的聚硅氧烷离子液体（PIL-C12-NTf₂）混配,制备了含纤维素的气相色谱固定相（CTA@PIL-C12-NTf₂）,并涂渍了毛细管柱。其柱效为3165 plates/m（110 ℃,萘,k=4.95）。麦氏常数及溶剂化参数模型的测试结果证明,该固定相属中强极性固定相,主要作用力是氢键碱性作用和偶极作用。值得注意的是,引入纤维素可明显改善三取代芳香化合物位置异构体及壬烷（C9）同分异构体的分离选择性。此外,该固定相对正构烷烃、醇、脂肪酸酯及邻苯二甲酸酯等也具有良好的分离选择性。该研究不仅初步展现了纤维素在分离选择性上的特点,而且也为探索纤维素衍生物在气相色谱中的应用提供了一条新的途径。     

Rapid dissolution of spruce cellulose in H<Subscript>2</Subscript>SO<Subscript>4</Subscript> aqueous solution at low temperature

Dissolution of cellulose is the key challenge in its applications. It has been discovered that spruce cellulose with high molecular weight (4.10 × 10⁵ g mol^?1) can be dissolved in 64 wt% H₂SO₄ aqueous solution at low temperature within 2 min, and the cellulose concentration in solution can reach as high as 5 % (w/v). FT-IR spectra and XRD spectra proved that it is a direct solvent for cellulose rather than a derivative aqueous solution system. The cold H₂SO₄ aqueous solution broke the hydrogen bonds among cellulose molecules and the low temperature dramatically slowed down the hydrolysis, which led to the dissolution of cellulose. The resultant cellulose solution was relatively stable, and the molecular weight of cellulose only slightly decreased after storage at ?20 °C for 1 h. Due to the high molecular weight of cellulose, cellulose solution could form regenerated films with good mechanical properties and transparency at low concentration (2 % w/v). This work has not only provided the new evidence of cellulose dissolution which facilitated the development of cellulose solvent, but also suggested a convenient way to directly transfer cellulose with high molecular weight into materials without structure modifications.     

Rheology of cellulose/KSCN/ethylenediamine solutions and coagulation into filaments and films

Dissolution of cellulose in ethylenediamine/potassium thiocyanate (KSCN) was studied as a function of cellulose and KSCN concentration. Concentrations of up to 9% (w/w) cellulose were obtained. Large variations in solution rheology with salt and cellulose concentration were observed, and phases including flowing solutions and gels were identified visually. Rheological data indicated that viscosity decreased with increasing salt or cellulose concentration in certain composition ranges. Viscosity decrease with concentration increase is associated with either onset of liquid crystalline ordering or phase separation in the system. Both of these are quite likely in the cellulose/ethylenediamine/KSCN system, depending on composition. Additionally, comparison of loss (G′′) and storage (G′) moduli confirmed that compositions that exhibited gel behavior at zero shear became liquid at shear rates as low as 1 Hz. Solutions were coagulated into filaments and films using ethanol (CH₃CH₂OH) and methanol (CH₃OH). Infrared spectroscopy (FTIR) indicated that significant quantities of KSCN salt remained in the fibers and films after coagulation. Subsequent washing removed residual KSCN and improved physical properties. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 2013–2022, 2005     

Lyotropic mesophases of cellulose in the ammonia/ammonium thiocyanate solvent system: Phase relationships

Mesophase formation of the cellulose/NH₃/NH₄SCN system has been studied as a function of system composition at 25°C. Compositions for incipience of mesophase formation and for wholly anisotropic phase formation have been determined and relevant phase diagrams constructed. The biphasic gap narrowed when the solvent composition approached 75.5 weight percent NH₄SCN and as the cellulose concentration decreased. As solvent composition was changed, the minimum cellulose volume fraction for mesophase formation ranged between 0.02 to 0.045.     

Kinetics and mechanism of nitration of cellulose with the HNO3-CH2Cl2 mixture

Complexing in the HNO₃-CH₂Cl₂ system was confirmed tensimetrically. The kinetics of nitration of wood cellulose by the HNO₃-CH₂Cl₂ mixture were investigated. A large part of the cellulose is nitrated in a first fast reaction in comparison to the HNO₃-H₂SO₄ mixture with the same concentration of HNO₃. The rate of the process is determined by the rate of diffusion of the HNO₃, the rate of the process decreases more rapidly in the case of HNO₃-CH₂Cl₂ than in the HNO₃-H₂SO₄ mixture, which is probably due to the effect of CH₂Cl₂ on the diffusion coefficient of HNO₃.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 11, pp. 2445–2450, November, 1989.     

Carboxymethylation of cellulose in unconventional media

Carboxymethylation of cellulose in the new and highly efficient aqueous solvent Ni(tren)(OH)₂, [tren=tris(2aminoethyl)amine] and in melts of LiClO₄· 3H₂O or NmethylmorpholineNoxide (NMMNO), which is now widely applied for cellulose fibre production, was investigated. In case of Ni(tren)(OH)₂, a totally homogeneous carboxymethylation of cellulose with sodium monochloroacetate, in the presence of an aqueous NaOH solution is possible for the first time. Structure analysis by means of HPLC and ¹ HNMR after chain degradation showed results comparable with findings for CMC obtained by the heterogeneous slurry process, that is, a statistic distribution of substituents along the polymer chain and functionalisation of the hydroxyl groups in the order C6 C2 > C3. The etherification of cellulose in a melt of LiClO₄· 3H₂O, a new type of cellulose solvent, was shown to be possible and gave products of a statistic functionalisation pattern as well. In contrast, carboxymethylation starting from solutions of cellulose in NMMNO initiated with solid NaOH particles yields polymers with a nonstatistic distribution of functional groups along the chain, as observed for cellulose ethers prepared in reactive microstrctures starting from solutions of cellulose intermediates in dimethyl sulfoxide as well as of unmodified cellulose dissolved in N,Ndimethyl acetamide/LiCl.     

The polymerization of isobutylene by AlCl3 in CH2Cl2 and the role of CH2Cl2 in the initiation reaction

A solution of AlCl₃ in CH₂Cl₂ prepared in advance was used 18 days after the mixing of the components as an initiation system in the polymerization of isobutylene performed in CH₂Cl₂ in the temperature range between ?10 and ?20°C. The ¹H-NMR analysis of polyisobutylene (PIB) samples synthesized to low and high conversion showed that it is the initiation reaction and not the transfer reaction to dichloromethane that is responsible for the ? CH₂Cl endgroup in the polymer chain. In case of the transfer to monomer formation of PIB with internal terminal unsaturation [PIB? CH?C(CH₃)₂] is preferred to external unsaturation [PIB? CH₂(CH₃)C?CH₂]. The solutions of AlCl₃ in CH₂Cl₂ showed an absorption band at λ_max = 302 nm.     

Morphological characteristics of the lyotropic and gel phases in the cellulose/NH3/NH4SCN system

Solutions of cellulose in the ammonia/ammonium thiocyanate (24.5/75.5 w/w) solvent form several stable phases. Of particular interest in this work are the temperature-dependent liquid crystalline and gel phases which are stable at cellulose concentrations above 6% w/v. While the temperature-composition conditions yielding these phases are reasonably well established, very little is currently known about the morphological characteristics of lyotropic and gelled cellulose. Polarized light microscopy is employed here to demonstrate that solutions at temperatures above the gel melting point are birefringent, composed of liquid crystals. Field-emission scanning electron microscopy has been used to (i) examine the three-dimensional network in cellulose gels, and (ii) correlate network morphology with cellulose molecular weight and solution concentration. Results obtained from two complementary sample preparation techniques (i.e., critical point drying and freeze drying) are compared to identify and minimize artifacts, and reveal that gel formation occurs as the solutions phase-separate into polymer-rich anisotropic and solvent-rich isotropic phases. The polymer-rich phase is highly interconnected and forms a fibrillar network, with fibrils measuring 20–70 nm in diameter. © 1996 John Wiley & Sons, Inc.     

A Novel Potentiometric Sensor for Thiocyanate Based on an Amide‐Linked Manganese Diporphyrin Xanthene

The synthesis of a new compound, amide‐linked manganese diporphyrin xanthene (Mn₂Cl₂ADPX), and its application for preparation of thiocyanate selective electrodes was described. The electrode was prepared with a PVC membrane combining Mn₂Cl₂ADPX as an electro active material, 2‐nitrophenyl octyl ether (o‐NPOE) as a plasticizer in the percentage ratio of 3 : 65 : 32 (Mn₂Cl₂ADPX: o‐NPOE: PVC, w : w : w). The electrode exhibited linear response within the concentration range of 2.4×10^?6 to 1.0×10^?1 M SCN^?, with a working pH range from 3.0 to 8.0 and a fast response time of less than 60 s. Several electroactive materials and solvent mediators have been compared and the experimental conditions were optimized. The Mn₂Cl₂ADPX based electrode shows obviously better response characteristics than that of monoporphyrin manganese in terms of working concentration range and slope. Selectivity coefficients for SCN^? relative to a number of interfering ions were investigated. The electrode exhibits anti‐Hofmeister selectivity toward SCN^? with respect to common coexisting anions. The electrode was applied to the determination of SCN^? in body urine with satisfactory results.     

An FTIR study of the Cl atom-initiated oxidation of CH2Cl2 and CH3Cl

The Cl atom-initiated oxidation of CH₂Cl₂ and CH₃Cl was studied using the FTIR method in the photolysis of mixtures typically containing Cl₂ and the chlorinated methanes at 1 torr each in 700 torr air. The results obtained from product analysis were in general agreement with those reported by Sanhueza and Heicklen. The relative rate constant for the Cl atom reactions of CH₂Cl₂ and CH₃Cl was determined to be k(Cl +CH₃Cl)/k(Cl + CH₂Cl₂) = 1.31 ± 0.14 (2σ) at 298 ± 2 K.     

Bildung siliciumorganischer Verbindungen. 110. Reaktionen von (Cl3Si)2CCl2, seiner Si-methylierten Derivate,von (Cl3Si)2CHCl, (Cl3Si)2C(Cl)Me und Me2CCl2 mit Silicium (Cu-Kat.)

Formation of Organosilicon Compounds. 110. Reactions of (Cl₃Si)₂CCl₂ and its Si-methylated Derivatives as well as of (Cl₃Si)₂CHCl, (Cl₃Si)₂C(Cl)Me and Me₂CCl₂ with Silicon (Cu cat.) The reactions of (Cl₃Si)₂CCl₂ 1 , its Si-methylated derivatives (Me₃Si)₂CCl₂ 8 , Me₃Si? CCl₂? SiMe₂Cl 9 , (ClMe₂Si)₂CCl₂ 10 , Me₃Si? CCl₂? SiMeCl₂ 11 , Cl₂MeSi? CCl₂? SiCl₃ 12 as well as of (Cl₃Si)₂CHCl 38 , (Cl₃Si)₂CClMe 39 and of Me₂CCl₂ with Si (Cu cat.) in a fluid bed reactor ( 38 and 39 also in a stirred solid bedreactor) arc presented. While (Cl₃Si)₂CCl₂ 1 yields C(SiCl₃)₄ 2 the 1,1,3,3-tetrachloro-2,2,4,4-tetrakis(trichlorsilyl)-1,3-disilacyclobutane Si₆C₂Cl₁₆ 3 and the related C-spiro linked disilacyclobutanes Si₈C₃Cl₂₀ 4 , Si₁₀C₄Cl₂₄ 5 , Si₁₂C₅Cl₂₈ 6 , Si₁₄C₆Cl₃₂ 7 this type of compounds is not obtained starting from the Si-methylated derivatives 8, 9, 10, 11 They Produce a number of variously Si-chlorinated and -methylated tetrasila- and trisilamethanes. However, Cl₂MeSi? CCl₂? SiCl₃ 12 forms besides of Si-chlorinated trisilamethanes also the disilacyclobutanes Si₆C₂Cl₁₅Me 34 and cis- and trans Si₆C₂Cl₁₄Me₂ 35 as well as the spiro-linked disilacyclobutanes Si₈C₃Cl₁₉Me 36 , Si₈C₃Cl₁₈Me₂ 37 . (Cl₃Si)₂CHCl 38 mainly yields HC(SiCl₃)₃ 31 and also the disilacyclobutanes cis- and trans-(Cl₃Si)HC(SiCl₂)₂CH(SiCl₃) 41 and (Cl₃Si)₂C(SiCl₂)₂CH(SiCl₃) 45 the 1,3,5-trisilacyclohexane [Cl₃Si(H)C? SiCl₂]₃ 44 as well as [(Cl₃Si)₂CH]₂SiCl₂, and (Cl₃Si)₂CClMe 39 mainly yields (Cl₃Si)₂C?CH₂and (Cl₃Si)₂besides of HC(SiCl₃)₃, MeC(SiCl₃)₃and (Cl₃Si)₃C? SiCl₂Me.,. Me₂CCl₂ 59 mainly yields Me(Cl)C?CH₂, Me₂CHCl and HCl₂Si? CMe₂? SiCl₃, besides of Me₂C(SiCl₃)₂ and Me₂C(SiCl₂H)₂ Compound 3 crystallizes triclinically in the space group P1 (Nr. 2) mit a = 900,3, b = 914,0, c = 855,3 pm, α = 116,45°, β = 101,44°, γ = 95,86° and one molecule per unit cell. Compound 4 crystallizes monoclinically in thc space group C2/c (no. 15) with a = 3158.3,b = I 103.7, c = 2037.4 pm, β = 1 16.62° and 8 molecules pcr unit cell. The disilacyclobutane ring of compound 3 is plane, showing a mean distance of d (Si-C) =19 1.8 pm and the usual deformations of endocyclic angles: α_Si = 94,2°> 85,8° = α_C.The spiro-linked disilacyclobutane rings of compound 4 are slightly folded by a mean angle of (19.0°). Their mean distances were found to be d (Si? C) = 190.4 pm relating to the central carbon atom and 192.0 pm to the outer ones, respectively. The deformations of endocyclic angles: α_Si = 93,9°> 84,4° = α_C are comparable to those of compound 3.