Liquid Oligomers Research Articles

ChemInform Abstract: Substituted Siloxysilanes and the Structure of Oligomeric Liquid Crystals.

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Substituted siloxysilanes and the structure of oligomeric liquid crystals

The sequential addition of 4-cyanobiphenyl moieties to a silyl core unit results in a modification of the molecular shape of the molecules from rod-like to cross-shaped. The variation of molecular size and shape determines the nature (interdigitated SmAd or monolayer SmAl) and the stability range of the liquid-crystalline phases of these materials.

New approach to recycling of thermosets

AbstractThe decrosslinking of thermosetting reaction injection molded (RIM) polyurethane‐urea products with the smallest amounts of glycols was studied. The effects of the reaction conditions on the properties of liquid oligomers were determined. Successful scale‐up studies and utilization of the resulting liquid oligomers for preparation of RIM products, coatings and adhesives are described.

New AFLC: a trimesogen presenting antiferroelectric smectic C phase (SmCA) and twist grain boundary smectic A phase (TGBA)

A first oligomeric antiferroelectric liquid crystal, a cyclohexane based trimesogen, was synthesized. It was characterized by microscopic observation, differential scanning calorimetry, helical pitch measurement, X-ray diffraction and electro-optical study. A large domain of antiferroelectric phase (DeltaT 55 C) and a very rich polymorphism (SmC*, SmC*, SmC*, A FI SmC*, TGBA, BP) are exhibited by the trimesogen.

Kinetics of the Three-Dimensional Thermopolymerization

A kinetic model of the three-dimensional radical polymerization of oligomers bulk is proposed. The presented analysis shows that the proposed equation agrees with the known experimental kinetic data of the three-dimensional polymerization. The construction of the equation is based on the concept of the microheterogenous model and the postulate that the rate of the three-dimensional polymerization is the sum of the rates of the homophase processes, which run in various phases and interphases, and that the initiator is distributed uniformly between the phases and interphase layer. The clusters of the solid polymer in liquid oligomer phase and clusters of the liquid oligomer in solid polymer matrix are assumed to have the fractal structure.

Models for formation of supermolecular oligomeric liquid structures: Theory and experiment

AbstractTwo theoretical models are proposed to describe rearrangement mechanisms for supermolecular structures of oligomeric liquids. The first is based on the concept of associate‐size distribution, varying with the addition of molecules to the associates. These molecules are activated by external action. The other model takes into account the fact that after activation, the equilibrium size distribution function is attained by way of an activated molecule redistribution between associates, owing to “cleavage‐addition.” Within the framework of accepted restrictions, the analytical solutions were obtained adequately to describe rheological and relaxation relationships revealed for various types of oligomeric systems.

Controlled degradation in tailor‐made macromolecules elaboration. Controlled chain‐cleavages of polydienes by oxidation and by metathesis

AbstractA chain cleavage reaction allowing the transformation of high molecular weight polymers in well‐defined oligomers can be considered as a step in a synthetic scheme. The control of oligomers with respect to their average molecular weights, their molecular weights distributions and their chain‐end microstructures implies the control of the cleavage reaction with respect to its yield, its regiospecificity and its chemiospecificity. Among several examples of efficient uses of this principle for the preparation of liquid oligomers from unsaturated polymers, attention is focused (I) on controlled oxidative degradation of rubber and (II) on metathetical controlled degradation of 1,4‐polydienes and polyakenamers. (I.a) The mechanism of the phenylhydrazine accelerated oxidation of rubber in the latex phase is described according to accurate structural studies on molecular model molecules. (I.b) The epoxidation of rubber and periodic acid cleavages of epoxides in the latex phase are interpretated referring to the influence of the biphasic medium. The results are in agreement with interfacial blocky epoxidation by the water‐soluble reagent and interfacial arrangement of the epoxidized block to be cleaved. Finally the metathetical degradations resulting from back‐bitting cyclisation and cross metathesis with acyclic alkenes are presented as preparative methods to get (II.a) well‐defined cyclic oligomers and (II.b) telechclic oligomers (i.e. terminally functionalized oligomers).

Synthesis and properties of oligomeric liquid crystals

Synthesis and properties of oligomeric liquid crystals

Heterotrimeric liquid crystalline thiadiazole derivatives

Abstract Various trimeric co-oligomers combining 2-phenyl-1,3,4-thiadiazole mesogenic moieties with a biphenyl mesogenic moiety were synthesized and their mesomorphic behaviour investigated by polarizing microscopy, calorimetry and X-ray scattering. Such co-oligomeric structures provide an opportunity to combine different mesogenic units. Thus readily accessible homochiral biphenyl mesogenic units were connected with thiadiazole mesogenic units leading to an oligomeric liquid crystal material with ferroelectric properties.

Layer-by-layer manufacture of parts from liquid photopolymerisable compositions by XeCl laser radiation

Layer-by-layer manufacture of parts from liquid oligomers (OKM-2 and TGM-3) was achieved with the aid of XeCl excimer laser radiation (λ = 308 nm). The method of projection printing was used in the manufacture of parts up to 50 cm3 in volume. The energy expenditure in the form of laser radiation did not exceed 1–2 J cm-3 (less than 200 J cm-3 if allowance was made for the laser efficiency) in the layer-by-layer manufacture of parts whose thickness was h = 100–200 μm. A machine for laser stereolithography based on an XeCl excimer laser is considered and its productivity is estimated.

An unusual dependence of viscosity on the water content in mixtures of water with oligomeric triblock copolymers of ethylene and propylene oxides

The addition of small amounts (less than 10%) of water to liquid oligomeric triblock copolymers (PEP) of ethylene oxide (E) and propylene oxide (P) increases the viscosity, η above that of pure liquid oligomers. Comparison with the concentration dependences of viscosity, η( c), for oligomeric homopolymers leads to the conclusion that the unusual shape of the dependences for PEP copolymers is due to the interaction of water molecules with hydrophobic propylene oxide units.

High orientation of toughened chalk‐filled isotactic polypropylene: Preparation and properties

AbstractChalk‐filled isotactic polypropylene (iPP) toughened by modifying the interfaces with liquid oligomer of ethylene oxide was subjected to high deformation at elevated temperature. Oriented chalk‐filled material exhibits interesting properties: high concentration of open interconnected pores, high elastic modulus, high tensile strength, ability to absorb large quantities of liquids, white color and roughness of the surface. A continuous process for the production of oriented, toughened, chalk‐filled isotactic polypropylene is described. The stretching ratios which can be achieved range from 4 to 8 for modified chalk concentrations with compositions of 60 and 40 wt%, respectively. Solid state extruded, toughened, chalk‐filled iPP prepared for comparison exhibits similar morphology and properties as drawn toughened chalk‐filled iPP although it contains much less voids.

Organometallic nickel catalysts bound to polymeric matrices in the oligomerization and/or polymerization of olefins with a replica of the support morphology

Organometallic nickel complexes with bidentate P O ⌢ chelating ligands of type Ph(PPh 3)Ni(Ph 2PCHCOPh) were heterogenized according to a new strategy — through the =CH— group of the ylidic ligand — and their behaviour in the polymerization and/or oligomerization of ethylene investigated. When anchored to polystyrene resins the catalytic systems showed a high and very selective activity in ethylene polymerization (1–2.5 kg of polymer (g Ni) −1 h −1) working in slurry or in gas—solid phase with reproduction of the morphology of the starting resins. When the matrix is a microspherical resin (0.1–0.3 mm diameter) the HDPE (high-density polyethylene) obtained is in the form of regular and very compact spheres of 3–7 mm diameter. Depending on the physical characteristics of the matrix (crosslinking, surface area, porosity, existence of spacing groups), compact spheres, hollow spheres (‘eggs’), geminates, polymer powders, or liquid oligomers were obtained.

Synthesis of perfluoropolyether with high molecular weight

Because of the mobile structure of the main chain, the polymer of hexafluoropropene oxide (HFPO) with high molecular weight is expected to be a new type of perfluoropolymer showing the flexibility and the low temperature workability, which are not observed for the perfluorocarbon type polymers such as polytetrafluroethene. In the polymerization of HFPO, however, the chain transfer reaction takes place easily to result in the formation of the viscous liquid oligomer with low molecular weight, at most. We investigated the method to prepare the polymer of HFPO with high moleculear weight by connecting the bifunctional oligomer of HFPO by means of a stable triazine group, as shown in Figure 1. Then, we established the method to form the polymer of HFPO with high molecular weight more than 1 × 10 6, which is an elastic solid and is useful as a new type of advanced material. The details of the preparation method and the characteristics of this polymer will be presented. ▪ Figure 1. Approach to the HFPO Polymer with High Molecular Weight

Synthesis of telechelic dithiol oligomers containing sulfur atoms‐moisture barrier properties

AbstractThe aim of this work was to synthesize new polysulfide materials from butadiene, styrene, isoprene, and methacrylate monomers and to study their moisture vapor permeability. For this purpose, a series of telechelic dithiol polysulfide oligomers were prepared by a polycondensation reaction between dianionic species of the corresponding monomer and sulfur or by reduction of the resulting cyclic polysulfide polymers. This last process was followed by 1H‐NMR and elemental analysis. It was established that the scission of the polysulfide linkages to thiol end groups was fastest with the greatest number of sequential sulfur atoms. The thiol reactivity was used to prepare cured materials from the liquid oligomers and manganese dioxide: Networks were obtained from butadiene dithiol oligomers, whereas chain extension occurred for the others. Infrared analysis suggests that the reticulation reaction results from thiol addition to the double bond. The moisture vapor transmission test applied to these different materials showed that these new compounds present good moisture barrier properties.

Splay elasticity in an oligomeric liquid crystal

Abstract A magnetically-induced Freedericksz transition was used in conjunction with capacitance techniques to determine the splay elastic constant of the 4,4′-dialkoxyphenylbenzoate monomer ‘5OO5rsquo; [C5H11OC6H4COOC6H4OC5H11] and its dimer. As a function of reduced temperature in the nematic phase, it was found that K 11 of the dimer is only about 20 per cent larger than that of the monomer. Moreover, the values of K 11/S 2 versus reduced temperature, where S is the scalar order parameter, are equal to within experimental noise. These results suggest that for short oligomers Meyer's entropic model for splay elasticity in polymer liquid crystals is not applicable. A lowest order correction to the entropic model is suggested, which partially accounts for excluded volume and dispersive effects.

Synthese de polysiloxanes fluores. Partie 7 Copolycondensation de 1,4 bis (hydroxydimethylsilyl) benzene avec les dichlorosilanes fluores.

We study the copolycondensation of 1,4-bis(hydroxydimethylsilyl)benzene HOSi (CH 3) 2C 6H 4Si(CH 3) 2OH with dichlorosilanes bearing fluorinated groups such as SI(CH 2CH 2CH 2OCH 2CH 2C 6F 13) and Si(H) or Si (vinyl) groups. By adding fluorinated monochlorosilanes, the molecular mass is controlled in order to obtain two series of liquid oligomers called ‘pompables’, cross-linkable through their complementary groups SiH/SiCH=CH 2. We have synthesized monodisperse molecules having molecular masses in the range of 500 to 3000 in order to draw a standardized weights curve for GPC studies an evaluation of the average molecular masses. Finally, using 1H and 29Si NMR have been able to calculate the composition of copolymers and to confirm the copolycondensation of the various monomers

Correlation between the equation of state and the temperature and pressure dependence of viscosity in polymer and simple liquids

A correlation between the equation of state and the temperature dependence of viscosity η in polymers such as polystyrene, polyisobutylene and polybutadiene, in melt and simple and oligomeric liquids such as argon, methane and n-hydrocarbons C 5C 64, and pressure dependence of η in polymer polymethyl methacrylate and simple liquids such as carbon dioxide, water and n-pentane, has been examined on the basis of the experimental data published by Fox and Flory 18,19, Colby, Fetters and Graessley 23, and Herrmann and Knappe 52 for polymers and Bridgman 3, Hubbard and Brown 32 for simple and oligomeric liquids. An expression of η obtained is given by ln η = A 0(M) + B 0{T c − T) T} n 0 + C(T)(P + P 0(T)) m 0(T) where A 0( M) is a function of molecular weight, T c is the critical temperature, C( T), P 0( T) and m 0( T) are functions of temperature, B 0 and n 0 are constants, which are determined from the experimental data of η over the wide range of temperature, including the critical region, and pressure up to 1.2 × 10 4 kgf/cm 2 for simple liquids and water up to 8 × 10 3 kgf/cm 2. The molecular weight dependence of η at constant temperature and pressure is also examined over the wide range of molecular weight 10 < M w < 10 6 g/mol and is expressed by ln η = A ∗ + a i ln M w for polymers ( i = 1) and simple liquids ( i = 0) with a 0 = 0.5 for simple liquids and a 1 = 1.0 for polymers except for high molecular weight polymers with a 1 = 3.4 where A ∗ is a constant around −11.0. The weak divergence of η in the vicinity of T c observed in simple liquids, such as carbon dioxide, has been discussed through the correlation between the P- η −1- T relation and the P- V- T relation for simple liquid in the critical region. Comparison between the WLF equation and the equation obtained in this work has been made based on the experimental data of η for a glass-forming liquid.

Magnetooptic investigation of chain conformation and Landau coefficients in oligomeric liquid crystals

Etude de la birefringence induite magnetiquement dans la phase isotrope du pentoxy-4 benzoate de pentoxy-4 phenyle, du dimere correspondant et de leur melange a des concentrations variables. Les resultats montrent que l'espaceur du dimere (OC 10 H 22 O) est extremement flexible dans la phase isotrope mais qu'il s'allonge dans la phase nematique

Structure and properties of oligomeric n,n′-diarylureas

Structure and properties of segmented oligomeric polyetherurea-urethanes of ABA structure, consisting of flexible oligoether or oligodiene blocks B and rigid urethane-urea blocks A was studied. The oligomers were found to be amorphous and microheterogeneous. The character of the starting oligomeric diol is decisive for the extent of microphase segregation of rigid and flexible blocks. The existence of two high-temperature transitions has been established, the first being attributed to glass transition in the rigid urea-urethane blocks. Survival of the heterophase structure in the liquid state is postulated; the second transition is important for the existence of heterophase structure in liquid oligomers.