Effect of monomer concentration and functionality on electro-optical properties of polymer-stabilised optically isotropic liquid crystals

Optically isotropic nature can open a new type of high-performance liquid crystal (LC) displays. The main features emerge from the interaction between LC and polymer network at the interface. At this point, we investigated the influence of cross-linking monomer concentration and functionality on electro-optic properties of optically isotropic liquid crystal (OILC) obtained by polymerisation-induced phase separation method. Interestingly, we obtained a pore-like network structure constructed by highly interlinked polymer beads in acrylate monomers and achieved fast decay response time (0.6 ms). We found that the voltage-dependent hysteresis was mostly eliminated (~0.25%), and the contrast ratio was enhanced (1:1550) for high functional monomers. The result inspires a simple way to optimise the materials to fabricate a high-performance OILC device and it shows high-transparency, low-driving voltage, hysteresis-free and sub-millisecond response time.     

Kinetics of the acid-catalysed formation of aliphatic peracids from hydrogen peroxide and aliphatic acids in dioxan

The acid catalysed formation of peracids from substituted acetic acids and hydrogen peroxide has been studied kinetically in dioxan. The rates of peracid formation together with equilibrium constants increase with increasing concentration of sulphuric acid and are correlated with the acidity of the media. The substituent effect suggests that the reaction is controlled by steric rather than polar effects. A mechanism similar to acid-catalysed esterification is discussed.     

Effects of functionality of thiol monomer on electro-optical properties of polymer-dispersed liquid crystal films

In this paper, polymer-dispersed liquid crystal (PDLC) films which based on the acrylate and the thiol monomers were first prepared by ultraviolet-initiated polymerisation. The electro-optical properties and morphologies of the PDLC films were systematically investigated. The functionality of thiol monomers and their feed ratio showed great influence on the properties of the fabricated PDLC films because of the existence of competition between thiol–acrylate reaction and acrylate monomer polymerisation reaction. This made the polymer network and electro-optical properties of the PDLC films easily tunable by the introduction of the thiol monomers. When added four-functional thiol monomer PETMP with appropriate concentration into the PDLC system, lower driven voltage and higher contrast ratio were achieved.     

Morphology of anisotropic polymer-dispersed liquid crystals and the effect of monomer functionality

The morphology of transmission gratings with varying Bragg spacings formed using polymer-dispersed liquid crystals were examined using high-resolution scanning electron microscopy and image analysis techniques. The effect on the morphology of small changes in the overall functionality of the prepolymer syrup was observed. An increase in the amount of monofunctional compound resulted in small, nearly spherical domains (<100 nm in diameter) confined in well-defined lamellae for samples with a 0.49 μm Bragg spacing. A decrease in concentration (an effective increase in monomer functionality) at this Bragg spacing resulted in larger domains (100–200 nm) with much greater distribution of sizes and shapes. The local volume fractions of discrete liquid crystalline (LC) domains was considerably larger in the latter case. An increase in the Bragg spacing to 1.35 μm also resulted in well-defined lamellae of LC domains, although much more coalescence into irregularly shaped individual domains was observed. Surprisingly, the local volume fraction of LC increased in the larger Bragg spacing samples. The morphology results are discussed qualitatively in terms of liquid–gel demixing where the inherent crosslink density and elasticity of the polymeric host must be considered in phase separation processes on the nanoscale. © 1997 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 35: 2825–2833, 1997     

Features of formation and viscoelastic properties of epoxyurethanes based on aliphatic cyclocarbonate oligomers

By the methods of dynamic mechanical analysis (DMA) and IR spectroscopy, the kinetics of curing and viscoelastic properties of epoxy urethanes of network structure based on epoxy diane resin and bifunctional oligocyclocarbonates (OCCs) are studied. The dependence of glass transition temperature and gel fraction of the obtained polymer on the amount of injected cyclocarbonate is established. It is shown that modification of epoxy diane oligomer by aliphatic OCCs results in an increase in its mechanical properties, particularly cohesive strength.     

Kinetics of polymerization by activated monomer mechanism

Polymerization of cyclic ethers by activated monomer mechanism involves consecutive additions of protonated monomer molecules to the growing macromolecules fitted with hydroxyl groups at their ends. For oxirane itself and symmetrically substituted oxiranes there is only one kind of hydroxyl groups and one, unique way of ring-opening. Unsymmetrically substituted oxiranes provide however two sites of attack and two different hydroxyls, resulting from these ring-openings. Kinetics of polymerization of epichlorohydrin (chloromethyloxirane) has been studied and all four rate constants determined, namely rate constants of the primary and secondary alcoholate chain ends with a protonated monomer, opening in result of the attack on substituted or unsubstituted carbon atom. These rate constants are (in mol⁻¹·1·s⁻¹ at 25°C, in CH₂Cl₂ solvent): k₁₁ = 0.055, k₁₂ = = 0.41, k₂₂ = 0.135, and k₂₁ = 0.0011 (e.g. k₁₂ is the rate of reaction of the primary alcohol producing the secondary alcohol). Thus, polymerization proceeds almost exclusively on the secondary alcoholate groups, reproducing themselves (k₂₂).     

Kinetics of uncatalyzed isomerization of aliphatic ketoximes

Three acyclic, aliphatic ketoximes studied show similar rates of isomerization at room temperature. From the rates of isomerization of one oxime at four temperatures, the thermodynamic activation parameters are calculated and a bimolecular transition state is postulated to account for the large negative entropy of activation.     

Water as a monomer: synthesis of an aliphatic polyethersulfone from divinyl sulfone and water

Using water as a monomer in polymerization reactions presents a unique and exquisite strategy towards more sustainable chemistry. Herein, the feasibility thereof is demonstrated by the introduction of the oxa-Michael polyaddition of water and divinyl sulfone. Upon nucleophilic or base catalysis, the corresponding aliphatic polyethersulfone is obtained in an interfacial polymerization at room temperature in high yield (>97%) within an hour. The polyethersulfone is characterized by relatively high molar mass averages and a dispersity around 2.5. The polymer was tested as a solid polymer electrolyte with lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) as the salt. Free-standing amorphous membranes were prepared by a melt process in a solvent-free manner. The polymer electrolyte containing 15 wt% LiTFSI featured an oxidative stability of up to 5.5 V vs. Li/Li⁺ at 45 °C and a conductivity of 1.45 × 10⁻⁸ S cm⁻¹ at room temperature.

This study describes the first example of the polymerization of water as one of two monomers. The obtained polymer allows for a solvent-free preparation of polymer electrolyte membranes exhibiting a high oxidative stability.     

Kinetics of OH reactions with aliphatic thiols

The kinetics of OH reactions with 1–4 carbon aliphatic thiols have been investigated over the temperature range 252–430 K. OH radicals were produced by flash photolysis of water vapor at λ > 165 nm and detected by time-resolved resonance fluorescence spectroscopy. All thiols investigated react with OH at nearly the same rate; k(298 K) = 3.2–4.6 × 10^?11 cm³ molecule^?1 s^?1, -E_act = 0.6–1.0 kcal/mol, A = 0.6–1.2 × 10^?11 cm³ molecule^?1 s^?1. CH₃SH and CH₃SD react with OH at identical rates over the entire temperature range investigated. We conclude that the dominant reaction pathway is addition to the sulfur atom.     

Effect of residual monomer on the spectroscopic properties of polythiophenes

The addition of some small molecules can red shift UV-Visible absorption and quench the fluorescence of poly(3-octadecylthiophene).     

Effect of cationic monomer on properties of fluorinated acrylate latex

Cationic fluorinated acrylate latex was prepared via semi-continuous emulsion copolymerization of cationic monomer and other monomers.The resultant latex and its film were characterized with dynamic light scattering detector and contact anglc meter. Influences of amount of DMDAAC on the propcrtics of resultant latex and its film were investigated in detail.Results show that the particle size of the latex has the minimum value and the zeta potential of the latex is increased when the amount of DMDAAC is increased.In addition,the particle size of the latex is unimodal distribution when the amount of DMDAAC is not more than 2.5%. However,the particle size of the latex is bimodal distribution when the amount of DMDAAC is more than 2.5%.The contact angle is varied slightly with the increase of amount of DMDAAC when it is not more than 2.5%.Nevertheless,the contact angle is decreased with the increase of the amount of DMDAAC when it is more than 2.5%.     

Kinetics of curing of diane and aliphatic epoxy oligomer blends: IR-spectroscopy study

The curing of diane and aliphatic epoxy oligomers and their blends is studied by IR spectroscopy. Methods for the quantitative determination of epoxy groups in diane and aliphatic oligomers and their blends during curing are developed. It is shown that, during the joint curing of epoxy oligomers, the reactivity of a more active (diane) oligomer remains practically the same, whereas the reactivity of a less active (aliphatic) epoxy oligomer increases. The rate constants for the consumption of epoxy groups of oligomers and primary amine groups of the curing agent are determined.     

Kinetics and mechanism of oxidation of aliphatic aldehydes by peroxomonosulphate

The kinetics of the oxidation of aliphatic aldehydes, formaldehyde, acetaldehyde, propionaldehyde, n-butyraldehyde, and trichloroacetaldehyde by Peroxomonosulphate (PMS) was carried out in aqueous perchloric acid medium (0.1–1 M H⁺) at constant ionic strength of 1.2 M in the temperature range 10°–60°C. The reactions of all the aldehydes were found to obey a total second-order kinetics, first order each with respect to [Peroxomonosulphate] and [aldehyde]. Acetaldehyde, propionaldehyde, and n-butyraldehyde exhibited acid catalysis with the concurrent occurrence of acid-independent reaction path conforming to the rate law Formaldehyde was found to undergo oxidation only by acid-dependent path (k_b = 0) and trichloroacetaldehyde exhibited only the acid-independent reaction path (k_a = 0). The products of oxidation were found to be the respective carboxylic acids in each case. The stoichiometry of the reaction, [Peroxomonosulphate]:[Aldehyde] = 1:1, indicated the absence of carbonyl-assisted decomposition and self-decomposition of peroxomonosulphate. The kinetic and thermodynamic parameters evaluated pointed to the mechanism of a fast nucleophilic attack of the oxidant on the aldehyde followed by slow acid catalyzed and/or uncatalyzed decomposition of the intermediate to product. A sharp comparison is made with the corresponding reactions of the similar peroxides, S₂O and H₂PO.     

Kinetics and thermodynamics of the blocking reaction of several aliphatic isocyanates

The oxime-blocking reaction of several aliphatic isocyanates, such as 1,6-Hexane diisocyanate (HDI), isophorone diisocyanate (IPDI), and dicyclohexylmethane-4,4′-diisocyanate (H₁₂MDI), is investigated. The reaction is carried on in various solvents that are divided into two categories: aromatic solvents and oxygen-contained solvents. In situ FT-IR is used to monitor the reaction and show the large difference of solvent and the structure of isocyanate. Kinetic studies indicate that the reaction rate appears faster in aromatic solvents although the polarity of aromatic solvents is lower. Then, thermodynamic parameters of the blocking reaction, such as activation energy (E_a), enthalpy (ΔH*) and entropy (ΔS*), are determined from the Arrhenius and Eyring equations. It is found that activation energy in aromatic solvents is higher, but the reaction rate is much faster, all of which are discussed corresponding to the reaction mechanism.     

Synthesis and properties of functional aliphatic polycarbonates

Two, functional, cyclic carbonate monomers, 5‐methyl‐5‐methoxycarbonyl‐1,3‐dioxan‐2‐one and 5‐methyl‐5‐ethoxy carbonyl‐1,3‐dioxan‐2‐one, were synthesized starting from 2,2‐bis(hydroxymethyl) propionic acid. The ring‐opening polymerization of the cyclic carbonate monomers in bulk with stannous 2‐ethylhexanoate as a catalyst under different conditions was examined. The results showed that the yield and molecular weight of polycarbonates were significantly influenced by the reaction conditions. The polycarbonates obtained were characterized by IR, ¹H NMR, and differential scanning calorimetry. Their molecular weight was measured by gel permeation chromatography. The in vitro biodegradation and controlled drug‐release properties of the polycarbonates were also investigated. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 4001–4006, 2003     

Kinetics and mechanism of oxidation of aliphatic aldehydes by quinolinium fluorochromate

Oxidation of aliphatic aldehydes by quinolinium fluorochromate (QFC) proceeds by a mechanism involving transfer of a hydride ion from the aldehyde to the oxidantvia an intermediate complex.     

Kinetics and mechanism of oxidation of aliphatic alcohols by tetrabutylammonium tribromide

Oxidation of nine primary aliphatic alcohols by tetrabutylammonium tribromide (TBATB) in aqueous acetic acid leads to the formation of the corresponding aldehydes. The reaction is first order with respect to TBATB. Michaelis-Menten type kinetics is observed with respect to alcohols. The reaction failed to induce the polymerization of acrylonitrile. Tetrabutylammonium chloride has no effect on the reaction rate. The proposed reactive oxidizing species is the tribromide ion. The oxidation of [1,1-²H₂]ethanol exhibits a substantial kinetic isotope effect. The effect of solvent composition indicates that the rate increases with increase in the polarity of the solvent. The reaction is susceptible to both polar and steric effects of substituents. A mechanism involving transfer of a hydride ion in the rate-determining step has been proposed.     

Kinetics and mechanism of the oxidation of aliphatic aldehydes by hexamethylenetetramine-bromine

Oxidation of aliphatic aldehydes by hexamethylenetetramine-bromine proceeds by a mechanism involving transfer of a hydride ion from the aldehyde to the oxidantvia an intermediate complex.