Rate Of Polycondensation Research Articles

Polycondensation in liquid crystalline phases of nonionic surfactants. Kinetics and morphology

We have investigated acid-catalyzed polycondensation of alkoxysilane monomers in liquid crystalline phases of nonionic CnEm surfactants. The liquid crystalline phase is retained when the monomers polymerize. The high molecular weight molecules formed phase separate from the mesophase and are subsequently organized by it to form micron-sized particles. A variety of particle morphologies are formed by organization of the polymer particles in the mesophase. For condensation of dimethyldimethoxysilane (DMS, with trimethoxysilane, TMS as crosslinker) in hexagonal and lamellar phases, specific reaction conditions, viz. slow condensation kinetics and low crosslink density, give rod-like particles in hexagonal phases and sheet-like structures in lamellar phases. However, when higher acid concentrations are used, the reaction kinetics accelerates and irregular particles form. Irregular particles also form when the fraction of trifunctional crosslinker is increased, and finally complex flower-like structures form for condensation of trimethoxysilane in the hexagonal phase. The particle morphology formed is crucially dependent on the details of the polycondensation rate, crosslinker density and surfactant-monomer/oligomer interactions.

Synthesis and characterization of new polyesters with enhanced phosphorus content

New polyesters were prepared from several aromatic phosphonic dichlorides and a diolic monomer bearing a cyclic bulky group containing phosphorus. From kinetic investigation, the rates of polycondensation in melt were calculated and compared with those of the reaction between aromatic diols and phosphonic dichloride. Polyesters were analytically, spectral and thermally characterized and effect of structure on optical properties was investigated.

Control of molecular weight distribution in polycondensation polymers 2. Poly(ether ketone) synthesis

Synthesis of aromatic poly(ether ketone) ( 3) with a narrow molecular weight distribution ( M w/ M n) was investigated via polycondensation. M ns of 3 could be controlled varying the feed ratio of monomer ( 1) and initiator ( 2) maintaining relatively narrow M w/ M ns (<1.3). The kinetics of polycondensation obeyed a first-order relationship between polycondensation time and –(1/[ 2] 0) ln([ 1]/[ 1] 0), and the rate of polycondensation was estimated as 2.57 mol −1 L h −1. MALDI-TOF mass analysis of 3 indicated that polycondensation should proceed via chain growth manner to give 3 having an initiator unit in each chain end.

Influences of synthesis conditions on the content of framework Cu species in Cu-AlPO&lt;Subscript&gt;4&lt;/Subscript&gt;-5 molecular sieve

Copper substituted aluminophosphate molecular sieves with type 5, Cu-AlPO 4 -5, were hydrothermally synthesized. The influences of Cu 2+ concentration in the original gel, Et 3 N/Al 2 O 3 molar ratio and different template on the content of Cu species in the framework were investigated by H 2 -TPR. The results showed that increasing the Cu 2+ concentration in the gel could not result in the formation of framework Cu species, but only increase the amount of extra-framework CuO clusters. The formation of the framework Cu species was observed when tertiary amines such as C 6 H 11 NH 2 , Pr 3 N and Et 3 N were used as templates, but failed with quaternary ammonium TPABr. For Et 3 N, the amount of the framework Cu species increased with the increment of Et 3 N/Al 2 O 3 ratio until Et 3 N/Al 2 O 3 = 1.40. It is inferred that Cu 2+ can be incorporated into the framework when the hydrolysis and polycondensation rates of Cu 2+ are slowed down and match those of Al- and P-containing species.

Highly Fluorinated Poly(arylene ether ketone) Prepared by a CaH2‐Mediated Polycondensation Reaction

AbstractSummary: A new reaction procedure has been developed for the polycondensation of hexafluorobisphenol A (6F‐BPA) with bis(pentafluorophenyl) ketone (BPK) in dimethylacetamide (DMAc). In this reaction, CaH2 has been used as a base to facilitate the formation of the phenolate; an alkali metal fluoride was used as a catalyst. Unlike the conventional polycondensation reactions, this procedure avoided producing water during the reaction, and hence, azeotropic distillation with the assistant of a low‐polar co‐solvent is not required. This improvement maintains the high polarity of the reaction medium; consequently, the selectivity of the reaction at the para‐position of BPK is significantly enhanced and polymers with high molecular weights ($\overline M _{\rm n}$ ca. 30 000 Da) can be obtained with very low branching contents (less than 3 mol‐%) and free of any cross‐linked gel particles. In addition to avoiding the formation of water in the reaction, the use of CaH2 also reduced the concentration of the fluoride ion in the solution. These effects minimize chain degradation reactions such as hydrolysis. The use of CaO instead of CaH2 for this reaction produces similar effects. In the case of CaO, traces of water can be introduced into the reaction. The presence of trace amounts of water increases the polycondensation rate, probably due to the enhanced ionization of the phenolate. However, it also causes a hydrolysis of polymer chains, resulting in the elimination of the ketone group in the polymer backbone. Fortunately, this side reaction is highly water and temperature dependent, and can be efficiently prevented by using CaH2 or conducting the reaction at a lower temperature (&lt;65 °C).CaH2‐mediated polycondensation for the preparation of highly fluorinated poly(arylene ether ketone).imageCaH2‐mediated polycondensation for the preparation of highly fluorinated poly(arylene ether ketone).

The Solid State Postcondensation of PET, 1

AbstractSummary: A review of the processes underlying the solid state postcondensation of poly(ethylene terephthalate) (PET) is presented. Fundamental aspects of the reactions are treated, and it is shown that the rate of polycondensation in the solid state depends on the relative rates of two types of diffusion. On the one hand, the diffusion of reaction by‐products (physical diffusion) controls the rate of the forward reactions. And on the other hand the diffusion of end‐groups (chemical diffusion) allows the reaction to proceed.The transesterification of BHET to form PET.magnified imageThe transesterification of BHET to form PET.

Metathesis Activity and Stability of New Generation Ruthenium Polymerization Catalysts

A kinetic study of three ruthenium carbene catalysts, (H2IPr)(PCy3)(Cl)2RuCHPh, 3 (investigated extensively by Mol), (H2IMes)(Cl)2RuCH(o-iPrOC6H4), 4 (Hoveyda's catalyst), and (H2IPr)(Cl)2RuCH(o-iPrOC6H4), 5 (a new catalyst structure), was conducted under ADMET polymerization conditions. The kinetic behavior of these catalysts was compared to the classical first- and second-generation Grubbs' complexes at 30, 45, and 60 °C. Complex 3 exhibits the highest initial ADMET rate (80 DP s-1) of any phosphine complex to date and efficiently promotes metathesis even at temperatures as low as 0 °C. Complex 4 alone does not polymerize 1,9-decadiene in the bulk; however, addition of a polar solvent induces polymerization. Combining elements of catalysts 3 and 4 yielded the new complex 5. This complex results in higher polycondensation rates than previous Hoveyda-type structures and exhibits an increased stability over its parent phosphine complex. The new catalyst polymerizes 1,9-decadiene in the bulk to high polymer...

Preparation and characterization of TiO2–SiO2 glass ceramics via the sol–gel process by adding organic additives

This paper deals with the preparation of TiO2–SiO2 ceramics by using formamide, glycerol, or oxalic acid as drying control chemical additives (DCCAs) in order to improve the physical properties of the products, control the rates of hydrolysis and polycondensation, as well as the particle size homogeneity and porosity distribution. It was found that when using DCCAs, the gelation time was longer than without any additives. In acidic solution, the hydrolysis reaction is rapid, and the gelation tends to be slow; in an alkaline medium, the polycondensation of Si–OH and Ti–OH groups takes place much faster. The higher rate of nucleophilic substitution associated with the DCCAs leads to larger particles of the bulk ceramics.

Silsesquioxanes Derived from the Bulk Polycondensation of [3-(Methacryloxy)propyl]trimethoxysilane with Concentrated Formic Acid: Evolution of Molar Mass Distributions and Fraction of Intramolecular Cycles

The polycondensation of [3-(methacryloxy)propyl]trimethoxysilane was performed in bulk, using 98 wt % formic acid (molar ratio HCOOH/Si = 3 or 6), at 50 or 70 °C, for periods of time of up to 1 month. The resulting silsesquioxanes (SSOs) were characterized by 1H NMR, FTIR, SEC, UV−MALDI−TOF MS (linear, reflector, and post-source decay modes), and ESI−TOF MS. The residual concentrations of Si−OCH3 groups, and generated CH3OH and HCOOCH3, were quantitatively monitored by 1H NMR during the initial stage of the synthesis. After 2 days of reaction at 50 °C, or about 6 h at 70 °C, the resulting SSO mainly contained residual Si−OH groups with only traces of Si−OCH3 groups, as was also confirmed by FTIR and UV−MALDI−TOF MS in the reflector mode. After this time, the polycondensation continued slowly during storage at room temperature, basically through Si−OH + Si−OH reactions. The average fraction of intramolecular cycles increased continuously during the polycondensation. An average value, fav = 0.81, was found for species containing 6−24 Si atoms in a typical reaction product. This evidenced the presence of species with relatively closed structures. In MS/MS spectra, fragmentation of one or more ester groups attached to Si atoms was observed, following a McLafferty rearrangement. The addition of water to the initial formulation (about 3:1 H2O/Si molar ratio) led to a slower polycondensation rate and to a decrease of the average fraction of intramolecular cycles (formation of more open structures). Therefore, the use of 98 wt % formic acid was useful to synthesize SSOs containing a higher fraction of intramolecular cycles than those resulting from conventional formulations.

Determination of optimal experimental conditions for the preparation of lead zirconate titanate via sol-precipitate process by applying statistical methods

A fractional factorial design was implemented to optimize the experimental conditions for the preparation of lead zirconate titanate (PZT) from acetate precursors. The effects of such preparatory conditions as the molar ratio of acetic acid to metal alkoxide, the water to alkoxide ratio, the pH value, reaction temperature and the stirring speed, were systematically studied by using a Taguchi orthogonal array design. Results indicated that the molar ratio of acetic acid to metal alkoxides and the reaction temperature were the key variables influencing the average particle size of the powders obtained. By combining the optimal setting of these two influential processing variables, a fine powder with a particle size of ≈2200 Å was obtained. Fourier transfer infrared spectroscopy (FTIR), thermogravimetric analysis (TGA) and X-ray diffraction (XRD) were used to investigate the effects of the chelation on the rate of formation of the precursor and PZT powder. The rates of hydrolysis and polycondensation of the acetate precursors were slow because of the chelation of a high ratio of acetic acid with the alkoxide. The particle size of the obtained PZT powder was small and a homogeneous distribution resulted.

Polycondensation of benzyl chloride over Ga- and In-modified ZSM-5 type zeolites and Si-MCM-41 or Montmorillonite-K10 supported GaCl3 and InCl3 catalysts

Performance of In- and Ga-modified ZSM-5 type zeolites (namely, In2O3/H-ZSM-5, Ga2O3/H-ZSM-5, H-GaMFI and H-GaAlMFI) and InCl3 or GaCl3 supported on high silica mesoporous MCM-41 or on Mont.-K10 in the liquid phase polycondensation of benzyl chloride to polybenzyl has been investigated. Influence of solvent (namely, dichloroethane, n-heptane and ethanol) and temperature on the rate of polycondensation of benzyl chloride over the catalyst (InCl3/Si-MCM-41) showing highest polycondensation activity has also been studied. The In- and Ga-containing solid catalysts show good or high activity in the polycondensation reaction at the reaction condition normally employed in the benzylation of aromatic compounds by benzyl chloride. However, the polycondensation is strongly influenced by the solubility of the polybenzyl polymer in the reaction medium and consequently by the solvent used as the reaction medium.

Spontaneous formation of polypeptides in the interfacial thin films of amphiphilic amino acid esters: acceleration of the polycondensation and control of the structure of resultant polymers

For the purpose of elucidating the effects of molecular arrangements on the reaction rates and the structure of products, polycondensation of long-chain esters of α-amino acids in the monolayer on the water surface and the LB multilayers deposited on CaF 2 plates were investigated by monitoring changes of the IR spectra. Spontaneous formation of the polypeptides occurs in the mono- and multilayers at room temperature without any catalyst. The rates of polycondensation in the monolayers are markedly influenced by the degree of molecular packing. Maximum polymerizability is obtained in the vicinity of the transition region from expanded to condensed films. The rates of polycondensation in the LB films are much higher than those in the bulk solids and the molten states. The polycondensation seems to be accelerated by regular arrangements of the monomer molecules in the LB films, where the functional groups are concentrated and situated more effectively for the reaction than in the bulk states. However, the polycondensation rates in the LB films are considerably slower when compared with those in the monolayers on the water surface kept at the optimum area or surface pressure, because the molecules in the LB films deposited under high compression are packed more closely than the optimum condition. Thus, suitably close packing of the monomer molecules, retaining a particular orientation together with some conformational freedom in the monolayer, is most favorable for the polycondensation. Two probable mechanisms for the polycondensation in the Y-type multilayers have been proposed. In the assembly of head-to-head double layers of the monomer molecules, the interlayer reaction propagates by sewing up the functional groups facing each other in the adjacent layers, and the polypeptide of a helical structure or random coil can be obtained. In contrast, for the alternating assembly of the amino acid ester and non-polymerizable octadecyl acetate, the polycondensation should proceed only in each single layer (intralayer reaction) and the polypeptide of the extended β-form can be formed. In the case of dioctadecyl glutamate LB films, as well as the monolayer on water, the resultant polypeptide is the comb-like polymer with unreacted long-alkyl ester groups as side chains and abundant in the β-form, indicating the dominant intralayer reaction. On the other hand, in the Y-type multilayer of the equimolar mixture of dioctadecyl glutamate (with two ester groups) and octadecyl ester of lysine (with two amino groups), both of the intra- and interlayer reactions occur effectively, resulting in a two-dimensional network structure of the polypeptide. In conclusion, not only the rate of polycondensation but also the higher-order structure of the resultant polypeptides can be controlled by organized arrangements of the monomer molecules in the interfacial thin films.

Preparation of mesoporous silica particles with controlled morphology from sodium silicate solutions and a non-ionic surfactant at pH values between 2 and 6

Isometric particles of mesoporous silica could be synthesized between 25°C and 45°C from reaction mixtures containing silicic acids, sodium chloride and a non-ionic surfactant (Triton X100). The size decreases from some tens of micrometers to less than 1 μm when the pH increases from 1.85 to 6. At pH lower than 3.5, glassy material forms a cement between the particles. The particle size distribution narrows at higher pH and at long reaction times (several days). A spheroidal shape is favored by low pH and high temperature, and a more polyhedral shape appears at high pH whatever the temperature. This behavior could be related to the polycondensation rate of the silicic acids, to the lifetime and disorder of the micelles and to the micelles–silicic acid interactions.

The kinetics of polycondensation of ?,??-dichloro-p-xylene with 4,4?-isopropylidenediphenol using benzyltriethylammonium chloride as a phase-transfer catalyst

The phase-transfer catalyzed polycondensation of α,α′-dichloro-p-xylene with 4,4′-isopropylidenediphenol was carried out using benzylethylammonium chloride in a two-phase system of an aqueous alkaline solution and benzene at 60 °C under nitrogen atmosphere. The rate of polycondensation was expressed as the combined terms of quaternary onium cation and 4,4′-isopropylidenediphenolate anion rather than the feed concentration of catalyst and 4,4′-isopropylidenediphenol. The measured concentrations of hydroxide and chloride anion in the aqueous solution and α,α′-dichloro-p-xylene in the organic phase were used to obtain the reaction rate constant with the integral method, and to analyze the polycondensation mechanism with a cyclic phase-transfer initiation step in the heterogeneous liquid–liquid system. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 3059–3066, 2000

Sol-gel derived macroporous titania films prepared from the system containing poly(ethylene glycol) together with long-chain alcohols

The effect of alcohol-type on macroscopic morphology has been examined for the macroporous titania (TIO2) films prepared by a sol-gel dip-coating method from the system containing poly(ethylene glycol) (PEG) and alcohols having larger alkyl groups than ethanol. The phase separation is enhanced by decreasing the compatibility between the solvent mixture and PEG as long as the polycondensation rate does not increase greatly. In the 1-butanol system, macroporous morphology appears clearly even at higher relative humidity as 70% RH due to the slower polycondensation. In contrast, the macroscopic domain formation is completely suppressed by the rapid polycondensation in the 2-propanol system.

HEAT AND MASS TRANSFER WITH POLYCONDENSATION IN RESIN FILM DURING DRYING

ABSTRACT In a drying process of dielectric resin films coated on electric conductive substances, phenomena such as polymerization of monomers, by-products yield, shrinkage and stress generation lake place simultaneously in addition to heat and mass transfer. For the enhancement of the drying with high efficiency and high quality, it is important to understand the drying mechanism. In this paper, the characteristics of heat and mass transfer in the resin film including polycondensation reaction are presented. The apparent drying rate of polyamideimide varnish films was measured in two different heating modes of radiation and convection. The reaction rate of polycondensation was analyzed both by the thermogravimetry and the differential scanning calorimetry. The apparent drying rate began to drop remarkably when the reaction rate became significant. It implies that the diffusion of the solvent is inhibited by skinning at the surface. Applying the Vrentas/Duda free-volume diffusion model to the prediction of diffusivity, the heat and mass transfer in the resin film were analyzed theoretically with a reasonable accuracy.

Synthesis and Polycondensation of a Cyclic Oligo(phenylsilsesquioxane) as a Model Reaction for the Formation of Poly(silsesquioxane) Ladder Polymer

A tetracyclo(phenylsilsesquioxane) (T4) was first synthesized by the oligomerization of the low molecular weight hydrolysate of trichlorophenylsilane (TCP) by catalysis of the weak base, NaHCO3, followed by KOH-catalyzed polycondensation in toluene to form poly(phenylsilsesquioxane) (PPQS). The rate of polycondensation of T4 was much slower than that of direct polycondensation of the TCP hydrolysate under identical conditions. The molecular weight of the former product (Mn=35800) was significantly lower than that of the latter product (Mn=110000). X-Ray scatterings of the PPQS prepared by both processes were slightly different, probably due to the difference in structural regularity or branched structure. These data suggest that the polycondensations of T4 and the TCP hydrolysate should be driven through different reaction mechanisms, although the formation of the double strand ladder chain in the produced PPQS should be common to both.

Synthesis and characterization of liquid crystalline polymers fromp-hydroxybenzoic acid, poly(ethylene terephthalate), and third monomers

Eight new p-hydroxybenzoic acid (PHB) and poly(ethylene terephthalate) (PET) copolymers containing vanillic acid (VA), p-aminobenzoic acid, m-hydroxybenzoic acid, hydroquinone/terephthalic acid (TPA), bisphenol A/TPA, 1,5-naphthalenediol/TPA, 2,7-naphthalenediol/TPA, and 1,4-dihydroxyanthraquinone/TPA as eight third monomers with a variety of structural features were synthesized by melted-state copolycondensation and were characterized through a thermal analyzer, proton nuclear magnetic resonance, wide-angle X-ray diffraction (WAXD), and a scanning electron microscope (SEM). The experimental results show that PHB/PET/VA copolymers exhibit a faster polycondensation rate, lower melting temperature, and higher thermostability than do the other seven copolymers and third monomer-free PHB/PET polymers. The as-spun fibers derived from the PHB/PET/VA copolymers with different VA contents show tensile strengths, Young's moduli, and break elongations of 0.6–1.5 GPa, 28–67 GPa, and 7–9%, respectively. A highly oriented fibrillar structure in the PHB/PET/VA copolymer fibers was observed using WAXD and SEM. The most effective third monomer of the eight third monomers for an enhancing polycondensation rate and molecular weight of the PHB/PET polymers and for improving their thermal and mechanical properties is found to be vanillic acid (VA). © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 66: 2129–2138, 1997

Fire-resisting properties in several TiO2 wood-inorganic composites and their topochemistry

A study of the wood-inorganic composites prepared by the sol-gel process with a metal alkoxide indicated that an inorganic modification of wood with TiO2 gels from tetraisopropoxytitanium (TPT) can not improve its properties due to the formation of the gels in the cell lumina by high hydrolysis rate of TPT. In this study, therefore, titanium alkoxides or titanium chelates which have the lower rate of hydrolysis and subsequent polycondensation than TPT were used for preparing TiO2 wood-inorganic composites to study the topochemical effects of the TiO2 gels for the property enhancement of wood. As a result, it was found by SEM-EDXA analysis that the TiO2 gels deposited within the cell walls could improve the properties of wood in dimensional stability and fire-resistance, whereas for the gels in the cell lumina, property enhancement could not be achieved, as observed in SiO2 wood-inorganic composites.

Preparation and Dielectric Properties of Sr(Ti, Nb)03Ceramic from Sol-Gel Route

Abstract IR, DSC/TGA and XRD were used to study the formation of Nb2O5-doped SrTi03 powder. The rates of hydrolysis and polycondensation of titanyl acylate precursors prepared by chelating of titanium isopropoxide with acetic acid were slow. Therefore, the particle size of the powder obtained was finer and the particle size distribution was more uniform. The powder obtained was about 0.1 um of primary particle size, and the powder was readily sintered. The activation energy of grain growth for the ceramics calculated by the Arrhenius' formula is 121 KJ mol−1. The dielectric constant and dissipation factor of the bulk powders were also determined at 1300 to 1450°C.