Initial Stage Of Polymerization Research Articles

Tuning of the activity and induction period of double metal cyanide catalyzed ring-opening polymerizations of propylene oxide by using ionic liquids

Polymerizations of propylene oxide (PO) have been carried out by using double metal cyanide (DMC) catalyst prepared by reacting ZnCl 2 and K 3[Co(CN) 6] in the presence of tert-butyl alcohol as a complexing agents. The DMC catalyst of the molecular formula, Zn 2.3Cl 1.0[Co(CN) 6] 1.0·2.0 t BuOH·1.0H 2O, is characterized by gas sorption measurements, infrared spectroscopy and X-ray powder diffraction. The structure of DMC catalyst with negligible surface area and broadened X-ray diffraction peaks is different from that of Prussian blue analogue, Zn 3[Co(CN) 6] 2·12H 2O of microporous crystalline materials. The PO polymerization behavior is tunable by combining it with various imidazolium based ionic liquids (ILs) as external additives. Thus, (1) they make the zinc-monomer bond faster activated during the initial stage of polymerization, (2) they make the zinc-monomer bond more active, (3) they stabilize the polymerization centers and prevent their decomposition, and (4) they improve important polymer properties such as molecular weight, viscosity and unsaturation level. The maximum rate of polymerization ( R p,max) of DMC catalyst increases from 2587 to 27,222 g-polymer/g-cat h by combining with 1-ethyl-3-methylimidazolium chloride (emimCl, [emimCl]/[Zn] = 1.25) at 115 °C. The induction period as the time to reach R p,max becomes short from 321 min for DMC catalyst to 29 min for DMC/emimCl binary catalyst. The unsaturation value of polyol (0.017 mequiv./g) produced by DMC decreases to 0.005 mequiv./g by simply combining with IL. The molecular weight polyol produced by DMC catalyst increases from M n = 3700 to more than 6000, and the viscosity of polyol decreases by combining with ILs.

Atom Transfer Radical Dispersion Polymerization in an Ethanol/Water Mixture

The atom transfer radical dispersion polymerization of 4-vinylpyridine (4VP) in an ethanol/H2O mixture displayed two stages of polymerization; the first stage is the formation of a diblock copolymer with the polymerization rate of 1.21 mol·L-1·h-1 before 1 h of polymerization, and the second is the main polymerization in micelles formed from the aggregation of the resultant block copolymers with the polymerization rate of 0.009 mol·L-1·h-1. The 2-bromoisobutyryl-terminated poly(ethylene glycol) methyl ether used in the polymerization acts as both a stabilizer and an initiator. The stable micelles with functional core were synthesized by a one-pot strategy via atom transfer radical dispersion copolymerization (ATRDCP) of 4VP and N,N‘-methylenebisacrylamide (MBA) in an ethanol/H2O solution for the first time. In the initial stage of polymerization, 4VP and MBA were copolymerized to form a block copolymer, PEG-b-(4VP-co-MBA), with pendent unreacted vinyl groups, and after phase separation at a critical chain...

Study of the growth process of in situ polyaniline deposited films

Polyaniline (PAni) thin films were deposited onto BK7 glass substrates using the in situ deposition technique. The control of the time and the aniline concentration in the PAni polymerization reaction on the film deposition allowed us to prepare films with different thickness, down to ∼25 nm. The film growth process was monitored by measuring the UV–vis spectra and the AFM height profiles of the film surface. The curves of adsorption kinetics were analyzed with the Avrami's model, yielding an exponent n = 3 , thus indicating nucleation of spheroids at the initial stages of polymerization that grow through a diffusion process. AFM images of the surface height profiles corroborate this hypothesis, with spheroids growing with no preferred orientation during the in situ deposition.

Reaction Mechanism Based on X-ray Crystal Structure Analysis during the Solid-State Polymerization of Muconic Esters

We have investigated a change in the crystal structures of di(4-alkoxybenzyl) (E,E)- and (Z,Z)-muconates during the solid-state polymerization by X-ray crystal structure analyses and have discussed a reaction mechanism for the polymerization. The solid-state polymerization is divided into a homogeneous polymerization which proceeds in the solid solution of the remaining monomer and the resulting polymer and a heterogeneous polymerization in which a crystal phase separation occurs between the monomer and polymer crystal domains during the reaction. According to the former model, the monomer crystal phase continuously changes into the polymer crystal phase without any phase separation when the slightest movement of atoms induces less strain in the crystals. The molecular dynamics of the muconates in the solid state were monitored by in situ single and powder X-ray diffraction experiments. In fact, we succeeded in the direct observation of the expanding crystal lattices and cell volume at the initial stage of polymerization, followed by subsequent shrinking in the process of the homogeneous reaction. On the other hand, a phase separation was observed during the reaction according to the heterogeneous polymerization model, in which a considerable movement of atoms is required. The monomer stacking structure determines the reaction path during the solid-state polymerization.

Polymerization of butadiene on a titanium catalyst in formation of a reaction mixture in turbulent flows

Fundamental aspects of the polymerization of butadiene in the presence of a titanium catalyst under intensive agitation of the reaction mixture in the initial stage of polymerization, provided by use of a tubular turbulent divergent-convergent prereactor, were examined.

Kinetic Study of Atom Transfer Radical Copolymerization of Methyl Acrylate and Methyl Methacrylate Initiated with Poly(vinyl acetate) Macroinitiator

Atom transfer radical bulk copolymerization of MA and MMA was performed in the presence of CuCl/PMDETA as catalyst system and trichloromethyl‐terminated poly(vinyl acetate) macroinitiator at 80°C. The overall monomer conversion was followed gravimetrically and chemical composition of the copolymer was determined by 1H‐NMR spectrometry. The results have been used to calculate monomer reactivity ratios by linear and nonlinear methods. Reactivity ratios calculated were in the range of 0.3766–0.4988 and 1.8832–2.0963 for MA and MMA, respectively. These values were in good agreement with the values reported for a similar system in the free radical copolymerization. It was observed that the copolymerization system tends to produce a random copolymer with longer sequences of MMA than MA in the initial stage of polymerization before any significant decrease of the concentration of MMA in the monomer mixture. Copolymer microstructures in this study indicated that radical stabilization capability of MMA compared to MA is higher. The accuracy of the reactivity ratios were confirmed by 95% joint confidence limits. It was found that considering the effect of conversion in these methods makes the calculation result more accurate. The theoretical composition drifts in the comonomer mixture and copolymer as a function of the overall monomer conversion are also reported.

Thiol−Allyl Ether−Methacrylate Ternary Systems. Polymerization Mechanism

The polymerization mechanism of the ternary thiol−allyl ether−methacrylate monomer system has been investigated. The effects of various factors including the thiol concentration, functionality, and structure on the polymerization mechanism, the polymer network structure, and mechanical properties were examined. The thiol−allyl ether−methacrylate ternary system uniquely exhibits two different polymerization regimes: a methacrylate homopolymerization dominated regime coupled with chain transfer to thiol followed by a second thiol−ene polymerization dominated regime. This polymerization mechanism is primarily due to the chemical nature of the methacrylate and allyl ether double bonds. Because methacrylate homopolymerization with chain transfer reactions to thiols dominates the initial stage of polymerization (up to 60% of the methacrylate conversion), the concentration and structure of the thiol significantly affect the polymerization processes and polymer network structure. The methacrylate chain length si...

Effects of propylene prepolymerization on ethylene/1‐hexene and ethylene/1‐octene copolymerization with an immobilized metallocene catalyst

It has been known for some time that the activity of a heterogeneous catalyst for ethylene polymerization can be increased if a prepolymerization is carried out first in the presence of propylene or another a-olefin. Recently, it has been demonstrated that the increased polymerization activity can be attributed to a significant lowering of the monomer diffusion barrier in ethylene homopolymerization. The aforementioned studies were based on the use of MgCl2-supported Ziegler–Natta catalysts. However, monomer diffusion limitation in ethylene polymerization is also a frequently encountered phenomenon in ethylene polymerization with immobilized single-center catalysts and provides the most likely explanation for the increase in activity when ethylene polymerization is carried out in the presence of an a-olefin comonomer. The presence of the comonomer reduces the crystallinity of the polymer, leading to increased monomer sorption and easier monomer mass transport through the growing polymer particle, and facilitates catalyst fragmentation. However, compositional heterogeneity in the resulting copolymer may still occur, even in the case of a single-center catalyst. Fink et al. ascribed the compositional distribution of ethylene/1hexene copolymers prepared with a SiO2/methylaluminoxane (MAO)/zirconocene system to the formation, during the initial stages of polymerization, of a copolymer envelope around the catalyst particle. Easier diffusion of the smaller monomer, ethylene, with respect to 1-hexene was proposed to lead to a polymer particle comprising an ethylene-rich center surrounded by an outer layer of the copolymer, thus giving a broad overall chemical composition distribution (CCD). In recent ethylene/1-hexene copolymerization studies carried out with a catalyst comprising a zirconocene and MAO immobilized on a silica support, we found that the CCD of the copolymers became broader as the polymerization time was increased as a result of the gradual formation of a relatively high molecular weight, ethylene-rich fraction. Again, this is a strong indication that significant monomer diffusion effects can play a role not only in ethylene homopolymerization but also in copolymerization. Taking into account that monomer diffusion effects may be reduced if a prepolymerization of the catalyst is carried out first with a Correspondence to: J. C. Chadwick (E-mail: j.c.chadwick@ polymers.nl)

Effect of additives on the initial stage of emulsion polymerization of styrene (St) using poly(vinyl alcohol) as a protective colloid

To realize the mechanism of particle formation followed by the grafting of styrene (St) onto poly(vinyl alcohol) (PVA) more precisely, we investigated the influence of additives on model experiments of emulsion polymerizations in 1 ml styrene (St) per 100 ml water at 70 °C using PVA as a protective colloid. In the case of a standard system without additive, experimental results indicate new particle formation, and that 30% of St feed and 30% of the PVA used were grafted. The sulfate radical seldom enters into particles but reacts with PVA, forming the PVA radical that yields the grafting of St onto PVA. The experimental results are thought to arise from a hydrogen abstraction from PVA with a sulfate radical. The addition of low-molecular-weight alcohol, such as isopropyl alcohol (i-PrOH) and n-propyl alcohol (n-PrOH), strongly affected the mechanism of particle formation in terms of a decrease in grafting, due to competition between hydrogen abstraction from PVA and the alcohols with a sulfate radical. Surprisingly, the addition of a low-reactive alcohol, such as t-butyl alcohol (t-BuOH), also resulted in the particle formation with a decrease in grafting, influenced the polymerization locus to be a monomer droplets dispersed by t-BuOH, and confirmed homogeneous nucleation with the increase in the solubility of St in the aqueous phase.

Kinetics of the anionic ring‐opening polymerization of octamethylcyclotetrasiloxane initiated by potassium isopropoxide

AbstractKinetics of the anionic ring‐opening polymerization of octamethylcyclotetrasiloxane (D4) in bulk initiated by potassium isopropoxide was studied. Several promoters including N‐methyl‐2‐pyrrolidinone (NMP), N,N‐dimethylformamide (DMF), and diglyme were used. It is indicated that the reactions are first‐order in D4 during the initial stage of polymerization. The polymerization rate of D4 is influenced by a number of factors, such as the nature of promoters, the molar ratio of promoter to initiator (Cp/Ci ratio), and the reaction temperatures. With the use of NMP as promoter, the polymerization rate constant at 30°C is 10.482 h−1 with the Cp/Ci ratio equal to 3.0. As the Cp/Ci ratio increases, the polymerization rate constant increases sharply and the cyclic oligomers content in polymer decreases evidently. The back‐biting reaction that leads to the formation of decamethylcyclopentasiloxane (D5) occurred in the polymerization of D4. The rate of the D5 formation relatively to the rate of D4 conversion increases with the conversion of D4. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 3510–3516, 2006

Heterogenized Methylaluminoxane and Isobutylaluminoxane as activators for metallocene catalysts

Heterogenized alkylaluminoxanes prepared in situ on the montmorillonite (MMT) surface by the partial hydrolysis of AIR3 with water of the support are effective activators for metallocenes. The thermal destruction of isobutylaluminoxane molecules in the MMT-H2O/Al(i-Bu)3 system has been studied by the temperature-programmed desorption method coupled with mass spectrometry (TPD-MS). The process begins at a lower temperature and is more complicated than the destruction of methylaluminoxane (MAO) in MMT-H2O/AlMe3. Isobutyl-substituted aluminoxane and the ansa-metallocene Me2Si(Ind)2ZrCl2 form metal-alkyl complexes that are more active in propylene polymerization than methyl-substituted aluminoxane. The TPD-MS study of the initial stages of gas-phase ethylene and propylene polymerization shows that the nature of the metallocene in the heterogenized metallocene catalysts is an essential factor in the distribution of active sites by the activation energy of the thermal destruction of active Zr-C bonds.

Polymerization of lactams: 97. Anionic polymerization of ε-caprolactam activated by esters

The anionic polymerization of ε-caprolactam initiated with 0.5 mol % ethyl magnesium bromide in the presence of cycloaliphatic esters (lactones), such as γ-butyrolactone, δ-valerolactone and ε-caprolactone, has been studied in the temperature range 150–190 °C and concentration up to 5 mol %. To explain reaction mechanism, the polymerizations carried out in the presence n-butyl acetate and dimethyl terephthalate were also evaluated. The apparent rate constants and apparent activation energies were determined for the initial stage of polymerization. The non-integer orders of the polyreaction with respect to the concentration of lactone introduced indicated complex polymerization mechanism.

Influence of the Addition of Tertiary Amine on the Sequence Length of Aromatic Polyamide Copolymers in the Solution Polycondensation

Sequence distribution in the aromatic polyamide copolymerization with 4,4’-diaminodiphenyl ether, 4,4’-diaminodiphenylsulfone and isophthaloyl chloride in N-methyl-2-pyrrolidone was changed from random to some block distribution by adding tertiary amine such as pyridine and triethylamine into the reaction system. The reaction mechanism was examined by some model reactions to clarify the initial stage of polymerization and following conclusion was derived: As reactivity of amino groups in 4,4’-diaminodiphenyl ether became faster than the diffusion of diacid chloride into the reaction solution with the existence of tertiary amine, 4,4’-diaminodiphenyl ether ⁄⁄ isophthaloyl chloride block segments were quickly formed at the initial stage of polymerization to give copolymers with some block tendency.

ポリマー粒子の最前線 ＰＶＡ保護コロイドラテックスの現状

Equal quantities (300 thousand tons) of vinyl emulsions and diene latices are produced in Japan. Main application fields are paints and pressure sensitive adhesives for acrylics, adhesives for vinyl acetate (VAc) and its copolymers, and clay-coating binders and rubber in ABS resin for dienes. As stabilizers, PVA for VAc and its copolymers, and emulsifiers for acrylics and rubber for ABS are utilized. PVA affords mechanical stability and low-thixotropy to the emulsions and strengthening effect and poor water resistance to the emulsion films. These effects are arisen from the canal-like morphology of PVA in the films. PVA has not been utilized in emulsions other than those of VAc and its copolymers. This has been attributed to the weak ability in grafting of acrylic and diene monomers onto PVA. In the model experiment using a very low concentration of MMA, which corresponds to the initial stage of emulsion polymerization of the PVA systems, it was clarified that grafting onto PVA takes place significantly yielding new polymer particles, and that there are almost no difference between VAc and MMA systems. Problem seems to exist after the consumption of PVA freely soluble in water. Recently, noticeable studies were reported: in the emulsion polymerizations of acrylics and styrene/butadiene in the presence of ethanol, continuous addition of monomers emulsified with PVA afforded successfully the stable emulsions.

Study of the morphology and kinetics of novel Ziegler–Natta catalysts for propylene polymerization

AbstractThe morphological and kinetic characteristics of novel Ziegler–Natta catalysts were studied. Catalysts were prepared by Borealis Polymers Oy using a new synthesis technique (emulsion technology). Video microscopy was used to study the growth of single catalyst particles during polymerization in the gas and liquid phases. The distribution of single particle activity was very narrow in the catalyst without external support and was rather broad in the the silica‐supported catalyst. Video microscopy of molten polymer particles allowed observation of the process and degree of fragmentation of the catalyst particles. A correlation between the activation period during the initial stage of polymerization and catalyst fragmentation was found. Fragmentation was faster and more uniform with the catalyst without external support than with the silica‐supported catalyst. Scanning electron microscopy provided information on morphology evolution and shape replication of the catalyst particles. With the catalyst without external support, good shape replication was observed, and compact and spherical particles were formed. With the silica‐supported catalyst, shape replication was poor, and nonspherical porous polymer particle were formed. Modeling of the kinetics of propylene polymerization was done using a simple three‐step reaction scheme neglecting mass and heat transport effects. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 98: 2191–2200, 2005

Fragmentation of Ziegler‐Natta Catalyst Particles During Propylene Polymerization

AbstractSummary: Analyzing polymer particles by microscopy technique at different polymerization times provided information regarding the catalyst support break‐up rate and degree of fragmentation during polymerization. Polymer samples were prepared at different polymerization times and melted under a video microscope to track the progress of fragmentation. Studies focused on effect of the catalyst support on the process and degree of catalyst fragmentation. Fragmentation behaviors of both a catalyst without an external support and a silica supported Ziegler‐Natta catalyst were compared. Fragmentation of catalyst was observed to occur in the whole catalyst matrix at the very beginning of polymerization. In the case of the catalyst without an external support, fragmentation was faster and more uniform than that of the silica supported catalyst. Results corresponded to the activity distribution of single catalyst particles as determined by video microscopy. The catalyst without an external support having particles of similar activities showed similar degrees of fragmentation. Conversely, silica supported catalyst having particles of different growth behavior produced particles having different degrees of fragmentation. The rate of increase in the number of catalyst fragments and their surface area with time during polymerization was investigated. Results correlated the catalyst activation period during the initial stage of polymerization to catalyst fragmentation.Poly(propylene) particles produced with silica supported (upper image) and non‐supported (lower image) Ziegler‐Natta catalysts.magnified imagePoly(propylene) particles produced with silica supported (upper image) and non‐supported (lower image) Ziegler‐Natta catalysts.

Transformation of Polymerization Sites into Hydrogen Dissociation Sites on Propylene Polymerization Catalyst Induced by the Reaction with Al-Alkyl Cocatalyst

Hydrogen (H2) is the most important chain-transfer agent to control the molecular weight (MW) of polymer in all industrial processes using Ziegler−Natta catalysts. However, the specific mechanism of chain-transfer reaction by H2 is still open for discussion. Stopped-flow techniques were utilized to investigate the chain-transfer mechanism by H2 on TiCl4/EB/MgCl2 catalyst pretreated by triethylaluminum (TEA) cocatalyst within an ultrashort time (0−1.1 s). First, the results obtained in the absence of H2 demonstrated the first experimental evidence of plausible guard effect on the active sites by coordinating growing polymer chain in the initial stage of propylene polymerization. A gradual decrease of active sites concentration, increase of chain propagation rate constant and isospecificity of active sites were observed even after an ultrashort period pretreatment due to the preferential deactivation of aspecific sites, which was found not to be affected by the presence of H2. On the other hand, H2 could no...

Role of tert‐Butyl Methyl Ether (TBME) as an External Donor in Propene Polymerization with Dibutyl Phthalate (DBP)‐Containing MgCl2‐Supported Ti Catalysts Activated with Al(i‐C4H9)3

AbstractSummary: Stopped‐flow polymerization of propene was first conducted at 40 °C using the TiCl4/DBP/MgCl2 catalyst (DBP = dibutyl phthalate) combined with Al(C2H5)3. An induction period was observed at the beginning of polymerization, and the resulted polymer contained a considerable amount of the isolated ethylene unit. The formation of such unusual structures was concluded to be the result of copolymerization with ethylene originating from the ethylated Ti4+ species. Catalyst washing with toluene and stopped‐flow polymerization at 70 °C brought about a drastic decrease in the contents of both Ti and DBP as well as a disappearance of both the induction period and isolated ethylene unit. The microstructures of polymers revealed that the highly stereoregular polymers are produced at the initial stage of polymerization. Changes in yield and molecular weight of polymers with polymerization time showed that the addition of tert‐butyl methyl ether (TBME) brought about an increase in the concentration of active sites, but did not affect the propagation rate of propene polymerization. Such an increase in the active site concentration caused by an external donor has hardly been reported so far in kinetic studies using the stopped‐flow method; thus, the present result is believed to be a unique example.Kinetic curves of propene polymerization with the Cat. IV‐Al(i‐C4H9)3 catalyst. (•): with TBME/Al = 0.1 and hydrogen, (♦): with TBME/Al = 0.1 and without hydrogen, (○): without TBME and with hydrogen, (⋄): without TBME and hydrogen.magnified imageKinetic curves of propene polymerization with the Cat. IV‐Al(i‐C4H9)3 catalyst. (•): with TBME/Al = 0.1 and hydrogen, (♦): with TBME/Al = 0.1 and without hydrogen, (○): without TBME and with hydrogen, (⋄): without TBME and hydrogen.

Facile Syntheses and Characterization of Hyperbranched Poly(ester−amide)s from Commercially Available Aliphatic Carboxylic Anhydride and Multihydroxyl Primary Amine

A new method for synthesis of novel hyperbranched poly(ester−amide)s from commercially available AA‘ and CBx type monomers has been developed on the basis of a series of model reactions. The hyperbranched poly(ester−amide)s with multihydroxyl end groups are prepared by thermal polycondensation of carboxyl anhydrides (AA‘) and multihydroxyl primary amine (CBx) without any catalyst and solvent. The reaction mechanism in the initial stage of polymerization was investigated with in situ 1H NMR. In the initial stage of the reaction, primary amino groups of 2-amino-2-ethyl-1,3-propanediol (AEPO) or tris(hydroxymethyl)aminomethane (THAM) react rapidly with anhydride, forming an intermediate which can be considered as a new ABx type monomer. Further self-polycondensation reactions of the ABx molecules produce hyperbranched polymers. Analysis using 1 H and 13C NMR spectroscopy revealed the degree of branching of the resulting polymers ranging from 0.36 to 0.55. These hyperbranched poly(ester−amide)s contain config...

Evidence of a redox equilibrium assisted chain propagation mode for aniline polymerization: in situ spectral investigation in dodecylbenzene sufonic acid based system

Detailed in situ absorption spectral investigation of chemical oxidative polymerization of aniline in dodecylbenzene sufonic acid (DBSA) based system revealed that the chain propagation is assisted by redox equilibrium intermediate (REI) rather than a fully oxidized pernigraniline. The continuous reduction (addition of aniline) and oxidation (by oxidant) of REI, propagate the chain. The polymerization process consists of three prominent stages called induction period (IP), chain propagation and termination. The initial stage of polymerization is realized as IP, the time taken to establish REI. The presence of fully developed polaron band indicates REI has delocalized structure. Invariant spectral features together with tremendous increase in absorbance at propagation phase indicate REI undergoes reductive addition of aniline and oxidation by APS (ammonium persulfate) while maintaining equilibrium structure. The greatly increased absorbance with time at this stage is due to well-known autoacceleration phenomenon observed for aniline polymerization. The increase in redox potential of REI with increase in chain length accelerates the reaction and accounts for autoacceleration. The termination of polymerization would be reduction or oxidation depending on the availability of aniline or oxidant respectively. In a system where the oxidant is the limiting agent, reduction continues until it reaches emeraldine salt that is incapable of further reduction. On the other hand an excess of oxidant, results in the formation of pernigraniline by continuous oxidation.