Polymerization in nonuniform latex particles. II. Kinetics of two-phase emulsion polymerization

A new theory, based on the concept of nonuniform distribution of free radicals in polymerizing latex particles, has been developed for the kinetics of two-phase emulsion polymerization reactions. This theory also takes into account the diffusion controlled termination and propagation reactions to describe the gel effect and limiting conversion. The kinetic model permits prediction of the distribution of free radicals in the two polymer phases and rate of polymerization as a function of reaction conditions. Experimental data for polystyrene/polymethyl methacrylate and polymethyl methacrylate/polystyrene (postformed polymer/preformed polymer) in the literature have been used to assess the proposed idea of nonuniform distribution of free radicals in the latex particle.     

Photophysical properties of ternary hybrid system of lanthanide center linking organically modified silica and polymeric chain

According to coordination chemistry principle and molecular assembly technology, series of ternary lanthanide centered hybrid systems have been constructed through coordination bonds. Among one component (ligand) is organically modified Si-O network, which originates from the functional molecular bridge (BFPPSi) by the functionalization of 1,3-bis(2-formylphenoxy)-2-propanol (BFPP) with 3-(triethoxysilyl)propyl isocyanate. In the second component (ligand), three different organic polymeric chains are introduced, poly-(methyl methacrylate) (PMMA, from the polymerization of MMA with the benzoyl peroxide [BPO] as the initiator), poly-(methyl acrylic acid) (PMAA, from the polymerization of MAA with the BPO as the initiator), polyvinyl pyridine, respectively. All these ternary hybrid materials show homogeneous, regular microstructure, suggesting the existence of assembly process of lanthanide centers, inorganic Si-O network and organic polymer chain. Compared to the binary hybrids without polymer chain, the photoluminescent properties of these ternary hybrids present stronger luminescent intensities, longer lifetimes and higher luminescent quantum efficiencies indicating that the introduction of organic polymer chain is favorable for the luminescence of the whole hybrid systems.     

Free-radical polymerization of methyl methacrylate in the presence of a ferrocenyl-containing iron(II) clathrochelate complex and initiators of various natures

Benzoyl peroxide-, lauryl peroxide-, and AIBN-initiated free-radical polymerization of methyl methacrylate has been studied in bulk and solution in the presence of macrobicyclic iron(II) bis(ferrocenyl borate) tris(nioximate). It has been found that the ferrocenyl-containing iron(II) clathrochelate forms efficient initiating systems with peroxides, whereas, in the case of AIBN, its presence has no effect on the kinetic parameters of the process and the properties of the resulting polymer. The use of clathrochelate complex-peroxide initiator systems accelerates the polymerization of methyl methacrylate and decreases the molecular mass of the polymer. The kinetic parameters of the process have been determined.     

Physical aspects of network polymerization from calorimetry and dielectric spectroscopy of a triepoxide reacting with different monoamines

Calorimetry and dielectric relaxation spectroscopy were used to study the evolution of molecular dynamics during the isothermal polymerization of two stoichiometric mixtures of a molecule with three epoxide groups with (i) aniline and (ii) 3-chloroaniline, whose dipole moments as well as the degrees of steric hindrance to chemical reactions differ. The heat evolved on polymerization was used to calculate the number of covalent bonds formed at any instant during the polymerization reaction. The approach of the DC conductivity towards a singularity as the reaction progressed agrees with the Flory-Stockmayer theory of connectivity at gelation and not the percolation theory. It is demonstrated that a plot of DC conductivity against the extent of reaction does not have the same shape as the plot against the time of reaction. The permittivity and loss spectra obtained for structural states containing a fixed number of covalent bonds could be described by equations analogous, but not equivalent to, or the same as, the equations used for describing the dielectric properties measured for a fixed frequency during the growth of a macromolecule's network structure. For a fixed temperature, the relaxation time of the structure formed increased as the exponential of the extent of reaction (raised to the power > 1) increased. Comparative parameter-fits to the spectra showed that the DC conductivity and interfacial polarization alter the shape of the dielectric spectra such as to make misleadingly alternative parameter fits possible. The decrease of the equilibrium dielectric permittivity on polymerization is attributed to a decrease in the dipolar orientational correlation as well as the net dipole moment on increase in the number of covalent bonds. The configurational entropy decreased with increase in the number of covalent bonds formed in a manner that differs from the decrease on cooling, and a formalism relating the two effects is given. As the network structure grew isothermally, a second, high-frequency relaxation process came into evidence. This relaxation is attributed to the availability and growth of local regions of low density and high density in the network structure of the macromolecule. A number of issues of a fundamental nature that have risen since our earliest report on this subject have been elaborated and analytically clarified. © 1997 John Wiley & Sons, Inc.     

Novel bio‐based IPNs obtained by simultaneous thermal polymerization of flexible methacrylate network based on a vegetable oil and a rigid epoxy

A series of novel vegetable oil‐based interpenetrating polymer networks (IPNs) have been successfully prepared: on one hand, methacrylated camelina oil (MCO) and a polyethyleneglycol dimethacrylate (PEG, MW 750 g/mol) and on the other hand, diglycidylether of bisphenol A (DER), in various blend ratios (75/25, 50/50, and 25/75 wt). Hence the appealing innovative direction of the current work was to build oil‐based poly(methacrylate) network using PEG macromonomer which is able to modulate adequately the crosslinking degree of the oil‐based network. These innovative combinations of cross‐linkable resins in terms of flexible methacrylate network based on camelina oil (CO) and PEG and a rigid epoxy (DER) were simultaneously polymerized using two independent non‐interfering curing reactions: free‐radical process for MCO and anionic polymerization of epoxy resin in the presence of a tertiary amine. The effect of the IPNs composition compositional characteristics on the reactivity of methacrylate or epoxy groups was studied using differential scanning calorimetry. The influence of the MCO‐PEG bio‐based polymer on the system properties was evaluated after curing by dynamic mechanical and thermogravimetric analyses. In addition mechanical and morphological studies were also carried out. The results suggested that blending of MCO and DER gave synergistic effects on the overall properties of the developed oil‐based IPNs and a dependence on the methacrylate/epoxy ratio was clearly noticed. Copyright © 2014 John Wiley & Sons, Ltd.     

High-conversion polymerization. IV. A definition of the onset of the gel effect

The gel effect in free radical polymerization of vinyl monomers has been recognized as the result of the increased viscosity of the reaction solution of polymer in monomer, which causes a decrease in the rate of the termination reaction. This effect manifests itself as an increase in the rate of polymerization over that rate to be expected in its absence. Definition of the onset of the gel effect has become necessary for several purposes. Previously, it has been common to define the onset phenomenologically, i.e., in terms of the increase in the rate of polymerization. It is proposed here that the onset of the gel effect is best defined on a fundamental basis, i.e., as occurring at that conversion at which the rate of segmental diffusion of the polymeric radicals equals the rate of their translational diffusion. Experimental evidence is presented that shows that the small minima predicted by this definition do exist for both rates and degrees of polymerization. Measurements of the viscosities of solutions of polymers in their monomers suggest that the polymer concentrations at which the “chain-entanglement” phenomena are observed are the same as those for the onset of the gel effect for styrene, methyl methacrylate, and butyl methacrylate.     

Hydrodynamic Activation of the Batch-Polymerization of Methyl methacrylate in a Taylor-Couette Reactor

Summary: In this work, the free radical batch polymerization of methyl methacrylate (MMA) premixed with xylene as a solvent, in the presence of an initiator, 2,2-azoisobutyronitrile (AIBN), in the Taylor-Couette reactor was studied. We observed an unexpected influence of hydrodynamic process parameters, i.e. angular velocity ω, on the polymer conversion, molecular weight and viscosity of the produced polymer. The polymerization process seems to be activated by hydrodynamic process parameters. Hydrodynamic activation is a promoting effect of process parameters on polymer product properties. The hydrodynamic activation is found to depend on the reaction time and the angular velocity of the inner cylinder. In addition, our results highlight both the reaction kinetics and the hydrodynamics during the polymerization. The conversion exhibits a significant difference between tests with and without the angular velocity of the inner cylinder. The conversion and the molecular weight strongly increase with the increase of the angular velocity of the inner cylinder, whereas the viscosity is less strongly dependent. There is more increase with decreasing solvent concentration. The radial Reynolds number decreases with increasing conversion. The polymerization is faster with a low solvent concentration, and the molecular weight is higher compared to the case of high solvent concentration.     

Polymerization and Copolymerization of Some Monomers as Adducts with β-Cyclodextrin

The feasibility of chemical bond formation, especially in the chain-transfer reaction between polymer and β-cyclodextrin (β-CD) molecules in the products of the radiation polymerization of β-CD with vinylidene chloride (VDC) its adducts has been considered. The lack of these bonds in the polymerization products of similar β-CD adducts with methyl methacrylate (MM), styrene (St), a mixture of VDC and allyl chloride (AC) and a mixture of VDC and MM (10:90 molar ratio) has been established. On the basis of the results obtained the lack of chemical bonds in the polymerization product of β-CD· VDC adduct is suggested.     

Poly(trialkylsilyl methacrylate)s: A family of hydrolysable polymers with tuneable erosion profiles

Polymers containing hydrolytically labile trialkylsilyl ester side groups were synthesised via a conventional and a controlled radical polymerization. The trialkylsilyl methacrylate monomer unit was chosen for its capacity to hydrolyse into basic, acid or sea water varying the hydrophilic character of the resulting polymer backbone with time. The hydrolysis or saponification reaction of the ester bond of the trialkylsilyl methacrylate was monitored through a ¹H NMR study showing the formation of siloxane side-products. Several copolymers and polymer blends were prepared as matrixes for controlled erodible systems. Their capacity to hydrolyse was demonstrated through SEM investigations with selective dissolution of free films containing hydrolysable copolymers and PMMA blends. Well-defined random and diblock copolymers with methyl methacrylate were investigated to show the effect of the microstructure on the erosion properties of the corresponding coatings. Poly(methyl methacrylate-b-tert-butyldimethylsilyl methacrylate) diblock copolymers synthesised through the RAFT process showed a better control of the erosion with a constant erosion rate over a long-time service in sea water at pH = 8.2. In addition, experiments showed that the erosion rate could be modulated by varying the molar proportion of hydrolysable side groups onto the copolymer backbone and the weight amount of copolymers mixed with PMMA in toluene solution.     

Effect of spatial constraints on phase separation during polymerization in sequential semi-interpenetrating polymer networks

The viscoelastic properties of sequential semi-interpenetrating polymer networks prepared via the swelling of network polyurethane in different monomers (butyl methacrylate, styrene) followed by their polymerization in the polyurethane matrix have been studied by means of dynamic mechanical analysis. It is found that the relaxation behavior of the test systems and the degree of segregation of the components depends on M _c of the polyurethane matrix because of a change in the molecular mass of the polymer block. The compatibility of the components in sequential semi-interpenetrating polymer networks substantially increases when the network inner space in the polyurethane matrix decreases.     

Synthesis of Epoxy Methacrylate Resin and Coatings Preparation by Cationic and Radical Photocrosslinking

This work involves the synthesis of hybrid oligomers based on the epoxy methacrylate resin. The EA resin was obtained by the modification of industrial-grade bisphenol A-based epoxy resin and methacrylic acid has been synthesized in order to develop multifunctional resins comprising both epoxide group and reactive, terminal unsaturation. Owing to the presence of both epoxy and double carbon–carbon pendant groups, the reaction product exhibits photocrosslinking via two distinct mechanisms: (i) cationic ring-opening polymerization and (ii) free radical polymerization. Monitoring of EA synthesis reactions over time using PAVs, MAAC and NV parameters, and the FT-IR method reveals that esterification reactions proceed faster at the start, exhibiting over 40% of conversion within the initial 60 min, which can be associated with a relatively high concentration of reactive sites and low viscosity of the reaction mixture at the initial reaction stage. With the further increase in the reaction time, the reaction rate tends to decrease. The control of the EA synthesis process can guide how to adjust reactions to obtain EAs with desired characteristics. Based on obtained values, one can state that the optimum synthesis time of about 4–5 h should be adopted to prepare EAs having both epoxy groups and unsaturated double bonds. The structure of the obtained EA was confirmed by FT-IR and NMR methods, as well as the determination of partial acid value and epoxy equivalent. Samples at various stages of synthesis were cured with UV radiation in order to study the kinetics of the process according to cationic and radical polymerization determined via photo-differential scanning calorimetry (photo-DSC) and real-time infrared spectroscopy (RT-IR) and then the properties of the cured coatings were tested. It turned out that the cationic polymerization was slower with a lower conversion of the photoreactive groups, as compared to the radical polymerization. All the obtained EA coatings were characterized by good properties of cured coatings and can be successfully used in the coating-forming sector.     

Steric hindrance effects on dielectric relaxation and polymerization kinetics of a monoamine–triepoxide mixture,thermochemistry, and diffusion control

Calorimetry and dielectric relaxation spectroscopy during the growth of a polymer network in the stoichiometric mixture of a triepoxide with 4-chloroaniline have been performed in separate experiments to investigate the increase in the relaxation time with the number of covalent bonds. A comparison with the corresponding study of triepoxide–aniline and triepoxide–3-chloroaniline mixtures shows that steric hindrance of the amine group by chlorine slows the molecular dynamics and the relaxation time of the state containing a fixed number of bonds. The polymerization kinetics measured during ramp heating does not yield a reliable activation energy. A recent empirical relation between the relaxation time and the extent of polymerization, and the condition for the onset of diffusion-control kinetics have been examined using the data for these three polymerizing mixtures. The results show substantial deviations from the empirical relation and appear to conflict with our basic understanding of the polymerization process. It is shown mathematically that features attributed to the onset of diffusion-controlled kinetics can arise from thermochemical behavior alone, without reference to the molecular dynamics. An earlier theory for the change in the kinetics of an addition reaction from mass control to diffusion control has been considered, and is seen as relevant to the polymerization reactions. It is argued that the dielectric relaxation rate does not directly indicate the chemical reaction rate because the reorientational motion of the dipolar entities may not be coupled to the rotational and translational diffusion that brings the sterically hindered chemically reacting sites together. © 1998 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 36: 2703–2716, 1998     

Kinetic gelation predictions of species aggregation in tetrafunctional monomer polymerizations

During the polymerization of tetrafunctional monomers, a heterogeneous distribution of species exists throughout the reaction mixture and dramatically complicates the network structural evolution. This work attempts to quantify this heterogeneity using kinetic gelation simulation predictions of a defining parameter called the heterogeneity index. The heterogeneity index directly measures how heterogeneous the polymerization is with respect to interactions of like species or pairs of species. Examples of the species are polymer segments, monomeric double bonds, pendant double bonds, initiator molecules, radicals, and free volume. By implementing this index, it is clear that the heterogeneity in the polymer network dramatically changes as a function of conversion and polymerization conditions. In particular, microgel formation and monomer pooling were characterized and quantified with the heterogeneity index. In addition to characterizing the structural heterogeneity, the influence of the heterogeneity on the initiator efficiency and trapping of free radicals was also studied and qualitatively compared to experimentally observed behavior. ©1995 John Wiley & Sons, Inc.     

Preparation of a novel polymer monolith with functional polymer brushes by two‐step atom‐transfer radical polymerization for trypsin immobilization

Novel porous polymer monoliths grafted with poly{oligo[(ethylene glycol) methacrylate]‐co‐glycidyl methacrylate} brushes were fabricated via two‐step atom‐transfer radical polymerization and used as a trypsin‐based reactor in a continuous flow system. This is the first time that atom‐transfer radical polymerization technique was utilized to design and construct polymer monolith bioreactor. The prepared monoliths possessed excellent permeability, providing fast mass transfer for enzymatic reaction. More importantly, surface properties, which were modulated via surface‐initiated atom‐transfer radical polymerization, were found to have a great effect on bioreactor activities based on Michaelis–Menten studies. Furthermore, three model proteins were digested by the monolith bioreactor to a larger degree within dramatically reduced time (50 s), about 900 times faster than that by free trypsin (12 h). The proposed method provided a platform to prepare porous monoliths with desired surface properties for immobilizing various enzymes.     

Graft and block copolymers with polysiloxane and vinyl polymer segments

A convenient new process to make silicone/organic block and graft copolymers has been recently demonstrated. This dual copolymerization process combines conventional condensation polymerization of the siloxane segments with free radical polymerization of the organic vinyl polymer segments. The copolymerization process is relatively simple and economical compared with other copolymerization techniques as it uses commonly available starting materials and available process equipment. Silicone segments containing alkene side chains or end-groups are prepared in the usual way by polycondensation using an acid or base catalyst. The double bonds of the alkene groups are oxidized to carbonyls which are then used to initiate vinyl monomer polymerization and link the siloxane with the vinyl segments. This initiation step is based on a redox system of copper^(II) salts which generates free radicals on the alpha carbons next to the carbonyl groups. This copolymerization process is relatively fast and proceeds at high yields.     

The effect of additives on the polymerization of methyl methacrylate. tris(1,2-dibromo-propyl)phosphate

The effect of the additive, Tris(1,2-dibromopropyl)phosphate, on the kinetics of free radical polymerization of methyl methacrylate is studied. No marked differences were observed in the homopolymerization despite the reported effect of this additive on the mechanical properties of the resulting polymer. It was concluded that the additive was a multifunctional transfer agent producing linear and branched polymer molecules. Several model transfer agents have been studied to confirm these conclusions. H-NMR spectra of the polymer confirm that there is no change in the stereoregularity of the polymer prepared in the presence of this additive, and no copolymerization of the phosphate unit.     

Tuning material properties of covalent adaptable networks containing boronate-TetraAzaADamantane bonds through systematic variation in electron density of ring substituents

An outstanding challenge in modern society remains how to make crosslinked polymers (thermosets) more recyclable. A breakthrough solution to this challenge has been the introduction of dynamic covalent bonds in polymer networks, yielding covalent adaptable networks (CANs). Ongoing research is focused on finding new suitable dynamic covalent chemistries and on how to tune the material properties of CANs derived from these new chemistries. Here, we first compare two different dynamic boronic acid based covalent adaptable networks, namely, a conventional boronate-diol and a novel boronate-TetraAzaADamantane (TAAD) system. We show that incorporating boronate-TAAD bonds in networks results in stiffer materials, as seen in a slower relaxation and higher shear and storage moduli. This offers access to more mechanically robust boronate-based materials, compared to conventional boronate-based gels. Next, we investigate the effect of molecular tuning via the electron density of meta-positioned ring substituents on the macroscopic material properties for the boronate-TAAD network. By comparing relaxation experiments on materials with different substituents, we show that the macroscopic network relaxation can be tuned through the Hammett parameter of the meta-substituent and the activation energy of the boronate-TAAD exchange. This enables subtle control over the (dynamic) material properties of these novel, robust boronate-based networks.     

Photocrosslinking of silicones. VI. Photocrosslinking kinetics of silicone acrylates and methacrylates

The photoinduced radical crosslinking of silicones containing pendant acrylate and methacrylate groups has been investigated with calorimetric and ESR measurements. Oxygen very strongly influences this process, which leads to a prolonged induction period and a pseudo first-order termination reaction between polymer radicals and oxygen. Kinetically, such reaction steps are responsible for light intensity and monomer exponents, both of unity. In the absence of oxygen, second-order processes take place between polymer and primary radicals. The results of conversion-time and reaction-rate time measurements using stationary irradiations and postpolymerization experiments agree with the corresponding kinetic expressions. Long-lived polymer radicals and their decay have also been determined with ESR techniques. Long-chain spacer groups, which link the unsaturated ester moiety at the silicone backbone, increase the crosslinking rate. The final conversions of the double bonds exceed high values in each case. © 1992 John Wiley & Sons, Inc.     

不饱和端基超支化聚合物/丙烯酸酯共聚乳液的研究

利用Si—H加成反应制得了以CC为端基的超支化含硅聚合物,并将其与丙烯酸酯类单体进行乳液共聚,对聚合反应机理及所得聚合物的性能进行了测试分析.结果表明,含有大量CC端基的超支化含硅聚合物能与丙烯酸酯类单体稳定聚合,制得了平均粒径小于100nm高度交联的乳胶粒子.共聚物的红外光谱证实,超支化聚合物的不饱和端基已全部反应,形成了以超支化聚合物为多臂交联点的交联型乳胶粒子.随聚合体系中超支化聚合物用量的增加,乳液聚合反应速率增大,乳胶粒粒径减小,共聚物热稳定性显著提高.     

Variation in the chromatographic,material, and chemical characteristics of methacrylate‐based polymer monoliths during photoinitiated low‐temperature polymerization

Both the separation behavior and the structure of a polymer monolith column depends on both the reaction solution composition and the polymerization conditions. In photoinitiated low‐temperature polymerization, polymerization temperature, irradiation intensity, and polymerization time were key factors to control the monolith characteristics. In this study, the effect of polymerization time on the chromatographic, material, and chemical characteristics of poly(butyl methacrylate‐co‐ethylene dimethacrylate) monoliths was studied using pyrolysis‐gas chromatography, Raman spectroscopy, inverse size exclusion chromatography, scanning electron microscopy, and chromatographic methods. Both butyl methacrylate and ethylene dimethacrylate monomers were incorporated into the monolith as the polymerization time increased, and it resulted in increases in both the flow resistance (decrease in both permeability and total/through pore porosities) and retention factors. The longer polymerization time led to lower relative amounts of free methacrylate functional groups in the monolith, i.e. cross‐linking was enhanced. The increase of the polymerization time from 8 to 12 min significantly reduced the separation efficiency for the retained analyte, whereas an increase in the fraction of the mesoporosity was observed.