Early Stage Of Polymerization Research Articles

Study of the polymerization of silicic acid in aqueous solution by trimethylsilylation—gas chromatography

The effects of pH, concentration of monosilicic acid and temperature on the formation of low-molecular-weight silicic acid species in the early stages of polymerization were studied by trimethylsilylation—gas chromatography (TMS—GC). The change with time in the distribution of silicic acid species up to the hexamer was measured. The results obtained by TMS—GC are compared with those obtained by colorimetry. In solutions of initial monosilicic acid concentration of 600 ppm SiO 2 at pH 1.8, 20°C and at pH 8.5, 90°C, it was found that a temporary equilibrium is set up among ▪, ▪ and ▪ during the induction period. On the other hand, for 2500 and 5000 ppm SiO 2 solutions at pH 1.8, 20°C, higher-molecular-weight silicic acid species than ▪ were formed during the induction period, and the distribution of these species changed with time. All of the silicic acid species formed during the induction period, and the distribution of these species changed with time. All of the silicic acid species formed during the induction period were determined by colorimetry.

Laminar tube flow with a thermosetting polymerization

AbstractTwo models describing the laminar flow of a polymerizing liquid through a tube have been developed and tested experimentally. One model is a full finite difference solution of the balance equations. The other is an approximate analytical solution which assumes that flow ceases after viscosity increases about tenfold. The models are compared to two experimental cases: (1) the pressure rise needed to keep the flow rate through the tube constant and (2) the flow rate decrease when pressure at the tube entrance is held constant. The finite difference model is more accurate in the early stages of polymerization while the approximate analytical model is more accurate at long times. The models have application to runner flow in reaction injection molding, to nozzles in thermoset molding, to thermoset dispensing equipment and to continuous reactive polymer processes in general.

Emulsifier‐free emulsion polymerization of tetrafluoroethylene by radiation. I. Effects of reaction conditions on the polymerization rate and polymer molecular weight

AbstractThe radiation‐induced emulsifier‐free emulsion polymerization of tetrafluoroethylene was carried out at an initial pressure of 2–25 kg/cm2, temperature of 30–110°C, and under a dose rate of 0.57 × 104−3.0 × 104 rad/hr. The rate of polymerization was shown to be proportional to 1.0 and 1.3 powers of the dose rate and initial pressure, respectively, and is maximal at about 70°C. The molecular weight of polytetrafluoroethylene (PTFE) lies in the range of 105−106, increases with reaction time in the early stage of polymerization, and is maximal at 70°C but is almost independent of the dose rate. An interesting discovery is that PTFE, a hydrophobic polymer, forms as a stable latex in the absence of emulsifier. When PTFE latex coagulates during polymerization under certain conditions, the polymerization rate decreases, probably because polymerization proceeds mainly on the polymer particle surface. The observed rate acceleration and successive increase in polymer molecular weight may be due to slow termination of propagating radicals in the rigid PTFE particles.

Oligomer separations by gradient elution high-performance liquid chromatography

Summary Gradient elution high-performance liquid chromatography (HPLC) on chemically modified silica is very suitable for both the qualitative and quantitative analysis of oligomeric mixture, as has been demonstrated for low-molecular-weight resins, pre-polymers and extracts obtained from high polymers and in studying the kinetics of the early stages of polymerization and polycondensation reactions. Examples are given of oligomer separations with epoxy resins, novolak resins, poly-(2,6-diphenyl- p -phenylene oxide). (Tenax), poly(ethylene terephthalate) and poly(ethylene oxide) derivatives. All of these separations easily permit quantification, as has been demonstrated for ethoxylated octylphenol, provided that strict standardization is maintained throughout the analysis. Coefficients of variation of the peak-area measurements of the 19 oligomers observed in this sample were low (1–4%); the coefficients of variation of the retention times ranged from 0.01 to 0.3%. Using commercially available chemically modified column packing materials, the resolution in the gradient elution HPLC of oligomers is adversely affected by size exclusion and sample solubility.

In vitro assembly of dogfish brain tubulin and the induction of coiled ribbon polymers by calcium

Dogfish brain tubulin exhibits properties which differ from mammalian and chick brain tubulin. Polymerization of dogfish brain tubulin occurs optimally between 18 and 21 °C. The high molecular weight proteins which typically co-purify with tubulin are nearly absent as shown by SDS-polyacrylamide gel electrophoresis. A “dynein-like” protein occasionally co-purifies with dogfish brain tubulin, but its absence does not affect polymerization. At 0 °C, tubulin exists almost exclusively in the form of 6S dimers as revealed by analytical ultracentrifugation. Samples negatively stained and observed in the electron microscope have insignificant numbers of ring and spiral structures present. In some preparations, short thin filaments, approx. 200 nm in length, are seen. During polymerization, large numbers of coiled sheet polymers appear. These coiled ribbons are present throughout the early stages of polymerization, but not after polymerization reaches a plateau. The helical ribbons have an average width of 35 nm and contain approx. 8 protofilaments. The pitch angle of the helix is 33 ° and two or three turns are usually seen. The addition of 10 mM CaCl 2 to a polymerized or polymerizing solution of tubulin induces the formation of rings which transform into stable coiled sheet polymers. Some of the coiled sheets form tubules when adjacent gyres of the spirals join together. The diameter of these “macrotubules” range between 50 and 100 nm. The data suggest that ring structures are not obligate intermediates of polymerization and bring into question the role of the microtubule-associated proteins.

The polymerization of N-vinylcarbazole in the presence of carbon black

In order to obtain more detailed information on the mechanism of the polymerization of N-vinyl-carbazole (N-VC) in the presence of carbon black, a comparison of the rates of conversion under various conditions was made and the following results were obtained. The phenolic hydroxyl groups on the surface of carbon black were found to have an ability to initiate the polymerization, and an increase in dielectric constant of the solvent increased the rate of polymerization. Using the mixture of N-VC and comonomers such as styrene or methyl methacrylate, we found that styrene gives a copolymer with N-VC, while methyl methacrylate gives no copolymer during the early stage of polymerization. The phenomena observed here indicate that the nature of polymerization of N-VC initiated by carbon black is cationic.

Particle morphology in the early stages of radiation‐induced heterophase polymerization of vinyl chloride

AbstractInvestigations of the particle morphology of poly(vinyl chloride) produced under quiescent conditions during radiation‐induced bulk polymerization over the temperature range −30 to 70°C were carried out. The observations were mainly confined to the early stages of polymerization. For polymerization temperatures below about 20°C, the systems remain predominantly homogeneous during the entire polymerization and the polymer particles increase in size linearly with conversion. At higher temperatures the polymer particles rapidly settle and become cemented together. The findings are discussed in the light of the kinetic data on vinyl chloride polymerization, and a process of particle formation and growth, resembling that recently proposed by Fitch for emulsion systems, was formulated. Primary particles are initially formed by the coiling up of single macromolecules or single macroradicals and, subsequently, they increase in size by sweeping up growing free radicals from the liquid monomer phase. The free radicals which escape capture give rise to new primary particles, but their number progressively decreases as the number of the dispersed particles increases. Simultaneously, the polymer particles undergo flocculation which in a short time results in the formation of large agglomerates. As the volume of the resulting agglomerates increases, the flocculation rate decreases and, eventually, becomes so low that the flocculation does not proceed further. At low temperatures the flocculation almost ceases when the agglomerates are still small enough for sedimentation to occur only very slowly. However, this is not the case at higher temperatures. The addition of substances such as alcohols, brings about a reduction in the flocculation rate and, hence, in the size of the agglomerates formed at the end of the flocculation process. In this way, one can also obtain at high temperatures agglomerates of small sizes which remain dispersed for a long time.

Branching in the base catalyzed hydrogen transfer polymerization of acrylamide in n-methyl-2-pyrrolidone at 100°C

The structure of poly(β-alanines) prepared by hydrogen transfer polymerization of acrylamide in N-methyl-2-pyrrolidone, has been investigated by end-group analysis and gas-chromatographic separation of hydrolysis products. Evidence is given that β,β′-iminodipropionic acid residues are present in the polymer chains as branching units, their proportion being greater in oligomers at the early stage of polymerization and decreasing with the stepwise growth of the polymer. A mechanism is proposed for the formation and elimination of these branching units.

Formation and structure of PVC particles

AbstractParticles present in commercial suspension and mass PVC polymers possess a wide range of sizes and structures. This paper concentrates on the influence of the processes on the formation and morphology of these particles.Suspension polymer particles are usually fairly irregular in shape and have an outer “skin” which often extends over the entire surface of the particle and this skin is frequently ruptured. Studies have indicated that the outer skin is formed during the early stages of polymerisation. Suspension PVC particles may have varying degrees of internal porosity which often consist of two types of pore, namely small interstitial voids between sub‐particles or “microgranules” and much larger voids which are often lined with skin. The size and structure of these particles is dependent on agitation conditions in the reactor, colloid stability and the interfacial tension of the vinyl chloride/aqueous phase system.Mass PVC is produced commercially by a two stage process. In many respects, the polymer produced is similar to suspension PVC but there are important morphological differences. Mass polymer has no “skin”, a microgranular structure persists from the particle surfaces to their interiors, and the voids, which constitute the internal porosity, are of the small type of interstices between microgranules. The particle number appears to be dependent on conditions prevailing in the first stage of the polymerisation while the final particle morphology is also influenced by the conditions in the second stage of the process.

Study of polymerizing styrene through depolarized light scattering

Abstract The thermal polymerization of clean styrene has been studied through Rayleigh-Brillouin light scattering. The frequency shifts, Rayleigh to Brillouin intensity ratios, Rayleigh depolarization ratios, and depolarized intensities were measured as the polymerization proceeded to completion at 90°C. The depolarized intensities decreased and the frequency shifts increased smoothly from the monomer to the polymer values. The Vv intensities and Rayleigh to Brillouin intensity ratios increase dramatically during the first stages of polymerization then decrease systematically to their final values. There is a large increase in the Rayleigh to Brillouin intensity ratio from the monomer to the final polymer value. The vertical depolarization ratio pv and the horizontal depolarization ratio pV were found to be respectively 0.4 and 1 for the polymer. Our observations are explained in terms of light being scattered from concentration fluctuations in the early stages of polymerization and from spherically symme...

The molecular structure of polycaproamides formed under the conditions of anionic polymerization of caprolactam

A study has been made of the viscosity characteristics of solutions of polycaproamides prepared by anionic polymerization of ϵ-caprolactam in the presence of acylated amide activators of different functionality (mono-, tri- and polyfunctional). It was found that [η] of these polymers shows a marked dependence on the functionality of the activator used. In the early stages of polymerization the degree of branching of the polymers is mainly dependent on the functionality of the activator, then in addition to polymerization reactions resulting in propagation of the main chain of the ϵ-caprolactam polymer, additional branching processes occur, which lead to formation of randomly branched macromolecules. The branching parameters (the number of branch points, the molecular weight of the branches and its distribution among fractions) of the polymers have been calculated.

Crystallization of polypeptides in the course of polymerization, 5. Effect of the steric hindrance on the crystal growth by the side chains

AbstractIn order to examine the effect of the steric hindrance by the polypeptide side chains on the growth mechanism of polypeptide crystals in the course of polymerization, we studied kinetics of the heterogeneous polymerization of L‐valine N‐carboxy anhydride (NCA), L‐isoleucine NCA, and L‐leucine NCA initiated by butylamine in acetonitrile and the structures and morphologies of the resultant polymers. In the early stages of polymerization, oligomers formed crystallized into thin ribbon‐like crystals with the antiparallel β‐conformation. The molecular arrangements in the crystals were studied by electron diffractions. In the later stages, the grown chains of poly(L‐valine) and poly(L‐isoleucine) continued to take the β‐structure and their active ends were occluded in the crystals formed, which resulted in the levelling off of the conversion at a low value. On the other hand, poly(L‐leucine) seemed to give the extended chain crystal, which made the conversion very high. This can not be accounted for without assuming the formation of β‐helical chains onto the β‐skeleton crystals formed in the early stages of polymerization as in the case of poly(L‐alanine) reported previously.

Crystallization of polypeptides in the course of polymerization, 6. Effect of the heteroatom attached to the β‐carbon on the crystal growth

AbstractIn order to examine the growth mechanisms of polypeptides with a heteroatom, S, on the β‐ and γ‐carbons which give the α‐conformation and the α‐helical conformation, resp., in the course of a heterogeneous polymerization, we have studied kinetics of the heterogeneous polymerization of S‐methyl‐L‐cysteine N‐carboxy anhydride (NCA), S‐benzyloxycarbonyl‐L‐cysteine NCA and L‐methionine NCA initiated by butylamine in acetonitrile and the morphologies of the resultant polymers. As was anticipated, it has been verified that poly‐(S‐substituted‐L‐cysteines), which take only the β‐structure as the ordered form, gave the chain‐folded crystals. In all the cases studied, long lath‐like crystals formed in the early stages of polymerization thickened into round rod‐like fibers as the polymerization proceeded. A possible model was proposed for the growth mechanism of these polymer crystals, taking into account the cross‐β‐structure. It has been revealed that poly(L‐methionine) with the α‐helical structure gave the extended chain crystals.

Kinetic Study on the Ring-Opening Polymerization of Tetrahydrofuran by Pyrosulfuryl Chloride Initiator

Abstract This paper deals with a kinetic study of the ring-opening polymerization of tetrahydrofuran (THF) initiated by pyrosulfuryl chloride (PSC). The kinetic analysis was based on the determination of the concentration of propagating species, [P*], by the phenoxyl end-capping method. The rate constants of the three elementary processes, propagation (kp), initiation (ki), and termination (kt), were determined. Activation parameters for the propagation were; ΔEp\eweq=12 kcal/mol, and Ap=7.6×106 l/mol·sec. From the kp values and the NMR study of the THF–PSC reaction, it is concluded that the propagation proceeds via the bis-oxonium species 5b. The ester type species 5a may be involved at a very early stage of polymerization. However, its contribution was quite small throughout the polymerization. The THF polymerization initiated by PSC was characterized by the fast initiation. The mechanism of termination was also examined. The THF polymerization by trifluoromethanesulfonic anhydride was also studied kinetically, which was characterized by a living propagation by bis-oxonium species.

чyвcтвитeльнocть к cпeцифичecким ингибитopaм paннич и пoзднич cтaдии caмocбopки фибpинa

Fibrinogen and its degradation products - specific inhibitors of fibrin polymerization, were added to dissolved fibrin prior to or during polymerization. Inhibitor additions were timed so as to cover the whole period of polymerization up to the outset of clotting. The results clearly demonstrated that when the addition delay was gradually increased the inhibitory effect decreased much sharper than expected, i.e. the actual retardation of clotting proved less than the value calculated on the admission that all the polymerization stages were equally susceptible. (In the Table I figures represent seconds of clotting retardation; column 3 - found, column 4 - calculated). At the latest polymerization stages the inhibitory effect vanished altogether. Both of the manifestations of the inhibitory activity, prolonged clotting time and deminished gel turbidity, subsided in parallel as the moment of inhibitor introduction was moving towards the moment of clotting. FIG. 1 shows turbidity increase during the clotting of two fibrin monomer preparations one of which (A) had been preliminarily activated (14); the upper curve corresponds to the inhibitor-free controle, the lowest curve - to the sample containing the inhibitor from the very beginning of the polymerization, the intermediate curve - a sample to which the inhibitor was added with a delay equal to 50% of the controle clotting time. Fibrinogen labelled with fluoresceineisothiocyanate was found to be incorporated into fibrin clot more readily at early polymerization stages. Electron microscopic examination revealed striking structural defects in fibrin fibres whose formation was influenced by the inhibitor throughout the polymerization process. If added at later stages the inhibitor caused little or no structural damage (FIG. 2–5). Thus, the susceptibility to specific inhibitors disappeares to a great extent during the early polymerization stages. In contrast with the specific inhibitors other inhibitors, like urea or hexamethylene glycol, are fully effective even if applied just before clotting would began. This striking difference suggest that the early and late polymerization stages differ from each other in respect to molecular mechanisms involved.

Studies on polymerization of N‐vinylcarbazole in the presence of some hydrogen halides

AbstractStudies on N‐vinylcarbazole polymerization were carried out in the presence of HF, HCl, HBr, and HJ using a variety of solvents. It was found that in the CCl4 solvent, each of the hydrogen halides cause polymerization of N‐vinylcarbazole, the obtained polymer including equimolar proportions of hydrogen halide and of N‐vinylcarbazole.To determine the influence of solvent polarity, some studies on the polymerization of N‐vinylcarbazole influenced by HCl were carried out in the following solvents: carbon tetrachloride, acetone, and methanol. A pronounced contribution of the solvent to the polymerization course was found. A polymerizate including a small proportion of the complex‐bonded HCl was obtained when using acetone or methanol solvent.Irrespective of the nature of the solvent used, the appearance of a green color was observed in all instances; hereafter the solution turned brown accompanied by the polymer precipitation.The polymerization proceeds without any disturbances in the presence of some species that capture the radicals, this being evidence for the ionic nature of the mechanism.Based on the UV and ESR spectra analyses, it was found that some change‐transfer complexes are formed during polymerization. The result obtained make us accept the following mechanism of N‐vinylpolymerization in the presence of hydrogen halides, depending on the reaction medium.Based on the results given, the following conclusions referring to the N‐vinylcarbazole polymerization process in the presence of some hydrogen halides can be drawn. In the early stage of polymerization of N‐vinylcarbazole, the initiation by means of HX occurs and hereafter the polymer is formed. Then, in a nonpolar medium, a charge‐transfer complex of the polymer with hydrogen halide is formed. On the other hand, in a polar medium, this complex cannot be formed.

Radiation‐induced postpolymerization of trioxane in the solid state. V. Studies on copolymer composition

AbstractStudies on the composition of copolymers obtained by the radiation‐induced solid‐state postpolymerization of trioxane with 1,3‐dioxolane have been carried out. Gas‐chromatographic analysis of the reaction mixtures showed that most of the 1,3‐dioxolane disappears rapidly from the reaction system in an early stage of polymerization, and that the fraction of ethylene oxide units in the copolymer chain [E] decreases markedly with increasing polymer yield. This finding was confirmed by NMR spectra of the copolymer. DSC thermograms of the copolymer indicated that the relationship between the melting point and the average composition of copolymers prepared in this study differed from that found for copolymers in which comonomer units are distributed statistically in the polymer chain. It was suggested that the copolymer formed by the radiation‐induced solid‐state postpolymerization of trioxane–1,3‐dioxolane is characterized by a heterogeneous distribution of ethylene oxide units in the copolymer chain. It was also found that, in the radiation‐induced solid‐state postpolymerization of trioxane–1,3‐dioxolane, the amount of tetraoxane formation increased linearly with increasing polymer yield. Although it is extremely small compared with that obtained in solution polymerization, it is slightly larger in the trioxane–1,3‐dioxolane system than in the trioxane system.

Polymerization of 2-Oxazolines. II. Kinetics of the Cationic Polymerization of 2-Phenyl-2-oxazoline Initiated by Oxazolinium Perchlorate in N, N-Dimethylacetamide Solution

Abstract The solution polymerization of 2-phenyl-2-oxazoline in N, N-dimethylacetamide media was carried out at 120-150°C with the use of the oxazolinium salt of monomer and perchloric acid as an initiator. A marked acceleration in rate was observed in the early stage of polymerization. After the period of acceleration the polymerization rate and the moles of polymer chains were shown to remain constant, whereas the number-average degree of polymerization increased almost proportionally with an increase in the degree of conversion. The kinetic discussion, divided into two stages, gave the following results: an early stage of polymerization with slow initiation where the moles of the active propagating species increased, and a later stage with a stationary state where the moles of the active propagating species remained constant and the growth of polymer chains proceeded. The kinetics was reformulated as a function of the differential monomer concentration. The simulation of the kinetics with the use of th...

Temperature effects in γ‐initiated polymerization of styrene. II

AbstractExperimental data are presented for the γ‐initiated polymerization of commercial styrene at a series of temperatures above ambient. Examination of the early stages of polymerization (up to 10% conversion) has led to the following conclusions. For this system, there exists a critical temperature (109°C) above which the rate of polymerization is independent of dose rate, over a wide range of γ‐intensities. This dose rate independence is ascribed to a “limiting rate of initiation,” characteristic of the intensity range. A consequence of this is that at a given temperature above the critical temperature the degree of polymerization is also dose rate‐independent. The above phenomena can be expected in any vinyl monomer where the monomer is fairly active and produces relatively stable radicals. Experimental procedure is described, and kinetic analysis presented to substantiate the conclusions.

Acid‐catalyzed polymerization of 1,6‐anhydro‐β‐D‐glucopyranose

AbstractA number of 1,6‐anhydrides were polymerized in the melt at 115°C by use of monochloroacetic acid as catalyst. In the early stages of polymerization (up to 40–50% monomer consumed), each monomer was found to disappear by a first‐order rate process. The 1,6‐anhydrides investigated and their relative rates of polymerization were: 1,6‐anhydro‐2‐O‐methyl‐β‐D‐glucopyranose, 1.0; 1,6‐anhydro‐3,4‐di‐O‐methyl‐β‐D‐glucopyranose, 1.4; 1,6‐anhydro‐2‐O‐methyl‐β‐D‐galactopyranose, 2.3; 1,6‐anhydro‐3‐O‐methyl‐β‐D‐glucopyranose, 2.6; 1,6‐anhydro‐4‐O‐methyl‐β‐D‐glucopyranose, 6.3; 1,6‐anhydro‐4‐O‐(β‐D‐glucopyranosyl) β‐D‐glucopyranose, 9.0; 1,6‐anhydro‐β‐D‐galactopyranose, 17; 1,6‐anhydro‐β‐D‐glucopyranose, 37; 1,6‐anhydro‐β‐D‐mannopyranose, 91; and 1,6‐anhydro‐2‐deoxy‐β‐D‐arabino‐hexopyranose, 240. The effect of substitution on the rate of polymerization suggests this reaction is mechanistically related to the acid hydrolysis of pyranosides. The results suggest that polymerization proceeds in two stages: (1) an initial build‐up of dimer followed by (2) a slower growth to higher molecular weight material.