Emulsion polymerization of ethylene. III. Factors affecting the stability of polyethylene latexes

A semiquantitative method for assessing the amount of visible solid matter in polyethylene latexes is described. As judged by this method and by the presence of particles larger than 50 μ, the stability of the latexes was related to (1) the type and concentration of post-emulsifier added to the latex, (2) the average size of the polymer particles, and (3) the concentration of solids. Generally, the appearance was better when the latexes had a low (30%) concentration of solids, a large (800 A.) average particle diameter, and enough post-emulsifier to cover most of the polymer surface. Specific samples, however, having a high (36%) concentration of solids and a small (300 A.) average particle diameter also showed good storage stability. According to tests on selected latexes, good resistance to coagulation by mechanical shear was obtained only if the surface of the polymer was completely covered with emulsifier. When polyethoxylated alkylphenols were used as post-emulsifiers, an inverse relation appeared to exist between latex stability and average number of ethylene oxide units per emulsifier molecule. Moreover, the addition of each ethylene oxide group increased the apparent area of the emulsifier molecule by about 4 A.²     

Epoxy polymers. III. Factors affecting the cure

The rate of cure of epoxy polymers appears to be diffusion-controlled, and after gelation is dependent upon the capillary dimensions in a floccular matrix. The floccule dimensions and packing determine the size of the interfloccular capillaries and are inversely related to the cure temperature. The degree of cure is inversely related to the pregelation cure temperature (thermal history, including preheat) and directly related to the total cure time.     

Polymerizations of ethylene and propylene initiated by milled metallic oxides. II. Characterizations of the mechanochemically produced polymers

Polyethylene was mechanochemically produced by milling of alumina powder at room temperature in the presence of ethylene monomer. Nearly 50% of the produced polyethylene was chemically bonded with the matrix of the alumina. The other 50% of the polymer was extracted by the organic solvents. The polyethylene extracted by the hot n-heptane was characterized as having a structure similar to that of the branched polyethylene of low density, and the toluene extracted polyethylene had a structure similar to that of the high density polyethylene. The molecular weights of the mechanochemically produced polyethylene were found to distribute from 10² to 10⁶ by gel permeation chromatography. The weight average molecular weight was estimated as 260,000 after the 3 days milling. Mechanochemical polymerization of ethylene was also demonstrated by milling of silica in the presence of ethylene monomer. Polymerization of propylene by milling of alumina under propylene atmosphere was performed. The obtained polymer was found to be an atactic by IR measurement and the molecular weight of the extracted product was determined as ? 400 by the vapor pressure osmometer.     

Radiation-induced polymerization of ethylene in pilot plant. III. Heavy-phase recycling process

Radiation-induced polymerization of ethylene using aqueous tert-butyl alcohol as medium was carried out in a large-scale pilot plant with a 50-liter central source-type reactor at a pressure of 105 to 395 kg/cm², temperature of 30° to 80°C, mean dose rate of 4.5 × 10⁴ to 1.9 × 10⁵ rads/hr, ethylene feed rate of 5.5 to 23.5 kg/hr, and medium feed rate of 21 to 102 l./hr. The space–time yield and molecular weight of the polymer were in the range of 4.7 to 16.8 g/l.-hr and 1.3 × 10⁴ to 8.9 × 10⁴, respectively. The space–time yield and molecular weight increased with mean residence time at 30°C, whereas at 80°C they became almost independent of the time. The space–time yield increased with pressure and dose rate, slightly decreased with temperature, and was maximum at ethylene molar fraction of 0.5. The polymer molecular weight increased with pressure and ethylene molar fraction, and decreased with dose rate and temperature. The total amount of deposited polymer on the reactor wall, source case wall, and scraping blades was usually less than 1 kg, which was negligibly small for the analysis of polymerization. Continuous discharge of the polymer slurry and production of fine-powder polyethylene were successfully carried out. In the central source-type reactor, a dose rate of 1.9 × 10⁵ rads/hr was obtained with a ⁶⁰Co source of ca. 12 kCi.     

Polymerization mechanisms and molecular weight distributions. III. Gamma-radiation-initiated polymerization of methyl methacrylate

The termination mechanism in gamma-radiation-initiated polymerization of methyl methacrylate was investigated. The termination mechanism and the associated rate constants were determined by comparing the theoretical molecular weight distribution (MWD) and the experimental MWD, which was determined by gel permeation chromatography. Disproportionation occurs 1.2 times as frequently as combination at 30°C and 0.5 times as frequently at 0°C. The activation energy for disproportionation is 5.5 kcal/mole greater than that for combination. The rates of initiation were determined by a new method and were found to compare well with those reported in the literature. It is also suggested that it is necessary for the theoretical MWD to have the same shape as the experimental MWD before a mechanism can be authenticated.     

Polymerization of ethylene by n-butyl lithium

The polymerization of ethylene with butyl lithium activated with tetramethyl ethylene diamine (TMEDA) has been investigated, and the mechanism proposed by McCabe et al. substantially vindicated. The active initiating species is considered to be free monomeric butyl lithium, unchelated to TMEDA, and the mechanism of propagation of olefin insertion between the metal-carbon bond, probably involving an intermediate π-complex between olefin and metal alkyl.     

Preparation of multiphase block copolymers by redox polymerization process, 4. Polymerization of methyl methacrylate by the redox system Mn(III)-poly(ethylene glycol) containing azo groups

Redox polymerization of methyl methacrylate using Mn(III) with poly(ethylene glycol) having azo and hydroxy functions was carried out to yield ethylene glycolmethyl methacrylate block copolymers with labile azo linkages in the main chain. These prepolymers were used to initiate free-radical polymerization of styrene through thermal decomposition of the azo groups, resulting in the formation of multiblock copolymers. Successful blocking has been confirmed by fractional precipitation, a strong change in the molecular weight, and spectral measurements.     

Polymerization of ethylene oxide by the activated monomer mechanism

The Polymerization of ethylene oxide catalysed by protonic acids and proceeding via the activated monomer mechanism differs from the polymerizations of substituted epoxides like propylene oxide and epichlorohydrin. The kinetics of ethylene oxide polymerization were investigated and compared with the kinetics of model reactions, namely addition of oligomers of ethylene oxide to ethylene oxide. The mechanism of polymerization involves, besides the addition of monomer to the terminal hydroxyl groups, the addition to the polymer ether groups. This reaction does not take place for substituted oxiranes, most probably because of steric hindrance.     

Low-pressure polymerization of ethylene. II

This paper presents the kinetic study of polymerization of ethylene with VOCl₃ and aluminum alkyls such as Et₃Al and Et₂AlCl. The effect of various parameters like the [Al]/[V] ratio, catalyst concentration, reaction time, temperature, solvents, and additives on rate of the reaction, yield, and molecular weight is reported. Each of these parameters has a remarkable effect on the yield and the rate of polymerization for both catalyst systems. Triethylamine is found to increase the catalyst efficiency and the rate. It is also observed that aliphatic hydrocarbons acted as a better polymerization medium than did the aromatic ones.     

Factors affecting the nascent structure and morphology of polyethylene obtained by heterogeneous Ziegler-Natta catalysts: 1. Polymerization kinetics

Kinetic measurements were carried out to study the influence of polymerization conditions on the morphology and macroconformation of nascent polyethylene obtained with a heterogeneous $\text{TiCl}{}_3\text{Al}\text{(}\text{C}{}_2\text{H}{}_5\text{)}{}_3$ Ziegler-Natta catalyst. The polymerization of ethylene in a n-paraffin viscous medium was studied for very different conditions, such as polymerization temperature from 0° to 120°C, pressures of 1 and 10 atm and stirring speed of 10 and 1000 r.p.m. It was established by electron microscopy that new polymer chains originate due to formation of new surfaces by break-up of catalyst aggregates and also through crystal scission. The average size of polymer globules growing on the catalyst surface was of the order of 10⁸cm^?2. The same kinetic relationships are approximately obeyed when the polymerization is controlled by mass transfer of the monomer. The overall activation energies for the maximum polymerization rate, decay period and the stationary polymerization rate were: 8.4, 3.4 and 5.0 kcal/mol, respectively. Molecular weight measurements combined with polymerization rate determinations lead to the conclusion that the number of growing polymer chains increases with the polymerization temperature, being of the order of 10¹²cm^?2 at low temperature. This corresponds to a concentration of active sites of about 10⁴ per polymerization locus.     

Aspects of the chemistry of poly(ethylene terephthalate): 5. Polymerization of bis(hydroxyethyl)terephthalate by various metallic catalysts

Bis(hydroxyethyl)terephthalate (BHET) was polymerized to poly(ethylene terephthalate) (PET) in the presence of various metallic catalysts. The influence of the nature and concentration of these catalysts on the rate of polymerization has been investigated. The effect of the reaction temperature has also been studied. The order of decreasing catalytic influence of various metal ions, on the polymerization of BHET was found to be: Ti>Sn>Mn>Zn>Pb>No.     

Factors affecting polymerization of 2-methyl-5-vinylpyridine in poly(ethylene terephthalate) fibers using benzoyl peroxide as initiator

Polymerization of 2-methyl-5-vinylpyridine (MVP) in the presence of poly(ethylene terephthalate) fibers (PET) using benzoyl peroxide (BP) as initiator caused a substantial increase in the weight of fibers. The mechanism of this polymerization is believed to be grafting by vinyl addition to PET radical formed under the influence of BP. Increasing the BP concentration up to 4.26 × 10^?3 mole/l. causes a significant enhancement in grafting, while further increase brings about a marked fall in the graft yield. Increasing the MVP concentration up to 10% also improves significantly the graft yield, but the latter, particularly in the later stages of the reaction, shows lower values at higher MVP concentrations. Raising the reaction temperature from 65° to 95°C causes a significant enhancement in the rate of grafting, though the maximum graft yield obtained at 95°C is much lower than at 85°C. Incorporation of Cu²⁺ ion in the polymerization system enhances the graft yield outstandingly. The same holds true for Fe³⁺ and Li ions, but the enhancement is much less than for Cu²⁺ ion. Addition of acetic or oxalic acid to the reaction decreases the magnitude of grafting. The same situation is encountered when a water/solvent mixture is used as reaction medium. Solvents employed were methanol, ethanol, propanol, and butanol. Also studied was the polymerization reaction with respect to homopolymer, total conversion, and graft efficiency.     

Selective activation of metallic center in heterobinuclear cobalt and nickel complex in ethylene polymerization

Heterobinuclear cobalt and nickel complex {2-[2,6-R₂-C₆H₃NC(CH₃)-(CH₃)CN-(3,5-R₂′)C₆H₂-CH₂-(3′,5′-R₂)C₆H₂NC(CH₃)]-6-[2,6-R₂-C₆H₃NC(CH₃)] pyridine}CoCl₂NiBr₂ (R = isopropyl) (N₅CoNi) was prepared by reaction of pentadentate nitrogen ligand containing 2,6-bis(imino)-pyridine and α-diimine moieties with CoCl₂ and NiBr₂(DME) in turn. The complex was applied as catalyst for ethylene polymerization activated by AlEt₃, MMAO and AlEt₃/[PhMe₂NH] [B(C₆F₅)₄] respectively. The performance of the heterobinuclear complex in ethylene polymerization was compared with corresponding mononuclear complexes (α-diimine nickel bromide and 2,6-bis(imino)-pyridine cobalt chloride) and their equivalent mixture (binary complexes). When the complex N₅CoNi was activated by AlEt₃ or MMAO, its ethylene polymerization activity was lower than its control, the binary complexes. Both heterobinuclear complex and binary complex produced PE with bimodal molecular weight distribution. The amount of high-molecular-weight polyethylene produced by nickel center of N₅CoNi was less than the binary complexes, which reveals that productivity of nickel center of N₅CoNi is selectively suppressed. When the heterobinuclear complex N₅CoNi is activated by AlEt₃/[PhMe₂NH][B(C₆F₅)₄], the relative productivity of nickel center increased, although the total activity of catalyst decreased compared with AlEt₃ as cocatalyst. With respect to AlEt₃, [PhMe₂NH][B(C₆F₅)₄] can preferably activate nickel center of heterobinuclear complex. The results suggest that metal site in the heterobinuclear complex is selectively activated by cocatalyst.     

乳液聚合中乳胶粒粒径大小及分布的影响因素

在乳液聚合中,乳胶粒的大小及分布对乳液的性能及其应用有很大的影响,同时也反映了乳液聚合反应进行的过程。本文综述了影响乳胶粒粒径大小及分布的各种因素,如聚合工艺、乳化剂、单体种类、聚合温度、引发剂等,并介绍了不同粒径乳液的性能及其应用。     

The kinetics of ethylene hydrogenation catalyzed by metallic palladium

The activity of Pd(111) for ethylene hydrogenation is measured using a high-pressure reactor incorporated into an ultrahigh vacuum chamber for temperatures between 300 and 475 K, ethylene pressures between 50 and 300 Torr and hydrogen pressures from 45 to 600 Torr. The reaction rate is found to be rapid with turnover frequencies up to 400 reactions/site/s (where rates are referenced to the atom site density on the (111) face of palladium). The measured activation energy is 35 kJ/mol. A hydrogen reaction order of 1.02 was found at a reaction temperature of 300 K and an ethylene pressure of 100 Torr, where the hydrogen reaction order was found to depend on temperature. A negative reaction order of –0.22 was found in ethylene pressure at a reaction temperature of 320 K and a hydrogen pressure of 100 Torr. The reaction rates are in good agreement with values obtained on silica-supported palladium and with other work on palladium single crystals.     

Polymerization of 2-allyl-1-methylenecyclohexane by the cyclic polymerization mechanism

2-Ally-1-methylenecyclohexane is a compound which is functionally capable of undergoing polymerization by the alternating intra-intermolecular propagation mechanism to produce poly[1,8-methylene[4.3.0] bicyclononane]. This monomer was synthesized and its polymerization through use of cationic and Ziegler-type initiators was studied. Synthesis of the monomer was accomplished by the following reaction sequence: (1) conversion of cyclohexanone to 2-allycyelohexanone by reaction wtih allyl bromide and sodium amide and (2) conversion of 2-allycyclohexanone to the desired monomer by reaction with the phosphorane derived from methyltriphenylphosphonium bromide. Polymerizaton was accomplished by use of boron trifluoride resulting in 44% conversion to polymer, of which 94% was soluble. Through use of infrared and nuclear magnetic resonance techniques, the soluble portion of the polymer was shown to contain 54% of bicyclic units and the remainder to be non-cyelized monomer units in which the residual unsaturation was composed predominantly of allyl groups.     

Polymerization of surface-active monomers. III. Polymer encapsulation of silica gel particles by aqueous polymerization of quaternary salt of dimethylaminoethyl methacrylate with lauryl bromide

Polymer encapsulation of silica gel particles (SiO₂) by aqueous, radical polymerization of a cationic, surface-active monomer, quaternary salt of dimethylaminoethyl methacrylate with lauryl bromide, in the presence of the solid was investigated. The polymerization gave the polymer encapsulating the solid particles (“C-polymer”), though accompanied by the formation of that suspended in form of latex (“L-polymer”). The proportion of C-polymer in the products increased with increasing the amount of SiO₂ at a constant monomer concentration and only C-polymer was formed under the conditions where the feed ratio of monomer to SiO₂ is about 0.13 or lower by weight. Increasing the monomer concentration in feed increased slightly the ratio of C-polymer to SiO₂. The results obtained here suggest that C-polymer is mainly formed through the polymerization of monomer adsorbed on the solid surface. An electron micrograph of the polymer-encapsulated SiO₂ revealed that the solid particles are uniformly encapsulated with the resulting polymer.     

Polymerization of ethylene by chromium acetylacetonate/methylaluminoxane catalyst system

Summary The present paper deals with polymerization of ethylene by chromium acetylacetonate - Cr(acac)₃ - activated by alkylaluminium, e.g. Al(C₂H₅)₃ or Al(i-C₅H₉)₃, or methylaluminoxane (MAO). The influence of polymerization parameters on catalyst performance, such as Al/Cr mole ratio, temperature, aging time, type of cocatalyst, was investigated. High activities were obtained only when MAO was the cocatalyst. The polymers were characterized by size exclusion chromatography (SEC) and differential scanning calorimetry (DSC) analyses. Received: 11 September 1997/Revised version: 5 January 1998/Accepted: 20 March 1998     

Polymerization of ethylene and propylene initiated by milled alumina powder

Generation of free radicals (mechano-radicals) by the milling of alumina powder at 77 K was demonstrated by ESR. After milling of alumina in the presence of ethylene (simultaneous milling) at 77 K, polyethylene-propagating radicals instead of the alumina mechano-radicals were detected by ESR. Also the contact of ethylene with the milled alumina converted alumina mechano-radicals into polyethylene propagating radicals at a temperature above the melting point of ethylene. The products extracted by hot toluene from the simultaneous milling were identified by IR to be polyethylene, and their molecular weights were roughly 10,000. The residues after the extraction were bonded with the alumina. Polypropylene was also produced by a similar method of milling of alumina in the presence of propylene. The obtained polyproylene was atactic, and its molecular weight was about 400.     

Ring-opening polymerization of activated cyclopropanes: polymerization of diethyl 1,1-cyclopropanedicarboxylate by metallic sodium

Summary Diethyl 1,1-cyclopropanedicarboxylate undergoes ring-opening polymerization under anionic conditions. If the cyclopropane is contaminated by diethyl malonate CH₂(COOEt)₂, polymerization can be initiated by metallic sodium. The mechanism of this initiation was found to involve an initial reduction of the malonate by sodium to give the salt (EtOOC)₂CH(^-) Na(⁺) which acts as the real initiator. Poly(diethyl 1,1-cyclopropane dicarboxylate) is soluble in halogenated solvents and was characterized by GPC, IR,¹H- and¹³C-NMR. Molecular weights are low to moderate (typically 10³–10⁴) and are compatible with the low monomer/initiator ratios used in these experiments.Part of this work was presented at the 1993 Spring National ACS Meeting: Penelle J, Clarebout G, Balikdjian I (1993) Polym. Prepr. (Am. Chem. Soc., Div. Polym. Chem.) 34(1): 473