Role of chain transfer in heterogeneous polymerization of ethylene

The role of chain transfer was studied for the radiation-induced polymerization of ethylene in precipitating media, namely n-butyl alcohol, tert-butyl alcohol and their mixtures. The affinities of those solvents for polyethylene are similar, but the chain-transfer coefficient of n-butyl alcohol is larger than that of tert-butyl alcohol. The polymerizations were carried out in a reactor of 100 ml under a pressure of 300 kg/cm², at 60°C, dose rate of 3.07 × 10⁴–1.75 × 10⁵ rad/hr in the presence of 50 ml of solvents. The polymerization in tert-butyl alcohol shows the kinetic behavior characteristic of a heterogeneous polymerization, such as rate acceleration, high dose rate dependence of polymerization rate, and low dose rate dependence of polymer molecular weight, whereas the polymerization in n-butyl alcohol does not exhibit such behavior and gives polymer having a molecular weight much lower than that of polymer obtained in tert-butyl alcohol. The polymer formed in tert-butyl alcohol exhibits a bimodal molecular weight distribution measured by gel permeation chromatography. In mixed tert-butyl alcohol and n-butyl alcohol solvent, with increasing fraction of n-butyl alcohol, the two peaks not only shift to lower molecular weight but the higher molecular weight peak becomes relatively small. Eventually, the polymer formed in n-butyl alcohol exhibits a unimodal distribution. Those results are well explained on the basis of the proposed scheme for heterogeneous polymerization.     

The morphology of polyethylene prepared by γ-ray-induced polymerization in various solvents

Polyethylenes were prepared by γ-ray-induced polymerization in ethyl and n-butyl alcohols, tert-butyl alcohol containing 5 vol-% of water, 2,2,5-trimethylhexane, 2,2,4-trimethylpentane, and cyclohexane in the temperature range 25–90°C. The morphology of the polymers as-polymerized and studied by electron microscopy depends on three factors through the degree of undercooling: the affinity of the solvent, polymerization temperature, and the polymer molecular weight. Large lamellar crystals are formed even in the alcohols when at least two of them are chosen properly.     

Effect of temperature on the radiation-induced polymerization of ethylene in various media

The effects of temperature on the radiation-induced polymerization of ethylene in bulk and in the presence of ethyl alcohol, n-butyl alcohol, tert-butyl alcohol, cyclohexane, 2,2,4-trimethylpentane, and 2,2,5-trimethylhexane were studied. The changes of the amounts of polymerized monomer with the reaction temperature were different from each other in these reaction systems, especially in the range lower than 60–80°C. At temperatures lower than 60–80°C, as the reaction temperature increases, the amount of polymerized monomer decreased in bulk and in the presence of tert-butyl alcohol. The amount was almost constant in the presence of ethyl alcohol and 2,2,4-trimethylpentane, and it increased in the presence of n-butyl alcohol, cyclohexane, and 2,2,5-trimethylhexane. However, in the temperature range higher than 60–80°C, the amount of polymerized monomer increased with increasing temperature in every reaction system except for bulk polymerization. The molecular weight of polymer decreased with increasing temperature in every reaction system except at temperatures lower than 25°C. The molecular weight of polymer formed in bulk, in tert-butyl alcohol, and also in 2,2,4-trimethylpentane were relatively higher than that in other reaction systems. A bimodal molecular weight distribution was observed for the polymer formed in bulk and in tert-butyl alcohol at 40–60°C. These results are discussed in connection with the heterogeneity of the reaction system. The differences due to temperature in each reaction system are explained as due to the difference in affinity of the reaction system for the propagating chain and in the facility of chain transfer to the medium.     

Radiation-induced heterogeneous polymerization of ethylene in the presence of ethyl alcohol

The radiation-induced heterogeneous polymerization of ethylene in ethyl alcohol was carried out in a reactor with a capacity of 100 ml under the following reaction conditions: temperature, 24 ± 3°C; pressure, 200–400 kg/cm²; amount of ethyl alcohol, 30–70 ml; dose rate, 3.7 × 10⁴?1.05 × 10⁵ rad hr. The effects of amount of ethyl alcohol, pressure, and dose rate on the rate of polymerization at the steady state, the amount of polymerized monomer, the molecular weight of polymer, and the number of polymer chains were studied compared with the results obtained in the polymerization in tert-butyl alcohol. It was found that there is an acceleration period in the early stage of reaction followed by a steady state. The rate of polymerization was maximum when about 50 ml of ethyl alcohol was used. The molecular weight of polymer increased with a decrease in the amount of ethyl alcohol. The dependences of pressure (p) and dose rate (I) on the rate of polymerization at steady state (R_s) and the molecular weight of polymer (M?_n) were expressed as follows; R_s ∝ p^0.74, M?_n ∝ p^0.3?0.4, R_s ∝ I^0.9 and M?_n ∝ I^{?0.1 ?0.0}. The results were analyzed by a kinetic treatment based on a reaction mechanism containing both first-and second-order terminations. The rate constant of first-order termination by radical occlusion was considerably larger than that in the polymerization in tert-butyl alcohol, because the affinity of ethyl alcohol for polyethylene is smaller than that of tert-butyl alcohol. It was found that chain transfer to ethyl alcohol takes place easily and the G value of ethyl alcohol for initiation is larger than 1.5.     

Kinetics of the gamma-radiation-induced polymerization of ethylene in tert-butyl alcohol

The gamma-radiation-induced polymerization of ethylene in the presence of 13–30 ml of tert-butyl alcohol was carried out under a pressure of 120–400 kg/cm² at a dose rate of 1 × 10³ to 2.5 × 10⁴ rad/hr at 30°C with a 100 ml reactor. The polymerization rate and the molecular weight of the polymer increased with reaction time and pressure and decreased with amount of tert-butyl alcohol. The polymer yield increased almost proportionally with the dose rate, while the molecular weight was almost independent of it. These results were graphically evaluated, and the rate constants of initiation, propagation, and termination for various conditions were determined. No transfer was observed. On the basis of these results the role of tert-butyl alcohol in the polymerization is discussed.     

Synthesis of tertiary-butyl acrylate polymers and preparation of diblock copolymers using atom transfer radical polymerization

The synthesis of tert-butyl acrylate by atom transfer radical polymerization (ATRP) is reported. This polymer was prepared using FeCl₂ · 4H₂O(PPh₃)₂ catalyst system in conjunction with methyl 2-bromopropionate as initiator, in bulk and in solution using acetone as a solvent. The addition of solvent was necessary in order to decrease the polymerization rate and to afford low polydispersity polymers. The number-average molecular weights of the resulting polymers increased in direct proportion to the monomer conversion, and the polydispersities (M_w/M_n) were as low as 1.2. In addition, the preparation of an AB diblock copolymer of poly (n-butyl methacrylate)-block-poly (tert-butyl acrylate) by ATRP is reported. The resulting polymers and copolymers were characterized by means of size exclusion chromatography and ¹H-NMR Spectroscopy.     

A novel scheme of heterogeneous polymerization of ethylene

The heterogeneous polymerization of ethylene initiated by radiation in tert-butyl alcohol was studied. The polymerization was carried out in a 100-ml reactor at 25–100°C and pressures of 200–300 kg/cm² in the presence of 50 ml of tert-butyl alcohol containing 7 wt-% water. The amounts of polymerized monomer, the average molecular weight of polymer formed, and the molecular weight distribution of polymer were measured at various stages of reaction and at various temperatures. The molecular weight distribution was found to be very much dependent on the reaction time and temperature. For the polymer formed at 50–60°C in the very early stages of reaction, the molecular weight distribution is unimodal, and in the intermediate stage a shoulder appears at a molecular weight higher than the first peak which increases as the polymerization proceeds; eventually a bimodal curve is formed. The bimodal distribution curves were analyzed to determine the fractions and average molecular weights of the each peak. On the basis of these data for the molecular weight distribution and kinetic behavior, a new scheme for the heterogeneous polymerization is proposed which indicates that the polymerization proceeds via propagating radicals in two different physical states, namely, loose and rigid states.     

Reactions of cationic living poly(tert-butyl aziridine)

The cationic polymerization of N-tert-butyl aziridine (TBA) can be conducted in such a way that the rate of termination is much slower than the rate of propagation, thus permitting preparation of a corresponding polymer which is “temporarily living”. Reactions of N-methyl-N-tert-butyl aziridinium triflate (which is the model for the active species of the living polymer) with different nucleophiles show that, at room temperature, the aziridinium ring reacts almost instantaneously with nucleophiles to form the corresponding ring-opened product. Analogous reactions with the aziridinium end group of living poly-TBA lead to polymers with varying end groups such as hydroxy, ester, primary, secondary or tertiary amino, halogen, and others. End group analysis by means of 360-MHz ¹H-NMR nuclear magnetic resonance spectroscopy showed that the concentration of the end groups was in all cases equal to the concentration of the methyl head group, originating form the initiation reaction, if the terminating nucleophile was added five minutes after initiation (at 15°C). Under these conditions the polymerization is quantitative for initiator concentrations down to 0.01 mol L^?1.     

Metallo esters. VII. Stabilizing effect of sodium tert-butoxide on the growth center in the anionic polymerization of methacrylic esters

The growth center in the anionic polymerization of methacrylic esters is stabilized with alkaline alkoxides, sodium tert-butoxide in particular. The lifetime of the growth center was investigated in the polymerization of methyl methacrylate by evaluating yield and molecular weight distribution of the polymer formed when the monomer was added in two doses. The average lifetime of the original growth center stabilized by sodium tert-butoxide at 20°C under the given conditions was longer than several minutes. The stabilization of the growth center was also used in the stepwise copolymerization of n-butyl methacrylate and methyl methacrylate. The copolymer thus obtained in high yield was characterized as a block copolymer on the basis of its solubility, nuclear magnetic resonance (NMR) spectra, and measurements of the complex shear modulus.     

Controlled radical polymerization of methacrylates of various structures in the presence of the AIBN-FeCl3-N,N-dimethylformamide catalytic system

The controlled radical polymerization of methyl methacrylate, 2-ethoxyethyl methacrylate, and tert-butyl methacrylate conducted via atom-transfer radical polymerization in the presence of the AIBN-FeCl₃· 6H₂O-N,N-dimethylformamide catalytic system is studied. For all the systems under study, the rate of reaction is first order with respect to the monomer concentration. The number-average molecular mass of the polymers linearly increases with conversion, and their polydispersity indexes are below 1.6. The rate of polymerization decreases in the following sequence: 2-ethoxyethyl methacrylate > methyl methacrylate > tert-butyl methacrylate. The presence of ω-terminal chlorine atoms in polymer macromolecules is confirmed by ¹H NMR spectroscopy and through the block copolymerization of methyl methacrylate with a poly(ethoxyethyl methacrylate)-based macroinitiator.     

Poly[2,4-bis(chloroamino)-6-vinyl-1,3,5-triazine] as a recyclable oxidizing agent of alcohols

A polymer containing dichlorotriazine moiety was prepared readily by the reaction of poly(2,4-diamino-6-vinyl-1,3,5-triazine) with tert-butyl hypochlorite. This polymer oxidizes various primary and secondary alcohols to the corresponding carbonyl compounds under mild conditions, while the reaction of the monomeric analogue N,N′-dichloroacetoguanamine with alcohols does not proceed. The polymer reagent can be handled easily and recycled for further use.     

Visible light-induced synthesis of polysulfone-based graft copolymers by a grafting from approach

The synthesis of polysulfone (PSU) graft copolymers by a two-step “grafting from” approach is described. First, a chlorofunctional PSU (PSU-Cl) is formed via chloromethylation of a commercial PSU. The formed polymers are used macroinitiator for the dimanganese decacarbonyl assisted free-radical polymerization of tert-butyl acrylate, methyl methacrylate, and styrene to give the desired graft copolymers. Moreover, amphiphilic graft copolymers are also formed via posthydrolyzation of poly(tert-butyl acrylate) containing graft copolymers. The intermediates at various stages and the ultimate graft copolymers are characterized by various analysis techniques. © 2020 Wiley Periodicals, Inc. J. Polym. Sci. 2020 , 58, 412–416     

Functional polymethacrylates as bacteriostatic polymers

Two copolymers, P(PCEMA-co-MMA) and P(t-BMA-block-PCEMA), were prepared via ATRP using 2-(phenoxycarbonyloxy)ethyl methacrylate (PCEMA) as reactive monomer and methyl methacrylate (MMA) or tert-butyl methacrylate (t-BMA) as co-monomers. Alternatively phenoxycarbonyloxy decorated polymethacrylates were obtained via polymer analogous reaction: P(HEMA) was reacted with phenyl chloroformate to yield P(PCEMA). The highly reactive phenoxycarbonyloxy groups were used for polymer analogous reactions with nucleophiles to obtain polymers with ionic/hydrophilic and hydrophobic side groups. Different amines with long alkyl chains or tertiary amine groups were reacted with phenoxycarbonyloxy decorated polymers and subsequently reacted with methyl iodide to obtain amphipathic polymers with bacteriostatic properties.     

Etherification of glycerol with tert-butyl alcohol catalysed by ion-exchange resins

The reaction of glycerol with tert-butyl alcohol in the liquid phase on acid Amberlyst-type ion-exchange resins was studied. The influence of temperature, mole ratio n(TBA)/n(G), water and swelling of gel, and macroreticular type of polymer catalysts on etherification reaction was investigated. The most favourable reaction temperature is 75°C. The conversion of glycerol and yield of glycerol tert-butyl ethers has increased with the mole ratio n(TBA)/n(G). Dry form of macroreticular catalysts provided the best results. Etherification reaction of glycerol with isobutylene in non-aqueous conditions gives the highest yield of desired ethers. The influence of water was studied. The gel forms of ion-exchange resins have very low catalytic activity. It can be concluded that water has an inhibition effect on ion-exchange resins. By comparing the gel and macroreticular forms of Amberlyst ion-exchange resins it can be concluded that very acid forms of macroreticular ion-exchange resins with a high degree of crosslinking are more active catalysts for the studied reaction due to their pores which are sufficiently large so that the voluminous tert-butyl ethers of glycerol can be formed. It was estimated that tert-butyl alcohol as tert-butylation agent is not suitable for etherification of glycerol with the formation of di-and triethers.     

Radiation-induced emulsion polymerization of ethylene. IV. Effect of pressure,temperature, and additives on rate in connection with number of polymer particles

The effects of pressure, temperature, and additives on the rate of radiation-induced emulsion polymerization of ethylene with FC-143 as emulsifier were studied kinetically. The rate of polymerization was proportional to the 2.5 power of ethylene fugacity, and the apparent rate constant (rate of polymerization/2.5 power of ethylene fugacity) was constant below 78°C. Above this temperature, the rate constant decreased with an apparent activation energy of ?8.2 kcal/mole. These facts can be interpreted in connection with the polymer structure and the change of rate of escape of radicals from the polymer structure and the change of rate of escape of radicals from the polymer particle into the aqueous phase. The rate of polymerization decreased on addition of a series of n-aliphatic alcohols due to the chain-transfer reaction and consequent escape of radicals to the aqueous phase. On the other hand, the addition of tert-butyl alcohol increased the rate of polymerization, probably because of its effect in increasing swelling of the polymer particles. Addition of electrolytes increased the rate of polymeriaztion as a result of the increase of the number of polymer particles.     

Photostabilizing activity of tertiary hindered amines

The influence of the N-alkyl group of tertiary hindered amines on the photostabilization of polymers was studied. The photostabilizing effects of the tertiary amine derivatives of 4-benzoyloxy-2,2,6,6-tetramethylpiperidine ( 1a ) in polypropylene were compared. All tertiary amine derivatives having α-H to hindered N showed higher effectiveness than 1a . Model liquid phase photoxidations were carried out by irradiating (UV-lamp) the solutions of tertiary hindered amines containing tert-butyl hydroperoxide as a photoinitiator. The tertiary hindered amines were oxidized more easily than corresponding parent hindered amine and converted to the parent amine, which was identified as its salt, resulting from the carboxylic acid produced from the N-alkyl group by oxidation. The thermal reaction of the tertiary hindered amines with tert-butyl hydroperoxide was also studied in the liquid phase. The tertiary hindered amines decomposed tert-butyl hydroperoxide more rapidly than the parent secondary hindered amine, and generated the parent amine. It was also found that the photostabilizing effects of tertiary hindered amines for polyolefins were higher than that of the parent secondary hindered amine.     

An Efficient and Highly Chemoselective Method to Desilylate Silyl Ethers

An efficient and highly chemoselective desilylating method is described. Trimethylsilyl ethers (0.25 M) in a CH₃OH/CCl₄ (1:1) solvent mixture are deprotected to their corresponding alcohols with ultrasound in a commercial ultrasonic cleaning bath. Selective deprotection of tert-butyldimethylsilyl ethers of benzyl alcohols and phenols is achieved under ultrasonic conditions. We deprotected also tert-butyldimethylsilyl ethers of primary alcohols, whereas tert-butyldimethylsilyl ethers of secondary and tertiary alcohols are stable under these conditions.     

Radiation-induced heterogeneous polymerization of methyl methacrylate in precipitants

The radiation-induced heterogeneous polymerization of methyl methacrylate in various precipitants, mainly methyl alcohol, was carried out, and the effects of reaction conditions on the polymerization behavior and the molecular weight distribution of polymer were studied. Bimodal molecular weight distributions were found for the polymer produced by the heterogeneous polymerizations in methyl alcohol and in tert-butyl alcohol. The apparent activation energy is 1.0 and 4.5 kcal/mole, respectively, for the polymerization at a monomer concentration of 10 vol-% in methyl alcohol above and below 35°C. The polymerization at a monomer concentration lower than 40 vol-% in methyl alcohol proceeded with the precipitation of polymer. The dose rate exponent of the mean rate of heterogeneous polymerization decreased from 0.5 to a smaller value as the polymerization progressed. The ratio of the two peaks in the bimodal molecular weight distributions of polymer produced in methyl alcohol was affected by the reaction conditions. These results show the coexistence in the polymerizations of two different physical states of propagating chain, a loose state and a rigid one. The reaction scheme is discussed in connection with the physical factors which affect the solubility or the mobility of propagating chains, and the rate of elementary reactions, which influences the degree of propagating chains.     

N-substitution of polybenzimidazoles: Synthesis and evaluation of physical properties

Series of N-substituted polybenzimidazoles (PBI) were synthesized using selective alkyl groups with varying bulk and flexibility, viz., methyl, n-butyl, methylene trimethylsilane and 4-tert-butylbenzyl. PBI-I based on 3,3′-diaminobenzidine (DAB) and isophthalic acid and PBI-BuI based on DAB and 5-tert-butyl isophthalic acid were chosen for N-substitution. Structural characterizations of substituted polymers by FT-IR and ¹H NMR revealed elimination of hydrogen bonding. Evaluation of their physical properties revealed that N-substitution rendered better solvent solubility in common organic solvents, more open polymer matrix, but reduced thermal properties in comparison to their respective parent PBI. 4-tert-butylbenzyl, methylene trimethylsilane or n-butyl group substituted polymers were soluble even in chlorinated solvents (CHCl₃ and TCE). Substantial variations in gas permeability of inert gases, He and Ar and attractive P_He/P_Ar selectivity, especially after methyl group substitution depicted potential of these materials for gas separation.     

TiCl4-activated selective nucleophilic substitutions of tert-butyl alcohol and benzyl alcohols with π-donating substituents

TiCl₄-activated selective nucleophilic substitution reactions of tert-butyl alcohol and benzyl alcohols with π-donating substituents in the presence of primary and secondary alcohols can be carried out with various oxygen, nitrogen and carbon nucleophiles in good yields.