Anionic polymerization initiated by lithium diethylamide in organic solvents. III. Investigation of the polymerization of styrene

The polymerization of styrene, initiated by lithium diethylamide in mixtures of benzene and THF, has been investigated. Kinetic and molecular weight measurements are interpreted on the basis of simultaneous initiation and propagation steps, and the effect of solvation and coordination processes on these reactions is discussed. Initiation of polymerization is thought to involve addition of solvated lithium diethylamide ion-airs to styrene, giving species with diethylamide end groups. The possible influence of these end groups on the initiation is considered in terms of an intramolecular cyclization process. Propagation of polymerization is believed to involve polystyryllithium ion-pairs, solvated to varying extents by THF. No evidence has been found to suggest that chain transfer, or termination, reactions are an integral part of the polymerization process. The polymerization has a number of similarities to the alkyllithium-initiated polymerization of styrene, but also exhibits some interesting differences.     

Kinetics of styrene homogeneous polymerization to atactic polypropylene

The rate of polymerization of styrene initiated by hydroperoxidized atactic polypropylene in a homogeneous toluene solution has been measured at 60 and 70°C. The reaction is first-order with respect to styrene concentration and independent of the polymeric hydroperoxide concentration above 2 × 10^?5N hydroperoxide. The individual rate constants, length and frequency of the grafted polystyrene chains along the polypropylene backbone have been calculated and their significance discussed. The initiation rate constant compares closely with values reported for the analogous tert-butyl hydroperoxide-initiated polymerization. The rate constant for the chain transfer termination elementary step at 70°C., however, is 18 times the value reported for the tert-butyl hydroperoxide-initiated polymerization of styrene. This high constant accounts for the relatively low rates of polymerization observed and high termination rates. Chain deactivation is presumably accelerated by increased collisions between growing styrene chains and inactive propylene hydroperoxide and polystyrene molecules. Distribution of polystyrene grafts on polypropylene is estimated from knowledge of effects of styrene concentration, polymeric hydroperoxide concentration, and temperature upon the rate of polymerization.     

Oligomer formation in the radiation-induced polymerization of styrene

Analyses of the oligomers formed in radiation-induced polymerization of purified styrene were performed. The principal dimeric products were cis- and trans-diphenyl-cyclobutane with a relatively small amount of 1-phenyltetralin; the trimeric products were the optical isomers of 1-phenyl-4-[1′-phenylethyl-(1′)]-tetralin in gamma-ray and 60 MeV proton irradiation. Oligomer formation increased with increasing dose, but more gradually than the linear formation of high polymer with dose. The yield was 0.25–3.1 μmol/J at low doses and decreased to an asymptotic value of 0.15 at higher doses. It appears that oligomers act as chain transfer agents during the polymerization reaction which would account for the observed decrease in molecular weight of the high polymer with increase in dose. Although the thermal and radiation-induced polymerization of styrene have different initiation steps, the oligomers produced by both reactions are similar in composition.     

Synthesis of block and graft copolymers of styrene by raft polymerization,using dodecyl‐based trithiocarbonates as initiators and chain transfer agents

A series of dodecyl‐based monofunctional trithiocarbonate chain transfer agents (CTAs) were successfully synthesized, toward the reversible addition‐fragmentations chain transfer (RAFT) polymerization of styrene. The CTAs were used as initiators for RAFT polymerization, in the absence of the conventional free radical initiator, at higher temperature. Polystyrene (PS) of narrow polydispersity index (PDI) is synthesized. Subsequently, poly(styrene‐b‐benzyl methacrylate) diblock and poly(styrene‐b‐benzyl methacrylate‐b‐2‐vinyl pyridine) triblock copolymers were synthesized from the PS macro‐RAFT agent by simply heating with the second and third monomer, respectively. These experiments suggest that it should be possible to control the RAFT polymerization initiated by a CTA through the adjustment of the temperature of polymerization in such manner that initiation is tailored to proceed at faster rate (at higher temperature) in comparison to propagation (lower temperature). For the specific CTAs studied in this work, the polymerization rate of styrene was high in the case of the reinitiating cyano (CN)‐substituted group (R group) compared to the other groups studied. The results further show that 4‐cyano pentanoic acid group is superior to the other R groups used for the RAFT polymerization of styrene, especially based on the polydispersity at a given conversion as well as the variation in the expected and experimental number‐average‐molecular weights. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2013     

枯基醇/三氟化硼在含水介质中引发苯乙烯可控正离子聚合的研究

研究了含水介质中,以枯基醇(CumOH)/三氟化硼(BF3)为引发体系的苯乙烯正离子聚合的特征,探讨了CumOH用量、体系中的水含量对苯乙烯正离子聚合转化率、聚合速率以及产物分子量及其分布的影响;并从分子模拟、分子量末端结构等角度探讨含水介质中苯乙烯正离子聚合的反应机理.结果表明,[H2O]≤0.11 mol/L条件下,苯乙烯正离子聚合具有可控聚合的特征;水对聚合速率、单体转化率以及分子量影响较小;[H2O]>0.11 mol/L,正离子聚合不能顺利进行.根据计算结果,CumOH/BF3引发体系相对于CumOH/H2O引发体系在参与引发所需要的活化能垒更小,说明CumOH/BF3更容易引发苯乙烯正离子聚合,这与实验结果一致.CumOH/BF3引发体系是通过活化C—O键来引发苯乙烯正离子聚合,水作为可逆终止剂有利于进行可控聚合,并得到了末端含有羟基的聚合物.     

Emulsion polymerization of styrene using irreversible addition–fragmentation chain transfer agents: effect on the course of the polymerization and molecular weight

The emulsion polymerization of styrene with three different chain transfer agents (CTAs) based on irreversible addition–fragmentation chain transfer (AFCT) mechanism was first reported in this work. The influences of these irreversible AFCT agents on the rate of polymerization, particle size, and molecular weight were investigated. It was found that the intrinsic activity and desorption behaviors of the CTAs determined the efficiency for molecular weight control, rate of polymerization, and particle size in the emulsion polymerization. It has been demonstrated that the rate of polymerization and particle size decreased dramatically in the presence of the irreversible AFCT agents with high chain transfer constant (ethyl α-p-toluenesulfonyl-methacrylate), meanwhile, the molecular weight of the polystyrene could not be controlled well, whereas the irreversible AFCT agents with low chain transfer constant (butyl(2-phenylallyl)sulfane and 2,3-dichloropropene) had a slight effect on the polymerization rate, particle size, and were fairly well for molecular weight control over the whole conversion range in the emulsion polymerization of styrene. The average number of radicals per particle and the number-average molecular weight were calculated by classical radical emulsion polymerization theory, and the experimental results were in good agreement with the results of model calculations, when the irreversible AFCT agents were used as CTAs. The effect of chain transfer agents on the kinetics and nucleation in the emulsion polymerization of styrene can be attributed to desorption of chain-transferred radicals from the polymer particles. The results of this work show that butyl(2-phenylallyl)sulfane as CTA in emulsion polymerization of styrene provides the best balance between the rate of polymerization and the efficiency for molecular weight control conflicting tendencies.     

The measurement of rates of initiation in the thermal polymerization of styrene

The thermal initiation of the polymerization of styrene has been studied at temperatures from 60–140°C using DPPH as a free radical scavenger. Rates of free radical formation, measured by the decrease in absorbance at 525 nm, are about seven times greater than those obtained from inhibition period measurements. The difference is probably due to the much greater reactivity of trinitrobenzene derivatives towards diradicals from styrene than towards styryl monoradicals. This view is supported by the different behaviour of the AIBN initiated polymerization of styrene in the presence of DPPH. The thermal initiation process has a low efficiency of initiation and the activation energy is 121 kJ/mole. The results strongly support the diradical mechanism for the thermal initiation of styrene polymerization.     

Polymerization kinetics in highly viscous media

The influence of the viscosity of the reaction medium on the rate of polymerization of styrene has been examined by adding different amounts of inert polystyrene to pure monomer and its solutions in benzene. Azobisisobutyronitrile was decomposed photochemically (λ = 365 mμ) at 25°C. or thermally at 70°C.; its rate of decomposition was followed by ultraviolet spectrometry. The rate of formation of dimethyl-N-cyanoisopropylketenimine (DKI) was followed by infrared spectrometry (2020 cm.^?1). The initiation efficiency was determined by the scintillation method with the use of a ¹⁴Clabeled initiator. The rate of polymerization was followed dilatometrically. An increase of viscosity does not affect the rate of decomposition of the initiator; on the contrary, during the photochemical decomposition, it causes an increase of DKI concentration and an appreciable decrease of efficiency (from 0.51 to 0.30). From the point of view of the rate of photopolymerization, an increase of viscosity causes a decrease in the order of the reaction with respect to the initiator (from 0.5 to 0.3) and an increase with respect to monomer from 1.5 to 2. These results are interpreted on the basis of a decrease of termination rate constant between two growing chains in favor of a termination reaction between a growing chain and a primary radical. These effects, due to an increase of the viscosity of the solution, on the initiation and termination reactions influence the rate of polymerization in opposite direction and compensate each other to approximatively 25%.     

Polymerization studies on allylic compounds. IV. Methallylic compounds

The free-radical polymerization of a series of 2-methyl-3-substituted propenes was investigated. These compounds were found to homopolymerize with difficulty to give low molecular weight polymers. Their effect upon the polymerization of methyl methacrylate and styrene was investigated by rate and viscosity measurements. Copolymerizations occurred with a retarding action attributed to pronounced chain transfer reactions.     

Anionic polymerization initiated by diethylamide in organic solvents. I. The use of lithium diethylamide as a polymerization catalyst and the effect of solvent type on the polymerization of isoprene and styrene

Lithium diethylamide has been found to be an active initiator for the polymerization of isoprene both in hydrocarbon media and in a variety of polar solvents, such as diethyl ether and tetrahydrofuran. The successful initiation of styrene polymerization is, however, strongly dependent upon the type of solvent employed. Thus no polymerization is observed in hydrocarbon media or in diethyl ether solution, but polymerization occurs rapidly in either tetrahydrofuran or 1,2-dimethoxyethane solution. These polymerization processes are anionic in nature and are characterized by sigmoidal conversion–time plots, indicating that the initiation reactions are relatively slow compared to chain propagation.     

An Approximate Kinetic Treatment of Slow‐Initiated Living Polymerization. II. First‐Order Initiation and Half‐Order Propagation

An approximate analytical solution of the set of differential equations modeling the anionic polymerization of styrene is presented. By using this solution, a new method for calculating the initiation rate constant for this polymerization process was developed.     

Investigation of autoacceleration effects during the solution polymerization of styrene

The possibility of obtaining increases in the rate and degree of polymerization through a decrease in the termination rate in nonviscous, homogeneous solution polymerizations of styrene has been investigated. Decreases in the termination rate were achieved through decreasing segmental diffusion of the propagating macroradical by greater occlusion, on the average, of the radical in the coiled polymeric chain. Coiling of the polymeric chain was effected by polymerizing styrene in thermodynamically poor (θ) solvents near the θ temperature for polystyrene. Examples of such systems are diethyl oxalate at 51.5°C. and cyclohexane at 34.6°C. Polymerization under these conditions did lead to a decrease in the k_t/k_p² kinetic ratio; this decrease resulted in increases in the degree of polymerization, but changes in the rate of polymerization, in contrast to the marked increases noted in viscous solution or heterogeneous polymerizations, were not observed. Possible explanations for the latter observations are discussed.     

Particle nucleation in emulsion polymerization. III. Nucleation in systems with anionic emulsifier investigated by seeded and unseeded polymerization

Studies of seeded and unseeded polymerization of styrene using sodium dodecylsulfate as emulsifier have been carried out in order to investigate the mechanism of particle nucleation in such systems and to test the theory presented in Part I of this series. The rate of capture of water-soluble oligomeric radicals was considered to be governed by absorption of oligomers with chain length one less than the critical chain length. It was concluded that the micelles became the dominating loci for particle nucleation above CMC for the emulsifier. A complete nonsteady-state model for particle initiation above CMC which takes into account radical desorption and reabsorption has been developed. It was indicated that, even for styrene, desorption of radicals may play a role in controlling the radical and particle number of interval I under certain conditions. The model also showed that the efficiencies of particles in absorbing radicals could be calculated from physical parameters, such as diffusion constants and surface charge densities, which are available for the system.     

Kinetics of polymerization initiated by peroxides containing heterocyclic groups. I. Kinetics of bulk polymerization of styrene and vinyl acetate initiated by difuroyl peroxide

The rate and degree of bulk polymerization of styrene and vinyl acetate initiated by difuroyl peroxide and, for comparison, by dilauroyl and dibenzoyl peroxides were measured at several temperatures as a function of the initiator concentration. Also the rates of initiation were determined by the inhibition method with Banfield's radicals. The rate of polymerization initiated by difuroyl peroxide appears to be lower than could be expected from the rate of initiation determined by the inhibition method and from the decomposition of difuroyl peroxide. In the case of polymerization of vinyl acetate there are significant deviations from the proportionality between R_p and the square root of the initiator concentration, which follows from the conventional kinetic scheme. The degrees of polymerization are also low, and the plots of P _n^?1 versus R_p are not linear. These deviations can be accounted for by postulating a retardation effect of the furan cycle and chain transfer to difuroyl peroxide.     

Vinyl Polymerization. 374. Radical Polymerization of Vinyl Monomer Initiated with Sodium Polystyrenesulfonate

The polymerization of vinyl monomer initiated by an aqueous solution of sodium polystyrenesulfonate (PSS-Na) was carried out at 85°C. Methyl methacrylate (MMA) and styrene were polymerized, while acrylonitrile was not. The rate of polymerization of MMA decreased with the increase of the degree of polymerization of PSS-Na. However, the polymerization was not initiated by sodium ethyl benzenesulfonate which was a unit molecule of PSS-Na. The polymerization proved to be a radical reaction. The polymerization was considered to commence with the formation of hydrophobic areas with PSS-Na in the aqueous phase. MMA is incorporated into these areas, and there the polymerization is initiated and proceeds. The hydrophobic areas were assumed to be similar to the micelles formed by anionic detergents such as sodium alkylbenzene sulfonate. An initiation mechanism is proposed.     

Polymerization photoinitiated by carbonyl compounds. VI. Mechanism of benzil photoinitiation

The mechanism of the photoinitiation of the vinyl polymerization sensitized by benzil and 4,4′-dimethoxybenzil was studied. The monomers considered were methacrylic acid esters and styrene derivatives. All these monomers are efficient quenchers of the excited triplet benzil. However, the initiation efficiency of the benzil is important only when styrene derivatives are employed as monomers. The main polymerization process follows a simple free radical mechanism. The initiation step is a consequence of the interaction (triplet benzil–monomer double bond) through a charge transfer complex.     

Ionic polymerization under an electric field. III. Cationic polymerizations of α-methylstyrene and styrene

Cationic polymerizations of α-methylstyrene and styrene were carried out in an electric field with iodine as a catalyst and ethylene dichloride as the solvent. The effects of the field on the rate of polymerization and the degree of polymerization were studied. It was found that the field increased the rate of polymerization of α-methylstyrene and, also slightly increased the degree of polymerization, whereas the field had no influence on these quantities in the case of styrene. The expressions for the rate of polymerization and the degree of polymerization, which were derived in a previous paper and refined in the present paper, show that these quantities are generally a function of the degree of dissociation of ion pairs at growing chain ends. For a comparatively large degree of dissociation, these expressions can account for the field effect as was observed on α-methylstyrene, if one assumes that the degree of dissociation in the presence of an electric field is larger than that in its absence, and that the free-ion propagation proceeds much faster than the ion-pair propagation. For a small degree of dissociation, however, these expressions become practically independent of the degree of dissociation so that a possible increase due to the presence of an electric field gives rise to no observable effect on the polymerization. This situation may be interpreted as corresponding to the case of styrene. In other words, the polymerization of α-methylstyrene has more free ionic character than that of styrene.     

不同结构Iniferter引发苯乙烯聚合反应的研究

以不同结构的含氯化合物与铜试剂反应合成了4种链引发-转移-终止剂(Iniferter)。研究了它们引发苯乙烯的聚合反应过程,重点考察了Iniferter结构对聚合产物的影响。采用核磁共振氢谱和凝胶渗透色谱对聚合物分子量和分子量分布进行了测定。结果表明:Iniferter结构对聚合反应速率、分子量实测值与理论值间的对应关系及分子量分布均有明显影响,当其形成的初级自由基上带有使其稳定的基团时,引发效率就高,聚合反应速率较快,而且分子量理论值与实测值两者更接近。加入四甲基秋兰姆化二硫组成双组份Iniferter引发体系可以在一定程度上使聚合物分子量分布变窄。     

Semi-continuous emulsion polymerization of styrene in the presence of poly(methyl methacrylate) seed particles. Polymerization conditions giving core-shell particles

This work reports the morphology of two-phase latex particles prepared by semi-continuous seed emulsion polymerization of styrene in the presence of polar poly(methyl methacrylate), PMMA, seed particles, using different conditions of non-polar styrene feed rate, rate of initiation, seed particle concentration and temperature of polymerization.The expected latex particle morphology at thermodynamic equilibrium is an inverted core-shell structure where the non-polar polystyrene would form the core. However, depending on the set of process conditions used the morphology of the resulting two-phase particles varied from that of a pure core-shell structure, over intermediate structures in which a shell of PS surrounded a PMMA core containing an increasing number of PS phase domains, to a structure in which the entire PS phase was present as discrete PS phase domain, more or less evenly distributed in a matrix of PMMA.By the use of a caloirimetric reactor system the monomer concentration in the particles during the different polymerization experiments could be calculated by comparing the integral of the polymerization rate curve with the integral of the monomer feed rate. A comparison between particle morphology and the calculated concentration of plasticizing monomer in the polymerizing particles strongly suggested that the diffusivity of the entering oligo radicals determined by the difference between polymerization temperature and the glass transition temperature of the monomer-swollen core polymer is a key factor determining the morphology of two-phase particles prepared by semi-continuous seed emulsion polymerization.Two-phase particles with a true core-shell structure were obtained in experiments where the estimated glass transition temperature of the PMMA phase was only a few degrees below the polymerization temperature. The results show that such particles can be obtained under conditions of high as well as low styrene feed rates, provided that the rate of initiation is properly adjusted.     

Polymerization studies on allylic compounds. V. 2-chloropropenes

The free-radical polymerization of three 2-chloro-3-substituted propenes have been investigated. Compounds studied were 2,3-dichloropropane, 2-chloro-3-hydroxypropene, and 2-chloro-3-acetoxypropene. These compounds were found to homopolymerize with difficulty to give low molecular weight polymers. Their effect upon the polymerization of methyl methacrylate and styrene was investigated by rate and viscosity measurements. Copolymerization occurred with a retarding action attributed to significant chain transfer processes and differences in monomer reactivities.