Studies on propagating species in cationic polymerization of styrene derivatives by acetyl perchlorate or iodine. I. Bimodal molecular weight distribution of polymers produced by acetyl perchlorate or iodine

To investigate the nature of the propagating species in cationic polymerization of para-substituted styrenes, p-chlorostyrene (pCIS), p-methylstyrene (pMS), and p-methoxystyrene (pMOS), were polymerized with acetyl perchlorate or iodine in various solvents at 0°C, and the molecular weight distribution (MWD) of the polymers was measured by means of gel-permeation chromatography. When ClO_4? was a counterion, poly(pCIS) having a bimodal MWD was produced, while polymers of pMOS and pMS possessed a unimodal MWD, regardless of the solvent polarity. When more nucleophilic I^? (or I₃^?) was a counterion, however, polymers having a bimodal MWD were produced from pMOS and pMS. These results showed that either dissociated or nondissociated propagating species existed in the cationic polymerization of styrene derivatives with acetyl perchlorate or iodine, and that the type of MWD was strongly dependent on the stability of the growing cation and the nucleophilicity of the counterion.     

Cationic polymerization of styrene by acetyl perchlorate. II. Steric structure of the polymer and nature of the propagating species

Cationic polymerization of styrene initiated by acetyl perchlorate in CH₂Cl₂ yields a polymer having a bimodal molecular weight distribution. The high molecular weight and the low molecular weight portions of the polymer were separated by thin-layer chromatography, and the steric structure of these separated polymers was investigated by ¹³C NMR spectra. The high molecular weight polymer had a larger racemic dyad content than the low molecular weight material. From the dependence of the steric structure of the polymer on the polarity of a solvent, it was estimated that the propagating species producing the high molecular weight material was a loose ion pair or a free ion, and that producing the high molecular weight material was a loose ion pair or a free ion, and that producing the low one was a nondissociated species.     

Cationic polymerization of p-methylstyrene initiated by acetyl perchlorate: An approach to living polymerization

The cationic polymerization of p-methylstyrene initiated by acetyl perchlorate at ?78°C led to long-lived (living-like) polymers with a narrow molecular weight distribution (M?_w/M?_n = 1.1–1.4) in methylene chloride containing a common ion salt (n-Bu₄NClO₄) or in a less polar solvent (CH₂Cl₂/toluene, 1/4v/v). Under these conditions, the number-average molecular weight (M?_n) of the polymers increased in proportion to monomer conversion and was regulated by the monomer-to-initiator ratio. When fresh feeds of the monomer were repeatedly added to a completely polymerized solution, the polymerization ensued at the same rate as before and the linear increase in M?_n with monomer conversion continued. The effects of solvent polarity and the common ion salt on the polymerization showed the suppression of the ionic dissociation of the propagating species, resulting in a “nondissociated species,” to be the key factor for the formation of the long-lived polymers.     

Cationic polymerization of styrene by acetyl perchlorate: Molecular weight distribution of polystyrene and nature of the propagating species

To clarify the nature of the propagating species in cationic polymerization of styrene catalyzed by acetyl perchlorate, the molecular weight distribution of the polymer was investigated under various conditions. The molecular weight distribution curve for the polymer obtained in methylene chloride at 0°C showed a double peak phenomenon. This suggests that two or more kinds of propagating species participate simultaneously in the propagation reaction. The weight fraction W(H) of the polymer corresponding to the higher molecular weight peak increased with increasing polarity of the solvent. W(H) decreased when the concentration of the ionic species was increased either by an increase of the catalyst concentration or by the addition of the common salt such as tetra-n-butylammonium perchlorate. On the other hand, the position of the peak in the molecular weight distribution curve was independent of polymerization conditions. It was concluded that the higher molecular weight part of the polymer was produced under conditions for conductive to dissociation of the propagating species and the less dissociated propagating species was responsible for the lower molecular weight part of the polymer.     

Cationic polymerization of styrene initiated by phosphorus oxychloride

Cationic polymerization of styrene (St) initiated by phosphorus oxychloride was carried out at 30° in dichloromethane and nitrobenzene. The rate of polymerization was proportional to (POCl₃) and (St)². The degree of polymerization of the polymer decreased with increasing conversion in the range beyond 30% and increased with increasing (St) although it was independent of (POCl₃) in both solvents. The rate and the degree of polymerization were enhanced with increasing dielectric constant of the mixed solvent composed of C₆H₅NO₂, CH₂Cl₂, and benzene. Addition of water revealed a cocatalytic effect in both systems. The molecular weight distribution (MWD) of the polymer was studied.     

Living cationic polymerization of isobutyl vinyl ether by EtAlCl2 in the presence of ether additives: Cyclic ethers,cyclic formals,and acyclic ethers with oxyethylene units

The living cationic polymerization of isobutyl vinyl ether (IBVE) was investigated in the presence of various cyclic and acyclic ethers with 1-(isobutoxy)ethyl acetate [CH₃CH(OiBu)OCOCH₃, 1 ]/EtAlCl₂ initiating system in hexane at 0°C. In particular, the effect of the basicity and steric hindrance of the ethers on the living nature and the polymerization rate was studied. The polymerization in the presence of a wide variety of cyclic ethers [tetrahydrofuran (THF), tetrahydropyran (THP), oxepane, 1,4-dioxane] and cyclic formals (1,3-dioxolane, 1,3-dioxane) gave living polymers with a very narrow molecular weight distribution (MWD) (M?_ω/M?_n ≤ 1.1). On the other hand, propylene oxide and oxetane additives resulted in no polymerization, whereas 1,3,5-trioxane gave the nonliving polymer with a broader MWD. The polymerization rates were dependent on the number of oxygen and ring sizes, which were related to the basicity and the steric hindrance. The order of the apparent polymerization rates in the presence of cyclic ether and formal additives was as follows: nonadditive ～ 1,3,5-trioxane ? 1,3-dioxane > 1,3-dioxolane ? 1,4-dioxane ? THP > oxepane ? THF ? oxetane, propylene oxide ? 0. The polymerization in the presence of the cyclic formals was much faster than that of the cyclic ethers: for example, the apparent propagation rate constant k in the presence of 1,3-dioxolane was 10³ times larger than that in the presence of THF. Another series of experiments showed that acyclic ethers with oxyethylene units were effective as additives for the living polymerization with 1 /EtAlCl₂ initiating system in hexane at 0°C. The polymers obtained in the presence of ethylene glycol diethyl ether and diethylene glycol diethyle ether had very narrow molecular weight distribution (M?_ω/M?_n ≤ 1.1), and the M?_n was directly proportional to the monomer conversion. The polymerization behavior was quite different in the polymerization rates and the MWD of the obtained polymers from that in the presence of diethyl ether. These results suggested the polydentate-type interaction or the alternate interaction of two or three ether oxygens in oxyethylene units with the propagating carbocation, to permit the living polymerization of IBVE. © 1994 John Wiley & Sons, Inc.     

Chain transfer to solvent in two-state anionic polymerization, 1. Fast exchange between propagating species

A theoretical consideration of molecular weights and molecular weight distribution (MWD) of polymers formed in anionic polymerization proceeding via active centres of two different types under conditions of chain transfer to solvent with a fast exchange between propagating species is presented. Analytical expressions for number-and weight-average degrees of polymerization are obtained. Expressions for P_n and P_w are shown to be the same as in a one-centre process with the apparent intensity of chain transfer proportional to the weight fraction of the polymer formed via “transferring” centres. The polymers formed possess a moderately wide unimodal MWD. The dependence of the polydispersity index on the effective intensity of chain transfer goes through a maximum; for M₀/I₀ = 10³ the maximum value of P_w /P_n is ca. 4,6. The method is suggested for the estimation of the relative reactivity in chain propagation of two active centres from the dependence of molecular weight on initiator mixture composition. The effects of association of active centres on the average molecular weights are analyzed. The case when one of the centres is dormant is also considered.     

Living cationic polymerization of p-alkoxystyrenes by free ionic species

In contrast to the common view, living cationic polymerization of p-methoxy- and p-t-butoxystyrenes proceeded in polar solvents such as EtNO₂/CH₂Cl₂ mixtures, and involvement of free ionic growing species therein was examined. For example, the two alkoxystyrenes were polymerized with the isobutyl vinyl ether-HCl adduct/ZnCl₂ initiating system at −15°C in such polar solvents as CH₂Cl₂ or EtNO₂/CH₂Cl₂ [1/1 (v/v)], as well as toluene. The number average molecular weight (M̄_n) of the polymers increased in direct proportion to the monomer conversion, even after sequential monomer addition, and the molecular weight distribution (MWD) stayed very narrow throughout the reaction. In addition, the M̄_n agreed with the calculated values, assuming that one adduct molecule generates one living polymer chain. In these polar media the addition of a common ion salt retarded the polymerization, indicating that dissociated ionic species are involved in the propagating reaction. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 3694–3701, 1999     

Living carbocationic polymerization. LXII. Living polymerization of styrene,p-methylstyrene and p-chlorostyrene induced by the common ion effect

The effect of common anion producing salt, tetrabutylammonium chloride (n-Bu₄NCl), on the livingness and kinetics of styrene (St), p-chlorostyrene (pClSt), and p-methylstyrene (pMeSt) polymerization initiated by the 2-chloro-2,4,4-trimethylpentane (TMPCl)/TiCl₄ system has been investigated. Uncontrolled (conventional) carbocationic polymerization of St and p MeSt can be converted to living polymerization by the use of n-Bu₄NCl. Under similar conditions the polymerization of p ClSt is living even in the absence of n-Bu₄NCl, although the molecular weight distribution (MWD) of the polymer becomes narrower in the presence of this salt. The apparent rates of polymerizations decrease in the presence of n-Bu₄NCl in proportion with the concentration of the salt. The rate of living polymerization of p ClSt is noticeably lower than that of St, while that of p MeSt is higher. The apparent rate constants, k_p^A, of these polymerizations have been determined, and the effects of the electron donating p Me- and electron withdrawing p Cl-substituents relative to the rate of St polymerization have been analyzed. [For part LXI, see J. Si and J. P. Kennedy, Polym. Bull., 33 , 651 (1994)]. © 1997 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 35 : 3341–3347, 1997     

Polymerization of N-vinylcarbazole by chlorides and oxychlorides of some group V elements. II. Kinetics and mechanism of the polymerization initiated by arsenic trichloride

The polymerization of N-vinylcarbazole (NVC) initiated by AsCl₃ in benzene and nitrobenzene solvents was studied at 33°C. R_p is proportional to the first power of the initiator concentration. R_p varies in a first-order manner with NVC concentration up to a certain optimum concentration of the latter, after which it falls and ultimately levels off. The rate and the molecular weight are depressed by the addition of various amines, preformed poly-NVC, and water. HCl does not have any cocatalytic effect on the system. Rate and the molecular weight are increased in nitrobenzene. The degree of polymerization stays independent of the initiator and NVC concentration and also of increasing conversion. These results suggest a conventional cationic mechanism, and overrule the possibility of a cation radical initiation. A suitable kinetic scheme has been proposed in conformity with the findings.     

Living cationic polymerization of vinyl ethers in the presence of added bases: Recent advances

The living cationic polymerization of vinyl ethers was carried out with organoaluminum compounds in the presence of various types of esters and ethers (cyclic and acyclic), to find out the suitable added bases available for the living polymerization. The effects of the basicity and steric hindrance of added bases were investigated in detail. On the basis of these results, a fast living polymerization system was realized. To synthesize water-soluble polymers such as thermally-induced phase separating polymers and polyalcohols with well-defined polymer structure, the living polymerization of various vinyl ethers was examined. The aqueous solution of living poly(vinyl ethers) having oxyethylene units exhibited a quite sensitive (ΔT_ps=0.3–0.5°C) and reversible phase separation on heating and cooling. The effects of polymer structures (pendant substituent, polymer sequence, molecular weight, and MWD) on the phase separation behavior were investigated. PVA and block copolymers containing PVA units with a narrow MWD were also prepared via living cationic polymerization of vinyl ethers and a deprotection reaction.     

Living cationic polymerization of vinyl ethers with carboxylic acid/tin tetrahalide initiating systems. I. New initiating systems based on acetic acid and selection of Lewis acid and basic additive leading to living polymers with low polydispersity

Cationic polymerization of isobutyl vinyl ether (IBVE) with acetic acid (CH₃COOH)/tin tetrahalide (SnX₄: X = Cl, Br, I) initiating systems in toluene solvent at 0°C was investigated, and the reaction conditions for living polymerization of IBVE with the new initiating systems were established. Among these tin tetrahalides, SnBr₄ was found to be the most suitable Lewis acid to obtain living poly(IBVE) with a narrow molecular weight distribution (MWD). The polymerization with the CH₃COOH/SnBr₄ system, however, was accompanied with the formation of a small amount of another polymer fraction of very broad MWD, probably due to the occurrence of an uncontrolled initiation by SnBr₄ coupled with protonic impurity. Addition of 1,4-dioxane (1–1.25 vol %) or 2,6-di-tert-butylpyridine (0.1–0.6mM) to the polymerization mixture completely eliminated the uncontrolled polymer to give only the living polymer with very narrow MWD (M _w/M _n ≤ 1.1; M _w, weight-average molecular weight; M _n, number-average molecular weight). The M _n of the polymers increased in direct proportion to monomer conversion, continued to increase upon sequential addition of a fresh monomer feed, and was in good agreement with the calculated values assuming that one CH₃COOH molecule formed one polymer chain. Along with these results, kinetic study and direct ¹H-NMR observation of the living polymerization indicated that CH₃COOH and SnBr₄ act as so-called “initiator” and “activator”, respectively, and the living polymerization proceeds via an activation of the acetate dormant species. The basic additives such as 1,4-dioxane and 2,6-di-tert-butylpyridine would serve mainly as a “suppressor” of the uncontrolled initiation by SnBr₄. The polymers produced after quenching the living polymerization with methanol possessed the acetate dormant terminal and they induced living polymerization of IBVE in conjunction with SnBr₄ in the presence of 1,4-dioxane. © 1998 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 36: 3173–3185, 1998     

Living anionic polymerization of lauryl methacrylate and synthesis of block copolymers with methyl methacrylate

Anionic polymerization of lauryl methacrylate (LMA) with 1,1‐diphenylhexyl lithium in tetrahydrofuran (THF) at ?40 °C resulted in a multimodal and broad molecular weight distribution (MWD) with poor initiator efficiency. In the presence of additives such as dilithium salt of triethylene glycol (G₃Li₂), LiCl, and LiClO₄, the polymerization resulted in polymers with a narrow MWD (≤ 1.10). Diblock copolymers of methyl methacrylate (MMA) and LMA were synthesized by anionic polymerization using DPHLi as initiator in THF at ?40 °C with the sequential addition of monomers. The molecular weight distribution of the polymers was narrow and without homopolymer contamination when LMA was added to living PMMA chain ends. Diblock copolymers with broad/bimodal MWD were obtained with a reverse‐sequence monomer addition. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 875–882, 2004     

Preparation of monodisperse hydrophilic polyamide by anionic polymerization of bicyclic oxalactam

The preparation of a monodisperse hydrophilic polyamide was achieved in the anionic polymerization of a bicyclic oxalactam, 8-oxa-6-azabicyclo[3.2.1]octan-7-one (abbreviated BOL) with the use of N-benzoyl BOL and potassium pyrrolidonate (2 and 0.5 mol % to BOL, respectively) in dimethyl sulfoxide at 25°C. The number-average molecular weight of the polyamide increased in direct proportion to the monomer conversion, and was consistent with the value calculated from the amounts of the consumed monomer and activator. The molecular weight distribution (MWD) of the polyamide obtained until the middle stage of polymerization (polymerization time, < 10 min; monomer conversion, < 60%) was found to be narrow (M_w/M_n = 1.1). The MWD was gradually broadened in the later stage of the polymerization, which may result from the redistribution of molecular weight of the resulting polyamide not only by the polymerization–depolymerization equilibrium, but also by transamidation between polymer chains.     

Cationic polymerization of α-methylstyrene in dichloromethane initiated with system 2,5-dichloro-2,5-dimethylhexene-BCl3. II. Continuous addition of monomer into initiator,quasiliving polymerization

A slow continuous addition of dichloromethana solutions of α-methylstyrene (α-MeSt) into a dichloromethane solution of 2,5-dichloro-2,5-dimethylhexane (DDH) with BCI₃ (initiating system II) prepared in advance resulted, in the temperature range between ?20 and ?40°, in a quasilving polymerization of α-MeSt. At ?20°C and a 100% conversion a polymer with a very narrow molecular weight distribution is formed, M?_w/M?_n - 1.1. Quasiliving polymerization of α-MeSt has not been achieved with freshly prepared dischloromethane solutions of DDH with BC₃ (initiating sytem I), or with solutions of BCI₃ alone (initiating system III). Polarity of the polymerization medium affected molecular weight distribution (MWD) of the polymer, and the polydispersity index decreased with decreasing polarity. MWD of the polymer samples were studied by the GPC method, the structure of poly (α-methylstyrene) (Pα-MeSt) was investigated by the ₁H-NMR analysis     

Studies on propagating species in cationic polymerization of styrene derivatives by acetyl perchlorate or iodine. III. Effect of salt on cationic copolymerization of styrene derivatives with vinyl ethers by acetyl perchlorate

A common-ion salt, tetra-n-butylammonium perchlorate, was found to affect the monomer reactivity ratios in the cationic copolymerization by acetyl perchlorate of styrene with p-methylstyrene and of 2-chloroethyl vinyl ether with p-methylstyrene, but not those for the copolymerization of 2-chloroethyl vinyl ether with isobutyl vinyl ether. In the copolymerization of p-methylstyrene with styrene or with 2-chloroethyl vinyl ether, the addition of the common-ion salt in a polar solvent shifted the monomer reactivity ratios to those in a less polar solvent. The molecular weight distribution analysis of the copolymer suggested that the addition of the common-ion salt depresses the dissociation of propagating species. Therefore, it was concluded that a propagating species with a different degree of dissociation shows a different relative reactivity towards two monomers. The nature of propagating species was also discussed on the basis of the common-ion effect on the monomer reactivity ratios in various solvents.     

阻聚剂对MMA原子转移自由基聚合的影响

Effect of a series of inhibitors as additives on atom transfer radical polymerization (ATRP) of methyl methacrylate (MMA) with FeCl2/PPh3 as catalyst system was studied, including 2,4,6-trinitrophenol (TNP), 4-methoxyphenol (4-MP), hydroquinone (HQ) and nitrobenzene (NB). It was found that TNP was the only. efficient additive for ATRP among these inhibitors. In the presence of small amounts of TNP, the polymerization proceeded rapidly after induction period to yield the polymers with controlled molecular weights and narrow molecular weight distributions (MWD). The initiating efficiency of the modified catalyst system with TNP was increased. The mechanism was proposed and confirmed by the end group analysis of the polymer.     

Mono‐ and binuclear nickel catalysts for 1‐hexene polymerization

Polymerization of 1‐hexene was carried out using a mononuclear (MN) catalyst and two binuclear (BN₁ and BN₂) α‐diimine Ni‐based catalysts synthesized under controlled conditions. Ethylaluminium sesquichloride (EASC) was used as an efficient activator under various polymerization conditions. The highly active BN₂ catalyst (2372 g poly(1‐hexene) (PH) mmol^?1 cat) in comparison to BN₁ (920 g PH mmol^?1 cat) and the MN catalyst (819 g PH mmol^?1 cat) resulted in the highest viscosity‐average molecular weight (M_v) of polymer. Moreover, the molecular weight distribution (MWD) of PH obtained using BN₂/EASC was slightly broader than those obtained using BN₁ and MN (2.46 for BN₂ versus 2.30 and 1.96 for BN₁ and MN, respectively). These results, along with the highest extent of chain walking for BN₂, were attributed to steric, nuclearity and electronic effects of the catalyst structures which could control the catalyst behaviour. Differential scanning calorimetry showed that the glass transition temperatures of polymers were in the range ? 58 to ?81 °C, and broad melting peaks below and above 0 °C were also observed. In addition, longer α‐olefins (1‐octene and 1‐decene) were polymerized and characterized, for which higher yield, conversion and molecular weight were observed with a narrower MWD. The polymerization parameters such as polymerization time and polymerization temperature showed a significant influence on the productivity of the catalysts and M_v of samples.     

Effect of polarity of the medium on the stereospecific polymerization of propylene by ansa-zirconocene catalyst

Propylene was polymerized with rac-ethylene-bis (1-η⁵-indenyl)dichlorozirconium/methylaluminoxane in solvents of different polarity. The poly (propylene) formed was separated by solvent extraction; ¹³C-NMR and DSC measurements were made on the polymer fractions. The poly(propylene) in each solvent fraction has its characteristic molecular weight steric pentad distributions, melting transition temperature, and enthalpy for fusion irrespective of the polymerization medium. The results suggest that the medium dielectric constant does not affect the polymerization rate or the intrinsic stereoselectivity, propagation and chain transfer rates a given catalytic species but can alter the occurrence of steric insertion errors through shifting of distributions of the propagating species producing poly(propylenes) of different stereoregularities. © 1994 John Wiley & Sons, Inc.     

Synthesis of regiocontrolled poly(4,6-di-n-butoxy-1,3-phenylene) by oxidative coupling polymerization

Poly(4,6-di-n-butoxy-1,3-phenylene) ( 6 ) was prepared by oxidative coupling polymerization of 1,3-di-n-butoxybenzene ( 1 ) or 2,2′,4,4′-tetra-n-butoxy biphenyl (3). Polymerizations were conducted in nitrobenzene in the presence of FeCl₃ at room temperature and produced polymers with number-average molecular weights up to 42,000. The effects of various factors, such as amount of FeCl₃ and reaction temperature and time were studied. The structure of polymer 6 was characterized by 270 MHz ¹H- and 68.5 MHz ¹³C-NMR spectroscopies and was estimated to consist of almost completely 1,3-linkage. The regiocontrolled polymer was readily soluble in common organic solvents. Thermogravimetric analysis of polymer 6 showed 10% weight loss at 390°C in nitrogen. © 1997 John Wiley & Sons, Inc. J Polym Chem 35 : 2259–2266, 1997