Polymerization Of Α-methylstyrene Research Articles

Cationic β-Scission of C-H and C--C Bonds for Selective Dimerization and Subsequent Sulfur-Free RAFT Polymerization of α-Methylstyrene and Isobutylene.

A series of exo-olefin compounds ((CH3)2C(PhY)-CH2C(=CH2)PhY) were prepared by selective cationic dimerization of α-methylstyrene (αMS) derivatives (CH2=C(CH3)PhY) with p-toluenesulfonic acid (TsOH) via β-C-H scision. They were subsequently used as reversible chain transfer agents for sulfur-free cationic RAFT polymerization of αMS via β-C-C scission in the presence of Lewis acid catalysts such as SnCl4. In particular, exo-olefin compounds with electron-donating substituents, such as a 4-MeO group (Y) on the aromatic ring, worked as efficient cationic RAFT agents for αMS to produce poly(αMS) with controlled molecular weights and exo-olefin terminals. Other exo-olefin compounds (R-CH2C(=CH2)(4-MeOPh)) with various R groups were prepared by different methods to examine the effects of R groups on the cationic RAFT polymerization. A sulfur-free cationic RAFT polymerization also proceeded for isobutylene (IB) with the exo-olefin αMS dimer ((CH3)2C(Ph)-CH2C(=CH2)Ph). Furthermore, telechelic poly(IB) with exo-olefins at both terminals was obtained with a bifunctional RAFT agent containing two exo-olefins. Finally, block copolymers of αMS and MMA were prepared via mechanistic transformation from cationic to radical RAFT polymerization using exo-olefin terminals containing 4-MeOPh groups as common sulfur-free RAFT groups for both cationic and radical polymerizations.

Synthesis of Sub-100 nm Nanoparticles by Emulsifier-free Emulsion Polymerization of α-Methylstyrene, Methyl Methacrylate and Acrylic Acid

The emulsifier-free emulsion copolymerization of α-methylstyrene (AMS) and methyl methacrylate (MMA) in the presence of functional monomer acrylic acid (AA) was carried out in batch process, giving birth to sub-100 nm nanoparticles. The kinetics of polymerization was investigated. The morphology and size of particles were monitored by TEM. The influences of the functional monomer AA concentration, initiator ammonium persulfate (APS) concentration, and polymerization temperature were studied. It was found that AMS caused a drastic decrease in both the rate of polymerization and the average degree of polymerization. The activation energy calculated from Arrhenius plot turned out to be 83.6 kJ/mol.

Electrophilic Reactivity of the α,α-Dimethylbenzyl (Cumyl) Cation

The cumyl cation was generated by laser flash photolysis of cumyl tris(4-chlorophenyl)phosphonium tetrafluoroborate in CH2Cl2 and identified by its UV spectrum. From the decay of its absorbance at λ = 335 nm in the presence of variable concentrations of several nucleophiles with CC double bonds, rate constants for the reactions of the cumyl cation with these π-nucleophiles were determined. The linear free energy relationship log k20°C = s(N + E) (eq 1) was used to calculate the electrophilicity parameter E = 5.74 of the cumyl cation from the rate constants determined in this work and the previously reported N and s parameters of the nucleophilic reaction partners. Substitution of E of the cumyl cation and of the previously reported N and s parameters of α-methylstyrene into eq 1 predicts the temperature-independent rate constant of the addition of the cumyl cation to α-methylstyrene (1.2 × 108 M−1 s−1), which is relevant for the cationic polymerization of α-methylstyrene.

Structure−Reactivity Scales in Carbocationic Polymerizations: The Case of α-Methylstyrene

The propagation rate constant, kp, for the cationic polymerization of α-methylstyrene (αMeSt) was determined. First, the polymerization of αMeSt was carried out initiated by the diαMeStHCl/SnBr4 initiator/coinitiator system in dichloromethane (DCM) or in DCM/methylcyclohexane (MeCHx) 1:1 (v/v) solvent mixture at −80 °C in the presence of allyltrimethylsilane (ATMS). Clean and quantitative addition of ATMS to the propagating end terminates the polymerization, and from the limiting conversion and molecular weights, the kp/kATMS ratio was calculated. The kp = (5.2 and 7.7) × 107 L mol−1s−1 in DCM and DCM/MeCHx 1:1 (v/v), respectively, were calculated from the kATMS values determined by the diffusion clock method. Competition polymerizations between αMeSt and each of the following monomers p-methylstyrene (pMeSt), isobutylene (IB), styrene (St), and p-chlorostyrene (pClSt) were performed in DCM/MeCHx 1:1 (v/v) at −80 °C. From the limiting conversions and molecular weights, the reactivity ratios kp/k12 were de...

Novel determination of the dimerization mechanism for thermal polymerization of α-methylstyrene

This study discussed the phenomena on thermal polymerization of α-methylstyrene (AMS). A curve scanned by temperature-programmed technique was performed by differential scanning calorimetry (DSC). Heat of polymerization (ΔH) and onset temperature of exothermic (T0) behavior were determined to be 280±10 J g-1 and about 138±1°C, respectively. A dimer formation mechanism was proposed for initiation of the propagating chain. Spectroscopic identification of dimer structure was conducted by infrared (IR) spectroscopy in the wavenumber from 650 to 1100 cm-1associated with molecular fingerprint characteristics. The mechanism of thermal polymerization on α-methylstyrene proposed in this study was similar to that of styrene suggested by Mayo.

Living poly(α-methylstyrene) near the polymerization line: VIII. Mass density, viscosity, and surface tension in tetrahydrofuran

We consider the polymerization of α-methylstyrene, initiated by sodium naphthalide in the solvent tetrahydrofuran on time scales that permit full thermodynamic equilibrium between the monomer and the polymer. We present new measurements as a function of temperature of the mass density, the shear viscosity, and the liquid–vapor surface tension, and we compare the data to theoretical expectations when the polymerization is viewed as a phase transition. The mass density is well described by either mean field or nonmean field theories. The shear viscosity increases as the average degree of polymerization (DP) increases, but the exponent 3.4 is not reached, presumably because the DP is too small. The surface tension increases as the DP increases, indicating depletion of the polymer from the surface.

High molecular weight poly(?-methylstyrene) formed by free radical polymerization in emulsions

Free radical polymerizations of α-methylstyrene (AMS) were performed in dispersions of oil in water using a mixture of nonionic nonylphenoxy poly(ethylene glycol) surfactants and initiated with ascorbic acid/hydrogen peroxide at temperatures ranging from 3 to 45 °C. A bimodal distribution of high (∼60,000 g/mol) and low molecular weight components (∼8000 g/mol) was analyzed by size-exclusion chromatography (SEC). The relative amount of the low molecular weight fraction increased with increasing the polymerization temperature. The polymer yields decreased from 52% at 3 °C to 3% at 45 °C. The syndiotactic content of PAMS decreased from 70% rr at 3 °C to 58% rr at 45 °C. © 2001 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 39: 525–529, 2001

Synthesis of block-graft polymers by anionic polymerizations

Two poly(4-methylstyrene) (P4MS)-block-polystyrene (PS)-block-P4MS triblock copolymers were prepared by successive anionic addition of styrene and 4-methylstyrene monomers as the core backbone (CB) for the architecture of block-graft polymers. Both terminal 4-methylstyrene blocks of CB were metalated with a sec-butyllithium (sec-BuLi)/tetramethylethylenediamine (TMEDA) complex in cyclohexane. The first-generation block-graft polymer (1BG) was prepared by anionic polymerization of α-methylstyrene by the lithiated CB in tetrahydrofuran (THF) at –78°C and subsequently the terminal graft ends were capped with a small amount of 4-methylstyrene. The characterization of those block-graft polymers was carried out in detail.

Synthesis of block-graft polymers by anionic polymerizations

Two poly(4-methylstyrene) (P4MS)-block-polystyrene (PS)-block-P4MS triblock copolymers were prepared by successive anionic addition of styrene and 4-methylstyrene monomers as the core backbone (CB) for the architecture of block-graft polymers. Both terminal 4-methylstyrene blocks of CB were metalated with a sec-butyllithium (sec-BuLi)/tetramethylethylenediamine (TMEDA) complex in cyclohexane. The first-generation block-graft polymer (1BG) was prepared by anionic polymerization of α-methylstyrene by the lithiated CB in tetrahydrofuran (THF) at –78°C and subsequently the terminal graft ends were capped with a small amount of 4-methylstyrene. The characterization of those block-graft polymers was carried out in detail.

Living polymerization of α-methylstyrene in tetrahydrofuran followed by dynamic light scattering near its polymerization temperature

We followed the polymerization reaction of living poly-α-methylstyrene in a solution of tetrahydrofuran as a function of temperature, near its ceiling temperature, using dynamic light scattering. We obtained three different relaxation times revealing three kinds of macromolecular species in the solution. One of the relaxation times corresponded to the formation of living polymer chains. In this particular case, we found that the average relaxation time increased as temperature was lowered due to polymer growth. Nevertheless, it did not follow the same track along a cooling–heating cycle. These results are consistent with an incomplete depolymerization reaction. For the other two species, we propose that they were the result of ionic aggregation.

The polymerization of actin: Study by small angle neutron scattering

We report measurements of small angle neutron scattering from solutions of rabbit muscle G-actin at 3.00 mg/mL in D2O buffer solution, with [Ca2+]=0.52 mM and with [KCl]=15, 8.9, and 5.4 mM. We observe the onset of the polymerization of G-actin to F-actin as the temperature is increased. The polymerization takes place on a time scale of 30–45 min for each temperature jump of 2 °C–3 °C. As the temperature is increased further, the average size of the polymers increases, and the characteristic length scale (or correlation length), ξ, of the F-actin in the dilute solution grows: ξ is about 10 Å below Tp, and about 70 Å a few degrees above Tp. The transition is sharper for lower concentrations of KCl. For the sample with [KCl]=8.9 mM, we observe a peak in ξ at about 2 °C above Tp, which indicates a crossover into the semidilute regime. The transition is essentially reversible, but shows evidence of incomplete depolymerization on cycling. We are unable to apply the available theoretical model for reversible polymerization to rabbit muscle actin because of a lack of information on the enthalpy and entropy of polymerization. However, our observations for rabbit muscle actin are quite analogous to observations on the equilibrium polymerization of α-methylstyrene [A. P. Andrews, K. P. Andrews, S. C. Greer, F. Boué, and P. Pfeuty, Macromolecules 27, 3902 (1994)].

The Living Cationic Polymerization of α-Methylstyrene with BCI3 as Coinitiator

ABSTRACT The cationic polymerization of α-methylstyrene (αMeSt) was studied using the cumyl chloride (CumCl), (CH3)3C-CH2- C(CH3)2-CH2-C(Ph)2-OCH3 (TMPDPEOMe) or (CH3)2C(Ph) CH2C(CH3)(Ph)Cl (the HCl adduct of αMeSt dimer, DiαMeStHCl)/BCl3 initiator/coinitiator systems in the presence of proton trap in methyl chloriderhexanes (MeCl:Hex) or MeCl: methylcyclohexane (MeChx) mixtures at −80 and −60°C. While CumCl is not an efficient initiator in conjunction with BCl3, TMPDPEOMe and Di αMeStHCl were found to be very efficient initiators. The polymerization was much faster in the MeCl:Hex mixture than in MeCl:MeChx. The polymerization rate was also higher at −80°C than at −60°C in the same solvent. The polymerization was found to be living at −80°C, as well as at −60°C, giving rise to poly(α-methylstyrene) (PαMeSt) with controlled molecular weight and narrow molecular weight distribution (Mw/Mn ∼ 1.1-1.2). The chain ends remained living for up to 40 minutes under monomer starved conditions at −80°C, but they rapidly decomposed at −60°C.

Initiation via Haloboration in Living Cationic Polymerization. 4. The Polymerization of α-Methylstyrene

he polymerization of α-methylstyrene was studied in the absence of a separately added cationogen (i.e., initiator) and in the presence of a proton trap, using boron halides (BX 3 , X = Cl, Br, and I). The effect of the monomer and BX 3 concentration, solvent polarity, and temperature was examined. The polymerization rates increased with decreasing temperature and with increasing solvent polarity. The molecular weight (M n ) of the products also increased with decreasing temperature; however it was relatively independent of solvent polarity. Under identical conditions the M n 's were highest with BCl 3 , lower with BBr 3 , and lowest with BI 3 . Kinetic experiments support that initiation is by haloboration, but direct proof was only obtained for BI 3 . For polymers made with BI 3 the presence of one boron per chain was confirmed by elemental analysis, while the high M n 's obtained with BCl 3 and BBr 3 prevented quantitative analysis of head and end groups.

Mechanism of “Autoacceleration” in the Thermal Oxidative Polymerization of α-Methylstyrene

Thermal oxidative polymerization of α-methylstyrene (AMS) has been studied at various temperatures (45−70 °C) and pressures (50−400 psi). Due to its high electron dense double bond, it undergoes thermal oxidative polymerization even at low temperatures fairly easily. The major products are poly(α-methylstyrene peroxide) (PMSP), and its decomposition products are acetophenone and formaldehyde. Above 45 °C the rate of polymerization increases sharply at a particular instant showing an “autoacceleration” with the formation of a knee point. The “autoacceleration” is supported from the fact that the plot of Rp vs T shows a rapid rise, and the plot of ln Rp vs 1/T is non-Arrhenius. The occurrence of autoacceleration is explained on the basis of acetophenone-induced cleavage of PMSP during polymerization, generating more initiating alkoxy radicals, which subsequently leads to the rapid rise in the rate of polymerization. The mechanism of autoacceleration is supported by the change in order, activation energy, and activation volume before and after the knee point.

The cationic polymerization of α-methylstyrene in liquid sulfur dioxide initiated by the HI/I2 system

The polymerization of α-methylstyrene (αMeSty) initiated by HI/I2 or HI in the presence of liquid sulfur dioxide has been investigated. The number-average molecular weight increased with the monomer concentration for reactions initiated by the HI/I2 system. I2 also participates in the initiation process, increasing the number-average polymer chain at higher monomer concentration. HI alone is also able to initiate the polymerization of αMeSty in the presence of SO2. With this initiator, transfer reaction can be minimized in systems containing low amount of SO2.

Ethylene, Styrene, and α-Methylstyrene Polymerization by Mono(pentamethylcyclopentadienyl) (Cp*) Complexes of Titanium, Zirconium, and Hafnium: Roles of Cationic Complexes of the Type [Cp*MR2]+ (R = Alkyl) as both Coordination Polymerization Catalysts and Carbocationic Polymerization Initiators

A variety of monocyclopentadienyl and mono(pentamethylcyclopentadienyl) complexes of titanium, zirconium, and hafnium are assessed for abilities to initiate polymerization of ethylene, styrene, and, in part, α-methylstyrene. In general, little or no activity was found for either neutral species of the types CpMMe3 and CpMMe2OR or for cationic 12- and 14-electron species of the types [CpMR2L]+ and [CpMR2L2]+, respectively (Cp = η5-cyclopentadienyl; R = alkyl; L = amine, phosphine ligands). In contrast, much better olefin polymerization initiators result from abstraction of a methyl carbanion from Cp*MMe3 (Cp* = η5-pentamethylcyclopentadienyl) by B(C6F5)3, a reaction which gives cationic, 10-electron species of the type “[Cp*MMe2][BMe(C6F5)3]”. Of these, the complex [Cp*TiMe2][BMe(C6F5)3] (A) is an excellent initiator or initiator precursor for the polymerization of ethylene and styrene, resulting in high yields respectively of high molecular weight polyethylene and atactic (a-PS) and/or syndiotactic polystyrene (s-PS), depending on conditions; the tacticity of purified s-PS, as judged by 13C{1H} NMR spectroscopy, approaches 100%. While the polymerization of ethylene probably involves a classical Ziegler−Natta process, polymerization of styrene to s-PS and a-PS apparently involves respectively a Ziegler−Natta process and carbocationic initiation. High yields of essentially syndiotactic poly(α-methylstyrene) are obtained by utilizing the same initiator system, also apparently via a carbocationic process.

Living Carbocationic Polymerization of α-Methylstyrene Using Tin Halides as Coinitiators

The polymerization of α−methylstyrene (αMeSt) was studied in conjunction with the (CH3)3CCH2C(CH3)2CH2C(Ph)2Cl (1,1-diphenylethylene-capped 2,4,4-trimethyl-2-chloropentane)/SnBr4 or SnCl4 initiatin...

Living Carbocationic Sequential Block Copolymerization of Isobutylene with .alpha.-Methylstyrene

The polymerization of α-methylstyrene (αMeSt) was investigated using the 2-chloro-2,4,4-trimethylpentane (TMPClTiCl 4 /methyl chloride :hexane (40 :60, v :v)/-80 °C system as a model to determine the efficiency of crossover from living polyisobutylene (PIB) to αMeSt. Low initiator efficiencies and broad molecular weight distributions were obtained. Living polymerization of αMeSt was achieved by first converting TMPCl to the corresponding diphenylalkylcarbenium ion by capping with 1,1-diphenylethylene (DPE), followed by the addition of titanium(IV) alkoxide to decrease the Lewis acidity. The initiator efficiencies, however, were lower than 100%. Living polymerization with ∼100% initiator efficiency was achieved by SnBr 4 as coinitiator. First, TMPCl is transformed to the corresponding diphenylalkylcarbenium ion by capping with 1,1-diphenylethylene. Subsequently, titanium(IV) isopropoxide is introduced to deactivate TiCl 4 , followed by the addition SnBr 4 and αMeSt. The success of the method was demonstrated by the synthesis of PIB-poly(α-methylstyrene) diblock copolymers without homopolymer contaminants.

Cationic polymerization of ?-methylstyrene in liquid sulfur dioxide initiated by p-methoxybenzyl chloride

The cationic polymerization of α-methylstyrene (α-MeSty) in liquid sulfur dioxide initiated by benzyl chloride and p-methoxybenzyl chloride was investigated at different temperatures. The p-methoxybenzyl chloride (p-MOBCl) was found to be effective in initiating α-MeSty polymerization while benzyl chloride yielded only traces of polymer under all conditions. Polymers with narrow molecular weight distribution were obtained indicating rapid exchange between p-MOBCl dormant species and the corresponding carbenium ion. The reaction seems to be controlled by termination.

Living Cationic Polymerization of α-Methylstyrene. 2. Synthesis of Block and Random Copolymers with 2-Chloroethyl Vinyl Ether and End-Functionauzed Polymers†

Abstract Both AB and BA block copolymers of α-methylstyrene (αMeSt) and 2-chloroethyl vinyl ether (CEVE) were synthesized by the sequential living cationic polymerization initiated with the HCl-CEVE adduct (1a)/SnBr4 system in CH2Cl2 at -78°C. αMeSt-CEVE (AB) block copolymers with narrow molecular weight distributions ([Mbar]w/[Mbar]n ∼ 1.15) were obtained when αMeSt was polymerized first, followed by addition of CEVE to the resulting αMeSt living polymer solution. The reverse order of monomer addition, from CEVE to αMeSt, also led to a BA-type block copolymer. In the polymerization of a mixture of the two monomers, almost random copolymers were obtained. Living polymerizations of αMeSt were also induced with functional initiating systems, HCl-functionalized vinyl ether adducts (1b-1d)/SnBr4, to give end-function-alized poly(αMeSt)s with a methacrylate, an acetate, or a phthalimide terminal.