Anionic Polymerization Of Methyl Methacrylate Research Articles

Hindered lithium dialkylamide initiators for the living anionic polymerization of methacrylic esters

AbstractLithium diisopropylamide is an efficient initiator for the anionic polymerization of methyl methacrylate in polar solvents at –78°C. Predictable molecular weights based on the initiator concentration were obtained, yields were quantitative, and molecular weight distributions were relatively narrow (<1.30). The presence of an amino end group and confirmation of the initiation mechanism were confirmed by potentiometric titration using HClO4. Number‐average molecular weights determined by titration agreed well with values determined by SEC. Other lithium dialkylamides that contain larger alkyl groups such as lithium diisobutylamide were less efficient initiators. This was attributed to the more nucleophilic anion due to less steric hindrance near the nitrogen atom. Molecular weight distributions were significantly broadened (>2.0), and molecular weight control was not achieved. However, polymer yields were quantitative. In all cases, PMMA stereochemistry was indicative of a solvent‐separated lithium counterion, and triad compositions were identical to organolithium initiated homopolymers, i.e., 78% syndiotactic, 20% heterotactic, and 2% isotactic. © 1994 John Wiley & Sons, Inc.

Study of the propagation centre in the anionic polymerization of acrylic monomers, 1. Spectroscopic study of methyl 2‐lithioisobutyrate, an initiator for the anionic polymerization of acrylic monomers

AbstractAs the simplest model for the propagation centre in the anionic polymerization of methyl methacrylate, the solution of methyl 2‐lithioisobutyrate (1) in tetrahydrofuran was studied by means of 1H, 6Li, 7Li and 13C nuclear magnetic resonance (NMR), and Raman spectroscopy at various concentrations and temperatures. A system of equilibria of differently solvated dimeric, tetrameric and two isomeric trimeric aggregates was found and their thermodynamic constants were established. On the basis of the analysis of NMR chemical shifts, heteronuclear nuclear Overhauser effect correlation spectroscopy (NOESY) spectra and relaxation data, structures of the aggregates are suggested. The kinetics of the exchange between the aggregates and the lifetime of individual aggregates was established. The results suggest that the aggregation can interfere with initiation in the early steps of anionic polymerization of acrylics.

Anionic Polymerization of Acrylic Monomers. 19. Effect of Various Types of Ligands Other Than Lithium Chloride on the Stereochemistry of Anionic Polymerization of Methyl Methacrylate

The effect of several types of ligands, i.e., 12-CE-4 (1), K211 (2), LiOtBu (3), and LiOEEM (4), on the stereochemistry of MMA anionic polymerization at -78°C in various solvents, i.e., toluene, THF, and a 9/1 toluene/THF mixture, has been studied. Similar to the LiCl-complexed system, the stereoregularity of MMA polymerization in the presence of these additives is seemingly controlled by association/complexation equilibria among associated, nonassociated, and ligand-complexed active species. Accordingly, complexation of active species by σ-chelating ligands such as 12-CE-4 and K211 simply shifts the association equilibrium toward the formation of ligand-complexed (nonassociated) species, giving preferably syndiotactic placements (rr) in a 9/1 toluene/THF mixture as well as in toluene

Phase separation in poly(methyl methacrylate)‐block‐poly(2,3‐dibromopropyl methacrylate) copolymers

AbstractAB block copolymers poly(methyl methacrylate)‐block‐poly(2,3‐dibromopropyl methacrylate) were prepared by a two‐stage process involving the sequential anionic polymerization of methyl methacrylate and allyl methacrylate followed by bromination of the pendant allylic groups. Transmission electron microscopy of thin sections of cast films revealed phase separation, the morphology depending upon composition of the block. In particulate form these copolymers gelled with methyl methacrylate to form doughs that could be moulded and heat cured to produce hard X‐ray opaque copolymers.

Use of the phenanthrene-based lithium initiator in the anionic polymerization of methyl methacrylate

A series of poly (methyl methacrylate) PMMA polymers with low polydispersity was synthesized anionically using sterically hindered (1-(9-phenanthryl)-1-phenyl-3-methylpentyl)lithium as an initiator. Results of absorption spectroscopy and gelpermeation chromatography (GPC) analyses were used to discuss the initiator efficiency.

Anionic polymerization of (meth)acrylic monomers. 12. Effect of lithium chloride on the stereochemistry of the anionic polymerization of methyl methacrylate in THF and in a 9/1 toluene/THF mixture

LiCl has been found to have an important effect on the E/Z ratio of the living chain ends of poly(methyl methacrylate) (PMMA) in THF, in contrast to the main-chain tacticity. In contrast, LiCl has a significant influence on the stereoregularity of the anionic polymerization of MMA in a 9/1 toluene/THF mixture. When the LiC/initiator molar ratio is increased, the syndiotactic placements (rr) are favored at the expense of the isotactic ones (mm)

Organoboron compounds as Lewis acid accelerators for the aluminum porphyrin-mediated living anionic polymerization of methyl methacrylate

The polymerization of methyl methacrylate (MMA) initiated with methylaluminum tetraphenylporphyrin was accelerated at room temperature upon addition of triphenylboron and tris(pentafluorophenyl)boron Lewis acids, affording polymers of narrow MWD with M n s close to the expected values. The living character of the polymerization was demonstrated by the two-stage polymerization of MMA. The trialkylboron tri-n-butylboron neither accelerated nor terminated the polymerization. Use of other boron-containing Lewis acids such as BF 3 -OEt 2 , BCl 3 , triphenyl borate, and trimethylbororin (trimethylcyclotribororane) for the polymerization of MMA resulted in rapid termination under similar conditions

The P4‐Phosphazene Base as Part of a New Metal‐Free Initiator System for the Anionic Polymerization of Methyl Methacrylate

The P4‐Phosphazene Base as Part of a New Metal‐Free Initiator System for the Anionic Polymerization of Methyl Methacrylate

Poly(ethylene oxide) gel as a novel polymerization medium anionic polymerization of methyl methacrylate

AbstractCrosslinked poly(ethylene oxide)‐(PEO‐N) is used as a novel medium for the anionic polymerization of methyl methacrylate (MMA) initiated by t‐BuOK and ethyl‐α‐lithioisobutyrate (α‐LiEtIB) in toluene. Comparative studies with linear poly(ethylene oxide)‐(PEO‐L) are performed as well. It is found that PEO‐N effectively binds both initiators, and the polymerization process takes place mainly in the gel phase. PEO‐N accelerates the polymerization process initiated by t‐BuOK enabling the formation of high‐molecular‐weight polymers with high yields. Part of poly(methyl methacrylate)‐(PMMA) remains in the gel particles yielding semi‐interpenetrating networks with amphiphilic properties. PEO additives do not influence profoundly the course of the polymerization, initiated by α‐LiEtIB. The influence of PEO‐N on the proceeding of the polymerization is discussed in some detail.

Anionic polymerization of methyl methacrylate initiated by thiophenol

Methyl methacrylate (MMA) was polymerized by thiophenol without oxidants. Hydroquinone had no effect on the polymerization, indicating that the polymerization proceeded via a non-radical process. Since other monomers with an x,β-unsaturated carbonyl group polymerized similarly, the initiation and propagation were explained by the Michael addition. Radical scavengers such as 1,1-diphenyl-2-picrylhydrazyl(DPPH) and galvinoxyl enhanced the polymerization because of an accompanying radical polymerization initiated by radical species formed by the reaction of them with thiophenol. Aluminium acetylacetonate, which has no effect on radical polymerization, accelerated the thiophenol-initiated polymerization supporting the postulated mechanism.

Grafting of polymers onto carbon whisker by anionic graft polymerization of vinyl monomers using metallized aromatic rings and/or phenoxy lithium groups on the surface as initiator

AbstractDuring the anionic polymerization of methyl methacrylate (MMA) initiated by n‐butyl‐lithium (n‐BuLi) in the presence of carbon whisker, PMMA was found to be grafted onto the surface depending on the propagation from OLi groups, which are produced by the reaction of oxygen containing groups on the surface with n‐BuLi. But no grafting of polystyrene was observed at all. By the activation of OLi groups by the addition of crown ether, however, the grafting of polystyrene onto the carbon whisker was achieved. On the other hand, it was found that metallized carbon whisker also initiates the anionic graft polymerization of MMA and styrene: percentage of grafting of PMMA and polystyrene reached 231.3 and 157.9%, respectively. The metalation of carbon whisker was achieved by the treatment with n‐BuLi in aprotic polar solvents, such as N,N,N′,N′‐tetramethylethylene‐diamine or hexamethylphosphorous triamide, and in toluene in the presence of complexing agent of cation such as crown ether or a small amount of aprotic solvent. In the polymerization, grafted polymer chains were considered to propagate both from metallized aromatic rings and from OLi groups. The polymer‐grafted carbon whisker gave a stable colloidal dispersion in organic solvents.

PMMA-block-polyisobutylene-block-PMMA prepared with ?,?-dilithiated polyisobutylene and its characterization

A triblock copolymer of PMMA and polyisobutylene(PIB), PMMA-block-PIB-block-PMMA, was prepared by anionic polymerization of methyl methacrylate initiated with α, ω-dilithiated poly(isobutylene) diisobutylate in tetrahydrofuran at -60°C. The molecular weight distribution of the block copolymer was close to that of the starting PIB. The stereoregularity of PMMA block was predominantly syndiotactic. Proton spin-lattice relaxation time and solution viscosity of the block copolymer in acetone, which is non-solvent for PIB, indicate that the block copolymer forms rigid spherical particles. Stereocomplex formation with isotactic PMMA was also studied.

Determination of E/Z and meso/racemic end-group stereochemistry in the anionic polymerization of methyl methacrylate in tetrahydrofuran

MMA is polymerized anionically in THF at −70 o C in the presence of Li + , Na + , K + , Cs + , and cryptated K + cations and the reaction is terminated by ClSiMe 3 . The 13 C NMR results are consistent with the following assumptions: 1) transition-state monomer approach to the living end is s-cis for Li + and Na + (leading to Z chain ends) due to coordination with the counterion and s-trans for Cs + and cryptated K + (leading to E chain ends) due to steric reasons; 2) tacticity is determined by the E/Z stereoisomerism of the chain end and possibly also by the stereochemistry of the preceding diad; 3) with increasing radius of the counterion, addition of monomer to E isomers results in an increasing fraction of racemic diads, while the Z isomers give a decreasing amount of racemic diads

The synthesis of polymers bearing terminal fluorescent and fluorescence‐quenching groups, 1. The incorporation of fluorescent groups at one end of the macromoleculer by means of the initiation process

AbstractSuitably substituted vinylidene compounds, incapable of undergoing anionic polymerisation, are reacted with butyllithium to produce an initiator for the anionic polymerisation of methyl methacrylate. Thus poly(methyl methacrylate)s are obtained, the macromolecules of which carry a single fluorescent (or fluorescence quenching) moiety at the initiating end of each chain.

Equilibria in the anionic polymerization of methyl methacrylate, 2. Effect of lithium tert‐butoxide on rate and equilibrium constants

AbstractThe effect of lithium tert‐butoxide (t‐BuOLi) on rate constants and equilibrium constants of reactions involved in the initial stage of the anionic polymerization of methyl methacrylate (MMA) in tetrahydrofuran, initiated by methyl α‐lithioisobutyrate (P) was investigated at 23 ± 3°C. Addition of t‐BuOLi decreases the rate constants of initiation and propagation by one order of magnitude; the rate constants of termination by cyclization decrease by two orders of magnitude. This leads to an overall tenfold higher preference of propagation with respect to termination and explains the favourable effect of alkoxide in the polymerization reported earlier. Within experimental error, the equilibrium constant for initiation is independent of alkoxide. The infrared spectra prove the interaction of lithiated MMA‐dimer with t‐BuOLi and show the changed properties of the Li‐enolate group as well as the increased extent of the γ‐ester group coordination to lithium.

Grafting of Polymers from Carbon Fiber. Anionic Graft Polymerization of Vinyl Monomers Initiated by Metallized Aromatic Rings on Carbon Fiber

Abstract The anionic graft polymerization of vinyl monomers onto carbon fiber initiated by metallized carbon fiber was investigated. The metalation of polycondensed aromatic rings of the carbon fiber surface was achieved by the treatment of carbon fiber with n-butyl-lithium (BuLi) in N, N, N′, N′ -tetramethylethylenediamine (TMEDA) or hexamethylphosphorous triamide (HMPT) at 0°C. The anionic polymerization of methyl methacrylate (MMA) and styrene (St) was initiated by the metallized carbon fiber, and these polymers were grafted onto the surface. The conversion and the percentage of grafting increased with increasing amount of BuLi used for the metalation of carbon fiber. When 0.20 g carbon fiber was treated with 0.3 mmol BuLi in TMEDA, the percentage of grafting of PMMA and PSt reached a maximum value (PMMA, 34.5%; PSt, 37.1 %). Furthermore, the metalation of aromatic rings of carbon fiber also proceeds by the treatment with BuLi in HMPT. On the contrary, no grafting was observed when carbon fiber was tre...

Synthesis of new amphiphilic block copolymers. Block copolymer of sulfonated glycidyl methacrylate and alkyl methacrylate

AbstractWater‐soluble amphiphilic block copolymers consisting of a hydrophobic block of poly(alkyl methacrylate) and a hydrophilic anionic polyelectrolyte block have been synthesized by a living anionic polymerization of methyl methacrylate and glycidyl methacrylate and subsequent selective modification of the oxirane groups of the glycidyl methacrylate block into hydroxysulfonate groups by a phase transfer catalyzed sulfonation reaction. The block copolymers were characterized by a predictable motecular weight and a narrow molecular weight distribution while the yield was quantitative. These amphiphilic block copolymers display surfaceactive behavior in water and they are characterized by a critical micelle concentration.

Polymerization of Methyl Methacrylate in the Presence of Imidazole Derivatives. Additive Effect of the Initiator Adduct and Copolymerization with Acrylamide

Abstract In the anionic polymerization of methyl methacrylate (MMA) induced by imidazole (Im), an Im‐MMA adduct forms as an initiator adduct in methanol at 30°C in an argon atmosphere by the equimolar reaction of Im with the MMA monomer. The additive effect of the adduct on the homopolymerization of MMA in tetrahydrofuran at 30°C was investigated by dilatometry. The existence of the adduct increased the duration of the propagation step without shortening the formation step of the initiator adduct. The H‐D exchange reaction of the adduct was observed in D2O by 1H NMR. Proton transfer of the MMA unit in the adduct was not observable until 45 h after initiation. The copolymerizability of MMA with acrylamide (AAm) induced by the Im catalyst in THF at 30°C was also investigated. It was found that the homo‐and copolymerizations proceeded at the same time. On the other hand, in the MMA homopolymerization system, the addition of AAm monomer during the initial propagation step yielded copolymer of MMA and AAm for near equimolar concentration of the charged monomers.

Hydrophilic modification of engineering polymers

Water-soluble carboxylated polymers were synthesized from engineering polymers via the metallation of poly(oxy-1,4-phenylenesulphonyl-1,4-phenyleneoxy-1,4-phenyleneisopropylidene-1, 4-phenylene) and poly(oxy-2,6-dimethyl-1,4-phenylene) with n-butyllithium followed by reaction with carbon dioxide. Interactions between lithium sites on the polymer backbones cause the precipitation of highly metallated polymers. Precipitation of PPO occurs at approximately 15% metallation based on polymer repeat unit. Reproducibility problems are encountered with highly metallated, precipitated polymers. An ester-functional comb-type graft copolymer is synthesized via the anionic polymerization of methyl methacrylate (MMA) from metallated sites on PPO. The ester functionalities can be transesterified with hydroxy functional reagents to yield well-defined comb-type graft terpolymers. Transesterification of oligomeric polyethylene glycol onto PPO-MMA yields a comb-type graft terpolymer with nonionic hydrophiles.

Equilibria in the anionic polymerization of methyl methacrylate, 1. Chain‐length dependence of the rate and equilibrium constants

AbstractThe rate constants of polymerization and cyclization and the equilibrium constants of polymerization are calculated from kinetic data of the anionic oligomerization of methyl methacrylate initiated by methyl α‐lithioisobutyrate in THF at 25°C, and of the “disproportionation” of living oligomers. The numeric method reported earlier was improved. The rate constants of cyclization decrease with chain‐length, due to increasing steric hindrance. The rate constants of polymerization depend on the concentration of active centres, due to the formation of associates. Rate and equilibrium constants of polymerization decrease with chain‐length. This is discussed in terms of intramolecular coordination of the counterion with ester groups of the chain.