Synthesis of stereoblock poly(methyl methacrylate) via transformation of isotactic-specific living polymer anion to syndiotactic-specific anion

Polymerization of methyl methacrylate (MMA) by isotactic poly(methyl methacrylate) (PMMA) living anion, prepared with t-C₄H₉MgBr in toluene at ?60°C, was carried out at ?78°C in the presence of trialkylaluminiums (R₃Al; R = CH₃, C₂H₅, and n-C₄H₉) to obtain a stereoblock PMMA, isotactic PMMA-block-syndiotactic PMMA. Among the R₃Als, (CH₃)₃Al gave most effectively the steroblock PMMA with narrow molecular weight distribution. The fraction of rr triad in the syndiotactic PMMA block increased with increase in the ratio of Al/Mg and reached about 76% at a ratio of Al/Mg ≥ 6. The method was also used to prepare stereoblock copolymer comprising isotactic PMMA block and syndiotactic block of butyl methacrylate. Stereocomplex formation and solution viscosity of the stereoblock PMMA were also studied.     

Living ring-opening polymerization of ɛ-caprolactone with combinations of tert-butyllithium and bilky aluminium phenoxides

Summary The polymerization of ɛ-caprolactone (ɛ-CL) with a combination of tert-butyllithium (t-BuLi) and bis(2,6-di-t-butylphenoxy)methylaluminum [MeAl(ODBP)₂] in toluene at 0°C proceeded in a living manner to give polymers with narrow molecular weight distributions (MWD) within a few minutes, while the polymerization with t-BuLi alone gave a polymer with much broader MWD. The yield of the polymer did not reach 100 % at the Al/Li ratio of 5, because the excess MeAl(ODBP)₂ coordinates with ɛ-CL to protect it from the attack by the propagating species. The polymerization with t-BuLi/EtAl(ODBP)₂ gave polymers in quantitative yields regardless of Al/Li ratio, and also narrower MWD even for higher molecular weight polymers. Received: 1 August 2000/Accepted: 11 August 2000     

Structurally controlled polymerizations of methacrylates and acrylates

Progress in the structure control of polymethacrylates and polyacrylates through stereospecific living polymerization are described. Three types of stereospecific living polymerizations have been developed for methacrylate polymerization: isotactic with t‐C₄H₉MgBr, syndiotactic with ­t‐C₄H₉Li/R₃Al, and heterotactic with t‐C₄H₉Li/bis(2,6‐di‐t‐butylphenoxy)methylaluminium [MeAl(ODBP)₂]. The last initiator system has been proved effective for monomer‐selective living copolymerization of methacrylates. The living nature of these polymerizations allows extensive use for the syntheses of stereoregular block polymers and copolymers, and end‐functionalized polymers such as macromonomers. Through stereospecific polymerizations and copolymerizations of macromonomers, comb polymers and graft copolymers with defined stereoregularities in the main chain and side chains could be obtained. Some properties of these stereoregular polymers are also described, including stereocomplex formation and solution viscosity. Stereospecific polymerizations of crotonates leading to diisotactic, diheterotactic and disyndiotactic polymers are also discussed. Supercritical fluid chromatography (SFC) has been proven to be useful for isolating uniform polymers from stereoregular poly(methyl methacrylate)s (PMMAs) with narrow molecular weight distribution. Uniform end‐functionalized polymers have been used to construct more elaborate uniform polymer architectures such as stereoblock, star, and comb polymers, and copolymers. The uniform polymers have been proven quite useful for the studies of the relationship between structures and properties such as glass transition temperature, melting temperature and solution viscosity. Particularly interesting is the use of isotactic and syndiotactic uniform PMMAs for the understanding of stereocomplex formation in certain solvents such as acetone. Furthermore, a uniform stereoblock PMMA was found to undergo intramolecular complexation in addition to intermolecular complexation in acetone. Uniform star and comb PMMAs were also prepared and found useful for discussing the effect of branching on the solution viscosity. © 2000 Society of Chemical Industry     

Preparation of highly syndiotactic block copolymers of methyl methacrylate and lauryl methacrylate and their characterization

Summary Highly syndiotactic diblock and triblock copolymers comprising lauryl methacrylate (LMA) and methyl methacrylate (MMA) with narrow molecular weight distributions were prepared by the living anionic polymerization with t-C₄H₉Li/(C₂H₅)₃Al in toluene at low temperature. The block copolymers were soluble in acetone which is a non-solvent for poly(lauryl methacrylate) (PLMA). ¹HNMR and vapor pressure osmometric analyses of the block copolymers indicated the aggregation of the copolymer in acetone through the interaction between PLMA blocks. Stereocomplex formation between the triblock copolymer and isotactic poly(methyl methacrylate) (PMMA) took place more effectively in solution than in the solid state.     

Highly syndiotactic poly(methyl methacrylate) with narrow molecular weight distribution formed by tert-butyllithium-trialkylaluminium in toluene

Summary Polymerization of MMA with t-C₄H₉Li in toluene in the presence of trialkylaluminum(alkyl=methyl, ethyl, butyl, isobutyl, and octyl) was examined at various Al/Li ratios. Triethyl-, tributyl and trioctylaluminums worked quite effectively in the polymerization to give highly syndiotactic PMMA with narrow molecular weight distribution (MWD) at the Al/Li ratio of 3 and higher than 3. The highest syndiotacticity of 96% was attained with t-C₄H₉Li/(n-C₈H₁₇)₃Al (1/3) at –93°C. The polymerization was initiated by t-C₄H₉ anion and proceeded in a living manner. The structure of the syndiotactic PMMA is chemically identical to that of isotactic PMMA prepared with t-C₄H₉MgBr. Consequently, highly isotactic and syndiotactic PMMAs with narrow MWD and with the same chemical structure from -end to -end were obtained.     

Preparation of highly isotactic and syndiotactic poly(methyl methacrylate) macromonomers having the same chemical structure and their polymerization

Summary Highly isotactic living poly(methyl methacrylate) (PMMA) anion prepared with t-C₄H₉MgBr in toluene at –78°C reacted quantitatively with p-bromomethylstyrene (p-BMST) in the presence of hexamethylphosphoramide or 1,8-diazabicyclo[5.4.0]-undec-7-ene to give the PMMA macromonomer with narrow molecular weight distribution. Highly syndiotactic PMMA macromonomer was also prepared by the reaction of p-BMST and the living PMMA anion formed by t-C₄H₉Li-(n-C₄H₉),Al (Al/Li=3) initiation in the presence of tetramethylethylenediamine. Radical polymerization and copolymerization of these macromonomers were studied in some detail. The results showed the higher reactivity of the isotactic PMMA macromonomer than the syndiotactic one.     

Living Anionic Polymerization of <Emphasis Type="Italic">N</Emphasis>,<Emphasis Type="Italic">N</Emphasis>–Dimethylacrylamide and Copolymerization with Methyl Methacrylate in the presence of Bulky Aluminum Phenoxide

Summary Anionic polymerization of N,N–dimethylacrylamide (DMAAm) was examined in toluene with tert–butyllithium (t–BuLi)/bis(2,6–di–tert–butylphenoxy)ethylaluminum [EtA1(ODBP)₂]. In the presence of excess amounts of the aluminum compound over t–BuLi, the polymerization proceeded in a living manner. Sequential block copolymerization of DMAAm and methyl methacrylate (MMA) with the same initiator underwent smoothly in both directions, that is, polymerization of MMA by poly(DMAAm) living anions and vice versa. Moreover, the copolymerization of an equimolar mixture of DMAAm and MMA proceeded in a monomer–selective manner to give a block–like copolymer; DMAAm was polymerized first followed by MMA polymerization through selective activation of DMAAm by the coordination of EtA1(ODBP)₂.     

1H NMR spectroscopic differentiation of block copolymer,random copolymer and mixture of the corresponding homopolymers through end group and monomer sequence analyses

Summary Highly isotactic block and random copolymers of methyl methacrylate (MMA) and ethyl methacrylate (EMA) were prepared witht-C₄H₉MgBr in toluene at-60°C.¹H NMR spectra of the copolymers were measured in nitrobenzene-d₅ at 110°C and 500 MHz and analyzed in regard to monomer sequence and the end group. NMR signals due to the monomeric units provide clear indications for distinguishing the block copolymers from the random copolymers. The chemical shift of the initiator fragment signal is so sensitive to the adjacent monomeric unit that PMMA-block-poly(EMA) and poly(EMA)-block-PMMA can be differentiated spectroscopically. The main part of the spectrum for a mixture of PMMA and poly(EMA) prepared witht-C₄H₉MgBr is identical to those for the block copolymers but the mixture shows twot-C₄H₉-signals arising from both homopolymers and thus can be distinguished from the block copolymers.     

Studies on the molecular weight dependence of tacticity of anionically prepared PMMAs by on-line GPC/NMR

Summary Several PMMA samples prepared in toluene with anionic initiators such as t-C₄H₉MgBr, n-C₄H₉MgCl, 1,1-diphenylhexyllithium, t-C₄H₉Li and t-C₄H₉Li(n–C₄H₉)₃Al complex were analyzed by the on-line GPC/NMR method using a 500 MHz ¹H NMR spectrometer as a real-time detector of GPC. The molecular method for a short time (60 min per sample) with a small amount of the sample (1 mg). The plots of intensities of the -methyl proton resonances due to mm- and rr-triads against elution time showed the variation of tacticity with molecular weight of the PMMA. On the basis of the results, the natures of active species in the polymerizations were discussed.     

Preparation and solution properties of uniform three-arm star poly(methyl methacrylate)

Syndiotactic (st-) poly(methyl methacrylate) (PMMA) with a hydroxy group at the chain end (st-PMMA-OH) was prepared by st-living polymerization with t-C₄H₉Li/(n-C₄H₉)₃Al in toluene at -78°C. The resulting st-PMMA-OH was fractionated into uniform polymers by means of supercritical fluid chromatography. Uniform st-PMMA-OH with degree of polymerization of 26 was reacted with 1,3,5-benzenetricarbonyl trichloride as a coupling agent and the three-arm star polymer uniform with respect to branch length was isolated from the reaction mixture by the aid of gel permeation chromatography (GPC). Viscometric property of the uniform star PMMA was studied in some detail by using a GPC-differential viscometer.     

Effect of polymer microstructure on methyl group torsional vibrations

Fundamental torsional frequencies of methyl groups have been measured with neutron incoherent inelastic scattering for isotactic poly(methyl methacrylate)-COOCD₃, and heterotactic, syndiotactic and head-to-head isomers of poly(α-methylstyrene). The measurements confirm that the spectrum of isotactic PMMA differs considerably from the syndiotactic polymer in the region of the fundamental vibration, but no difference is found for the two stereoregular forms of poly(α-methylstyrene). However, the torsional frequency of the methyl group in the head-to-head configuration of α-methylstyrene lies at lower wavenumbers than that observed in the head-to-tail.     

Synthesis and characterization of poly(methyl methacrylate) nanoparticles by emulsifier‐free emulsion polymerization with a redox‐initiated system

In this study, the emulsifier‐free emulsion polymerization of methyl methacrylate (MMA) was initiated directly by a Cu²⁺/HSO redox system. Latex particles with negative charge due to the bonded anionic sulfite ion were successfully synthesized after 2 h of reaction at 40–60°C. Scanning electron microscopy pictures showed a uniform particle size distribution, and the average size decreased from 223 to 165 nm wit increasing reaction temperature from 40 to 60°C. The initiation step in the polymerization mechanism was proven to be a redox reaction, in which Cu²⁺ oxidized the bisulfite ion to produce an anionic sulfite radical and proton. The produced anionic sulfite radical then initiated the polymerization of MMA. Moreover, Cu²⁺ not only served as one component in the redox initiator system but also as a chain‐transfer agent that terminated growing polymer chains to produce chains with unsaturated end groups [poly(methyl methacrylate) (PMMA)? CH?CH₂]. For this system, about 17% PMMA? CH?CH₂ was produced. The tacticities of the PMMA latex prepared at 40–60°C were almost the same, about 62–64% syndiotactic, 33–35% heterotactic, and 3% isotactic. These PMMA latexes had almost the same glass‐transition temperature, 125–127°C, regardless of the reaction temperatures, and their weight‐average molecular weights were in the range between 254,000 and 315,000. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Monomer-selective living copolymerization of butyl acrylate and methyl methacrylate with a difunctional initiator—a facile synthesis of ABA-type triblock copolymer

A difunctional initiator was synthesized through the addition reaction of tert-butyllithium (t-BuLi) to 1,3-diisopropenylbenzene (DIB) in the presence of triethylamine (Et₃N). Under optimized conditions, that is dropwise addition of a mixture of DIB and Et₃N to a stirred toluene solution of t-BuLi at 50 °C at a molar ratio of DIB/Et₃N/t-BuLi=1/2/2, the difunctional initiator was formed without oligomeriazation of DIB. Copolymerization of butyl acrylate (n-BuA) and methyl methacrylate (MMA) with the difunctional initiator in the presence of bis(2,6-di-tert-butylphenoxy)ethylaluminum [EtAl(ODBP)₂] in toluene at low temperature proceeded in a monomer-selective manner; n-BuA is polymerized first, followed by MMA polymerization, to form an ABA-type triblock copolymer [PMMA-block-poly(n-BuA)-block-PMMA], which exhibits microphase separation.     

Anionic polymerization of methyl methacrylate in the presence of chromium carbonyl [Cr(CO)6]

Summary The presence of Cr(CO)₆ in nBuLi-initiated anionic polymerization of methyl methacrylates (MMA) was found to effectively enhance stereoselectivity of the polymerization in toluene at 0°C. nBuLi/Cr(CO)₆ afforded an isotactic PMMA with 86 % of mm triad, and the polymers obtained with nBuLi/Cr(CO)₆/tBuOK were rich in heterotactic structures (mr = ca. 54%). In both cases, the selectivity was improved in ca. 10% compared to those of the polymerization conducted under the similar conditions without Cr(CO)₆. Received: 20 January 2003/Revised version: 21 April 2003/Accepted: 21 April 2003 Correspondence to Eiji Ihara     

Highly efficient block copolymerization of methyl and t-butyl methacrylates by an incomplete and slow initiation system

Summary Block copolymerization of methyl methacrylate (MMA) with t-butyl methacrylate (t-BMA) was carried out in toluene at-78°C with triphenylphosphine (Ph₃P)-triethylaluminum (Et₃Al) initiating system. Polymerization of MMA with Ph₃P-Et₃Al under the same conditions gave highly syndiotactic PMMA living anion with low initiator efficiency. Even though a large part of the initiator remained unreacted, polymerization of t-BMA with the living anion of PMMA gave block copolymer without formation of poly(t-BMA), since t-BMA alone could not be polymerized under the same conditions due to the inability of initiation with Ph₃P-Et₃Al.     

Anionic polymerization of acrylates. XIV. Synthesis of MMA/acrylate block copolymers initiated with ester-enolate/tert-alkoxide complex

Diblock copolymers of methyl methacrylate (MMA) with 2-ethylhexyl, butyl, ethyl or tert-butyl acrylate (EtHA, BuA, EtA, t-BuA) have been prepared by the ligated anionic polymerization initiated with methyl 2-lithioisobutyrate (MIB-Li) in the presence of an excess of Li tert-butoxide (t-BuOLi) in toluene/THF mixture at −60 or −78 °C. The copolymers, prepared at −60 °C, show MWD with a hint of bimodality, indicating partial deactivation of the living PMMA upon addition of acrylic monomer. At −78 °C, the extent of this deactivation is distinctly lower, the formed block copolymers, in particular, poly(MMA-b-EtHA), have unimodal MWD and exhibit tails only in the lower-molecular-weight region. Poly(MMA-b-EtHA)s were extracted with acetonitrile dissolving PMMA; very small parts of the crude products dissolved, whereas prevailing parts remained as solids documenting thus formation of block copolymer in a high yield. Surprisingly, the highest amount of self terminated PMMA was found in block copolymerization of MMA with t-BuA at both the temperatures, the products of which had clearly bimodal MWDs. This finding is shortly discussed on the basis of relatively slow propagation of t-BuA in comparison with EtHA, BuA and EtA.     

Characterization of the anionic polymerization of 2-(ethoxy)ethyl methacrylate by t-C4H9MgBr in toluene

Anionic polymerizations of 2-(ethoxy)ethyl methacrylate (EOEMA) were carried out under several conditions that allowed for living polymerization of methyl methacrylate (MMA). It was found that the polymerization rate of EOEMA by t-C₄H₉MgBr in toluene was much lower than that of MMA under these conditions. However, the polymerization rate of EOEMA by t-C₄H₉MgBr in tetrahydrofuran was not much lower than the polymerization of MMA. Interactions between the counter cation (magnesium) and the ether oxygen of the ester moiety in the EOEMA unit are considered important to delay the polymerization. Random and block copolymerizations of EOEMA and MMA by t-C₄H₉MgBr in toluene were also carried out and the results support the interaction of ether oxygen. 4-(Ethoxy)butyl methacrylate (EOBMA) was successfully prepared from 4-ethoxy-1-butanol and methacryloyl chloride and purified. Polymerization of EOBMA with t-C₄H₉MgBr in toluene provides a polymer with good yield, suggesting that the number of carbon atoms between the ester group and the ether oxygen is important to the interactions with the ether oxygen. Some of the thermal properties of the polymers and copolymers, including their glass transition temperature and thermal stability, were also evaluated.     

Steric effects in the basic hydrolysis of poly(ethylene terephthalate)

A comparative study of the reactivity of hydroxide and various alkoxide anions was made by determining percentage weight loss of poly(ethylene terephthalate) fiber. Regardless of the basicity of the anions, the order of reactivity was found to be hydroxide < tert-butoxide < sec-propoxide < methoxide < ethoxide. This observed order follows the nucleophilicity of the bases, and the relatively lower reactivity of sec-propoxide and tert-butoxide is assumed to be due to steric retardation during the equilibrium reactions.     

Parameters,affecting the sensitivity of poly(methyl methacrylate) as a positive lithographic resist

The contribution of parameters such as molecular weight, molecular weight distribution and stereochemistry to electron beam sensitivity of poly(methyl methacrylate), PMMA, has been investigated. The sensitivity is interpreted here as the minimum radiation dose required to obtain a predetermined solubility rate ratio, S/S_o = S_R, of the exposed, S, and unexposed, S_o, material. The G-value was foam be independent of molecular weight, molecular weight distribution, and stereochemistry. Data indicate that the weight average molecular weight ratio correlates better with S_R than the number average molecular weight ratio. The tacticity of the resist and the developer solvent molecular weight or size have a large effect on solubility rate. Although the solubility rate pf isotactic PMMA is much greater than the syndiotactic and heterotactic stereoforms, the sensitivity appears to be independent of tacticity. In a homologous series of n-alkyl acetate developer solvents, the molecular size of the solvent has a greater effect on the solubility rate than the molecular weight of the resist. A developer solvent has been selected from the n-alkyl acetates which enhanced the sensitivity of PMMA.     

Pentacoordinated iron(II) complexes with 2,6-bis[(imino)ethyl]pyridine-Schiff base ligands as new catalyst systems mediated atom transfer radical polymerization of (meth)acrylate monomers

2,6-bis[1-(cis)-myrtanylimino)ethyl]pyridineiron(II) chloride (2) and 2,6-bis[(1-phenylimino)ethyl]pyridineiron(II) chloride (3) were investigated as novel complexes for iron-mediated atom transfer radical polymerization (ATRP) of methyl methacrylate (MMA) and tert-butyl acrylate (tBA) using toluene as the solvent, and ethyl 2-bromoisobutyrate as the initiator. A catalyst/initiator molar ratio as low as 0.1/1 was used in order to reduce catalyst contamination to the polymers. Both complexes produced PMMA and PtBA polymers with controlled structures and very low molecular weight distributions as low as 1.07, in particular for complex 3. High to moderate conversions (30–45%) were obtained in 20 h, although very diluted amount of catalyst was used and in the absence of any reducing agent which indicates an efficient catalyst system. The resulting polymers were characterized by NMR, GPC, and DSC. Syndio-rich atactic poly(t-BA) and poly(MMA) with relatively high [rr] diads (50%, 42%, respectively) were isolated.