Effect of tetraalkylammonium salts on the tacticity of poly(methyl methacrylate), 2.. Initiation by potassium tert-butoxide

The anionic polymerization of methyl methacrylate was carried out in the presence of potassium tert-butoxide (t-BuOK)/quaternary ammonium salts (QAS) in toluene and tetrahydrofuran at −60°C. It was found that in toluene some QAS additives substantially increase the syndiotacticity of poly(methyl methacrylate). Two types of QAS were distinguished, quite different in their action. The addition of QAS with one or two longchain alkyl groups (>C₁₂), does not change significantly the mode of the monomer addition, whereas the polymerization in the presence of tetraalkylammonium salts with four equal substituents and dimethyldidodecylammonium bromide yields predominantly a syndiotactic polymer with high conversion and comparatively low polydispersity (M̄_w/M̄_w = 1.3−1.5). In some cases QAS additives are more effective modifiers than cryptand [2.2.2].     

New initiator system for the anionic polymerization of (meth)acrylates in toluene. IV. Random copolymerization of (meth)acrylates in toluene initiated by s-BuLi ligated by lithium silanolates

Copolymerization of binary mixtures of alkyl (meth)acrylates has been initiated in toluene by a mixed complex of lithium silanolate  (s-BuMe₂SiOLi) and s-BuLi (molar ratio > 21) formed in situ by reaction of s-BuLi with hexamethylcyclotrisiloxane (D₃). Fully acrylate and methacrylate copolymers, i.e., poly(methyl acrylate-co-n-butyl acrylate), poly(methyl methacrylate-co-ethyl methacrylate), poly(methyl methacrylate-co-n-butyl methacrylate), poly(methyl methacrylate-co-n-butyl methacrylate), poly(isobornyl methacrylate-co-n-butyl methacrylate), poly(isobornyl methacrylate-co-n-butyl methacrylate) of a rather narrow molecular weight distribution have been synthesized. However, copolymerization of alkyl acrylate and methyl methacrylate pairs has completely failed, leading to the selective formation of homopoly(acrylate). As result of the isotactic stereoregulation of the alkyl methacrylate polymerization by the s-BuLi/s-BuMe₂SiOLi initiator, highly isotactic random and block copolymers of (alkyl) methacrylates have been prepared and their thermal behavior analyzed. The structure of isotactic poly(ethyl methacrylate-co-methyl methacrylate) copolymers has been analyzed in more detail by Nuclear Magnetic Resonance (NMR). © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 2525–2535, 1999     

Synthesis of Styrenic‐Terminated Methacrylate Macromonomers by Nitroanion‐Initiated Living Anionic Polymerization

N‐Isopropyl‐4‐vinylbenzylamine (PVBA) was synthesized and used as an initiator for the polymerization of methacrylates to synthesize macromonomers with terminal styrenic moieties. LiPVBA initiated a living polymerization and block copolymerization of methyl methacrylate, 2‐(N,N‐dimethylamino)ethyl methacrylate and tert‐butyl methacrylate and produced polymers having well‐controlled molecular weights and very low polydispersities (M̄_w/M̄_n < 1.1) in quantitative yield. ¹H NMR analysis revealed that the polymers contained terminal 4‐vinylbenzyl groups. The macromonomers were reactive in the copolymerization with styrene.     

Polymers of α- and β-substituted acrylates with controlled structures

Isotactic and syndiotactic living polymerizations of methacrylates with t-C₄H₉MgBr and t-C₄H₉Li-R₃Al (Al/Li≥2), respectively, were utilized to prepare highly stereoregular block and random copolymers, stereoblock PMMAs, highly branched star polymers with stereoregular arms, stereoregular PMMA macromonomers with methacryloyl functions and stereoregular comblike and graft polymers derived therefrom. A combination of t-C₄H₉Li and bis(2,6-di-t-butylphenoxy) methylaluminum was found to be an efficient initiator for heterotactic living polymerization of methacrylates in toluene at −78°C; e.g. ethyl methacrylate gave a polymer with mr content of 87%. Polymerization of triphenylmefhyl crotonate (TrC) with fluorenyllithium (FILi)/N,N,N′,N′-tetramethylethylenediamine in toluene at −78°C gave a threodiisotactic polymer with narrow MWD, whose stereochemistry was confirmed from the x-ray analysis of the pentamer of methyl crotonate (MeC) derived from the TrC pentamer and ¹H NMR spectral comparison of the pentamer and the poly(MeC). The poly(TrC) prepared with FILi/(S,S)-(+)-2,3-dimethoxy-1,4-bis(dimethylamino) butane also gave a threodiisotactic polymer which showed optical activity due to the one-handed helix. Polymerization of t-butyl crotonate was also discussed in some detail.     

Synthesis of traditional and ionic polymethacrylates by anion catalyzed group transfer polymerization

The hydrophobic ionic liquid 1‐butyl‐1‐methylpyrrolidinium bis(trifluoromethylsulfonyl)imide was successfully used as solvent in group transfer polymerization of traditional methacrylates (methyl methacrylate, n‐butyl methacrylate, and benzyl methacrylate) and of ionic liquid methacrylates (ILMAs). This demonstrates that this ionic liquid makes reaction conditions, which do not require the use of ultra‐dried solvents. The ILMAs were N‐[2‐(methacryloyloxy)ethyl]‐N,N‐dimethyl‐N‐alkylammonium bis(trifluoromethylsulfonyl)imides bearing methyl, ethyl, propyl, butyl, or hexyl substituents. Increasing size of the alkyl substituent at the cation results in decreasing glass transition temperature in case of both ionic liquid methacrylates and polymers derived of them. Furthermore, the glass transition temperature is significantly higher for these polymers compared with the ionic liquid methacrylates, and the effect of glass transition temperature reduction with increasing size of the alkyl substituent is stronger for the polymers. A mechanism was proposed explaining the catalytic function of the ionic liquid used as solvent for polymerization. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2015 , 53, 2849–2859     

Radical polymerization of various alkyl methacrylates in liquid crystalline solvents

The polymerization of methacrylates of methyl, ethyl, butyl, hexyl, octyl, dodecyl, and octadecyl alcohols was studied with 2,2′-azobisisobutyronitrile in the smectic, nematic, cholesteric, and isotropic liquid phases at 50–75°C. N-(4-Methoxyphenylmethylene)phenylamine, N-(4-ethoxyphenyl-methylene)-4-butylphenylamine, cholesteryl octadecanoate, and benzene were used as the solvents. The viscosities of the polymers were enhanced in the mesomorphic solvents. The polymer was converted to the corresponding poly(methyl methacrylate) through hydrolysis and esterification. Tacticities of the resultant poly(methyl methacrylates) were determined by nuclear magnetic resonance spectroscopy. The isotacticities of the polymers obtained in the smectic and the nematic phases were basically the same and appeared to be larger than those of the polymers in the cholesteric and isotropic liquid states. The polymerization of the methacrylates of butyl and longer-chain alcohols deviated from Bernoullian statistics and gave polymers more isotactic than those of methyl and ethyl methacrylates.     

Stereospecific polymerization of 9-fluorenyl methacrylate: Tacticity effects on the thermal and photophysical properties of the polymers

Poly(9-fluoreneyl methacrylate) was obtained through anionic polymerization with t-BuLi and t-BuMgBr and through radical polymerization with α,α′-azobisisobutyronitrile. Anionic polymerization with t-BuLi in tetrahydrofuran and radical polymerization afforded syndiotactic polymers (rr ∼ 90%), whereas anionic polymerization with Li and Mg initiators in toluene and CH₂Cl₂ led to isotactic polymers. The thermal and photophysical properties of the polymers were examined. A syndiotactic polymer tended to show higher glass transition and decomposition temperatures than an isotactic polymer. However, polymers with different tacticities were not likely to assume specific, distinctive conformations such as a helix or a π-stacked conformation in solution. An isotactic polymer showed stronger interactions in a CH₂Cl₂ solution with 2,4,7-trinitro-9-fluorenylidenemalononitrile, an electron-acceptor molecule, than a syndiotactic polymer. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 4656–4665, 2004     

Polymerization of Methyl Methacrylate Initiated with Organomanganate Reagents

Organomanganate reagents [R₃Mn]^–Li⁺ (R = Bu, Me) were found to polymerize methyl methacrylate in the presence of potassium tert‐butylate. A conversion of the tacticity of the resulting poly(methyl methacrylate)s from heterotactic (mr = 54%) to isotactic (mm = 58%) was observed upon changing the R group of the initiator from Bu to Me. The addition of triisobutylaluminium was found to efficiently control M̄_w and M̄_w/M̄_n of the resulting polymers.     

Anionic living polymerization of alkyl methacrylate at ambient temperature and its mechanism research

In order to break through the bottleneck of anionic polymerization, polar monomers such as methyl methacrylate (MMA), ethyl methacrylate, butyl methacrylate, and hexyl methacrylate are subjected to anionic polymerization at room temperature in tetrahydrofuran (THF) using potassium tert‐butoxide (t‐BuOK) as the initiator. The polymerization of alkyl methacrylates is studied by multidetector gel permeation chromatography, proton nuclear magnetic resonance (¹H‐NMR) and ¹³C‐NMR spectroscopy, and dynamic laser light scattering. It is found that t‐BuOK can initiate the living anionic polymerization of polar alkyl methacrylate, and the polymerization conversion almost reaches up to 100%. t‐BuOK exists into two kinds of agglomerates, whose hydrodynamic volumes are 10 and 80 nm, respectively. t‐BuOK in THF is similar to emulsion and has a critical active species concentration of about 0.0265 mol L^?1 and does not depend on how much t‐BuOK is added. After the initiation of the polymerization, the large agglomerates of a loose and less regular structure that have occupied the main part of t‐BuOK are greatly reduced, but they do not continue to decrease until they disappear according to the equilibrium theory. Similarly, the active chain after initiation also will not aggregate again. Furthermore, t‐BuOK also has an active species with smaller average vibration size between cation and anion pairs, which can only initiate the polymerization of MMA with rather slow rate but cannot initiate other alkyl methacrylates. At last, because t‐BuOK can make the dormant species caused by side reactions to be revived, the anionic polymerization of MMA could obtain a high yield. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2019 , 57, 1130–1139     

Stereocontrol in the free‐radical polymerization of methacrylates with fluoroalcohols

The free‐radical polymerization of methyl methacrylate (MMA), ethyl methacrylate (EMA), isopropyl methacrylate (IPMA), and tert‐butyl methacrylate (t‐BuMA) was carried out under various conditions to achieve stereoregulation. In the MMA polymerization, syndiotactic specificity was enhanced by the use of fluoroalcohols, including (CF₃)₃COH as a solvent or an additive. The polymerization of MMA in (CF₃)₃COH at −98 °C achieved the highest syndiotacticity (rr = 93%) for the radical polymerization of methacrylates. Similar effects of fluoroalcohols enhancing syndiotactic specificity were also observed in the polymerization of EMA, whereas the effect was negligible in the IPMA polymerization. In contrast to the polymerizations of MMA and EMA, syndiotactic specificity was decreased by the use of (CF₃)₃COH in the t‐BuMA polymerization. The stereoeffects of fluoroalcohols seemed to be due to the hydrogen‐bonding interaction of the alcohols with monomers and growing species. The interaction was confirmed by NMR measurements. In addition, in the bulk polymerization of MMA at −78 °C, syndiotactic specificity and polymer yield increased even in the presence of a small amount {[(CF₃)₃COH]/[MMA]_o < 1} of (CF₃)₃COH. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 4693–4703, 2000     

Highly stereospecific protonation of stereoregular living PMMA anions with several alcohols

Living and highly isotactic poly(methyl methacrylate) (PMMA) anion (M̄n = 2.5 × 10³) prepared with t-C₄H₉MgBr as an initiator was protonated with phenol in toluene at −78°C. The reaction was stereospecific toward meso addition, and the meso/racemo ratio at the chain-end of the resultant polymer was 89/11. Addition of 1,4-dioxane to the living isotactic PMMA anion in toluene at −78°C remarkably reduced the viscosity of the system, and protonation of the PMMA anion with phenol in the presence of 1,4-dioxane enhanced the meso-specificity to 94%. On the other hand, the protonation reaction of the living syndiotactic PMMA anion (M̄n = 2.5 × 10³), which was generated by t-C₄H₉Li/(n-C₄H₉)₃Al in toluene at −93°C, with t-butanol was found to be 97% racemo-specific. These highly stereospecific protonation reactions of the stereoregular PMMA anions were in contrast to the protonation of the anions with methanol or benzyl alcohol which was almost non-stereospecific.     

Stereochemistry of the free‐radical polymerization of zinc methacrylates coordinated with a bidentate ligand

The polymerization of zinc methacrylates coordinated with a bidentate ligand ( 1 – 4 ) was carried out in chloroform at 60°C. The polymerization of these monomers gave chloroform‐insoluble polymers. Stereoregularity of the polymers was estimated from ¹H NMR spectra of poly(methyl methacrylate)s (PMMAs) derived from the original polymers. Monomers 1 and 2 gave slightly different polymers compared with conventional ones obtained by polymerization of methacrylic acid, while 3 afforded higher amounts of isotactic polymers than 1 and 2 . Conversely, 4 gave a polymer of high syndiotacticity. Furthermore, the relationship between triad tacticity and monomer concentration in the feed was studied. Consequently, it was demonstrated that the structure of bidentate ligands coordinated with zinc ion influences the stereoregularity of the resulting polymers.     

Synthesis and polymerizations of six aminophosphonate‐containing methacrylates

Two different groups of novel aminophosphonate‐containing methacrylates were synthesized. The route to the first group involves reactions of ethyl α‐bromomethacryate (EBBr) and t‐butyl α‐bromomethacryate (TBBr) with diethyl aminomethylphosphonate and diethyl 2‐aminoethylphosphonate. Bulk and solution polymerizations at 60–80 °C with 2,2′‐azobis(isobutyronitrile) (AIBN) gave crosslinked or soluble polymers depending on monomer structure and polymerization conditions. Increasing bulkiness from ethyl to t‐butyl decreases the polymerization rate, correlated well with the chemical shift differences of double bond carbons and consistent with the lower molecular weights of t‐butyl ester polymers (M_n = 1800–7900 vs. 50,000–72,000). The route to the second group involves the Michael addition reaction between diethyl aminomethylphosphonate and diethyl 2‐aminoethylphosphonate with 3‐(acryloyloxy)‐2‐hydroxypropyl methacrylate (AHM) to give secondary amines. The photopolymerization using differential scanning calorimeter showed that these monomers have similar or higher reactivities than AHM, even though AHM has two double bonds. The high rates of polymerization of these monomers were attributed to both hydrogen bonding interactions due to additional NH groups as well as chain transfer reactions. All the homopolymers obtained produced char (17–35%) on combustion. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011.     

Anionic polymerization and copolymerization of S-methyl thiomethacrylate

S-Methyl thiomethacrylate (methyl thiolmethacrylate, MTMA) was polymerized with a variety of anionic initiators such as n-BuLi, octylpotassium, PhMgBr, and Et₂AlNPh₂ in toluene and THF. Stereoregularity of the polymer (PMTMA) was determined from the ¹H-NMR spectrum of poly(methyl methacrylate), which had been derived from PMTMA, because the α-methyl resonance in the ¹H-NMR spectrum of PMTMA was not satisfactorily solved owing to the overlap of pentad signals. The ¹³C-NMR spectrum of PMTMA also showed the splitting due to pentad sequences. Stereoregularity of PMTMA was always low compared with that of poly(methyl methacrylate), which was prepared under the same reaction conditions. MTMA was much more reactive than methyl methacrylate and methacrylonitrile in the copolymerization with n-BuLi in toluene and in THF at ?78°C. The lower stereoregulation of the polymerization of MTMA and the higher reactivity of MTMA were mainly ascribed to the higher resonance effect of MTMA.     

Branching of anionic poly(methyl methacrylate)

A viscometric determination of the degree of branching γ, of poly(methyl methacrylate) obtained by anionic polymerization proved the reaction of the growing center of poly(methyl methacrylate) with the ester group of another polymer molecule, accompanied by the formation of a trifunctional branch point. This reaction occurs if the solution polymerization of methyl methacrylate is initiated: (1) with butyllithium at ?78°C only on attaining 100% conversion and after a long time or at +20°C immediately after the polymerization has set in; (2) with lithium tert-butoxide at +20°C after a long time. The degree of branching of poly(methyl methacrylates) obtained under similar conditions in the presence of tetrahydrofuran reaches higher values than for polymers prepared in toluene. The tacticity of polymers does not affect the experimentally determined γ values.     

Rare Earth Metal-Initiated Polymerizations of Polar and Nonpolar Monomers

Abstract

Organolanthanide(III) initiated polymerization of methyl methacryate gave both syndiotactic and isotactic living polymers of high molecular weight. Organolanthanide(III) initiated polymerization of alkyl acrylates also gave high molecular weight poly(alkyl acrylate)s with very narrow molecular weight distribuion in high yield. Molecular weights of the resulting polymers increased linearly with the conversion. Random and block copolymerizations of alkyl acrylates with methyl methacrylate were realized successfully. For the sake of development of the olefin polymerization catalyst, bulky substituents were introduced into Me₂Si bridged Cp rings and they were used as ligands for the lanthanide complexes. Tri- and divalent lanthanide complexes with such ligands showed high activity for olefin polymerization and gave high molecular weight polyolefins.     

Stereospecific polymerization of o-methoxystyrene by anionic initiators

o-Methoxystyrene was polymerized with n-butyllithium (n-BuLi), Na naphthalene, and K dispersion as initiators in tetrahydrofuran (THF) and toluene. The stereoregularity of the polymer was investigated by means of the NMR spectroscopy. The methoxy resonance of the spectrum split into ten components due to the tactic pentads. It was found by x-ray examination that the polymer obtained by n-BuLi in toluene at ?45°C was crystalline and highly isotactic. In THF, the stereospecificity of the polymerization was independent of the initiator, and the isotacticity of the polymer increased with increasing reaction temperature. In toluene, the stereospecificity depended on the initiator; i.e., n-BuLi gave a polymer with higher isotacticity than that given by phenylsodium. The fraction of isotactic triad of the polymer obtained by n-BuLi in toluene at ?78°C was more than 90%, but 50% at 50°C. The presence of ca. 1% THF in toluene led to a steep decrease in the isotacticity even at ?78°C. The tacticity of the polymer given by Na naphthalene was not affected by the existence of NaB(C₆H₅)₄ in THF. The polymerization in THF could be explained by Bovey's “single σ” process, while a penultimate effect was observed in the polymerization by n-BuLi in toluene.     

Reactivity of methacrylates in anionic copolymerization with methyl methacrylate by n-BuLi

Monomer reactivity ratios, r₁ and r₂ were determined in the anionic copolymerizations of methyl methacrylate (MMA, M₁) with ethyl (EtMA), isopropyl (i-PrMA), tert-butyl (t-BuMA), benzyl (BzMA), α-methylbenzyl (MBMA), diphenylmethyl (DPMMA), α,α-dimethylbenzyl (DMBMA), and trityl (TrMA) methacrylates (M₂) by use of n-BuLi as an initiator in toluene and THF at -78°C. The order of the reactivity of the monomers towards MMA anion was DPMMA > BzMA > MMA > EtMA > MBMA > i-PrMA > t-BuMA > TrMA > DMBMA in toluene and TrMA > BzMA > MMA > DPMMA > EtMA > MBMA > i-PrMA > DMBMA > t-BuMA in THF. Except for the extremely low reactivity of TrMA and DPMMA in toluene due to steric hindrance, the order was explained in terms of the polar effect of the ester groups. A linear relationship was found between log (1/r₁) and Taft's σ* values of the ester groups, where the ρ* value was 1.1. The plots of log (1/r₁) vs. the ¹H_a (cis to the carbonyl) and ¹³C_ß chemical shifts of the monomers were also on straight lines. The polymer obtained in the copolymerization of MMA with TrMA in toluene by n-BuLi at -78°C was a mixture of poly-MMA and a copolymer, suggesting that there exist two kinds of growing centers.     

Modeling the free radical polymerization of acrylates

Acrylates have gained importance because of their ease of conversion to high‐molecular‐weight polymers and their broad industrial use. Methyl methacrylate (MMA) is a well‐known monomer for free radical polymerization, but its α‐methyl substituent restricts the chemical modification of the monomer and therefore the properties of the resulting polymer. The presence of a heteroatom in the methyl group is known to increase the polymerizability of MMA. Methyl α‐hydroxymethylacrylate (MHMA), methyl α‐methoxymethylacrylate (MC₁MA), methyl α‐acetoxymethylacrylate (MAcMA) show even better conversions to high‐molecular‐weight polymers than MMA. In contrast, the polymerization rate is known to decrease as the methyl group is replaced by ethyl in ethyl α‐hydroxymethylacrylate (EHMA) and t‐butyl in t‐butyl α‐hydroxymethylacrylate (TBHMA). In this study, quantum mechanical tools (B3LYP/6‐31G*) have been used in order to understand the mechanistic behavior of the free radical polymerization reactions of acrylates. The polymerization rates of MMA, MHMA, MC₁MA, MAcMA, EHMA, TBHMA, MC₁AN (α‐methoxymethyl acrylonitrile), and MC₁AA (α‐methoxymethyl acrylic acid) have been evaluated and rationalized. Simple monomers such as allyl alcohol (AA) and allyl chloride (AC) have also been modeled for comparative purposes. © 2005 Wiley Periodicals, Inc. Int J Quantum Chem, 2005     

Synthesis of new,functionalized poly(butyl vinyl ether) oligomers and novel copolymers containing these materials

This paper reports the synthesis and characterization of new, functionalized poly(alkyl vinyl ether) oligomers, and block copolymers containing poly(alkyl vinyl ether) and poly(methyl methacrylate). Using the HI/ZnI₂ initiating system in nonpolar solvents (hexane, toluene) at −20°C, both monofunctional and difunctional poly(alkyl vinyl ether) oligomers of predicted molecular weights precisely terminated with aldehyde, primary hydroxyl and ester endgroups have been prepared. Novel diblock copolymers comprised of poly(methyl methacrylate) and poly(butyl vinyl ether) have also been synthesized using a combination of living cationic and living group transfer polymerization.