Effect of a π-donor on the radical bulk polymerization of methyl methacrylate

Bulk polymerizations of methyl methacrylate (MMA) at 60°C initiated with 2,2′-azoisobutyronitrile are influenced by the presence of an organic π-donor such as tetrathiafulvalene (TTF). Upon addition of TTF, the ratio of weight- to number-average molecular weights M̄_w/M̄_n are significantly reduced and the thermal stability of the poly(methyl methacrylate) samples is increased. Kinetic investigations indicate that TTF acts as a retarder on the polymerization mechanism.     

Highly heterotactic polymerization of methacrylates — Higher order stereoregulation and stereochemical significance

A combination of tert-butyllithium (t-BuLi) and bis(2,6-di-t-butylphenoxy)methylaluminium (MeAI(ODBP)₂) was found to be an efficient initiator for heterotactic living polymerization of certain alkyl methacrylates in toluene at low temperatures. The polymerization of methyl methacrylate (MMA) with t-BuLi/MeAI(ODBP)₂ (AI/Li=5 mol/mol) in toluene at −78°C gave heterotactic-rich poly(methyl methacrylate) (PMMA) with narrow molecular weight distributions (MWDs) (heterotactic triad fraction mr = 68%, ratio of weight- to number-average molecular weights M̄w/M̄n = 1.06-1.17). Other alkyl methacrylates also gave heterotactic polymers under the same conditions; in particular, ethyl and butyl methacrylates gave polymers with heterotactic triad fractions of 87%. The highest triad heterotacticity of 91.6% was obtained for the polymerization of ethyl methacrylate at −95°C. Some characteristic features of this stereospecific polymerization were discussed based on the polymerization results combined with other structural information of the polymer such as chain-end stereostructure and stereosequence distribution in the main chain.     

A novel group transfer polymerization of 1-trimethylsiloxy-benzocyclobutene via hetero Diels-Alder reaction

A novel group transfer polymerization via hetero-Diels-Alder reaction is described. When 1-trimethylsiloxybenzocyclobutene ( 1 ) was treated with a catalytic amount of p-anisaldehyde (4-methoxybenzaldehyde) and TASF (tris(dimethylamino)sulfonium difluorotrimethylsilanide) at room temperature for 0.5 h, poly[1,2-phenylene-1-(trimethylsiloxy)ethylene] was obtained quantitatively. The number-average molecular weight of the polymer was M̄_n = 2000 and the molecular weight distribution was narrow (ratio of weight-to number-average molecular weights M̄_w/M̄_n = 1.18). Structural characteristics suggested a polymerization mechanism involving isomerization of 1 to o-quinodimethane and successive hetero-Diels-Alder reaction leading to poly[1,2-phenylene-1-trimethylsiloxy ethylene]. The living-like nature of the polymerization was supported by a monomer addition experiment in which the molecular weight increased according to the increase of the added monomer.     

Living radical polymerization of methyl methacrylate with a zerovalent nickel complex,Ni(PPh3)

A zerovalent nickel complex, Ni(PPh₃)₄, induced living radical polymerization of methyl methacrylate (MMA) in conjunction with an organic bromide as an initiator [R–Br: CCl₃Br, (CH₃)₂C(CO₂Et)Br, (CH₃)₂C(COPh)Br] in the presence of Al(Oi-Pr)₃ additive. The molecular weight distributions were narrow (M̄_w/M̄_n ∼ 1.2) throughout the reactions, and the number-average molecular weights (M̄_n) increased in direct proportion to monomer conversion. In contrast, the polymers obtained with CCl₄ in place of R–Br had broader MWDs (M̄_w/M̄_n > 2). The Al(Oi-Pr)₃ additive should be added for the smooth polymerizations of MMA to occur, similarly to those with a divalent nickel bromide, NiBr₂(PPh₃)₂. The Ni(PPh₃)₄-mediated living polymerization apparently proceeds via the activation of the C Br bond from the initiators R Br, assisted by the redox reaction of the complex between Ni(0) and Ni(I) species. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 3003–3009, 1999     

Structure and properties of cellulose graft copolymers. III. Cellulose–methyl methacrylate graft copolymers synthesized by the ceric ion method

The ceric ion-initiated graft copolymerization of methyl methacrylate onto wood cellulose was found to depend on the concentrations of initiator, monomer, and cellulose. The structure of cellulose—methyl methacrylate graft copolymers was studied by hydrolyzing away the cellulose backbone to isolate the grafted poly(methyl methacrylate) branches. The molecular weights and molecular weight distributions of the grafted poly(methyl methacrylate) were determined by using gel-permeation chromatography. The number-average (M?_n) molecular weights ranged from 36 000 to 160 000 and the polydispersity ratios (M?_w/M?_n) varied from 4.0 to 7.0. The grafting frequency or the number of poly(methyl methacrylate) branches per cellulose chain calculated from the per cent grafting and molecular weight data varied from 0.38 to 3.2. The structure of cellulose—methyl methacrylate graft copolymers and the effect of stepwise addition of initiator on the structure are discussed.     

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.     

Influence of polymolecularity on the second virial coefficient of polymers

Scaling theory is applied to derive expressions describing the influence of polymolecularity on the second virial coefficient, A₂, as obtained from osmotic pressure and light scattering measurements. Numerical values of polymolecularity correction factors are calculated for Schulz-Zimm and logarithmic normal distributions of the molecular weight, different qualities of the solvent and several ratios of the weight-average and the number-average molecular weights M̄_w/M̄_n. It is found that in the equation $ A_2 = K_{A_2 } \cdot M_{{\rm av}}^{a_{A_2 } } $ the weight-average molecular weight is a good approximation for M_av if A₂ is measured via light scattering, while the number-average molecular weight can be inserted for M_av if A₂ stems from osmotic pressure measurements.     

Polymerization of ethene initiated with a mixture of siloxane-bridged mono- and dinuclear zirconocenes

In the polymerization of ethene cocatalyzed with modified methylaluminoxane, the catalyst activities of the siloxane-bridged dinuclear zirconocenes, tetramethyldisiloxanediylbis(cyclopentadienylindenylzirconium dichloride) ( 3 ) and hexamethyltrisiloxanediylbis(cyclopentadienylindenylzirconium dichloride) ( 4 ) were lower than that obtained with the siloxane-bridged mononuclear zirconocene, tetramethyldisiloxanediyldicyclopentadienyldimethylzirconium ( 1 ). On the other hand, weight-average molecular weight M̄_w and ratio of weight- to number-average molecular weights M̄_w/M̄_n of polyethene (PE) obtained with 3 or 4 were higher than those of PE obtained with 1. For a binary mixture of 1/3 or 1/4 , it was found that the obtained PE exhibits a bimodal molecular weight distribution for an appropriate composition of the mixed zirconocenes. M̄_w/M̄_n of PE could be adjusted by changing the relative concentrations of the two zirconocenes.     

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.     

Modelling free-radical copolymerization kinetics—evaluation of the pseudo-kinetic rate constant method, 1. Molecular weight calculations for linear copolymers

The moment equations for binary copolymerization in the context of the terminal model have been solved numerically for a batch reactor operating over a wide range of conditions. Calculated number- and weight-average molecular weights were compared with those found using pseudo-kinetic rate constants with the method of moments and with the instantaneous property method for homopolymerization. With the pseudo-kinetic rate constant method under polymerization conditions where number-average molecular weights (M̄_n) are below about 10³ the error in calculating M̄_n exceeds 5%. The error increases rapidly with decrease in molecular weight for M̄_n < 10³. M̄_n measured experimentally for polymer chains (homo- and copolymers) have error limits of greater than ±5% at the 95% confidence level. Therefore, for all practical purposes, the pseudo-kinetic rate constant method is valid for M̄_n greater than 10³. Errors in calculating weight-average molecular weights (M̄_w) or higher averages are always smaller than those for M̄_n when applying the pseudo-kinetic rate constant method. The assumptions involved in molecular weight modelling using the pseudo-kinetic rate constant approach are thus proven to be valid, and therefore it is recommended that the pseudo-kinetic rate constant method be employed with the instantaneous property method to calculate the full molecular weight distribution and averages for linear chains synthesized by multicomponent chain growth polymerization.     

Polymerization of ϵ-caprolactone using heterobimetallic lanthanocene complexes

The chiral heterobimetallic complexes Li[Ln(η⁵ : η¹-C₅R₄¹SiMe₂NCH₂CH₂R²)₂] (Ln = Y, Lu; C₅R₄¹ = C₅Me₄, C₅H₄, 3-C₅H₃ t Bu; R² = OMe, NMe₂; Me: methyl; tBu: tert-butyl) have been found to polymerize ϵ-caprolactone to give a polymer of high molecular weight (M̄_n < 20 000) and moderate polydispersity (M̄_w/M̄_n < 2.0). Failure to observe a correlation between monomer/initiator ratio and molecular weight suggests a polymerization mechanism different from a pseudo-anionic mechanism.     

Narrow-polydispersity polystyrene/poly[styrene-co-(butyl methacrylate)] block copolymers by an N-oxyl mediated free radical polymerization process

Polystyrene/poly[styrene-co-(butyl methacrylate)] block copolymers with controlled molecular weights and with polydispersities generally below M̄_w/M̄_n = 1,45 and partially as low as M̄_w/M̄_n = 1,19 were synthesized by a free radical bulk copolymerization using a 2,2,6,6-tetramethylpiperidine-N-oxyl (TEMPO)-capped polystyrene macroinitiator. The influence of the macroinitiator concentration on the block copolymerization was studied. The polymerization rates are independent of the macroinitiator concentration and are close to that of thermally self-initiated styrene/butyl methacrylate copolymerizations showing the important role of self-initiation for N-oxyl mediated free radical polymerizations.     

Synthesis and mesomorphic behavior of poly(dipropylsilylenemethylene)

Based on the reaction of trichloro(chloromethyl)silane ( 1 ) with 2 equivalent amounts of the respective Grignard-reagent and subsequent cyclization, 1,1,3,3-tetrapropyldisilacyclobutane ( 3 ) has been prepared. Catalytic polymerization with H₂PtCl₆ was employed to prepare the corresponding poly(dipropylsilylenemethylene) (PDPSM, 4 ) with strictly alternating SiR₂/CH₂ backbone structure. A high-molecular-weight fraction of the material (weight-average molecular weight M̄_w = 166 500 and number-average molecular weight M̄_n = 115 200) obtained by fractionating precipitation was investigated with respect to glass transition and formation of conformationally disordered mesomorphic phases. The glass transition temperature T_g = 232 K of PDPSM evidenced lower backbone flexibility than observed for the analogous poly(dipropylsiloxane), (PDPS). PDPSM exhibited mesomorphic behavior. In contrast to poly(dipropylsiloxane), PDPSM showed a surprisingly narrow mesomorphic regime between 355 K and 365 K. Based on polarizing microscopy and ²⁹Si-MAS (magic angle spinning) solid-state NMR the mesophase is described as a conformationally disordered state, which is most probably columnar in analogy to PDPS.     

Ethylene polymerizations with novel tantalum(V) aminopyridinato complex/MAO systems

The use of two kinds of tantalum(V) aminopyridinato complexes, bis(2-benzylaminopyridinato)trichlorotantalum(V) and trichlorobis[2,6-di(phenylamino)pyridinato-N,N′]-tantalum(V), activated by methylaluminoxane was studied in polymerization of ethylene. The activities of these homogeneous catalyst systems are comparable to those of metallocenes. The weight-average molecular weights (M̄_w) of the produced polyethylenes are between 60 000 and 200 000 and M̄_w/M̄_n ≈ 2.     

Thermal polymerizations of alkali 4-(2-bromoethyl)benzoates in bulk

Thermal polymerizations of alkali 4-(2-bromoethyl)benzoates (2-BEBAs) were investigated. The polymerization of the lithium salt at 220°C for 2 h under reduced pressure in bulk, followed by esterification, produced poly(methyl 4-vinylbenzoate), having a number-average molecular weight (M̄_n) of 9500 in a 54% yield. Thus, elimination of hydrogen bromide to form a double bond occurred, followed by vinyl polymerization. In contrast, polymerization of the potassium salt at 200°C for 2 h afforded poly(oxycarbonyl-1,4-phenylene-ethylene) (polyester 1), having an inherent viscosity of 0.19 dL g⁻¹ in a 95% yield: i.e., polycondensation proceeded to afford the polyester. Reaction of the sodium salt at 220°C for 2 h produced polyester 1 having M̄_n of 4000 in a 28% yield as well as 4-vinylbenzoic acid in a 9% yield. In the reaction of the sodium salt, both polycondensation and double bond formation occurred. Thus, these polymerizations depended on the counter cations of 2-BEBAs. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 2055–2060, 1999     

Zero shear viscosity in miscible polymer blends of polystyrene and poly(2,6-dimethylphenylene ether)

The dynamic viscosities of blends of high molecular weight, narrowmolecular-weight distributed polystyrene and poly(2, 6-dimethylphenylene ether) are studied. The zero shear viscosity η_o depends on the weight average molecular weight M̄_w and on the average entanglement molecular weight M̄_e in the blend according to η_o ≈︁ M̄^3.4 _w(blend)/M̄^2.4_e(blend).     

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].     

Reverse atom transfer radical polymerization of methyl acrylate using AIBN as the initiator under heterogeneous conditions

Reverse atom transfer radical polymerization of methyl acrylate in the presence of a conventional radical initiator (2,2′-azoisobutyronitrile, AIBN) in bulk was successfully implemented via a new polymerization procedure. The system first reacts at 65–70°C for ten hours, then polymerizes at 100°C. Various mole ratios of AIBN to Cu^IICl₂ were used in this work, all of which result in a well-controlled radical polymerization with high initiation efficiency and narrow molecular weight distribution, i.e., the polydispersity is as low as M̄_w/M̄_n = 1.36.     

Glass Transition Temperatures of Poly[(methyl methacrylate)‐co‐(butyl acrylate)]s Synthesized by Atom‐Transfer Radical Polymerization

Glass transition temperatures T_g of methyl methacrylate/butyl acrylate copolymers obtained by means of atom‐transfer radical polymerization are measured using differential scanning calorimetry. Due the nature of this polymerization method an increase in molecular weight is produced as the reaction progresses, which gives rise to an increase in T_g. Simultaneously, a composition gradient with the enrichment of butyl acrylate causes a decrease in T_g. These opposite effects almost compensate each other and, therefore, no influence on the molecular weight at M̄_n < 10000 is found. This fact allows the application of the Johnston's equation and the Mayo‐Lewis terminal model to describe and predict the variation in T_g with copolymer conversion for the copolymers and under the experimental conditions investigated.     

Anionic synthesis of in-chain 3° amine-functionalized polybutadienes

Anionic copolymerizations of butadiene (M₁) with excess 1-(4-dimethylaminophenyl)-1-phenylethylene (M₂) were conducted in benzene at room temperature for 24–48h using sec-butyllithium as initiator. Anisole, triethylamine and t-butyl methyl ether were added in ratios of [B]/[RLi] = 60, 20, 30, respectively, to promote copolymerization. Narrow molecular weight distribution copolymers with M̄n = 14 × 10³ to 32 × 10³ g/mol (M̄_w/M̄n =1.02–1.03) and 8,12 and 30 amine groups per chain for anisole, triethylamine and t-butyl methyl ether, respectively, were obtained. The butadiene monomer reactivity ratios (r1) were 42, 33 and 14 for anisole, triethylamine and t-butyl methyl ether, respectively.