Stereospecific anionic polymerization of styrene initiated by R2Mg/ROMt ‘ate’ complexes

Various ‘ate’ complexes formed by reaction of alkali metal (Li, Na, K) derivatives and alkyl metals (Mg, Al, Zn) were used as initiator for the styrene anionic polymerization in hydrocarbon media and their influence on polystyrene microstructure has been investigated. A strong dependence of the polymer tacticity on both the nature of the alkali metal and of the associated metal alkyl used is observed. Binary systems like potassium derivatives/dialkylmagnesium yield isotactic-rich polystyrene. Eighty-five percent isotactic polystyrene (mm triad) is obtained in methylcyclohexane at −40 °C with the potassium tert-butoxide/n,s-dibutylmagnesium system. The characteristics of solubility of the stereoregular polystyrenes are in agreement with isotactic polystyrene chains containing some stereostructural defects and suggest that one single type of isospecific propagating centres is operating during the polymerization. When lithium or sodium derivatives are used in association to dialkylmagnesium instead of a potassium derivative, a strong decrease of the isotacticity is observed. The influence, on the extent of stereoregulation, of other parameters of these initiating systems as well as that of the solvent has also been investigated. The stereoregulation mechanisms involved in these styrene anionic polymerizations may be related to styrene insertion into carbon-metal bonds of the ‘ate’ complexes with a covalent character.     

Tactic poly(crown ether)s with pendant benzocrown ethers

Summary Tactic and atactic poly(crown ether)s, poly(methacryloyloxymethylbenzo-15-crown-5), were synthesized by polymer reaction of the respective poly(methacrylic acid) with chloromethylbenzo-15-crown-5 and radical polymerization of methacryloyloxymethylbenzo-15-crown-5. By solvent extraction of alkali metal picrates with these poly(crown ether)s, the isotactic poly(crown ether) was found to be a little more selective for K⁺ and Rb⁺ than the syndiotactic and atactic ones.     

Stereocomplex formation between isotactic PMMA and syndiotactic polymethacrylates in bulk and in solution

Summary Blend of isotactic PMMA and syndiotactic poly(benzyl methacrylate) was found to form stereocomplex when annealed at 80°C. The blend showed endotherm in DSC thermogram due to the melting of the complex. The complex was also formed in toluene, which was evidenced by¹H NMR spectroscopy and thermal analysis. Several syndiotactic polymers of substituted benzyl methacrylates and aliphatic methacrylates having primary alkyl ester group with branching at -position, such as methallyl and cyclopropylmethyl methacrylates, were also found to form stereocomplexes with isotactic PMMA in bulk by annealing.     

Effect of a combination of hexamethylphosphoramide and alkyl alcohol on the stereospecificity of radical polymerization of N-isopropylacrylamide

Radical polymerization of N-isopropylacrylamide (NIPAAm) was investigated at low temperatures in the presence of both hexamethylphosphoramide (HMPA) and alkyl alcohols. Although HMPA and alkyl alcohols separately induced syndiotactic specificity in NIPAAm polymerization in toluene at low temperatures, a combination of HMPA and less bulky alkyl alcohols, such as methanol and ethanol, was found to induce isotactic specificity at −80 °C. NMR analysis of mixtures of NIPAAm, ethanol and HMPA suggested the formation of a 1:1:1 complex through O-H•••O=C and N-H•••O=P hydrogen bonding. It is believed that the steric effect of HMPA enhanced by cooperative hydrogen bonding was responsible for the combined effect of HMPA and alkyl alcohols in inducing isotactic specificity.     

Electronic Structure and Ground State Properties of PMMA Polymer: I. Step-By-Step Formation and Stereo-Regularity of the Polymeric Chain—AM1-MO Treatment

ABSTRACT

The equilibrium ground state geometric parameters of benzoyl peroxide (as free radical initiator), methylmethacrylate monomer (as a reference molecule), benzoyl-MMA radical (I), phenyl-MMA radical (II) and the three polymeric chain of PMMA (syndiotactic, isotactic, and atactic) are investigated theoretically using AMI-MO method. The stability of phenyl, benzoyl-MMA radicals, and the conformational properties of isotactic, syndiotactic, and atactic structures of PMMA polymers are discussed. The initiation and propagation steps of polymerization are investigated theoretically. The calculated geometric parameters are analyzed in terms of heat of formation, total energy, dipole moment, net charge, ionization potential, electron affinity, energy gap, and charge density maps (Total, HOMO, and LUMO).     

Measurement of the unperturbed dimensions of stereoregular poly(methyl methacrylate)

The results of measurements of unperturbed dimensions for a series of stereoregular poly(methyl methacrylates) are reported. The measurements were made by a recently developed method involving a gel permeation chromatograph coupled with an on-line low angle laser light scattering photometer. Measurements were performed in a thermodynamically good solvent, tetrahydrofuran at 25°C. The unperturbed dimensions were obtained by means of viscosity plots. Comparison of the results obtained by this method with those currently available in the literature, as well as with values predicted by statistical calculations, show good agreement. It was determined that a measurable difference occurs in the Mark-Houwink relationship between isotactic and syndiotactic poly(methyl methacrylate); isotactic poly(methyl methacrylate) is 30% more extended than syndiotactic poly(methyl methacrylate) in its unperturbed state; and isotactic poly(methyl methacrylate) exhibits a smaller degree of polymer solvent interaction than the syndiotactic form.     

Stereoregular oligomers of methyl methacrylate

Summary Packed column SFC has been found suitable for the rapid and detailed analysis of the isotactic and syndiotactic oligomers of MMA, when the temperature gradient technique was applied and the modifier was employed. Oligomer components from trimer to 20-mer separated completely. The heptamer fraction collected three times by SFC gave the ¹H NMR spectrum of satisfactorily high S/N ratio; the spectrum agreed well with that of the standard sample. Separation by tacticity as well as by molecular weight was observed for the SFC of a mixture of the isotactic and syndiotactic oligomers. The isotactic oligomers had longer retention time than the syndiotactic oligomers of the corresponding degree of polymerization. Part 3: cf. Ute K. Nishimura T, Hatada K, Polym J (1989) 21: 1027     

Stereoregular poly(alkyl methacrylate)s: polymer-polymer and copolymer-polymer blends

Amorphous blends of isotactic and syndiotactic poly(methyl methacrylate) were found to be compatible. To evaluate the interaction between these tactic polymers, random copolymers of isotactic poly(methyl/ethyl methacrylate) were blended with syndiotactic poly(methyl methacrylate). Only the copolymers with an ethyl methacrylate content below 45% were compatible with syndiotactic poly(methyl methacrylate). Using a Flory-Huggins type treatment of copolymer mixtures, the segmental interaction parameters for poly(methyl methacrylate) with poly(ethyl methacrylate) and for isotactic with syndiotactic poly(methyl methacrylate) were calculated. The interaction parameter for the tactic poly(methyl methacrylate) pair was found to be small and negative.     

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.     

Molecular aggregation in poly(vinyl chloride). III. Role of molecular structure

The present study offers a visualization of the process of molecular aggregation in PVC polymerized at low temperatures in bulk. “Kinks” along with the chains are responsible for molecular entanglement with subsequent microcrystallization of the syndiotactic sequences. The crystallites act as bonding nuclei. The “kinks” are the result of the different chain conformations of isotactic and syndiotactic sequences. The number of “kinks” increases on lowering the polymerization temperature both because the chains are longer and also because of the more frequent switching between isotactic and syndiotactic placements.     

Wettability and microstructure of polymer surfaces: stereochemical and conformational aspects

Stereoregular poly(methyl methacrylates) (PMMAs) solvent-cast in the form of films against a glass substrate were employed as model systems for a systematic study of the relationship between the molecular structure (as characterized by the stereochemistry and conformations of macromolecules), the functional-group composition, and the wettability of polymer surfaces. The water wettability of a syndiotactic surface was found to be highly sensitive to the polarity of the adjacent phase in the film-casting process, whereas the wettability of an isotactic surface was invariant to the polarity of the contacting medium. The tacticity-dependent wetting behavior arises from the difference in the extent of functional-group surface segregation or, in other words, from the different surface activity of the different tactic versions of the polymer. This difference, in turn, is associated with fundamental distinctions in the conformational structures energetically allowed for the isotactic and syndiotactic configurations of the polymer chain; the syndiotactic macromolecule is capable of adopting an amphiphilic surface conformation, whereas the energetically allowed conformational structures of the isotactic macromolecule do not possess amphiphilic character. In view of these findings, the isotactic surfaces can be regarded as 'ideal' model surfaces for research on the fundamentals of wetting phenomena. In addition, there is evidence for failure of the basic assumption of the Cassie approach, i.e. the assumption of macroscopic chemical heterogeneity, to describe adequately the wetting behavior of isotactic PMMA surfaces.     

The influence of ester groups on the stereocomplex formation between different polyalkylmethacrylates

Isotactic poly(ethyl methacrylate) (it-PEMA) and syndiotactic poly(isobutyl-methacrylate) (st-PiBMA) were synthesized to investigate the stereocomplex formation with syndiotactic and isotactic poly(methyl methacrylate) (st- and it-PMMA) respectively. A d.s.c. study pointed out that it-PEMA and st-PMMA form incompatible mixtures whereas st-PiBMA and it-PMMA form compatible mixtures in which stereocomplex formation can occur as indicated by viscometry and X-ray diffraction. These results confirm the idea that the methyl ester groups of the isotactic chain and the α-methyl groups of the syndiotactic chain are responsible for stereocomplex formation.     

Methacrylate-based block ionomers I: Synthesis of block ionomers derived from t-butyl methacrylate and alkyl methacrylates

Diblock and triblock copolymers of t-butyl methacrylate (tBMA) with 2-ethylhexyl methacrylate (EHMA) and n-hexyl methacrylate were prepared via alkyl lithium initiation and sequential addition techniques in THF at ?78°C. The tBMA blocks were quantiatively and selectively hydrolyzed to afford poly(methacrylic acid) (PMAA) blocks which were then neutralized with alkali metal bases to form block ionomers. The unhydrolyzed copolymers had a phase mixed morphology as evidenced by thermal analysis while the hydrolyzed and neutralized polymers were multiphase materials. The carboxylic acid and ioncontaning triblock copolymers formed gels in nonpolar solvents which could be disrupted by the addition of polar additives. Certain carboxylic acid and ioncontaining EHMA/tBMA diblock copolymers also showed this behavior. The triblock ionomers did not show thermoplastic flow prior to degradation, except at the lowest ionic content studied (2%).     

Synthesis of oligocarbonate diols from ethylene carbonate and aliphatic diols catalyzed by alkali metal salts

The influence of alkali metal salt catalysts and reaction conditions on the oxyethylene units formation in the synthesis of oligocarbonate diols from five-membered cyclic carbonates and aliphatic diols is presented. The reaction mechanism, involving the alkoxide group formation from cyclic carbonate and alkali metal salts has been proposed and discussed. The oligomeric products were analyzed by means of MALDI-TOF mass spectrometry and NMR spectroscopy.     

Preparation of 8-methyl-2-decanol: General synthesis of diastereomeric mixtures of alkyl branched insect pheromones

A general method for synthesis of insect pheromones having alkyl branched carbon skeletons is demonstrated with the preparation of a diastereomeric mixture of 8-methyl-2-decanol, whose propionate is an attractant of someDiabrotica species. The procedure involves reaction of a ketone with lithium acetylide ethylenediamine complex to afford a propargylic alcohol containing the branch of the target molecule. Copper (1) mediated alkylation of the derived propargylic acetate with a primary alkyl halide yields a trisubstituted allene having the desired chain length, and isomerization with an alkali metal amide of either ethylenediamine or 1,3-diaminopropane, affords the alkyl branched terminal acetylene. The triple bond is converted to the methyl ketone and reduced to the methyl carbinol. The reactions proceed in good yield, and can be conveniently carried out on large scale. The method should prove useful for production of pheromone components in cases where diastereomeric mixtures can be employed.Issued as NRCC No. 27519.     

Inorganic salt catalysis in the process for the conversion of alcohols/alkylphenols into ethoxychloride surfactant intermediates

The process for the preparation of alkyl/alkylphenylethoxychlorides, precursors to a range of speciality surfactants, was investigated. The original manufacturing procedure involved ethoxylation with ethylene oxide catalysed by potassium hydroxide of the alcohol/alkylphenol followed by uncatalysed chlorination with thionyl chloride. The chlorination stage was a batch process requiring long reaction times (4–18 h) at 80°C and resulted in cleavage of the ethyloxylate chain as 1,4-dioxan. Using a model alkylethoxyalcohol, we demonstrated that the chlorination stage may be effectively catalysed by alkali metal salts/bases. Rate enhancement and suppression of 1,4-dioxan production resulted. Investigation of a range of inorganic salts/bases for the catalysis of the chlorination of commercially realistic alkylphenylethoxyalcohols indicated lithium hydroxide monohydrate (0.2%) to be the most versatile and cost effective catalyst. Chlorination was complete after less than 0.25 h at 80°C and the benefits of a continuous process based upon this catalyst are discussed. Alkaline earth metal salts/bases were also found to be effective catalysts but transition and B-Group metal salts retarded chlorination and facilitated ethoxylate chain cleavage. The application of a single catalyst for the conversion of alcohols/alkylphenols into ethoxychlorides is proposed. We demonstrated that strontium hydroxide effectively catalysed both ethoxylation and chlorination of hexadecanol. The advantages of using lithium hydroxide monohydrate (strontium hydroxide) as a single catalyst for the manufacture of broad-(narrow-) distribution alkyl/alkylphenylethoxychlorides from alcohols/alkylphenols are discussed.     

Preparation of PMMA macromers by o-vinylbenzylmagnesium chloride and their polymerization

Summary Polymerization of MMA with o-vinylbenzylmagnesium chloride was examined in toluene and in tetrahydrofuran (THF) at various temperatures. The polymer formed in toluene at –78°C was highly isotactic (mm=94%) and containing one vinylbenzyl group at the -end of the chain, although the methanol-soluble fraction concomitantly formed in an appreciable amount was less isotactic. The PMMAs formed in THF at –78 and –98°C were mostly methanol-soluble and highly syndiotactic (rr=88% at –78°C and 96% at –98°C), and also contained one vinylbenzyl group. The methanol-soluble, isotactic and syndiotactic PMMA macromers were polymerized or copolymerized with styrene by AIBN in toluene at 60°C. The isotactic macromer exhibited slightly higher reactivity than the syndiotactic one.     

Preparation of syndiotactic polyolefins by using metallocene catalysts

Summary Polyolefins having syndiotactic structure were obtained by using 1-methyl-1-ethylidene-(cyclopentadienyl-1′-fluorenyl) zirconium dichloride and methylaluminoxane as a catalyst. 1-Butene and 4-methyl-1-pentene gave crystalline polymers having syndiotactic structure, while 1-pentene, 1-hexene and 1-octene gave noncrystalline polymers having syndiotactic structure. The identification of syndiotactic and isotactic polyolefins was made by ¹³C-NMR, X-ray diffraction, and differential scanning calorimetry.     

The transport phenomena of some model solutes through postcrosslinked poly(2-hydroxyethyl methacrylate) membranes with different tactic precursors

Two series of membranes of various degree of hydration have been prepared by postcrosslinking highly syndiotactic and isotactic poly(2-hydroxyethyl methacrylate) [P(HEMA)] with various amounts of hexamethylene diisocyanate (HMDIC). The equilibrium water content, the partition coefficient, and the permeability of the model solutes such as urea, acetamide, NaCl, 2-propanol, and isobutanol for these membranes were measured. In addition, differential scanning calorimetry (DSC) study for the membranes was performed. The membranes of the isotactic precursor are more hydrated at 25°C compared to the ones of its syndiotactic counterpart. This may be due to the more hydrophobic nature of syndiotactic P(HEMA). The partition coefficient data show that the solutes of urea, acetamide, and NaCl are partitioned only into the water-containing region, whereas the alcohol solutes are preferentially sorbed on to polymer matrix. The permselectivity data of urea to NaCl reveal that the permselectivity of crosslinked isotactic P(HEMA), (ISO) membranes increases as the amount of HMDIC is increased from 2.5 to 10 mol %, while the trend is reversed for crosslinked syndiotactic P(HEMA), (SYN) membranes. The apparent diffusivity order of urea, acetamide, and NaCl is not the same in those two characteristic membranes: the order is urea > NaCl > acetamide for highly crosslinked ISO membranes, and NaCl > urea > acetamide for all SYN membranes, which was compared with the free diffusion data in aqueous solution and interpreted in terms of the water-structural orderlines within membranes.     

Preparation and properties of stereoregular poly(hydroxyethyl methacrylate) polymers and hydrogels

Linear poly(hydroxyethyl methacrylate) (PHEMA) has been synthesized in highly syndiotactic and highly isotactic configurations. The high syndiotactic PHEMA prepared by u.v. photolysis at ?40° C was found by ¹³C n.m.r. to have a tactic triad content of 84% syndio, 16% hetero and 0% iso. High isotactic PHEMA was prepared by anionic polymerization of benzoxyethyl methacrylate in toluene followed by selective hydrolysis of the benzoate ester, and was observed by ¹³C n.m.r. to have a 5% syndio, 15% hetero and 80% isotactic triad content. A linear PHEMA polymer formed by radical polymerization at 60°C in ethanol solvent was found to have a tactic triad content of 58% syndio, 42% hetero and 0% iso. These polymers have been crosslinked with hexamethylene diisocyanate and their water swelling properties determined as functions of temperature and crosslinker concentration. Isotactic PHEMA exhibited greater aqueous swelling below 30° C than the syndiotactic PHEMA samples. The stereochemistry of the polymer chain is shown to be a factor in determining the swelling behaviour of hydrophilic methacrylate gels.