A proposal on the steric course of propagation in the homogeneous cationic polymerization of vinyl and related monomers

A stereochemical scheme of propagation was proposed for polymerizations of vinyl and related monomers by Friedel-Crafts catalysts. For the cationic propagation proceeding via the simple carbonium ion pair, the following two factors were considered to be of primary importance in determining the steric course of propagation: (1) the conformation of the last two units of the propagating polymer segment and the direction of approach of the incoming monomer; (2) the tightness of the growing ion pair. Thus, the front-side (less hindered site) attack to the carbonium ion gives rise to a syndiotactic placement and the back-side attack an isotactic placement. The present model can satisfactorily explain the effects of substituents, catalysts, polymerization media, and polymerization temperature on the steric structure of polymers in cationic polymerization of vinyl ethers. Extension of the scheme to polymerization of the β-substituted vinyl ethers in nonpolar solvents predicts formation of the diisotactic structures consistent with the experimental result. The influences of the polymerization condition on the steric structure of polymer were studied for cationic polymerizations of α-methylstyrene at low temperatures. Highly syndiotactic polymers were obtained for homogeneous reactions in toluene-rich media. The isotactic unit increased by increasing the content of methylcyclohexane in the solvent mixture. The effect of catalysts, though insignificant in toluene-rich media, was clearly noted in methylcyclohexane-rich media, less active catalysts (e.g., SnCl₄) yielding higher amounts of the isotactic unit than more active catalysts (e.g., AlCl₃). These results can be readily accommodated in the present model.     

Studies of polymers from cyclic dienes. V. Cationic polymerization of cyclopentadiene,influence of polymerization conditions on the polymer structure

Cationic polymerization of cyclopentadiene was studied with several Friedel-Crafts catalysts, and the influence of polymerization conditions on the polymer structure was investigated. Polycyclopentadiene contained higher amounts of the 1,2 structure when a stronger catalyst and a more polar solvent were used. This fact is discussed in terms of the tightness of the growing ion pair. The polymer structure did not vary with polymerization temperature in toluene solvent. In methylene chloride at around 0°C. the structural variation with catalysts was much smaller, suggesting a freer nature of the growing ion pair. The viscosity data also support the change in the structure of the ion pair under similar conditions. The use of aliphatic hydrocarbon solvents gave the highest contents of the 1,2 structure. This results was ascribed to the lack of solvation, considering the dependence of the polymer structure on the monomer concentration, which was found only in this solvent. Furthermore, isomerization during propagation was observed in polar solvents at higher temperature.     

Some new developments in vinyl ether polymerization

Different combinations of acetals with trimethylsilyl iodide have been explored as new initiating systems for the vinyl ether polymerization. The resulting polymers are characterized by controlled molecular weights and narrow molecular weight distributions, confirming the living polymerization mechanism. Acetals can also be used as transfer agents in the polymerization of vinyl ethers. When using 1,1-diethoxyethane (DEE) as transfer agent and isobutyl vinyl ether (IBVE) as monomer, a transfer constant of 0.2 was obtained (at −40°C in toluene). This method, transposed to functional acetals, provides a new way to prepare polyvinyl ethers with one or two functional end groups. The cationic polymerization of isobutyl vinyl ether initiated with the combination triflic acid/thietane, where thietane acts as electron donating moderator, leads to star-shaped polyvinylether-polythietane block-copolymers (at −40°C in dichloromethane). The block-copolymer structure is obtained because the vinyl ether polymerization is stopped when the α-alkoxy thietanium ion (active species) is attacked by a thietane molecule, which is at the same time an initiation reaction for the thietane polymerization. The star-shaped structure of the block-polymer is the result of the intermolecular termination in the cationic polymerization of thietane. When using a bifunctional initiator system, a polymer network is obtained consisting of linear polyIBVE-segments interconnected by branched polythietane segments. These findings support the sulfonium ion structure of the active species in the cationic polymerization of vinyl ethers initiated by the acid-sulfide system.     

Sulfur-containing vinyl monomers. XIII. Cationic copolymerizations of vinyl sulfides with some vinyl monomers

Cationic copolymerizations of vinyl sulfides (VS) with some vinyl monomers with boron tri-fluoride-diethyl etherate catalyst were investigated to evaluate their monomer reactivities. The effects of VS on the copolymer yield and viscosity of the resulting copolymers revealed the inhibition or retardation mechanism which was explained in terms of the formation of a stable vinylsulfonium salt by the reaction between a propagating carbonium ion and VS monomer. From the results of copolymerizations of phenyl vinyl sulfide (PVS) with isobutyl vinyl ether (IBVE), β-chloroethyl vinyl ether (CEVE), α-methylstyrene (α-MeSt), and styrene (St), the relative reactivities of these monomers were found to be in the following order: IBVE > CEVE > PVS > α-MeSt > St. The relatively higher reactivity of PVS than St derivatives was explained on the basis of the conjugative and electron-donating nature of the VS monomer. The effects of alkyl and para-substituted phenyl groups in vinyl sulfides on their reactivities toward the propagating carbonium ion were correlated with polar factors and compared with those of the hydrolysis of α-mercaptomethyl chlorides. The transition state for the propagation reaction in cationic polymerization of VS was proposed to be a π-complex type structure.     

Synthesis of various stimuli‐responsive gradient copolymers by living cationic polymerization and their thermally or solvent induced association behavior

Stimuli‐responsive gradient copolymers, composed of various monomers, were synthesized by living cationic polymerization in the presence of base. The monomers included thermosensitive 2‐ethoxyethyl vinyl ether (EOVE) and 2‐methoxyethyl vinyl ether (MOVE), hydrophobic isobutyl vinyl ether (IBVE) and 2‐phenoxyethyl vinyl ether (PhOVE), crystalline octadecyl vinyl ether (ODVE), and hydrophilic 2‐hydroxyethyl vinyl ether (HOVE). The synthesis of gradient copolymers was conducted using a semibatch reaction method. Living cationic polymerization of the first monomer was initiated using a conventional syringe technique, followed by an immediate and continuous addition of a second monomer using a syringe pump at regulated feed rates. This simple method permitted precise control of the sequence distribution of gradient copolymers, even for a pair of monomers with very different relative monomer reactivities. The stimuli‐responsive gradient, block and random copolymers exhibited different self‐association behavior. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 6444–6454, 2008     

NMR studies on the stereospecific polymerization of methyl vinyl ether. Part II. Polymerization by sulfuric acid–aluminum sulfate complex: Enantiomorphic catalyst sites model

Highly crystalline poly(methyl vinyl ether) (PMVE) was produced in toluene in a temperature range of 0 to ?20°C. with the use of sulfuric acid–aluminum sulfate complex (SA catalyst). It was found from the NMR spectra that these polymers contained more than 50% of the triad isotactic fraction and the melting point of the unfractionated polymer was about 130°C. However, PMVE containing a large amount of the isotactic fraction was insoluble in nitromethane, so the triad tacticity of highly crystalline PMVE could not be quantitatively determined. The molecular weight of PMVE increased with increasing conversion and increasing polymerization temperature. This behavior is different from that in metal halide catalysts. Also, the stereoregularity of PMVE decreased with increasing monomer concentration. However, addition of a polar solvent and increasing the polymerization temperature had little effect on the stereoregularity of the polymer. The increase in the isotactic fraction at high catalyst concentration and the difference in the monomer composition in the copolymerization of methyl vinyl ether with 2-chloroethyl vinyl ether by SA catalyst from that obtained by BF₃·O(C₂H₅)₂ suggest that the absorption of MVE on a catalyst surface is an important step in the propagation step by SA catalyst. The fraction of the triad tacticity calculated from the enantiomorphic catalyst sites model⁸ coincided with the experimental results. This fact shows that the steric structure of the adding monomer is determined only by the nature of the catalyst irrespective of the nature of a growing chain end. It is concluded, on considering also the results of the previous paper, that completely different factors can control the steric structure of a polymer even for the same monomer when different catalysts are used.     

The polymerization of methyl methacrylate by ion pairs

The reactions of the polymethylmethacrylate anion have been investigated at 200 K and 250 K in both THF and 9/1 toluene/THF. Sodium-α methyl styrene tetramer and fluorenyl sodium were used as initiators. Only ion pair reactions were investigated. The rate constant of monomer addition to the ion pair at 200 K was determined to be 80 ± 6 M^?1 sec^?1. At 250 K in the presence of excess monomer, the poly MMA anion reacts with the monomer vinyl function and the monomer ester function at comparable rates. Once fully reacted, the poly MMA anion terminates very slowly in THF at 250 K by an intermolecular mechanism. This rate of termination is enhanced in the toluene/THF system. No evidence was found for different reaction mechanisms for the two initiators.     

Implications of monomer and initiator structure on the dissociative electron‐transfer step of SET‐LRP

The heterolytic dissociation process associated with the activation of Single Electron‐Transfer Living Radical Polymerization is examined through the use of energy profile modeling. Monomer and initiator structure is correlated with the approximate activation barriers, energies of electrostatic ion‐radical pair formation, and stability of ion‐radical pair generated from the counteranion halide leaving group and the radical atom with partial positive charge density induced by its electron‐withdrawing substituent. Energy profiles permit access not just to one, but to all local minima, in the dissociation pathway and the identification of a global minimum. The location and energy of this global minimum allows for the placement of various initiators and dormant propagating macroradicals on the spectrum between stepwise and concerted dissociative electron‐transfer. The barrier for the activation step for alkyl‐halides derived from acrylates, vinyl halides, and styrenes, as well as from initiators bearing electron‐withdrawing groups is decreased in comparison to relatively more electron‐rich alkyl halides. This rate enhancement is explained through the sticky dissociative model wherein electron‐transfer is accelerated by the formation of strong ion‐radical pairs between radicals with partial positive charge density and their counteranion leaving group. Greater electron‐withdrawing capacity of the alkyl halide substituent increases the stability of the ion‐radical pair, reduces its equilibrium bond length, and accelerates electron‐transfer. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 5663–5697, 2008     

Near‐infrared spectroscopy investigation of water effects on the cationic photopolymerization of vinyl ether systems

Real‐time Fourier transform near‐infrared spectroscopy has been used to monitor monomer and water concentrations simultaneously during cationic vinyl ether photopolymerization. The use of near‐infrared peak area methods allows the water content to be conveniently and nondestructively determined in any monomer or polymer for which the water peak has previously been calibrated by gravimetric analysis. Although the shape of the absorption band due to absorbed water in a monomer changes with the quantity of water, the integrated intensity from about 5350 to 4900 cm^?1 can be correlated directly to the water concentration, and this region is well removed from the vinyl‐based absorption at approximately 6190 cm^?1. This approach provides a highly informative, dynamic technique for examining the influence of moisture on polymerization reactions. Significant differences have been observed in the effects of absorbed water on the cationic photopolymerization kinetics of vinyl ether monomers with or without an ? OH group. Along with the rapid consumption of water coupled to vinyl ether polymerization, acid‐catalyzed hydrolysis reactions have also been spectroscopically observed, giving rise to the formation of aldehyde groups. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 1985–1998, 2004     

Photopolymerization of vinyl monomers with quaternary ammonium salts

Photopolymerization of vinyl monomers with a series of quaternary ammonium salts has been investigated. However, quaternary ammonium salts used are not photosensitizers but rather photoinitiators. The salts photoinitiation activity was observed to vary widely with the counteranion in quaternary salts used and also with the alkyl group in their amine components. In general, the halide salts were more effective than tetrafluoroborate salts. It was also found that the overall activation energy for the photopolymerization of methyl methacrylate with dimethylbenzylanilinium tetrafluoroborate was 5.9 kcal/mole, and its rate was proportional to the 0.32 and 1.0 order of the concentration of the salt and the monomer used, respectively. An endgroup similar to dimethylaniline was found to be present in the methyl methacrylate polymer obtained by above system; this is probably a methylanilinomethyl group, from the characteristics of its ultraviolet spectrum.     

Electropolymerization : direct film formation on metal substrates-I: Kinetics and mechanism

Attempts have been made to produce, in situ, polymer films on tinplate cathodes by the electrolysis of conducting solutions of vinyl monomers for use in the can-lacquering industry. Study of a range of vinyl monomers revealed that film formation occurs at low monomer conversion only in the electrolysis of acrylonitrile and methacrylonitrile in NN'-dimethyl formamide. The highest rates of film formation were obtained by constant current electrolysis when tetraethyl ammonium p-toluene sulphonate (McKee Salt) was used as electrolyte. The rate of film formation increases with monomer concentration to a maximum and then falls rapidly. Chain propagation occurs by an anionic mechanism with ion pair formation favoured at high monomer concentrations. The physical properties of the coloured films produced rarely approach those required industrially and the method does not represent an alternative approach to the lacquering of food and beverage cans.     

Synthesis of monomers that expand on polymerization. Synthesis and polymerization of 3,9-dimethylene-1,5,7,11-tetraoxaspiro[5.5]undecane

A spiro ortho-carbonate containing two double bonds, 3,9-dimethylene-1,5,7,11-tetraoxaspiro[5.5]undecane (III) was prepared from 2-methylene-1,3-propanediol (VI). The structure of the monomer was indicated by its elementary analysis as well as its infrared and NMR spectra. When the crystalline monomer was polymerized with Lewis acids such as trifluoride etherate as catalysts, soluble polymer with a high molecular weight was obtained. The infrared and NMR spectra indicated that the polymer was an alternating copolymer of ether and carbonate having double bonds. When the usual monomers such as vinyl chloride and styrene polymerize, shrinkage occurs. However, this monomer underwent expansion on polymerization.     

Alternating copolymerization of 2,3-dichloro-5,6-dicyano-p-benzoquinone with styrene and polymerization behavior with vinyloxy compounds

2,3-Dichloro-5,6-dicyano-p-benzoquinone (DDQ) was found to copolymerize alternatingly with styrene (St). DDQ–isobutyl vinyl ether and DDQ–2-chloroethyl vinyl ether systems gave homopolymers of vinyl ethers, while DDQ–phenyl vinyl ether and DDQ–vinyl acetate systems gave oligomers containing both monomer units. In the terpolymerization of DDQ, p-chloranil (pCA), and St, terpolymers obtained were found to have about 50 mole % of St units regardless of monomer feed ratio and DDQ was incorporated much more rapidly into the terpolymer than pCA. The difference in the reactivity of the acceptor monomers could be attributed to that in their electron-accepting character.     

Stereospecific polymerization of isobutyl vinyl ether. III. Polymerization with VCl3 • LiCl

The polymerization of isobutyl vinyl ether by vanadium trichloride in n-heptane was studied. VCl₃ ? LiCl was prepared by the reduction of VCl₄ with stoichiometric amounts of BuLi. This type of catalyst induces stereospecific polymerization of isobutyl vinyl ether without the action of trialkyl aluminum to an isotactic polymer when a rise in temperature during the polymerization was depressed by cooling. It is suggested that the cause of the stereospecific polymerization might be due to the catalyst structure in which LiCl coexists with VCl₃, namely, VCl₃ ? LiCl or VCl₂ ? 2LiCl as a solid solution in the crystalline lattice, since VCl₃ prepared by thermal decomposition of VCl₄ and a commercial VCl₃ did not produce the crystalline polymer and soluble catalysts such as VCl₄ in heptane and VCl₃ ? LiCl in ether solution did not yield the stereospecific polymer. It was found that some additives, such as tetrahydrofuran or ethylene glycol diphenyl ether, to the catalyst increased the stereospecific polymerization activity of the catalysts. Influence of the polymerization conditions such as temperature, time, monomer and catalyst concentrations, and the kind of solvent on the formed polymer was also examined.     

Novel synthesis of photocrosslinkable polymers

A new preparative route to photocrosslinkable polymers in which the polymers are produced directly from the polymerization of vinyl monomers having photocrosslinkable groups has been investigated. The photosensitive resins thus produced have higher sensitivity and resolution than conventional photosensitive resins. The monomers were synthesized from the esterification of vinylphenols or vinyl β-chloroethyl ether with cinnamic acid, β-styrylacrylic acid, and their homologs, and from the etherification of vinyl β-chloroethyl ether with hydroxychalcones. Homopolymerizations of these monomers and their copolymerizations with other comonomers were investigated with the use of both radical and ionic initiators. It is shown that radical polymerization of the monomers gave soluble polymers only at low conversion. Anionic initiators did not initiate polymerization. Cationic polymerization imparted soluble polymers in high yield, except for the monomers bearing cyano groups, which generally gave insoluble polymers. Infrared and NMR spectroscopic investigation of the cationically obtained soluble polymers and comparative investigation by cationic polymerization of model compounds indicated that polymerization of the monomers proceeds through the vinyl double bond without affecting the photosensitive unsaturated bond. Thus, linear photocrosslinkable polymers with an intact photoreactive group may be produced by cationic polymerization. In general, these polymers have uniform structure and modifiable physical properties depending on the monomer used. The polymer thus obtained from β-vinyloxyethyl cinnamate has been shown to have excellent properties for use as a photo-resist.     

Synthetic applications of non-polymerizable monomers in living carbocationic polymerization

The foundation and methodology of using highly reactive but non-polymerizable monomers in living cationic polymerizations is introduced. The chemistry and kinetics of 1,1-diphenylethylene (DPE) addition to living polyisobutylene (PIB) in methyl chloride/n-hexanes 40/60 v/v at −80°C is reported. Monoaddition occurred even when large excess of 1,1-diphenylethylene was used. The methanol quenched polymer of the DPE capped PIB carried -OCH₃ functionality exclusively, suggesting that the diphenyl alkyl chain-ends are completely ionized, which was confirmed by conductivity studies. By in-situ functionalization using soft nucleophiles a variety of functional groups were obtained, most notably ester upon reaction with silyl ketene acetal. It was found that the diphenyl carbenium ion is an efficient initiating species for the polymerization of reactive monomers such as vinyl ethers and α-methylstyrene. The synthesis of PIB based block copolymers was accomplished by sequential monomer addition, using para-methylstyrene, α-methylstyrene or isobutyl vinyl ether as the second monomer. It involved capping with DPE, followed by tailoring the Lewis acidity to the reactivity of the second monomer by the addition of titanium(IV) alkoxide, by replacing the Lewis acid with a weaker one or by the use of a common ion salt. PIB-b-PMMA was obtained by the combination of living cationic and group transfer (GTP) polymerizations.     

一种新型侧链液晶聚合物的喇曼光谱研究

The Raman scattering on a novel liquid crystal side chain polymer, poly-2,5-bis (p-meth-oxybenzoyloxy) styrene, has been performed. We observed that the characteristic Raman sp-ctra of the vinyl group in the monomer changed much deeply in the polymer, especially for the Raman line correponding to the C=C of the vinyl group which disappeared completly in the polymer. Contrast with that, the Raman spetra of the rest group did not present any substantial difference between the monomer and the polymer. These experimental facts show-ed that the vinyl group of the monomer was tranfered to the polymeric backbone while the chemical structure of the mesogenic unit in the monomer remained after the polymerization,and also conformed that it was successful in the synthesis of a liquid crystal side chain plymer without a flexible spacer between the mesomorphic unit and the molecular main chain.     

Kinetics of Radical Polymerization of a Monomer Derived from Monoethanolamine Vinyl Ether and 1,4-Benzoquinone: A Polarographic Study

Radical polymerization of a disubstituted monomer derived from monoethanolamine vinyl ether and 1,4-benzoquinone was studied by classical polarography. The optimal conditions for the synthesis of the redox polymer were found. The polymerization rate constants, preexponential term in the Arrhenius equation, and activation energy were calculated.     

Antithetic function of alcohol in living cationic polymerization: From terminator/inhibitor to useful initiator

We employed alcohols as initiators for living cationic polymerization of vinyl ethers and p‐methoxystyrene, coupled with tolerant Lewis acid, borontrifluoride etherate (BF₃OEt₂), although they were known to be poisonous reagent to bring about chain‐breaking such as chain transfer/termination rather than such beneficial one for propagation and polymerization‐control. As well known, without assistance of additive, ill‐defined polymers with broad molecular weight distributions (MWDs) were produced. Even addition of conventional oxygen‐based bases, for example, ethyl acetate (AcOEt), 1,4‐dioxane (DO), tetrahydrofran (THF), and diethyl ether (Et₂O) was less efficient in this system to control molecular weights and MWDs (M_w/M_n > 2.0). In contrast, by addition of dimethyl sulfide (Me₂S), MWDs of the resultant polymers became much narrower (M_w/M_n < 1.23) and the number‐average molecular weight (M_n) increased in direct proportion to monomer conversion in agreement with the calculated values assuming that one alcohol molecule generates one polymer chain. Studying changed feed‐ratio of alcohol to monomer and structural analyses with NMR and MALDI‐TOF‐MS indicated that quantitative initiation from alcohol giving alkoxide counteranion. This system opens a new way to use a variety of alcohols as initiators, which would allow us to design variety of structures and functions of counteranion. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 4194–4201, 2009     

Non-fouling surfaces produced by gas phase pulsed plasma polymerization of an ultra low molecular weight ethylene oxide containing monomer

The pulsed plasma polymerization of low molecular weight molecules containing only one (ethylene oxide vinyl ether) and two (diethylene oxide vinyl ether) ethylene oxide units were investigated. The surface density of EO units retained in the polymer films increases sharply with decreasing average power input during deposition, particularly at very low plasma duty cycles. The protein adsorption properties of these plasma synthesized polymer were investigated using ¹²⁵I-labeled albumin and fibrinogen. Surprisingly effective, non-fouling surfaces were observed with films synthesized from the monomer containing two ethylene oxide units; however, the monomer containing only one EO unit gave surfaces that were not particularly effective in preventing protein adsorptions. The results obtained show that ultra short chain length PEO modified surfaces can be biologically non-fouling. This, in turn, has interesting consequences in terms of trying to identify the basic reason for the effectiveness of EO units in preventing biomolecule adsorptions on surfaces.