Ionic polymerization of p-vinylbenzyl methyl ether

Ionic polymerizations of vinylbenzyl methyl ether initiated by either carbanions or Lewis acids has been found to lead to crosslinked polymers. By comparative studies of strong carbanionic bases and Lewis acids with benzyl ethers, it has been possible to define details of mechanisms which in conjunction with cationic or anionic propagation lead to crosslinks. The α-hydrogens of benzyl ethers have been found to be sufficiently acidic to terminate anionic polymerization of styrene and displacement of alkoxide anion from the benzyl ether linkage by nucelophilic polymer anions is proposed as a mechanism leading to branching and eventual crosslinking in anionic polymerization of vinylbenzyl methyl ether. Cationic polymerization of vinylbenzyl methyl ether is quite complex. In addition to propagation, chain transfer, and spontaneous termination of cation chain carriers, there is evidence for complex formation between Lewis acid initiator and the benzyl ether substituent. A slow decomposition of ether–Lewis acid complexes produces benzylcarbonium ions which alkylate aromatic rings of polymer and thereby crosslink the polymer. Benzyl ether has been found to be an effective chain terminator for cationic styrene polymerization.     

Stereospecific polymerization of benzyl α-(alkoxymethyl) acrylates

α-(Alkoxymethyl) acrylates, such as methyl α-(phenoxymethyl) acrylate, benzyl α-(methoxymethyl)acrylate (BMMA), benzyl α-(benzyloxymethyl)acrylate, and benzyl α-(tert-butoxymethyl)acrylate, were synthesized, and their polymerizability and the stereoregularity of the polymers obtained by radical and anionic methods were investigated. The radically obtained polymers were found to be atactic by ¹³C- and ¹H-NMR analyses, but the polymers obtained with lithium reagents in toluene at −78°C were highly isotactic. Further, it is noteworthy that isotactic polymers were also produced with lithium reagents even in tetrahydrofuran. Effects of polymerization temperature and counter cation on stereoregularity were clearly observed in the polymerization of BMMA, and a potassium reagent afforded an almost atactic polymer. © 1997 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 35: 721–726, 1997     

Semicontinuous seeded emulsion copolymerization of vinyl acetate and methyl acrylate

The semicontinuous seeded emulsion copolymerization of vinyl acetate and methyl acrylate was investigated. The effect of type of process (starved process versus semi-starved process), type of feed (neat monomer addition versus monomer emulsion addition), amount of seed initially charged in the reactor, and feed rate on the time evolution of the overall conversion, copolymer composition, and polymer particle size was analyzed. It was found that, in the case of the starved process, both monomers, but mainly vinyl acetate, accumulated in the reactor. The preferential accumulation of vinyle acetate resulted in a drift of the copolymer composition. Both monomers accumulation and copolymer composition drift were reduced by increasing the amount of seed initially charged in the reactor and by decreasing the feed rate. For the semi-starved process, it was found that a vinyl aceatate rich copolymer was formed when a low methyl acrylate feed was used, whereas a methyl acrylate rich copolymer was obtained at high methyl acrylate feed rates. For both starved process and semi-starved process, the total number of polymer particles, after an initial increase, reached a plateau value which was the same in all of the experiments carried out. These results were analyzed by means of a mathematical model developed for this system.     

A tracer study of the hydrolysis of methyl methacrylate and methyl acrylate units in homopolymers and copolymers

Homopolymers and copolymers were prepared from methyl methacrylate, methyl acrylate, and styrene by radical reactions at 60°C. Monomers suitably labeled with carbon-14 were used so that it was possible to monitor the hydrolysis of ester groups in the polymers during treatment under alkaline conditions. It was found that methyl acrylate units were hydrolyzed completely whatever their environment in a polymer chain. Under the same conditions only about 9% of the ester groups in a homopolymer of methyl methacrylate reacted; the proportion was increased by the introduction of comonomer units into the polymer chain. For copolymers of methyl methacrylate with methyl acrylate the extent of reaction may be correlated with the lengths of the sequences of methyl methacrylate units.     

Mechanical activation of catalysts for C-C bond forming and anionic polymerization reactions from a single macromolecular reagent

Coupling of pyridine-capped poly(methyl acrylate)s, PyP(M) (where M corresponds to the number average molecular weight in kDa), to the SCS-cyclometalated dipalladium complex [(1)(CH(3)CN)(2)] afforded organometallic polymers [(1)(PyP(M))(2)] with a concomitant doubling in molecular weight. Ultrasonication of solutions containing [(1)(PyP(M))(2)] effected the mechanical scission of a palladium-pyridine bond, where the liberated PyP(M) was trapped with excess HBF(4) as the corresponding pyridinium salt, harnessed to effect the stoichiometric deprotonation of a colorimetric indicator, or used to catalyze the anionic polymerization of α-trifluoromethyl-2,2,2-trifluoroethyl acrylate. The mechanically induced chain scission also unmasked a catalytically active palladium species which was used to facilitate carbon-carbon bond formation between benzyl cyanide and N-tosyl imines. Spectroscopic and macromolecular analyses as well as a series of control experiments demonstrated that the aforementioned structural changes were derived from mechanical forces that originated from ultrasound-induced dissociation of the polymer chains connected to the aforementioned Pd complexes.     

Preparation and Characterization of Head-to-Head Polymers. II. Head-to-Head Poly(methyl Acrylate)

Head-to-head poly(methyl acrylate) was prepared by esterification of the known alternating copolymer of ethylene and maleic anhydride. Some of the chemical,physical, and mechanical properties and the thermal degradation behavior of head-to-head poly(methyl acrylate) were studied and compared with those of head-to-tail poly(methyl acrylate). The T_g of the head-to-head polymer was higher than that of the head-to-tail polymer, but the solubilities of both types of polymers of comparable molecular weight were similar. Head-to-head poly(methyl acrylate) degraded thermally at approximately the same temperature and with a rate similar to head-to-tail poly(methyl acrylate). Unlike poly(methyl cinnamates) which cleanly degraded to monomers, poly(methyl acrylates), head-to-head and head-to-tail, degrade to very small molecules, such as CO₂, methanol, but also larger polymer fragments and char. Trace amounts of monomers (methyl acrylate) were also observed.     

Thermal degradation of vinylidene chloride/[4-(t-butoxycarbonyloxy)phenyl]methyl acrylate copolymers

Vinylidene chloride polymers containing comonomer units capable of consuming evolved hydrogen chloride to expose good radical-scavenging sites might be expected to display greater thermal stability than similar polymers containing simple alkyl acrylates as comonomer. Incorporation of a comonomer containing the phenyl t-butyl carbonate moiety into a vinylidene chloride polymer has the potential to afford a polymer with pendant groups which might interact with hydrogen chloride to expose phenolic groups. Copolymers of vinylidene chloride with [4-(t-butoxycarbonyloxy)phenyl]methyl acrylate have been prepared, characterized, and subjected to thermal degradation. The degradation has been characterized by thermal and spectroscopic techniques. The degradation of vinylidene chloride/[4-(t-butoxycarbonyloxy)phenyl]methyl acrylate copolymers is much more facile than the same process for similar copolymers containing either [4-(isobutoxycarbonyloxy)phenyl]methyl acrylate or methyl acrylate, a simple alkyl acrylate, as comonomer. During copolymer degradation, [4-(t-butoxycarbonyloxy) phenylmethyl acrylate units are apparently converted to acrylic acid units by extensive fragmentation of the sidechain. Thus, the phenyl t-butyl carbonate moiety does function as a labile acid-sensitive pendant group but its decomposition in this instance leads to the generation of a phenoxybenzyl carboxylate capable of further fragmentation.     

Monomer reactivity ratios in graft copolymerization

This paper discusses monomer reactivity ratios in various radiation- and redox-initiated graft copolymerizations. The polymers studied were polyethylene, cellulose acetate, poly(vinyl chloride), polytetrafluoroethylene, poly(vinyl alcohol), and poly(methyl methacrylate); the comonomer mixtures were styrene–acrylonitrile, methyl acrylate–styrene, acrylonitrile–methyl acrylate, and vinyl acetate–acrylonitrile. The polymer–comonomer mixture systems were so chosen as to permit study of both homogeneous and heterogeneous systems. The homogeneous systems included systems of low and high viscosity. The heterogeneous systems included both polymers swollen by the comonomer mixture and polymers not swollen by the comonomer mixture. None of the homogeneous grafting systems studied showed deviations from the normal copolymerization behavior under a variety of experimental conditions. Monomer reactivity ratios in graft copolymerization were the same as the values in nongraft copolymerization. The heterogeneous systems in which the polymer was swollen by the comonomer mixture yielded grafted copolymer compositions which were the same as those in nongraft copolymerization. The heterogeneous grafting system polytetrafluoroethylene/styrene–acrylonitrile showed deviations from normal copolymerization behavior at low degrees of grafting when the reaction was only on the polymer surface. The behavior became normal at higher degrees of grafting when the system approaches that in which the polymer is swollen by the comonomers. In all reaction systems, it was found that the use of radiation to initiate the reaction does not in any way affect the copolymerization behavior of the two monomers in a comonomer pair.     

Radical copolymerization of acrylic monomers. VIII. Copolymerization of methyl methacrylate with methyl α-p-chlorobenzylacrylate and methyl methacrylate with methyl α-p-methoxybenzylacrylate

Free-radical copolymerization of methyl methacrylate with methyl α-p-chlorobenzylacrylate and methyl methacrylate with methyl α-p-methoxybenzylacrylate have been studied in benzene solution at 40°C. Although a simple copolymerization model fits the composition data, the kinetic behavior of both copolymerization systems are analyzed from simple and reversible copolymerization models, taking into account the relatively low ceiling temperature of both methyl α-(p-substituted benzyl)acrylates and considering that the overall rate of copolymerization drastically decreases with the increase of the corresponding methyl α-(p-substituted benzyl)acrylate molar fraction in the feed.     

Grafting of poly(ethylene oxide) on poly(methyl methacrylate) by transesterification

The grafting of the potassium alkoxide derivative of poly(ethylene oxide) on poly(methyl methacrylate) in homogeneous solution in toluene was studied. The alkoxide was prepared by reaction with potassium metal with methanolic potassium methoxide, or with potassium naphthalene. The last was the most suitable for the systematic investigation of the grafting process. Soluble graft polymers were formed, and essentially the initial poly(ethylene oxide) (PEO) and poly(methyl methacrylate) (PMMA) participated in the production of graft polymer. The composition of the graft polymers and the frequency of grafting of the side chains were determined by NMR. The solubility of the graft polymers in methanol and water increased with increasing PEO contents, while the melting ranges decreased. Fractionation of the crude graft polymers showed that the grafting reaction was random, and graft polymers containing one PEO side chain per about 10–170 MMA units were obtained.     

Dynamics of adsorbed poly(methyl acrylate) and poly(methyl methacrylate) on silica

Deuterium NMR and modulated differential scanning calorimetry (MDSC) were used to probe the behavior of ultrathin adsorbed poly(methyl acrylate) (PMA). The spectra for the bulk methyl-labeled PMA-d₃ were consistent with the motions of the polymer segments being spatially homogeneous. For the polymers adsorbed on silica, multicomponent line shapes were observed. The segmental mobility of the surface polymers increased with increased adsorbed amounts. In contrast to the behavior of the polymers in bulk, the adsorbed lower-molecular-mass PMA-d₃ was less mobile than the adsorbed high-molecular-mass polymer. The presence of a polymer overlayer was sufficient to suppress the enhanced mobility of the more-mobile segments of the adsorbed (inner) polymer. MDSC studies on adsorbed poly(methyl methacrylate) showed that the glass-transition temperature of the thin polymer films increased and broadened compared to the behavior of the polymer in bulk. The presence of a motional gradient with the less-mobile segments near the solid-polymer interface and the more-mobile segments near the polymer-air interface was consistent with the experimental observations.     

Anionic graft polymerization of methyl methacrylate on starch and dextrin

The anionic graft polymerization of methyl methacrylate on the potassium alkoxide derivative of starch or dextrin in DMSO was studied. The effects of monomer and alkoxide concentrations as well as temperature were investigated. The yield of graft polymer increased with increasing alkoxide concentration. With increasing monomer concentration and with increasing temperature the extent of homopolymer formation increased. The composition of the graft polymers was found to depend on the reaction conditions. Graft polymers having about 10–40% poly(methyl methacrylate) were obtained. There were quantitative differences in yield of isolated graft polymer between starch and dextrin and these were ascribed to differences in the solubility properties of the carbohydrates. Evidence on the structure of the graft polymers and on the mechanism of the graft polymerization was obtained from acid hydrolysis of the graft polymers and determination of the molecular weights of the cleaved side chains.     

Linear polymers of allyl acrylate and allyl methacrylate

Allyl acrylate and allyl methacrylate were polymerized by anionic initiators to soluble linear polymers containing allyl groups in the pendant side chains. The pendant unpolymerized allyl groups of the resulting linear poly(allyl acrylates) were shown to be present by: (1) the disappearance of the acrylyl and methacrylyl double bond absorptions in the infrared spectra in the conversions of monomers to polymers; (2) postbromination of the allyl bonds in the linear polymer; (3) the disappearance of the allyl groups absorptions in the infrared spectra of the brominated linear polymers; and (4) the thermal- and radical-initiated crosslinking of the linear polymers through the allyl groups. Allyl acrylate and allyl methacrylate show great reluctance to copolymerize with styrene under anionic initiation, but copolymerize readily with methyl methacrylate and acrylonitrile. Block copolymers were prepared by reacting allyl methacrylate with preformed polystyrene and poly(methyl methacrylate) anions. The linear polymers and copolymers of allyl acrylate may be classified as “self-reactive” polymers which yield thermosetting polymers. Bromination of the linear polymers offers a convenient method of producing self-extinguishing polymers.     

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.     

Introduction of 2-methoxycarbonylallyl end group by copolymerization of methyl α-(phenoxymethyl)acrylate accompanying with addition-fragmentation reaction

Copolymerizations of methyl α-(phenoxymethyl)acrylate (MPMA) with methyl acrylate, methyl methacrylate, styrene, and methyl α-ethylacrylate were carried out. Addition of a polymer radical to MPMA followed by the subsequent fragmentation of poly(MPMA) radical resulted in the 2-methoxycarbonylallyl end group and phenoxy radical in the course of the copolymerization. The extent of the fragmentation determined by ¹H-NMR spectroscopy depends on reactivity of the MPMA radical toward the reference monomers. An increase in the addition rate of the MPMA radical to the reference monomer brought about suppression of the fragmentation. The addition of the MPMA radical to styrene seems to be sufficiently fast to prevent the fragmentation. Since the rate of the fragmentation relative to the propagation was considerably accelerated by raising the temperature to 110°C, MPMA can be used as a novel chain transfer agent to control molecular weight and end group at a temperature above 100°C. © 1993 John Wiley & Sons, Inc.     

Photoinitiated polymerization of methyl methacrylate and methyl acrylate with 14C-labeled benzoin methyl ethers

Three ¹⁴C-labeled benzoin methyl ether (α-methoxy-α-phenylacetophenone) derivatives were utilized as photoinitiators in the polymerization of methyl methacrylate (MMA) and methyl acrylate (MA). The results of polymer end-group analysis are in accord with a mechanism of benzoin ether photocleavage into initiator radicals and dispute earlier labeling studies which were interpreted as evidence for copolymerization of excited-state benzoin ethers with reactive monomers. In MMA polymerization, the results indicate a preference for termination by disproportionation (～60%) and provide evidence for primary radical termination at 0.041M photoinitiator (optically dense solutions) in neat MMA. Evidence for chain branching by initiator radical hydrogen abstraction from poly(methyl acrylate) (PMA) is also presented. The benzoyl and α-methoxybenzyl radicals, produced on photolysis of benzoin methyl ether, appear to be equally effective in both initiation and hydrogen-abstraction processes. Quantum yields at 366 and 313 nm indicate the absence of a wavelength effect.     

Polymerization of complexed monomers. II. Alternating copolymers of indene with methyl acrylate and methyl methacrylate

Indene has been copolymerized with polar monomers in the presence of ethylaluminum sesquichloride. The polymers have molecular weights in the 7,000–10,000 range and soften at temperatures above 150°C. The NMR spectra of the copolymers are discussed with reference to polymer structures and chain conformations. Indene is comparable to cyclopentene in reactivity in copolymerizations with methyl acrylate but is much more reactive than cyclopentene toward methyl methacrylate.     

Anionic graft polymerization of methyl acrylate to protein functional groups

Graft polymerization of methyl acrylate to functional groups in proteins was studied with model compounds and with whole gluten proteins. Polymerization was carried out in the presence of sodium hydride or sodium in dimethyl sulfoxide. Initiation proceeds by an anionic mechanism, and the rate-determining step is the production of the initially formed carbanion. The rate of disappearance of methyl acrylate was followed via gas chromatography. Amino acid analyses indicated that the functional groups of the amino acids, as well as the peptide bonds, were acting as the initiation sites in proteins. Reaction rates of the functional groups were determined on model compounds in the presence of sodium and sodium hydride. With both the model compounds and the proteins, polymerization was initially rapid and then leveled off, although rates depended on the concentration of activator and acrylate. Methoxyl group analyses of modified model compounds and proteins indicated that from 5 to 10 methyl acrylate residues were introduced per reactive site.     

Preparation and Characterization of Head-to-Head Polymers. III. Head-to-Head Poly (methyl Crotonate)

Alternating copolymers of cis-butene-2 and maleic anhydride were esterfied to the methylester which corresponds to head to head (H-H) poly(methyl crotonate).

The chemical, physical, and mechanical properties and thermal degradation behavior of H-H poly (methyl crotonate) was studied and compared with the properties of head to tail (H-T) poly(methyl crotonate). This latter polymer was made by a known anionic polymerization technique and was, unlike the amorphous H-H polymer, partially crystalline. The T_g of H-H polymer was found to be higher than that of the H-T polymer. Thermal degradation behavior of H-H and H-T polymer was between the degradation behavior of H-H and H-T poly(methyl cinnamate) and poly (methyl acrylate). Poly (methyl crotonates) degraded to a substantial part to small molecules and char; methyl crotonate was found among the degradation products. H-H Poly (methyl crotonate) gave also butene-2 and a mixture of dimethyl maleate and dimethyl fumarate on pyrolysis.     

Polymerization reactivity of unsaturated end group generated during the disproportionation in termination reaction of methyl methacrylate polymerization: A study using model compounds

Polymerizations of some vinyl monomers were carried out with 2,2′-azobisisobutyronitrile at 60°C in the presence of a methyl methacrylate (MMA) dimer ( I ) or a MMA polymer ( II ) with a double bond at their ends to confirm the polymerization reactivity of unsaturated end group generated during the disproportionation in termination reaction of MMA polymerization. It was found that the polymerizations of α-monosubstituted monomers have been much retarded than those of α,α-disubstituted monomers by the addition of I . Kinetic study on MMA and methyl acrylate polymerizations showed that the rate constant for the reaction of a propagating radical with I was 5.4 and 29.2 L/mol s in their polymerizations, respectively. ESR study using I and II suggested that an addition reaction was a predominant mechanism for the reaction of an unsaturated end group with a radical rather than a hydrogen abstraction.