Polymerization and copolymerization in associated monomer aggregates

The polymerization of acrylic acid in bulk is controlled by linear plurimolecular H-bonded aggregates of the monomer which lead to the formation of a syndiotactic polymer. Polar solvents do not dissociate these aggregates unless high dilutions are reached. In contrast, “normal” kinetics are observed in the presence of 10–20 per cent toluene, n-hexane or chloroform. The polymerization of methacrylic acid is not affected to the same extent by molecular aggregates. In the copolymerization of acrylic acid with methyl acrylate or acrylonitrile, the reactivity ratios are altered by solvents. The acrylic acid content is higher in copolymers formed in bulk than in toluene solution. But similar effects are observed in the presence of DMF which does not dissociate the aggregates of acrylic acid; moreover, copolymerization data obtained with methacrylic acid indicate that other factors may be involved in determining reactivity ratios.Acrylamide also forms H-bonded aggregates and its copolymerization behaviour is strongly affected by solvents. No simple correlation holds, however, between reactivity ratios and extent of association.A very strict control of chain propagation occurs when 4-vinylpyridine is polymerized in the presence of polycarboxylic acids. A considerable rate increase was observed when vinylpyridine was grafted into polytetrafluoroethylene films which contained poly(acrylic acid) branches. This effect is explained by assuming that the pyridine groups form strong associations with the carboxylic sites, thereby providing a very favourable orientation of the vinyl groups for chain propagation.     

Influence of the solvents on the γ-ray polymerization of acrylic acid. I.

Bulk polymerization of acrylic acid is controlled by linear plurimolecular H-bonded aggregates of the monomer. It is proved that it is not the precipitating medium that is responsible for the accelerated rate of the polymerization, but the presence of the H-bonded plurimolecular aggregates. It has been shown that the presence of the previously formed polymer is important, as it gives a matrix effect which allows the monomer aggregated to be stabilized by associating with the polymer. In polymerizing acrylic acid solutions, two types of solvents have been characterized: first, the polar solvents which do not destroy the H-bonded aggregates up to high dilutions. Then, in the presence of hydrocarbons or chlorinated solvents, 10–20% of the solvents dissociate the aggregates. A very striking parallelism is observed between the polymerization kinetics and the associated form of the monomer.     

Polymerisation de l'acide methacrylique en masse et en solution

In spite of the fact that the bulk polymerization of methacrylic acid proceeds under precipitating conditions, all conversion curves are linear and start from the origin. The overall activation energy of the gamma ray initiated reaction is very small: 1.3 kcal/mol. Methanol and water are solvents for the polymer but also form monomer-solvent complexes through H-bonds. It was found that, over a limited concentration range in these solvents, the reaction becomes auto-accelerating both in precipitating and homogeneous reaction media. Non-polar solvents (hydrocarbons) lead to a significant reduction in the polymerization rate but this effect is not as pronounced as for acrylic acid. Chlorinated derivatives reduce the polymerization rate of acrylic acid to the same extent as hydrocarbons but, for methacrylic acid, chlorinated derivatives lead to sensitization. By analogy with earlier results for acrylic acid, it is assumed that the auto-acceleration observed in water and methanol solutions is caused by a “matrix effect”. In bulk, the monomer undoubtly also associates with the polymer but, in view of the bulky methyl groups, the regularly oriented structure which favours propagation presumably never arises. The very small activation energy of the polymerization suggests that chain termination requires a significant activation energy. The mechanism of this process is not clear.     

Reactivities of carboxylic acid vinyl monomers differentiated by the aggregation forms and their simple molecular orbital interpretation

Plasma-exposed solution polymerizations of carboxylic acid vinyl monomers [methacrylic acid (MAA) and acrylic acid (AA)] in carbonyl solvents were found to be highly efficient, particularly in high-temperature postpolymerizations. Thermal polymerizations in these solvents were also accelerated to a considerable extent. Obviously the carbonyl solvents and/or the increased temperature caused the monomer aggregates to accelerate the rate of polymerization. The molecular orbital features of the simple models of monomer aggregates, that is, the monomeric form, singly hydrogen bonded open-dimer and doubly hydrogen bonded cyclicdimer of MAA and AA, supported by the CNDO/2 method, were capable of distinguishing the variations in the reactivities of the aggregates; the open-dimer was shown to be responsible for the enhanced reactivities under the abovementioned conditions.     

Peculiar swelling properties of PVC films grafted with acrylic and methacrylic acids

It was found that PVC films grafted with methacrylic acid do not swell in either water or methanol, two solvents of poly(methacrylic acid), even for high grafting ratios. The swelling of these films was examined in mixtures of methylene chloride with methanol and curves of different shapes were obtained depending on the grafting ratio. PVC films grafted with acrylic acid readily swell in both water and methanol but they remain hard in the swollen state. The equilibrium swelling increases with swelling temperature but this process is not reversible; films swollen at high temperature keep a high degree of swelling even when the system is cooled.     

Frontal Polymerization of Deep Eutectic Solvents Composed of Acrylic and Methacrylic Acids

Frontal polymerization of deep eutectic solvents (DESs) made with acrylic or methacrylic acid as the monomer and hydrogen bond donor was studied. Fronts with acrylic acid and choline chloride propagated more uniformly than with pure acrylic acid, so an exploration into how the DES affected frontal polymerization was performed. The hydrogen bond acceptor of the DES was replaced by several analogs to determine the effect on the DES front behavior. The analogs used were talc, DMSO, lauric acid, and stearic acid, which acted as a heat sink, inert diluent, hydrogen bonding diluent, and inert phase change material, respectively. None of the methacrylic acid‐analog systems were able to sustain a front. While the acrylic acid‐analog systems did sustain a front (with the exception of stearic acid), none of the fronts replicated the acrylic acid DES behavior. The acrylic acid–talc sample behaved more violently—like pure acrylic acid polymerization—than the acrylic acid DES, and the DMSO and lauric acid samples produced slower fronts than that of the acrylic acid DES. We propose that the reactivity of the acrylic acid and methacrylic acid is enhanced in the DES. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017 , 55, 4046–4050     

SYNTHESIS OF AMPHIPHILIC COIL-ROD-COIL BLOCK COPOLYMERS USING ATOM TRANSFER RADICAL POLYMERIZATION

ABSTRACT

Coil-rod-coil block copolymers composed from luminescent rigid units and acrylate flexible blocks have been synthesized using atom transfer radical polymerization. α,ω-Difunctionalized oligophenylenes properly modified to act as ATRP initiators have been used for the polymerization of the various acrylates. Copolymers with controlled shape and in some cases, relatively low polydispersities have been obtained as proved by size exclusion chromatography and NMR. In cases, where t-butyl acrylate blocks have been used as the flexible part, selective hydrolysis resulted in coil-rod-coil copolymers containing poly(acrylic acid) blocks. The solution behavior of the synthesized copolymers was explored in various solvents. The poly(acrylic acid) copolymers in aqueous solutions form large aggregates, while in organic selective solvents for the flexible block, monomolecular micelles seem to be formed.     

Solubilization of phenols in anionic polyelectrolyte gels with adsorbed cationic surfactant

Solubilization isotherms for various phenols in cetylpyridinium chloride (CPC)-polyelectrolyte gel aggregates have been determined in order to compare solubilization within these aggregates with that in free micelles and to examine the effects of gel chemistry and structure on solubilization. The isotherms describing solubilization are quite similar to those found for free surfactant in solution. Solutes that are more hydrophobic give rise to larger solubilization constants with trends similar to what is seen for hydrophobic effects in adsorption from aqueous solutions onto hydrophobic solids. The solubilization constants decrease as the fraction of solute in the aggregates increases, indicating that the solutes partition into the palisade region of the aggregates. Solubilization is found to be quite insensitive to changes in gel structure (cross-linker varying from 1% to 3%) and chemistry (poly(acrylic acid) versus poly(methacrylic acid) and neutralization from 50% to 100%). However, the switch from poly(acrylic acid) to poly(methacrylic acid) did give rise to a slight decrease in magnitude of the slope of the isotherm. The most significant factors appear to be the initial concentration of surfactant in solution and the ratio of surfactant solution to gel amount. A decrease in surfactant concentration (especially combined with an increase in solution volume) gives rise to a decrease in solubilization constants.     

Study on soap‐free P(MMA‐EA‐AA or MAA) latex particles with narrow size distribution

Soap‐free poly(methyl methacrylate‐ethyl acrylate‐acrylic acid or methacrylic acid) [P(MMA‐EA‐AA or MAA)] particles with narrow size distribution were synthesized by seeded emulsion polymerization of methyl methacrylate (MMA), ethyl acrylate (EA) and acrylic acid (AA) or methacrylic acid (MAA), and the influences of the mass ratio of core/shell monomers used in the two stages of polymerization ([C/S]_w) and initiator amount on polymerization, particle size and its distribution were investigated by using different monomer addition modes. Results showed that when the batch swelling method was used, the monomer conversion was more than 96.0% and particle size distribution was narrow, and the particle size increased first and then remained almost unchanged at around 600 nm with the [C/S]_w decreased. When the drop‐wise addition method was used, the monomer conversion decreased slightly with [C/S]_w decreased, and large particles more than 750 nm in diameter can be obtained; with the initiator amount increased, the particle size decreased and the monomer conversion had a trend to increase; the particle size distribution was broader and the number of new particles was more in the AA system than in the MAA system; but the AA system was more stable than the MAA system at both low and high initiator amount. Copyright © 2006 John Wiley & Sons, Ltd.     

Polymerisation radiochimique de l'acide acrylique en solution dans l'alcool isopropylique et le dimethylformamide

The radiation-induced polymerization of acrylic acid in isopropyl alcohol and dimethylformamide solutions was investigated between?196°and40°. Mixtures which form glasses at low temperatures exhibit a maximum in the rate of polymerization at 30° and 50° above the glass transition temperature (T_g). The difference between the most favourable temperature for polymerization and T_g is larger than in systems studied previously. This fact could be due to the presence of H-bonded aggregates.The study of the polymerization of acrylic acid in dimethylformamide solution at 20° led to a correlation between this reaction and the presence of plurimolecular aggregates. The very high polymerization rate and the syndiotacticity of the resulting poly(acrylic acid) confirm the earlier assumption of a favourable orientation for propagation of the molecules of acrylic acid in these aggregates.     

Influence of the solvents on the γ-ray polymerization of acrylic acid. II.

The presence of plurimolecular H-bonded aggregates in the acrylic acid allows the polymer to involve some stereoregular sequences. This effect is made easier when some polymer is already formed in the reacting medium: the aggregates are stabilized by hydrogen bonds with the polymer which gives rise to a matrix effect. Two groups of solvents have been characterized by examination of the monomer's association forms in solution. In a first group of solvents (methanol–dioxan–water), the aggregates are maintained and reinforced; in the second one, acrylic acid exists only as cyclic dimers (hydrocarbons–chlorinated solvents). The difference between the association forms of the monomer involves some important modifications on the kinetics of polymerization and the structure of the obtained polymers. In the solvents of the first group, the obtained polymers are crystallizable and may involve syndiotactic sequences, while in the presence of the solvents of the second group no crystallization or stereoregularity of the polymer can occur. A very close correlation is thus found between the aggregated structure of the monomer, the polymerization kinetics, and the structure of the polymers.     

Hydrogels based on polycarboxylic acid-agar-agar complexes

IR spectroscopy and viscometry data have shown that poly(acrylic acid) and poly(methacrylic acid) form complexes with agar-agar in aqueous solutions as they do with other polysaccharides. The polyacid-agar-agar complexes are typical hydrogels. The swelling index of hydrogels based on the poly(methacrylic acid)-agar-agar complex has been found to be markedly lower than that of poly(acrylic acid)-agaragar complex. The hydrogels based on the complex of cross-linked poly(acrylic acid) with agar-agar can be of practical interest as polymeric carriers for drugs.     

Effect of heat and solvent treatment on radiation grafting of acrylic acid to poly(ethylene terpehthalate)

Direct radiation graft polymerization of acrylic acid onto oriented poly(ethylene terephthalate) films and fibers subjected to thermal treatment and treated with structure-active solvents, such as dichloroethane and dioxane, was studied. Based on the results of thermomechanical analysis, X-ray diffraction, sorption, and acrylic acid grafting, conclusions were drawn concerning the character of structural changes in poly(ethylene terephthalate) exposed to structure-active solvents. The physicochemical properties of the graft copolymers obtained were examined, including the resistance against γ-radiation.     

Complexation and rate of polymerization of acrylic acid and methacrylic acid in the presence of poly(4-vinylpyridine) in dilute methanol solution

A 1:1 hydrogen-bonded complex was formed between acrylic acid (AA) or methacrylic acid (MA) and the pyridine group of poly(4-vinylpyridine) (P4VP) in dilute solutions. A shift of infrared absorption of the hydrogen-bonded acid O? H to a lower energy direction and an upfield shift of acid proton in the NMR were observed when the monomers were added with pyridine. The equilibrium constants of the 1:1 complexation with P4VP measured by using a semipermeable membrane were 0.58 and 0.26 for AA and MA, respectively, at 25°C in methanol. The bromometrically measured initial rate of radical polymerization showed only a slight enhancement in the presence of P4VP, the rate being maximum at the 4VP unit:monomer mole ratio of 0.25 and 0.5 for AA and MA, respectively, in dilute methanol solution at 60°C.     

Pulse radiolysis of vinyl monomers, in the pure state and with added pyrene

Pulse radiolysis studies have been used to investigate the early phenomena in the radiolysis of acrylic acid, methyl acrylate, butyl vinyl ether, propionic acid, methyl acetate and butyl ether; the latter three solvents were used as model compounds for these vinyl monomers. The triplet state, radical cation, radical anion, and free radical of pyrene (cyclohexadienyl type) were observed to various degrees in the radiolysis of pyrene in these monomers. In acrylic acid, where the free radical and the cation dominate, the monomer polymerizes efficiently, whereas in butyl vinyl ether, where the anion dominates, polymerization does not occur. The behavior of methyl acrylate lies between that of acrylic acid and butyl vinyl ether. However, the high intensity of the electron pulses creates a high concentration of radicals leading to a short lifetime of the radical which in turn leads to a much smaller yield of polymerization. The mechanism of polymerization under high energy radiation is found to be free radical in nature.     

Free-radical synthesis of block copolymers on an industrial scale

Controlled free-radical polymerization has been monitored with great interest in recent years since it offers an opportunity to combine the advantages of conventional free-radical polymerization with those of living ionic polymerization. We present the 1,1-diphenylethene (DPE) method which enables us to produce block copolymers on an industrial scale by a free-radical mechanism. This DPE process enables industrially relevant monomers, such as styrene, methacrylates, acrylates, methacrylic acid, acrylic acid and N-vinyl compounds, to be converted into block copolymers. The synthesis can be carried out in organic solvents, without solvents or in water. We have been able to demonstrate, that the addition of 1,1-diphenylethylene to a normal free-radical polymerization results in polymers whose molar mass, after a short uncontrolled phase, increases in a linear manner with conversion. The amount of 1,1-diphenylethylene added also determines the order of magnitude of the final molar mass. It was also possible to employ the polymers isolated during this polymerization as initiators for the polymerization of a further monomer, resulting in the formation of block copolymers. With possibly somewhat reduced claims on the perfection of the structures, a wide variety of possibilities arise with the known advantages of free-radical polymerization. The one-pot synthesis is carried out by simple successive addition of the desired monomers and has already been used successfully on an industrially relevant scale.     

Copolymerization of acrylic and methacrylic acids with N-vinylpyrrolidone

The copolymerization of an acidic monomer (acrylic or methacrylic acid) and a basic monomer (N-vinylpyrrolidone) (NVP) is investigated. Various physical measurements revealed a strong molecular interaction between the two monomers. However, the resulting association complex does not seem to control the copolymerization. A slight solvent effect is observed with dimethylformamide for the acrylic acid-NVP system. Methacrylic acid appears to be much more reactive than acrylic acid in its copolymerization with NVP. The results obtained with methacrylic acid-NVP system conflict with earlier published results.     

Novel temperature‐responsive water‐soluble copolymers based on 2‐hydroxyethylacrylate and vinyl butyl ether and their interactions with poly(carboxylic acids)

Novel water‐soluble amphiphilic copolymers have been synthesized by free radical copolymerization of 2‐hydroxyethylacrylate with vinyl butyl ether. In water these copolymers exhibit lower critical solution temperature, which depends on the content of hydrophobic vinyl butyl ether units. The interaction between these copolymers and poly(acrylic acid) or poly(methacrylic acid) in aqueous solutions results in formation of interpolymer complexes stabilized by hydrogen bonds and hydrophobic interactions. An increase in hydrophobicity of the copolymers leads to the enhancement of their complex formation ability with respect to poly(acrylic acid) and poly(methacrylic acid). Poly(methacrylic acid) forms stronger complexes with the copolymers when compared with poly(acrylic acid). The complexes exhibit dual sensitivity to pH‐ and temperature and this property may be easily adjusted regulating the strength of interaction. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 195–204, 2006     

Effects of solvent in photo-induced graft copolymerization of vinyl monomers on cellulose

The effects of swelling of the sample and polymerization solvents were studied for photo-induced graft copolymerization of vinyl monomers on cellulose. The graft copolymerization of methyl methacrylate (MMA) was activated by swelling of the sample or organic solvent-water solutions within a certain range of their concentrations. Though each organic solvent gave a maximum in per cent grafting and the number of grafts at about 25 vol-% concentration, the initiation reaction scarcely took place at 100% concentration; thus, the solvent itself is considered to have a negative effect. The solvents used in the experiments were all hydrophilic, such as methanol, acetone, and dioxane. The average molecular weight of the grafted PMMA differed in each solvent, indicating a different characteristic effect of solvent on the growing grafted polymer radicals. The presence of ferric ion as a sensitizer stimulated further the contributions of the sample swelling and the organic solvents to the copolymerization reaction. A similar effect was observed for styrene as for MMA, but not for acrylic acid and methacrylic acid.