Exceptional chiroptical behavior near ceiling temperature in free radical polymerization of menthyl 2-acetamidoacrylates

Effect of polymerization conditions on chiroptical properties of polymer has been studied in the polymerization of (−)- and (+)-menthyl 2-acetamidoacrylates using radical initiators under the conditions with various temperatures, monomer concentrations, and reaction times. Specific rotation and circular dichroism of the resulting polymers indicated that a ceiling temperature (T_c) affected the chiroptical properties of the polymers and the polymerizations would give preferentially a helical polymer through a radical vinyl polymerization near T_c. In addition, the helical structure of the polymer was maintained intact even heating at 120 °C in anisole.     

Free radical polymerization of unconjugated dienes: 18. Cyclopolymerization of o-divinylbenzene at 70°C

The free radical polymerization at 70°C of o-divinylbenzene in toluene solutions takes place according to a cyclopolymerization mechanism. By fitting the experimental data with two different relationships between the mole fraction of residual unsaturation in the polymers and the monomer concentration at which they were obtained, it has been possible to show that, in the chain propagation steps, intramolecular cyclization could occur involving the two monomeric units entered last in the polymer chain, with formation of seven-membered ring structures.     

Synthesis of syndiotactic poly(methacrylic acid) by free‐radical polymerization of the pseudo‐divinyl monomer formed with methacrylic acid and catechol

Syndiotactic poly(methacrylic acid) (Syn‐PMAA, r diad = 91 mol %) was synthesized by free radical polymerization of methacrylic acid (MAA) with catechol. The pseudo‐divinyl monomer was formed with one catechol and two MAA molecules by the hydrogen bonding between OH groups of catechol and COOH group of MAA. When the free radical polymerization of the pseudo‐divinyl monomer was carried out, intra‐ and intermolecular addition proceeded with racemic addition. The hydrogen bonding was the driving force to control tacticity. We discussed the effects of solvent, temperature, and the concentrations of MAA and catechol on the pseudo‐divinyl monomer formation. The highly syndiotactic PMAA was successfully obtained. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Simplified TERP to achieve living free radical polymerization with crude ethyl 2-phenyltellanyl-2-methylpropionate as mediator

Organotellurium compounds-mediated living radical polymerization (TERP) is one of the most robust tools of living free radical polymerizations (LRP). However, synthesis and purification of organotellurium compounds are time-consuming and to be operated in an inert atmosphere due to their extreme sensitivity to trace oxygen. In this article, a simple process of TERP, operating in open air, has been reported. It has demonstrated that the crude organotellurium compound, ethyl 2-phenyltellanyl-2-methylpropionate, could mediate 2,2′-azobis (isobutyronitrile) initiated styrene (St) and butyl acrylate (BA) polymerization as an LRP system. For the bulk and solution polymerization of St and the solution polymerization of BA, the molecular weights of produced polymers increased linearly with the monomer conversions. During the same time, the molecular weight distributions kept under 1.3. The UV–vis spectrum showed that the PS polymer chain bearing C-TePh end group. With the sequential monomer addition technique, a clean diblock polymer of PS-b-PBA was also obtained.     

Equilibrium bulk polymerization of 1,3-dioxolan

Cationic bulk polymerization of 1,3-dioxolan has been carried out in sealed ampoules using a high vacuum technique. The polymerization is initiated with triethyl oxonium hexafluorophosphate and the equilibrium between monomer and active polymer is attained within a few hours. Specific volumes of pure monomer and polymer in solution of its own monomer have been measured. Equilibrium measurements have been performed in the 40° to 141·4°C temperature range and the ceiling temperature is estimated to be 144° ± 2°C. The effect of short polymer chains on the equilibrium is discussed briefly. Values of ΔG_lc, the free energy of polymerization of one mole of pure liquid monomer to one base-mole of amorphous polymer, are computed making allowance for the non-ideal mixing. Respective values of ?17.5 ± 0.8 kJ/mol and ?47.9 ± 2.2JK^?1mol^?1 are deduced for the corresponding ΔH_lc and ΔS_lc. ΔG_lc is also computed from published data on equilibrium polymerization of 1,3-dioxolan in various solvents and the combined results for both types of polymerization yield ΔH_lc = ?16.7 ± 0.5kJ/mol and ΔS_lc = ?45.8 ± 1.5JK^?1mol^?1 for the 20° to 140°C range.     

Free radical polymerization of unconjugated dienes: 19. Temperature dependence of the cyclopolymerization of o-divinylbenzene

The temperature dependence of the extent of cyclization in the free radical polymerization of o-divinylbenzene has been investigated. The results have been interpreted on the basis of a kinetic relationship derived by assuming that three different cyclization reactions can occur during the chain growth: it has been found that of these reactions one largely prevails over the others. The difference between the activation energy of the main cyclization reaction and that of the intermolecular addition of the growing chain onto a monomer molecule compares well with the analogous differences already found in the cyclopolymerizations of acrylic and methacrylic anhydrides. The corresponding difference between the activation entropies is in highly satisfactory agreement with the one which can be calculated for the formation of a seven-membered ring structure. Both these facts strongly support the hypothesis that, in the main cyclization reaction occurring in the free radical polymerization of o-divinylbenzene, benzocycloheptene structures, practically free of strain, are formed.     

Stereoselectivity and chemoselectivity in Ziegler-Natta polymerization of conjugated dienes. 2. Mechanism for 1,2 syndiotactic polymerization of diene monomers with high energy s-cis η coordination

Possible mechanisms of Ziegler-Natta polymerizations of conjugated dienes have been investigated by density functional methods, by considering η² or η⁴ (both cis and trans) coordination of the monomer and η¹ or η³ (syn or anti) allyl coordination of the growing chain. In agreement with previous studies, for diene monomers presenting a low s-cis-η⁴ coordination energy (like butadiene), the favored insertion reaction would involve a s-cis-η⁴ monomer coordination and an anti η³ allyl coordination of the growing chain (mechanism I). On the other hand, for diene monomers presenting high s-cis-η⁴ coordination energy (like (Z)-pentadiene and 4-methyl-pentadiene), the favored insertion reaction would generally involve a 5-trans η² monomer coordination and a back-biting syn allyl (η³-η²) coordinated growing chain (mechanism II). However, these monomers would present an s-cis-η⁴ coordination whenever the formation of the back-biting of the penultimate unit of the growing chain would be unfeasible, as for initiation steps as well as for insertion steps following an ethylene insertion. A switch from mechanism II toward mechanism I is able to rationalize the correspondingly observed loss of chemoselectivity. Mechanism II is also able to account for the high stereoselectivity in favor of 1,2 syndiotactic polymerization which has been observed for these dienes. The chain end stereocontrol would be dictated by the chirality of coordination of the syn allyl terminal of the back-biting growing chain.     

Preparation and characterization of polyelectrolyte copolymers containing methyl methacrylate and 2-hydroxyethyl methacrylate. I. Polymers based on methacrylic acid

Acidic polyelectrolyte copolymers containing 2-hydroxyethyl methacrylate (HEMA), methyl methacrylate (MMA), and methacrylic acid (MAA) were prepared by free radical polymerization to high conversion in solution. Copolymer yields were obtained by gravimetry (all in the 30–50% range), relative molecular weights estimated by intrinsic viscosity measurements (all in the 50–70 cc/g range), tacticity by ¹³C nuclear magnetic resonance (NMR) spectroscopy (all polymers predominantly syndiotactic with some atactic content), and composition by acid/base titrations in conjunction with ¹H-NMR spectroscopy (all close to the monomer charge ratios). Acid strengths or apparent pKa's were examined as a function of extent of ionization. Measurements performed in water indicated that the compact/extended coil transformation in predominantly syndiotactic polymethacrylic acid occurs also in copolymers of similar tacticity containing moderate to high concentrations of MAA. The apparent pKa of such polymers containing only small amounts of MAA did not vary with extent of ionization, indicating a low degree of interaction between the acid groups. In copolymer pairs containing similar amounts of MAA but differing HEMA and MMA contents, the polymer containing more HEMA appeared the stronger acid, presumably due to a better solvation of that polymer which would increase the net spatial charge–charge separation and decrease cooperative effects that lead to suppressed ionization.     

A novel polymer chain growing mode and styrene copolymer prepared with low molecular weight copolymer of α‐methylstyrene and styrene as macroinitiator

A new polymer chain growth mode, having multiple potential chain propagation sites, initiated by oligomer of α‐methylstyrene (AMS) and styrene (St) (PAS) is presented in this article. The effects of PAS content, AMS fraction in PAS and reaction temperature on bulk polymerization of St have been investigated. It is demonstrated that the PAS performed as macroinitiator in the polymerization of St. The average molecular weights of products increase significantly with the evolution of the polymerization, which is different from conventional free radical polymerization. With 20 wt % macroinitiator, the molecular weights increase from 1.21 × 10⁵ to 3.00 × 10⁵ with the monomer conversion increasing from 15.3 to 83.0%. This unique feature is tentatively attributed to both the reversible polymerization–depolymerization of AMS segments at high temperature which could generate more than one propagation sites in a polymer chain and the combination termination of St free radical polymerization. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41460.     

Vinyl polymerization: 414. Polymerization of vinyl monomer initiated by poly(N,N,N-trimethyl-N-2-methacryloxyethyl)ammonium chloride

The polymerization of vinyl monomer initiated by an aqueous solution of poly(N,N,N-trimethyl-N-2-methacryloxyethyl)ammonium chloride (poly(Q-DMAEM-CI) has been carried out at 85°C. The effects of the amounts of vinyl monomer, poly(Q-DMAEM-CI) and water on the conversion of vinyl monomer have been studied. The overall activation energy in the polymerization of MMA is estimated as 41.9 kJ mol^?1. The polymerization proceeds through a radical mechanism. The location in which the polymerization occurs is discussed. The selectivity for vinyl monomer is explained by ‘the concept of hard and soft hydrophobic areas and monomers’.     

Surface-initiated atom transfer radical polymerization of methyl methacrylate on magnetite nanoparticles

The synthesis of magnetite nanoparticles coated with a well-defined graft polymer is reported. The magnetite nanoparticles with an initiator group for copper-mediated atom transfer radical polymerization (ATRP), 2-(4-chlorosulfonylphenyl) ethyltrichlorosilane (CTCS) chemically bound on their surfaces were prepared by the self-assembled monolayer-deposition method. The surface-initiated ATRP of methyl methacrylate (MMA) was carried out with the CTCS-coated magnetite nanoparticles in the presence of free (sacrificing) initiator, p-toluenesulfonyl chloride. Polymerization proceeded in a living fashion, exhibiting first-order kinetics of monomer consumption and a proportional relationship between molecular weight of the graft polymer and monomer conversion, thus providing well-defined, low-polydispersity graft polymers with an approximate graft density of 0.7 chains/nm². The molecular weight and polydispersity of the graft polymer were nearly equal to those of the free polymer produced in the solution, meaning that the free polymer is a good measure of the characteristics of the graft polymer. The graft polymer possessed exceptionally high stability and remarkably improved dispersibility of the magnetite nanoparticles in organic solvent.     

Theoretical confirmation of in situ monitoring of monomer conversion during acrylamide polymerization via pyranine flouroprobe

In this study, a new approach for in situ monitoring of the monomer conversion based on the chemical interaction of a fluoroprobe, pyranine (8‐hydroxypyrene‐1,3,6‐trisulfonic acid, trisodium salt), with polymer chains during the free radical crosslinking copolymerization of acrylamide/bisacrylamide system (AAm/Bis) has been developed. Recently, we have shown that the pyranine fluoroprobes added to the prepolymerization solution in trace amounts bind covalently to the vinyl groups of the growing polymer chains via OH group by radical addition when the free radical polymerization of acrylamide (AAm) is initiated. This covalent binding results in a considerable blue shift in the emission spectrum of the pyranine, from 515 to ～ 420 nm. In this study 0.5, 0.7, and 1.0 mol L^?1 linear and crosslinked polymers including trace amounts of pyranine were synthesized. The change in the emission spectra of pyranine during polymerization and gelation were monitored as function of time. Here, we showed that both by theoretically and by comparing the fluorescence data with gravimetric measurements, the fluorescence intensity of pyranine monitored during the polymerization process can be used for in situ monitoring of the monomer conversion with great sensitivity. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Solubility characteristics of poly(N-vinylcarbazole) prepared by Co(II) loaded 13X molecular sieve

During the polymerization of N-vinylcarbazole (NVC) by Co(II)-13X the resultant polymer (¯M_n=6000) is soluble in benzene or toluene but partly soluble in methylethyl ketone (MEK). To ascertain whether the MEK insolubility is due to polymer tacticity, the polymer has been further characterized by¹³C NMR analysis. The atactic structure of polyN-vinylcarbazole (PNVC) initiated by Co(II) has been established from a comparison of methine carbon ( ) peaks with the same for a cationic PNVC(BF₃/Et₂O, isotactic) and radical PNVC (AIBN, atactic).     

Electrochemical polymerization of N-vinylcarbazole

The electrolysis of N-vinylcarbazole in the solution of quaternary ammonium salts in dichloroethane leads to polymer formation in the anolyte. The effect of monomer concentrations, current levels, and nature of supporting electrolytes on the polymerization has been investigated. The polymerization is free radical with bromide salt and cationic with perchlorate or hexachloroantimonate salt. The poly(N-vinylcarbazole) gets oxidized at the anode and can be cycled between the oxidized and neutral states. The oxidized polymers at the electrode may exhibit electrical conductivity.     

New nanocomposite materials based on polymerization of [oligo(oxyethylene) methacrylates] in the presence of montmorillonite clay

Intercalation of poly[oligo(oxyethylene) methacrylates] onto sodium montmorillonite (MMT) clay has been investigated. A polymer–clay hybrid has been synthesized through intercalation of the monomer followed by its solution free‐radical polymerization. Eight polymer–clay hybrids were prepared using different weight ratios of clay, different oligo(oxyethylene) lengths and different proportions of crosslinker. Evidence of the development of nanostructures is obtained from scanning electron microscopy, and wide‐angle X‐ray diffraction studies support these results which show disappearance of the peak characteristic to d₀₀₁ spacing. In this hybrid MMT is dispersed homogeneously in the polymer matrix. © 2003 Society of Chemical Industry     

Synthesis, characterization polymerization and antibacterial properties of novel thiophene substituted acrylamide

Ethyl 2-acrylamido-4,5,6,7-tetrahydrobenzo [b] thiophene-3-carboxylate (ETTCA) has been synthesized and its structure has been elucidated by elemental analysis and spectral tools. Free radical polymerization of (ETTCA) has been conducted in several solvents using azobisisobutyronitrile (AIBN) as an initiator. The kinetic parameters of polymerization of the ETTCA were investigated, and it was found that the polymerization reaction follows the conventional free radical scheme. The overall activation energy of polymerization ΔE was determined (ΔE = 45.11 kJ mol⁻¹). The copolymerization of ETTCA with three conventional monomers was carried out in dioxane at 65 °C. The monomer reactivity ratios for the copolymerization of ETTCA with methyl methacrylate (MMA), vinyl acetate (VA) and vinyl ether (VE) were calculated. Thermal stability of the ETTCA polymer and its copolymers were investigated by thermogravimetric analysis. It has been found that the prepared polymer (PETTCA) and its copolymers with VA have moderate biological activity and highly dependent on the copolymer composition.     

One-Pot Synthesis of Poly(linoleic acid)-g-Poly(styrene)-g-Poly(ε-caprolactone) Graft Copolymers

One-pot synthesis of graft copolymers by ring-opening polymerization and free radical polymerization using polymeric linoleic acid peroxide (PLina) is reported. Graft copolymers having structures of poly(linoleic acid)-g-polystyrene-g-poly(ε-caprolactone) were synthesized from PLina, possessing peroxide groups on the main chain by the combination of free radical polymerization of styrene and ring-opening polymerization of ε-caprolactone in one-step. Principal parameters, such as monomer concentration, initiator concentration, and polymerization time, which effect the one-pot polymerization reactions were evaluated. The obtained graft copolymers were characterized by ¹H-NMR and DOSY-NMR spectroscopy, gel permeation chromatography, thermal gravimetric analysis and differential scanning calorimetry techniques.     

Stereochemical analysis of acrylic copolymers with large polar side groups by NMR spectroscopy

NMR spectra give abundant information at the microstructural level. When pseudoasymmetric carbon atoms are present in the monomeric repeating units, it is possible to obtain valuable information about the relative stereochemical configuration of the side substituents of the pseudoasymmetric center. This is the best way to know the tacticity of a polymer and the cotacticity parameters of copolymers, as well as the average distribution of comonomeric units along the chains, according to the polymerization mechanism. In this work, we present the microstructural and stereochemical characterization of acrylic copolymers prepared by free radical copolymerization of 2-hydroxyethyl methacrylate with a methacrylic ester or methacrylamide derivative, bearing polar side groups of biomedical interest. These copolymer systems were analyzed by ¹H-NMR spectroscopy to determine the average molar composition, and the corresponding reactivity ratios, and by ¹³C-NMR to study the microstructural and stereochemical configuration of comonomer sequences in terms of triads and pentads. Analyses account for the mechanism of polymerization, which fits first order Markov statistics for the addition of comonomers to free radical growing ends. The stereochemical distribution is described by a Bernoullian trial.     

In-situ polymerization of styrene in AAO nanocavities

One of the most promising aspects of the anodic aluminium oxide (AAO) template is the ability to generate a variety of different hierarchical one-dimensional (1D) polymer morphologies with structural definition on the nanometric scale. In-situ polymerization of monomers in reduced space of porous AAO template nanocavities can give rise to the direct production of versatile polymer nanostructures. In this work, porous AAO devices of 35 nm of diameter have been obtained by a two-step electrochemical anodization process and used as a nanoreactor to study the radical polymerization kinetics of styrene (St) in confinement and the results compared to those of polymerization in bulk. SEM morphological study has been conducted to establish the final structure of obtained polymer nanostructures. Confocal Raman microscopy has been performed to study the formation of the polymer through the AAO cavities as a function of time and with this methodology it has been possible to establish the monomer conversion for styrenic polymerization in AAO devices. Polystyrene obtained in the nanoreactor was characterized by SEC, NMR, TGA and DSC and the properties compared with those of bulk polymer. It was found that both the average molecular weights and polydispersity index of nanostructured polymer are lower than those obtained for bulk polymer. NMR studies have shown that the use of a reactor with nanometric size dimensions gave the obtained polystyrene greater stereospecificity than that obtained in bulk. Thermal stability and glass transition temperature (T_g) values are higher for nanostructured than bulk polymers. Moreover, the methodology proposed in this work, using AAO nanocavities as nanoreactors for polymerization reaction, can be generalized and applied to obtain polymer nanostructures of very different chemical nature and morphology by choosing the appropriate monomer or monomer reactants and by tailoring the dimension of AAO cylindrical nanocavities, that is, diameter from 20 to 400 nm and length from a few to hundreds of microns.     

A novel method for preparing poly(alkyl methacrylates) and poly(methacrylic acids) of varying tacticity

In order to synthesize poly(methacrylic acid) and poly(alkyl methacrylates) over a wide range of polymer tacticity, the anionic polymerization of the following alkyl methacrylates (ethyl, n-propyl, isopropyl, n-butyl, sec-butyl, isobutyl, tert-butyl, n-amyl, n-hexyl, n-octyl, n-decyl, n-lauryl, and n-octadecyl) in toluene using phenylmagnesium bromide initiation was studied. It was found that the amount of isotactic polymer structure generally decreased as the size of the ester group increased. In all cases, the polymers had greater than 50% isotactic triad structure. Whether the polymerization was carried out at 0° or ?78°C had little or no effect on the tacticity of the polymer produced. It was found that the poly(alkyl methacrylates) produced could be hydrolyzed in concentrated sulfuric acid to poly(methacrylic acid). The poly(methacrylic acid) produced in the hydrolysis could be esterified with diazomethane to give poly(methyl methacrylate) or with diazoethane to give poly(ethyl methacrylate) with the same tacticity as the poly(alkyl methacrylate) from which the poly(methacrylic acid) was derived. It is possible, therefore, to produce poly(alkyl methacrylates) of a desired tacticity by polymerizing the appropriate monomer, hydrolyzing, and reesterifying the resultant poly(methacrylic acid) with a diazoalkane to give the desired poly(alkyl methacrylate).