Effects of substituants in stilbene upon its reactivity in radical polymerizations

Summary Polymerizations of methyl methacrylate and styrene have been performed in the presence of thecis andtrans isomers of 4-methoxy-4-chlorostilbene (SSTL) using as initiators benzoyl peroxide and 2-cyano-2-propylazoformamide, both enriched with carbon-13.¹³C-NMR spectra of the polymers show that SSTL units are present at many of the sites adjacent to benzoate end-groups but not to a detectable extent at sites adjacent to 2-cyano-2-propyl end-groups. The presence of the substituents in the molecule of stilbene greatly enhances its reactivity towards the benzoyloxy radical.     

Reaction behaviour of N-methacryloyl pyrrole in radical polymerizations

Summary N-methacryloyl pyrrole NMP was synthesized via the pyrrylpot-assium salt and radically polymerized. Thereby crosslinked and partially insoluble products were obtained. Synthesis of the model system N-acetyl pyrrole 1 and carefylly directed reactions thereon made the explanation of the way of the radical polymerization possible.     

New chain transfer agents for free radical polymerizations

The palmitoyl ester of N-hydroxypyridine-2-thione displayed useful chain transfer properties in free radical polymerizations of methyl methacrylate and styrene. Retardation, however, accompanied the lowering of molecular weight in methyl acrylate and vinyl acetate polymerizations. 4-Methyl-3-palmitoyloxythiazol-2(3H)-thione had good chain transfer activity with methyl methacrylate, styrene and methyl acrylate. Although benzyl thionobenzoate exhibited virtually ‘ideal’ behaviour (chain transfer constant C_x ～1) in styrene and methyl acrylate polymerizations, it was ineffective in lowering molecular weight of poly(methyl methacrylate). Severe retardation was observed with vinyl acetate. Addition-fragmentation pathways are postulated for chain transfer.     

Kinetics of ‘living’ radical polymerizations of multifunctional monomers

The polymerizations of multifunctional monomers with an iniferter, p-xylylene bis-(N,N-diethyldithiocarbamate) (XDT), were studied with differential photocalorimetry. The iniferter was used to simulate a ‘living’ radical polymerization. The normal autoacceleration behavior that is often observed in the polymerization of multifunctional monomers was not evident in the reactions with the iniferter. The reversible reaction between the propagating polymer chain and the sulfur radical from the XDT molecule dominated the reaction and drastically decreased the rate of polymerization. Various parameters of the reaction (length between functional groups in the monomer, iniferter concentration, UV light intensity, and temperature) were investigated to determine the effect on the polymerization. The rate of polymerization and the final conversion of the polymer were increased significantly by increasing the temperature, initiator concentration and UV light intensity, and decreasing the length between functional groups. Mechanical properties of the resulting polymers were also examined. It was concluded that the presence of the iniferter during the polymerization of the multifunctional monomers had no effect on the heterogeneity of the polymer network. This was in agreement with previous modeling results.     

Free radical polymerizations of some vinyl monomers in carbon dioxide fluid

The effect of pressure ranging from ambient atmosphere to 28.5 MPa on the free radical polymerizations of methyl methacrylate (MMA) in carbon dioxide (CO₂) was investigated and discussed. The poly(methyl methacrylate) (PMMA) with high molecular weight was synthesized at quite high conversion of MMA in the polymerization at or below 9.2 MPa, as compared to those polymerized under 11.8–28.5 MPa. A phase transition behavior of MMA‐CO₂ binary mixture from homogeneous state to vapor‐liquid equilibrium (VLE) state was observed below 10.51 MPa. In such a VLE system, almost all MMA was found to exist in the liquid phase with higher concentration than that in homogenous system. Thus, the fast polymerization rate of MMA and high molecular weight of PMMA could be related to the VLE state of MMA/CO₂ under low pressure. Similar phenomena were also observed in the polymerization systems of styrene and vinyl acetate in CO₂, respectively. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Photocationic and radical polymerizations by novel N‐phenacylammonium salts

Novel N‐phenacylammonium salts [N‐(α‐benzoylbenzyl)‐, N‐(1‐benzoylethyl)‐, N‐phenacyl‐, pyrazinium, 3‐bromoquinolinium, benzothiazolium, or p‐cyanopyridinium hexafluoroantimonates] were synthesized by the reaction of α‐benzoylbenzyl bromide, 2‐bromopropiophenone or phenacylbromide, and the corresponding N‐hetero aromatic compound, followed by anion exchange with KSbF₆. These N‐phenacylammonium salts showed higher activity than previously reported N‐benzyl‐2‐cyanopyridinium hexafluoroantimonate in the photopolymerization of epoxides. Further, these N‐phenacylammonium salts served as photoradical and thermal cationic initiators as well as photocationic initiators. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 91: 3470–3476, 2004     

First nitroxide-mediated free radical dispersion polymerizations of styrene in supercritical carbon dioxide

Controlled/living character has been demonstrated for the first time in nitroxide-mediated free radical dispersion polymerizations in supercritical carbon dioxide. Styrene was polymerized in the presence of N-tert-butyl-N-(1-diethylphosphono-2,2-dimethylpropyl) nitroxide (SG1) at 110 °C. Stabilization was achieved using the inistab concept (initiator+stabilizer), employing a poly(dimethylsiloxane) (PDMS) based azo initiator as well as a polymeric alkoxyamine macroinitiator with the expected structure SG1-polystyrene-PDMS-polystyrene-SG1. In the presence of sufficient amounts of the inistab, the polymerizations proceeded to high conversion to yield the polymeric product as a powder. Control was indicated by the number-average molecular weights increasing linearly with conversion in reasonable agreement with the theoretical values. Although the molecular weight distributions were broad in many cases, chain extensions in bulk and solution using styrene indicated high degrees of ‘living’ character.     

Investigation of a system capable of photoinitiating radical polymerizations in thick pigmented media

A new system consisting of a xanthenic dye, a ferrocenium salt, a hydroperoxide, and an amine, capable of photoinitiating the radical polymerization of thick and pigmented films exhibiting a thickness of ca. 100 microns was studied. This is a one‐step process, with a working speed of 10 m min⁻¹, involving four 80‐W cm⁻¹ lamps. This is one present‐day system capable of working under industrial conditions. The photolysis investigation in solvent medium of its various components is a first approach to discuss the photochemical mechanism involved in this four‐component system. Thus, one can assume that both mechanisms could occur through charge transfer : dye/amine interaction and dye/ferrocenium salt interaction, the latter one being presumably the most efficient. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 79: 1911–1923, 2001     

Living radical polymerizations in homogeneous solution by using organic sulfides as photoiniferters

Summary Some examples for living radical polymerization in homogeneous solution by four organic sulfides as photoiniferters have been proposed. In the photopolymerization of styrene (St) with diphenyl disulfide (DPD), tetraethyl thiuram disulfide (TD), benzyl diethyldithiocarbamate (BDC) and 2-phenylethyl diethyldithiocarbamate (PEDC), both the yields and the average-molecular weights of the polymers were found to increase as a function of the reaction time. The results obtained suggested that these polymerizations proceeded via a living radical mechanism. When these photoiniferters except DPD were used, the propagating polymer chain end was confirmed to be always the diethyldithiocarbamate [(C₂ H₅)₂NCSS] group, which can further photodissociate into a reactive propagating radical and a less reactive small radical[(C₂H₅)₂NCSS·] in order to result in successive insertion of monomer molecules into the dissociated bond.     

One‐step,one‐pot photoinitiation of free radical and free radical promoted cationic polymerizations

We describe here a novel approach to photoinitiate free radical and cationic polymerizations concurrently, involving the use of benzoin in conjunction with an onium salt such as diphenyl iodonium or N‐alkoxy pyridinium salt. On photolysis, benzoyl radicals formed from the decomposition of benzoin initiate free radical polymerization of methyl methacrylate. The hydroxy benzyl radicals formed concomitantly are readily oxidized to the corresponding cation by the onium salt to initiate cationic polymerization of cyclohexene oxide in the same system. Evidence for two independent polymerizations was obtained from studies involving gel permeation chromatography, extractions, and infrared and proton nuclear magnetic resonance analysis of the polymers. The effect of the type of the onium salt on each polymerization was also investigated. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 85: 2389–2395, 2002     

Use of genetic algorithms in the optimization of free radical polymerizations exhibiting the trommsdorff effect

The genetic algorithm (GA) is adapted and used to obtain optimal temperature histories for methyl methacrylate polymerizations. The reaction time is minimized, while simultaneously requiring the attainment of design values of the final monomer conversion and number average chain length. The technique is robust, and gives near-global optimal solutions. As such, it can easily be used for on-line optimizing control of free radical polymerization reactors in which the reaction is associated with the Trommsdorff effect. The results obtained from GA can be improved further if these are provided as initial guesses to a computer code using the Pontryagin minimum principle with the first order control vector iteration method. © 1997 John Wiley & Sons, Inc.     

Syntheses of new amino‐functionalized methacrylates and their use in free radical polymerizations

For use in emulsion and solution copolymerization a series of novel amino‐functional methacrylates has been synthesized, most of which have seldom, or never, been described in the literature before. In this investigation, the preparation of the hydrochloric and/or tosylate salt of the monomers aminoethyl, 3‐amino‐1‐propyl, 5‐amino‐1‐pentyl, 6‐amino‐1‐hexyl and 11‐amino‐1‐undecyl methacrylate will be described, along with the characterization of the parameters water solubility, pK_a and chemical stability. The homopolymers of these monomers have been prepared and characterized. Results show the occurrence of an acyl migration upon neutralization of the monomers aminoethyl‐ and 3‐amino‐1‐propyl methacrylate. This migration does not occur in the monomer 5‐amino‐1‐pentyl methacrylate, which makes it possible to synthesize the neutralized monomer although, after neutralization, a Michael addition occurs, resulting in a limited lifetime. Copolymerizations have been performed in emulsion. The monomer aminopentyl methacrylate especially proved to be suitable for emulsion copolymerizations when used under controlled conditions. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 80: 1401–1415, 2001     

Atom transfer radical polymerizations of methyl methacrylate and styrene with an iniferter reagent as the initiator

Three novel iniferter reagents were synthesized and used as initiators for the polymerizations of methyl methacrylate (MMA) and styrene (St) in the presence of copper(I) bromide and N,N,N′,N″,N″‐pentamethyldiethylenetriamine at 90 and 115°C, respectively. All the polymerizations were well controlled, with a linear increase in the number‐average molecular weights during increased monomer conversions and relatively narrow molecular weight distributions (weight‐average molecular weight/number‐average molecular weight ≤ 1.36) throughout the polymerization processes. The polymerization rate of MMA was faster in bulk than that in solution and was influenced by the different polarities of the solvents. A slight change in the chemical structures of the initiators had no obvious effect on the polymerization rates of MMA and St. The initiator efficiency toward MMA was lower than that toward St. The results of ¹H‐NMR, matrix‐assisted laser desorption/ionization time‐of‐flight mass spectrum analysis, and chain‐extension experiments demonstrated that well‐defined poly(methyl methacrylate) and polystyrene bearing photolabile groups could be obtained via atom transfer radical polymerization (ATRP) with three iniferter reagents as initiators. The polymerization mechanism for this novel initiation system was a common ATRP process. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

Polyisobutylene-based miktoarm star polymers via a combination of carbocationic and atom transfer radical polymerizations

Poly(isobutylene-b-styrene) (PIB-PS) copolymers and polyisobutylene (PIB) homopolymers were synthesized via quasiliving carbocationic polymerization from the initiator 3,3,5-trimethyl-5-chlorohexyl acetate, which contains a protected hydroxyl group. The PIB block was created at −70 °C in a methylcyclohexane/methyl chloride (60:40) cosolvent system, using TiCl₄ as co-initiator, followed optionally by sequential addition of styrene. Using a strong base, the acetate head group of the resulting block copolymer was cleaved to yield a hydroxyl group, which was subsequently esterified with the branching agent 2,2-bis((2-bromo-2-methyl)propionatomethyl)propionyl chloride (BPPC) to create dual initiating sites for atom transfer radical polymerization (ATRP). ATRP of tert-butyl acrylate was carried out using a Cu(I)Br/1,1,4,7,7-pentamethyldiethylenetriamine (PMDETA) catalyst system. In some cases, the ester side chains of the poly(tert-butyl acrylate) (PtBA) blocks were cleaved to create poly(acrylic acid) (PAA) blocks. The final miktoarm star polymers had compositions that were very close to theoretical.     

Chemically-initiated solution polymerizations and radiation-initiated bulk polymerizations of isopropyl vinyl ether

The unusually high rates of polymerization of isopropyl vinyl ether initiated in bulk by high energy radiation, compared with other vinyl ethers, reported previously have been confirmed. The rates, molecular weights and heats of polymerization initiated by triphenylmethyl hexachlorantimonate have now been measured in methylene dichloride solution. Both methods of initiation are believed to involve essentially free ions. The chemically initiated polymerization rates however were similar to those found with the other vinyl ethers. The conflicting results are explained in terms of solvation effects rather than to differences in the methods of initiation. Qualitatively these results have been interpreted in terms of the Eyring theory of reaction rates between an unpaired ion and a neutral molecule.     

Free radical polymerizations associated with the trommsdorff effect under semibatch reactor conditions. I: Modeling

Several important polymerizations [e.g., poly(methyl methacrylate) (PMMA), polystyrene] exhibit gel and glass effects during polymerization. These are associated with the decrease of the diffusivities of the macroradicals and monomer molecules with increasing viscosities of the reaction mass. A new model has been developed to account for the gel and glass effects, both under batch and semibatch reactor operations. The free volume theory of Vrentas and Duda has been used to account for the changes in the diffusion coefficients. The model parameters are tuned using experimental data on the isothermal bulk and solution polymerizations of MMA in batch reactors. Conversion histories and molecular weights have been obtained for cases where solvent, initiator or monomer are added to (or removed from) the reaction mass after some reaction has taken place. In addition, studies involving step changes in temperature hav been carried out. It is found that the conversion vs. time behavior after such step changes depend upon a complex interplay of three factors: Polymer concentration, molecular weight, and the temperature at the point these changes are effected.     

Design and synthesis of star polymers with hetero-arms by the combination of controlled radical polymerizations and click chemistry

An alternative approach to the synthesis of well-defined star polymers with hetero-arms was described. An azide-functionalized dithioester chain transfer agent (CTA-N₃) was designed and synthesized. Using CTA-N₃ as the reversible addition-fragmentation chain transfer (RAFT) agent, styrene was polymerized in a controlled manner. The so-obtained polystyrene showed a high proportion of azide-functionalized chains (PS-N₃, about 92%). The azide end-capped PS-N₃ could be assembled, via click reaction with a bromide-containing trialkyne coupling agent, to form a 3-arm star polystyrene (PS₃-Br) with a narrow molecular weight distribution. PS₃-Br could further serve as a macro-initiator for the atom transfer radical polymerization (ATRP) of methyl methacrylate (MMA). Accordingly, well-defined star polymers containing three polystyrene and one poly(methyl methacrylate) (PMMA) arms, and with a narrow molecular weight distribution, were successfully prepared.