Radical polymerization of N-vinylcaprolactam in homogeneous solution. II

The polymerization of N-vinylcaprolactam in toluene, dioxane, chlorobenzene, dimethylformamide, and ethylene carbonate with various peroxides, perbenzoates and azobisisobutyronitrile as initiators at 60–80°C, was studied. Under these conditions azobisisobutyronitrile and tert-butyl perbenzoate have satisfactory activity as initiators. Under these conditions N-vinylcaprolactam polymerization in homogeneous solution is first order towards the monomer and 0.5 order towards the initiators.     

Phosphonamidates as thermally latent initiators in the polymerization of epoxides

Summary Phosphonamidates, O,O-di-tert-butyl 1-piperidinyl phosphonamidate (BP-1) and O-tert-butyl di-1-piperidinyl phosphonamidate (BP-2), were synthesized by the reaction of phosphorus oxychloride and piperidine in the presence of triethylamine, followed by the reaction with tert-butyl alcohol in the presence of sodium hydride. The polymerization of GPE was carried out at 110–190 °C for 12 h with BP-1 and BP-2 as thermally latent initiators (3 mol %). The polymerization with O-tert-butyl P-phenyl 1-piperidinyl phosphonamidate (BP) previously reported was also examined for comparison. No polymerization of GPE took place below 110 °C, whereas it proceeded rapidly above the temperature. The activity order was BP-2 > BP > BP-1. Epikote 828 was cured with BP (5 mol %) at 190 °C to afford the solvent-insoluble gelled epoxy resin quantitatively. A mixture of GPE and phosphonamidate BP (3 mol %) did not react at 50 °C for 4 months. Received: 26 February 2001/Revised version: 12 April 2001/Accepted: 13 April 2001     

Mechanism of anionic polymerization of (meth)acrylates in the presence of aluminium alkyls

Summary Methyl methacrylate was polymerized with tert-butyl lithium in the presence of triethylaluminium or triisobutylaluminium at 78°C in toluene. As indicated by GPC and MALDI-TOF mass spectrometry, the polymerization is accompanied by side reactions. The lower oligomers were fractionated by distillation and characterised by NMR, FT-IR, UV and electron impact (EI) mass spectrometry. All these data show that part of the polymer chains are carrying exactly one tert-butyl isoprenyl ketone unit. In order to avoid the formation of tert-butyl isoprenyl ketone a molar ratio of Al/Li>2 is necessary.Part 2, cf. Ref. 10     

Butadiene polymerisation using ternary neodymium-based catalyst systems

Summary Ternary catalyst systems for the polymerisation of 1,3-butadiene to high cis content were studied. The systems Nd(carboxylate)₃/tert-butyl chloride/diisobutylaluminium hydride (carboxylate = naphthenate, versatate) were studied with respect to the order of catalyst component addition on catalyst activity and polymer characteristics. Stable catalysts which give relatively narrow molecular weight distribution are give by component addition order Nd(carboxylate)₃+diisobutylaluminium hydride+tert-butyl chloride. Less stable systems giving broader polymer molecular weight distributions are given by addition orders tert-butyl chloride+diisobutylaluminium hydride+Nd(carboxylate)₃ and Nd(carboxylate)₃ +tert-butyl chloride+diisobutylaluminium hydride.     

Rapid ambient temperature atom transfer radical polymerization of tert‐butyl acrylate

BACKGROUND: Atom transfer radical polymerization (ATRP) is considered to be one of the better and easier synthetic tools for the preparation of polymers with controlled molecular weights and polydispersities. Ambient temperature ATRP of tert‐butyl acrylate (tBA) was studied in a detailed manner with ethyl 2‐bromoisobutyrate (EBrB) and tert‐butyl 2‐bromoisobutyrate (tBuBrB) as the initiators for three different degrees of polymerization. RESULTS: Details pertaining to the kinetics of polymerization using different initiators are reported. It is observed that dimethylsulfoxide accelerates the polymerization at room temperature. The use of Cu(II) as the deactivator produces very narrow dispersity polymers. A diblock copolymer, poly(tert‐butyl acrylate)‐block‐poly(methyl methacrylate), was synthesized from the poly(tBA) macroinitiator demonstrating the controlled living nature of the polymerizations. CONCLUSIONS: The rate of polymerization is more rapid with a secondary initiator (ethyl 2‐bromopropionate) compared to the tertiary initiators EBrB and tBuBrB. From the detailed kinetic results it is observed that tris(2‐dimethylaminoethyl)amine was a better ligand compared to tris(2‐aminoethyl)amine in terms of achieving controlled polymerization. Copyright © 2007 Society of Chemical Industry     

The use of spin traps for the kinetic investigation of elementary events of pseudoliving radical reversible addition-fragmentation chain-transfer polymerization

The spin-trapping technique is used for the first time to study the kinetics and mechanism of addition and fragmentation elementary events in reversible addition-fragmentation chain-transfer pseudoliving radical polymerization. As shown by the example of the spin-trap-reversible addition-fragmentation chaintransfer agent model system, the constants of addition (substitution) of the model tert-butyl radical to polymeric reversible addition-fragmentation chain-transfer agents (poly(styrene dithiobenzoate), poly(n-butyl acrylate) dithiobenzoate, etc.) are one to two orders of magnitude higher than the constants of addition reactions involving low-molecular-mass reversible addition-fragmentation chain-transfer agents (tert-butyl dithiobenzoate, benzyl dithiobenzoate, di-tert-butyl trithiocarbonate, and dibenzyl trithiocarbonate). This circumstance makes it possible to significantly widen the synthetic possibilities of reversible addition-fragmentation chain-transfer polymerization. Rate constants of the fragmentation reaction for a number of intermediates are estimated, and the relationship between their structure and stability is ascertained. For the model reaction of the interaction (addition and fragmentation) of the tert-butyl radical with low-molecular-mass reversible addition-fragmentation chain-transfer agents, equilibrium constants are calculated via the methods of computational chemistry.     

Preparation and morphological characterization of two- and three-component natural rubber-based latex particles

Different emulsion polymerization processes allowed variation in the microstructure of composite natural rubber (NR)-based latex particles. A prevulcanized and a not-crosslinked natural rubber latex were coated with a shell of crosslinked poly(methyl methacrylate) (PMMA) or polystyrene (PS). The bipolar redox initiating system tert-butyl hydroperoxide/tetraethylene pentamine promoted a core–shell arrangement. Furthermore, PS subinclusions were introduced into the NR core. The initiators used for the subinclusion synthesis were azobisisobutyronitrile at high temperature and a redox initiation system consisting of tert-butyl hydroperoxide/dimethylaniline at low temperature. The morphology of the resulting latex interpenetrating networks (IPN) was characterized by transmission electron micros-copy (TEM) and scanning electron microscopy (SEM). Different staining methods allowed us to increase the contrast between the NR phase and the secondary polymers in the composite latex particles. A semicontinuous feeding process decreased the PS subinclusions size by a factor of 6 in comparison with a batch reaction. Depending on the NR/styrene swelling ratio, the crosslinking degree, and the polymerization temperature used, distinct differences of the phase arrangement of polymers in the latex particles were revealed. © 1996 John Wiley & Sons, Inc.     

Polymerization of 1,3-butadiene using aluminoxane-based Nd-carboxylate catalysts

The ternary neodymium-based catalyst for the polymerization of 1,3-butadiene, Nd(versatate)₃/AliBu₂H/tert-butyl chloride, has been examined with respect to the effects of replacing the alkylaluminium hydride with aluminoxane, namely methylaluminoxane (MAO) and tetraisobutyldialuminoxane (TIBAO). Catalysts based on MAO were found to be active even in the absence of a halogen source, whereas TIBAO catalysts were active only when a halogen was present (catalyst activity TIBAO > MAO). Using catalysts prepared both preformed and in situ, the effects of polymerization temperature, solvent and MAO level on catalyst activity and the characteristics of the final polymer are discussed. Polybutadiene cis contents and molecular weights were higher with MAO-based catalysts than with AliBu₂H-based catalysts. Cis contents were also higher when MAO catalysts containing tert-butyl chloride were used, compared to their non-chloride counterparts.     

Seeded emulsion terpolymerization of dimethyl meta-isopropenyl benzyl isocyanate (TMI®) with acrylic monomers

Dimethyl meta-isopropenyl benzyl isocyanate (TMI®) is a novel bifunctional monomer. It has a double bond and an isocyanate group. The seeded emulsion terpolymerization of TMI with the acrylic monomers, methyl methacrylate and n-butyl acrylate, has been studied. A copolymer of methyl methacrylate and n-butyl acrylate was used as the seed latex. In order to minimize the risk of hydrolysis of TMI, polymerizations were carried out at 40°C using redox initiators. No additional surfactant was added during the second-stage polymerization in order to avoid the nucleation of secondary particles. TMI was found to retard the polymerization kinetics. The effect of variables, such as the total number of particles, initiator concentration, and the monomer feed rate on polymerization kinetics, was investigated. The composition of the second-stage polymer could be controlled by running the polymerization under monomer-starved conditions. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 67: 685–694, 1998     

Emulsion polymerization of ethylene. V. Kinetics and mechanism

The solubility of ethylene was measured in water, water–tert-butyl alcohol, water-emulsifier, water-tert-butyl alcohol-emulsifier, and water–tert-butyl alcohol–emulsifier–polyethylene. The polymerization of ethylene in an emulsion system differs from that of other vinyl monomers in several ways: the rate of polymer formation is inversely proportional to the emulsifier concentration and to the number of particles, the molecular weight of the polymer increases as the particle size increases, the polymer contains bound emulsifier whose concentration depends inversely on the particle diameter. These peculiarities are attributed to a transfer reaction between polymer radicals and emulsifier adsorbed on the surface of the polymer particle. In the presence of a fatty-acid soap, the transfer probably occurs primarily at the carbon α to the carboxyl group.     

Bulk polymerization of vinyl chloride–commercial initiator systems

The applicability of a model after Talamini for the bulk polymerization of vinyl chloride with several commercial initiators has been examined. The model agrees well with experimental rate data for the initiators: diisopropyl peroxydicarbonate, disecbutyl peroxydicarbonate, t-butyl peroxypivalate, lauroyl peroxide and benzoyl peroxide.     

Electron transfer processes in photoinitiating systems composed of hemicyanine sec-butyltriphenylborate ion pairs

Summary Borate hemicyanine salts, namely sec-butyltriphenyl styrylbenzoxazole borates are shown to be effective photoinitiators for the polymerization of vinyl monomers. Mechanism of the photoinitiation involves sec-butyl radicals formed from the heterolytic cleavage of carbon-boron bond that follows the electron transfer process. The capability of the salts to act as initiators for the polymerization of multifunctional monomer is documented.     

Butadiene polymerisation using ternary neodymium-based catalyst systems

Summary Ternary catalyst systems for the polymerisation of 1,3-butadiene to high cis content were studied. The systems Nd(carboxylate)₃/tert-butyl X /diisobutyl aluminium hydride (carboxylate=naphthenate, versatate; X=Cl, Br, I) were studied with respect to the halide:Nd ratio and halide type on catalyst activity and polymer characteristics. A lowering of the halide:Nd ratio results in lower conversions to polymer and a change in polymer molecular weight distribution. Catalyst stability is affected by halide type; instability, or tendency to precipitate, following the order I>Br>Cl. Less active catalysts (e.g. based on tert-butyl iodide) give low conversions and broad polymer MWD. Cis content remains at 98% and is unaffected by a lowering of halide:Nd ratio or a change in halide type.     

Radical entry mechanisms in redox-initiated emulsion polymerizations

The mechanisms and kinetics of radical entry in emulsion polymerizations utilizing redox initiation are investigated using polymerization rate data obtained by reaction calorimetry and electrospray mass spectroscopy analysis of initiator-derived aqueous-phase products. These data have been used to evaluate an initiation scheme for redox-initiated emulsion polymerizations of common monomers such as styrene and methyl methacrylate based around the oxidant, tert-butyl hydroperoxide. Redox initiators are broadly classed by the solubility of their radical products: Hydrophilic radicals enter by propagating to a critical degree of polymerization to become surface-active whilst more hydrophobic radicals may enter particles directly. When direct entry is applicable (the hydrophobic case), initiation efficiency will always be very high.     

Preparation of functional poly(acrylates and methacrylates) and block copolymers formation based on polystyrene macroinitiator by ATRP

The polymerization by ATRP of hydroxy and amino functional acrylates and methacrylates with tert-butyldimethylsilyl (TBDMS) or tert-butyloxycarbonyl (BOC) protective groups has been studied for the first time achieving high control over molecular weight and polydispersity. Detailed investigation of the ATRP of 2-{[tert-butyl(dimethyl)silyl]oxy}ethyl acrylate (M2b) in bulk and 2-[(tert-butoxycarbonyl)amino]ethyl 2-methylacrylate (M3a) in diphenyl ether (DPE) showed that the type of ligand plays an important role on either the polymerization rate or the degree of control of the polymerization. Among the ligands used, N,N,N,′N″N″-pentamethyl diethylenetriamine (PMDETA) was the most suitable ligand for ATRP of all functional acrylates and methacrylates. The kinetics of M2b and M3a polymerization using PMDETA as a ligand was reported and proved the living character of the polymerization. Well-defined block copolymers based on a halogen terminated polystyrene (Pst) macroinitiator and the functional acrylate and methacrylate monomers were successfully synthesized by ATRP, and subsequent deprotection of the protective groups from the acrylate or methacrylate segment afforded amphiphilic block copolymers with a specific solubility behavior.     

Preparation of amphiphilic PS-b-PMAA diblock copolymer by means of atom transfer radical polymerization

Amphiphilic diblock copolymers of polystyrene-b-poly(methacrylic acid) were synthesized by means of atom transfer radical polymerization. First, the polystyrene with a bromine atom at the chain end (PS-Br) was prepared using styrene as the monomer, 1-bromoethyl benzene as the initiator, and CuCl/2,2′-bipyridyl (bpy) as the catalyst ([1-bromoethyl benzene]/[CuCl]/[bpy] = 1:1:3). The polymerization was well controlled. Second, the diblock copolymer of polystyrene-b-poly(tert-butyl methacrylate) was synthesized also by atom transfer radical polymerization using PS-Br as the macro-initiator, CuCl/bpy as the catalyst, and tert-butyl methacrylate (tBMA) as the monomer. Finally, the amphiphilic diblock copolymer, PS-b-PMAA, was obtained by hydrolysis of PS-b-PtBMA under the acid condition. The molecular weight and the structure of aforementioned copolymers were characterized with gel permeation chromatography, infrared, and nuclear magnetic resonance. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 82: 2381–2386, 2001     

Synthesis of cyclophane carrying poly(acrylic acid) chains and its complexation behavior

Poly(tert-butyl acrylate)-coupled cyclophane was obtained by coupling 1,6,20,25-tetraaza[6.1.6.1]paracyclophane with carboxyl-terminated poly(tert-butyl acrylate). The poly(tert-butyl acrylate) was quantitatively hydrolyzed to poly(acrylic acid). The cyclophane carrying poly(acrylic acid) was soluble in alkaline water and formed an inclusion complex with trimethyl-2-naphthylmethylammonium bromide as a guest. Received: 2 July 1997/Revised: 22 August 1997/Accepted: 29 August 1997     

Crystalline Di-Tert-Butyl Trioxide and Dicumyl Trioxide

Di-tert-butyl trioxide has been prepared at ?50° by photolysis of solid di-tert-butyl diperoxymonocarbonate and, more conveniently, by the reaction of ozone in Freon 12 (CF₂Cl₂) or methyl chloride with either dissolved tert-butyl hydroperoxide or suspended hydrated sodium tert-butyl peroxide. A low-temperature procedure for freeing the product from accompanying tert-butyl alcohol and other impurities is described. The ozone - sodium salt method has also been applied to the preparation of crystalline dicumyl trioxide. These trioxides have the properties previously observed in solution. They are unstable at temperatures above ?30°. NMR spectra of the trioxides are reported and compared with those of related compounds. Approximate rate constants for the thermal decomposition of dicumyl trioxide are reported.     

Mechanistic studies of methyl methacrylate polymerization in the presence of cobalt complex with sterically-hindered redox-active ligand

The influence of bis[4,6-di-tert-butyl-N-(2,6-dimethylphenyl)-o-iminobenzosemiquinono]cobalt (II) on radical polymerization of methyl methacrylate initiated by AIBN at 70–90 °C was studied. The introduction of cobalt complex bearing redox ligands into reaction media allows to provide polymerization of methyl methacrylate without self-acceleration with linear increase of molecular weight with conversion giving polymers with relatively low molecular weight distribution. The results of IR and NMR spectrometry and MALDI mass spectroscopy measurements show that the possibility of β-hydrogen transfer between complex and propagating radical during polymerization is minimal. The electron donating additives as tert.-butyl amine and pyridine have no activating effect on polymerization. The results of our experiments provided at different concentrations of initiator show that polymerization proceeds via degenerative chain transfer mechanism.     

Radical polymerization behavior of 2-tert-butylcyclohexyl methacrylate

The polymerization of 2-tert-butylcyclohexyl methacrylate (2BCHMA) was carried out in benzene at 60 °C. The polymerization reactivity of 2BCHMA decreased due to the steric effect of the ester substituent compared to other alkyl methacrylates (RMA) including 4-tert-butylcyclohexyl methacrylate (4BCHMA). The evaluation of propagation and termination rate constants by electron spin resonance spectroscopy revealed that both the propagation and the termination were suppressed by the 2-tert-butyl substituent in the cyclohexyl moiety. The microstructure and thermal properties of poly(2BCHMA) were also examined and compared with those of poly(4BCHMA).