Hydrogen effects in propylene polymerization reactions with titanium‐based Ziegler–Natta catalysts. II. Mechanism of the chain‐transfer reaction

Hydrogen is a very effective chain‐transfer agent in propylene polymerization reactions with Ti‐based Ziegler–Natta catalysts. However, measurements of the hydrogen concentration effect on the molecular weight of polypropylene prepared with a supported TiCl₄/dibutyl phthalate/MgCl₂ catalyst show a peculiar effect: hydrogen efficiency in the chain transfer significantly decreases with concentration, and at very high concentrations, hydrogen no longer affects the molecular weight of polypropylene. A detailed analysis of kinetic features of chain‐transfer reactions for different types of active centers in the catalyst suggests that chain transfer with hydrogen is not merely the hydrogenolysis reaction of the Ti? C bond in an active center but proceeds with the participation of a coordinated propylene molecule. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 1899–1911, 2002     

Controlled ring-opening polymerization of cyclic carbonates and lactones by an activated monomer mechanism

This article reviews recent topics in the controlled synthesis of polycarbonates and polylactones with small polydispersity indices by activated monomer cationic ring-opening polymerizations, especially with new initiator systems, such as alcohol/protonic acid and boron alkoxide/protonic acid. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 2190–2198, 2002     

Synthesis of a soluble vinyl‐type polynorbornene with a half‐titanocene/methylaluminoxane catalyst

Norbornene polymerization was performed with monocyclopentadienyltitanium tribenzyloxide activated with methylaluminoxane (MAO). The catalyst afforded a pure vinyl‐type polymer at temperatures below 80 °C and at appropriate MAO concentrations. However, at higher temperatures or high MAO concentrations, a portion of the titanium species was pyrolyzed to form an alkylidene compound that catalyzed the ring‐opening metathesis polymerization of norbornene. As a result, both vinyl‐type and ring‐opening polymers were produced under the reaction conditions. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 1421–1425, 2002     

Emulsion polymerization of styrene using polystyrene‐block‐poly(ethylene oxide) macromonomers as stabilizers

New diblock macromonomers were used as reactive emulsifiers in the emulsion polymerization of styrene. The nature of the reactive group, the molecular weight, the length of the poly(ethylene oxide) (PEO) block, and the molecular structure of the macromonomer were systematically investigated during this process by analyzing the evolution of the conversion and particle diameters. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 2819–2827, 2002     

Emulsion polymerization of divinyl monomers stabilized by sodium dodecyl sulfate and bis(2‐ethylhexyl)sulfosuccinate sodium salt

The emulsion polymerization of divinyl monomers is investigated. Emulsions were obtained in the presence of sodium dodecyl sulfate and bis(2‐ethylhexyl)sulfosuccinate sodium salt as surfactants. The influence of monomer type and kind of surfactant on the particle size distribution is studied. The porous structure of the broken emulsions is also determined. The results indicate that the diameter of nanospheres obtained from two divinyl monomers are significantly larger than those obtained from polystyrene. Aggregation of the particles and the pore‐forming diluent added to the emulsion are responsible for the existence of pores. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 3967–3973, 2002     

Long‐lived intermediates in reversible addition–fragmentation chain‐transfer (RAFT) polymerization generated by γ radiation

A novel experimental procedure is presented that allowed probing of reversible addition–fragmentation chain‐transfer (RAFT) free‐radical polymerizations for long‐lived species. The new experimental sequence consisted of gamma irradiation of a mixture of initial RAFT agent (cumyl dithiobenzoate) and monomer at ambient temperature, a subsequent predetermined waiting period without initiation source also at ambient temperature, and then heating of the reaction mixture to a significantly higher temperature. After each sequence step, the monomer conversion and molecular weight distribution were determined, indicating that controlled polymer formation occurs only during the heating period. The results indicated that stable intermediates (either radical or nonradical in nature) are present in such experiments because thermal self‐initiation of the monomer can be excluded as the reason for polymer formation. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 1058–1063, 2002     

Terminology of kinetics,thermodynamics, and mechanisms of polymerization

This article, after a short introduction, written by a coordinator of the International Union of Pure and Applied Chemistry (IUPAC) Project devoted to the Terminology of the Kinetics, Thermodynamics, and Mechanisms of Polymerization presents the Provisional Document prepared by the IUPAC Macromolecular Division (Commission Nomenclature). It contains 95 entries, from “activated monomer polymerization” to “zwitterionic polymerization.” © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 1665–1676, 2002     

Phosphines: Nucleophilic organic catalysts for the controlled ring‐opening polymerization of lactides

A new metal‐free synthetic approach to the controlled ring‐opening polymerization (ROP) of lactide with nucleophilic phosphines as transesterification catalysts is described. P(Bu)₃, PhPMe₂, Ph₂PMe, PPh₃, and related phosphines are commercially available, inexpensive catalysts that generate narrowly dispersed polylactides with predictable molecular weights. These organic catalysts must be used in combination with an initiator, such as an alcohol, to generate an alcoholate ester α‐end group upon ROP. A likely polymerization pathway is through a monomer‐activated mechanism, with minimal active species, facilitating narrow molecular weight distributions. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 844–851, 2002; DOI 10.1002/pola.10168     

Ruthenium‐based metathesis initiators: Development and use in ring‐opening metathesis polymerization

For many years, olefin metathesis has been a central topic of industrial and academic research because of its great synthetic utility. The employed initiators cover a wide range of compounds, from simple transition‐metal salts to highly sophisticated and well‐defined alkylidene complexes. Currently, ruthenium‐based catalysts are at the center of attention because of their remarkable tolerance toward oxygen, moisture, and numerous functionalities. This article focuses on recent developments in the field of ring‐opening metathesis polymerization using ruthenium‐based catalysts. ruthenium‐based initiators and their applications to the preparation of advanced polymeric materials are briefly reviewed. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 2895–2916, 2002     

Atom transfer radical homo‐ and block copolymerization of methyl 1‐bicyclobutanecarboxylate

A non‐olefinic monomer, methyl 1‐bicyclobutanecarboxylate (MBC), was successfully polymerized by the controlled/“living” atom transfer radical polymerization (ATRP) technique, resulting in a well‐defined homopolymer, PMBC, with only cyclobutane ring units in the polymer chain. An AB block copolymer poly(methyl 1‐bicyclobutanecarboxylate)‐b‐polystyrene (PMBC‐b‐PS), having an all‐ring unit segment, was also synthesized with narrow polydispersity and designed number‐average molecular weight in addition to precise end groups. The ¹H NMR spectra, glass‐transition temperature, and thermal stability of PMBC, PMBC‐b‐PS, and PS‐b‐PMBC were investigated. The experimental results showed that the cyclobutane rings in the two block polymers improved their thermal stability. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 1929–1936, 2002     

Single-electron and two-electron transfer in the anionic polymerization of vinyl monomers and the ring-opening polymerization of lactones*

Single-electron-transfer (SET) and two-electron-transfer reactions and their mechanisms were examined in the anionic polymerization of vinyl monomers and in the ring-opening polymerization of lactones. SET resulted in the formation of radical anions or enolates at the initiation step of styrene or lactone polymerization with naphthalene sodium as a catalyst. However, alkali-metal supramolecular complexes such as M⁺crown–M⁻ (M = Na or K) were able to transfer two electrons to both these monomers to form carbanions as reactive intermediates. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 2158–2165, 2002     

Functional polymers by living anionic polymerization

The application of living anionic polymerization techniques for the functionalization of polymers and block copolymers is reviewed. The attachment of functional groups to polymeric chains of predetermined lengths and narrow molecular weight distributions is described. Carboxyls, hydroxyls, amines, halogens, double bonds, and many other functional groups can be placed at one or two ends in the center or evenly spaced along polymeric chains. Subsequent transformations of the functional groups further contribute to the versatility of such treatments. General methods based on the use, as terminators, of substituted haloalkanes, as well as the addition of living polymers or their initiators to diphenylethylenes, substituted with appropriate functional groups or molecules, are discussed. Another approach, based on the living polymerization of monomers with protected functional groups, is also discussed. It has been used for the preparation of polymers and copolymers with evenly spaced functional groups. The combination of living anionic polymerization techniques with controlled radical and cationic polymerizations is also described. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 2116–2133, 2002     

Knowledge‐based choice of the initiator type for monomer removal by postpolymerization

The mechanisms involved in monomer removal by postpolymerization were investigated to establish a criterion to select the most effective initiator systems. Three redox systems yielding radicals of different hydrophobicities were studied. Efficiency in monomer removal by postpolymerization increased with the hydrophobicity of the radical formed from the initiator system. This result was independent of the water solubility of the residual monomer. The mechanistic reasons for this finding are discussed. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 4245–4249, 2002     

Initiation mechanisms of an anionic ring‐opening polymerization of lactam‐12

A novel liquid system has been developed to initiate the anionic polymerization of lactam‐12. This system, containing both an activator and a catalyst, has the primary advantage over previous systems of permitting infinite storage of the reactant, and it avoids premixing of batches. The anionic species of the system were identified with matrix‐assisted laser desorption/ionization time‐of‐flight measurements, and Fourier transform infrared was used to measure the change in their concentrations during the polymerization. A guanidine anion was formed, and the system initiated the polymerization by this guanidine and by the catalyst. The kinetics of the anionic polymerization of lactam‐12 into polyamide‐12 were followed with differential scanning calorimetry measurements. The determined reaction rates indicated that this liquid system was particularly well suited for initiating in situ polymerization during liquid molding. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 3406–3415, 2002     

Complex formation of polyethyleneimine with copper(II), nickel(II), and cobalt(II) ions

An influence of the structure of a globule of polyethyleneimine on the complex formation of one with the copper(II), nickel(II), and cobalt(II) ions is described. A change of the coordination number from the pH of solution for complexes of ethylenediamine, diethylenetriamine, and polyethyleneimine with metal ions was found. The fraction of monomer links, bound with metal ions, depends on the volume of the globule of macromolecule as well as the condition of the proceeding reaction. The reaction of complex formation is controlled by the diffusion of metal ions into the polymer globule in solution. The effective equilibrium constants of complex formation were found. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 914–922, 2002; DOI 10.1002/pola.10157     

Viscosity effects in cobaloxime‐mediated catalytic chain‐transfer polymerization of methacrylates

The effect of bulk viscosity on the cobaloxime‐mediated catalytic chain‐transfer polymerization of methacrylates at 60 °C was investigated by both the addition of high molecular weight poly(methyl methacrylate) to methyl methacrylate polymerization and the dilution of benzyl methacrylate polymerization by toluene. The results indicate that the bulk viscosity is not directly linked to the chain‐transfer activity. The previously measured relationship between chain‐transfer‐rate coefficient and monomer viscosity therefore probably reflects changes at the molecular level. However, the results in this article do not necessarily disprove a diffusion‐controlled reaction rate because cobaloxime diffusion is expected to scale with the monomer friction coefficient rather than bulk viscosity. Considering the published data, to date we are not able to distinguish between a diffusion‐controlled reaction rate or a mechanism directly affected by the methacrylate substituent. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 782–792, 2002; DOI 10.1002/pola.10152     

Synthesis and photoactivity of novel 5‐arylthianthrenium salt cationic photoinitiators

5‐Arylthianthrenium salts are a class of efficient triarylsulfonium salt photoinitiators for cationic polymerization. These compounds were prepared by a simple, straightforward, versatile, and high yield route. The new photoinitiators were characterized by standard analytical and spectroscopic techniques, and their activity as cationic photoinitiators was compared with related triarylsulfonium salts of similar structures using Fourier transform real‐time infrared spectroscopy. Through the use of electron‐transfer photosensitizers, the response of these photoinitiators can be readily spectrally broadened into the long‐wavelength UV–visible regions of the spectrum. The results obtained suggest that 5‐arylthianthrenium salts are potential replacements for now available triarysulfonium salt photoinitiators in many applications. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 3465–3480, 2002     

Synthesis of new graft copolymers containing polyisobutylene by a combination of the 1,1‐diphenylethylene technique and cationic polymerization

The synthesis of macroinitiators for the cationic polymerization of isobutylene via radical polymerization is presented. The 1,1‐diphenylethylene system was used to obtain macroinitiators consisting of 4‐chloromethylstyrene and methyl methacrylate units. The resulting polymers were used for the cationic polymerization of isobutylene, yielding graft copolymers that were characterized by gel permeation chromatography and NMR. The dependence of the molar mass and polydispersity on the temperature and monomer concentration was studied. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 3725–3733, 2002     

Application of ketenes to well‐defined polyester synthesis (4): End‐capping reactions in living anionic polymerization of ethylphenylketene

End‐capping reactions of a living polyester, obtained by anionic polymerization of ethylphenylketene (EPK), were carried out. As end‐capping reagents, electrophiles such as alkyl halide and acyl halide were successfully used. Reactivity of the terminal enolate and the resulting terminal structures were elucidated by model reactions, using lithium enolates having low molecular weights, obtained by an equimolar reaction of EPK with butyllithium. Polymerization of EPK by lithium alkoxide and the subsequent end‐capping reaction afforded the corresponding polyester having functional groups at both chain ends and a narrow molecular weight distribution. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 3103–3111, 2002     

Reverse atom transfer radical solution polymerization of methyl methacrylate under pulsed microwave irradiation

The reverse atom transfer radical polymerization (RATRP) of methyl methacrylate (MMA) was successfully carried out under pulsed microwave irradiation (PMI) at 69 °C with N,N‐dimethylformamide as a solvent and with azobisisobutyronitrile (AIBN)/CuBr₂/tetramethylethylenediamine as an initiation system. PMI resulted in a significant increase in the polymerization rate of RATRP. A 10.5% conversion for a polymer with a number‐average molecular weight of 34,500 and a polydispersity index of 1.23 was obtained under PMI with a mean power of 4.5 W in only 52 min, but 103 min was needed under a conventional heating process (CH) to reach a 8.3% conversion under identical conditions. At different [MMA]₀/[AIBN]₀ molar ratios, the apparent rate constant of polymerization under PMI was 1.5–2.3 times larger than that under CH. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 3823–3834, 2002