Using cobalt acetate as a catalyst, the controlled/“living” polymerization of MMA was carried out. PMMA with a predicted molecular weight and a low polydispersity was obtained. Using the obtained PMMA as a macroinitiator, a chain extension reaction was carried out. This increased the molecular weight of PMMA from 23 600 to 36 100, in good agreement with the predicted value, and the polydispersity index became lower . This indicated the “living” character of the polymerization. Bulk polymerization of styrene catalyzed by cobalt acetate using the obtained polystyrene as a macroinitiator yielded well‐defined PS‐b‐PMMA.
New perylene‐3,4:9,10‐bis(dicarboximide) (PBI) photoinitiators/photosensitizers derived from perylene‐3,4:9,10‐tetracarboxylic dianhydride are synthesized and investigated for the formation of free radicals under air and under very soft irradiation (i.e., halogen lamp) or laser diode exposure at 532 nm. Such a PBI in combination with a diphenyl iodonium salt and N‐vinylcarbazole or a silane very efficiently promotes the ring‐opening polymerization of epoxides and can also generate acrylate/epoxide interpenetrated polymer networks. It partly behaves as a metal‐free organic photocatalyst operating in an oxidative catalytic cycle. The different chemical intermediates are characterized by ESR and laser flash photolysis experiments. The mechanisms involved in the initiation step are discussed.
Three accessible azobenzene mesogen‐substituted diacetylene monomers (DA1, DA2, and DA3) were synthesized and the effect of the molecular structure on the photopolymerization behavior and self‐assembled structures of the resulting azobenzene‐substituted polydiacetylene (PDA) films had been investigated in detail. The films derived from DA1 were substantially polymerized into blue phase. However, the films derived from DA2 and DA3 were polymerized into red phase directly. The morphology, packing structure, and thermal stability of the resulting azobenzene‐substituted PDA films were characterized in detail by SEM, XRD as well as POM measurements. PDA1 formed micrometer‐sized lamellar crystal structures, while PDA2 and PDA3 both formed spherulitic crystal structures. The strong π–π stacking interaction among side chains was essential for maintaining high stability upon thermal stimulus.
New initiating systems for the thermal cationic polymerization of epoxides and vinyl ether derivatives are proposed. They are based on a silane/silver salt interaction, which ensures a good to excellent polymerization at room temperature. Moreover, the polymerization is much more efficient under air. The effects of the silane, silver salt, and monomer structures are investigated. Interestingly, silver nanoparticles Ag(0) are formed in situ. A coherent picture of the involved chemical mechanisms is presented.
A new 1,2,3‐triazole incorporated diacrylate monomer is designed for free radical cyclopolymerization through the formation of 11‐membered rings. NMR analysis on the cyclopolymers including 1H, 13C, DEPT‐135, and 1H–13C HMQC spectra support a high degree of cyclization. GPC profiles of the obtained cyclopolymers show unimodal distributions indicative of no chain branching reactions.
Organometallic‐mediated radical polymerization (OMRP) has emerged as a powerful new class of living controlled radical polymerization. In order to fulfill its potential in the polymerization of vinyl acetate (VOAc) and other challenging monomers, the effects of ancillary ligands on the metal‐alkyl bond dissociation energy in OMRP reagents must be thoroughly explored. Recent results investigating structure‐activity relationships in well‐defined cobalt, iron and chromium complexes will be discussed. The involvement of radical intermediates in oxidative addition of secondary alkyls for catalytic cross‐coupling reactions catalyzed by first row transition metals will also be examined for relevant design concepts.
Photoinduced CRP of methyl methacrylate initiated by in situ generation of copper (I) complex from higher oxidation state species in methanol was investigated. The polymerizations proceeded in a well‐controlled manner under UV light at room temperature as evidenced by kinetic and chain extension studies. The evolution of molecular weight with conversion showed good correlation between experimental and theoretical molecular weights, which confirmed good control over polymerization and ensured a narrow MWD. The effect of the methanol on the polymerization was also investigated, and a better agreement between experimental and theoretical molecular weights with a quite narrow MWD was obtained by using methanol as solvent.
Kinetic investigations on the cationic ring‐opening polymerization of 2‐ethyl‐2‐oxazoline were conducted using acetyl chloride, acetyl bromide, and acetyl iodide as initiators. Various polymerization temperatures ranging from 80 to 220 °C were applied under microwave irradiation. The resulting polymerization mixtures were characterized with GC and GPC for the determination of monomer conversion and molecular weight distribution, respectively. Well defined polymers with narrow molecular weight distributions ( = 6 000 Dalton, PDI ≈ 1.10) were obtained with all three initiators.
Coatings from blends of cycloaliphatic epoxides and vinyl ethers were cross‐linked by UV‐induced cationic photopolymerization. The conversion of the vinyl double bonds during postcuring was followed by NIR reflection spectroscopy. The effect of various parameters such as the composition of the reactive formulation or the applied radiation dose on the kinetics of the postcuring process was studied. Finally, it was demonstrated on a pilot‐scale curing line that NIR spectroscopy can be used for inline monitoring of the actual conversion in UV‐cured coatings from cationic photopolymers.
The effect of photopolymerization on the structure, stability and encapsulation properties of polydiacetylene micelles containing nitrilotriacetic acid head groups are investigated. Micellar nanostructures of 7–10 nm diameter are identified that are invariant after polymerization. In the micelles, the polymerized ene‐yne chains are much shorter than in planar lipid membranes. SANS confirmed the presence of a monodisperse population of small particles before and after polymerization. It is shown that the CMC decreases manifold after micelle photopolymerization, indicating that it stabilizes the micellar structure. After photopolymerization, these micelles preserved their strong ability to solubilize a hydrophobic pigment, which makes them potentially interesting as drug delivery vehicles.
Nitroxide‐mediated controlled/living radical precipitation polymerization of styrene in supercritical carbon dioxide has been performed using SG1 and AIBN as mediator and initiator, respectively. The equivalent bulk polymerization proceeded at a rate ≈1.58 times faster than the precipitation polymerization. The number of chains increased with conversion to a similar extent in precipitation and bulk systems. A chain transfer mechanism to the Diels‐Alder dimer is used to explain the increase in numbers of chains. High conversions were also achieved for a conventional precipitation polymerization of styrene in scCO2 at 110 °C. The polymer was obtained as a powder, which contained cavities when observed under an SEM.
Commercially available poly(ethylene oxide) macromonomers are successfully used as reactive stabilizers for atom transfer radical dispersion/precipitation polymerization of styrene. Polystyrene particles with PEO chains covalently anchored on the surfaces are obtained. Control over both the particle size and polymer chain growth is achieved using a two‐stage technique consisting of an initial free radical polymerization (FRP) for the nucleation followed by a reverse atom transfer radical polymerization (ATRP) for the controlled polymerization process. The limited monomer conversion at the FRP step ensures that the overall polymerization process is mainly controlled by the reverse ATRP step, resulting in the formation of particles containing well‐defined polymer chains.
Cationic ring‐opening polymerization techniques are very sensitive to nucleophiles, which make it difficult to introduce different functional groups into these polymers. Clickable poly(2‐oxazoline)s were synthesized and functionalization was performed by the copper(I)‐catalyzed 1,3‐dipolar cycloaddition between alkynes and azides. Therefore, an alkyne function is introduced into the polymer backbone by utilizing alkyne toluene‐4‐sulfonates as an initiator. The polymerization kinetics were investigated for four different 2‐substituted‐2‐oxazolines and well‐defined acetylene‐functionalized poly(2‐ethyl‐2‐oxazoline)s with different lengths were synthesized having ≈100% functionality. One of these polymers was used to demonstrate its applicability in the azide‐alkyne click reaction by reaction with different azide compounds.
A method for measuring initiator efficiency in radical polymerization using ESI‐MS is presented. The method is based on the evaluation of relative MS peak intensities of polymer that has been initiated by a mixture of initiators, of which one serves as an internal reference. The method is quickly and easily performed and was found to be reproducible and robust. In polymerization of methyl methacrylate in solution, the efficiency of BTMHP at 80 °C was determined to be fBTMHP = 0.57 ± 0.08, and the efficiency of DBPO at 100 °C was measured to be fDBPO = 0.89 ± 0.08.
The effects of binding ligand variation on the externally initiated Ni catalyzed polymerization of P3HT were investigated using a novel methodology allowing facile screening of ligands. P3HT was synthesized with >80% initiator incorporation for both mono‐ and bidentate phosphine ligands. Variation of the initiating aryl group demonstrated vastly superior results for o‐tolyl over p‐tolyl substituents.
Branched α‐olefin 4‐methyl‐1‐pentene (4MP) is polymerized with a cationic α‐diimine palladium catalyst. The influences of polymerization parameters including reaction temperature and monomer concentration on polymer architecture are evaluated in detail. Increasing temperature and lowering monomer concentration can lead to the formation of more complex branched polyolefin because of chain walking. At 0 °C, complex branched polyolefins are generated from quasi‐living polymerization of 4MP with α‐diimine palladium catalyst.
The generation of thiyl radicals in various multicomponent photosensitive systems based on a ketone, a coumarin or a ketocoumarin and containing a thiol or a disulfide and eventually chloro bis‐imidazole has been studied through laser flash photolysis. A set of more than 70 new interaction rate constants is provided. The measurements of the quantum yields in sulfur radicals and the rate constants of the different processes in many combinations as well as the molecular orbital calculations allow to discuss the driving factors of the involved reactions. This approach should shed some light on the possible explanations of the high performance of some of these combinations when used as photoinitiating systems for radical photopolymerization reactions.
Living free‐radical copolymerization of the inimer 4‐vinylbenzyl N,N‐diethyldithiocarbamate with maleic anhydride in the presence of methyl methacrylate produces highly branched poly(methyl methacrylate) star polymers. Subsequently, mikto‐arm stars can be synthesized by condensation of poly(ethylene glycol methyl ether) monosodium alkoxide with functional maleic anhydride sites in the hyperbranched core. The solution properties of these mikto‐arm star copolymers are discussed.
A new catalyst is reported for atom transfer radical polymerization (ATRP) for the synthesis of copper‐free poly(2‐diethylaminoethyl methacrylate (PDEAEM)‐based pentablock copolymeric biomaterials that have been shown to be effective gene delivery vectors. Biocompatibility is an increasing concern with growing applications for functional polymers with potential applications in drug and gene delivery, because of the residual soluble copper salts used as catalysts. The reported ATRP synthesis method utilizes novel copper(I) oxide nanoparticles as catalysts that can be easily removed after polymerization, with X‐ray spectroscopy (XPS) showing no residual copper in the final product.
A novel conjugated oligomer, oligo(9,9′‐dioctylfluorene‐alt‐bithiophene) (OF8T2), was found to exhibit a unique phase transition between crystalline and liquid‐crystalline states, and a liquid‐crystalline glass was easily generated, offering better TFT device performance. In thin films, upon annealing the OF8T2 molecules oriented preferentially with their planes of conjugation being normal to the substrate, and both film thickness and annealing temperature were critical to the film morphology and the molecular orientation. When the OF8T2 film was deposited on a rubbed polyimide surface and annealed, the molecules aligned their long axes along the rubbing direction.
