Radical–radical coupling of polystyrene chains using AGET ATRC

Activators generated by electron transfer (AGET) was integrated into atom transfer radical coupling (ATRC) systems to drastically reduce the amount of copper catalyst required to achieve dimerization of monohalogenated polystyrene (PStX) precursors. PStCl or PStBr, prepared by ATRP, were activated and coupled in ATRC systems with varying equivalents of the reducing agent tin(II) ethyl hexanoate (Sn(EH)₂) with ligand‐bound copper(I) and/or copper(II) present. Effective coupling was only observed in PStBr systems, with total copper content in the reaction mixture able to be reduced into the range of 10–25% of what is typically reported in traditional ATRC reactions of PSt while maintaining coupling yields of >50%. Additional reducing agents, glucose and ascorbic acid, were also studied and were found to be even more effective in some AGET ATRC reactions compared with Sn(EH)₂. Best results were achieved with ascorbic acid as the reducing agent (>80% coupled product) with total copper content 25% of what was used for a traditional ATRC. Using an activators regenerated by electron transfer ATRP–AGET ATRC sequence resulted in an overall reduction of total copper down to 0.1–0.25% for the overall reaction sequence (compared with a traditional ATRP–ATRC sequence). © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2010     

Novel diblock copolymer‐grafted multiwalled carbon nanotubes via a combination of living and controlled/living surface polymerizations

Diels–Alder cycloaddition reactions were used to functionalize multiwalled carbon nanotubes (MWNTs) with 1‐benzocylcobutene‐1′‐phenylethylene (BCB‐PE) or 4‐hydroxyethylbenzocyclobutene (BCB‐EO). The covalent functionalization of the nanotubes with these initiator precursors was verified by FTIR and thermogravimetric analysis (TGA). After appropriate transformations/additions, the functionalized MWNTs were used for surface initiated anionic and ring opening polymerizations of ethylene oxide and ε‐caprolactone (ε‐CL), respectively. The OH‐end groups were transformed to isopropylbromide groups by reaction with 2‐bromoisobutyryl bromide, for subsequent atom transfer radical polymerization of styrene or 2‐dimethylaminoethyl methacrylate to afford the final diblock copolymers. ¹H NMR, differential scanning calorimetry (DSC), TGA, and transmission electron microscopy (TEM) were used for the characterization of the nanocomposite materials. TEM images showed the presence of a polymer layer around the MWNTs as well as the dissociation of MWNT bundles. Consequently, this general methodology, employing combinations of different polymerization techniques, increases the diversity of diblocks that can be grafted from MWNTs. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 1104–1112, 2010     

Photoinitiated alternating copolymerization of dialkyl maleates and fumarates with vinyl ethers

A systematic study of the free radical photoinitiated alternating crosslinking copolymerizations of dialkyl maleates and furmarates with multifunctional vinyl ethers was carried out. The photocopolymerizations were fast and highly efficient when carried out using a variety of α‐cleavage photoinitiators. The effects of the structures of the both the unsaturated esters and the vinyl ether monomers were examined. Dialkyl maleates were observed to be more reactive than the corresponding fumarate esters. The photopolymerization rates of several of these comonomer pairs were compared with standard diacrylate and dimethacrylate monomers. A range of different physical properties can be obtained by varying the length of the alkyl chain on alcohol portion of the unsaturated ester monomer. Prospects for the use of these comonomer systems in UV curable coatings, adhesives, printing inks, and composites are discussed. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2010     

Synthesis of main chain polymeric benzophenone photoinitiator via thiol‐ene click chemistry and Its use in free radical polymerization

Main chain polymeric benzophenone photoinitiator (PBP) was synthesized by using “Thiol‐ene Click Chemistry” and characterized with ¹H NMR, FTIR, UV, and phosphorescence spectroscopies. PBP as a polymeric photoinitiator presented excellent absorption properties (ε₂₉₄ = 28,300 mol^?1L^?1cm^?1) compared to the molecular initiator BP (ε₂₅₂ = 16,600 mol^?1L^?1cm^?1). The triplet energy of PBP was obtained from the phosphorescence measurement in 2‐methyl tetrahydrofurane at 77 K as 298.3 kJ/mol and according to phosphorescence lifetime, the lowest triplet state of PBP has an n‐π* nature. Triplet–triplet absorption spectrum of PBP at 550 nm following laser excitation (355 nm) were recorded and triplet lifetime of PBP was found as 250 ns. The photoinitiation efficiency of PBP was determined for the polymerization of Hexanedioldiacrylate (HDDA) with PBP and BP in the presence of a coinitiator namely, N‐methyldiethanolamine (MDEA) by Photo‐DSC. The initiation efficiency of PBP for polymerization of HDDA is much higher than for the formulation consisting of BP. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2010     

Oxygen‐sensing properties of 5,10,15,20‐tetraphenylporphinato platinum(II) and palladium(II) covalently bound on poly(isobutyl‐co‐2,2,2‐trifluoroethyl methacrylate)

A novel methacrylate monomer bearing 5,10,15,20‐tetraphenylporphyrinato palladium(II) (PdTPP) (monomer 1a ) was synthesized and copolymerized with isobutyl methacrylate (IBM) and 2,2,2‐trifluoroethyl methacrylate (TFEM) to give poly (IBM‐co‐TFEM) bearing PdTPP (copolymer 2a ) as a dye‐conjugated oxygen‐permeable polymer for pressure‐sensitive paint applications. The introduction of PdTPP into copolymer 2a was confirmed by UV–vis spectroscopy and extended X‐ray absorption fine structure analysis. The Stern–Volmer plots of the copolymer 2a and a mixture of PdTPP and poly(IBM‐co‐TFEM) both showed downward curvature, unlike that of the platinum complex analogue (copolymer 2b ) previously reported. The plots were successfully fitted with a two‐site model to give two distinct Stern–Volmer constants (K_SV1 and K_SV2) and the partition ratio f₁. Interestingly, the f₁ values for the copolymer 2a were almost constant at about 0.98, whereas those of the mixture of PdTPP and poly(IBM‐co‐TFEM) increased from 0.889 to 0.967 as the temperature was increased. This finding suggests that there are two distinct microheterogeneities, one temperature‐dependent and the other temperature‐independent, in the mixture of PdTPP and poly(IBM‐co‐TFEM). The dye‐conjugation approach effectively eliminates the temperature‐dependent, but not the temperature‐independent microheterogeneity. The luminescence decays of copolymers 2a and 2b and the corresponding mixtures in the absence of oxygen indicated that the temperature‐dependent microheterogeneity involves an oxygen diffusion process, whereas the temperature‐independent one appears to be inherent nature in PdTPP. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 663–670, 2010     

Application of copper sulfate pentahydrate as an ammonia removal reagent for the determination of trace impurities in ammonia by gas chromatography

Rapid analysis of trace permanent gas impurities in high purity ammonia gas for the microelectronics industry is described, using a gas chromatograph equipped with a phtoionization detector. Our system incorporates a reactive precolumn in combination with the analytical column to remove the ammonia matrix peak that otherwise would complicate the measurements due to baseline fluctuations and loss of analytes. The performance of 21 precolumn candidate materials was evaluated. Copper sulfate pentahydrate (CuSO₄·5H₂O) was shown to selectively react with ammonia at room temperature and atmospheric column pressures, without affecting the hydrogen, oxygen, nitrogen, methane or carbon monoxide peak areas. To prevent loss of trace carbon dioxide, an additional boron trioxide reactant layer was inserted above the copper sulfate pentahydrate bed in the reactive precolumn. Using the combined materials, calibration curves for carbon dioxide proved to be equivalent in both ammonia and helium matrix gases. These curves were equivalent in both matrix gases. The quantitative performance of the system was also evaluated. Peak repeatabilities, based on eight injections, were in the range of 4.1–8.2% relative standard deviation; and detection limits were 6.9 ppb for H₂, 1.8 ppb for O₂, 1.6 ppb for N₂, 6.4 ppb for CH₄, 13 ppb for CO, and 5.4 ppb for CO₂.     

Synthesis of statistical and block copolymers containing adamantyl and norbornyl moieties by reversible addition‐fragmentation chain transfer polymerization

The synthesis of statistical and block copolymers, consisting of monomers often used as resist materials in photolithography, using reversible addition‐fragmentation chain transfer (RAFT) polymerization is reported. Methacrylate and acrylate monomers with norbornyl and adamantyl moieties were polymerized using both dithioester and trithiocarbonate RAFT agents. Block copolymers containing such monomers were made with poly(methyl acrylate) and polystyrene macro‐RAFT agents. In addition to have the ability to control molecular weight, polydispersity, and allow block copolymer formation, the polymers made via RAFT polymerization required end‐group removal to avoid complications during the photolithography. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 943–951, 2010     

Synthesis of NMP/RAFT inifers and preparation of block copolymers

Two different initiator/transfer agents (inifers) containing an alkoxyamine and a dithiobenzoate were synthetized and used to trigger out either reversible addition‐fragmentation chain transfer (RAFT) polymerization or nitroxide‐mediated polymerization (NMP). α‐Dithiobenzoate‐ω‐alkoxyamine‐difunctional polymers were produced in both cases which were subsequently used as precursors in the formation of block copolymers. This synthetic approach was applied to N‐isopropylacrylamide (NIPAM) or polyethylene oxide methacrylate (EOMA) to form α,ω‐heterodifunctional homopolymers via RAFT at 60°C which were chain extended with styrene by activating the alkoxyamine moiety at 120°C. Under such temperature conditions, it is proposed that a tandem NMP/RAFT polymerization is initiated producing a simultaneous growth of polystyrene blocks at both chain‐ends. Self‐assembled nanostructures of these amphiphilic block copolymers were evidenced by scanning electron microscopy. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012