bluuebunny/crossref_metadata_2025_split huggingface dataset:
Primary processes in the photosensitized polymerization of cationic monomers
Authors: Manivannan G. , Fouassier J. P. 
Published: April 2003

AbstractA detailed time‐resolved laser spectroscopy investigation has been carried out on the electron transfer reactions of substituted thioxanthone derivatives with diphenyliodonium (Ph‐I+) salts having different metal halide counterions (MX−n). Quenching of thioxanthones' triplet state has been followed under various conditions, by changing the number and nature of substituents on the thioxanthone skeletone, using anion with different nucleophilicity and employing different solvents, namely methanol and acetonitrile. A Photosensitization mechanism is proposed involving an electron transfer from thioxanthone to diphenyliodonium salt. The absorption spectra of the thioxanthone's excited state and the formed new transient are recorded and the rate constants of the excited state processes are measured. The triplet state of thioxanthone derivatives has been quenched by cationically polymerizable monomers and the quantum yield of the major processes has been evaluated. Photolytic experiments have been performed to measure the extent of acid formation. Form photopolymerization experiments using different photoinitiating systems, the rate of polymerization and percentage of monomer conversion have been determined. Both the reactivity in the excited states and the nucleophilicity of the anions affect the efficiency of the photopolymerization reaction.
Preparation of microspheres by radiation‐induced polymerization. I. Mechanism for the formation of monodisperse poly(diethylene glycol dimethacrylate) microspheres
Authors: Naka Y. , Kaetsu I. , Yamamoto Y. , Hayashi K. 
Published: April 2003

AbstractMonodisperse microspheres of poly(diethylene glycol dimethacrylate) with diameters in the size range 0.4–4.8 μm were prepared by the radiation‐induced polymerization. Effects of solvent viscosity and monomer solubility were investigated for various kinds of solvents. The number of the nuclei, produced in the early stage of the polymerization, was found to be constant during the remainder of the polymerization. The nuclei grow to be monodisperse polymer particles without aggregation. This is attributed to the low mobility of the growing polymer particles.
Thermo‐oxidative aging in surface layer of cis‐1,4‐polybutadiene vulcanizates
Authors: Kecheng Gong , Guangji Li , Qiuxiong Hu 
Published: April 2003

AbstractA study of the microstructural changes occurring in the surface layer of cis‐1,4‐polybutadiene (BR) vulcanizates during thermo‐oxidative aging in the temperature range of 120–180°C was carried out by using optical microscope, SEM, MIR–IR, XPS, and swelling. The physical properties, structural changes, and interreaction between rubber and filler (clay) in the surface layer comparing with the center bulk of BR vulcanizates are observed.
Syndiospecific polymerization of styrene. I. Tetrabenzyl titanium/methylaluminoxane catalyst
Authors: Chien James C. W. , Salajka Zdenek 
Published: April 2003

AbstractSyndiospecific polymerization of styrene (S) was catalyzed by Bz4Ti/MAO (tetrabenzyltitanium/methylaluminoxane). The product was separated into syndiotactic polystyrene (s‐PS) and atactic polystyrene (a‐PS) by extraction of the latter with boiling 2‐butanone. Over the broad range of catalyst concentrations, compositions, and polymerization temperatures, the catalytic activity is 150 ± 80kg PS (mol Ti mo S h)−1 with 89 ± 5% yield of s‐PS (SY). The concentration of active species has been determined by radiolabeling. Only about 1.7% of Bz4Ti initiates syndiospecific polymerization at 60°C with values of rate constants for propagation and for chain transfer to MAO of 1.38 (M s)−1 and 5.2 × 10−4s−1, respectively. Nonspecific polymerization was initiated by 16.8% of the Ti having values of 0.056 (M s)−1 and 6.5 × 10−4 s−1 for the rate constants of propagation and transfer, respectively. The effect of solvent polarity on the polymerization was studied using toluene mixed with chlorobenzene of o‐dichlorobenzene as solvents. An increase of effective dielectric constant from 2.43 to 5.92 reduces the polymerization activity by a factor of two and lowers SY to mere 39%. In 1 : 1 toluene/chlorobenzene solvent mixture, it was found that 1.3% and 26% of the Bz4Ti initiate syndiospecific and nonspecific polymerizations of styrene, respectively. The Bz4Ti/MAO catalyst is poor in both productivity and stereoselectivity.
On the main locus of radical formation in emulsion polymerization initiated by oil‐soluble initiators
Authors: Alduncin Juan A. , Forcada Jacqueline , Barandiaran María J. , Asua José M. 
Published: April 2003

AbstractThe effect of the monomer/water ratio on the rate of polymerization per polymer particle in both seeded emulsion polymerizations and miniemulsion polymerizations was used in an attempt to elucidate the main locus of radical formation in emulsion polymerization initiated by an oil‐soluble initiator (AIBN). It was found that, for the rest of conditions constant, the polymerization rate per polymer particle increased when the monomer/water ratio increased, namely when the amount of initiator dissolved in the aqueous phase per polymer particle decreased. This is an evidence against a dominant aqueous phase formation of radicals. On the other hand, these results are consistent with a mechanism in which the radicals are mainly produced in the oil‐phase with significant aqueous phase termination.
Water‐soluble photoinitiators: Primary processes in hydroxy alkyl phenyl ketones
Authors: Fouassier Jean‐Pierre , Burr Dominique , Wieder Fernand 
Published: April 2003

AbstractPhotopolymerization of acrylamide in water has been investigated in the presence of watersoluble hydroxy alkyl phenyl ketones. The processes involved in the excited states (α‐cleavage, electron transfer, monomer quenching) have been studied by time‐resolved laserspectroscopy. Substitution at the para position of the phenyl ring changes drastically the reactivity and influences the possibility of synergistic effects when combining these photoinitiators with thioxanthone derivatives.
Copolymers of pyrrole and bithiophene by oxidative electropolymerization
Authors: Peters Eric M. , Van Dyke John D. 
Published: April 2003

AbstractPyrrole (PY) and 2,2′‐bithiophene (BT) have been electropolymerized at various feed ratios in LiClO4/Propylene carbonate (PC) and the mer ratios in the copolymer determined by N and S. microanalysis. A strong correlation was observed between the copolymer compositions and the monomer feed ratios using the copolymer equation, and reactivity ratios were determined by a nonlinear error‐in‐variables approach. Although PY predominates in these copolymers, the proportion of BT increases with increasing applied potential. It is shown that reactivity ratios do not have to be understood in the traditional sense, but may be simply a measure of the relative ease of oxidation of the monomers at the electrode.
Optically active polymers containing side‐chain photochromic moieties. Synthesis and chiroptical properties of copolymers of trans‐N(4‐azobenzene)‐maleimide with (−)‐menthyl vinyl ether and (+)(S)‐2‐methylbutyl vinyl ether
Authors: Angiolini Luigi , Carlini Carlo 
Published: April 2003

AbstractThe copolymers of trans‐N(4‐azobenzene)‐maleimide (ABM) with optically active alkyl vinyl ethers, such as (−)‐menthyl vinyl ether (MtVE) and (+)S‐2‐methylbutyl vinyl ether (MBVE), have been prepared either by direct copolymerization or by functionalization with trans‐4‐amino‐azobenzene of the corresponding alternating copolymers of maleic anhydride with MtVE and MBVE. The chiroptical properties of the above copolymers have been studied by CD measurements. The induced optical activity on the side‐chain trans‐azobenzene moieties is discussed in terms of different conformational rigidity of the macromolecules.
Copolymerization of styrene oxide and cyclohexene oxide
Authors: Pasika W. M. , Chen Dian Jia 
Published: April 2003

AbstractStyrene oxide (SO) (phenyl oxirane) and 1,2‐cyclohexene oxide (CO) (7‐oxa bicyclo[410] heptane) have been copolymerized neat with the aid of the carbocation salt triphenylmethyl hexachloroantimonate (Ph3CSbCl6) (HC) at 0, 30, and 56°C. NMR spectra of the polymeric products before and after extraction with acetone indicated that the copolymerization products were copolymers and not mixtures of the respective homopolymers. Both, the Kelen‐Tüdos and Fineman‐Ross methods for the determination of the monomer reactivity ratios yielded identical results. These were: 0°C: r1 (CO) = 4.34, r2(SO) = 0.34; 30°C, r1(CO) = 4.19, r2(SO) = 0.42; 56°C, r2(CO) = 3.94, r2(SO) = 0.46.
Polyimides containing carbonyl and ether connecting groups. III
Authors: Hergenrother P. M. , Beltz M. W. , Havens S. J. 
Published: April 2003

AbstractSeveral new polyimides were prepared from the reaction of three aromatic dianhydrides with two new methyl substituted aromatic diamines containing carbonyl and ether connecting groups between the aromatic rings. The diamines were prepared from the reactions of 3‐methyl‐4‐aminophenol and 3,5‐dimethyl‐4‐aminophenol with 1,3‐bis(4‐fluorobenzoyl) benzene in the presence of potassium carbonate. The 300°C cured polyimides containing methyl substituents were shown to be armorphous by wide angle X‐ray diffraction and exhibited glass transition temperatures between 231–281°C. The properties of these new polyimides containing methyl substituents were compared with polymides of the same chemical structure but without methyl substituents.
Kinetic studies on light‐induced cationic ring‐opening reactions on 2,3‐epoxypropyl phenyl ether
Authors: Rajendran Arolickal G. , Timpe Hans‐Joachim 
Published: April 2003

AbstractLight‐induced cationic ring‐opening reactions of 2,3‐epoxypropyl phenyl ether (phenyl glycidyl ether, PGE) in acetone, methanol and bulk were studied. Cations are produced by electron transfer from excited sensitizers (anthracene, An; 9,10‐phenanthrenequinone, PQ; benzophenone, BP) or from photolytically cleaved sensitizer (benzoin isoproyl ether, BIPE) to diphenyliodonium hexafluorophosphate. With excess of acetone and methanol, addition reactions take place resulting in 2,2‐dimethyl‐4‐phenoxymethyl‐1,3‐dioxolane and 1‐methoxy‐3‐phenoxy propan‐2‐ol as main products. The efficiency of the sensitizers taken from the quantum yields of PGE conversion, follows the order An ≫ BIPE > PQ > BP in acetone and An ∼ BP > BIPE ≫ PQ in methanol. Unlike bulk polymerization, in these addition reactions no steady‐state concentration of cations exists and the reaction accelerates with time. When alcohol is added in only small proportions, the initial addition reactions goes over into a linear oligomerization. The relatively higher basicity of methanol over PGE influences the nature of the active center, and the course of reaction depends on methanol concentration. Kinetic expressions, which account for all possible types of active centers, have been derived to express the rate of PGE reactions in methanol.
Thermally induced cationic polymerization of divinyl ethers using iodonium and sulfonium salts
Authors: Sundell Per‐Erik , Jönsson Sonny , Hult Anders 
Published: April 2003

AbstractCationic polymerization of diethyleneglycoldivinyl ether was thermally induced by diphenyliodonium, alkylbenzylsulfonium, and phenacyltetramethylenesulfonium salts. The reactivity was enhanced by using free radical sources in combination with diphenyliodonium or phenacyltetramethylenesulfonium salts. Even at low onium salt concentrations extremely reactive formulations could be obtained, e.g., the polymerization was complete within 1 minute at 100°C when using the most reactive salts. Polymerizations were induced at temperatures ranging from 50 to 180°C. The Counterion, Supplied by the onium salts, strongly influenced the appearance of the resulting crosslinked polymer: salts containing SbF−6 usually gave highly discolored samples due to the large heat evolution during polymerization whereas polymerization with PF−6 proceeded smoother resulting in transparent, uncolored polymers. The purity of the monomer greatly affected the initiation by the diphenyliodonium and phenacyltetramethylenesulfonium salts. Adventitious radical sources, e. g., hydroperoxides on oxidized monomer, lowered the activation temperature but also led to poor storage stability of these formulations.
Semicontinuous emulsion copolymerization of methyl methacrylate and ethyl acrylate
Authors: Arzamendi Gurutze , Leiza José R. , Asua José M. 
Published: April 2003

AbstractThe monomer addition policies required to produce homogeneous methyl methacrylateethyl acrylate copolymers of different compositions were determined by means of a semiempirical approach. This approach is useful for systems about which only a limited information is available. Applying this method only three reactions were needed to obtain homogeneous copolymers in a minimum process time. Comparisons were made between the results obtained using this monomer addition strategy and those from copolymerizations carried out under the classical starved conditions.
Initiation and termination mechanisms in kinetic gelation simulations
Authors: Bowman Christopher N. , Peppas Nikolaos A. 
Published: April 2003

AbstractA kinetic gelation simulation is presented which includes a distinct initiator species decaying exponentially with time such that the rate of initiation varies as in an actual polymerization. The effects of the initiator quantity and the initiator decay constant on the polymerization are shown along with the effect of varying the probability that two radicals on adjacent sites will terminate. Varying the initiation rate and termination probability are examined in order to determine their influence on the trapping of radicals, the relative reactivity of pendant functional groups, and the overall structure of the polymer. In general it appears that the incorporation of an initiator enables the simulation to more adequartely describe the polymerization reaction, particularly time‐dependent phenomena such as rate of reaction and radical concentrations.
Olefin copolymerization with metallocene catalysts. II. Kinetics, cocatalyst, and additives
Authors: Chien James C. W. , He Dawei 
Published: April 2003

AbstractThe kinetics of ethylene/propylene copolymerization catalyzed by (ethylene bis (indeyl)‐ZrCI2/methylaluminoxane) has been investigated. Radiolabeling found about 80% of the Zr to be catalytically active. The estimates for rate constants at 50°C are k11 = 1104 (Ms)−1, k12 = 430 (Ms)−1, k22 = 396 (Ms)−1,k21 = 1020 (Ms)−1, and kAtr,1 + kAtr.2 = 1.9 × 10−3 s−1. Substitution of trimethylaluminum for methylaluminoxane resulted in proportionate decrease in polymerization rate. The molecular weight of the copolymer is slightly increased by loweing the [Al]/[Zr] ratio, or addition of Lewis base modifier but at the expense of lowered catalytic activity and increase in ethylene content in the copolymer. Lowering of the polymerization temperature to 0°C resulted in a doubling of molecular weight but suffered 10‐fold reduction in polymerization activity and increase of ethylene in copolymer.
Olefin copolymerization with metallocene catalysts. III. Supported metallocene/methylaluminoxane catalyst for olefin copolymerization
Authors: Chien James C. W. , He Dawei 
Published: April 2003

AbstractSupported catalyst for fluidized bed polymerization processes has been prepared by reacting macroporous SiO2 first with MAO (methylaluminoxane) and then with Et [Ind]2ZrCl2. It contains 0.60 wt % of Zr and an [Al]/[Zr] ratio of 50. This catalyst produces homogeneous E/P (ethylene/propylene) copolymers with truly random copolymerization behaviors and required to achieve the same copolymerization activity for the Et[Ind]2ZrCl2/MAO would be required a total [Al]/[Zr] of only 670. Several time larger amount of MAO would be required to achieve the same copolymerization activity for the Et [Ind]2ZrCl2/MAO catalyst in solution. This random copolymerization is independent of catalyst concentration and composition. Activation of the supported catalyst with i‐butylaluminoxane, tri‐i‐butylaluminum, or trimethylaluminum resulted in lower activity and copolymers having high ethylene content and crystallinity.
Molecular engineering of liquid crystal polymers by living polymerization. XI. Synthesis and characterization of poly{ 11‐[(4‐cyano‐4′‐trans‐α‐cyanostilbene) oxy] undecanyl vinyl ether}
Authors: Percec Virgil , Gomes Ailton De Souza , Lee Myongsoo 
Published: April 2003

AbstractA convenient method for the synthesis of 11‐[(4‐cyano‐4′‐ trans‐α‐cyanostilbene) oxy]‐ undecanyl vinyl ether (6) which is the first member of a new class of mesogenic monomers is described. The polymerization of 6 initiated with CF3SO3H/S (CH3)2 in methylene chloride at 0°C proceeds through a living cationic mechanism leading to polymers with controllable molecular weights and polydispersities narrower than 1.10. The mesomorphic behavior of both 6 and poly(6)s with various molecular weights was determined by using a combination of thermal optical polarized microscopy and differential scanning calorimetry. 6 is only crystalline. Poly(6)s with degrees of polymerization from 4 to 30 exhibit an enatiotropic smectic A mesophase and side chain crystallization.
Silicone polycarbonates from new aryl‐terminated siloxane precursors
Authors: McDermott Philip J. , Krafft Terry E. , Rich Jonathan D. 
Published: April 2003

AbstractSeveral synthetic routes to silicon polycarbonate copolymers utilizing aryl‐terminated siloxanes have been examined. Anhydride capped siloxanes with varying polydimethylsiloxane units were prepared by the acid equilibration of 1,3‐bis(4,4′‐phthalicanhydride)tetramethyldisiloxane. These siloxanes were then imidized with aminophenol to the corresponding phenol capped siloxane. Reaction of these materials with 4,4′‐isopropylidenediphenol (BPA) and phosgene (interfacially and non‐interfacially) produced silicone polycarbonate copolymers. Similar copolymers were obtained by reaction with bis‐chloroformate derivatives of 4,4′‐isopropylidenediphenol (monomer and oligomers). The different synthetic routes significantly affect the thermal and mechanical properties as well as the composition of the new polymers. Materials synthesized by the bis‐chloroformate route exhibit good hydrolytic and melt stabilities. Those made interfacially underwent phase separation in the melt.
Synthesis of substituted polymethylenes by radical polymerization of N,N,N′,N′‐tetraalkylfumaramides and their characterization
Authors: Matsumoto Akikazu , Fukushima Katsuhiko , Otsu Takayuki 
Published: April 2003

AbstractRadical polymerization of N,N,N′,N′‐tetraalkylfumaramides (TRFAm) bearing methyl, ethyl, n‐propyl, isopropyl, and isobutyl groups as N‐substituents (TMFAm, TEFAm, TnPFAm, TIPFAm, and TIBFAm, respectively) was investigated. In the polymerization of TEFAm initiated with 1,1′‐azobiscyclohexane‐1‐carbonitrile (ACN) in benzene, the polymerization rate (Rp) was expressed as follows: Rp = k [ACN]0.28 [TEFAm]1.26, and the overall activation energy was 102.1 kJ/mol. The introduction of a bulky alkyl group into N‐substituent of TRFAm decreased the Rp in the following order: TMFAm > TEFAm > TnPFAm > TIBFAm > TIPFAm ∼ 0. The relative reactivities of these monomers were also investigated in radical copolymerization with styrene (St) and methyl methacrylate (MMA). In copolymerization of TRFAm (M2) with St (M1), monomer reactivity ratios were determined to be r1 = 1.07 and r2 = 0.20 for St–TMFAm, and r1 = 1.88 and r2 = 0.11 for St–TEFAm, from which Q2 and e2 values were estimated to be 0.35 and 0.44 for TMFAm, and 0.19 and 0.47 for TEFAm, respectively. The other TRFAm were also copolymerized with St, but copolymerization with MMA gave polymers containing a small amount of TRFAm units. The polymer from TRFAm consists of a less‐flexible poly(N,N‐dialkylaminocarbonylmethylene) structure. The solubility and thermal property of the polymers were also investigated.
Preparation of ultrathin films of aromatic polymides by vapor deposition polymerization from N‐silylated aromatic diamines or aromatic tetracarboxylic dithioanhydride
Authors: Iijima Masayuki , Takahashi Yoshikazu , Oishi Yoshiyuki , Kakimoto Masa‐Aki , Imai Yoshio 
Published: April 2003

AbstractA novel method for the preparation of ultrathin films of aromatic polyimides was developed through vapor deposition polymerization from combinations of monomer pairs of either N,N′‐bis (trimethylsilyl)‐substituted aromatic diamines and pyromellitic dianhydride or aromatic diamines and pyromellitic dithioanhydride. Both diamine component and tetracarboxylic dianhydride component were evaporated simultaneously at a stoichiometric molar ratio under vacuum, giving a deposited film on a substrate, which consisted of a polyamic acid derivative formed by the ring‐opening polyaddition. The deposit was then converted to polyimide by thermal imidization at a relatively lower temperature, compared with a conventional method using the parent diamine and tetracarboxylic dianhydride. The properties of polyimide ultrathin films such as thermal stability, chemical resistance, and dielectric behavior were almost the same as those of the polyimide films prepared by a conventional method.
Synthesis and characterization of SPUU–PEO–heparin graft copolymers
Authors: Park Ki Dong , Piao Al Zhi , Jacobs Harvey , Okano Teruo , Kim Sung Wan 
Published: April 2003

AbstractA new synthetic approach for the preparation of segmented polyurethaneurea (SPUU)–PEO–Heparin graft copolymers (B–PEO–Hep) has been developed. The procedure involved the coupling of hexamethylene diisocyanate (HMDI) to soluble Biomer® (B) through an allophanate/biuret reaction. The free isocyanate (NCO) groups attached to Biomer® were then coupled to PEO terminal hydroxyl groups to form PEO grafted Biomer® (B–PEO). B–PEO free hydroxy groups were modified with HMDI to introduce terminal isocyanate groups. The NCO functionalized B–PEO was then coupled to heparin (Hep) functional groups (OH, NH2) producing B–PEO–Hep graft copolymer. Synthetic intermediates were confirmed by FTIR, NCO group determination, and toluidine blue heparin assay. Physical characterization techniques, such as contact angle measurements, water swelling, light scattering measurements, and DSC thermal analysis, detailed properties of the graft copolymer containing covalently bound heparin. This new heparinized copolymer can be applied as a coating on other existing blood contacting surfaces without changing bulk properties. The heparin bioactivity observed attests to the usefulness of this new procedure as a coating to improve the blood compatibility of blood‐contacting surfaces.