bluuebunny/crossref_metadata_2025 huggingface dataset:
A multitechnique surface analytical study of a segmented block copolymer poly(ether‐urethane) modified through an H2O radio frequency glow discharge
Authors: Vargo Terrence G. , Hook Daniel J. , Gardella Joseph A. , Eberhardt Mary A. , Meyer Anne E. , Baier Robert E.
Published: April 2003

Recent work in our laboratories has fully characterized the surface region of a segmented poly(ether‐urethane) (PEU) extending from the air/polymer interfacial region through bulk depths in the micron range. This characterization utilized energy and angle dependent Electron Spectroscopy for Chemical Analysis (ESCA), Attenuated Total Reflectance–Fourier Transform Infrared Spectroscopy (ATR–FTIR), and Comprehensive Wettability Profiling (contact angle using a homologous series of liquids) as defined by Zisman. In this study this same multi‐analytical‐technique approach is used to elucidate changes in these PEU surfaces induced through an H2O Radio Frequency Glow Discharge (RFGD) plasma. This investigation reports both qualitative and quantitative changes due to the modification treatments as well as the permanency of the changes effected on these surfaces through the plasma treatment. From our analyses, the amount of surface residing polyurethane (hard segment) is observed to increase due to a proposed plasma etching mechanism. Further, the addition of oxygen containing functionality is detected at the modified surfaces unique with respect to the unmodified PEU. These surface modifications which show large increases in wettability, are finally observed to be semi‐permanent over a time period of 6 months.
Catalytic epoxidation of polyisobutylene‐co‐isoprene with hydrogen peroxide
Authors: Jian Xigao , Hay Allan S.
Published: April 2003

Polyisobutylene‐co‐isoprene (PIBI) can be epoxidized with hydrogen peroxide in the presence of methyltrioctylammonium tetrakis (diperoxotungsto) phosphate(3‐) as the catalyst in a biphasic system. The effects of the reaction time and temperature, the ratio of the organic phase to the aqueous phase, the concentration of the catalyst and polymer and stirring intensity, respectively, are studied on the conversion of double bonds to oxirane groups. 1H‐NMR analysis confirms the absence of ring opening side reactions in this epoxidation reaction system. The kinetics of the reaction are discussed. The rate constants are measured at four temperatures and the activation energy for the reaction is determined as 54.2kJ/mol. The optimum reaction temperature is about 60°C.
Polyepichlorohydrin diols free of cyclics: Synthesis and characterization
Authors: Biedron Tadeusz , Kubisa Przemyslaw , Penczek Stanislaw
Published: April 2003

Polymerization of epichlorohydrin (ECH) in the presence of diols, catalyzed by Lewis or protic acids, proceeds by activated monomer mechanism (AMM), i.e., by subsequent additions of protonated monomer molecules to the terminal hydroxyl groups of the growing chain. As opposed to the typical active chain end mechanism, side reactions, including cyclization, are strongly suppressed in the polymerization by AMM and well‐defined linear product are obtained. It follows from kinetic considerations, that in order to achieve the high contribution of AMM, the reaction should be carried out at low instantaneous concentration of monomer, and this can be accomplished by slowly adding ECH to the reaction mixture. Using this approach, polyepichlorophydrin diols have been prepared in the M̄n ∼ 2500 products with DPn = [M]0/[I]0 can be obtained practically free of cyclic by‐products with the yields approaching quantitative. Polyepichlorohydrin diols obtained by AM polymerization are strictly bifunctional, regular head‐to‐tail polymers containing mainly (≥ 95%) secondary hydroxyl and groups.
Chemical modification of polymers: Catalytic hydroformylation and hydroxymethylation of styrene–butadiene copolymers
Authors: Sibtain F. , Rempel G. L.
Published: April 2003

Styrene‐butadiene (SB) copolymers can be readily hydroformylated to various degrees of conversion under mild conditions with HRh(CO) (PHh3)3 as the catalyst. Utilization of a novel automated gas consumption apparatus allows fairly reliable control of the degree of formyl loading and the preparation of infrared calibration curves for various SB‐copolymers. In a subsequent reaction, also under homogeneous conditions, the hydroformylated SB‐copolymers can be hydrogenated with HRuCI (CO) (PPh3)3 to give overall hydroxymethylated polymers. The transformations were characterized by infrared, 13C‐, and 1H‐NMR spectroscopy.
Synthesis of poly(dimethylsiloxane) oligomers with pendant amine groups via co‐equilibration anionic polymerization reactions
Authors: Spinu M. , McGrath J. E.
Published: April 2003

The present study describes a method of incorporating amine functional groups on poly(dimethylsiloxane) chains as pendant groups on silicon atoms. This method allows for independent control of the molecular weight and the amine content of the oligomer. The new molecular design was achieved by co‐equilibration of the cyclic tetramer octamethylcyclotetrasiloxane (D4) with a new cyclic siloxane monomer containing aliphatic amine substituents on the silicon atoms. The co‐equilibration of the two cyclic siloxanes was carried out in the presence of a silanolate catalyst, using the nonfunctionalized hexamethyldisiloxane as the end‐capper. The distribution of the molecular species at thermodynamic equilibrium and the efficiency of incorporation of siloxane units containing pendant amine functionalities into the poly(dimethylsiloxane) chains were investigated as a function of oligomer chemical composition and molecular weight.
Photochemical property of the polymer‐bearing pendant norbornadiene moiety and storage stability of the resulting quadricyclane group in the polymer
Authors: Nishikubo Tadatomi , Hijikata Chikara , Iizawa Takashi
Published: April 2003

A polymer bearing pendant norbornadiene (NBD) moieties and a low molecular weight model compound ([2‐carbobenzyloxy‐3‐phenyl‐2,5‐norbornadiene CBPNB)], were synthesized by substitution reaction of poly(p‐chloromethylstyrene) and benzyl chloride, respectively, with the potassium salt of 3‐phenyl‐2,5‐norbornadiene‐2‐carboxylic acid. Photochemical valence isomerization and storage stabilities of the resulting polymer having corresponding pendant quadricyclane (QC) groups and the low molecular weight QC compound were investigated in dichloromethane solution. It was found that the rate of photochemical valence isomerization of the pendant NBD moiety in the polymer was the same as or slightly higher than that of CBPNB, and the storage stability of the QC group in the polymer was higher than that of the QC compound resulting from CBPNB in the solution. The photochemical reaction of the pendant NBD moiety within the polymer without catalyst proceeded quantitatively in the film state. However, the photochemical reaction of the polymer films blended with 5,10,15,20‐tetraphenyl‐21H,23H‐porphine cobalt (II) catalyst (Co‐TPP) did not proceed quantitatively, and the degree of conversion of the pendant NBD moiety in the polymer decreased with increasing amounts of Co‐TPP in the film. The QC group produced in the polymer by photo‐irradiation had excellent storage stability in the film state without Co‐TPP. On the other hand, the QC group in the polymer films blended with Co‐TPP Catalyst reverted gradually to the NBD group at room temperature.
Photooxidation of ABS of long‐wavelengths
Authors: Jouan Xavier , Gardette Jean‐Luc
Published: April 2003

The evolution of the photochemical degradation of ABS has been studied in conditions of long wavelength irradiation (λ's> 300 nm). The main photoproducts involved in the oxidative evolution have been identified by using FTIR spectroscopy and chemical titrations. A particular attention has been devoted to α–β unsaturated ketones that appear as secondary photoproducts. Those ketones present a low photochemical stability when exposed in the range 300–400 nm. Conditions for their formation have been experimentally studied. Formation of oxidation photoproducts has been also studied at the macroscopic level and it has been shown that their repartition in the polymer is heterogeneous. The origins of the heterogenities have been studied.
A microcomputer program for estimation of copolymerization reactivity ratios
Authors: Dube M. , Sanayei R. Amin , Penlidis A. , O'Driscoll K. F. , Reilly P. M.
Published: April 2003

A user‐friendly program has been developed to estimate copolymerization reactivity ratios based on a nonlinear minimization algorithm. The use of an optimal experimental design for copolymerization when the Mayo–Lewis model applies is presented. The applicability of the program is demonstrated using actual and simulated experimental data.
Photodegradation of UV‐cured coatings II. Polyurethane–acrylate networks
Authors: Decker C. , Moussa K. , Bendaikha T.
Published: April 2003

Highly crosslinked aliphatic and aromatic polyurethane‐acrylate (PUA) coatings have been obtained by photopolymerization of multifunctional monomers. The discoloration and chemical modifications occurring upon accelerated QUV aging were monitored by UV and IR spectroscopy. The polymers were found to undergo photooxidation and loss of carbamate and phenyl groups, with lower quantum yields (10−3 mol photon−1) than in related linear polymers. Hydroxy‐phenyl benzotriazole UV‐absorbers have a limited effect on the degradation rate, at the concentration used (0.5%). Hindered amines (HALS) are substantially more effective, especially in aliphatic PUA. A 20‐fold increase in the stabilization efficiency was found with the UVA + HALS combination. Aromatic PUA are more difficult to stabilize, because of the strong absorption and photolysis of the phenyl group which yields colored products. Radical‐induced oxidation is predominant in aliphatic PUA and develops with long kinetic chains, while in aromatic PUA it competes with direct photolysis.
A comparative study on the structural changes in leucoemeraldine and emeraldine base upon doping by perchlorate
Authors: Neoh K. G. , Kang E. T. , Tan K. L.
Published: April 2003

The changes in the structure of leucoemeraldine (LM) and emeraldine (EM) base upon doping by perchlorate anions are studied by X‐ray photoelectron spectroscopy (XPS) and infrared (IR) absorption spectroscopy. In the case of LM, interactions of the amine nitrogens with the perchlorate anions result in a nitrogenonium ion structure analogous to that arising from the protonation of imine nitrogens in EM by HCl except the chloride anion in the latter has been replaced by the perchlorate anion. A small amount of partially ionic and covalent chlorine is also incorporated in the LM–perchlorate complexes. The maximum electrical conductivity that is achieved in these complexes is about 4 S/cm. In contrast, the maximum conductivity of the EM–perchlorate complexes is three orders of magnitude lower. The interactions of perchlorate anions with EM base result in the preferential disappearance of the imine units over the amine units.
Synthesis of aromatic polythers by Scholl reaction. IV. Homopolymerization and copolymerization of α,ω‐bis[4‐(1‐napthoxy)phenylsulfonyl]perfluoroalkanes
Authors: Percec Virgil , Wang James H. , Oishi Yoshi , Feiring Andrew E.
Published: April 2003

Polyether sulfones containing perfluoroalkyl segments were prepared by room temperature radical‐cation polymerization (Scholl reaction) of 1,4‐bis[4‐(1‐napthoxy)phenylsulfonyl]perfluorobutane (1a) and 1,8‐bis [4‐(1‐napthoxy) phenylsulfonyl] perfluoroctane (1b) in nitrobenzene, using anhydrous ferric chloride as oxident. The homopolymerization of 1a and of 1b performed under various polymerization conditions, resulted in polymers with number average molecular weight (M̄n) up to 33,000 and 38,000 g/mol, respectively. Copolymerization of the fluorinated monomers 1a with 1b, and either 1a or 1b with 4,4′‐bis(1‐naphthoxy) diphenyl sulfone (4) and 1,5‐bis (1‐naphthoxy) pentane (5) produced copolymers of M̄n up to 18,100 g/mol. The reactivity of the various monomers was discussed on the basis of the induction and resonance stabilization effects.
Liquid crystalline properties of a series of thermotropic copolyesters containing both mesogenic and nonmesogenic units
Authors: Reddy C. Rami , Lenz Robert W.
Published: April 2003

A series of copolymers containing triad ester mesogenic units, with pendent n‐octyl substituents, and triad ester nonmesogenic units, both with flexible spacer groups, was prepared and characterized for the effect of the nonmesogenic unit content on transition temperatures and thermodynamic parameters. The mesophase temperature range increased, but temperature, enthalpy, and entropy of isotropization decreased in a linear manner with increasing nonmesogen comonomer content. The entropy of isotropization is considered to be a quantitative measure of the degree of order of the nematic phase, but this order may include both the amount and the order parameter of the mesophase if, as proposed, both the isotropic and nematic phase exist below the isotropization temperatures of the copolymers.
Styrene–isoprene block copolymers. I. Synthesis and solution properties
Authors: Velichkova R. , Toncheva V. , Getova C. , Pavlova S. , Dubrovina L. , Gladkova E. , Ponomareva M.
Published: April 2003

Copolymers with a different degree of distribution of styrene and isoprene blocks are prepared by anionic polymerization. The products are characterized by means of 1H‐NMR spectroscopy, GPC, viscometry, and light scattering. The results show that the copolymers are homogeneous in molecular weight and chain composition. In the investigated selective solvents, cyclohexane and base lubricating oil, and equilibrium exists between micelle aggregates and individual polymer coils. The influence of the copolymer structure on the micellization is more pronounced in cyclohexane.
Primary processes in the photosensitized polymerization of cationic monomers
Authors: Manivannan G. , Fouassier J. P.
Published: April 2003

A 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

Monodisperse 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

A 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

Syndiospecific 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

The 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

Photopolymerization 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

Pyrrole (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

The 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

Styrene 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

Several 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

Light‐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

Cationic 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

The 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

A 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

The 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

Supported 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

A 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

Several 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

Radical 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

A 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

A 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.
Hydroxy‐terminated poly(ε‐caprolactone‐co‐δ‐valerolactone) oligomers: Synthesis, characterization, and polyurethane network formation
Authors: Storey Robson F. , Herring Kent R. , Hoffman Douglas C.
Published: April 2003

Difunctional hydroxy‐terminated poly(ε‐caprolactone‐co‐ε‐valerolactone) (PCV) oligomers were synthesized by the diol‐initiated bulk copolymerization of ε‐caprolactone (C) and δ‐valerolactone (V). The two homopolymers were semicrystalline, with almost identical melting temperatures; copolymerization significantly lowered the melting point (Tm) compared to either homopolymer. Copolymer melting points were found to decrease with decreasing molecular weight and to be dependent on composition, i.e., the incorporation of a comonomer into either homopolymer resulted in a decrease in Tm, with the maximum decrease occurring at a copolymer composition of about 60 mol % ε‐caprolactone. The molar compositions of the copolyesters were determined from 13C‐NMR spectra. The reactivity ratios of the two monomers (M1 = C, M2 = V) were determined to the r1 = 0.25 and r2 = 0.49. Number average molecular weight (M̄n) of the PCV diols was inversely proportional to the initial diol concentration within the studied molecular weight range of 900 to 11,100 g/mol. Crosslinked polyurethane networks were prepared by reacting PCV diols with triphenylmethane triisocyanate. Network characterization included determination of sol content by solvent extraction, glass transition (Tg) and Tm by DSC, and tensile properties by stress‐strain measurements. Completely amorphous networks resulted from PCV diols of M̄n ≤ 2,400; semicrystalline networks resulted from PCV diols of M̄n ≥ 3,600.
Novel platinum‐containing initiators for ring‐opening polymerizations
Authors: Crivello J. V. , Fan M.
Published: April 2003

A novel class of platinum‐based initiating systems for the ring‐opening polymerization of a wide variety of heterocyclic compounds including epoxides, oxetanes, and 1,3,5‐trioxane have been discovered. In addition to a platinum complex as a catalyst, a cocatalyst, consisting of a compound or polymer containing silicon‐hydrogen bonds must also be present. This article reports on a preliminary survey of the scope and limitations of these new initiator systems. Particular emphasis in this article has been placed on the ring‐opening polymerization of epoxides which have been studied in some detail and which proceed rapidly and exothermically at room temperature. A number of mechanistic studies have been conducted and the best current evidence suggests that polymerization proceeds by a cationic mechanism. Evidence is also presented which suggests that platinum metal colloids may function as the active initiating species.
Mesomorphic polyacrylates containing isomeric methyl‐substituted azobenzene mesogens
Authors: Angeloni A. S. , Caretti D. , Laus M. , Chiellini E. , Galli G.
Published: April 2003

The synthesis and characterization are reported of two new series of structurally isomeric polyacrylates containing the azobenzene moiety spaced away from the backbone by a hexamethylene spacer and substituted in 4‐position with linear alkoxy groups (C1C6, C10) and with a lateral methyl group in 2′‐ or 3′‐position. Thermal optical and X‐ray analyses of the prepared polymer samples, with molecular weight ranging from 50 × 103 to 35 × 104 Dalton (M̄w/M̄n = 2−3), provide evidences for the establishment of liquid crystalline behavior in the melt in a fairly broad range of temperature. In any case, quenching from the mesophase allows for the lock‐in of the liquid crystalline structure in the glassy state. The presence of the lateral methyl‐substitutents causes a drop as high as 50–100 K. in the stability of the mesophase with respect to the corresponding samples of the methyl‐unsubstituted series. A parallel depletion of the smectogenic character is also observed. Typical even‐odd effects on the isotropization temperature and relevant thermodynamic parameters have been detected along with the formation of interdigitated smectic structures.
Synthesis of monomers containing guanine or guanine precursors as substituent groups
Authors: Toucet Isabel , Aponte Maria A.
Published: April 2003

The synthesis of four new monomers containing guanine or a guanine precursor was achieved. These were two isomeric acid ester derivatives of guanine and two isomeric vinyl ether derivatives of N2‐acetylguanine. In the case of the synthesis of the guanine acid esters IV and V, it was necessary to prepare first the guanine alcohol derivatives II and III. These N‐7 and N‐9 isomeric alcohols of guanine were separated by fractional crystallization. Subsequent esterification of these alcohols with maleic anhydride gave the desired products. In the other case, N2‐acetylguanine was alkylated with 2‐chloroethyl vinyl ether to yield the N‐7 and N‐9 isomer VI and VII, respectively. These were separated using flash column chromatography.
Synthesis and characterization of a new monomer with pendant hindered amine group
Authors: Lee C. S. , Lau Wayne W. Y. , Lee S. Y. , Goh S. H.
Published: April 2003

A new monomer, 1,2,2,6,6‐pentamethyl‐4‐piperidinyl m‐isopropenyl‐α, α‐dimethylbenzyl carbamate, was synthesized by direct addition of 1,2,2,6,6‐pentamethyl‐4‐piperidinol to m‐isopropenyl‐α, α‐dimethylbenzyl isocyanate in the presence of dibutyltin dilaurate catalyst at elevated temperatures. It was characterized by FT‐IR, 1H‐NMR. MS, and elemental analysis. It is a potential hindered amine light stabilizer as it contains the 2,2,6,6‐tetraalkylpiperidine moiety and its vinylic functionality makes it polymerizable.
N‐(2‐hydroxypropyl) methacrylamide copolymers containing pendant saccharide moieties: Synthesis and bioadhesive properties
Authors: Rathi Ramesh C. , Kopečková Pavla , Říhová Blanka , Kopeček Jindŕich
Published: April 2003

A new route for the synthesis of bioadhesive water soluble polymeric drug carriers has been developed. Novel monomers, namely, N‐methacryloylglycylglycylgalactosamine (MA‐Gly‐Gly‐GalN) [8], MA‐Gly‐Gly‐FucN [9], MA‐Gly‐Gly‐GlcN [10], and MA‐Gly‐Gly‐ManN [11], and copolymers [12–16] based on N‐(2‐hydroxypropyl) methacrylamide (HPMA) containing different content of pendant saccharide moieties (galactosamine, fucosylamine, glucosamine, or mannosamine), were synthesized. Copolymerization parameters for the copolymerization of HPMA [M1] and MA‐Gly‐Gly‐GalN [M2] have been determined (r1 = 0.82, r2 = 0.38). Bioadhesion studies with everted sacs of guinesa pig small intestine and colon in vitro demonstrated that HPMA copolymers containing side‐chains terminated in fucosylamine bind selectively to the colonic tissue. The extent of binding was dependent on the fucosylamine content of copolymers.
Thermal degradation mechanisms of liquid crystalline aromatic polyesters studied by pyrolysis–gas chromatography/mass spectrometry
Authors: Sueoka K. , Nagata M. , Ohtani H. , Nagai N. , Tsuge S.
Published: April 2003

The thermal degradation mechanisms of liquid crystalline aromatic polyesters (LCPs) prepared from p‐hydroxybenzoic acid (PHB), biphenol (BP), and terephthalic acid (TA) were studied by pyrolysis–gas chromatography/mass spectrometry (Py‐GC/MS). The LCP containing deuterated terephthalate units and the LCPs that have different comonomer ratios were examined. On the basis of the pyrolysis products determined, the origin of the main pyrolysis products (benzene, phenol, biphenyl, phenyl benzoate, etc.) from the corresponding comonomer units were estimated and their thermal degradation mechanisms were eventually discussed in detail.
Living cationic polymerization of vinyl ethers by electrophile/lewis acid initiating systems. VII. Living cationic polymerization of isobutyl vinyl ether by trimethylsilyl halide/zinc halide initiating systems in the presence of p‐methoxybenzaldehyde: Effects of halide anions and zinc halides
Authors: Kamigaito Masami , Sawamoto Mitsuo , Higashimura Toshinobu
Published: April 2003

Trimethylsilyl halides (Me3SiY), in conjunction with zinc halides (ZnX2) (Y and X:I, Br, Cl), were employed to investigate the living cationic polymerization of isobutyl vinyl ether (IBVE) in toluene at −15°C in the presence of p‐methoxybenzaldehyde; with the aldehyde and IBVE monomer, Me3SiY yields an initiating species [Me3SiOCHC6H4(OMe) CH2CH(OiBu) Y] that triggers the IBVE polymerization via the activation of its carbon‐halogen bond (CY) by ZnX2 into Cδ+…︁Yδ−…︁ZnX2. Living polymerizations occurred with the silyl iodide and bromide irrespective of the type of ZnX2, either when Y = X (Me3Sil/Znl2 and Me3SiBr/ZnBr2) or when Y ≠ X (Me3Sil/ZnBr2, Me3SiI/ZnCl2, and Me3SiBr/Znl2). With these five initiating systems, the number‐average molecular weights (M̄n) of the polymers increased in proportion to monomer conversion, and the molecular weight distributions (MWDs) of the polymers were narrow (M̄w/M̄n = 1.1−1.2). The Me3SiCl‐based systems (Me3SiCl/ZnCl2 and Me3SiCl/Znl2), in (Me3SiCl/Znl2), in contrast, failed to give perfectly living polymerization; the M̄n indeed increased with conversion, but the MWDs of the polymers were broader (M̄w/M̄n = 1.3−1.5). Thus, the living nature of the polymerizations with Me3SiY/Znx2 is primarily determined by the halogen Y in Me3SiY, which generates the terminal carbon‐halogen bond (CY) that is activated by ZnX2 for the propagation via a species Cδ+…︁Yδ−…︁ZnX2. For Y−, not only the iodide but the bromide anion also is suited for living cationic polymerization. The virtual absence of the effects of X in ZnX2 implies that the halogen exchange between ZnX2 and Y from Me3 SiY at the growing end (Cλ+…︁Yδ−…︁ZnX2 ⇄Cδ+…︁Xδ−…︁ZnXY) is absent or negligible.
Anionic polymerization of 4‐methyl‐2‐oxetanone (β‐butyrolactone)
Authors: Duda Andrzej
Published: April 2003

Polymerization of 4‐methyl‐2‐oxetanone (1) initiated with potassium acetate‐dibenzo‐18‐crown‐6 complex (2) in THF as solvent, was studied. Transfer reactions, leading to both crotonate anions and carboxylic acid formation, have been observed. Two kinetic effects of these reactions, hampering the living polymerization, have been established. The first results from reinitiation with the crotonate anions and thereby lowers the polymer molecular weight. The second is the decrease in the overall polymerization rate due to complexation of the growing carboxylate anions with carboxylic acid moieties. Kinetic scheme of polymerization involves propagation accompanied by transfer followed by slow reinitiation. This scheme, including complexation of the active species has been solved numerically. The apparent rate and equilibrium constants (kp, ktr, kri, and Kass and respectively) have been determined. Although these kinetic parameters depend strongly on the polymerization conditions, but the ratio of the rate constants kp : kt : kri is fairly constant and equal to 10−4 : 10−6 : 10−6, respectively (at 20°C). Conditions of the controlled anionic synthesis of the amorphous poly(4‐methyl‐2‐oxetanone) with \documentclass{article}\pagestyle{empty}\begin{document}$\bar M_n$\end{document} as high as 1.7 × 104 and \documentclass{article}\pagestyle{empty}\begin{document}${{ \le \bar M_n } \mathord{\left/ {\vphantom {{ \le \bar M_n } {\bar M_n }}} \right. \kern-\nulldelimiterspace} {\bar M_n }} \le 1.20$\end{document} have also been elaborated.