Showing papers in "Journal of Polymer Science Part A in 1991"

Synthesis and characterization of polymers produced by horseradish peroxidase in dioxane

Abstract: Polymers were synthesized from substituted phenolic and aromatic amine compounds with hydrogen peroxide as the source of an oxidizing agent and horseradish peroxidase enzyme as the catalyst. The polymerization reaction was carried out in a monophasic organic solvent with small amounts of water at room temperature. Conditions for the synthesis of polymers with respect to reaction time and yield were studied with a number of monomers at different concentrations and in solvents with different buffers with pH range of 5.0–7.5. Physical and chemical properties of these homo-and copolymers were determined with respect to melting point, solubility, elemental analysis, molecular weight distribution, infrared absorption (including FTIR), solid-state 13C nuclear magnetic resonance, thermal gravimetric analysis, and differential scanning calorimetry. The enzyme catalyzed reactions produced polymers of molecular weight greater than 400,000 which were further fractionated by differential solubility in solvent mixtures and the molecular weight distribution of the polymer fractions were determined. In general, the polymers synthesized have low solubilities, high melting points, and some degree of branching.

A microcomputer program for estimation of copolymerization reactivity ratios

Abstract: 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.

Olefin copolymerization with metallocene catalysts. I. Comparison of catalysts

Abstract: A number of metallocene/methylaluminoxane (MAO) catalysts have been compared for ethylene/propylene copolymerizations to find relationship between the polymerization activities, copolymer structures, and copolymerization reactivity ratio with the catalyst structures. Stereorigid racemic ethylene bis (indenyl) zirconium dichloride and the tetrahydro derivative exhibit very high activity of 10 7 g (mol Zr h bar)−1, giving copolymers having comonomer compositions about the same as the feed compositions, molecular weights increasing with the increase of ethylene in the feed, random incorporation of comonomers, and narrow molecular weight distribution indicative of a single catalytic species. Nonbridged bis (indenyl) zirconium behaved differently, favoring the incorporation of ethylene over propylene, producing copolymers whose molecular weight decreases with the increase of ethylene in the feed, broad molecular weight distribution, and a methanol soluble fraction. This catalyst system contains two or more active species. Simple methallocene catalysts have much lower polymerization activities. CpTiCl2/MAO produced copolymers with tendency toward alternation, whereas Cp2HfCl2/MAO gave copolymer containing short blocks of monomers.

Polyisobutylene‐containing block polymers by sequential monomer addition. II. Polystyrene–polyisobutylene–polystyrene triblock polymers: Synthesis, characterization, and physical properties

Abstract: New linear and three-arm star thermoplastic elastomers (TPEs) comprising a rubbery polysobutylene (PIB) midblock flanked by glass polystyrene (PSt) blocks have been synthesized by living carbocationic polymerization in the presence of select additives by sequential monomer addition. First, isobutylene (IB) was polymerized by bi- and trifunctional tert-ether (dicumyl- and tricumyl methoxy) initiators in conjunction with TiCl4 conintiator in CH3Cl/methylcyclohexane (MeCHx) (40/60 v/v) solvent mixtures at −80°C. After the living, narrow molecular weight, distribution PIB (Mw/Mn = 1.1-1.2) has reached the desired molecular weight, styrene (St) together with an electron pair donor (ED) and a proton trap (di-tert-butylpyridine, DtBP) were added to block PSt from the living chain ends. Uncontrolled initiation by protic impurities that produces PSt contamination is prevented by the use of DtBP. PSt-PIB-PSt blocks obtained in the absence of additives are contaminated by homopolymer and /or diblocks due to inefficient blocking and initiation by protic impurities, and exhibit poor physical properties. In contrast in the presence of the strong ED N,N-dimethylacetamide (DMA) and DtBP the blocking of St from living PIB chain occurs efficiently and block copolymers exhibiting good mechanical properties can be prepared. Virgin TPEs can be repeatedly compression molded without deterioration of physical properties. The products exhibit a low and a high temperature Tg characteristic of phase separated PIB and PSt domains. Transmission electron microscopy of linear triblocks containing ∼ 34 wt % PSt also indicates microphase separation and suggests PSt rods dispersed in a PIB matrix.

Kinetics and stereochemical control of propylene polymerization initiated by ethylene bis(4,5,6,7‐tetrahydro‐1‐indenyl) zirconium dichloride/methyl aluminoxane catalyst

Abstract: The kinetics and sterochemical control of propylene polymerization initiated by rac-ethylene bis (4,5,6,7-tetrahydro-1-indenyl) zirconium dichloride/methyl aluminoxane (1/MAO) and by rac-ethylene bis (1-indenyl) zirconium dichloride/MAO (2/MAO) were investigated. The polymerization activities increase monotonically with temperature corresponding to an overall activation energy of 10.6 kcal mol−1. This is accompanied, however, by reduction of stereochemical control as reflected in the amount of the polypropylene (PP) soluble in low boiling solvent. At a temperature of 30°C and higher, polymerization initiated by 1/MAO produced no PP insoluble in refluxing n-heptane. Tritium radiolabeling showed that at [Al]/[Zr] ≥ 3500 and 30°C, two-thirds of 1 becomes catalytically active. There are at least two kinds of active species formed in about equal amounts; one has more stereoselectivity, 10–20 times greater rate constant of propagation, and a factor of 5–15 faster chain transfer to MAO than the second kind of Active species. This is also true at low [Al]/[Zr] of 350, except that the total amount of the two active species corresponds to only 13% of the [1]. Replacement of MAO with trimethyl aluminum resulted in the decrease of stereoselectivity and loss of catalytic activity proportional to the amount of replacement. A comparison was made with the polymers obtained with 2/MAO.

Molecular engineering of liquid crystal polymers by living polymerization. II. Living cationic polymerization of 11‐[(4‐cyano‐4′‐biphenyl) oxy] undecanyl vinyl ether and the mesomorphic behavior of the resulting polymers

Abstract: Le comportement mesomorphique du polymere est etudie en Fonction de la masse moleculaire et compare avec celui du monomere et d'un compose modele de l'unite structurale. Les resultats montrent que la transformation de la mesophase nematique du monomere en mesophase smectique apres polymerisation a lieu au niveau de l'unite structurale

Synthesis and characterization of new soluble aromatic polyimides from 3,4-bis (4-aminophenyl)-2,5-diphenylfuran and aromatic tetracarboxylic dianhydrides

Abstract: New soluble polyimides with inherent viscosities of 0.2–0.6 dL/g were synthesized from 3,4-bis (4-aminophenyl)-2,5-diphenylfuran and various aromatic tetracarboxylic dianhydrides by the conventional two-step method which involved ring-opening polyaddition and subsequent cyclodehydration. Almost all of the polymides were generally soluble in a wide range of organic solvents such as N,N-dimethylacetamide, 1,3-dimethyl-2-imidazolidone, m-cresol, o-chlorophenol, and pyridine. The polyimide prepared from pyromellitic dianhydride was crystalline, whereas the other polyimides were amorphous. All the polyimides have glass transition temperatures in the range of 281–344°C and showed no appreciable weight loss up to 410°C in both air and nitrogen atmospheres.

Polychloromethylstyrene microspheres: Synthesis and characterization

Abstract: The synthesis and characterization of polychloromethylstyrene microspheres are described. The effect of various factors, e.g., monomer concentration, surfactant concentration, solvents, crosslinker, etc., on the yield, diameter, and size distribution of these microspheres was elucidated. Conditions to covalently bind various primary amino ligands to these microspheres in aqueous solution were also established. The possible routes to modify the surface of these microspheres to obtain functional groups other than chloromethyl are discussed.

New TiPTMO and ZrPTMO ceramer hybrid materials prepared by the sol gel method: Synthesis and characterization

Abstract: New transparent flexible hybrid network “ceramer” materials have been synthesized by incorporating triethoxysilane capped polytetramethylene oxide with highly reactive titanium isopropoxide or zirconium n-propoxide without adding chelating agents. Both of these types of ceramer materials display high transparency while the zirconium systems show considerable transparency in the UV region. The titanium systems exhibit higher refractive index than the corresponding zirconium materials of equal alkoxide content.

Syndiospecific polymerization of styrene. II, Monocyclopentadienyltributoxy titanium/methylaluminoxane catalyst

Abstract: Syndiospecific polymerization of styrene was catalyzed by monocyclopentadienyltributoxy titanium/methylaluminoxane [CpTi (OBu)3/MAO]. The atactic and syndiotactic polystyrenes were separated by extracting the former with refluxing 2-butanone. The activity and syndiospecificity of the catalyst were affected by changes in catalyst concentration and composition, polymerization temperature, and monomer concentration. Extremely high activity of 5 × 107 g PS (mol Ti mol S h)−1 with 99% yield of the syndiotactic product were achieved. The concentration of active species, [C*], has been determined by radiolabeling. The amount of the syndiospecific and nonspecific catalytic species, [C] and [C] respectively, correspond to 79 and 13% of the CpTi(OBu)3. The rate constants of propagation for C and C at 45°C are 10.8 and 2.0 (M s)−1, respectively, the corresponding rate constants for chain transfer to MAO are 6.2 × 10−4 and 4.3 × 10−4s−1. There was no deactivation of the catalytic species during a batch polymerization. The rate constant of chain transfer with monomer is 6.7 × 10−2 (M s)−1; the spontaneous β-hydride transfer rate constant is 4.7 × 10−2 s−1. The polymerization activity and stereospecificity of the catalyst are highest at 45°C, both decreasing with either higher or lower temperature. The stereoregular polymer have broad MW distributions, Mw/Mn = 2.8–5.7, and up to three crystalline modifications. The Tm of the s-PS polymerized at 0–90°C decreased from 261.8 to 241°C indicating thermally activated monomer insertion errors. The styrene polymerization behaviors were essentially insensitive to the dielectric constant of the medium.

Preparation of microspheres by radiation‐induced polymerization. I. Mechanism for the formation of monodisperse poly(diethylene glycol dimethacrylate) microspheres

Abstract: 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.

Photodegradation of UV‐cured coatings II. Polyurethane–acrylate networks

Abstract: 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.

Polyepichlorohydrin diols free of cyclics: Synthesis and characterization

Abstract: 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 Mn ∼ 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.

Polyanhydrides. IV. Unsaturated and crosslinked polyanhydrides

Abstract: Le polymere de l'anhydride fumarique de ses copolymeres avec les anhydrides sebacique, dodecanedioique et adipique sont obtenus par polycondensation en solution ou a l'etat fondu. Leur masse moleculaire Mw atteint 30000 et ils sont reticulables via les doubles liaisons intactes des motifs fumarique. Les copolymeres presentent des vitesses d'hydrolyse et de liberation de la p-nitroaniline presque constantes en conditions physiologiques

Amorphous celluloses stable in aqueous media: Regeneration from SO2–amine solvent systems

Abstract: Amorphous celluloses were prepared by regeneration of cellulose from its solutions in the SO2–diethylamine–dimethylsulfoxide (SO2–DEA–DMSO) solvent system, and other selected SO2–amine–organic solvents. The celluloses were amorphous whether regenerated in water or in alcohols or other organic solvents; in this respect the observations differ from all prior experience in the regeneration of cellulose. These celluloses retain their amorphous character even after extended soaking in water at room temperature. Viscosity measurements have shown that little or no depolymerization occurs during the dissolution, regeneration, and drying processes. Thus the procedures allow the preparation of amorphous celluloses of a wide range of molecular weights for use to model the behavior of amorphous domains in fibrous celluloses. The unusual stability of the amorphous cellulose structures prepared by these procedures is attributed to very rapid decomposition of the SO2–amine complex with the cellulosic hydroxyl groups which is believed to occur in the solvated state. The rate of decomposition of this complex appears to be sufficiently high so that the cellulose chains aggregate in an amorphous state before they have any opportunity to realign into crystalline domains.

Hydrogen/liquid vapor radio frequency glow discharge plasma oxidation/hydrolysis of expanded poly(tetrafluoroethylene) (ePTFE) and poly(vinylidene fluoride) (PVDF) surfaces

Abstract: Through this multitechnique analysis of both expanded PTFE and PVDF treated surfaces, a model is supported which illustrated surfaces possessing both high and low energy regions comprising both oxygen and fluorine functionnality in close molecular proximity

Primary processes in the photosensitized polymerization of cationic monomers

Abstract: 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.

N‐(2‐hydroxypropyl) methacrylamide copolymers containing pendant saccharide moieties: Synthesis and bioadhesive properties

Abstract: 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.

Interfacial polycondensation and characterization of polyphosphates and polyphosphonates

Abstract: The synthesis of four bisphenol A-based polyphosphates and phosphonates was accomplished. The polymerization involved a condensation between bisphenol A and a phosphorodichloridate. The heterophasic polycondensation technique was used with the aid of a phase transfer catalyst to yield molecular weights in the range of 20,000–40,000. The polymers were characterized by FT-IR, FT-NMR, and DSC. Systematic studies on the interfacial polymerization indicated that a more concentrated organic phase and a slight excess of diol favored the production of high molecular weight polymers. An optimum concentration of 5–10 mol % was observed for three different phase transfer catalysts. Kinetic studies showed that the polymerization was complete within the first 10 min. The degree of agitation was shown to be important, as the overhead mechanical stirrer was not as effective as the blender. In addition, crosslinking with pentaerythritol yielded significant increases in the molecular weights of these polymers.

Liquid crystalline polymers containing mesogenic units based on half-disc and rod-like moieties. I, Synthesis and characterization of 4-(11-undecan-1-yloxy)-4'-[3,4,5-tri(p-n-dodecan-1-yloxybenzyloxy)benzoate]biphenyl side groups

Abstract: Preparation du polysiloxane [Si(Me)(R)O] n (R=(CH 2 ) 11 O-Ph-Ph-O-CO-Ph(OCH 2 PhO-(CH 2 ) 11 CH 3 ) 3 par hydrosilylation de l'olefine correspondante par le poly(hydro methyl siloxane). Etude des transitions de phase des produits intermediaires de depart et du polymere; l'olefine et le polymere presentent une mesophase plasmidique monotrope avec une texture optique en eventail

On the main locus of radical formation in emulsion polymerization initiated by oil-soluble initiators

Abstract: 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.

Surface grafting of polymers onto inorganic ultrafine particles: Reaction of functional polymers with acid anhydride groups introduced onto inorganic ultrafine particles

Abstract: Des groupes anhydride sont introduits en surface de particules ultrafines de silice, d'oxyde de titane et de ferrite par reaction avec le 4-trimethoxysilyl 4-trimethoxysilyl-tetrahydrophtalique. Un poly(propeneglycol) et un α,ω-diamido poly(dimethylsiloxane) sont greffes sur ces particules. Le pourcentage de greffage augmente avec la quantite de groupes anhydride en surface. Les particules greffees donnent des dispersions colloidales stables dans les solvants organiques

Catalytic epoxidation of styrene–butadiene triblock copolymer with hydrogen peroxide

Abstract: Styrene-butadiene-styrene linear block copolymer (SBS) 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 reaction time, temperature, solvent, the ratio of the organic phase to the aqueous phase, the concentration of the catalyst, hydrogen peroxide and polymer, respectively, are studied on the conversion of double bonds to oxirane groups. 1H-NMR analysis confirms the absence of ring opening side reaction in this epoxidation reaction system up to at least 70% conversion of the double bonds. When the conversion of double bonds is over about 70% the resultant polymer is insoluble in chloroform even at reflux but soluble in polar solvents such as DMSO when heated. Toluene is a better solvent for the reaction than dichloroethane. The reaction rate constants are measured at four temperatures and the activation energy for the reaction with toluene as solvent is determined as 49.9 kJ/mol.

Polyisobutylene-containing block polymers by sequential monomer addition. i, the living carbocationic polymerization of styrene

Abstract: The living carbocationic polymerisation of styrene (St) has been investigated by the 2-chloro-2,4,4-trimethylpentane (TMPCI)/TiCl4 initiating system in the presence of various additives such as electron pair donors (EDs) and the proton trap 2,6-di-tert-butylpyridine (DtBP) by the use of the mixed solvent CH3Cl/methyl-cyclohexane (MCHx) (40/60 v/v) at −80°C under conventional laboratory conditions. The TMPCl/TiCl4 system in the absence of additives produces ill-defined bimodal molecular weight distribution (MWD) polymers. Much better defined polystyrenes (PSt) can be obtained in the presence of EDs, such as N,N-dimethylacetamide (DMA) and hexamethylphosphoramide (HMPA). Monomer depletion should be avoided to prevent intra- or intermolecular alkylation yielding indanyl end groups or branched polymers, respectively. In the combined presence of an ED and the proton trap, i.e., DMA + DtBP, the living polymerization of St has been achieved and thus the foundations for the carbocationic synthesis of PSt block polymers by sequential monomer addition have been laid.

Syndiospecific polymerization of styrene. I. Tetrabenzyl titanium/methylaluminoxane catalyst

Abstract: 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.

The synthesis of soluble, substituted silane high polymers by Wurtz coupling techniques

Abstract: The Wurtz-type coupling of a number of representative classes of substituted dichlorosilane monomers was investigated in considerable detail. Low temperature polymerization techniques, including ultrasonic activation, were also studied. Similarly, the effect of dipolar additives on the polymerization process was examined. The conclusions drawn from these studies provide some insight into the selection of useful polymerization conditions for the conversion of various monomer types into linear high polymers.