Showing papers in "Journal of Polymer Science Part A in 1993"

Synthesis and properties of polyimide–clay hybrid

Abstract: A polyimide hybrid with montmorillonite clay mineral has been synthesized from a dimethylacetamide (DMAC) solution of poly(amic acid) and a DMAC dispersion of montmorillonite intercalated with an ammonium salt of dodecylamine. Montmorillonite consists of stacked silicate sheets about 2000 A in length, 10 A in thickness. In this hybrid, montmorillonite is dispersed homogeneously into the polyimide matrix and oriented parallel to the film surface. Thanks to this special structure, this hybrid showed excellent gas barrier properties. Only 2 wt % addition of montmorillonite brought permeability coefficients of various gases to values less than half of those of ordinary polyimide. Furthermore, this hybrid had low thermal expansion coefficient. © 1993 John Wiley & Sons, Inc.

Synthesis of nylon 6-clay hybrid by montmorillonite intercalated with ε-caprolactam

Abstract: It was found that montmorillonite was intercalated with ϵ-caprolactam. X-ray diffraction revealed that the chain axes of the ϵ-caprolactam were parallel to the montmorillonite plates. The intercalated montmorillonite was swollen by molten ϵ-caprolactam at 200°C. ϵ-Caprolactam and 6-aminocaproic acid (accelerator) were polymerized with the intercalated montmorillonite at 260°C for 6 h, yielding a nylon 6-clay hybrid. X-ray diffraction and transmission electron micrography revealed that the silicate layers of the hybrid were uniformly dispersed in the nylon 6 matrix. Mechanical properties of the hybrid were improved. The strength and the modulus of the hybrid increased compared with the previously reported nylon 6 clay-hybrid (NCH) synthesized by montmorillonite intercalated with 12-aminolauric acid. The heat distortion temperature (HDT) of the hybrid was 164°C, which was 12°C higher than that of NCH. © 1993 John Wiley & Sons, Inc.

One‐pot synthesis of nylon 6–clay hybrid

Abstract: Nylon 6–clay hybrid is a molecular composite of nylon 6 and uniformly dispersed silicate layers of montmorillonite. One-pot synthesis of the hybrid was carried out by the following procedures. Montmorillonite was dispersed in water, and then e-caprolactam, acid (phosphoric acid, hydrochloric acid, benzenesulfonic acid, isophthalic acid, trichloroacetic acid, or acetic acid), and 6-aminocaproic acid were added to the dispersion. The mixtures were reacted at 260°C for 6 h, yielding the nylon 6–clay hybrids (1potNCHs). X-ray diffraction revealed that the silicate layers of 1potNCH by phosphoric acid were uniformly dispersed in the nylon 6 matrix. The 1potNCH had excellent mechanical properties. The strength and the modulus of the hybrid increased compared with previously reported nylon 6–clay hybrid (NCH) synthesized by montmorillonite intercalated with 12-aminolauric acid. The heat distortion temperature (HDT) of the 1potNCH was 160°C, which was 8°C higher than that of NCH. In other 1potNCHs, montmorillonite had a smaller effect on the increase of those properties, and interlayer spacing of montmorillonite was observed at ca. 20 A. © 1993 John Wiley & Sons, Inc.

Synthesis of monodisperse poly(divinylbenzene) microspheres

Abstract: Highly crosslinked monodisperse poly(divinylbenzene) microspheres were produced by precipitation polymerization with acetonitrile as solvent. The radical initiators AIBN, BPO, and ADVN were used. The process does not require stabilizers of any type, and produces monodisperse particles with diameters between 2 and 5 μm, depending on the conditions. These microspheres do not swell or dissolve in any common solvent, and have clean, stabilizer-free surfaces. The particle formation and growth mechanism is proposed to resemble that of dispersion polymerization, except that the particles are stabilized against coagulation by their rigid, crosslinked surfaces rather than by added stabilizers. Spherical particles were formed only at effective crosslinker/monomer or divinyl/monovinyl ratios larger than 1 : 2. © 1993 John Wiley & Sons, Inc.

Synthesis of fusible and soluble conducting polyfluorene derivatives and their characteristics

Abstract: Conducting poly(9-alkylfluorene)s and poly(9,9-dialkylfluorene)s have been synthesized by chemical polymerization utilizing FeCl 3 as an oxidizing agent. The polymers obtained are found to be soluble in conventional organic solvents such as chloroform and have been characterized by 1 H- and 13 C-NMR. The results indicate that the fluorene moeities are mainly linked in the 2,7'-fashion to yield the straight chain polymer. The degree of polymerization is estimated (by GPC) to be of the order of 10. The polymers are found to be fusible and the thermal properties of the polymers have been characterized by DSC

Control of particle size in dispersion polymerization of methyl methacrylate

Abstract: Poly(methyl methacrylate) (PMMA) particles ranging in diameter from 2 to 10 μm were prepared by dispersion polymerization. The effects of various polymerization parameters on the size and monodispersity were systematically investigated. The particle size was found to increase with increasing polymerization temperature, concentration and decomposition rate of the initiator, and solvency of the dispersion medium. It also increased with increasing concentration and molecular weight of the polymeric stabilizer, poly(vinyl pyrrolidone) (PVP). As the monomer concentration was increased from 5 to 20 wt %, a minimum was found in the particle size at a monomer concentration of 10 wt %. A costabilizer was found to be necessary for preparing monodisperse particles at stabilizer concentrations below 2 wt %. A recycling experiment showed that the consumption of PVP was quite small in each cycle and the residual materials in this system could be reused readily. © 1993 John Wiley & Sons, Inc.

Synthesis and properties of poly(hydroxyurethane)s

Abstract: Bis(cyclic Carbonate)s 1 were prepared by the reaction of bis(epoxide)s and atmospheric pressure of CO2 in the presence of sodium iodide and triphenylphosphine as catalysts at 100°C in high yield. Polyaddition of 1 and hexamethylenediamine (2a) or dodecamethylenediamine (2b) in dimethylsulfoxide or N,N-dimethylacetamide (DMAc) at 70 or 100°C for 24 h afforded corresponding poly(hydroxyurethane)s with Mn 20,000–30,000. When ethylenediamine (2c) or 1,3-propanediamine (2d) was used as a diamine, poly(hydroxyurethane)s with lower molecular weight were obtained. The presence of water, methanol, or ethyl acetate in the solvent had little effect on the Mn of the polymer obtained, because of the high chemoselectivity of the reaction of the five-membered cyclic carbonate and amine. Polyaddition of bis(cyclic carbonate) bearing ester groups and 2a also afforded the corresponding poly(hydroxyurethane) without aminolysis of the ester groups. Poly(hydroxyurethane) 3 obtained from the bis(cyclic carbonate) derived from bisphenol A was less soluble in organic solvents than model polyurethane 8 having no hydroxy groups obtained from 4,4′-isopropylidenebis(2-hydroxyethoxybenzene) and hexamethylene diisocyanate, and was thermally stable as well as 8.3 easily undertook crosslinking at room temperature by the treatment with hexamethylene diisocyanate or aluminium triisopropoxide in DMAc or tetrahydrofuran. The gel crosslinked by aluminium triisopropoxide regenerated the original polymer at room temperature by treatment with 1.5 equiv of 1.2M HCl in N-methylpyrollidinone for 1 h. © 1993 John Wiley & Sons, Inc.

Enzymatic polyesterification in organic media. Enzyme-catalyzed synthesis of linear polyesters. I: Condensation polymerization of linear hydroxyesters. II: Ring-opening polymerization of ε-caprolactone

Abstract: The condensation polymerization of linear ω-hydroxyesters using the commercially-available crude porcine pancreatic lipase (PPL), suspended in organic solvents as the preferred enzyme for the reactions, was investigated. The optimal conditions for the condensation polymerization were determined. Film-forming polyesters with a degree of polymerization up to about 100 were obtained from linear aliphatic hydroxyesters in refluxing n-hexane. For the ring opening polymerization of lactones, the reaction of e-caprolactone with methanol as the preferred nucleophile was studied. Polyesters witha DP of up to 35 were obtained in hexane at temperatures between 25 an 40°C

Squid chitin as a potential alternative chitin source: Deacetylation behavior and characteristic properties

Abstract: β-Chitin was isolated from squid pens, and the characteristic chemical and physical properties were elucidated in comparison with those of shrimp chitin, α-chitin. Deacetylation behavior of the squid chitin was first studied to look into the reactivity of β-chitin and also to establish an efficient procedure for preparing squid chitosan. The squid chitin proved to show much higher reactivity in alkaline deacetylation than shrimp chitin. Although it was deacetylated quite easily, the product assumed a dark brown color under the ordinary reaction conditions for shrimp chitosan. Squid chitosan was successfully prepared by repeated alkaline treatments under mild conditions, particularly with high concentration alkali at low temperatures, without appreciable discoloration. The structural characteristics of the squid chitin were discussed on the basis of the IR and x-ray analysis data. The crystalline structure of squid chitin was destroyed easily on deacetylation compared to that of shrimp chitin, and moreover, the resulting squid chitosan was amorphous unlike crystalline shrimp chitosan. The squid chitin was characterized by the remarkable affinity for organic solvents and water. Squid chitin and chitosan also showed much higher hygroscopicity and retention of the absorbed water than shrimp chitin and chitosan and are considered to be useful as highly hydrophilic materials. © 1993 John Wiley & Sons, Inc.

Synthesis and characterization of aromatic poly(ether sulfone)s containing pendant sodium sulfonate groups

Abstract: Poly(ether sulfone)s containing pendant sodium sulfonate groups were prepared by the aromatic nucleophilic substitution reaction of 4,4′-dichlorodiphenylsulfone (1) and sodium 5,5′-sulfonylbis (2-chlorobenzenesulfonate) (2) with bisphenols (3) in the presence of potassium carbonate in N,N-dimethylacetamide. A new monomer 2 containing the sodium sulfonate groups was synthesized by the sulfonation of 1 with fuming sulfuric acid. The polycondensation proceeded smoothly at 170°C and produced the desired poly(ether sulfone)s containing the sodium sulfonate with inherent viscosities up to 1.2 dL/g. The polymers were quite soluble in strong acid, dipolar aprotic solvents, m-cresol, and dichloromethane. The thermogravimetry of the polymers showed excellent thermal stability, indicating that 10% weight losses of the polymers were observed in the range above 460°C in nitrogen atmosphere. Both the glass transition temperatures and hydrophilicity of the polymers increased with increasing their concentrations of sodium sulfonate groups. © 1993 John Wiley & Sons, Inc.

Novel polycationic biocides: Synthesis and antibacterial activity of polymeric phosphonium salts

Abstract: Various polymeric phosphonium salts and the corresponding low-molecular-weight model compounds were prepared and their antibacterial activities against Staphylococcus aureus and Escherichia coli were explored by the viable cell counting method in sterile distilled water. Antibacterial activity of the polymers was found to be higher than that of the corresponding model compounds, particularly against S. aureus. Furthermore, the polymeric phosphonium salt exhibited a higher activity by 2 orders of magnitude than the polymeric quaternary ammonium salt with the same structure except the cationic part

Ozone‐induced graft polymerization onto polymer surface

Abstract: Ozone-induced graft polymerization was carried out to improve polymer surfaces. The polymers were exposed to ozone and the surface density of peroxides formed was determined by three methods; iodide, DPPH, and peroxidase method. The peroxide production could be readily controlled by the ozone concentration and the ozone exposure time. In addition, it was dependent on the kind of polymer. Further, it seemed probable that the ozone oxidation introduced peroxides not only on the outermost surface but also into a layer deeper from the outermost surface. Such polymeric peroxides were capable of initiating graft polymerization onto PU. All the physical and biological measurements on the grafted surface indicated that ozone-induced graft polymerization has effectively made the PU surface covered with the grafted water-soluble chains, their location being restricted to the film surface region. The interaction of the PU surface with blood components could be greatly reduced by the surface graft polymerization. © 1993 John Wiley & Sons, Inc.

Macromolecular engineering of polylactones and polylactides. X. Selective end‐functionalization of poly(D,L)‐lactide

Abstract: Functional aluminum alkoxides, such as Et 3-p Al(O-CH 2 -X) p , where p= 1,3 and X= a functional group, are very effective initiators for the (D,L)-lactide polymerization in toluene at 70°C. The coordination-insertion type of polymerization is living. Linear polyesters of a predictable molecular weight and a narrow MWD are obtained within the period of time required for the total monomer conversion. The functional group X associated with the active alcoxy group of the initiator is selectively and quantitatively attached to one chain, whereas the second end group is systematically a hydroxyl function

Perfluorocyclobutane aromatic ether polymers

Abstract: Novel polymers containing alternating perfluorocyclobutane and aromatic ether subunits are prepared from aryl poly(trifluorovinyl ether) monomers via the thermal [2π+2π] dimerization of the trifluorovinyl ether functionality. A model study is described, which probes the nature of the perfluorocyclobutane rings formed during the polymerization reaction. The bifunctional monomer 4,4'-bis(trifluorovinyloxy) biphenyl and the trifunctional monomer 1,1,1-tris(4-trifluorovinyloxyphenyl)ethane are prepared and polymerized to provide thermoplastic and thermoset polymers, respectively. Characterization of the mechanical and dielectric properties of these new polymers is presented

Gamma-, photo-, and thermally-initiated oxidation of isotactic polypropylene†

Abstract: The detailed oxidation products have been identified and compared from the γ-, photo-, and thermally-initiated oxidation of unstabilized polypropylene films. Products were identified and quantified by a combination of iodometric analysis and infrared spectroscopy. Spectral resolution was enhanced by derivatization reactions which allow the quantification of primary, secondary, and tertiary hydroperoxide and alcohol groups as well as more reliable analysis of carbonyl species. In contrast to polyethylene oxidation which yields predominantly ketone with lesser amounts of secondary hydroperoxide and carboxylic acid, polypropylene oxidizes to give predominantly tertiary hydroperoxide and lesser quantities of secondary hydroperoxide and ketone. In addition carboxylic acid groups are a minor product except at high degrees of thermal and photoinitiated oxidation. © 1993 John Wiley & Sons, Inc.

Polymeric phosphonium salts as a novel class of cationic biocides. III: Immobilization of phosphonium salts by surface photografting and antibacterial activity of the surface-treated polymer films

Abstract: Immobilized polycationic biocides with phosphonium salt on the surface of poly (propylene) film were prepared by surface photografting. These films with phosphonium salts were found to exhibit high antibacterial activity against S. aureus and E. coli-particularly against E. coli. Furthermore, morphological changes of the cells of S. aureus and E. coli in contact with the immobilized phosphonium salt were estimated by SEM. It was found that the immobilized biocides exhibited surface bactericidal activity against both strains as evidenced by shrunken and deformed cells of these species in contact with the immobilized biocides

Photopolymerization kinetics of oligo(ethylene oxide) and oligo(methylene) oxide dimethacrylates

Abstract: The influence of temperature on the photopolymerization kinetics of oligo(methylene) oxide and oligo(ethylene oxide) dimethacrylate series has been investigated by isothermal DSC. The DSC curves showed a rapid rise in rate due to the Trommsdorff effect, and then a slow decline. A shoulder, apparent on many of the DSC curves at low conversions, became more prominent when the cure temperature was lowered. The kinetics were relatively insensitive to the dimethacrylate structure in the early stages of the reaction, but became more dependent as the reaction proceeded

Synthesis, characterization, and curing of hyperbranched allyl ether-maleate functional ester resins

Abstract: SYNTHESIS, CHARACTERIZATION, AND CURING OF HYPERBRANCHED ALLYL ETHER MALEATE FUNCTIONAL ESTER RESINS

Ethylene–hexene copolymerization by heterogeneous and homogeneous Ziegler–Natta catalysts and the “comonomer” effect

Abstract: Homopolymerization of ethylene and 1-hexene and their copolymerizations were compared to investigate the influence of α-olefin on the enhancement of ethylene polymerization rate (Rp), which is often referred to as the “comonomer” effect. With the two homogeneous Ziegler–Natta catalysts, Et[Ind]2ZrCl2/MAO and (π-C5H5)2ZrCl2/MAO (MAO = methylaluminoxane), hexene causes reduction of Rp—in other words a negative “comonomer” effect. In the case of the high activity MgCl2 supported TiCl3 catalysts there is a slight positive “comonomer” effect; the Rp increases by 25 to 70% with the addition of 15 mol % of hexene. The “comonomer” effects in there catalyst systems are much smaller than that observed for the classical TiCl3 catalyst. © 1993 John Wiley & Sons, Inc.

Syntheses and properties of aromatic polyamides and polyimides derived from 9,9‐bis[4‐(p‐aminophenoxy)phenyl]fluorene

Abstract: 9,9-Bis[4-(p-aminophenoxy)phenyl]fluorene (II) was used as a monomer with various aromatic dicarboxylic acids and tetracarboxylic dianhydrides to synthesize polyamides and polyimides, respectively. The diamine II was derived by a nucleophilic substitution of 9,9-bis(4-hydroxyphenyl)fluorene with p-chloronitrobenzene in the presence of K2CO3 and then hydro-reduced. Polyamides IVa-g having inherent viscosities of 0.73–1.39 dL/g were prepared by the direct polycondensation of the diamine II with various aromatic diacids using triphenyl phosphite and pyridine as condensing agents. All the aromatic polyamides were amorphous and readily soluble in various polar solvents such as N,N-dimethylacetamide, N,N-dimethylformamide, dimethylsulfoxide, and N-methyl-2-pyrrolidone. Transparent and flexible films of these polymers could be cast from the DMAc solutions. These aromatic polyamides had glass transition temperatures in the range of 283–309°C and 10% weight loss occurred up to 460°C. The polyimides were synthesized from diamine II and various aromatic dianhydrides via the two-stage procedure that included ring-opening poly-addition in DMAc to give poly(amic acid)s, followed by thermal or chemical conversion to polyimides. The poly(amic acid)s had inherent viscosities of 0.62–1.78 dL/g, depending on the dianhydrides. Most of the aromatic polyimides obtained by chemical cyclization were found to be soluble in NMP. These polyimides showed almost no weight loss up to 500°C in air or nitrogen atmosphere. © 1993 John Wiley & Sons, Inc.

Polymeric phosphonium salts as a novel class of cationic biocides. II. Effects of counter anion and molecular weight on antibacterial activity of polymeric phosphonium salts

Abstract: Various poly[tributyl(4-vinylbenzyl)phosphonium salt]s with different counter anions were prepared and their antibacterial activities against Staphylococcus aureus were explored by the viable cell counting method in sterile distilled water. Antibacterial activity was found to be affected by the structure of the counter anions. The activity was low for a counter anion which tends to form a tight ion-pair with phosphonium ion, while it was high for those facilitating ionic dissociation to free ions. Furthermore, the molecular weight dependence of the antibacterial activity was investigated for poly[tributyl(4-vinylbenzyl) phosphonium chloride] with various molecular weights against S. aureus. Antibacterial activity was found to increase with molecular weight. Various copolymers were prepared in which the compositional ratio of tributyl(4-vinylbenzyl)phosphonium chloride to acrylamide, N-vinyl-2-pyrrolidone, or styrene was altered, and the effect of the positive charge density on the antibacterial activity was investigated against S. aureus. Antibacterial activity of the copolymers was much higher than that of the low-molecular-weight model compound and enhanced with the molar fraction of the phosphonium units in the copolymers. © 1993 John Wiley & Sons, Inc.

Influence of the seed polymer on the chromatographic properties of size monodisperse polymeric separation media prepared by a multi-step swelling and polymerization method

Abstract: Monodisperse polymer particle-based separation media were prepared by a multi-step swelling and polymerization method with two pairs of monomers and two porogenic solvents. Their chromatographic properties were compared to those of beads prepared by a corresponding suspension polymerization method without the use of seed polymer to ascertain the influence of the seed polymer on their porous structures. A large change in porous structure was observed when the swollen particle consisting of monomers and porogenic solvents contained at least one good solvent for the polystyrene seed polymer, allowing it to remain in the polymerizing medium. In contrast, when the polystyrene seed particle was excluded from the swollen oil droplets, due to its poor solubility in the monomers and the porogenic solvents, there was no difference in the chromatographic properties such as pore volume, pore size, pore size distribution, or retention selectivity between the multi-step swelling and polymerization method and the suspension polymerization method. Since the only difference between the multi-step swelling and polymerization method and the suspension method is the use of the seed polymer, it appears that a very small amount (< 1% v/v) of seed polymers in the enlarged swollen droplets plays an important role as a porogen and affects the porous structure as well as the chromatographic properties of the monodisperse polymer particle-based separation media. © 1993 John Wiley & Sons, Inc.

Absorbable biopolymers derived from dimer fatty acids

Abstract: A new class of aliphatic copolyanhydrides was synthesized from nonlinear hydrophobic dimers (FAD) of erucic acid and sebacic acid which possessed the desired physico-chemical and mechanical properties for use as a carrier for drugs. The polymers were synthesized by melt condensation to yield film-forming polymers with molecular weights of 250,000. The copolymer composition was determined by 1H-NMR and gravimetric methods. In vitro degradation studies showed that these polymers degrade following a first-order kinetics with a rapid degradation in the first 10 days leaving a residue which is mostly the FAD comonomer. The drug release from the polymer also followed a first-order kinetics which correlates with the degradation process of the polymer. Drugs like carboplatin, methotrexate, tetracycline, and gentamicin were released in vitro for over 2 weeks and in some cases over 6 weeks. In vivo biocompatibility tests in rats and rabbits in the brain, muscle, and subcutaneously, demonstrated their toxicological inertness and biodegradability. The 1 : 1 copolymer of FAD : SA was selected as a carrier for various applications including a gentamicin-releasing implant which is now undergoing human clinical trials for the treatment of osteomyelitis. © 1993 John Wiley & Sons, Inc.

Insoluble polystyrene-bound quaternary onium salt catalysts for the synthesis of cyclic carbonates by the reaction of oxiranes with carbon dioxide

Abstract: The addition reaction of oxiranes with CO 2 was performed using insoluble polystyrene beads containing pendant quaternary ammonium or phosphonium salts as catalysts under atmospheric pressure. The reaction of oxiranes with CO 2 proceeded smoothly catalyzed by 1-2 mol % of the polymer-supported quaternary onium salts to give the corresponding cyclic carbonates in high yields at 80-90°C. The catalytic activity of the polymer-supported quaternary onium salts was strongly affected by the degree of ring substitution of the onium salt residues to the polymer, the degree of crosslinking of the polystyrene beads, the hydrophobicity of of the alkyl group on the onium salts and the kind of onium salt

Infrared spectroscopy studies of the cyclic anhydride as the intermediate for the ester crosslinking of cotton cellulose by polycarboxylic acids. I. Identification of the cyclic anhydride intermediate

Abstract: The mechanism of esterification of cotton cellulose by a polycarboxylic acid was investigated using Fourier transform infrared spectroscopy (FT-IR). The infrared spectroscopic data indicate that a polycarboxylic acid esterifies with cotton cellulose through the formation of an acid anhydride intermediate. A five-member cyclic anhydride intermediate was identified in the cotton fabric treated with poly(maleic acid). The five-member cyclic anhydride is a reactive intermediate and readily esterifies when reaction sites are available. We also found that those polycarboxylic acids, which form five-member cyclic anhydride intermediates, crosslink cotton cellulose more effectively than those polycarboxylic acids which form six-member cyclic anhydride intermediates. © 1993 John Wiley & Sons, Inc.

Thermogravimetric study of polyacrylamide with evolved gas analysis

Abstract: Dried samples of polyacrylamide in an He atmosphere have been subjected to thermogravimetric analysis in the 30-600°C range, and the evolved gases were monitored by FTIR. Water, ammonia, and small quantities of CO 2 are released in the first stages of decomposition (220-340°C), where the polymer chains remain intact and the reaction occurs on the pendant amide groups. In the second stage of decomposition (340-440°C), the majority of the weight loss occurs, and main chain breakdown occurs, releasing CO 2 , water, nitrile compounds, and imides. GC-FTIR and GC-MS results reveal the presence or more than 20 decomposition products and confirm that a large proportion of these can be assigned to glutarimide and its substituted analogues

The influence of microstructure and monomer properties on the erosion mechanism of a class of polyanhydrides

Abstract: The erosion of three different polyanhydrides consisting of sebacic acid (SA) and 1,3-bis(p-carboxyphenoxy) propane (CPP) was investigated. Melt cast polymer matrices were prepared from the homopolymer p(SA) and two copolymers, p(CPP-SA) 20 : 80 and p(CPP-SA) 50 : 50. Particular attention was paid to the influence of the polymer matrix microstructure and of the monomers on erosion. Using polarized light microscopy we found that p(SA) and p(CPP-SA) 20 : 80 matrices consist of spherulites. SEM investigations showed that their crystalline parts are more resistant to erosion than their amorphous areas. The matrices erode into highly porous devices, whose porosity is detectable by mercury porosimetry. Using wide-angle x-ray diffractometry we found that monomers crystallize inside the pores. DSC investigations showed a maximum of crystallized SA after 2-6 days and a continuous increase of CPP, which stays in the devices for weeks. We conclude that the microstructure and the monomer properties are the two main factors which determine the erosion of these polymers. The obtained data on changes in porosity, crystallinity, polymer matrix thickness, erosion front velocities, crystalline monomer content, and monomer release provides the basis for quantitatively describing the erosion process.

Synthesis and characterization of novel epoxy monomers and liquid crystal thermosets

Abstract: Four new epoxy monomers have been synthesized and characterized as part of a program to prepare novel liquid crystal thermoset (LCT) materials. Three of the new epoxy monomers contained a biphenyl mesogen and were not liquid crystalline (LC). The remaining epoxy monomer, which contained a 1,4-dibenzoyloxybenzene mesogen, was synthesized in an overall yield of 30% and displayed a broad (83°C) nematic liquid crystalline phase. The new liquid crystalline epoxy monomer was cured at 120°C and postcured at 175°C with a stoichiometric amount of 1,4-phenylenediamine. The thermal transitions of the resulting LCT were studied by differential scanning calorimetry (DSC), polarized light optical microscopy (POM), thermomechanical analysis (TMA), and wide angle x-ray diffraction (WAXD) as a function of cure time and temperature. A process characterization diagram was constructed which shows that LCTs based on this new LC monomer can be processed in the liquid crystalline phase over a broad range of times and temperatures. Qualitative agreement with previous epoxy LCT results was found, as LCT's with smectic phases and without clearing temperatures were observed at long cure times (high crosslink densities), whereas nematic phases with clearing temperatures predominated in networks at short cure times (low crosslink densities). © 1993 John Wiley & Sons, Inc.

Effects of diamine monomer structure on the gas permeability of polyimides. I. Bridged diamines

Abstract: Permeability measurements for oxygen and nitrogen were carried out on polyimides prepared from 5,5'-[2,2,2-trifluoro-1-(trifluoromethyl)ethylidene]bis-1,3-isobenzofuranedione (6FDA) and a variety of substituted methylene dianilines and benzidines. A correlation between the diamine monomer structure and polymer permeability was found, particularly with diamine monomer variations at the ortho positions of the diamine relative to the amino moiety. These correlations were semilogarithmic, relative to the summation of the substituent volumes. Direct correlations were observed between the measured properties of polymer density and interchain d-spacings and the oxygen permeability of each of these polyimides

Light-induced polymerization of new highly reactive acrylic monomers

Abstract: Acrylic monomers containing an oxetane, dioxolane, oxazolidone or carbonate group in their structural unit have been shown to copolymerize rapidly and extensively with a poly-urethane-diacrylate, upon UV radiation. For the most reactive resin, 50% conversion was reached within 3 ms of exposure to a medium-pressure mercury lamp. The kinetics of these ultrafast polymerizations was studied quantitatively by IR spectroscopy. The rate of polymerization, photosensitivity, and amount of residual acrylate in the cured polymer were determined for the various monomers studied, and compared to the values obtained with conventional mono-, di-, and triacrylates