摘要:

AbstractPolylactide (PLA)‐poly(ethylene glycol) (PEG) copolymers were synthesized from polyethylene glycol andD,L‐lactide using low toxic stannous octoate as catalyst at 180°C by bulk polymerization. The copolymers were characterized by GPC, IR, and13C‐NMR. A full assignment NMR spectrum is presented. The physical, drug release, and biodegradable propertiesin vitroof PLA–PEG copolymers were investigated. The result indicates that the rates of drug release and biodegradation could be tailored by adjusting polymer composition. This amorphous material might be used as a drug carrier in medical appl

ISSN:0021-8995    

DOI:10.1002/app.1990.070390101

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1990

数据来源: WILEY

摘要:

AbstractStarch graft superabsorbents were prepared by graft copolymerization either with polyacrylonitrile (PAN) and saponification of the resulting copolymer or with trimethyl–aminoethylacrylate chloride (CMA) and methylene bisacrylamide as crosslinking agent. The influence of several structural parameters on the swelling properties of these absorbents have been studied: crosslink density, ionic content, and composition of the starch. As expected, the absorbency decreases with an increase of the crosslink density. It increases with the ionic content of the graft copolymer up to a maximum, an excess of charges leading to a swelling decrease. The PAN branch length depends on the origin of the starch. High molar weight PAN was grafted onto waxy corn, a starch with high amylopectin content. The swelling increases with increasing molar weight of PAN up to 5 × 105. In saline solution the absorbency of both ionic gels decreases significantly. However, in the presence of multivalent ions their behavior is different. For cationic absorbents the swelling depends on the ionic strength but not on the ion valency. On the other hand, anionic absorbents are significantly affected by multivalent catio

ISSN:0021-8995    

DOI:10.1002/app.1990.070390102

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1990

数据来源: WILEY

摘要:

AbstractHandsheets of post‐treated chemithermomechanical pulps (CTMP) and a sample of Whatman paper no. 1 were analyzed using an ESCA spectrometer. All of these samples revealed the presence of the C1, C2, and C3components in the carbon (1s) peak and the O2component in the oxygen (1s) peak; the O1peak component which was present in the other samples was missing from the Whatman paper. Pulp sulfonation produced a reduction in C1representing the group of carbon not bonded to oxygen, and an increase in C2with C3remaining relatively constant. These changes imply reductions in lignin and extractives and a corresponding increase in cellulose content on the fiber surface. Extrapolation of the C1, C2, C1/C2, and O/C curves of CTMP to zero percent sulfonation yielded the same values as those obtained for pure TMP. ESCA analysis allows us to monitor the increase of sulfur content as a function of sulfonation in accordance with results obtained from bulk pulp sulfonate content titratio

ISSN:0021-8995    

DOI:10.1002/app.1990.070390103

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1990

数据来源: WILEY

摘要:

AbstractPermeabilities of cast films of certain cationic acrylate methacrylate copolymers have been determined using a double (donor and acceptor) compartment cell. Permeation rates of urea (nonionic permeant) and sodium chloride (ionic permeant) were determined as functions of the polymer cation content. A decrease in film permeability accompanied the decrease in polymer cation content generally; the change was more marked with sodium chloride compared with urea. The films were also generally more permeable to urea; the difference increased at lower polymer cation content to about 400‐fold. While urea promoted film swelling, sodium chloride decreased it. Electron micrographs of the film section displayed compact skin zones which must be swelled to allow solute permeation. Asymmetry characterized the flux, the film lower surface (in contact with the mold during casting) being more permeable than its upper surface. This effect was more pronounced when sodium chloride was used as permean

ISSN:0021-8995    

DOI:10.1002/app.1990.070390104

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1990

数据来源: WILEY

摘要:

AbstractEffects ofE/Pratio of the EPDM rubber on the flow behavior and morphology of the crosslinkable polyethylene and EPDM blends have been studied as a function of shear rate and processing temperature. High‐E/P‐ratio EPDM rubber exhibits high viscosities within the temperature range studied but the extrudate swell is higher for the lowE/Pratio EPDM. Shear modulus, stored elastic energy and flow activation energy are higher for highE/Pratio EPDM but relaxation time is higher for lowE/Pratio EPDM. At a particular blend ratio these rheological parameters show a change in their pattern. This point of change in pattern occurs at a lower level of EPDM having a highE/Pratio; this suggests an early phase inversion as corroborated by the SEM studies. Melt fracture occurs to a larger extent for the lowE/Pratio EPDM in its blends with X

ISSN:0021-8995    

DOI:10.1002/app.1990.070390105

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1990

数据来源: WILEY

摘要:

AbstractHigh pressure injection molding of HDPE with relatively high molecular weight is known to give products with significantly increased modulus and strength. The extent of this improvement is reduced when the thickness of the molded sample increases. The present paper is an account of experiments with varying mold filling rates and gate geometries. After choosing proper gating and then optimizing the filling rate, thick samples with tensile moduli previously characteristic of thinner samples have been obtained. The modulus data are supplemented by measurements of the melting point of the normal and high‐strength HDPE structures at different locations in the molded test bars. Corresponding crystallinity data are also included. The structure of the samples appears to provide some guidance in interpreting the observed modulus variation

ISSN:0021-8995    

DOI:10.1002/app.1990.070390106

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1990

数据来源: WILEY

摘要:

AbstractPoly(4,4′‐thiodiphenyl phthalates) (iso/tere) have been synthesized using both low temperature step‐growth and phase‐transfer catalyzed polymerization techniques. These polymers were characterized using conventional techniques like elemental analysis, solubility characteristics, X‐ray diffraction, infrared, and proton nuclear magnetic resonance spectroscopy. 4,4′‐Thiodiphenyl dibenzoate was used as a m

ISSN:0021-8995    

DOI:10.1002/app.1990.070390107

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1990

数据来源: WILEY

摘要:

AbstractNew phenolic resins containing titanium and silicon in the main polymer structure were synthesized and some of their properties were investigated. Titanium and silicon contents of the polymers ranged from 2 to 13% titanium and from 2 to 5% silicon. These polymers became insoluble and infusible as the titanium and silicon contents of the products were increased. IR spectra of these modified resins were presented. The thermal oxidative degradations of the phenolic resins modified with titanium and silicon were also investigated using thermogravimetry and differential thermal analysis. Titanium and silicon‐modified polymers, showed considerably lower weight changes as compared with those of unmodified or titanium‐modified polymers, but the rate of the last oxidative degradation increased and the final degradation temperature decreased with increasing titanium concentration. The best results for the thermal resistance was found to be 2% ≤ Ti ≤ 6% and

ISSN:0021-8995    

DOI:10.1002/app.1990.070390108

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1990

数据来源: WILEY

摘要:

AbstractIn order to shed light on the relationship of monomer structure and adhesiveness to tooth enamel, methacrylamides having various substituents were synthesized and evaluated as dental adhesives. Among 17 methacrylamides synthesized here, those havingN‐m‐ andN‐p‐carbethoxyphenyl,N‐p‐fluorophenyl, andN‐3‐carboxycyclohexyl groups showed adhesive tensile strength of more than 100 kg/cm2with minimal drops in strength on standing, indicating high potentials as novel adhesives. It was also confirmed that a carboxyl group enhances adhesive tensile strength peculiarly regardless of skel

ISSN:0021-8995    

DOI:10.1002/app.1990.070390109

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1990

数据来源: WILEY

摘要:

AbstractPotassium aluminium sulfate, hereafter referred to as alum, was used as a flame retardant for some Nigerian timbers. It was observed that flame spread rate and after‐glow time were drastically reduced. Thermogravimetric analysis shows that alum functions as a flame retardant (FR) by a complex process that entails the dehydration, condensed phase, and the vapor phase mechanism

ISSN:0021-8995    

DOI:10.1002/app.1990.070390110

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1990

数据来源: WILEY