摘要:

AbstractA wide range of infinite urethane polymer networks were prepared from poly(ethylene glycol) (PEG) and hexamethylene diisocyanate (HMDI) using 1,1,1‐tris‐(hydroxymethyl) ethane (THME) as the cross‐linking agent. The influence of temperature, cross‐linking, and crystallinity on the swelling character of the hydrogel has been discussed. The toxicity of the network polymer by intravaginal implants in rats was studied. Implantation of the polymer did not result in alteration in behavior and feed intake or any pathological changes in the tissue. Vaginal fluids from the polymer‐implanted rats or the polymer extract when inoculated on a listeria monocytogene culture plate were unable to inhibit the bacterial growth. © 1993 John Wiley

ISSN:0021-8995    

DOI:10.1002/app.1993.070491201

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

年代:1993

数据来源: WILEY

摘要:

AbstractA series of poly(tert‐butyl acetylene) (PTBA) polymers was prepared withciscontents, as characterized by13C NMR spectroscopy, ranging from 44% to 100%. The sorption and transport properties of propane in this systematically varied series were determined by a sensitive gravimetric sorption technique. As theciscontent of the polymer increased, propane solubility and diffusivity decreased markedly and thed‐spacing, determined by wide angle x‐ray diffraction spectroscopy, decreased monotonically with increasingciscontent, suggesting that higher order molecular structure, related explicitly to configurational variations, may strongly influence chain packing in these rigid, glassy materials and, in turn, sorption and transport properties of small molecules in this polymer series. © 1993 John Wiley&Son

ISSN:0021-8995    

DOI:10.1002/app.1993.070491202

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

年代:1993

数据来源: WILEY

摘要:

AbstractHydrophilic sodium carboxymethylcellulose (NaCMC) matrices were chemically modified into hydrophobic gels by ionotropic crosslinking with cupric or ferric ion under ambient temperature and pH. Insoluble matrices were also prepared using an interactive polymer gelatin in combination with NaCMC. These matrices underwent erosion at the crosslinks, followed by matrix erosion when released in water. The matrix erosion in water was influenced by the gelling agent, initial crosslinker density, and gelatin content in the insolubilized matrices. The apparent diffusion coefficients of fenthion ranged from 7.2 × 10−9to 175.6 × 10−9cm2/sec, with matrices prepared under different conditions. These erosion‐controlled matrices can be used for the controlled release of various biologically active agents. © 1993 John Wiley&S

ISSN:0021-8995    

DOI:10.1002/app.1993.070491203

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

年代:1993

数据来源: WILEY

摘要:

AbstractConventional polymers are compared as gas separation membrane materials with “tailormade” polymers. The increased permeability of the latter are due to their higher free volume available for gas transport. The increased free volume is associated with the rigidity polymer backbone. Free volume is obtained by subtracting the occupied volume, calculated using group contributions from the polymer specific volume. Wide Angle X‐ray techniques are used to obtain averaged‐spacings that are interpreted in terms of average intermolecular space, and that are related to permeability data. These highly permeable rigid polymer membranes have high glass transition temperatures. The physical parameters, that is, Tgand the jump in heat capacity (ΔCp), are obtained with Differential Scanning Calorimetry, and are used to obtain an estimation of free volume. A good correlation for a series of random copoly[p,m‐phenylene(4‐phenyl)‐1,2,4‐triazoles] is obtained. A relationship between permeability and a free volume term, which can be estimated from thermodynamic properties, is equally valid for a wide variety of conventional polymers. © 1993 Joh

ISSN:0021-8995    

DOI:10.1002/app.1993.070491204

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

年代:1993

数据来源: WILEY

摘要:

AbstractBiodegradable thermoplastic composites reinforced with wheat straw fibers were prepared. The matrix was an expensive polyester, poly‐3‐hydroxy‐butyrate (PHB), produced by bacterial fermentation. Before being mixed with the PHB, the wheat straw fibers were subjected to a steam explosion process that induces morphological and structural changes in lignocellulosics. Such changes enhance the interaction with the thermoplastic matrix. The two components were melt mixed and the composite molded under hot compression. Compared with neat PHB, not only does the composite material show better mechanical properties but, moreover, production costs are dramatically reduced because wheat straw is a very inexpensive product. Finally, FTIR measurements revealed some PHB/straw fiber molecular interactions that interfere with the PHB crystallization. © 1993 John Wiley&Son

ISSN:0021-8995    

DOI:10.1002/app.1993.070491205

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

年代:1993

数据来源: WILEY

摘要:

AbstractA series of semi‐interpenetrating polymer networks (semi‐IPN) have been prepared from acetylene‐terminated sulfone (ATS‐C) oligomer and high‐performance thermoplastic (TP) blends. The cure characteristics and thermal properties of ATS‐C and semi‐IPNs are presented in this paper. The addition of thermoplastics has no effect on the mechanism of ATS‐C cure reaction and thermal behavior of cured systems. The glass‐transition temperature (Tg) and heat distorsion temperature (HDT) of thermoplastics are remarkably decreased with adding ATS‐C. The higher theTgand HDT of the thermoplastics, the more obvious the reduction ofTgand HDT. In the case of fully cured semi‐IPNs, theTgand HDT value of the TP phase are higher than or equal to theTgand HDT of pure TP. The thermal stabilities of semi‐IPNs decrease as the content of ATS‐C oligomer increases. ©

ISSN:0021-8995    

DOI:10.1002/app.1993.070491206

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

年代:1993

数据来源: WILEY

摘要:

AbstractDrawn poly(ethylene terephthalate) fibers (D.R. 5 : 1) were treated unrestrained in dimethylformamide and benzaldehyde at 100°C for varying amounts of time. A rapid diffusion of liquids into the polymer occurred, the latter experiencing considerable retention of the absorbed liquids at 60°C. The increase in chain mobility brought about by both the liquids absorbed and the liquid‐induced crystallisation that followed allowed orientation strains existing in the polymer structure to be relieved. This brought about a 20% shrinkage in the polymer and a change in its overall geometry. Subsequently, a sharp drop occurred in the level of liquid retention within the polymer signifying expulsion of liquids from the crystallising domains and ultimately a levelling off (equilibrium) in the weight retention kinetics.However, precrystallisation of the fibers at 200°C for 3 h using dry hot air prior to liquid treatment study at 100°C and retention at 60°C, led to a linear increase in the amount of liquid retained in the polymer as a function of time until an equilibrium was established. The essential feature of the latter liquid retention kinetic is that a plot of the amount of relative liquid retained, that isMt/M∞as a function of square root of time, ($\[ \sqrt t \]$) agrees with Fick's standard diffusion process. © 1993 John Wiley&

ISSN:0021-8995    

DOI:10.1002/app.1993.070491207

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

年代:1993

数据来源: WILEY

摘要:

AbstractWater‐insoluble proteases were prepared by immobilizing lipoprotein lipase (LPL) onto the surface of porous polyvinyl alcohol (PVA) beads by covalent fixation. The relative activity of the immobilized proteases was found to remain high toward small ester substrates,p‐nitrophenyl laurate (pNPL). The relative activity of the immobilized LPL by cyanogen bromide (CNBr) method decreased gradually with the decreasing surface concentration of the immobilized LPL on the porous PVA beads. On the contrary, the immobilized LPL by hexamethylene diisocyante (HMDI) method gave an almost constant activity for the substrate hydrolysis within the surface concentration region studied and gave higher relative activity (RA) than that by the CNBr method. The Michaelis constant,Km, and the maximum reaction velocity,Vm, were estimated for the free and the immobilized LPL. The apparentKmwas larger for the immobilized LPL than for the free one, andVmwas smaller for the immobilized LPL. The pH, thermal, and storage stabilities of the immobilized LPL were higher than those of the free ones. The initial enzymic activity of the immobilized LPL maintained almost unchanged without any leakage and inactivation of LPL when the batch enzymic reaction was performed repeatedly, indicating excellent durability of the immobilized LPL. © 1993 John Wiley&Sons,

ISSN:0021-8995    

DOI:10.1002/app.1993.070491208

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

年代:1993

数据来源: WILEY

摘要:

AbstractCardanol was functionalised to incorporate elements such as phosphorus and bromine and polymerised with formaldehyde or hexamethylenetetramine (HMTA) to get flame retardant polymers. Thus, monocardanyl phosphoric acid (MCPA), its bromoderivative (BrMCPA), and their formaldehyde condensates (MCPAF and BrMCPAF) and cross‐linked polymers were prepared and characterized by IR, NMR, and GPC. Flammability and thermal stability of these polymers were evaluated by LOI and TGA, respectively, and compared with those of conventional cardanol‐formaldehyde (CF) resin and its bromoderivative. TGA of MCPAF showed that although it is initially less stable than that of CF, its stability increases above 500°C over that of CF. Char yields of MCPAF and BrMCPAF are 21 and 27, respectively, and corresponding LOI values are 27 and 49. The present data do not support any synergism nor any additive effect between phosphorus and bromine, but a positive interaction between them is indicated with phosphorus mainly contributing in the condensed phase and bromine in the vapour phase mechanism. The activation energies in the range 20–30 kcal/mol for MCPAF suggest an ionic mechanism for its decomposition, whereas mainly a free radical type of decomposition is inferred for BrMCPAF with an activation energy in the range of 35–50 kcal/mol. © 1993 John Wiley&

ISSN:0021-8995    

DOI:10.1002/app.1993.070491209

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

年代:1993

数据来源: WILEY

摘要:

AbstractThe determination of transient and/or steady‐state conductivity of polyethylene terephthalate (PET) ultrathin films by means of electrode configurations involving any load or stress imposed on the measuring area during measurement usually leads to anomalous behaviours of the charging current and thus prevents a good evaluation of the electrical properties of the samples. This can be avoided by the use of a two‐electrode system with lateral contacts, to obtain reproducible results without any requirement for previous mechanical, thermal, or electrical treatments (as is often recommended in the literature), and that permits the characterization of industrial films down to 1.5‐μm thick in true storage conditions after production. © 1993 John Wiley&So

ISSN:0021-8995    

DOI:10.1002/app.1993.070491210

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

年代:1993

数据来源: WILEY