Indomethacin release behaviors from pH and thermoresponsive poly(vinyl alcohol) and poly(acrylic acid) IPN hydrogels for site-specific drug delivery

A temperature- and pH-responsive drug delivery system was studied by using interpenetrating polymer network (IPN) hydrogels constructed with poly(acrylic acid) (PAAc) and poly(vinyl alcohol) (PVA). The release of indomethacin incorporated into these hydrogels showed pulsatile patterns in response to both pH and temperature. Indomethacin diffused from the polymer matrices through the swelling and deswelling mechanism. The release amount increased at higher temperature because of the swelling caused by the dissociation of hydrogen bonding. The drastic change of drug release was achieved by alternating pH of the buffer solution and was attributed to the change of states of ionic groups within IPN hydrogels. The free water contents were calculated by using differential scanning calorimetry (DSC), and were proved to be the main factor in the swelling. These results demonstrated that the drug release could be controlled by the swelling/deswelling degree of IPN hydrogels as functions of pH and/or temperature. © 1997 John Wiley & Sons, Inc. J Appl Polm Sci 65: 685–693     

Effect of synthesis parameters on thermal behavior of phenol–formaldehyde resol resin

Differential scanning calorimetry (DSC) was used to investigate the influence of resin synthesis parameters on the thermal behavior of low molecular weight phenol–formaldehyde (PF) resol resins prepared with different formaldehyde/phenol (F/P) molar ratios, different sodium hydroxide/phenol (NaOH/P) molar ratios, and different catalysts. As the F/P molar ratio increased, the molecular weight and activation energy increased while the gel time, peak temperature, resin pH, and nonvolatile solids content decreased. By contrast, the molecular weight, gel time, resin pH, resin solids content, and peak temperature increased with an increasing NaOH/P molar ratio. However, the activation energy decreased with an increasing NaOH/P molar ratio. The polydispersity increased with both F/P and NaOH/P ratios. Calcium hydroxide gave a faster curing resin compared to sodium and potassium hydroxides. All DSC thermograms of this study showed just a single exothermic peak for the resins that were used. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 83: 1415–1424, 2002     

Possible phosphorus‐bromine synergy in polyester‐cotton fabrics treated with tetrabromobisphenol‐A and diammonium phosphate

Polyester/cotton fabrics were treated with tetrabromobisphenol‐A (TBBA)/epichlorohydrin (EPI) aqueous solution, followed by being treated with diammonium phosphate (DAP)/urea solution. The optimum mole ratio of EPI to TBBA was determined. The synergism of TBBA and DAP was found to operate on the treated fabrics. The maximal synergism was obtained when the bath concentration of TBBA was equal to that of DAP. The mechanism of flame‐retardancy was analyzed by thermogravimetry and residue number. The flame‐retardancy of the polyester/cotton fabrics treated with TBBA/DAP was found operative mainly in the condensed‐phase mechanism. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 84: 172–177, 2002; DOI 10.1002/app.10292     

Modeling light scattering by spherical pores for calculating the transmittance of transparent ceramics – All you need to know

In this paper transmittance predictions based on residual pore scattering in transparent ceramics with cubic crystallites via Mie theory and its approximations (Rayleigh, Fraunhofer, van de Hulst and Rayleigh-Gans, including the small- and large-size limits) are recalled and systematically compared. Due to the high phase contrast, the difference between different types of ceramics is of secondary importance, so that the essential conclusions are of general validity for all types of transparent ceramics. It is shown that the Rayleigh-Gans approximation and its large-size limit provide surprisingly good transmittance predictions, although it has not often been used in the ceramic literature. The main conclusion of this paper is that, of all the approximations presented here and used in ceramic science so far, the van de Hulst approximation is the one that most closely approaches the exact Mie results, although it has been largely ignored in the literature on transparent ceramics so far.     

The effect of limited monomer solubility in heterogeneous step-growth polymerization

Limited monomer solubility imposes very intriguing features on poly(p-phenylenebenzobisoxazole) polymerization. Only one type of functional group is detected at oligomer chain ends, and a high-molecular-weight polymer is obtained even when an excess of the monomer with low solubility is used. These remarkable phenomena are interpreted as an unprecedented "spoon-feeding-of-monomer" mechanism. A novel apparatus for staged polymerization is described that was triggered by the uniqueness of the heterogeneous step-growth polymerization. Hyperbranched polyesters and a polyurethane/polyethylene blend, which represent two phases in the polymerization process, are also discussed.     

Simulation and experimental study of microwave heating of single lap adhesive‐bonded polypropylene joint

Microwave heating of modeled single lap adhesive‐bonded polypropylene joint was simulated using a computer program. The modeled joint was heated in an applicator based on a standard rectangular waveguide WR340 operating at 2.45 GHz with TE₁₀ mode. The heating process was represented by a 2‐dimensional numerical model developed previously by the authors. The temperature distribution in the adhesive layer and the heating rate of the joint were predicted. The simulated results were validated by experiments. It was found that the simulation gave reasonably accurate prediction of the microwave heating of an adhesive joint. Polym. Eng. Sci. 44:728–735, 2004. © 2004 Society of Plastics Engineers.     

Preparation of porous poly(D,L‐lactide) and poly(D,L‐lactide‐co‐glycolide) membranes by a phase inversion process and investigation of their morphological changes as cell culture scaffolds

Porous membranes composed of the biodegradable polyesters poly(D,L ‐lactide) (PLA) and poly(D,L ‐lactide‐co‐glycolide) (PLGA) were prepared by a phase inversion process. The molecular weights of the polymers and the concentrations of the polymer solutions affected the pore size and structure of the PLA and PLGA membranes. The molecular weights and morphological changes of the membranes as a function of time were investigated under incubation at 37°C in a humidified 5% CO₂ atmosphere. The pores that formed in the membranes changed dramatically with increasing time under these conditions. From the thermal characterization of the polymers in their dry and wet states, we found that the glass‐transition temperatures of PLA and PLGA affected morphological structure changes in the porous membranes. We also prepared a collagen‐coated membrane to improve the interaction between the cell and the substrate, and we observed that the collagen coating enhanced the attachment and growth of Chinese hamster ovary cells on the substrate. Finally, we found that only PLA was a suitable material to prepare a porous membrane scaffold with the phase inversion process with PLA, and a collagen coating was necessary for cell culture on the membrane. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 2082–2092, 2004     

Optical thermometry of Sm3+ on laser‐induced local heating for precipitation of PbS quantum dots in glasses

Fluorescence intensity ratios (FIRs) of the 640 nm and 602 nm emissions from Sm³⁺ were recorded at various temperatures T to identify the temperature increases ΔT associated with laser‐induced local heating of Ag nanoparticles. The FIRs increased as intensities of the excitation beam from a 532‐nm continuous‐wave laser increased. Estimated T of the irradiated region increased to as high as 586°C when at laser irradiation of 1.5 W on the surface containing Ag nanoparticles. Local heating due to the surface plasmon resonance of Ag nanoparticles is a main reason for the ΔT that eventually leads to precipitation of PbS quantum dots in glasses.     

Durable flame‐retardant treatment of polyethylene terephthalate (PET) and PET/cotton blend using dichlorotribromophenyl phosphate as new flame retardant for polyester

Dichlorotribromophenyl phosphate (DCTBPP) was synthesized via the reaction of tribromophenol and phosphorous oxychloride and characterized by elemental analysis, IR, ¹H‐NMR, thermogravimetric analysis, and differential scanning calorimetry. To impart durable flame retardancy the poly(ethylene terephthalate) (PET) fabric was treated with DCTBPP via pad–dry–thermosol fixation and the PET/cotton (50/50) blend fabric was treated with both DCTBPP and tetrakis(hydroxymethyl) phosphonium chloride (THPC)/urea precondensate via a two‐bath sequential treatment. The treated PET fabric's increased limiting oxygen index value was proportional to the increasing DCTBPP application level and showed self‐extinguishing properties at 8.1% add‐on, even after 50 washes. The blend fabric treated with 15% DCTBPP and 30% THPC/urea precondensate became self‐extinguishable and durable to 50 washes, and the treated fabric retained over 85% of its breaking strength without excessive stiffness. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 81: 793–799, 2001