Dynamic light scattering measurements on the polystyrene/ethyl acetate system at semi-dilute concentrations as a function of temperature

Summary Measurements of autocorrelation functions extending over a broad time range are reported for a sample of polystyrene in ethyl acetate as a function of temperature between –44°C (-temperature) and 70°C. The corresponding spectra of decay times are obtained by two mathematical methods. The existence of three dynamic processes is shown and their temperature and angular behaviour is studied.     

Thermal properties measurements of renatured gelatin using conventional and temperature modulated differential scanning calorimetry

The thermal properties of amorphous gelatin films and gelatin films with renatured structural order were measured by using conventional and temperature modulated differential scanning calorimetry (DSC). Different amounts of gelatin structural order associated with a melting enthalpic change in the DSC measurement were prepared based on different gelatin drying conditions. Two consecutive heating and cooling DSC measurements on the gelatin films showed that there was no change in the glass‐transition temperature (T_g) for the amorphous gelatin but there was a decrease in the T_g for the structural gelatin on the second DSC scan. This decrease was attributed to the plasticizing effect from the release of originally hydrogen‐bonded water associated with the structural gelatin. In addition, a reversing endotherm observed upon melting of the structural gelatin during a temperature modulated DSC measurement indicated that the transition of bound water to free water occurred as the partial triple‐helix gelatin melted. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 99: 1795–1801, 2006     

Effects of melt‐extension and annealing on row‐nucleated lamellar crystalline structure of HDPE films

The row‐nucleated lamellar crystalline structure of high‐density polyethylene (HDPE) films was prepared by applying elongation stress to HDPE melt during T‐die cast film extrusion and subsequently annealing the extruded films. This unusual crystalline structure was analyzed in terms of lamellar crystalline orientation, long‐period lamellar spacing, crystallite size, and degree of crystallinity. The contribution of melt‐extension represented by draw‐down‐ratio (DDR) to the overall orientation was found to be most noticeable than other processing variables. Meanwhile, the long‐period lamellar spacing, the crystallite size, and the degree of crystallinity were influenced predominantly by the annealing temperature. Finally, the processing (melt extension and annealing temperature) – structure (lamellar crystalline structure) – property (hard elasticity) relationship of HDPE films was investigated. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 3326–3333, 2007     

Preparation and characterization of modified starch‐based plastic film reinforced with short pulp fiber. II. Mechanical properties

Native corn starch‐ and hydroxypropylated starch (HPS‐) based plastic films were prepared using the short pulp fiber as the reinforcement and the glycerol as the plasticizer. The results of tensile test showed that the strain and stress at break and elastic modulus increased with pulp content. With glycerol content, the strain at break increased considerably, but the breaking stress and elastic modulus decreased. And the stress–strain curves showed that the brittleness problem of films was overcome by the pulp, glycerol, and water content. The hydroxypropyl starch films showed results similar to those of the native starch films. The results of the three‐point bending test showed that maximum deflection, flexural strength, and specific work increased with pulp content, but the flexural modulus was the highest at a pulp content of 20%. And with the glycerol content, the maximum deflection and specific work of rupture increased, but the bending elastic modulus decreased. The hydroxypropyl starch films showed results similar to those of native starch films as far as the maximum deflection and flexural strength were concerned, but the bending elastic modulus and specific work of the hydroxypropyl starch films were considerably lower than those of starch films. So it was concluded that the flexibility of films was improved by the hydroxypropylation. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 2108–2117, 2003     

Toughness response of vinylester/epoxy‐based thermosets of interpenetrating network structure as a function of the epoxy resin formulation: Effects of the cyclohexylene linkage

Vinylester/epoxy (VE/EP)‐based thermosets of interpenetrating network (IPN) structures were produced by using a VE resin (bismethacryloxy derivative of a bisphenol A–type EP resin) with aliphatic (Al‐EP) and cycloaliphatic (Cal‐EP) EP resins. Curing of the EP resins occurred either with an aliphatic (Al‐Am) or cycloaliphatic diamine compound (Cal‐Am). Dynamic mechanical thermal analysis (DMTA) and atomic force microscopy (AFM) suggested the presence of an interpenetrating network (IPN) in the resulting thermosets. Fracture toughness (K_c) and fracture energy (G_c) were used as the toughness characterization parameters of the linear elastic fracture mechanics. Unexpectedly high K_c and G_c data were found for the systems containing cyclohexylene units in the EP network, such as VE/Al‐EP+Cal‐Am and VE/Cal‐EP+Al‐Am. This was attributed to the beneficial effects of the conformational changes of the cyclohexylene linkages (chair/boat), which were closely analogous to those in some thermoplastic copolyesters. The failure mode of the VE/EP thermoset combinations was studied in scanning electron microscopy (SEM) and discussed. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 2124–2131, 2003     

Effects of nano‐ and micro‐fillers and processing parameters on injection‐molded microcellular composites

The effects of submicron core‐shell rubber (CSR) particles, nanoclay fillers, and molding parameters on the mechanical properties and cell structure of injection‐molded microcellular polyamide‐6 (PA6) composites were studied. The experimental results of PA6 nanocomposites with 5.0 and 7.5 wt% nanoclay loadings and of CSR‐modified PA6 composites with 0.5 and 3.1 wt% CSR loadings were compared to their neat resin counterparts. This study found that nanoclay was more efficient in promoting a smaller cell size, larger cell density, and higher tensile strength for microcellular injection molding parts. A higher nanoclay loading led to more brittle behavior for microcellular parts. It was found that a proper amount of CSR particles could be added to the microcellular injection‐molded PA6 to reduce the cell size, increase the cell density, and enhance the toughness of the molded part. However, CSR particles were less effective cell nucleation agents as compared to nanoclay for producing desirable cell structures, and a higher CSR loading was found to have diminishing effects on the process and on the properties of the parts. POLYM. ENG. SCI., 45:773–788, 2005. © 2005 Society of Plastics Engineers     

Study on esterification of acrylic phenolic resin by maleic anhydride and photocrosslinking properties of the alkali‐soluble product

An alkali‐soluble, photocrosslinkable polymer was synthesized by esterification of OH groups of acrylic phenolic resin with maleic anhydride. The OH groups were formed by the ring‐opening reaction of epoxy groups of epoxy phenolic resin with acrylic acid. The esterification conditions were studied. The results showed that it is better to use tetramethyl ammonium bromide as catalyst than N,N‐dimethylbenzylamine. The conversion of maleic anhydride in acetone can reach about 80% at 56°C for 4 h. The purified product was characterized by IR, DSC, and TGA. The product containing acrylate and maleic acid monoester groups, above a certain content, can be dissolved in 1% Na₂CO₃ solution. The photocrosslinkable properties of the product were investigated through selection of photoinitiator, accelarator, crosslinkable diluent monomer, etc. The acrylate and maleic acid monoester group‐containing phenolic resin exhibited very good photocrosslinking behavior, since it contains double bonds from both acrylate groups and maleic acid monoester groups. The activity of photoinitiator decreases in the order: isopropylthioanthraquinone > benzoin ethyl ether (BE) > anthraquinone (AQ) > benzophenone > Michel ketone (MK) > 2,2‐diethoxyacetophenone. The combination of some photoinitiators showed synergistic effects. The order of increasing activity for the accelerator is as follows: MK > ethyl p‐(dimethylamino)benzoate > N,N‐dimethylaniline > triethanolamine. The optimum diluent monomer is trimethylolpropane trimethacrylate. The gel content of the mixture of the resin and trimethylolpropane trimethacrylate could reach 85% using the combined photoinitiators of BE and AQ under UV exposure for 120 s. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 98: 1607–1614, 2005     

Micromechanical properties on the surface of PVC/SBR blends spatially resolved by a nanoindentation technique

The microhardness and micromodulus on the surface of poly(vinyl chloride) (PVC)/styrene‐butadiene rubber (SBR) blends were determined using a nanoindenter. A flat surface was obtained by microtoming the sample at ?100°C in liquid nitrogen. Dozens of indents along a line with a spatial interval of 0.5 μm were performed. From the loading and unloading curves of each indentation, the stiffnesses of the unloading curve and the contact area between the sample and the indenter were evaluated, and the local modulus and hardness were calculated. Profiles of the local hardness and modulus were obtained from the lines of indents. Pure PVC and a miscible PVC/acrylonitrile‐butadiene rubber (NBR) (40/10) blend showed constant modulus and hardness values. In the case of an immiscible PVC/SBR (50/50) blend, which has a morphology of elongated PVC droplets in the SBR matrix, the hardness and modulus profiles showed regions of the different phases. At the interface between the SBR and PVC phases, a step change in the modulus and hardness profiles was observed. The force required to deform the material at the same displacement increased systematically across the interface from the SBR to the PVC phase because of the increasing contribution of the PVC phase. Polym. Eng. Sci. 44:609–614, 2004. © 2004 Society of Plastics Engineers.     

Random Copolymers with 2,2′-Dioxy-1,1′-biphenyl-phosphazene and Chiral 2,2′-dioxy-1,1′-binaphthylphosphazene Units Functionalized in the 6,6′-Positions with PPh<Subscript>2</Subscript> Groups as Precursors for Ru(arene) Catalysts

The chiral phosphazene copolymers {[NP(O₂C₁₂H₈)]_0.9[NP(O₂C₂₀H₁₂)]_0.1} (1) and {[NP(O₂C₁₂H₈)]_0.9[NP(O₂C₂₀H₁₀Br₂)]_0.1} _n (2) [(O₂C₁₂H₈) = 2,2′-dioxy-1,1′-biphenyl; (O₂C₂₀H₁₂) = R-2,2′-dioxy-1,1′-binaphthyl and (O₂C₂₀H₁₀Br₂) = R-6,6′-dibromo-2,2′-dioxy-1,1′-binaphthyl] were prepared by sequential substitution from [NPCl₂] _n and the corresponding dihydroxy-biphenyl or binaphthyl reagents in the presence of Cs₂CO₃ and K₂CO₃. The reaction of (2) with ^tBuLi in THF, followed by addition of PPh₂Cl and a treatment with SiHCl₃/PPh₃ to eliminate any oxidized OC₆H₄P(O)Ph₂ groups, gave the phosphine containing copolymer {[NP(O₂C₁₂H₈)]_0.9[NP(O₂C₂₀H₁₀[PPh₂]₂)]_0.1} _n (3), that was used as a chiral ligand to support [Ru(p-cymene)Cl] complexes. The resulting catalyst was active for hydrogen transfer from isopropyl alcohol to acetophenone but the placement of the Ru centers in the 6,6′-positions of the binaphthoxyphosphazene units induced no enantioselectivity. Dedicated to Professor Christopher Allen.     

Synthesis and characterization of novel,temperature‐sensitive microgels based on N‐isopropylacrylamide and tert‐butyl acrylate

A series of temperature‐sensitive microgels based on N‐isopropylacrylamide as the main monomer, tert‐butyl acrylate (tBA) as the comonomer, and N,N′‐methylene‐bis(acrylamide) as the crosslinker were synthesized with a modified surfactant‐free emulsion polymerization method. The chemical structure and global shape with an excellent monodispersity of the microgels were confirmed by Fourier transform infrared spectroscopy and scanning electron microscopy, respectively. The temperature‐sensitive behavior of the microgels was investigated by dynamic light scattering and ultraviolet–visible spectrophotometric analysis. The results show that the volume phase‐transition temperature of the poly(N‐isopropylacrylamide‐co‐tert‐butyl acrylate) [poly(NIPAM‐co‐tBA)] microgels were tuned over a broad range by the incorporated amount of tBA comonomer and their temperature sensitivity decreased with increasing content of tBA units incorporated into the microgel network. Furthermore, the swelling ratios of the poly (NIPAM‐co‐tBA) microgels were lowered gradually with increasing tBA unit content within the microgel network. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 2962–2967, 2007