Zenjiro Osawa

Role of metals and metal-deactivators in polymer degradation

Abstract The interaction between metals or metallic compounds and polymers is inevitable in the practical use of polymeric articles, and the stability of the polymers is often modified by these materials. Furthermore, the effect of the metallic compounds on the degradation of the polymers is extremely complicated, and is influenced by various factors. This contribution deals with the possible role of metals or metallic compounds in the degradation of polymers, and this is followed by some typical examples of degradation by metallic compounds, mostly commercial pigments and transition metal compounds of stearic acid and acetylacetone, in typical commercial polymers. Recent studies of the inhibition of the copper-catalyzed thermo-oxidative degradation of polyolefins by deactivators, both commercial reagents and novel products, are discussed.

Chemiluminescence study on the oxidation of several polyolefins—I. Thermal-induced degradation of additive-free polyolefins

Abstract Chemiluminescence (CL) has been applied to evaluate the oxidation susceptibility of various polyolefins: low-density polyethylene (LDPE), linear low-density polyethylene (LLDPE), high-density polyethylene (HDPE) and isotactic polypropylene (i-PP). The intensity of CL emission in inert atmosphere could be related to the previous oxidation level. The thermal stability at 170 °C of the hydroperoxides in LDPE seems to be lower than that in LLDPE or HDPE. The kinetic parameters of the oxidation at 170 °C in oxygen, calculated from CL data, suggest the following stability order: HDPE > LLDPE > LDPE⪢i-PP. The intensity of CL emission was related to the CH 3 content as evaluated by Fourier transform infra-red spectroscopy.

Thermal stability of shielding effectiveness of electromagnetic interference of composites

A series of composites were prepared using polyethylene and various chatter-machined metal fibres (aluminium, copper, steel and brass) and carbon fibre, and the effects of the concentration of the fillers and the thermal treatment of the composites at 80° C in air on the shielding effectiveness (SE) of eleotronnagnotic interference were examined. The order of the generation of SE was, brass > steel > copper ≈ aluminium > carbon. Thermal degradation of SE was scarcely observed in the carbon fibre system and very slightly in the brass and steel systems, while remarkable degradation was observed in the copper and aluminium systems. This degradation was assumed to be due to the formation of an oxidized surface to increase the contact resistance between fillers. Stabilization of the thermal degradation of SE of the aluminium composite was possible to some extent when the aluminium surface was pretreated with certain reagents.

Chemiluminescence study on the oxidation of several polyolefins: II. Chemiluminescence from γ-irradiated polymers

Abstract Chemiluminescence (CL) from isotactic polypropylene (i-PP) and several types of polyethylene, namely low density (LDPE), linear low density (LLDPE) and high density (HDPE), subjected to γ-irradiation in the presence of air, was recorded in both inert (nitrogen) and oxidative (oxygen or air) atmospheres. CL data can be related to the radiation-induced changes observed in the IR spectra of the polymers. The signal recorded in nitrogen may be accompanied by a thermo-luminescence emission, mainly occurring at the melting point of the polymers. The decay of CL emission at 170 °C seems to follow second-order kinetics. It could be related to the presence of two types of luminescent species, perhaps associated with free hydroperoxides. The stability of the polymers subjected to thermal oxidation after irradiation is found to depend on both the polymer type and post-irradiation treatments, such as the thermal decomposition in the inert atmosphere of radiation-induced peroxide products. The shape of the CL curves recorded in air from irradiated LDPE could be related to a competition between oxidation and scission.

Hydrophobic and hydrophilic interpenetrating polymer networks (IPNs) composed of polystyrene and poly(2-hydroxyethyl methacrylate): 2. Gradient composition in the IPNs synthesized by photopolymerization

Abstract Sequential interpenetrating polymer networks (SIPNs) composed of poly(2-hydroxyethyl methacrylate) (PHEMA) and polystyrene (PS) were synthesized by photopolymerization at room temperature. A common solvent, N,N-dimethylformamide, was used to impregnate the styrene monomer into the PHEMA network. The IPNs had a microphase-separated structure of the order of 100 nm. It was found that the gradient composition in the surface region (to a depth of 0.1 mm) was obtained by polymerization inhibition with oxygen which had diffused from the surfaces of the swollen PHEMA gel. X-ray photoelectron spectroscopy measurements revealed that the PS component was enriched in the surface of the IPN. Thermodynamic effects on the composition of the outermost surface layer are discussed.

Hydrophobic and hydrophilic interpenetrating polymer networks composed of polystyrene and poly(2-hydroxyethyl methacrylate): 1. PS-PHEMA sequential IPNs synthesized in the presence of a common solvent

Abstract Interpenetrating polymer networks (IPNs) composed of hydrophobic polystyrene (PS) and hydrophilic poly(2-hydroxyethyl methacrylate) (PHEMA) were synthesized by a sequential IPN method, and they showed a microphase-separated structure. A common solvent, dimethylformamide, which swells the polymer I network and dissolves monomer II, was used to impregnate monomer II into the network of polymer I. The content of polymer II in the IPNs became large when the crosslink density of polymer I was low and that of polymer II was high. It was found that certain monomer II concentration in the swelling agent existed that maximized the polymer II fraction in the IPN. Contact angle and Fourier-transform infra-red measurements revealed that the polymer II content decreased gradually towards the surface of the IPNs. The gradient composition observed in the IPNs was explained by the polymerization inhibition by oxygen and the thermodynamic effect.

Properties and chemiluminescence of polypropylene stored for a long period

Abstract Unstabilized isotactic polypropylene (IPP) powder, finer than 100 mesh, degraded strongly even under ambient atmosphere in the dark when stored for a long period. Thus, the molecular weight of the polymer dropped strongly and a large amount of oxygenated groups such as hydroperoxide, hydroxyl and carbonyl were formed. The intensity of chemiluminescence of the stored IPP was a good deal higher than that of the fresh polymer, and was reduced by the addition of commercial stabilizers such as antioxidants and hydroperoxide decomposers. On the basis of the effect of 9,10-dibromoanthracene, an excited carbonyl sensitizer, and β-carotene, a singlet oxygen quencher, on the intensity and spectral distribution analysis of chemiluminescence emitted from the stored IPP, chemiluminescence species are discussed.

Preparation of Ultraviolet Stabilizing Polymers. I. Copolymerization of 2-Hydroxy-4-acryloyloxybenzophenone and Its Ultraviolet Stability

Abstract To obtain ultraviolet stabilizing polymers, 2-hydroxy-4-acryloyloxybenzophenone was prepared from 2,4-dihydroxybenzophenone and copolymerized with styrene. Copolymers containing three different amounts of ultraviolet absorber were prepared. These copolymers, unstabilized pure polystyrene and a series of stabilized polystyrene, were exposed to ultraviolet, and the ultraviolet stability of these polymers was compared by the relative amount of infrared absorption around 1700 cm−1 due to the carbonyl group. Ultraviolet stability of the copolymers is very similar to that of blend polymers and is higher than that of unstabilized pure polystyrene.

Effect of stereoregularity on the thermo-oxidative degradation of polypropylenes

The effect of stereoregularity on the thermo-oxidative degradation of polypropylenes, isotactic (IPP) and syndiotactic (SPP), was examined by means of chemiluminescence (CL), infrared spectroscopy and molecular weight measurement and their thermal stability was compared with that of high density polyethylene (HDPE). SPP was extremely stable to the thermal oxidation and CL signals appeared much later than in IPP and even later than in HDPE. For example, at 130°C SPP showed no CL signals at all even after 7600 min, while IPP showed a maximum peak after 100 min and HDPE first peak after 460 min. At 140°C, CL signals from SPP appeared at last after 2835 min, and after 45 min from IPP and 240 min from HDPE. Changes in infrared (IR) spectra and molecular weights of the oxidized samples coincided with the results obtained from CL measurement. From the results obtained it was concluded that the stereoregularity of polypropylenes definitely affects their thermal oxidation and SPP is much more stable than IPP.

Synthesis of sulfated derivatives of curdlan and their anti-HIV activity

Abstract Sulfopropyl curdlan was synthesized, its structure was determined, and the anti-HIV activity was compared with that of standard curdlan sulfates obtained with piperidine N -sulfonic acid in dimethyl sulfoxide. It was shown that sulfopropyl curdlan exhibits weaker anti-HIV activity than curdlan sulfate. Curdlan sulfates were synthesized with a SO 3 -pyridine complex in a heterogeneous phase. It was shown from 13 C-NMR spectra of acetylated curdlan sulfates that they had a different substituent distribution from standard curdlan sulfate. The cytotoxicity of the curdlan sulfates was attributed to their heterogeneous structure.