Toxicity of polymethylmethacrylate thermodegradation products

Advances in the Synthesis of Chemically Recyclable Polymers

The development of modern society is closely related to polymer materials. However, the accumulation of polymer materials and their evolution in the environment causes not only serious environmental problems, but also waste of resources. Although physical processing can be used to reuse polymers, the properties of the resulting polymers are significantly degraded. Chemically recyclable polymers, a type of polymer that degrades into monomers, can be an effective solution to the degradation of polymer properties caused by physical recycling of polymers. The ideal chemical recycling of polymers, i. e., quantitative conversion of the polymer to monomers at low energy consumption and repolymerization of the formed monomers into polymers with comparable properties to the original, is an attractive research goal. In recent years, significant progress has been made in the design of recyclable polymers, enabling the regulation of the "polymerization-depolymerization" equilibrium and closed-loop recycling under mild conditions. This review will focus on the following aspects of closed-loop recycling of poly(sulfur) esters, polycarbonates, polyacetals, polyolefins, and poly(disulfide) polymer, illustrate the challenges in this area, and provide an outlook on future directions.

Free radicals and side products released during methylmethacrylate polymerization are cytotoxic for osteoblastic cells

Polymerization of orthopedic cements makes use of a peroxide initiator which is decomposed by an accelerator to provide free radicals. Free radicals which act on the monomer molecules are also known to induce cell lesions and cell death. We used an in vitro model of cement polymerization to study the effects of free radicals release on osteoblast-like cells. Initiation of methylmethacrylate was done with benzoyl peroxide and acceleration by N,N-dimethylaniline. Bulk polymerization was done in calibrated test tubes which were left aging until use. Polymers (aged from J1 to J31 days after completion of the polymerization process) were sawed to produce slices. Slices were rinsed in distilled water and free radical release was measured by spectrophotometric titration with p-iodonitrotetrazolium. Saos-2 osteoblast-like cells were cultured in parallel on the slices. Cells appeared to be round and were altered when grown on slices prepared freshly after polymerization. Cytomorphometric analysis of the cell shape (surface area and form-factor polyethylene confirmed that they spread and flatten on slices prepared a long time after polymerization. Free radical release from polymethylmethacrylate cements is a long-lasting event that can induce bone cells alterations in their neighborhood. Two cytotoxic mechanisms were evidenced: (a) polymer slices released a stable toxic component which could be removed by extensive washing; (b) they released free radicals which were still detectable several days after the end of polymerization. The titration curve was a negative exponential.

Pulmonary abnormalities and serum immunoglobulins in facsimile machine repair technicians exposed to butyl methacrylate fume

Seven repair technicians (RT, site A) repeatedly exposed to facsimile machine fume developed recurring sore throat, fever, lymphadenopathy, chest tightness, dry cough, and dyspnea. The fume concentration was low (0.6 mg/m3 of breathing-zone air) but it contained butyl methacrylate (BMA), a known skin sensitizer. Although chest radiographs were normal, three of the seven RT-A had lung crackles and spirometric abnormalities, and increased serum levels of immunoglobulins IgE or IgM. Symptoms and most other abnormalities improved when exposure to BMA was stopped. We later evaluated workers in two other sites (B and C). Six RT-B had daily contact with BMA fume (0.14 to 0.40 mg/m3 of air) at a field repair depot. Six administrative and six sales staff members (AS-B, SS-B) without regular fume exposure served as controls. All RT-B had elevated serum IgE levels (202+/-69 U/mL [SEM]; normal <41 U/mL). IgE and fume levels were positively correlated (r=0.83). four RT-B had lung crackles, but few symptoms and normal results of spirometry. The crackles cleared 8 weeks after substitution of a BMA-free paper, but IgE levels remained high (201+/-69). The nonexposed AS-B and SS-B had no crackles. Their IgE levels were normal (19+/-4 U/mL [SEM]; p<0.01). The crackles suggest BMA fume might have caused inflammation in terminal airways units. The significance of the IgE elevations is also uncertain since this class of antibodies is usually associated with asthma, not pneumonitis. In view of these uncertainties, BMA was eliminated from the facsimile transceiver process. Follow-up of group C workers (n=32) found no symptoms, lung crackles, or abnormal results of spirometry. However, IgE concentrations were elevated in 15 and remained so for 21 months, perhaps because of continuing exposure to residual low levels of BMA. These findings suggest that BMA-bearing facsimile fume caused increased IgE levels in RT at sites A, B, and C, and might have resulted in permanent lung injury if such exposure had continued.

m-Xylene inhalation destroys cytochrome P-450 in rat lung at low exposure

Rats were exposed to 0, 75, 150 or 300 ppm (1 ppm = 1 cm3/m3 = 4.35 mg/m3) m-xylene for 24 h and then killed. In the lungs, the cytochrome P-450 decreased to 45, 13 and 20% of the control value with the increasing exposure intensity and the activity of 7-ethoxycoumarin O-deethylase to 70, 27 and 14%, respectively. The activity of epoxide hydrolase increased slightly after exposures both at 150 (1.6-fold) and 300 cm3/m3 (1.4-fold), while the other measured drug-metabolizing enzyme activities showed no consistent changes. The non-protein sulfhydryl group content of the lungs was not affected. The concentrations of m-xylene in blood indicated that the solvent uptake increased in the different exposure groups more than expected, based on atmospheric concentrations alone. Morphologic studies of the lungs with scanning electron microscopy showed no apparent changes after exposure to 300 cm3/m3 or after a high oral dose (2 ml/kg/day, 3 days). Inhalation exposure to m-xylene for 5 weeks (7 h/day, 4 days/week) at a concentration of 300 ppm lowered the contents of cytochrome P-450 in rat lungs to 65% and the activity of 7-ethoxycoumarin O-deethylase to 41% without any other marked effects on the other drug-metabolizing enzymes or on the levels of non-protein sulfhydryl groups. In this study, the selective destruction of cytochrome P-450 in rat lung could be shown both after acute and subacute exposures and at concentrations low enough to warrant occupational concern.