Effect of aging tem perature on butadiene—isoprene copolym erization with neodymium —based catalyst(陈化温度对稀土催化剂共聚合丁二烯-异戊二烯的影响)

考察了陈化温度对新癸酸钕（简称Nd）、氢化二异丁基铝（简称Al）和氯化二异丁基铝（简称Cl）组成的催化剂共聚合丁二烯-异戊二烯的影响。结果表明，催化剂的陈化温度对聚合产物的相对分子质量分布有明显的影响，采用较高陈化温度（50℃）所得催化剂，在催化剂3组分的加入顺序为Al、Cl、Nd或Cl、Nd、Al时，可获得窄相对分子质量分布（小于3．00）共聚物；催化剂3组分的加入顺序和陈化温度对共聚物的微观结构影响不大，2种单体单元的顺式-1，4-结构摩尔分数均在98％以上

Aging behavior and mechanical properties of Mg-Gd-Ho alloys

The Mg-8Gd-0.6Zr-xHo (x = 1, 3 and 5, mass%) alloys were prepared by casting technology, and structures, aging strengthening mechanism and mechanical properties of the alloys were investigated. The age behaviors and the mechanical properties are improved by adding Ho addition. The structures of the alloys are characterized by the present of rosette-shaped equiaxed grains. The peak hardness value of the Mg-8Gd-0.6Zr-3Ho alloy is 100 Hv, which is about 30% higher than that of Mg-8Gd-0.6Zr alloy.

Poly(ethylene glycol-co-propylene glycol) as a Macromolecular Plasticizing Agent for Polylactide: Thermomechanical Properties and Aging

Finding a Suitable plasticizer for polylactide (PLA) is necessary to overcome its brittleness and enlarge its range of applications. In this study, commercial PLA was melt-blended with a new plasticizer, an ethylene glycol/propylene glycol random copolymer [poly(ethylene glycol-co-propylene glycol) (PEPG)] with a typical number-average molecular weight of 1.2 kDa and an ethylene glycol content of 78.7 mol %. The thermal properties, crystallization behavior, and mechanical properties of the quenched blends and the properties of the blends after storage for 2 months under the ambient conditions were investigated in detail. The advantage of using PEPG is that it does not crystallize at room temperature and has good compatibility with PLA. The quenched PLA/PEPG blends were homogeneous and amorphous systems. With an increase in the PEPG content (5-20%), the glass-transition temperature, tensile strength, and modulus of the blends decreased, whereas the elongation at break and crystallizability increased dramatically. The cold crystallization of PLA resulted in phase separation of the PLA/PEPG blends by annealing of the blends at the crystallization temperature.

Effect of physical aging on fracture behavior of polyphenylquinoxaline films

The influence of physical aging on the tensile fracture behavior of notched Polyphenylquinoxaline (PPQ-E) samples has been studied. The dependence of fracture stress and strain on physical aging has been explained. The glass transition temperature (T-g) and the endothermic peak at the end of T-g transition with different physical aging were characterized using differential scanning calorimetry (DSC) and the results have also been explained. The morphology of fracture surface was observed by scanning electron microscopy (SEM). (C) 2000 John Wiley & Sons, Inc.

Effect of physical aging on the microstructure and the crystallization of amorphous poly(aryl ether ether ketone ketone) (PEEKK)

Physical aging of poly(aryl ether ether ketone ketone) (PEEKK) has been investigated. Heat flow responses were measured after annealing the amorphous samples obtained by quenching the melt into an ice-water bath close to, but below, the glass transition temperature. The extent of aging is related to the supercooling from the glass transition temperature and to the aging time. The activation energy of the aging process, which was estimated by a Williams-Watt expression, is similar in magnitude to that obtained for the cold crystallization for the aged samples. The quenched glass is a metastable glass. The conformation of molecular chains rearranges with physical aging which results in the formation of a denser packing in the amorphous phase. The dense amorphous phase may form an initial nucleus for crystallization. Isothermal cold crystallization of the aged samples was carried out. The Avrami equation was used to determine the kinetic parameters, and the Avrami constant n is about 2. An Arrhenius expression was used to evaluate the activation energy of relaxation upon physical aging and the activation energy of transportation upon isothermal crystallization. The activation energy of relaxation is similar in magnitude to that of crystallization for aged samples. Results obtained are interpreted as kinetic effects associated with the glass formation process.

Aging in EPDM used for outdoor insulation

The effect of accelerated weather aging an ethylene-propylene-diene monomer(EPDM) rubber used for outdoor insulation was studied by surface roughness measurement and X-ray photoelectron spectroscopy(xps). The surface roughness of EPDM rubber changed with aging time. The surface oxygen and aluminum content were found to increase and that of carbon, silicon and nitrogen to decrease with time. The detailed XPS analysis indicated that the concentration of carbon in C-C decreased and that of highly oxidized carbons in C-O, C=O and O=C-O increased with time, which was due to the oxidation of EPDM rubber polymer. The appearance of O=C-O on the surface of EPDM rubber was a signal that EPDM rubber became aged. The aging speed decreased with time. The aging mechanism is discussed also.

Physical aging and crystallization of amorphous poly(aryl ether ether ketone ketone)

Physical aging of poly(aryl ether ether ketone ketone) (PEEKK) was investigated. Heat flow responses were measured after annealing the amorphous samples that were obtained by quenching the melt into an ice-water bath at just below the glass transition temperature. Isothermal cold crystallization of the aged samples was carried out. The Avrami equation was used to determine the kinetic parameters, and the Avrami constant it is about 2. An Arrhenius form was used to evaluate the relaxation activation energy of physical aging and the transport activation energy of isothermal crystallization. The activation energy of physical aging was similar in magnitude to that observed for the temperature dependence of crystallization under conditions of transportation control. Results obtained were interpreted as purely kinetic effects associated with the glass formation process. (C) 1998 John Wiley & Sons, Inc.

Effect of physical aging on phenolphthalein polyethersulfone/poly(phenylene sulfide) blend .1. Mechanical properties

The effect of physical aging at 210 degrees C on the mechanical properties of phenolphthalein polyether sulfone (PES-C) and a PES-C/poly(phenylene sulfide) (PPS) blend, with 5% content of PPS, were studied using DMA, tensile experiments, an instrumented impact tester, and SEM observations. The blend shows good mechanical properties in comparison with the corresponding PES-C. The mechanical properties of both materials exhibit characteristics of physical aging, with only the aging rate of the blend relatively slower, which should be attributed to the constraint effect of PPS particles and the good interfacial adhesion. The morphology of the PPS phase in the blend did not change with aging time. The principal role of PPS particles is to induce crazes, which dissipate energy, under applied loading; thus, the blend shows good toughness. On the other hand, the multiple crazing mechanism depends on the molecular mobility or structural state of the matrix. (C) 1996 John Wiley & Sons, Inc.

PHYSICAL AGING OF HIGH-PERFORMANCE THERMOPLASTICS - ENTHALPY RELAXATION IN PEK-C AND PES-C

The developments of physical aging in phenolphthalein poly(aryl-ether-ketone) (PEK-C) and poly(aryl-ether-sulfone) (PES-C) with time at two aging temperatures up to 20 K below their respective glass transition temperatures (T-g = 495 and 520 K) have been studied using differential scanning calorimetry (DSC). Substantial relaxation within the aging course of several hours were observed by detecting T-g decreasing during physical aging process at the two aging temperatures. The relaxation processes of both polymers are extremely nonlinear and self-retarding. The time dependencies of their enthalpies during the initial stages of annealing were approximately modeled using the Narayanaswamy-Tool model. The structure relaxation parameters obtained from this fitting were used to predict the possibility of physical aging occurring at their respective using temperatures. (C) 1995 John Wiley and Sons, Inc.

In vivo antioxidant activity of polysaccharide fraction from Porphyra haitanesis (Rhodephyta) in aging mice

Sulfated polysaccharide fraction F2 from Porphyra haitanesis (Rhodephyta) showed inhibitory effect on the in vitro lipid peroxidation. In the present study, the age-related changes in the antioxidant enzyme activity, lipid peroxidation, and total antioxidant capacity (TAOC) in different organs in mice were investigated and the in vivo antioxidant effect of F2 in aging mice was checked. Increased endogenous lipid peroxidation and decreased TAOC were observed in aging mice. Intraperitoneal administration of F2 significantly decreased the lipid peroxidation in a dose-dependent manner. F2 treatment increased TAOC and the activity of superoxide dismutase (SOD) and glutathione peroxidase (GSH-Px) in all the organs tested in aging mice. It is concluded that the sulfated polysaccharide fraction F2 can be used in compensating the decline in TAOC and the activities of antioxidant enzymes and thereby reduces the risks of lipid peroxidation. (C) 2003 Elsevier Science Ltd. All rights reserved.

'Adipaging': Aging and obesity share biological hallmarks related to a dysfunctional adipose tissue

The increasing aging of our societies is accompanied by a pandemic of obesity and related cardiometabolic disorders. Progressive dysfunction of the white adipose tissue is increasingly recognized as an important hallmark of the aging process which in turn contributes to metabolic alterations, multi-organ damage, and a systemic pro-inflammatory state ('inflammaging'). On the other hand, obesity, the paradigm of adipose tissue dysfunction, shares numerous biological similarities with the normal aging process such as chronic inflammation and multi-system alterations. Accordingly, understanding the interplay between accelerated aging related to obesity and adipose tissue dysfunction is critical to gain insight into the aging process in general as well as into the pathophysiology of obesity and other related conditions. Here we postulate the concept of 'adipaging' to illustrate the common links between aging and obesity and the fact that, to a great extent, obese adults are prematurely aged individuals.

Premature ovarian aging in mice deficient for Gpr3

After becoming competent for resuming meiosis, fully developed mammalian oocytes are maintained arrested in prophase I until ovulation is triggered by the luteotropin surge. Meiotic pause has been shown to depend critically on maintenance of cAMP level in the oocyte and was recently attributed to the constitutive Gs (the heterotrimeric GTP-binding protein that activates adenylyl cyclase) signaling activity of the G protein-coupled receptor GPR3. Here we show that mice deficient for Gpr3 are unexpectedly fertile but display progressive reduction in litter size despite stable age-independent alteration of meiotic pause. Detailed analysis of the phenotype confirms premature resumption of meiosis, in vivo, in about one-third of antral follicles from Gpr3-/- females, independently of their age. In contrast, in aging mice, absence of GPR3 leads to severe reduction of fertility, which manifests by production of an increasing number of nondeveloping early embryos upon spontaneous ovulation and massive amounts of fragmented oocytes after superovulation. Severe worsening of the phenotype in older animals points to an additional role of GPR3 related to protection (or rescue) of oocytes from aging. Gpr3-defective mice may constitute a relevant model of premature ovarian failure due to early oocyte aging.

Aging African American Women and the Impact of Positive Psychological Factors on Quality of Life

Aging African-American women are disproportionately affected by negative health outcomes and mortality. Life stress has strong associations with these health outcomes. The purpose of this research was to understand how aging African American women manage stress. Specifically, the effects of coping, optimism, resilience, and religiousness as it relates to quality of life were examined. This cross-sectional exploratory study used a self-administered questionnaire and examined quality of life in 182 African-American women who were 65 years of age or older living in senior residential centers in Baltimore using convenience sampling. The age range for these women was 65 to 94 years with a mean of 71.8 years (SD = 5.6). The majority (53.1%) of participants completed high school, with 23 percent (N = 42) obtaining college degrees and 19 percent (N = 35) holding advanced degrees. Nearly 58 percent of participants were widowed and 81 percent were retired. In addition to demographics, the questionnaire included the following reliable and valid survey instruments: The Brief Cope Scale (Carver, Scheier, & Weintraub, 1989), Optimism Questionnaire (Scheier, Carver, & Bridges, 1994), Resilience Survey (Wagnild & Young, 1987), Religiousness Assessment (Koenig, 1997), and Quality of Life Questionnaire (Cummins, 1996). Results revealed that the positive psychological factors examined were positively associated with and significant predictors of quality of life. The bivariate correlations indicated that of the six coping dimensions measured in this study, planning (r=.68) was the most positively associated with quality of life. Optimism (r=.33), resilience (=.48), and religiousness (r=.30) were also significantly correlated with quality of life. In the linear regression model, again the coping dimension of planning was the best predictor of quality of life (beta = .75, p <.001). Optimism (beta = .31, p <.001), resilience (beta = .34, p, .001) and religiousness (beta = .17, p <.01) were also significant predictors of quality of life. It appears as if positive psychology plays an important role in improving quality of life among aging African-American women.

Walking in old age and development of metabolic syndrome: the health, aging, and body composition study.

BACKGROUND: The specific health benefits of meeting physical activity guidelines are unclear in older adults. We examined the association between meeting, not meeting, or change in status of meeting physical activity guidelines through walking and the 5-year incidence of metabolic syndrome in older adults. METHODS: A total of 1,863 Health, Aging, and Body Composition (Health ABC) Study participants aged 70-79 were followed for 5 years (1997-1998 to 2002-2003). Four walking groups were created based on self-report during years 1 and 6: Sustained low (Year 1, <150 min/week, and year 6, <150 min/week), decreased (year 1, >150 min/week, and year 6, <150 min/week), increased (year 1, <150 min/week, and year 6, >150 min/week), and sustained high (year 1, >150 min/week, and year 6, >150 min/week). Based on the Adult Treatment Panel III (ATP III) panel guidelines, the metabolic syndrome criterion was having three of five factors: Large waist circumference, elevated blood pressure, triglycerides, blood glucose, and low high-density lipoprotein (HDL) levels. RESULTS: Compared to the sustained low group, the sustained high group had a 39% reduction in odds of incident metabolic syndrome [adjusted odds ratio (OR) = 0.61; 95% confidence interval (CI), 0.40-0.93], and a significantly lower likelihood of developing the number of metabolic syndrome risk factors that the sustained low group developed over 5 years (beta = -0.16, P = 0.04). CONCLUSIONS: Meeting or exceeding the physical activity guidelines via walking significantly reduced the odds of incident metabolic syndrome and onset of new metabolic syndrome components in older adults. This protective association was found only in individuals who sustained high levels of walking for physical activity.