Poly physical aging

In the vicinity of glass transition, both Eqs. (47) and (48) become Eqs. (42) and (43), respectively. The calculated dependence of the physical aging rate on temperature for polystyrene (PS), poly(vinyl chloride) (PVC), and poly(vinyl acetate) (PVAc) is shown in Fig. 17. There are five parameters (e, p, f xr, 7 ) in Eqs. (23), (2), (15) and (19). We have chosen p = 1/2. ft = 1/30, and xr = 30 min for these linear polymers in our theoretical calculation. The other two parameters r. = h and Tr are listed in Table 1. The calculation reveals that the Struik exponent (p) increases from zero above 7 to a constant below Tg, and then decreases to zero at 200 K below Tg. The three polymers all show a similar type of temperature dependence of physical aging rate, which compares well with the reported observations (see Fig. 15 of Ref. 2). 

In another development, thermal analysis of POSS-containing ABA triblock methacrylate/butyl acrylate copolymers (Fig. 4) indicated the presence of two clear glass transitions in the microphase-separated system, with strong physical aging observed in samples annealed at temperatures near the Tg of the poly(methacryl-POSS) phase [122]. 

Rueda et al. (1995), have followed the physical ageing of another glassy polymer. They investigated the variation in microhardness of poly(ethylene naphthalene-2,6-dicarboxylate) (PEN) stored in an ambient atmosphere for different times and after annealing at different temperatures below Tg for different periods of time. This material has stiffer molecules than PET due to the presence of a naphthalene ring instead of the benzene ring in the backbone chain. 

J. S. Royal and J. M. Torkelson, Photochromic and fluorescent probe studies in glassy polymer matrices. 5. Effects of physical aging on bisphenol-A polycarbonate and poly(vinyl acetate) as sensed by a size distribution of photochromic probes, Macromolecules 25, 4792-4796 (1992). 

Cowie, J.M.G. and Ferguson, R. Physical aging studies in poly (vinyl methyl ether). 1. Enthalpy relaxation as a function of aging temperature. Macromolecules, 22, 2307,1989. 

Physical Aging of Poly(phenylene Ether)/Polystyrene Blends. 185... 

A. Celh, M. Scandola, Thermal properties and physical aging of poly(L-lactic acid). Polymer 33 (1992) 2699-2703. 

C.G. Robertson, G.L. Wilkes, Physical aging behavior of miscible blends ofpoly(methyl methacrylate) and poly(styrene-co-acrylonitrile). Polymer 42 (2001) 1581-1589. 

Polybutadiene-PMMA (80 20) core-shell particles of 0.18 pm diameter have been shown to reduce the rate of embrittlement of polycarbonate degraded by physical ageing just below the glass transition temperature [132]. The unmodified polycarbonate became brittle (as assessed by 80% of specimens showing brittle fracture) after 5 h at 135 °C in air, whereas a blend containing 10 wt% of the core-shell particles withstood these conditions for 800 h before embrittlement. By using more thermally stable particles with a poly(n-butyl acrylate) core, embrittlement was further delayed to times greater than 4500 h,... 

Kobayashi, Y., Zheng, W., Meyer, E. F., McGervey, J. D., Jamieson, A. M., and Simha, R., Free volume and physical aging of poly(vinyl acetate) studied by positron annihilation. Macromolecules, 22, 2302-2306 (1989). 

Dorkenoo, K. D., and Pfromm, P. H., Accelerated physical aging of thin poly[l-(trimethylsilyl)-l-prop5me] films. Macromolecules, 33, 3747-3751 (2000). 

Huang, Y, and Paul, D. R., Effect of molecular weight and temperature on physical aging of thin glassy poly(2,6-dimethyl-l,4-phenylene oxide) films, J. Polym. Sci. B, 45, 1390-1398 (2007a). 

Rrishnaswamy, R. K., Geibel, J. F., and Lewis, B. J., Influence of semicrystaUine morphology on the physical aging characteristics of poly(phenylene sulflde). Macromolecules, 36, 2907-2914(2003). 

Arrighi, V., Cowie, J. M. G., Ferguson, R., McEwen, 1. J., McGonigle, E.-A., Pethrick, R. A., and Princi, E., Physical ageing in poly(4-hydroxy styrene)/poly(vinyl methyl ether) blends, Polym. Int., 55, 749-756 (2006). 

Cowie, J. M. G., and Ferguson, R., Physical ageing of poly(methyl methacrylate) from enthalpy relaxation measurements. Polymer, 34, 2135-2141 (1993). 

McGonigle, E.-A., Daly, J. H., Jenkins, S. D., Liggat, J. J., and Pethrick, R. A., Influence of physical ageing on the molecular motion and structural relaxation in poly(ethylene terephthalate) and related polyesters. Macromolecules, 33, 480 89 (2000). 

Mijovic, J., and Kwei, T. K., Physical ageing in poly(methyl methacrylate)/poly(styrene-co-acrylonitrile) blends II. Enthalpy relaxation, Polym. Eng. ScL, 29,1604—1610 (1989). 

Mijovic, J., Devine, S. T., and Ho, T., Physical ageing in polyfmethyl methacrylate)/ poly (styrene-co-acrylonitrile) blends. I. Stress relaxation, J. Appl. Polym. Sci., 39,1133-1151 (1990). 

Cowie, J. M. G., Elliott, S., Ferguson, R Simha, R Physical aging smdies on poly(vinyl acetate) - enthalpy relaxation and its relation to volume recovery. Polymer Communications, 28(11), pp. 298-300 (1987). 

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