Polymer, rejuvenation

L. Billiet, D. Fournier, R Du Prez, Step-growth polymerization and click chemistry the oldest polymers rejuvenated. Polymer 50 (July 31, 2009) 3877-3886. 

The area of molecular nonlinear optics has been rejuvenated by efforts to investigate three-dimensional multipolar systems, functionalized polymers as optoelectronic materials, near infrared optical parametric oscillators and related aspects.71 There have been some advances in chromophore design for second-order nonlinear optical materials 72 these include onedimensional CT molecules, octopolar compounds and organometallics. Some of the polydiacetylenes and poly(/>-phenylenevinylene)s appear to possess the required properties for use as third-order nonlinear optical materials for photonic switching.73... 

Thermo-reversible has the following meaning if an amorphous polymer is heated to above Tg, it readily reaches thermodynamic equilibrium by definition the sample has then "forgotten" its history, any previous ageing it may have undergone below Tg having been erased. In other words it is completely rejuvenated. Ageing therefore is a thermo-reversible process to which one and the same sample can be subjected an arbitrary number of times. It has just to be retreated each time to the same temperature above Tg. 

Struik showed furthermore that for amorphous and semi-crystalline polymers the ageing effect after complicated thermal histories is strikingly similar. In both cases high stresses can erase previous ageing and "rejuvenate" the material. 

Keywords Aging dynamics Glass transition Heterogeneous dynamics Interfacial interaction Memory and rejuvenation effects Stacked thin polymer films... 

In summary, it is clear that the o-Ps lifetime determined via the PALS technique provides accurate information on the apparent mean size of the nanoholes, which comprise the free volume in amorphous polymers. It also seems well established (see Chapter 11) that provided that the noise level in the PALS spectrum is sufficiently reduced, the distribution of o-Ps lifetimes can be obtained, which generates information regarding nanohole-size distribution. Concerns have been raised about the utility of the o-Ps intensity, I3, to characterize the number density of nanoholes and hence the fractional free volume via Eq. (12.2), because the value of I3 can be influenced significantly by the presence of species that inhibit or enhance positronium formation. We feel that we can utilize I3 values to evaluate fl actional free volumes via Eq. (12.2), provided either that the sample is rejuvenated by heating above Tg prior to measurement, and/or experiment indicates that the value of I3 remains constant within experimental error, during the time of exposure to the positron source. 

The idea of using polymers as supports for catalysis chemistry is not new. Prior work with heterogeneous polymer bound transition metal catalysts extends back to the 1960s.(/-i) At that time there was considerable industrial interest in insoluble polymer supports. That interest continued through the 1970s but dwindled because homogeneous and heterogeneized catalysts were not always as comparable to one another as anticipated and because catalysts could not always be recovered and reused with the expected simplicity. Since that time there has been a rejuvenation of... 

De Koning GJM, Lemstra PJ (1993) Crystallization phenomena in bacteria poly[(/ )-3-hydtoxy-butyrate] 2. Embrittlement and rejuvenation. Polymer 34 4089 094 De Koning GJM, Lemstra PJ (1994) Crystallization phenomena in bacteria poly[(R)-3-hydioxy-butyrate] 3. Toughening via texture changes. Polymer 35 4598—4605 Doi Y (1990) Microbial polyesters. VCH, New York... 

Injectable poly-L-lactic acid is a biocompatible, biodegradable, synthetic polymer that is approved for correction of HIV-related facial Upoatrophy, as well as for cosmetic processes. After injection, it elicits a gradual increase in facial volume by hypothesized endogenous production of fibroblasts and collagen, enabling global facial rejuvenation to be tailored, as required, over time. Substantial increases in dermal thickness after injection have been observed to last for up... 

It seems from our measurements that volume variation during torsion resulted from two superposed phenomena contraction at small strains, followed by dilation (figure 1). The small strain contraction may be attributed to nonlinear elasticity (4,5), as already shown for other polymers (7). Concerning the dilation at larger strains, which has been observed for the first time in our experiments, it may be explained by Struik s hypothesis (1) that a sufficiently large deformation should produce free volume, rejuvenating the material. This appears to invalidate other theories (3) for deformation induced rejuvenation. 

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