Polystyrene lifetime data

Solid Films. The excimer fluorescence of solid films of polystyrene was observed using pulse radiolysis. The decay curves of the excimer fluorescence observed at 340 nm for solid films of polystyrene and CMS are shown in Figures 4(a) and (b), respectively. The lifetime of the excimer fluorescence of polystyrene agree with the reference data (12). In CMS, the initial yield decreases and the decay rate of excimer fluorescence increases with increasing chloromethylation ratio of CMS. These experimental results indicate that the chloromethyl part of CMS quenches the excimer of CMS and scavenges the precursors of the excimer as described below. 

The affect of polymer stereoregularity in the chains on the PAL data has also been studied. Hamielec et al [56] found what appears to be an increased lifetime (hole size) with increased randomness of the chain configuration in a series of polyvinlychloride (PVC) polymers, despite the large degree of scatter in the sample (probably due to the fact that a series of commercially available products were used.). They however found little correlation with tacticity in polypropylene. More recently a PAL study on a series of very well characterized polystyrene and poly(p-methlystyrene) samples of differing tacticity [57] was performed. In addition to finding that the polystyrene samples have smaller free volume holes than the poly(p-methylstyrene) samples, they found that the syndiotactic samples had broader hole distributions than the attactic samples. 

The delayed trapping experiments of an ester enolate in 10% cross-linked polystyrene, a benzyne in 2% cross-linked polystyrene, and a glycine active ester in 4% cross-linked polystyrene all gave lifetimes of about 1-10 minutes. Site isolation syntheses in tiie most common solvent-swollen polystyrene supports can be achieved if the reactive species is trapped quickly. More highly cross-Unked supports and poorly swelling solvents may give longer lifetimes of reactive intermediates, but no data are available. 

Fig. 6 (a) Fluorescence image of single DiD molecules embedded in a polystyrene film (5x5 xm ). The pseudo color scale shows the polarization direction of the fluorescence, indicating the molecular orientation (b) Fluorescence decay curves for one DiD molecule at different times. The red lines are the single-exponential functions fitted to the data (c) Time traces of fluorescence intensity and lifetime with 100 ms time interval. Reprinted with permission of [30], copyright (2004) American Chemical Society... 

What is the lifetime of polystyrene in vacuum at 350 K if the process responsible for degradation takes 5.0 minutes at 600 K (give range set by 2 standard deviations (Use data of Fig. 730.)... 

It is evident from the above discussion that the free volume data derived from positron lifetime measurements is incapable of providing information on the composition-dependent miscibility level of the blend. At this point, a new method based on the same free volume data measured from positron lifetime measurements was introduced to determine the miscibility of binary blends. The new method was based on hydrodynamic interactions (the mathematics required have been explained in detail earlier), and calculations of the y parameter derived from the hydrodynamic interaction approach were made for three selected polymer blends, namely poly(styrene-co-acrylonitrile) (SAN)/poly(methyl methacrylate) (PMMA) (completely miscible), poly(vinyl chloride) (PVC)/poly(methyl methacrylate) (PMMA) (partially miscible) and poly(vinylchloride) (PVC)/polystyrene (PS) (immiscible) (see Figure 27.13). As can be seen, this parameter behaves similar to the interchain interaction parameter /3, in the sense that it exhibits a complex behavior making it difficult to determine the composition-dependent miscibility of the blends. 

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