Quenched polymers

Density, mechanical, and thermal properties are significantly affected by the degree of crystallinity. These properties can be used to experimentally estimate the percent crystallinity, although no measure is completely adequate (48). The crystalline density of PET can be calculated theoretically from the crystalline stmcture to be 1.455 g/cm. The density of amorphous PET is estimated to be 1.33 g/cm as determined experimentally using rapidly quenched polymer. Assuming the fiber is composed of only perfect crystals or amorphous material, the percent crystallinity can be estimated and correlated to other properties. 

In Fig. 5.1, the densities of the annealed and of the quenched polymers are plotted against Mh the inverse molecular mass of the network strands. All the annealed samples were denser by about 0.15% than the quenched ones. Bero and Plazek [52] observed an effect of similar magnitude between quenched samples and samples cooled at 0.2 K/h. 

Apparently, annealing was not impeded by crosslinks (Fig. 5.1). The density effects observed agree with the results of the glass transition temperature measurements (Sect. 4.2). There, the Tg of the annealed (and therefore denser) sample was consistently higher by about 2 K than the Tg of the quenched polymer. 

Fig. 5.1. Densities of annealed and of quenched polymers are plotted against 1/MC, that is the inverse molecular mass between crosslinks. Test temperature 23 °C. The density of the thermoplastic Phenoxy is indicated. The diamond represents polymer E.

The flexural strength of the annealed polymers proved to be consistently about 30% higher than the strength of the quenched polymers as shown in Fig. 6.1. Tests were evaluated in accordance with ISO 178 [54]. As the samples yielded, they deformed plastically. Therefore, the assumptions of the simple beam theory were no longer justified and consequently the yield strength was overestimated. 

We will then examine other flexible polymer crystallization instances which may be interpreted, at least qualitatively, in terms of the bundle model. We will concentrate on crystallization occurring through metastable mesophases which develop by quenching polymers like isotactic polypropylene, syndiotactic polypropylene etc. In principle also hexagonal crystallization of highly defective polymers, and order developing in some microphase-separated copolymer systems could be discussed in a similar perspective but these two areas will be treated in future work. A comparison between the bundle approach and pertinent results of selected molecular simulation approaches follows. 

A number of systems which in polymer literature are normally referred to as mesophases are obtained under kinetic control. Examples are the smectic phase of isotactic polypropylene [18,19], mesomorphic syndiotac-tic polypropylene [20-22], mesomorphic PET [23,24], and other instances where intermediate degrees of order result after quenching polymers from the melt to temperatures often close to Tg. In these cases disorder is plausibly more static than in bundles close to T0 and these phases usually crystallize upon heating to an appropriate temperature in the stable crystal phases. 

Dual lifetime referencing (DLR) is another powerful technique that enables referenced measurements in case of fluorescent indicators [23]. In this method, the analyte-dependent signal from an indicator is referenced against the signal from an inert luminophore. This can be realized in both the time domain [24] and in the frequency domain [25]. Often, a luminescent reference dye is embedded into gas blocking nanobeads to avoid oxygen quenching. Polymers with very low gas permeability such as poly(acrylonitrile) [24] or poly(vinylidene chloride-co-acry-lonitrile) [26] are the best choice here. 

Fig. 10 Protease assay using beads with emissive polymer and avidin [87] cartoon. Emissive polymer is represented by green lines, quenched polymer by grey...

Fig. 12 Cartoon representing two versions of a kinase assay, (a) The tum-off version is a direct assay the extent of phosphorylation of the substrate is reflected in the binding of the quencher to the bead and hence to the quenching [88]. (b) The tum-on version is a competition assay increased phosphorylation of the substrate leads to it competing with the quencher in binding to the beads, and hence to increased emission [44]. Emissive polymers are represented by green lines quenched polymers by grey lines...

Landis and coworkers [140] have developed an active-site counting method based on H-labelling, for the metallocene-catalyzed alkene polymerization. After quenching the reaction by addition of methanol, the polymer is analyzed by NMR, which allows the quantification of Zr-alkyl sites. A typical NMR of quenched polymer is shown in Scheme 1.7 (label is found at terminal positions only). This technique has been applied to the polymerization of 1-hexene catalyzed by [Zr(rac-C2H4(l-indenyl)2)Me][MeB(QF5)3], 91. As shown in Scheme 1.7, there are two possible approaches ... 

Scheme 1.7 Active-site counting method based on H-labelling, in the zirconocene-catalyzed polymerization of 1-hexene. Lower left typical NMR of the quenched polymer according to method A. The integrals allow the quantification of the Zr-alkyl active sites. All labels are found in the terminal position. Lower right comparison of fractional active-site counts using Method A (open circles, o) or Method B (diamonds ).

Emissive polymer = Quenched polymer = Analyte molecule... 

Sometimes, small structural differences in morphology of polymer samples can be isolated by using a double subtraction technique. For example, with polyethylene terephthalate) PET, differences in the amorphous phase of the melt-quenched polymer and solution-cast polymer can be isolated by first subtracting out the contribution due to the trans isomer and then subtracting the two difference spectra from each other 214). (Fig. 16) shows the resultingdifference spectrum obtained after the second subtraction. Obviously the two amorphous structures are different from each other. 

The Space Fractional Dimension dc, the Cutoff Time of the Scaling in the Time Domain To, and the Characteristic Frequency coo for Quenched Polymer (QN), Crystalline (CN) and Microcomposite Samples (MCN). 

Figure 10. Arrhenius plot of the rale constants k of the thermal cis—trans isomerization of the azochromophore incorporated in the soft segment (solid film) k, and k2, annealed polymer k3, quenched polymer (1 lk...

Semicrystalline polymers, VDC copolymer and aromatic nylon MXD-6 (Table II) showed little if any reduction in permeability at these moderate orientation levels. In fact, recent unpublished work has shown that aromatic nylon MXD-6 exhibits an initial increase in permeability up to 3X orientation followed by a significant reduction in permeability at higher orientation levels. The VDC copolymer also showed higher permeability with moderate biaxial orientation — 1.5 times the permeability of the unoriented film. This is believed to be due to orientation of the polymer after crystallinity is fully developed. If the orientation of VDC copolymers is induced prior to full development of crystallinity in the material, one would not expect to see an increased oxygen permeability. In commercial practice, therefore, forming of VDC copolymer structures is normally done on rapidly quenched polymer to orient it while still in the amorphous state at temperatures near or above the Tm of VDC copolymer. 

An optical transducer is an attractive option in that selectivity can be enhanced through the use of optical filters to select specific wavelengths. When this is combined with a very specific optical sensing material, e.g. photo-luminescent quenching polymers, the possible limit of detection is extremely impressive (see chapter 23 of reference [5]) and [11]. 

The ratiometric response (i.e., the ratio of the quenching responses recorded by each sensor channel) can also be used to improve selectivity. Figure 11 illustrates the response of two different AFPs to TNT and 2,4-DNT. The ratio of the percent quench (Polymer A/B) was calculated for each polymer. The ratio of responses (A B) for TNT was 2.1, while the ratio for... 

We quench polymer blends with critical or off-critical compositions inside the spinodal phase boundary, and we investigate their self-assembling (ordering) processes, patterns (morphology), and dynamics via spinodal decomposition (SD) (1, 2). Basic information obtained in the studies of self-assembly will eventually lead us to control the patterns, functionalities and properties of polymer blends. As a methodology for controlling the patterns, we shall discuss various processes which pin down the pattern growth. 

Glass Transition Time Magnification and Quenching. Polymers are glass-forming materials. If no crystallization occurs, this means that the spectrum of relaxation time depends on temperature via the difference T — where is the glass transition temperature. For all kinds of glasses the dependence is similar all the times of the spectrum are multiplied by the same factor a = f(T — The closer to T, ... 

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