Polymeric samples

D-TEM was introduced into rubber technology field in 2004 by the authors of this chapter [4]. In a recent review of 3D-TEM applied in materials science field [5], only two papers were cited on polymeric samples—one on block copolymers [6] and the other on rubbery composites with conventional and in situ silica [4]. Starting from the latter, 3D-TEM measurements have been carried out on rubbery nano-composites [7-16], and this recent and very important topic is described in this review. 

Figure 3.10 Optimisation strategy for supercritical fluid extraction of polymeric samples. After Lou et al. [145]. Reproduced from the Journal of Chromatographic Science by permission of Preston Publications, A Division of Preston Industries, Inc.

The efficiency of extraction is mainly dependent on temperature as it influences physical properties of the sample and its interaction with the liquid phase. The extraction is influenced by the surface tension of the solvent and its penetration into the sample (i.e. its viscosity) and by the diffusion rate and solubility of the analytes all parameters that are normally improved by a temperature increase. High temperature increases the rate of extraction. Lou et al. [122] studied the kinetics of mass transfer in PFE of polymeric samples considering that the extraction process in PFE consists of three steps ... 

The parameters K1/ K2/ and K3 are defined by the refractive indices of the crystal and sample and by the incidence angle [32]. If the sample has uniaxial symmetry, only two polarized spectra are necessary to characterize the orientation. If the optical axis is along the plane of the sample, such as for stretched polymer films, only the two s-polarized spectra are needed to determine kz and kx. These are then used to calculate a dichroic ratio or a P2) value with Equation (25) (replacing absorbance with absorption index). In contrast, a uniaxial sample with its optical axis perpendicular to the crystal surface requires the acquisition of spectra with both p- and s-polarizations, but the Z- and X-axes are now equivalent. This approach was used, through dichroic ratio measurements, to monitor the orientation of polymer chains at various depths during the drying of latex [33]. This type of symmetry is often encountered in non-polymeric samples, for instance, in ultrathin films of lipids or self-assembled monolayers. 

In fluorescence spectroscopy, the orientation distribution of the guest probe is not necessarily identical to the actual orientation of the polymer chains, even if it is added at very small concentrations (i.e., a probe with high fluorescence efficiency). As a matter of fact, it is generally assumed that long linear probes are parallel to the polymer main chain, but this is not necessarily the case. Nevertheless, if the relation between the distribution of the probe axes and those of the polymer axes is known, the ODF of the structural units can be calculated from that of the probe thanks to the Legendre s addition theorem. Finally, the added probe seems to be mainly located in the amorphous domains of the polymer [69] so that fluorescence spectroscopy provides information relative to the noncrystalline regions of the polymeric samples. 

Used largely for the separation of non-volatile substances including ionic and polymeric samples complementary to gas chromatography. 

Furthermore, polymeric samples are usually a mixture of macromolecular chains terminated by different end-groups and thus, an interesting quantity to be determined (in order to characterize the mixture) is the relative abundance of end-groups [1—3]. Other two important quantities are Mn and Mw, the number-average and the weight-average molar masses [1—3]. 

If one assumes that, in this case, ion abundances are (approximately) proportional to chain abundances in the polymeric sample, it can be concluded that chains terminated with phenolcarbonate on both sides are the most abundant ones (since peaks labeled as A are the most intense ones). In this way, a full polymer characterization is achieved. 

The substituted diphenylmethane dye, auramine O, is weakly fluorescent in fluid solvents but highly fluorescent in viscous or rigid media. It was originally used to probe the viscosity of viscous polymeric samples. Such a strong dependence on solvent viscosity can be explained in the same way as for triphenylmethane dyes. 

Figure 4 If )/I(initial) at 566 nm for Re-complex fluorescence measured over time from two separate polymerizing samples.

So far, most of the experimental studies have been limited to fully polymerized samples or samples with a high plastic content. That is because the earlier Interest was mainly focused on the effect of properties of the constituents, such as crosslink density and miscibility, ease of TEM studies, etc. 

DMTA of partially polymerized samples of TEGDA reveals an increase of Young s modulus due to thermal aftercure near 120°C. Parallel DSC-extraction experiments show that this aftercure requires the presence of free monomer. Near the end of the polymerization the free monomer is exhausted and only crosslinks are formed. T(tan then increases markedly with double bond conversion. 

Fig. 3 shows the maximum extents of double bond conversion x, obtained at various light intensities for polymerizations of TEGDA at 20 and 80"C, respectively. The increase of ultimate conversion with light intensity is observed at both temperatures. This effect is not caused by self-heating of the polymerizing samples (9). 

When high-resolution NMR spectra have to be recorded of a polymeric sample, one has to recognize that polymer solutions are in general highly viscous. To prevent excessive signal broadening caused by this restricted mobility of the solution, polymer solutions for NMR studies have to be highly diluted (approx. 

Solvents 1 and 2 are known to be good solvents for poly(methyl methacrylate) solvent 3 readily dissolves polystyrene.The solubility tests show that the radically polymerized sample is insoluble in all three solvents.The solubility isthusdifferentfrom that of both poly(methyl methacrylate) and polystyrene.The anionically polymerized product dissolves on warming in the acetone/methanol mixture and also in acetonitrile it is insoluble in cyclohexane/toluene.The solubility is thus similar to that of poly(methyl methacrylate). For the cationically initiated polymerization the product is only slightly soluble in acetone/methanol, insoluble in acetonitrile, but very readily soluble in cyclohexane/toluene.The solubility thus resembles that of polystyrene. 

The time at which a glass pipet lowered or pushed into a very high viscosity poured sample will no longer pick up or have cling to the pipet any of the polymerizing sample. 

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