Polymer blends interaction spectrum

Coleman et al. 2471 reported the spectra of different proportions of poly(vinylidene fluoride) PVDF and atactic poly(methyl methacrylate) PMMA. At a level of 75/25 PVDF/PMMA the blend is incompatible and the spectra of the blend can be synthesized by addition of the spectra of the pure components in the appropriate amounts. On the other hand, a blend composition of 39 61 had an infrared spectrum which could not be approximated by absorbance addition of the two pure spectra. A carbonyl band at 1718cm-1 was observed and indicates a distinct interaction involving the carbonyl groups. The spectra of the PVDF shows that a conformational change has been induced in the compatible blend but only a fraction of the PVDF is involved in the conformational change. Allara M9 250 251) cautioned that some of these spectroscopic effects in polymer blends may arise from dispersion effects in the difference spectra rather than chemical effects. Refractive index differences between the pure component and the blend can alter the band shapes and lead to frequency shifts to lower frequencies and in general the frequency shifts are to lower frequencies. 

Infrared spectroscopy is frequently used to study blends. As explained in section 2.6.4, the infrared spectrum of a mixture of substances can be used to determine the concentrations of the various components, provided that there is no change in the spectrnm of either component on mixing. This will be the case for a polymer blend when the components are immiscible. Miscibility nsnally involves some strong interaction between the two polymers, so the spectrnm of the blend is then not simply a weighted sum of the spectra of the individual polymers. One of the most important types of interaction in polymer blends is hydrogen-bonding, particularly when one of the polymers contains carbonyl groups, >C=0. 

Information regarding the possible interaction between the components in a polymer blend can be obtained by comparison of the infrared spectra of the base material with that of the blends [20,21]. Figures 5.10a and 5.10b represent the typical Fourier transform infrared (FTIR) spectra of PMMA and PMMA/EMA (90/10) blends, respectively. The spectrum of PMMA shows a very sharp peak around 3398 cm due to overtones of stretching vibrations... 

Polymer blends are mixtures of polymeric materials and consist of at least two polymers or copolymers. Infrared spectroscopy is now quite a commonly used technique for examination of the interactions in polymer blends [9, 10]. If two polymers are immiscible, the infrared spectrum should be the sum of the spectra of the two components. Phase-separation implies that the component polymers in the blend will have an environment similar to the pure polymers. If the polymers are miscible, there is the possibility of chemical interactions between the individual polymer chains. Such interactions may lead to differences between the spectra of the polymers in the blend and the pure components. Generally, wavenumber shifts and band broadening are taken as evidence of chemical interactions between the components in a blend and are indicative of miscibility. 

A study of the polymer blends of poly(vinyl phenol) and poly(methyl acrylate) using 2D C- H correlation NMR have been reported. From the spectrum, a direct interaction between the hydroxyl hydrogen of poly(vinyl phenol) and the carbonyl carbon of poly(methyl acrylate) can be deduced. The miscibility in annealed 50 50 blends of a random, copolyester Vectra-A, containing 73% p-hydrojy-benzoic acid and 27% hydroxy naphthoic acid, and poly(ethylene terephthalate) (PET) has been discussed by using a standard 2D exchange experiment. The small cross peaks between the peak of aliphatic PET and that of quaternary Vectra-A carbons diagonal lines indicated intimate mixing. 

Factor analysis can be used as a quantitative method to establish the existence of a measurable interaction spectrum [23]. To determine whether the interaction spectrum is a contributing factor to the spectrum of the blend, a series of polymer blends with different volume fractions of each homopolymer is prepared, and the spectrum of each blend is obtained. The number of components present in these blend spectra is then determined by factor analysis. In the case of compatible blends, three components are expected, but for incompatible blends, only two should be observed. 

An interesting method of forcing two polymers that do not exhibit hydrogen bonding between each other to be compatible is to introduce into one of the systems a small amount of comonomer that can hydrogen bond and that can act as the chemical link between the polymer chains [26]. The spectra of the styrene (92%)-acrylic acid copolymer, the 89% styrene-acrylic acid (SAAS)-poly(methyl methacrylate) (PMMA) blend (4 1), and the interaction spectrum obtained after double subtraction are shown in Fig. 4.27. Hydrogen bonding has been introduced in the blends to make these two polymers compatible. 

In the solid, dynamics occurring within the kHz frequency scale can be examined by line-shape analysis of 2H or 13C (or 15N) NMR spectra by respective quadrupolar and CSA interactions, isotropic peaks16,59-62 or dipolar couplings based on dipolar chemical shift correlation experiments.63-65 In the former, tyrosine or phenylalanine dynamics of Leu-enkephalin are examined at frequencies of 103-104 Hz by 2H NMR of deuterated samples and at 1.3 x 102 Hz by 13C CPMAS, respectively.60-62 In the latter, dipolar interactions between the 1H-1H and 1H-13C (or 3H-15N) pairs are determined by a 2D-MAS SLF technique such as wide-line separation (WISE)63 and dipolar chemical shift separation (DIP-SHIFT)64,65 or Lee-Goldburg CP (LGCP) NMR,66 respectively. In the WISE experiment, the XH wide-line spectrum of the blend polymers consists of a rather featureless superposition of components with different dipolar widths which can be separated in the second frequency dimension and related to structural units according to their 13C chemical shifts.63... 

Usually two different polymers do not mix at the segmental level but a favourable interaction between the two polymers can allow one to obtain homogeneous blends. FT-IR is a potential tool for the investigation of the mutual compatibility of various polymers. The small spectral changes due to these interactions can be detected by this method. If two polymers are immiscible, one can synthesise a spectrum of the blend by co-adding, in the appropriate... 

Specific interactions between PCL and PVC are clearly indicated. In the solid state (Figure 5.9a) the spectrum of neat PCL indicates the presence of crystalline (1724 cm 1) and amorphous (1737 cm"1) bands. At mole ratios up to 2 1 of PVC to PCL, the spectra indicate that in the solid state the blends consist of crystalline and amorphous phases. As the PVC concentration increases, a parallel increase of the intensity of the amorphous band is observed. Moreover, the frequency shifts observed for both the crystalline and amorphous bands as a function of the composition of the blend suggests that specific interactions between the two polymers occur. No shift is observed in the carbonyl stretching vibration of PPL/PVC blends, in the molten state or in the solid state over the entire range of compositions and the two polymers are incompatible [28]. 

Figure 12.13 shows the Xe spectra of a iPP/EP blend obtained with single pulse excitation and with => 129Xe cross-polarisation at -33 °C [13]. In the cross-polarisation spectrum only the Xe line from Xe in iPP is observed, because the dipolar interaction between the polymer spins and the 129Xe spins due to the Xe mobility is too weak in EP. Also the cross-polarisation signal of iPP disappears at temperatures higher than the Tg of iPP. 

More frequently than chemical techniques, the spectroscopic methods of analysis are used for the determination of polymer chemical composition. Among these techniques the use of infrared (IR) absorption spectra as fingerprints for polymer identification is probably the most common. The IR absorption is produced tjy the transition of the molecules from one vibrational quantum state into another, and most polymers generate characteristic spectra. Large databases containing polymer spectra (typically obtained using Fourier transform infra-red spectroscopy or FTIR) are available, and modern instruments have efficient search routines for polymer identification based on matching an unknown spectrum with those from the library. For specific polymers, the IR spectra can reveal even some subtle composition characteristics such as interactions between polymer molecules in polymeric blends. 

By comparing the NMR spectrum of each component polymer with that of a blend, we can often see that some changes occur in a chemical shift and/or a lineshape. Such apparent changes can be attributed to modifications of both chemical structure and polymer conformation upon blending, reflecting a specific interpolymer interaction. 

The difference of relaxation times in different domains makes it possible to observe the spectrum of one of the domains. Figure 10.23(a), shows the Ti-selected spectrum of PVPh/PEO = 40/60 [34]. Since the Ti of crystalline PEO ( 15 s) is much longer than that of the amorphous phase (—0.1 s), it is possible to observe the spectrum of crystalline PEO selectively (indicated by arrow in Fig. 10.23(a)). On the other hand, for the miscible PVPh-rich blend (PVPh/PEO = 58/42), the crystalline-PEO peak is not appreciable. This is in agreement with the above-mentioned results (Table 10.2). The signals of mobile domains/component polymers can be observed selectively by utilizing the weaker dipolar interaction between H. To name a few examples, the dipolar dephasing [128,131,152], the cross-polarization-depolarization [152] and the pulse saturation transfer [151] techniques have been applied. 

We have applied the ultrafast confocal microscope to map excited state dynamics in thin films of poly(9,9-dioctylfluorene) (PFO, see chemical structure in figure 2(a)), blended with polymethylmethacrylate (PMMA, 10% wt. PFO in PMMA). PFO is a blue-emitting polymer, with an absorption maximum at 385 nm (see Fig. 2(a)), while PMMA is transparent at our pump wavelength and it does not interact with PFO [6] so that it is optically inert. Figure 2(b) shows the macroscopic AT/T spectrum of PFO measured at x = 1 ps at 570 nm probe wavelength we observe a photo-induced absorption (PA) due to photo-generated polarons [7],... 

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