Poly vibrational modes

Both vibrational spectroscopies are valuable tools in the characterization of crystalline polymers. The degree of crystallinity is calculated from the ratio of isolated vibrational modes, specific to the crystalline regions, and a mode whose intensity is not influenced by degree of crystallinity and serves as internal standard. A significant number of studies have used both types of spectroscopy for quantitative crystallinity determination in the polyethylenes [38,74-82] and other semi-crystalline polymers such as polyfethylene terephthalate) [83-85], isotactic poly(propylene) [86,87], polyfaryl ether ether ketone) [88], polyftetra-fluoroethylene) [89,90] and bisphenol A polycarbonate [91]. 

FIGURE 10.11 Tip enhanced spontaneous Raman spectrum of DNA sample (poly(dA-dT)-poly(dA-dT)). The vibration at 1337 cm is employed as the target vibration. The corresponding vibration mode is illustrated in the figure. 

Fig. 4.25 Illustration of mass sensitivities to sorption of octane by poly(dimethylsiloxane) coating, of different vibrational modes (adapted from Kim et al., 2001)...

In the following we will first discuss examples of polytriacetylenes (Fig. 19) and then compare these results with the ones of other molecular structures. Monomers of poly triacetylenes with the three neutral end groups TMS (trimeth-ylsilyl), TES (triethylsilyl), and TIPS (triisopropylsilyl) have been investigated. By deconvolution of the absorption spectra assuming Gaussian fine shapes the wavelengths A00 for the absorption process from the ground state to the zero vibrational mode of the lowest excited state are obtained as described below. 

A few of these UV resonance Raman studies have reported excitation profiles of oligonucleotides [158, 177], These studies show that the hypochromism in the resonance Raman intensities can be as large as 65% for bands enhanced by the ca. 260 nm absorption band for poly(dG-dC) and that the hypochromism can vary substantially between vibrational modes [177], In the duplex oligonucleotide poly(rA)-poly(rU) [158], similar hypochromism is seen. Although theUV resonance Raman excitation profiles of oligonucleotides have been measured, no excited-state structural dynamics have been extracted from them. 

The IR spectrum of poly(vinyl methyl ether) (PVME) in Fig. 17 is quite similar to the spectrum of PEG. PVME has also a strong C-O-C stretching band which is composed of the antisymmetric and symmetric vibration mode (Schmidt et al. 2003). The vibrations of the aliphatic chain between 1,250 and 1,350 cm are very weak or even nonexistent. 

Poly(acrylic acid) (PAA) has several vibrational modes in the 900-1350-cm region whose activity depends on the tacticity of the polymer. Figure 4... 

No.24, 30thNov.l999, p.8161-6 VIBRATION MODE INTERACTION IN THE RAMAN SPECTRA OF POLY(l,6-BIS(N-CARBAZOLYL)-2,4-HEXADIYNE)... 

In some cases, vibration bands are also conformation-sensitive. In particular, when a polymer exists in several crystal forms, different chain conformations may exist in these crystal modifications one example is poly(vinyhdene fluoride) (PVDF). At least four types of crystal modifications are known forms I, II, Hpoiar, and III (26). Form I has nearly a zig-zag chain conformation. Forms II and Ilpoiar exhibit the glide-type TGTG conformation, while form HI has a TTTGTTTG conformation. The ir spectra of these crystal modifications are shown in Fig. 9 (27). For example, the intensive bands observed in the spectra of form I are 1275, 840, and 510 cm and others correspond to the vibration modes intrinsic to long trans sequences of. .. TTTT. The bands at 800, 766, 610, and 530 cm and others in the spectra of form II are attributed to the conformation sequence of TG. On the other hand, in form III, the TG and TT bands coexist in addition to the bands characteristic of the TTTG sequence (27). 

The CNTs generally exhibit well-defined Raman peaks. It is possible to use Raman peak shift to characterize the load transfer mechanism of the CNT/poly-mer composites. When a strain is applied to a material, the interatomic distances change, leading to variations in the firequeucy of vibrational modes. Accordingly, Raman spectroscopy can provide useful information related to the load transfer between the polymer matrix and CNTs. The Raman spectrum of SWNTs generally shows characteristic peaks located at 1350 cm (D band), 1550-1605 cm (G band) and 2700 cm (D band) [35-37]. The D-band derives from the disorder-induced mode and its second-order harmonic is D (G ) band. The G-band is associated with the graphite-like in-plane mode. Dresselhaus et al have provided an in-depth review of the Raman spectra of... 

Sengupta A., Quitevis E. L., Holtz M. W. Effect of high pressure on vibrational modes of polyiodides in poly(vinyl alcohol) films. 

Infrared spectra result from transitions between quantized vibrational energy states. Molecular vibrations can range from the simple coupled motion of the two atoms of a diatomic molecule to the much more complex motion of each atom in a large poly functional molecule. Molecules with N atoms have 3N degrees of freedom, three of which represent translational motion in mutually perpendicular directions (the X, y, and z axes) and three represent rotational motion about the x, y, and z axes. The remaining 3N — 6 degrees of freedom give the number of ways that the atoms in a nonlinear molecule can vibrate (i.e., the number of vibrational modes). 

A specific example is poly(vinyl chloride) (PVC), which is a monosubstituted vinyl polymer that has a syndiotactic-rich character and a conformation that can be either an extended all-trans structure or a folded syndiotactic structure. The vibrational modes of these conformational models obey different selection rules and have different dichroic properties that can be used to spectroscopically test these structures [7]. The folded syndiotactic model of PVC has the [p,0] classification that requires unique Raman lines (no coincident IR frequency) that are polarized. The extended syndiotactic model has the two unique classifications of [d,0] and [p,(r], which means that the unique Raman lines are depolarized, and the Raman lines that are polarized have perpendicular dichroism in the IR spectrum. In the Raman spectrum of PVC [8], polarized lines are observed at 363, 638, 694, 1172, 1335, 1430 and 1914 cm and IR bands are also observed at each of these frequencies. This result rejects the folded syndiotactic structure, because this structure requires the polarized lines to be unique. In addition, each of these frequencies is perpendicularly dichroic in the IR spectrum, a fact that supports the planar syndiotactic structure. 

In our tip-enhanced near-field CARS microscopy, two mode-locked pulsed lasers (pulse duration 5ps, spectral width 4cm ) were used for excitation of CARS polarization [21]. The sample was a DNA network nanostructure of poly(dA-dT)-poly(dA-dT) [24]. The frequency difference of the two excitation lasers (cOi — CO2) was set at 1337 cm, corresponding to the ring stretching mode of diazole. After the on-resonant imaging, CO2 was changed such that the frequency difference corresponded to none of the Raman-active vibration of the sample ( off-resonant ). The CARS images at the on- and off- resonant frequencies are illustrated in Figure 2.8a and b, respectively. 

Here m is the mode order (m — 1,3,5. .., usually 1 for polyethylenes), c the velocity of light, p the density of the vibrating sequence (density of pure crystal) and E the Young s modulus in the chain direction. The LAM band has been observed in many polymers and has been widely used in structural studies of polyethylenes [94—99,266], as well as other semi-crystalline polymers, such as poly (ethylene oxide) [267], poly(methylene oxide) [268,269] and isotactic poly(propylene) [270,271], The distribution of crystalline thickness can be obtained from the width of the LAM mode, corrected by temperature and frequency factors [272,273] as ... 

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