Pendant group vibrations

The in-phase and quadrature spectra in the region between 1050 and 900 cm are shown in Figure 12.11. The peak at 1018 cm in the quadrature spectrum has been assigned to a vibration of the THT pendant group. The phase of the pendant group vibrations is different from that of the C—C ring stretches and the vinylene C—H stretch indicating that these vibrations are independent of the backbone vibrations. 

The resonant effect, which concerns mainly vibrational modes belonging to the coordination site, is manifested by changes in the relative intensity of several bands. The band about 1,600 cm decreases its intensity and the bands around 1,300, 900, 700 and at 340 and 298 cm increase their intensities. Other bands at 1,367, 1,222, 1,006, 839 and 650cm maintain or slightly decrease their relative intensities. The intensity decreasing of the coupled vCC/vCN band at 1,600 cm indicates that this mode is an asymmetric vibration with an important vCC component of the pendant group. The spectral behavior of the bands which increase their intensity indicates that the corresponding modes are symmetric vibrations. 

In SBR, the benzene rings protrude like branches from the mbber backbone and absorb molecular vibrations caused by the elastomer chain touching the road surface thereby improving the traction properties. In ENR, the epoxide group performs a similar function like the benzene rings pendant from the backbone. 

The 980-cm 1 Band. This band appears to be due to the symmetric stretching vibration of COC groups in the pendant side-chains -CF2CF-0-CF2CF- of Nafion (2 ). In the ATR spectra of... 

The Tg of polymers is very much a function of chain structure. Repeat units which introduce stiffness into the backbone chain or bulky side groups pendant from the backbone tend to increase the observed Tg. Strong interchain forces, such as hydrogen bonding, also reduce the crankshaft-like motion of the polymer backbone at any given temperature and tend to increase the Tg. The glass transition temperature is often termed the a-transition. If the temperature is lowered below that of the Tg, temperatures are reached where the rotation of side groups - and eventually, at even lower temperatures, the vibrational behaviour of bonds - are frozen . These lower transition temperatures are known as j - and y-transitions respectively. 

Infrared spectra of the zeolite/polymer inclusions and of PAN extracted from the zeolites show also peaks characteristic of the bulk polymer,including methylenic C-H stretching vibrations of the backbone (2940 cm l and at 2869 cm"l), and a band at 2240 cm l due to the pendant nitrile group. The spectra of the extracted intrazeolite polymers are indistinguishable from the spectrum of the bulk polymer. We conclude that the polymer formed in the zeolites is polyacrylonitrile. 

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