Conformation and crystallinity in polymers : a study using novel Roman techniques

Royaud, Isabelle Anne-Marie (1989) Conformation and crystallinity in polymers : a study using novel Roman techniques. University of Southampton, Doctoral Thesis.

Record type: Thesis (Doctoral)

Abstract

Crystallinity and conformation of biopolymers, polyamides and even numbered normal paraffins were studied using novel Raman techniques. The newly developed Fourier transform Raman method was used for characterization of biopolymers and polyamides. Low frequency modes of vibration by conventional Raman spectroscopy were investigated in terms of structure for the paraffins. The temperature dependence of the low frequency and internal mode regions were studied for even n-paraffins from C₂₂H₄₆ to C₃₆H₇₄ and for the binary mixture C₂₈H_{58 +} C₃₀H₆₂. Particular emphasis was placed on temperatures just below the melting point. The lattice packing in the crystals was found to depend on the history of the sample crystallization. As the temperature was raised up to the solid-solid phase transition, a change from two chains per unit cell to one chain was observed. The degree of order was found to decrease as the temperature increased but no evidence of the presence of defects was detected. The study of the binary mixture suggests that the chains in the mixture do not vibrate as isolated rods but rather like the longest hydrocarbon component. The FT Raman spectra of three solid homopolypeptides were acquired for the first time. These spectra show mainly sharp bands arising from the characteristic side group vibrations. The corresponding infrared spectra exhibit predominantly bands arising from secondary amide vibrations broadened by OH species absorptions. Thus identification was more readily achieved with the Raman technique. Studies in the liquid state led to the conclusion that considerable improvements in sensitivity are needed before the method becomes useful to biochemists. Aliphatic polyamides of the type nylon X and nylon X,Y were characterized by FT Raman. The spectra obtained tended towards that of polyethylene as the number of methylene group per repeat unit increases. The FT Raman study of samples of nylon 6 with different crystallinity led to the conclusion that this technique has the potential to give a quantitative measure of percentage crystallinity. Evidence is presented that FT Raman spectroscopy may be capable of distinguishing between various nylon copolymers. In contrast, it was confirmed that the infrared study of aliphatic polyamides does not provide an easy means to their identification since the strongest bands arise from the secondary amide vibrations and sample preparation in the form of film was required.

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