Vibrational Spectroscopy를 이용한 Syndiotactic Polypropylene과 Syndiotactic Polystyrene의 분자구조 및 배향에 관한 연구 :

다국어 초록 (Multilingual Abstract)

Syndiotactic polypropylene (s-PP) was first synthesized and its configuration and conformation characterized by Natta et al. It was the first α-olefin polymer to be obtained in a highly regular, syndiotactic form. Syndiotactic polypropyleme can be prepared in two crystalline modifications corresponding to different conformation of the chain : the more stable helical conformation, and a planar zig-zag form. The helical conformation can be achieved by either crystallizing from the melt or by annealing of planar zig zag s-PP. This stable crystalline phase have a periodic TTGG helix conformation chains where T indicates a dihedral angle of 180。, and G a dihedral angle of 60。 and are olderly packed in a lattice is obtained. The conformation can be made by cold stretching quenched samples from the melt, the chains get a planar zig zag conformation.
The calculated frequency, the infrared, and the Raman spectrum of s-PP in both two-fold helix and planar zig-zag conformations have been recorded and studied.
In order to understand polymer deformation phenomena at the molecular level, the time-resolved FTIR spectroscopy was employed. By investigating the changes in IR spectra with drawing the s-PP film, the macroscopic deformation properties reflected by
stress-strain diagrams were correlated with polymer structure and orientations. Once the neck was formed by stretching the s-PP film, first the chain conformation transformed from helix to planar zigzag structure, and then changes in the chain orientation were observed. In the necking region, the polymer chains of the amorphous as well as the crystalline domains were oriented, whereas only the chains in the crystalline domain were oriented in the strain hardening region.
Crystallization and melting behaviors of syndiotactic polypropylene (s-PP) were studied by using the differential scanning calorimetry (DSC). s-PP exhibits the double melting behavior which strongly depends on a thermal history of smaples. To understand the
morphology two crystals formed during isothermal crystallization, DSC experiments were carried out for samples prepared with different cooling rates. During the crystallization process, s-PP forms a kinetically favored structure with higher melting temperature and
a thermodynamically favored structure with lower melting temperature. The relative amounts of these two structures are dependent on the cooling rate of crystallization and annealing conditions.
Syndiotactic polystyrene(s-PS) presents a very complex polymorphic behavior. It can exist in four main crystalline polymorphic structures, designated α, β, γ, and δ. The α and β forms have been shown to have an all-trans planar zigzag (tttt)n backbone conformation, whereas the crystalline γ and δ forms contain chains in the (2/1)2 helical (ttgg)n backbone conformation. The planar zigzag conformation is the more thermodynamically favored state as compared to the helical conformation. The α form has been shown to exist in trigonal crystal structure arising from groups of backbone triads, where as the β form packs in an orthorhombic crystal structure. The γ and δ
forms can only be formed from solvent swelling of glassy s-PS and have been shown to have effectively the same monoclinic crystal structure. The δ form is found to be a crystalline-solvent, complex and is stable up to ∼120。C. On heating above this temperature, the δ form changes to the γ form, accompanied by removal of the solvent, while the conformation is retained. A solid phase transformation of the γ form to the α form is possible at around 180。C. We studied the nature of these crystalline forms and the phase transition of s-PS by FTIR, FT-Raman.