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Segmental Order in Lamellar Block Copolymers

It is well known that block copolymers segregate under the condition of strong segregation limit (SSL). Such behavior make these materials extremly atractive for fundamental research. Different chemical comoposition of block copolymers leads to different microdomains structure and some of them are expected to have anisotropic properties. Particularly, one can expect that the dynamics of chain segments is different along the axis perpendicular and parallel to the lemellar microdomains. Deuterium NMR spectroscopy is a powerful tool in studying anisotropic molecular motions. The approach consist in measuring how quadrupolar interaction is time averaged by molecular motions. In a particular case of uniaxial systems, such as lamellar block copolymers, the quadrupolar interaction which is averaged to a nonzero value by molecular motions, splits the single NMR line into a doublet structure. The value of the quadrupolar splitting is a direct measure of the mean orientational order parameter S. The results obtained by the use of NMR probes (deuterated block like chains of low molecular weight) as well as by selectively labeled block copolymers will be presented. The influence of the temperature on segmental order in lamellar diblock and symmetric triblock copolymer will be discussed. A strong motional and orientational gradient along the matrix chain can be detected by NMR spectroscvopy. In a very special case of semicrystalline block copolymers, the dynamics of the chain segments in the presence of a crystalline phase was studied by labelled solvent molecules (preferental solvent for semicristalline block).

deuterium NMR spectroscopy; orientational dynamics; lamellar block copolymers

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