Molecular topology affects the polymer segmental dynamics and hence the glass temperature. In addition, chain topology strongly affects the crystallization process in semicrystalline polymers. The best example of topological constraints is that of a ring polymer. The absence of entanglements and the lower effective viscosity for rings has consequences both on the segmental dynamics and crystallization behavior. In the first part we review recent results on the crystal structure, degree of crystallinity, chain folding and the segmental dynamics of linear and cyclic poly(ethylene oxides). Both linear and ring polymers form the same crystal structure. Furthermore they have similar segmental dynamics within the restricted amorphous phase. However, the melting temperature of rings is systematically higher than of linear chains. On heating, linear chains melt via lamellar thickening in a continuous process. Rings melt with discontinuous jumps in lamellar spacing towards the equilibrium crystal phase with the twice-folded conformation.  These finding are discussed in view of the pre-defined chain topology of rings. In the second part we discuss the effect of ring topology on the glass temperature. We investigate cyclic polystyrene structures, all with a similar molecular weight, designed with a number of coupling points located at strategic sites to control the shape of the polymer coil. For this purpose we employ dielectric spectroscopy and temperature modulated TM-DSC. To quantify the effect of topology we define (i) the number of branching segments and (ii) the loop molecular weight. Glass temperature increases with the number of branching segments and decreases with the loop molecular weight. In addition there exist small changes in fragility (or steepness index) with topology. The steepness index decreases with the number of constrained segments and increases with the loop molecular weight. The role of the polar triazol units at the coupling points is discussed. <br/>

Influence of chain topology on polymer crystallization and glass temperature: Rings vs. linear chains

255th National Meeting (2018)

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