Effect of Spacer Stiffness on the Properties of Hyperbranched Polymers

A series of peripherally clickable hyperbranched polyesters were prepared wherein the stiffness of the spacer segment between branching junctions was systematically varied. Three different four-carbon spacers were studied: one was fully saturated (HBPC4-S), another bears a double bond (HBPC4-DBc), and a third carries a triple bond (HBPC4-TB); in the case of the sample with a double bond c indicates cis-rich isomer. The glass transition temperatures of the HB polyesters were seen to increase with the stiffness of the spacer segment from 27 to 60 °C. Furthermore, when the peripheral propargyl groups of the HB polyesters were quantitatively clicked with a crystallizable docosyl (C-22) azide, all the derivatives exhibited sharp melting/crystallization peaks in the DSC traces, indicative of segregation and colocalization of the peripheral segments. WAXS data confirmed the crystallization of the alkyl segments in a paraffinic lattice, while SAXS profiles revealed the formation of a lamellar morphology; the interlamellar spacing reflected the compactness of the HB polymeric core and also the adaptability of the core toward the self-segregation. Whereas the effect of such structural variations in linear polyesters has been examined extensively, this represents the first study that reveals the implications chain stiffness and geometry on the properties of hyperbranched polymers.