ja411583f_si_001.pdf (1.36 MB)
Periodically Clickable Polyesters: Study of Intrachain Self-Segregation Induced Folding, Crystallization, and Mesophase Formation
journal contribution
posted on 2014-02-12, 00:00 authored by Joydeb Mandal, S. Krishna Prasad, D. S. Shankar Rao, S. RamakrishnanA series of polyesters
based on 2-propargyl-1,3-propanediol or
2,2-dipropargyl-1,3-propanediol or 2-allyl-2-propargyl-1,3-propanediol
and 1,20-eicosanedioic acid were prepared by solution polycondensation
using the corresponding diacid chloride; these polyesters were quantitatively
“clicked” with a fluoroalkyl azide, namely CF3(CF2)7CH2CH2N3, to yield polyesters carrying long-chain alkylene segments in the
backbone and either one or two perfluoroalkyl segments located at
periodic intervals along the polymer chain. The immiscibility of the
alkylene and fluoroalkyl segments causes the polymer chains to fold
in a zigzag fashion to facilitate the segregation of these segments;
the folded chains further organize in the solid state to form a lamellar
structure with alternating domains of alkyl (HC) and fluoroalkyl (FC)
segments. Evidence for the self-segregation is provided by DSC, SAXS,
WAXS, and TEM studies; in two of the samples, the DSC thermograms
showed two distinct endotherms associated with the melting of the
individual domains, while the WAXS patterns confirm the existence
of two separate peaks corresponding to the interchain distances within
the crystalline lattices of the HC and FC domains. SAXS data, on the
other hand, reveal the formation of an extended lamellar morphology
with an interlamellar spacing that matches reasonably well with those
estimated from TEM studies. Interestingly, a smectic-type liquid crystalline
phase is observed at temperatures between the two melting transitions.
These systems present a unique opportunity to develop interesting
nanostructured polymeric materials with precise control over both
the domain size and morphology; importantly, the domain sizes are
far smaller than those typically observed in traditional block copolymers.