Segment Sizes of Supramolecular Polymers of N,N′,N′′-Tris(3,7-dimethyloctyl)benzene-1,3,5-tricarboxamide in n-Decane

Abstract

The average segment sizes of rather flexible supramolecular polymers formed by a racemic mixture of N,N',N"-tris(3,7-dimethyloctyl)benzene-1,3,5-tricarboxamide (DO3B) in n-decane (C10) (DO3B/C10) and a mixture of DO3B and homochiral (S)-N,N',N"-tris(3,7-dimethyloctyl)benzene-1,3,5-tricarboxamide ((S)DO3B) in C10 (DO3B:(S)DO3B/C10) were determined using mechanical relaxation techniques, including linear and nonlinear viscoelastic experiments in addition to dielectric relaxation measurements. To evaluate the average sizes of segments for the supramolecular polymers formed in these systems, the conventional rubber elasticity theory was employed for the linear viscoelastic behavior and a non-Gaussian-type three-chain model assuming chains constructed with freely joined chain segments with finite sizes for nonlinear viscoelastic responses. Concentration-independent similar segment sizes for the supramolecular polymer formed in DO3B/C10 were evaluated using both the mechanical techniques. However, the segment size of the formed supramolecular polymer increased upon increasing the component of (S)DO3B to the total amount of DO3B and (S)DO3B in DO3B:(S)DO3B/Ci0o. The formed supramolecular polymer in the racemic DO3B/C10 system possessed threefold intermolecular hydrogen bonding aligned along its stiff columnar structure, with equimolar right- and left-handed helicities connected by defective portions, which were DO3B molecules containing defects in hydrogen bond formation. In the case of DO3B:(S)DO3B/C10, the addition of the chiral (S)DO3B component induced the majority rule effect for the helicity of the system to increase the major part of helicity, which led to the reduction of the number of defects and an increase in segment seizes. Because large macrodipoles are naturally generated by helical three-fold hydrogen bonding of amide groups in a head-to-tail arrangement, as in type-A polymers possessing parallel electric dipoles along their backbones, profound dielectric behavior provided a concentration-independent segment size for a supramolecular polymer formed in both the DO3B/ C10 and DO3B:(S)DO3B/C10 systems, the value of which was about one-third of that determined mechanically. A free-rotation chain model that is slightly more realistic than the freely jointed chain model was employed to consider the discrepancy in the evaluated segment sizes. Then, helical columns consisting of nine DO3B molecules and supramolecular polymer chain portions formed by a three-column connection behaved as equivalent freely jointed (Kuhn) segments.