Preparation And Characterization Of Chain Folding Polyurea

In nature, the foldamer formed by oligomers or polymers can produce complex three-dimensional structures, generating macromolecules possessing lots of functions in transport, recognition, catalysis, and charge-and energy-transfer. Therefore, the studies of the foldamers were favored by many researchers in recent decades. By using of intramolelular hydrogen bonds interaction, ?-? or donor-acceptor interaction, chemists can use these foldamer to mimic related bio-process. However, the assemble morphology of foldamer and the mechanical properties of its composite are rarely reported. Based on previous work, in this paper we designed and synthesized a new kind of polyurea foldamer, and studied its self-assembling behavior and mechanical properties of its composite.The main content is depicted as followes:1. A new kind of polyurea foldamer was designed and synthesized. The hydrogen-bond and ?-? interactions of the backbone can facilitate the folding process of the polymer. Because of the existence of the long alkyl chain, this kind of polyurea possesses good solubility in common organic solvent. Moreover,the special structure provided the possibility for forming well-defined assemble morphology. The polyurea was synthesized by tetramethylguanidine-promoted efficient esterfication. Four types of monomers were as follows:4,4'-(carbonyldiimino)-bis-benzoic acid (A) and 3,5-bis(4-bromobutoxy)-benzoicacid hexadecylester (B1),3,5-bis(6-bromohexyloxy)-benzoic acid butyester (B2),3,5-bis(12-bromododecyloxy)-benzoic acid hexadecylester (B3).2. The degree of polymerization and the structure of polyurea were characterized by nuclear magnetic resonance hydrogen spectrum (1H-NMR) and infrared spectroscopy(IR). The esterification reaction dynamics were studied by 1H-NMR tracking. Thus, we got to know that the esterification efficiency were high and bromated monomers with longer alkly chain decreased the rate of reactions. Thermal stability of polyurea was studied by using thermogravimetric analysis (TGA). The self-assembled structures of polyurea were observered and characterized by scanning electronic microscopy (SEM) and transmission electron microscope (TEM). The results showed that the polyurea could form spherical tubular and discal morphology drived by hydrogen bond and crstallization.3. The synthesized polyurea self-assembled in mixture organic solvent. We next studied the influence of the dgree of polymerization (DP) and the structures of the foldamer on the morphologies of assembled aggregates. The results suggested that the assemble morphologies were affected considerably with the DP, while changing the length of the alkyl chain only altered the size of the aggregates.4. The ends of polyurea were modified with double bond, and then co-polymerized with ethyl acrylate by using photo-induced polymerization. The mechanical properties of polyurea and photo-crosslinked copolymers were studied by uniaxial tensile test.The results showed that strain of photo-crosslinked copolymers increased and stress decreased with stretching.