title: Utilizing peptidic ordering in the design of hierarchical polyurethane/ureas.
abstract: One of the key design components of nature is the utilization of hierarchical arrangements to fabricate materials with outstanding mechanical properties. Employing the concept of hierarchy, a new class of segmented polyurethane/ureas (PUUs) was synthesized containing either a peptidic, triblock soft segment, or an amorphous, nonpeptidic homoblock block soft segment with either an amorphous or a crystalline hard segment to investigate the effects of bioinspired, multiple levels of organization on thermal and mechanical properties. The peptidic soft segment was composed of poly(benzyl-l-glutamate)-block-poly(dimethylsiloxane)-block-poly(benzyl-l-glutamate) (PBLG-b-PDMS-b-PBLG), restricted to the β-sheet conformation by limiting the peptide segment length to <10 residues, whereas the amorphous soft segment was poly(dimethylsiloxane) (PDMS). The hard segment consisted of either 1,6-hexamethylene diisocyanate (crystalline) or isophorone diisocyanate (amorphous) and chain extended with 1,4-butanediol. Thermal and morphological characterization indicated microphase separation in these hierarchically assembled PUUs; furthermore, inclusion of the peptidic segment significantly increased the average long spacing between domains, whereas the peptide domain retained its β-sheet conformation regardless of the hard segment chemistry. Mechanical analysis revealed an enhanced dynamic modulus for the peptidic polymers over a broader temperature range as compared with the nonpeptidic PUUs as well as an over three-fold increase in tensile modulus. However, the elongation-at-break was dramatically reduced, which was attributed to a shift from a flexible, continuous domain morphology to a rigid, continuous matrix in which the peptide, in conjunction with the hard segment, acts as a stiff reinforcing element.
authors.affiliation: Department of Macromolecular Science and Engineering, Case Western Reserve University, Cleveland, Ohio 44106, USA.
authors.forename: J Casey
authors.initials: JC
authors.lastname: Johnson
authors.forename: Nandula D
authors.initials: ND
authors.lastname: Wanasekara
authors.forename: Lashanda T J
authors.initials: LT
authors.lastname: Korley
mesh_terms: D008958:Models, Molecular; D015394:Molecular Structure; D010316:Particle Size; D010455:Peptides / Q000737:chemistry*; D011140:Polyurethanes / Q000138:chemical synthesis* / Q000737:chemistry; D013696:Temperature; D014508:Urea / Q000031:analogs & derivatives / Q000138:chemical synthesis* / Q000737:chemistry
chemical_list: D010455:Peptides; D011140:Polyurethanes; D014508:Urea