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Selective replacement of the amorphous peptide domain of a spider silk with poly(ethylene glycol) gave N. clavipes silk-inspired polymers having similar solid-state structures and very good mechanical properties. The tendency of poly(alanine) having appropriate chain length to form beta-sheets and the facility with which the beta-sheets self-assemble have been retained in the polymers. Solid-state (13)C NMR, solid-state FTIR, X-ray diffraction, and AFM studies showed that the polymers formed predominantly antiparallel beta-sheets that self-assembled into discrete nanostructures. The longer the peptide segment was, the greater was the tendency to self-assemble into antiparallel beta-sheet aggregates. AFM revealed that the morphology of the polymers was a microphase-separated architecture that contained irregularly shaped 100-200 nm poly(alanine) nanodomains interspersed within the PEG phase. The results suggest that the poly(alanine) domain influences the solid-state properties of spider silk through beta-sheet self-assembly into temporary cross-links. The results further demonstrate that by selectively replacing certain segments of a naturally occurring biopolymer with a judiciously selected nonnative segment while, at the same time, retaining other segments known to be critical for the essential properties of the native biopolymer, a synthetic polymer with similar properties and function can be obtained.

Oxyanions form a new class of catalysts for group-transfer polymerization (GTP) of acrylic monomers.Active catalysts in this class include aliphatic and aromatic carboxylates, phenolates, sulfinates, phosphinates, sulfonamidates, perfluoroalkoxides, nitrite, and cyanate. Catalytic activity is found in oxyanions whose conjugate acids have a p (in DMSO) within the range 4.5-23. Best results in terms of livingness and polydispersity of the resulting polymers are obtained with the lowest operable concentrations of the most active catalysts and with somewhat higher concentrations of catalysts of moderate activity. Bioxyanions (1:1 complexes of oxyanions with their conjugate acids) also are active but show reduced activity compared to the corresponding monooxyanions. They give better control of molecular weight than is obtained with the corresponding monooxyanions. In contrast to the more potent catalysts, the weaker catalysts show little activity at temperatures substantially below room temperature. Relative catalyst efficiency correlates well with pKa(DMSO) of the conjugate acids of the corresponding catalysts. The stereochemistry of PMMA prepared with oxyanion catalysts does not differ substantially from that of PMMA prepared with bifluoride catalysis.

Biomolecular Bombyx mori silk-based multiblock copolymers of poly(ethylene oxide)(PEO) and GlyAlaGlyAla prepared by step-growth polymerization based on a modular chemical method have been found to self-assemble into nanostructures. Solid-state 13C NMR, solid-state FTIR, and powder X-ray diffraction provided evidence for the β-sheet self-assembly. The overall β-sheet content was as high as 90%. The building blocks had significant impact on the solid-state structure of the resulting polymer. Longer PEO spacers lowered the tendency to self-assemble into antiparallel β-sheets and implicated the existence of PEO-sequestered isolated β-sheets. Differential scanning calorimetry, transmission electron microscopy, and atomic force microscopy confirmed nanostructure formation and microphase separation. The microphase-separated morphology of the polymers contained 20−50 nm peptide domains dispersed in a continuous PEO phase on which was superimposed a 100−150 nm superstructure due to the polymers' polydispersity and multiblock character. Instron measurements suggested that mechanical properties could be modulated by manipulating the building blocks.

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