ABSTRACT
Polyelectrolyte complexes present new opportunities for self-assembled soft matter. Factors determining whether the phase of the complex is solid or liquid remain unclear. Ionic polypeptides enable examination of the effects of stereochemistry on complex formation. Here we demonstrate that chirality determines the state of polyelectrolyte complexes, formed from mixing dilute solutions of oppositely charged polypeptides, via a combination of electrostatic and hydrogen-bonding interactions. Fluid complexes occur when at least one of the polypeptides in the mixture is racemic, which disrupts backbone hydrogen-bonding networks. Pairs of purely chiral polypeptides, of any sense, form compact, fibrillar solids with a ß-sheet structure. Analogous behaviour occurs in micelles formed from polypeptide block copolymers with polyethylene oxide, where assembly into aggregates with either solid or fluid cores, and eventually into ordered phases at high concentrations, is possible. Chirality is an exploitable tool for manipulating material properties in polyelectrolyte complexation.
Subject(s)
Peptides/chemistry , Polymers/chemistry , Hydrogen Bonding , Protein Structure, Secondary , StereoisomerismABSTRACT
Recently, polyesters based on the diol monomer 2,2,4,4-tetramethyl-1,3-cyclobutanediol (TMCBDO) have been shown to exhibit excellent thermal stability, mechanical properties, and optical clarity. In particular, the ability of TMCBDO to replace bisphenol A as a diol monomer in polycarbonates and polyesters has resulted in significant commercial and academic interest in these types of monomers. Herein, we report a versatile synthetic strategy based on the dimerization of ketenes derived from the thermal treatment of Meldrum's acid for the synthesis of structurally diverse cyclobutanediol (CBDO) monomers. This strategy allows a library of CBDO monomers amenable to standard polyester polymerization procedures to be prepared and the structural diversity of these CBDO monomers provides polymers with tunable physical properties, such as glass transition temperature ranging from 120 to 230 °C. The versatility and modularity of this Meldrum's acid-based approach to substituted cyclobutanediols, combined with the ease of synthesis, will be important for the further development of high-performance polyester materials that are not based on bisphenol A.
ABSTRACT
Allyl glycidyl ether, polymerized from potassium alkoxide/naphthalenide initiators under both neat and solution conditions was shown to be a highly-controlled process. In both cases, molar masses (10-100 kg/mol) were determined by the reaction stoichiometry, and low polydispersity indices (1.05-1.33) could be obtained with a full understanding of the dominant side reaction, isomerization of the allyl side chain, being developed. The degree of isomerization of allyl to cis-prop-1-enyl ether groups (0 - 10 % mol.) was not correlated to the molar mass or polydispersity of the polymer but was dictated by the polymerization temperature. This allows the extent of isomerization to be reduced to essentially zero under either melt or solution conditions at polymerization temperatures of less than 40 °C.
ABSTRACT
A facile, ketene-based strategy for the synthesis of polyesters from stable Meldrum's acid monomers has been developed which overcomes many issues associated with traditional step-growth procedures. A significant increase in polymerization efficiency is observed with only 10 min reaction time at 220 °C being needed to obtain high molecular weight polymers.
