Aqueous Assembly and Hydrogel Rheology of Sustainable Glyoxylate-Based Copolymers

Abstract

The self-assembly of poly(ethyl glyoxylate)−poly(ethylene oxide)−poly(ethyl glyoxylate) (PEtG−PEO−PEtG) triblock copolymers in aqueous environments was systematically studied by using rheology and small-angle neutron scattering (SANS). These systems form associative micellar gels in water, with the PEtG end-blocks forming micelle cores and the PEO midblocks forming loops in the micelle coronas and intermicellar bridges. As PEtG block length is increased, rheology shows slower relaxation behavior, consistent with a longer lifetime of intermicellar bridges and associations. The length of the self-immolative PEtG block can be used to tailor the mechanical properties, size of nanoscale hydrophobic domains, and larger-scale assembly behavior of the block copolymer gels. These results can guide the design of self-immolative block copolymers with desirable rheological properties and nanoscale structures for a variety of applications.

Effect of Chain Architecture on the Structure, Dynamics, and Rheology of Thermoresponsive Poloxamer Hydrogels and Associated Blends

“…[12][13][14]16,21,25,26 Depending on the composition of the polymer blocks and solvent, such bridged networks display interesting rheological behaviors, such as timedependent recovery following shear, relatively high dynamic moduli, and long relaxation times. 11,16,24 At high concentrations, the micelles in certain systems can order into periodic packings�most commonly body-centered cubic (BCC)�and this packing dominates the rheological properties within this region. 12,25,27 Previously, AB diblocks have been blended with BAB triblocks to alter the fraction of bridging A blocks and the resulting rheological properties.…”

“…Block polymers composed of two or more chemically distinct blocks can self-assemble into micelles when placed in a selective solvent for one of the blocks. − Characteristics such as the composition, block architecture (AB vs ABA vs BAB), and solvent selectivity dictate the micelle size and shape, as well as the critical micellization temperature (CMT) and concentration (CMC). − These effects are widely studied as micelles have broad industrial relevance, particularly as drug delivery vehicles and viscosity modifiers. , Symmetric triblock polymers composed of solvophobic end blocks and a solvophillic midblock (BAB), often referred to as telechelic or associative triblocks, are of particular rheological interest. − Due to the block arrangement, chains must form either loops (flower-like micelles) or bridges to neighboring micelles for both end blocks to be contained within a micelle core. As micelle bridges can serve as dynamic physical crosslinks which alter rheological properties such as modulus and relaxation time, the fraction of bridges versus loops formed within various BAB/solvent systems has been the focus of numerous computational and experimental works. − ,− …”

“…To minimize corona stretching while allowing for the formation of intermicelle bridges, dilute BAB formulations often phase-separate into a polymer-rich region composed of clusters of bridged micelles and a polymer-poor region. , In concentrated solutions above a critical volume fraction, the bridged clusters become system-spanning and a percolated bridged network phase is formed. − ,,,, Depending on the composition of the polymer blocks and solvent, such bridged networks display interesting rheological behaviors, such as time-dependent recovery following shear, relatively high dynamic moduli, and long relaxation times. ,, At high concentrations, the micelles in certain systems can order into periodic packingsmost commonly body-centered cubic (BCC)and this packing dominates the rheological properties within this region. ,, …”