Understanding associative polymer self-assembly with shrinking gate fluorescence correlation spectroscopy.

The self-assembly of polymers is integral to their role in liquid formulations. In this study, we combine a dye whose lifetime is sensitive to the nanoviscosity of its local environment with shrinking gate fluorescence correlation spectroscopy (sgFCS) to study the self-assembly of a model telechelic polymer, hydrophobically modified ethoxylated urethane (HEUR). Fluorescence lifetime measurements show a monotonic increase in average lifetime with increasing HEUR concentration driven by a small fraction of dye (<1%) with long lifetimes strongly bound to HEUR. Despite this small fraction, sgFCS isolates the diffusional dynamics of the bound fraction with no a priori assumptions as to the distribution of lifetimes. Sensitivity is greatly enhanced compared to standard FCS, revealing micellar aggregates forming between 0.2 and 1 wt% followed by formation of a percolated network. This sgFCS approach, which we apply for the first time to polymers in this work, is readily extendable to any dye that changes lifetime on binding.

One Step Closer to Coatings Applications Utilizing Self-Stratification: Effect of Rheology Modifiers.

Self-stratification of model blends of colloidal spheres has recently been demonstrated as a method to form multifunctional coatings in a single pass. However, practical coating formulations are complex fluids with upward of 15 components. Here, we investigate the influence of three different rheology modifiers (RMs) on the stratification of a 10 wt % 7:3 w:w blend of 270 and 96 nm anionic latex particles that do not stratify without RM. However, addition of a high molar mass polysaccharide thickener, xanthan gum, raises the viscosity and corresponding Péclet number enough to achieve small-on-top stratification as demonstrated by atomic force microscopy (AFM) measurements. Importantly, this was possible due to minimal particle-rheology modifier interactions, as demonstrated by the bulk rheology. In contrast, Carbopol 940, a microgel-based RM, was unable to achieve small-on-top stratification despite a comparable increase in viscosity. Instead, pH-dependent interactions with latex particles lead to either laterally segregated structures at pH 3 or a surface enrichment of large particles at pH 8. Strong RM-particle interactions are also observed when the triblock associative RM HEUR10kC12 is used. Here, small-on-top, large-enhanced, and randomly mixed structures were observed at respectively 0.01, 0.1, and 1 wt % HEUR10kC12. Combining rheology, dynamic light scattering, and AFM results allows the mechanisms behind the nonmonotonic stratification in the presence of associative RMs to be elucidated. Our results highlight that stratification can be predicted and controlled for RMs with weak particle interactions, while a strong RM-particle interaction may afford a wider range of stratified structures. This takes a step toward successfully harnessing stratification in coatings formulations.

Diels-Alder-Chitosan based dissociative covalent adaptable networks.

For the first time, Diels-Alder and retro Diels-Alder reactions were evidenced by 1H NMR spectroscopy and DSC on chitosan based systems. At first, preliminary studies led to structural identification and better understanding of the Diels-Alder reaction. Then, chitosan of 30,000 g/mol and 150,000 g/mol were modified by furfuryl glycidyl ether with 20% substitution degree. The resulting products were cross-linked with bis and trismaleimide crosslinkers to produce films possessing interesting mechanical properties. Unprecedented for chitosan-based films, DMA measurement highlighted retro Diels-Alder between 110 and 130 °C. Films showed interesting hydrophobicity and fat absorption. They also exhibited resistance in acidic media whereas crude chitosan films were dissolved.

Isocyanate-Free Fully Biobased Star Polyester-Urethanes: Synthesis and Thermal Properties.

A green strategy for the synthesis of nonisocyanate polyester-urethanes (NIPHEUs) was developed. These NIPHEUs were synthesized by step growth polymerization combining sugar-derived dimethyl-2,5-furan dicarboxylate (DMFD) with polyhydroxylurethanes (PHUs) adducts bearing four hydroxyl groups. The later hydroxyl urethane tetraols (HU-tetraols) building blocks were prepared by aminolysis of glycerol carbonate with two different aliphatic diamines having different chain lengths, 8 and 12 carbons. Qualitative and quantitative NMR analyses of the HU-tetraols showed the presence of primary and secondary hydroxyl moieties at different ratios. Hence, in the polycondensation stage, the stoichiometry of the diester was varied from 1 to 6 equiv in order to tailor the structural features of the prepared NIPHEUs. The success of the chain extension through polycondensation was confirmed by FTIR and NMR analyses. Thermal analyses of these new polymers demonstrated satisfactory thermal stability, with onset degradation temperatures ranging from 170 to 220 °C where the main first degradation stage occurs. Their melting temperatures ranged between 93 and 110 °C and seem to be driven by the thermal behavior of HU-tetraol monomers. Surprisingly, preliminary results from thermal analyses revealed the occurrence of a striking thermal change in the NIPHEUs upon repetitive heating cycles. This behavior may be related to a thermal-induced bond exchange probably driven by transcarbamoylation reaction. Such interesting vitrimer-like behavior for this new type of NIPHEUs would be unique and should be confirmed by a deeper study before leading to a new range of functional green materials.