Co‐Assembly and Self‐Sorting Effects in Gels of Blends of Polyurethane Model Compounds

Abstract

We present studies on two‐component organo‐gels of small molecule analogues of polyurethanes. Whereas the two‐component organo‐ or polymer gels reported in the literature so far involve two types of polymers or polymer/ small molecules, this paper deals with blends of homologous pairs of biscarbamates, which differ only in the number of CH2 groups in the side chain. The mixture of any two biscarbamates self‐sort when crystallized from the melt or solution. We also showed before that these molecules, with a side chain shorter than (CH2)6 do not form gels by themselves as a single component. However, in this work, it was found that a blend of biscarbamates with side chains (CH2)3 and (CH2)15 (denoted as C3/ C15 henceforth) formed a homogeneous gel with benzonitrile as the solvent. A small ratio of the C15 component is sufficient to depress the precipitation of C3 and form a gel, leading to co‐assembly in these gels. Such an effect was also seen in the gelation of blends of C8 and C9, which differ by just one CH2 group in the side chains (Δx=1). With the gels of C7/C9 blends (Δx=2), an ageing effect was seen in that the as‐prepared gel did not show any self‐sorting, but the aged gel did. Self‐sorting was observed in the two‐component gels of biscarbamates with Δx > 2. We believe that this is the first case of two‐component organo‐gels of homologous pairs in which co‐assembly and self‐sorting phenomena were observed.

Design Rules for Binary Bisamide Gelators: toward Gels with Tailor-Made Structures and Properties

“…Primary structures in multicomponent gels can form either via the co-assembly of gelators with alternating order or random organizations or via their self-sorting into discrete structures. − It is also likely that the final gel structure is the mixture of all these assembly modes . Another advantage of using multicomponent gelator systems is the reinforcement in the mechanical properties of the final gel formulation by inducing co-assembly of the gelator molecules or via encouraging the self-sorting of gelator molecules in pH-triggered hydrogels where each gelator component responds to a certain pH …”