Two component gels of immiscible blends of biscarbamates (polyurethane model compounds) and poly(ε-caprolactone)

Abstract

We describe the gelation of two-component immiscible blends consisting of a set of low molecular weight organogelators and a polymer. We studied the blends of poly(3-caprolactone) (PCL) and biscarbamates (model compounds for polyurethanes) with two hydrogen bonding motifs separated by a (CH 2 ) 6 spacer and symmetrically attached alkyl side chains. Neither PCL nor the biscarbamates form gels with chloroform in their neat forms, although the latter form gels with several other solvents. It is known that PCL does not form a gel by itself in any solvent. Being part of a copolymer or an inclusion complex is necessary for a PCL based gel. In the current work, mixtures of biscarbamates and PCL in chloroform led to phase separation and gelation upon cooling the solution. This gelation behavior depends on the alkyl side chain length of the biscarbamates. Those with alky side chain length below C 11 remained soluble and beyond C 13 precipitated within the concentration range studied here. Morphological studies showed immiscibility between the biscarbamate and PCL, similar to the case of polyurethanes with PCL as the soft segment. When biscarbamates are minor components in the solvent cast blend films, they form aggregate crystals in the PCL matrix. Upon melting and recrystallizing, PCL forms droplets in the matrix of biscarbamates, although it is the major component. X-ray diffraction studies of the xerogels confirmed the immiscibility of the PCL and biscarbamates and ATR-FTIR spectra showed no change in the hydrogen bonding of these self-assembling biscarbamate molecules. Microscopic studies revealed fibrous morphology of the composite gels, which consist of biscarbamate fibers dispersed in the matrix of PCL fibers. The biscarbamate fibers impregnated in the polymer matrix show the same eavestrough and hollow tube morphology as seen in our previous work (Khanna et al., Langmuir, 2009, 25, 13183).

Small molecule self‐assembly in polymer matrices

“…Another case of a small molecule organic gelator leading the polymer gelation was reported by Khan et al These authors have studied the crystallization and gelation characteristics of biscarbamates, with various alkyl side chain lengths . These are model compounds for polyurethanes (PU).…”

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

“…They would self‐sort irrespective of the way they were crystallized. In an earlier study, we found that biscarbamates did not form gels with chloroform. Poly(ϵ‐caprolactone) (PCL) by itself is not known to gel any solvent.…”

“…Our studies on melt‐crystallization of these molecules showed that the rates of crystallization and spherulite growth to be maximum with a C 8 or C 9 side chain. On the basis of simple energy calculations, we showed that a balance between the hydrogen bond and van der Waals interaction energies occurs with side chain lengths of C 8 or C 9 .…”

“…Studies on two‐component organo‐gels have been reported by a number of authors including our group . It should be noted that the components were of different types of molecules in these cases.…”

“…Although studies on two‐component organo‐ and polymer gels are known, in this paper we discussed the features of binary organo‐gels which consist of a homologous pair of biscarbamate molecules, which have identical hydrogen bonding groups separated by a C 6 spacer, but differ only in the number of CH 2 groups in the side chain. Our previous studies found that biscarbamates with side chains shorter than C 6 did not form a gel, but precipitated from the solution.…”