Lactone-layered double hydroxide networks: Towards self-assembled bioscaffolds

This paper describes the conversion of a layered anionic initiator (carbonate-intercalated layered double hydroxide, (LDH-carbonate)) into a self-assembled resin-embedded network during the in-situ polymerization of one or more lactone monomers using the LDH-carbonate as the sole initiator. Uniquely in this paper, no long-chain acid intercalant is present in the LDH-carbonate to act as an additional initiator species, and this is the first known report of a copolymerisation of these lactones using LDH as an initiator. The formation of a network is in marked contrast to the behavior of most in-situ polymerisations using layered species, where the latter retains its layered structure at the molecular level and is either intercalated or exfoliated to form a nanocomposite. The molecular disintegration of the LDH sheets is unusual. Nine new insoluble materials (scaffolds) are isolated from various l,d-lactide & ε-caprolactone (LC) and l,d-lactide & δ-valerolactone (LV) copolymer hybrids. The latter hybrids are polymerised using the LDH-carbonate as initiator at 150 °C for 24 h without using conventional metal catalysts. Each insoluble phase is isolated from each primary hybrid product using dichloromethane (DCM) to selectively dissolve the soluble polymer phase. X-ray diffraction (XRD) is used to verify the morphology of the insoluble phases. This demonstrates that the molecular sheets of the LDH-carbonate are fully dismantled during the polymerization. Porous, network morphology is established for some of the insoluble phase structures using scanning electron microscopy (SEM). This indicates potential suitability of these self-assembled insoluble phase materials as bioscaffolds for artificial cell growth. Nuclear magnetic resonance spectrometry (NMR) was used to determine the ratio of ester to acidic carbonyls in the insoluble phase. Energy Dispersive X-ray spectroscopy (EDX) was also used to determine the ratio of magnesium to aluminium in the insoluble phases.