Microporous polymers prepared from non-porous hyper-cross-linked networks by removing covalently attached template molecules
Abstract
A new method for the formation of permanent micropores in hyper-cross-linked networks is reported. This method is based on a template approach, using small molecules (4-methylaniline and 4-methylbenzaldehyde) as templates.
These molecules are covalently attached via azomethine links to parent non-porous hyper-cross-linked polyacetylene networks prepared by chain-growth homo and copolymerization of ethynylated monomers. Highly efficient and well-defined postpolymerization hydrolysis of the networks leads to (i) cleavage of azomethine links and (ii) removal of the template molecules from the networks.
Although up to 40 wt % of the mass of the networks are removed via hydrolysis, the hyper-cross-linked scaffold of the networks is not collapsed and micropores are formed in the networks. In this way, the parent non-porous networks are transformed into networks with permanent micropores (diameter approx. 1 nm) and a specific surface area up to 623 m(2)/g(-1).
Simultaneously with the formation of micropores, functional groups (NH2, CHO) are introduced into the networks. The prepared microporous networks adsorb the model adsorptives (up to 1.73 mmol CO(2)/g and up to 6.53 mmol I(2)/g.).
The detemplating and micropores formation is confirmed by solid state NMR spectra and N(2) adsorption/desorption isotherms. The reported method of micropores formation could find a wider application for the preparation of microporous polymers with a well-defined texture and surface functionalization.
Not only azomethine links but also many other groups with cleavable bonds could potentially be used for templating with covalently attached small molecules.