Post-crosslinking Procedure

Reproduced with permission. Copyright 2007, Royal Society of 

Compared with MCDE, tetrachloromethane is also a good crosslinker with less toxicity. Hradil and Kralova reported a series of crosslinked resins with surface areas up to 1000 m g , which were obtained by post-crosslinking styrene-divinylbenzene eopolymer precursors with tetrachloromethane via a Friedel-Crafts reaction in the presence of aluminium or ferrie ehloride. 

As a result, the hypercrosslinked polymers prepared from this gel-type precursor only contain micropores in the networks. 

Despite a great deal of work on the synthetic methods of MOPs, the controllable pore size and size distribution has rarely been reported. The Tan group investigated the influence of the precursor structure on the porosity in detail. By adjusting the DVB content in DVB-VBC, the pore size of the hypercrosslinked DVB-VBC (HCP-DVB-VBC) can be precisely tailored from the macropore to micropore scale. 

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Other important factors include monomer sequence distribution, distribution of graft and crosslink sites along the chains, the occurrence of branching per se, and the general phenomena of side reactions. In addition, stirring rate, the detailed post-reaction "workup procedure, the temperature history, subsequent processing and fabrication conditions, etc. must be considered since these have major effects on the nature of the product. 

LOI was determined on 10 x 150 mm specimens of 3 mm thickness using the NF EN ISO 4589-1 [34], NF EN ISO 4589-2 [35] and NF EN ISO 4589-3 [36] procedures. Analyses were conducted at ambient temperature, with a 40 ml/sgas flow in the quartz column. The oxygen ratio variation in the gas was 0.2%. Results were obtained on three samples tested in the same conditions. LOI were determined for samples crosslinked at ambient temperature, without post cure, and for samples after post cure. 

C-NMR spectra of the labelled networks were obtained by direct polarisation, liquid-state method with fully CDCl3-swollen samples, and by the solid-state, CP-MAS with solid samples. By both methods, the 1 % crosslinked samples prepared at 70 "C and at 95 °C showed a peak at 137 ppm due to the labelled carbon of unpolymerised vinyl groups. The 137 ppm signal was not seen after further polymerisation of the 1 % crosslinked sample at 135-155 C. Polystyrenes prepared with 10% and 20% of the labelled DVB by the same procedures showed residual vinyl groups before and after the 135-155 °C post-polymerisation. With the 10% and 20% crosslinked samples, only CP-MAS spectra gave peaks of labelled carbon narrow enough to analyse. 

The crosslinkable epoxy thermoplastic modified with 5 wt % grafted rubber concentrate (CET-GRC) was prepared according to published procedure (5). The rubber domains are nominally 0.1 micron in diameter and consist of a core-shell structure with a 0.03 micron diameter polystyrene seed. Blocks of the CET-GRC were cryo-polished at -90°C using a diamond knife to provide a smooth face for SPM imaging. Some of these surfaces were post stained in OSO4 vapors by suspending the polished blocks in sealed containers over an aqueous solution of... 

Fig. 2 The general synthetic procedure to prepare amine-functionalized hydrogels by a post-polymerization crosslinking reaction...

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