Polymerisation, in situ

Fig. 6. Flow diagram of microencapsulation process that utilises acid-cataly2ed in situ polymerisation of melamine or urea with formaldehyde to form a...

Cochet M, Maser WK, Benitor A, Callejas A, Martinez MT, Benoit JM, Schreiber J, Chauvet O (2001). Synthesis of a new polyaniline/nanotube composite in-situ" polymerisation and charge transfer through site-selective interaction. Chem. Commun. 16 1450-1451. 

This section is devoted to the strategies for the syntheses of monolithic MIP and to the influence of the pre-polymerisation mixture and preparation protocol on the monolith properties. Monolithic MIPs can be prepared by in situ polymerisation of functional monomers and crosslinkers in the presence of the template. This most... 

The first reported technique for the preparation of monolithic MIPs used an in situ polymerisation protocol, which is a simple and easy procedure to perform. 

The in situ polymerisation consists of filling a capillary or a column with the prepolymerisation mixture containing the template, the functional monomer, the crosslinker, the initiator and the porogenic solvent (Fig. 11). Then the column is heated or submitted to UV radiation for polymerisation. In the in situ thermally initiated polymerisation process, the tube with the pre-polymerisation mixture is submerged in a controlled-temperature water bath, whereas for in situ photoinitiated polymerisation, a UV-transparent capillary or column is needed. The resulting continuous rod of polymer is washed with an appropriate solvent to remove the template and the excess of monomer. 

Compared to the in situ polymerisation of a monolith, the grafting approach does not need re-optimisation of the protocol in order to obtain an appropriate porosity and flow properties for the monolith when monomer or template is changed. Moreover, the properties of the core materials are generally preserved and the imprint generated on the surface of the materials only requires a minimum amount of template and provides well-accessible recognition sites. 

The fabrication of imprinted monolithic solid-phase microextraction fibres has been developed for the selective extraction and preconcentration of diacetylmorphine and its structural analogues, triazines, bisphenol A, anaesthetics, and antibiotics followed by GC or HPLC analysis [156,163,179,196,197]. In addition, the on-line coupling of the imprinted monolith as a preconcentration column with a conventional analytical column has been proposed for the enrichment and cleanup of environmental and food samples [163]. However, at present, the capacity of the imprinted fibres and thus the degree of recovery of analytes are very variable and obviously need some improvement. For example, the recoveries of triazines after SPME with an imprinted monolith prepared by in situ polymerisation of MAA as... 

Self-supported MIP membranes can be seen as an alternative format to the traditional MIP particles for applications in separation and sensor technology, avoiding the limitations of mass transfer across conventional MIP materials. Two main approaches have been used for the preparation of membranes composed of an MIP in situ polymerisation and polymer solution phase inversion. 

It is also possible to prepare chiral PANI by in situ polymerisation with CSA, and in this case the reaction can afford chiral nanotubes [63]. The optically active materials contain nanotubes with 80 to 200 nm outer diameter and an internal diameter of between 20 and 40 nm, as revealed through microscopy images. A self-assembly process was proposed in which anilinium cations and CSA anions form micelles which act as templates for the growing polymer chains. Nanotubes are also formed when (R)- or (S)-2-pyrrolidone-... 

Polymerisation Coacervation Micellar formation Interfacial Coacervation chilling Interfacial Polymerisation Coacervation In situ polymerisation Liposomes... 

Solution blending was found to produce a mixed immiscible intercalated nanocomposite with the clay causing a change in the degradation path (94). In situ polymerisation of polymer layered silicate nanocomposites has been investigated (36). 

Three main ways exist for making homogeneous blends of polymers mechanical mixing, mixing in a common solvent, and in situ polymerisation. Mixing in a common solvent has been the commonest method in academic studies though this method, including the recovery of the blend by solvent evaporation or precipitation of the polymers in a non-solvent, would have very limited industrial application. 

Other examples of solvent effects in casting blends include epoxy resin/copoly-ester/tetrachloroethane polyethersulphone/poly(ethylene oxide)/cyclohexanone and mixtures of PVC with various polyacrylates in solvents such as THF One particular pair of polymers PVC/poly(ethyl acrylate) appear to be miscible but no suitable solvent has been found as yet. Homogeneous blends can only be prepared by in situ polymerisation though it is possible that miscibility is enhanced by small amounts of graft copolymer which is inevitably formed by this technique. 

In situ polymerisation does not however guarantee homogeneous blends as two phase regions can exist within the polymer/polymer/monomer three component phase diagram. In the case of vinyl chloride polymerisation with solution chlorinated polyethylene, the vinyl chloride has limited solubility in both poly(vinyl chloride) and chlorinated polyethylene. The phase diagram has the form shown in Fig. 3 The limit of swelling of vinyl chloride in the chlorinated polyethylene is A and the highest concentration of PVC prepared by a one-shot polymerisation is B. 

Homogeneous blends can also be prepared by in situ polymerisation of butyl acrylate in PVC but a much larger two phase region exists and many steps are necessary for some compositions... 

In situ polymerisation may have wide applicability in preparing blends of polymers such as engineering plastics which have few solvrats. Because the solvents interact strongly with the polymers they are more likely to induce phase separation. This has been shown to be true for PVC which also has few solvents. 

Table 1. ThemisdlHlity of polymethacrylates with PVC when prepared 1 in situ polymerisation and by solvent casting, (+) misdble, (—) immisdble...

In polyaddition, cross-linking occurs by means of chain extension. The majority of ambient-cured construction products are based on this type of reaction, where in situ polymerisation occurs after the epoxy resin base and the curing agent are mixed. The curing agent causes the epoxide or hydroxyl groups to react (Ellis, 1994). 

In-situ Polymerisation with Radiation Curing Monomers and Resins... 

Dehydration techniques and methods involving in situ polymerisation are not considered suitable for anything other than small wooden artefacts. Freeze drying offers the conservator a safe method of drying small PEG-treated objects while air drying is more suited to the drying of larger structures, such as intact ships if the condition allows it. 

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