Polymerisation technique variations

Reaction injection moulding techniques, developed primarily for polyurethanes (see Chapter 27), have also been adapted for nylon 6 in what must be considered as a variation of the polymerisation casting technique. 

A preliminary study of polymerisations co-catalysed by trifluoroacetic acid, with an improved technique [77], showed that at [C4H8] = 0.94 mole/l, [TiCl4] = 5.68 x 10"3 mole/l, and [CF3C02H] = 0.81 x 10"3 and 1.22 x 10 3 mole/l, the variation of DP with temperature gave EDP = -3.5 1.5 kcal/mole. Unfortunately, the large difference between this and the EDP obtained with trichloroacetic acid as co-catalyst cannot be interpreted in detail without a knowledge of the temperature dependence of the individual chainbreaking coefficients. 

The test (b) we carried out typically as follows but we have also used many variations of this procedure [18]. We used an assembly of connected reaction tubes attached to the vacuum line. In one tube we polymerised (I) by perchloric acid in methylene dichloride. Reaction was stopped by adding sodium phenate, and any phenol formed from secondary oxonium ions was neutralised with sodium hydride. The volatile compounds were distilled into a second tube where the same experiment was repeated. This technique is based on that of Saegusa and Matsumoto [19] phenol and phenyl ethers can be estimated separately by their UV spectra. 

The third method is to grow the polymer into its desired shape and form. An insulating polymer impregnated with a catalyst system is fabricated into its desired form. This is then exposed to the monomer, usually a gas or a vapour. The monomer then polymerises on the surface of the insulating plaslic producing a thin film or a fibre. This is then doped in the usual manner. A variation of this technique is electrochemical polymerisation with the conducting polymer deposited on an electrode either at the polymerisation stage or before the electrochemical polymerisation. 

The polymeric adsorbents are usually prepared by variations of two-phase suspension processes. These refer to systems where microdroplets of monomers and solvent are converted into solid beads upon polymerisation. In the case where the monomers are not water soluble, as in the case of styrene-based polymers and many methacrylate-based polymers, the monomers, a solvent and a droplet stabiliser are suspended as droplets by stirring in water and then polymerised (o/w suspension polymerisation). The particle size and dispersity can be influenced by the stirring speed and the type of stabiliser. So far, only a few examples of the preparation of imprinted polymers in bead format have been described [4-8] and these are thoroughly reviewed in Chapter 12. In non-covalent imprinting, the main limitation to the use of these techniques is that the imprinting method often requires the use of polar partly water soluble monomers or templates in combination with less polar water insoluble components. Use of the o/w suspension method... 

Not all kinds of low molecular weight monomers can be used for these polymerisations, since for example an unsaturated group RHC = CH. must be present. However, this technique will allow ionic groups (both acidic and basic) and neutral groups to be introduced. Table III.2 gives some examples of monomers which can be used. Very specific membranes can be developed by this technique because of the large number of possible variations. 

In essence, the technique involves changing the composition of the monomer phase in a sequential manner as the polymerisation progresses. This leads to a variation in polymer composition firom the particle core to the particle shell. 

---