Polymer Neutralisation

Since the overwhelming majority of commercially available water reducible polymers are carboxyl functional, the discussion in this chapter will consider the use of arrtines. However, the calcirlations used to determine the quantities of neutralising agent reqitired by a given polymer can be used with modification for acid neutraUsed systems. 

The choice of arrtine used to neutralise a given polymer system depends on many factors. Amongst those are volatility, solvent strength , and amine efficiency. 

The amine efficiency is the amount of amine required to neutralise the polymer system to a specific pH. Amine efficiency may vary from 1 for DMEA to 0.7 for morpholine. The amount of amine required to neutralise the acid functionality of a given polymer may be calculated using the following equation  

Note that for amine functional systems, the above equation could be used replacing the function AV/1000 x Eq. Wt. KOH by the number of equivalents of amine present per gramme of base polymer. 

The whole phenomenon becomes more complex when one considers that the viscosity solids relationship is effected by the temperature at which the polymer is neutralised and thinned. The optimum temperature for neutralisation is approximately 70°C. 

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A typical penicillin broth contains 20-35 mg/1 of antibiotic. Filtration is used to remove mycelial biomass from fermentation broth. The filtration may be subjected to filter aided polymers. Neutralisation of penicillin at pH 2-3 is required. Amyl acetate or butyl acetate is used as an organic solvent to remove most of the product from the fermentation broth. Finally, penicillin is removed as sodium penicillin and precipitated by a butanol-water mixture. 

Sodium polyacrylate (NaPAA) [9003-04-7]. Commercial polyacrylamide was neutralised with an aqueous solution of NaOH and the polymer ppted with acetone. The ppte was redissolved in a small amount of water and freeze-dried. The polymer was repeatedly washed with EtOH and water to remove traces of low... 

At the end of the reaction the polymer-solvent layer is separated from the aqueous acid layer and neutralised. A portion of the solvent is then distilled off until the correct solids content is reached. 

The epoxy-acrylic resin referred to above is a graft copolymer prepared by the polymerisation of acrylic monomers in the presence of the epoxy resin in such a way that grafting of the acrylic onto the epoxy takes place. Water dispersibility is achieved by neutralising carboxyl groups in the acrylic polymer chain with ammonia or amine. Amino or phenolic resins are used as crosslinkers. Alternatively, solvent-borne epoxy-amino or epoxy-phenolic lacquers can be used. 

Table 6.5 Change in titre o/O.OlM NaOH needed to neutralise 50 mg of polyester with relative molar mass of polymer (after H. Batzer and E. Lohse, Introduction to Macromolecular Chemistry , 2nd Edn., John Wiley Sons, Chichester, 1979)...

The pyrolysis produets obtained from a variety of mixed plasties eontaining PVC are investigated. While hydroehlorie aeid is the major chlorinated product produced by PVC pyrolysis, other chlorinated hydroearbons are produced. However, the composition and yield of these compounds are very much dependent upon the other polymers present in the plastic mixture. In the ease of a polymeric waste stream containing inorganic fillers, sueh as ealcium carbonate, the HCl produced by the PVC ean be neutralised in situ, leading to the produetion of inorganic chlorides, alleviating many of the concerns associated with HCl formation. 9 refs. 

Nicholson, J. W., Wasson, E. A. Wilson, A. D. (1988). Thermal behaviour of films of partially neutralised poly(acrylic acid). 3. Effect of calcium and magnesium ions. British Polymer Journal, 20, 97-101. 

Obviously, use of such databases often fails in case of interaction between additives. As an example we mention additive/antistat interaction in PP, as observed by Dieckmann et al. [166], In this case analysis and performance data demonstrate chemical interaction between glycerol esters and acid neutralisers. This phenomenon is pronounced when the additive is a strong base, like synthetic hydrotalcite, or a metal carboxylate. Similar problems may arise after ageing of a polymer. A common request in a technical support analytical laboratory is to analyse the additives in a sample that has prematurely failed in an exposure test, when at best an unexposed control sample is available. Under some circumstances, heat or light exposure may have transformed the additive into other products. Reaction product identification then usually requires a general library of their spectroscopic or mass spectrometric profiles. For example, Bell et al. [167] have focused attention on the degradation of light stabilisers and antioxidants... 

The termination of Ziegler-Natta synthesis is obtained by neutralisation of the catalytic site using, for instance, alcohol. The reaction can also simply be stopped (with no clear termination) by embedding of the catalyst into the polymer. Industrially, the control of final molecular mass is often accomplished by a hydrogen transfer reaction (see Figure 28). 

The linkage between two chains can also be ionic. Thus the copolymer between ethylene and methacrylic acid (MA) (up to 15% MA), made by free radical polymerisation, yields a polymer with pendant carboxyl groups. Neutralisation with zinc ions gives a crosslinked, thermo-reversible polymer (Surlyn ). The resulting polymer (ionomer) has limited properties, although it is the favoured material for the outer covering of golf balls. 

UV stabilisers protect polymers by restricting UV penetration to the surface and therefore confine the damage to surface layers. Protection is important because the energy possessed by UV radiation is sufficient to break chemical bonds. The initial breakage can either be by a radical (Norrish type I) or non-radical (Norrish type II) pathway. The effects are similar to degradation of the polymer by oxidation routes the radical intermediates can be neutralised by anti-oxidants. 

Consider a polyester prepared the polycondensation of a hydroxy acid. From the structure of the polymer it is known that this polyester has a carboxyl group for each molecule and when titrated one mole of sodium hydroxide is used per mole of polyester. To calculate the Molecular weight of the polyester, we have only to calculate how much polyester (in grams) gets neutralised by... 

For the first method exact equivalence of reactants are used to obtain high Molecular weight polymer. In the first step an aqueous solution of adipic acid is neutralised with hexamethylene diamine to form nylon salt. 

This type of mechanism is likely to be partly operative in systems containing inorganic electrolytes as, for example, in the case of aluminium species. Some polyelectrolytes may also induce flocculation by charge neutralisation but the adsorbed polymer may also be able to bridge from one particle surface to another ( polymer bridging ). 

The second form of neutralisation involves the fragmentation of the anion, or the detachment of an ionic component from it, as shown in the reaction (N2) if that fragment is a halide ion the resulting polymer-halide can be regarded as an ester of the hydro-halidic acid. 

Tritium in the C-O-T groups, resulting from neutralisation of the carbenium ions, is removed by exchange during work-up of the polymers. 

Hydrolysis and analysis The purified and dried polymer (0.1 g) and 1 ml of aqueous HC1 (0.1 mol l 1), together with a measured amount of acetone (as internal GLC standard), was heated for 1 h at 100 °C in a sealed tube to hydrolyse the polymer. The solution was then neutralised and the ethanol content was determined by GLC by means of a calibration graph. As polymers of 4 and 5 are strongly hydrophobic and are thus hydrolysed only very slowly in water, they were hydrolysed in aqueous dioxane. 

In the standard procedure the neutralised polymer is purified and hydrolysed and the hydrolysate is examined for ethanol. The absence of ethanol indicates that no tert.-oxonium ions containing a polymeric moiety and no polymeric oxycarbenium ions could have been present in the reaction mixture. 

What we require now in order to consolidate our understanding is more work with a variety of monomers and solvents, with the simplest possible initiator systems, aimed at obtaining the maximum amount of information on the polymerisations (rates, equilibria, conductivities, constituents of the reaction mixtures before and after neutralisation) and on the polymers (existence, nature and concentration of end-groups, DP distributions). There are unfortunately still too many who think they can base a valid theory on the determination of only one or two features of a polymerisation system. 

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