Acrylate polymerisation

The reaction between acrylonitrile and formaldehyde (as paraformaldehyde or tri-oxane), under strong acid catalysis (usually sulphuric) and most often in presence of catalytic quantities of acetic anyhydride, to produce triacrylohexahydrotriazine, is inclined to violent exotherm after an induction period. The runaway can be uncontrollable on sub-molar scale. It may be due to acrylate polymerisation or to increasing reactivity of the formaldehyde equivalent due to progressive de-oligomerisation. Procedures claimed to prevent the risk have been described in the literature but do not seem reliable. 

A five year old bottle, originally stabilised with phenothiazine, was found to have polymerised explosively in storage. The resultant black goo was not acidic, suggesting something more complicated than an acrylate polymerisation. It is recommended that this monomer be stored under refrigeration. 

ATRP has been used to polymerise styrenic, acrylic and methacrylic monomers. However, conventional ATRP of styrenic and methacrylic monomers is rather sluggish typically many hours are required at high temperatures (> 90 °C) for incomplete conversions (< 90%) even under bulk polymerisation conditions. Acrylates polymerise much faster than methacrylates or styrenics and the rapid, efficient polymerisation of n-alkyl acrylates at room temperature with various... 

Figure 4.16 Photoinitiation system for acrylate polymerisation using an argon ion laser (488 nm).

By measuring the presence of functional groups at finite depths from the crystal surface by real time ATR-FTIR spectroscopy, the conversion during acrylate polymerisations was measured. By varying the film thickness, the reactivity of multiacrylates could be spatially resolved (262). The simultaneous monitoring of vinyl acetate (VA) and erucamide additive concentrations in EVA copolymers was undertaken with NIR spectroscopy using an in-line flow cell attached to an extruder (130). 

Figure 12.4 shows that the a,oo-difunctional silicone acrylate is more reactive than the mono- and trifunctional acrylate. The heat of reaction evolved in each case permits the calculation of the conversion of the acrylate groups by means of the standard heat of acrylate polymerisation. A comparison with the initial acrylate contents determined by titration clearly demonstrates that the acrylate functions of the trifunctional siloxane react incompletely. 

Values are calculated with 77.9 kj/mol for the standard heat of acrylate-polymerisation... 

Although ROMP or ADMET reactions hold a prominent position among polymerisation processes initiated by NHC-Ru complexes, other catalytic paths leading to macromolecular products were also investigated. The activity of compounds 30 and other similar monometallic [(NHQRuCl2(p-cymene)] complexes was tested in the atom transfer radical polymerisation (ATRP) of vinyl monomers by Delaude and Demonceau, along with 32. These complexes led to the controlled polymerisation of methyl methacrylate at 85 °C (Equation (7.8)). Attempts to polymerise n-butyl acrylate and styrene turned out to be more challenging, because of difficulties to control the acrylate polymerisation and of competition with the self-metathesis of styrene. 

The four methods of polymerising acrylic monomers, namely bulk, suspension, solution and emulsion are considered. Chapter I concerns itself with the chemistry of acrylic polymerisation and solvent based acrylics. Chapter II is devoted to waterborne resins, especially emulsion polymerisation, because of its signiricant differences from the other types of polymerisation. 

Thus an overall equation for acrylic polymerisation can be written as... 

The acrylic polymerisation is carried out in the presence of a high free radical concentration to favour the generation of sites for the grafting mechanism. 

Table 2.3 Branching densities for butyl acrylate polymerisation from Ahmed et al. (1998).

---