DISPERSION COPOLYMERISATION

No.lO, 30th July 1996, p.1977-92 DISPERSION COPOLYMERISATION OF STYRENE AND BUTYL ACRYLATE IN POLAR SOLVENTS... 

Monodisperse copolymer particles from 1.1 to 2.6 micrometers in diameter were obtained by unseeded batch dispersion copolymerisation of styrene and butyl acrylate in an ethanol-water medium. A two-level factorial design using bottle polymerisations was initially carried ont including the following variables stabiliser concentration, initiator concentration, polarity of the dispersion medium, initial monomer concentration, and temperature. Once the region of experimental conditions in which monodisperse latexes can be prepared was identified, further effort was devoted to analyse the effect of other variables. 51 refs. 

For general aspects on sonochemistry the reader is referred to references [174,180], and for cavitation to references [175,186]. Cordemans [187] has briefly reviewed the use of (ultra)sound in the chemical industry. Typical applications include thermally induced polymer cross-linking, dispersion of Ti02 pigments in paints, and stabilisation of emulsions. High power ultrasonic waves allow rapid in situ copolymerisation and compatibilisation of immiscible polymer melt blends. Roberts [170] has reviewed high-intensity ultrasonics, cavitation and relevant parameters (frequency, intensity,... 

A major drawback of synthetic thickeners when used with dyes is their sensitivity to electrolytes. Most soluble dyes behave as highly ionised electrolytes and disperse dyes contain anionic polyelectrolyte dispersing agents unless they have been formulated with nonionic systems specifically for use with acrylic thickeners. Consequently there is a loss of viscosity this can be quite pronounced although it depends on circumstances, particularly on the dye concentration. As already mentioned, this can be alleviated to some extent by copolymerisation with acrylamide during manufacture. Otherwise it is necessary to try to eliminate all electrolytes from the system or to increase the concentration of thickener. Such measures have their limitations in practice, however. Alternative synthetic thickening... 

Polyelectrolytes provide excellent stabilisation of colloidal dispersions when attached to particle surfaces as there is both a steric and electrostatic contribution, i.e. the particles are electrosterically stabilised. In addition the origin of the electrostatic interactions is displaced away from the particle surface and the origin of the van der Waals attraction, reinforcing the stability. Kaolinite stabilised by poly(acrylic acid) is a combination that would be typical of a paper-coating clay system. Acrylic acid or methacrylic acid is often copolymerised into the latex particles used in cement sytems giving particles which swell considerably in water. Figure 3.23 illustrates a viscosity curve for a copoly(styrene-... 

Dieuxieme Collogue Internationale sur les Copolymerisations et les Copolymers en Milieu Disperse, Lyons, 1989. 

The dispersions obtained by copolymerisation of styrene with ACN, with low ACN content (ACN being around 25-30% in the monomer mixture), are more difficult to stabilise. For such low ACN content polymer polyols, or for polymer polyols based exclusively on styrene, more efficient NAD are necessary. These are discussed in the next chapters, i.e., macromers (reactive NAD) and nonreactive NAD. 

The macromers used in the stabilisation of polymer dispersions are in fact polyether polyols with terminal double bonds, able to copolymerise with vinylic monomers (ACN, styrene) and to form graft species during the radical copolymerisation. The resulting graft polyether polyol, formed in situ by the copolymerisation process, is in fact a NAD ... 

MA can be used as comonomer together with the vinylic monomers (ternary copolymerisation ACN - styrene - MA) and the graft species is formed in situ by the reaction of the resulting copolymer ACN - styrene - MA with the polyether polyol, by its terminal hydroxyl groups. Another variant is to use a styrene - MA copolymer as NAD. This copolymer proved to be a very good NAD for high styrene content polymer dispersions in polyethers. Of course the real NAD is made by the reaction of a MA unit with the terminal hydroxyl group of the poly ether [57]. 

A direct method to obtain an efficient macromer useful as NAD for polymer dispersion stabilisation is the PO homopolymerisation or random PO-EO copolymerisation initiated by fumaric acid and catalysed by DMC catalyst [53] ... 

A very simple method to obtain polymeric dispersions in liquid polyethers is to make a mixture between a polyether polyol and a polymeric latex, such as the azeotropic copolymer styrene - ACN (StACN copolymer), obtained by emulsion copolymerisation, having around 20-40% solid content. The water is eliminated step-by-step by vacuum... 

A versatile, simple and inexpensive method has been recently proposed for the synthesis of sequence-controlled multiblock copolymers by one-pot polymerisation at ambient temperature. Aciylic block copolymerisation under UV irradiation 360 nm) was obtained in the absence of conventional photoredox catalysts and dye-sensitizers, by means of low concentrations of CuBra in synergy with MCe-Tren [MCe-Tren Tren = tris(2-aminoethyl)amine]. The potential of the method was demonstrated by alternating four different aciylate monomers in various combinations within the polymer composition. Quantitative conversion and narrow dispersity were achieved. " The procedure is versatile, as demonstrated by polymerisation of a number of (meth)aciylate monomers, including poly(ethylene glycol) methyl ether aciylate (PEGA480), te/t-butyl aciylate, methyl methaciylate, and styrene. Moreover, hydrojyl- and vic-diol-functional initiators are tolerated, forming a,co-heterofunctional poly(aciylates). Notably, temporal control is... 

The polymer investigated here is a polymethylmethacrylate (PMMA) copolymerised with methacrylate esters of a dicyanovinyl-terminated bisazo dye derivative. A nitro-terminated version of the bisazo dye derivative and a typical monoazo dye. Disperse Red 1 (DRl), derivative is also discussed in [47]. These azo dyes are hereafter referred as 3RDCVXY, 3RNO2, and 2RNO2, respectively. The molecular structure of 3RDCVXY is shown in Figure 3.12a. 

Bis(2-chloroethyl)vinylphosphonate, CH CH P(0)(0CH2CH2C1)2 can be used to form emulsion copolymers with vinyl halides, or it may be used on its own and mechanically incorporated into textile fibres. Compound (12.212a) when dispersed in rayon is an effective retardant additive [44], while (12.212b), when copolymerised with a suitable monomer, will act as an intumescent flame retardant. 

Copolymerisation of these macromonomers with norbomene or norbomene acetate has yielded a series of poly(norbomene)-graft-poly-(e-caprolactone) copolymers of well-defined structures. Furthermore, PCL macromonomers were also homopolymerised in high yield into high molecular weight comb chains of narrow molecular weight distribution MJM =1.10). Such copolymers have potential applications as surface modifiers, polymeric surfactants, compatibilisers in polymer blends, and dispersion stabilisers. 

A broad range of monomers with relatively low water solubility have been polymerised by conventional emulsion polymerisation. Acrylics, methacrylics, styrene and vinyl acetate are the most common monomers used in preparing latexes for paints, textile binders, and adhesives. Acrylic, polyester, epoxy and urethane dispersions are used in industrial coatings, where higher strength is required. Butadiene is often copolymerised with styrene in producing synthetic rubber for tyre manufacture. 

Surfmers , i.e. surfactants which also acted as copolymerisable monomers, were synthesised from the hemi-ester of a fatty alcohol and maleic anhydride and were then used in the preparation of self-crosslinking dispersions by seeded semi-continuous emulsion polymerisation of acrylate monomers. Water-borne exterior wood stains were prepared from the dispersions and their properties were studied. The use of surfmers as sole emulsifiers in emulsion polymerisation was considered and data were obtained on the effects of surfmers on film formation, water barrier properties, gloss retention and mechanical properties. Environmental aspects of the use of products involving surfmers were examined. 6 refs. 

Details are given of the preparation of model ethyl acrylate-methacrylic acid copolymer latices by non-seeded semicontinuous emulsion copolymerisation. Polydispersity was examined using dynamic and static light scattering. Correlations between hydrodynamic volume and viscosity properties of the dispersions are discussed. The different character of the particle structure was confirmed by differences in particle disintegration after alkali addition or in the presence of methanol. 19 refs. 

Aminated PS-based latices were prepared by dispersion polymerisation and were characterised. Mixtures of Boc-p-aminostyrene and styrene monomers at various compositions were copolymerised under dispersion conditions in 2-propanol/water 3 1 by volume in the presence of AIBN as free radical initiator at 75C. Copolymer microspheres with uniform size distributions and average diameters between 0.9 and 1.8 micrometres were obtained. Aminated microspheres were obtained by the simple removal of the Boc protective group under acidic conditions, followed by neutralisation, thus leading to p-aminostyrene/styrene copolymers. These chemical treatments, when carried ont nnder mild conditions (room temp, and dilute acid and basic solutions), were efficient without causing any major alteration of the microsphere morphology. X-ray photoelectron spectroscopy analysis of the prepared microspheres showed an increase of amino groups with increase of the Boc-p-aminostyrene in the copolymer feed up to 10 mol %. 26 refs. 

An overview is presented on the merits of polyurethane dispersions in waterborne paint formulations. In addition to the characteristics listed which they impart to coatings, such binders can offer an even wider range of properties by means of blending or copolymerisation, producing binders which are tailor made for specific applications, it is stated. 

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