Polymers Acrylic

For the purposes of this chapter, acrylic polymers are defined as polymers based on acrylic acid and its homologues and their derivatives. The principal commercial polymers in this class are based on acrylic acid itself (I) and methacrylic acid (II) esters of acrylic acid (III) and of methacrylic acid (IV) acrylonitrile (V) acrylamide (VI) and copolymers of these compounds. Copolymers of methacrylic acid and ethylene are described in Chapter 2. The important styrene-acrylonitrile and acrylonitrile-butadiene-styrene copolymers are discussed in Chapter 3 whilst acrylonitrile-butadiene copolymers are dealt with in Chapter 18. 

The standard route for the preparation of acrylic acid is from ethylene oxide (Section 8.4.1.1) as follows  

The addition of hydrogen cyanide to ethylene oxide takes place at 55—60°C in the presence of a basic catalyst such as diethylamine. The reaction is exothermic and is carried out in solution to facilitate control the solvent is conveniently 

Several alternative routes to acrylic acid have now been developed and are becoming of increasing importance. One such method involves the reaction of acetylene, carbon monoxide and water  

In one process, the reaction is conducted in solution in tetrahydrofuran at about 200°C and 60—200 atmospheres. Nickel bromide is used as catalyst. The solution of acrylic acid in tetrahydrofuran, after separation of the unconverted acetylene and carbon monoxide in a degassing column, passes to a distillation tower where tetrahydrofuran is taken overhead and acrylic acid is the bottom product. The reaction between acetylene, carbon monoxide and water may also be carried out by using nickel carbonyl as the source of carbon monoxide. In this case, milder reaction conditions are possible (cf.. Section 6.2.3). 

There are three routes to acrylic acid which have commercial significance they are based on propylene, acetylene and ethylene respectively. At the present time, most acrylic acid is produced via the propylene route. 

A mixture of propylene, air and steam is fed into a reactor containing a catalyst at about 320°C to give acrolein. This intermediate is not isolated but is passed directly to a second reactor, also containing a catalyst, at about 280°C. The effluent is cooled by contact with cold aqueous acrylic acid. Acrylic acid is extracted from the solution with a solvent and then separated by distillation. Because of the ready availability of low cost propylene, this route has become the preferred route for the production of acrylic acid. 

The production of ethylene oxide is described in section 9.4.1. The addition of hydrogen cyanide to ethylene oxide takes place at 55-60°C in the presence of a basic catalyst such as diethylamine. The reaction is exothermic and is carried out in solution to facilitate control the solvent is conveniently ethylene cyanohydrin. The reaction mixture is neutralized and ethylene cyanohydrin is separated by distillation. The second stage of the synthesis involves the dehydration and hydrolysis of ethylene cyanohydrin these reactions are carried out in one step by heating the cyanohydrin with aqueous sulphuric acid at about 175°C. (It is possible, of course, that the 

Since that time, many studies by NMR and other techniques on the microstructure of acrylic and methacrylic polymers formed by radical polymerization have proved their predominant head-to-tail structure. 

There has been a slight increase in activity in this area compared with that in the previous two year period. For the polymeric esters of acrylic, methacrylic acids, and related polymers the simplest reaction, apart from thermal depolymerization, is hydrolysis, and one or two papers on this subject have appeared. One of these concerns a comparison of the kinetics of hydrolysis of a number of methacrylate esters and a further two deal with the formation of copolymers containing carboxylic acid functions. Methyl trifluoroacrylate forms alternating copolymers with cE-olefins (ethylene, propylene, isobutylene) and these are readily hydrolysed in boiling aqueous methanolic sodium hydroxide to yield hydrophilic fluoropolymers. Hydrolysis is reported to be nearly quantitative with no chain scission. An alternating copolymer is also formed by radical polymerization of maleic anhydride with A-vinyl succinimide. On hydrolysis this copolymer is 

Control of triboelectric charging properties of polymers by chemical modification is the subject of a paper by Gibson, Bailey, and co-workers. The base polymer was a copolymer of styrene and butyl methacrylate. The latter comonomer units were subjected to aminolysis (ca. 30% conversion) with the 6-aminohexane derivatives RCCHjjjNHj, R = NHj, OH, H, and the resulting amino- and hydroxy-functional polymers were subjected to further reactions including acylation and coupling with dyes. 

Crosslinked functional polymethacrylates have also been used as reactive resins, though to a lesser extent than crosslinked polystyrenes. The epoxide ring on glycidyl methacrylate-ethylenedimethacrylate copolymers provides a convenient site for further reaction and this has been used by Svec, Kalal, et al. to prepare several selective chelating macroporous resins. In their latest work they describe resins in which the epoxide ring is opened with ammonia (structure 15) and 

2-diaminoethane to give sorbents for heavy-metal ions. In the latter paper, the kinetics of the reaction of the resin with metal ions are reported. On hydrolysis and treatment with propane sultone in aqueous sodium hydroxide, a sulphonated resin is formed. The extent of sulphonation depends on the concentration of the base and the surface area of the polymeric matrix. Other heavy-metal absorbing resins have been prepared by treating polymers of acrylamide and dimethylacrylamide with PS which converts the amides into thioamide groups.  

The Hofman reaction on polyacrylamide is not a good method of preparing poly(vinyl amine). Nevertheless, it has been shown that with a small excess of NaOCl in a high concentration of sodium hydroxide at low temperature, it is possible to push the degree of amination of 90%. The excess of NaOCl causes some degradation, but this is minimized if the temperature is controlled. The Mannich reaction of polyacrylamide with formaldehyde and dimethylamine has been studied with the aid of C n.m.r. Reaction rates, equilibria, and mechanism for the base-catalysed reaction were characterized.  

Before the advent of NMR spectroscopy, a number of reports appeared suggesting the possibility of substantial head addition during polymerization of acrylate ester derivatives. Marvel et reported chemical degradation 

Plasticisers, most lubricants, most stabilisers, UV absorbers 

PVC polymer, filler, pigment, stabiliser, modifier, processing aid, residual plasticiser, emulsifier, some lubricants 

PVC polymer, processing aid, residuai plasticiser, modifier (in suspension), some lubricants 

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Fig. XV-1. Plots of t/CRT vs. C for a fractionated poly(methyl acrylate) polymer at the indicated temperatures in degrees Celsius. [From A. Takahashi, A. Yoshida, and M. Kawaguchi, Macromolecules, 15, 1196 (1982) (Ref. 1). Copyright 1982, American Chemical Society.]...

Acrylate copolymers Acrylate ester Acrylate esters Acrylate grouts Acrylate polymers Acrylates... 

Acrylates are primarily used to prepare emulsion and solution polymers. The emulsion polymerization process provides high yields of polymers in a form suitable for a variety of appHcations. Acrylate polymer emulsions were first used as coatings for leather in the eady 1930s and have found wide utiHty as coatings, finishes, and binders for leather, textiles, and paper. Acrylate emulsions are used in the preparation of both interior and exterior paints, door poHshes, and adhesives. Solution polymers of acrylates, frequentiy with minor concentrations of other monomers, are employed in the preparation of industrial coatings. Polymers of acryHc acid can be used as superabsorbents in disposable diapers, as well as in formulation of superior, reduced-phosphate-level detergents. 

Solution Properties. Typically, if a polymer is soluble ia a solvent, it is soluble ia all proportions. As solvent evaporates from the solution, no phase separation or precipitation occurs. The solution viscosity iacreases continually until a coherent film is formed. The film is held together by molecular entanglements and secondary bonding forces. The solubiUty of the acrylate polymers is affected by the nature of the side group. Polymers that contain short side chaias are relatively polar and are soluble ia polar solvents such as ketones, esters, or ether alcohols. As the side chaia iacreases ia length the polymers are less polar and dissolve ia relatively nonpolar solvents, such as aromatic or aUphatic hydrocarbons. 

Acrylic polymers are considered to be nontoxic. In fact, the FDA allows certain acrylate polymers to be used in the packaging and handling of food. However, care must be exercised because additives or residual monomers present in various types of polymers can display toxicity. For example, some acryflc latex dispersions can be mild skin or eye irritants. This toxicity is usually ascribed to the surfactants in the latex and not to the polymer itself. 

Adhesives. Acryhc emulsion and solution polymers form the basis of a variety of adhesive types. The principal use is in pressure-sensitive adhesives, where a film of a very low T (<—20 " C) acrylic polymer or copolymer is used on the adherent side of tapes, decals, and labels. Acrylics provide a good balance of tack and bond strength with exceptional color stabiUty and resistance to aging (201,202). AcryUcs also find use in numerous types of constmction adhesive formulations and as film-to-film laminating adhesives (qv). 

Preparation, Properties and Uses of Acrylic Polymers, CM-19, Rohm and Haas Co., Philadelphia, Pa. 

Acrylamide—acrylic polymers are made by free-radical polymerization of monomers containing the acryHc stmcture, where R is —H or —CH and is —NH2 or a substituted amide or the alkoxy group of an ester. 

The most common VI improvers are methacrylate polymers and copolymers, acrylate polymers (see Acrylic ester polymers), olefin polymers and copolymers, and styrene—butadiene copolymers. The degree of VI improvement from these materials is a function of the molecular weight distribution of the polymer. VI improvers are used in engine oils, automatic transmission fluids, multipurpose tractor fluids, hydrautic fluids, and gear lubricants. Their use permits the formulation of products that provide satisfactory lubrication over a much wider temperature range than is possible using mineral oils alone. 

T is the glass-transition temperature at infinite molecular weight and is the number average molecular weight. The value of k for poly(methyl methacrylate) is about 2 x 10 the value for acrylate polymers is approximately the same (9). A detailed discussion on the effect of molecular weight on the properties of a polymer may be found in Reference 17. 

Acrylic Polymers. Although considerable information on the plasticization of acryUc resins is scattered throughout journal and patent hterature, the subject is compHcated by the fact that acryUc resins constitute a large family of polymers rather than a single polymeric species. An infinite variation in physical properties may be obtained through copolymerization of two or more acryUc monomers selected from the available esters of acryUc and methacryhc acid (30) (see Acrylic esterpolya rs Methacrylic acid and derivatives). 

Catalysts. Silver and silver compounds are widely used in research and industry as catalysts for oxidation, reduction, and polymerization reactions. Silver nitrate has been reported as a catalyst for the preparation of propylene oxide (qv) from propylene (qv) (58), and silver acetate has been reported as being a suitable catalyst for the production of ethylene oxide (qv) from ethylene (qv) (59). The solubiUty of silver perchlorate in organic solvents makes it a possible catalyst for polymerization reactions, such as the production of butyl acrylate polymers in dimethylformamide (60) or the polymerization of methacrylamide (61). Similarly, the solubiUty of silver tetrafiuoroborate in organic solvents has enhanced its use in the synthesis of 3-pyrrolines by the cyclization of aHenic amines (62). 

The most commonly used scale inhibitors are low molecular weight acrylate polymers and organophosphoms compounds (phosphonates). Both classes of materials function as threshold inhibitors however, the polymeric materials are more effective dispersants. Selection of a scale control agent depends on the precipitating species and its degree of supersaturation. The most effective scale control programs use both a precipitation inhibitor and a dispersant. In some cases this can be achieved with a single component (eg, polymers used to inhibit calcium phosphate at near neutral pH). 

The most effective and widely used dispersants are low molecular weight anionic polymers. Dispersion technology has advanced to the point at which polymers are designed for specific classes of foulants or for a broad spectmm of materials. Acrylate-based polymers are widely used as dispersants. They have advanced from simple homopolymers of acryflc acid to more advanced copolymers and terpolymers. The performance characteristics of the acrylate polymers are a function of their molecular weight and stmcture, along with the types of monomeric units incorporated into the polymer backbone. 

Fig. 5. Effect of surfactant type on surface resistivity, (a) Concentration of surface-active compound in low density polyethylene (LDPE) requked to achieve 10 Q/sq surface resistivity and (b) effect on surface resistivity of an acrylic polymer. Concentration of surface-active compound is 0.3%.

Maxillofacial polymers include the chlorinated polyethylenes, polyethemrethanes, polysiloxanes (see Elastomers), and conventional acrylic polymers. These are all deficient in a number of critical performance and processing characteristics. It is generally agreed that there is a need for improved maxillofacial polymers that can be conveniently fabricated into a variety of prostheses (218,227,228). 

Acrylic polymers Scruh-resistant Poor Poor Poor Poor Fair Excellent Easy... 

Today plasticisers are used in a variety of polymers such as polyvinyl acetate, acrylic polymers, cellulose acetate and, most important of all, poly(vinyl chloride). 

Poly(methyl methacrylate) (Figure 15.1, I) is, commercially, the most important member of a range of acrylic polymers which may be considered structurally as derivatives of acrylic acid (II). 

In 1901 Otto Rohm reported on his studies of acrylic polymers for his doctoral dissertation. His interest in these materials, however, did not cease at this stage and eventually in 1927 the Rohm and Hass concern at Darmstadt, Germany commenced limited production of poly(methyl acrylate) under the trade names... 

In addition to poly(methyl methacrylate) plastics and polyacrylonitrile fibres, acrylic polymers find widespread use. First introduced in 1946, acrylic rubbers have become established as important special purpose rubbers with a useful combination of oil and heat resistance. Acrylic paints have become widely accepted particularly in the car industry whilst very interesting reactive adhesives, including the well-known super-glues are also made from acrylic polymers. 

Figure 15.8. Light transmission of acrylic polymer (5 in thick moulded Diakon. Parallel light beam normally incident on surface). (Reproduced by permission of ICI)...

Following the success in blending rubbery materials into polystyrene, styrene-acrylonitrile and PVC materials to produce tough thermoplastics the concept has been used to produce high-impact PMMA-type moulding compounds. These are two-phase materials in which the glassy phase consists of poly(methyl methacrylate) and the rubbery phase an acrylate polymer, usually poly(butyl acrylate Commercial materials of the type include Diakon MX (ICI), Oroglas... 

Over the years many attempts have been made to produce commercial acrylic polymers with a higher softening point than PMMA. The usual approach was to copolymerise MMA with a second monomer such as maleic anhydride or an N-substituted maleimide which gave homopolymers with a higher Tg than PMMA. In this way copolymers with Vicat softening points as high as 135°C could be obtained. 

In the early 1990s attention appeared to be focusing on the imidisation of acrylic polymers with primary amines. 

A number of acrylic polymers other than those already described have been produced but these are not generally of interest as plastics materials... 

Poly(methyl acrylate) is water-sensitive and, unlike the corresponding methacrylate, is attacked by alkalis. This polymer and some of the lower acrylate polymers are used in leather finishing and as a textile size. 

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