Polyacrylates

Polyacrylates are based on acrylic acid, methacrylic acid, and their esters. Among them, polymethylmethacrylate (PMMA) and polyhydroxy ethyl-methacrylate (PHEMA) have found wide applications as biomedical materials. The clinical history of polyacrylates began when it was unexpectedly discovered that the fragments of PMMA plastic aircraft canopies stayed in the body of the wounded without any adverse chronic reactions (Jones and Denning, 1988 Park and Lakes, 1992). 

In normal conditions, PMMA is a hard transparent material. Molecular weight is the main property determinant. High molecular weight PMMA can be manufactured by free radical polymerization (bulk, emulsion, and suspension polymerisation). Bulk polymerization is used for cast semifinish products (sheet, profiles and even tubes), and the cast polymer is distinguished by superior mechanical properties and high surface finish 

Several techniques have been used in thermal degradation studies on polyacrylates including TGA [25, 28-31, 35] and various procedures based on pyrolysis followed by MS. 

These included studies of polymethylacrylate - cellulose copolymer [32], poly-2-acrylates [33] and copolymer-2-vinyl naphthalene methacrylate [34]. 

Polyisopropyl acrylate degradation has been examined by Grassie and Speakman [36] using a bulk technique with low temperature heating at 265 °G. The major products were reported to be carbon dioxide and propylene with small amounts of carbon monoxide and isopropylene. It was reported that no chain fragment fractions, as experienced with other primary esters, were produced. 

The branched chain poly tertiary-butyl acrylate has been considered by several workers [36] at low temperatures. Schaefgen and Sarasohn [37] have studied this degradation at several low temperatures. At 160 °C isobutylene was lost quantitatively while above 180 °C approximately half of the weight of the polymer was lost after 12 hours of heating with the gaseous products being 36% isobutylene, 11% water, and 3% carbon dioxide. Elemental analysis of the pyrolysis residue corresponded approximately to polyacrylic anhydride (C H Oj). 

Grant and Grassie [38] and Grassie and Weir [39] have discussed the degradation of poly tertiary-butyl acrylate in terms of the work of Schaefgen and Sarasohn [37] and all observed autocatalytic behaviour in the elimination of olefin from the polymeric ester. 

A series of papers on the thermal degradation of the alkali-metal salts of poly(methacrylic acid) and of their copolymers with methyl methacrylate has appeared. The principal decomposition products have been identified and the variation in their yield with polymer composition determined. Similar experiments have been made on the barium salt of poly(methacrylic acid). Copolymer studies have included methyl methacrylate-styrene, methyl methacrylate-flE-methylstyrene, methyl methacrylate-ethylene, methyl 

Takahara, T. Katami, M. Umemura, and T. Hayakawa, Taikl Osen Gakkaishl, 1979, 14, 382 (Chem.Alatr., 1980,93,137 037). 

144 -J. shimono, M. Tanaka, and T. Shono, J. AaaL Appl. Pyrot, 1979,1,77. 

145 J Takeuchi, Asahi Garasu Kogyo Gyulsu Shoreikai Kenkyu Hoieoku, 1978, 32, 249 Chem. Abstr., 1979,91, 75 040). 

Morisaki, Therm. Analysis Proc. Internat. Conf, 5th, 1977, 297. 

Polyacrylate leveling additives are homopolymers or copolymers of acrylates with alkyl, polyester or polyether modifications. They are normally supplied as solvent-free materials or as solutions. The performance of these additives is tailored through variations in their chemical composition (polarity and type of monomers) and MW, because their solubility and compatibility in coatings are dependent on these factors. Linear acrylic polymers are more incompatible than branched ones and those with higher MW are more incom- 

The poly alkyl acrylates and poly cyano acrylates generally resist biodegradation. In soil-burial tests, weight loss has been reported for copolymers of ethylene and propylene with acrylic acid, acrylonitrile, and acrylamide. The rapidly polymerizable systems such as poly(alkyl-2-cyanoacrylate)s adhered to moist surfaces have been examined in biomedical applications. Poly(methyl-2-cyanoacrylate) is the most degradable among the alkyl esters, and its degradability decreases as alkyl size increases (Holland etal., 1990). 

These compounds were then injected subcutaneously into castrated rats, and the amount of androgen in the lavatory muscle. 

This work shows, contrary to earlier research conducted at low temperatures, that substantial yields of liquid products are obtained on the high temperature degradation of the isomeric polypropylacrylates and polybutylacrylates. The products of the degradation reactions are identified and a comparison is possible with the results of studies of the polymers of the normal esters, i.e., methyl to butyl, the branched chain propyl, and the three branched butyl esters, all of the polymers having been examined under the same conditions. 

A mechanism involving random homolytic scission of the chain followed by a series of inter and intramolecular transfer reactions has previously been shown to be applicable to the simple n-alkyl polyacrylates and is suggested to be generally applicable to the lower branched chain esters. 

Reprinted with permission from J. K. Haken and L. Tan, Journal of Polymer Science Polymer Chemistry Edition, 1987, 25, 5, 1451. 1987, Wiley Interscience [7]  

---

VI additives to improve the viscosity index polymethacrylates, polyacrylates, olefin polymers. 

Sun F, Castner D G and Grainger D W Ultrathin 1993 Self-assembled polymeric films on solid-surfaces. 2. Formation of 11-(n-pentyldithio)undecanoate-bearing polyacrylate monolayers on gold Langmuirs 3200-7... 

Synthetic Rubbers. Synthetic rubbers are polymers with rubberlike characteristics that are prepared from dienes or olefins. Rubbers with special properties can also be prepared from other polymers, such as polyacrylates, fiuorinated hydrocarbons, and polyurethanes. 

Duolite C-464 3.0 1.13 Polyacrylic resin with high capacity and outstanding resistance to osmotic shock. 

Eig. 27. Optical absorption spectra of thin, 1 p.m-films of novolac, polyhydroxystyrene and polyacrylate polymers. The novolac resin is transparent only above 300 nm. While polyhydroxystyrene also absorbs strongly below 300 nm, it exhibits a region of adequate transparency centered near 248 nm. The... 

Both side-chain and main-chain scission products are observed when polyacrylates are irradiated with gamma radiation (60). The nature of the alkyl side group affects the observed ratio of these two processes (61,62). 

Suitable protective coUoids for the preparation of acryhc suspension polymers include ceUulose derivatives, polyacrylate salts, starch, poly(vinyl alcohol), gelatin, talc, clay, and clay derivatives (95). These materials are added to prevent the monomer droplets from coalescing during polymerisation (110). Thickeners such as glycerol, glycols, polyglycols, and inorganic salts ate also often added to improve the quahty of acryhc suspension polymers (95). 

The combination of durability and clarity and the ability to tailor molecules relatively easily to specific applications have made acryflc esters prime candidates for numerous and diverse applications. At normal temperatures the polyacrylates are soft polymers and therefore tend to find use in applications that require flexibility or extensibility. However, the ease of copolymerizing the softer acrylates with the harder methacrylates, styrene, acrylonitrile, and vinyl acetate, allows the manufacture of products that range from soft mbbers to hard nonfilm-forming polymers. 

Polyacrylate elastomers find limited use in hydrauhc systems and gasket apphcations because of their superior heat resistance compared to the nitrile mbbers (219,220). Ethylene—acrylate copolymers were introduced in 1975. The apphcations include transmission seals, vibration dampers, dust boots, and steering and suspension seals. Further details and performance comparisons with other elastomers are given in reference 221 (see also Elastomers, SYNTHETIC-ACRYLIC ELASTOTffiRS). 

Finally, a modification has been carried out in which a polyacrylate emulsion is added to a normal tetrakis(hydroxymethyl)phosphonium sulfate [55566-30-8] (THPS), urea, and TMM fire-retardant treatment in an attempt to completely alleviate the strength loss during the finishing. Indeed, better retention of tensile properties is achieved with no loss in fire resistance (85). 

Decabromodiphenyl Oxide—Polyacrylate Finishes. An alternative to the diffusion technique is the appHcation of decabromodiphenyl oxide on the surface of fabrics in conjunction with binders (131). Experimental finishes using graft polymerization, in situ polymerization of phosphoms-containing vinyl monomers, or surface halogenation of the fibers also have been reported (129,130,132,133). 

Decabromododiphenyl Oxide—Polyacrylate Finish. This finish, effective on both polyester and nylon fabrics, is one of the most effective finishes available (ca 1993) for cotton—polyester blends (131). Relatively high cost and difficulty in appUcation may have prevented more widespread use. 

Most elastomers can be made iato either opea-ceUed or closed-ceUed materials. Natural mbber, SBR, nitrile mbber, polychloroprene, chlorosulfonated polyethylene, ethylene—propylene terpolymers, butyl mbbers, and polyacrylates have been successfuUy used (4,111,112). 

Carboxylic acid hydiazides are prepared from aqueous hydrazine and tfie carboxylic acid, ester, amide, anhydride, or halide. The reaction usually goes poody with the free acid. Esters are generally satisfactory. Acyl halides are particularly reactive, even at room temperature, and form the diacyl derivatives (22), which easily undergo thermal dehydration to 1,3,4-oxadiazoles (23). Diesters give dihydtazides (24) and polyesters such as polyacrylates yield a polyhydrazide (25). The chemistry of carboxyhc hydrazides has been reviewed (83,84). 

Examples of photothermoplasts include polyacrylates, polyacrylamides, polystyrenes, polycarbonates, and their copolymers (169). An especially well-re searched photothermoplast is poly(methyl methacrylate) (PMMA), which is blended with methyl methacrylate (MMA) or styrene as a monomer, and titanium-bis(cyclopentadienyl) as a photoinitiator (170). 

Table 3. Comparison of Mechanical Properties of Polyacrylate and Methyl Methacrylate ...

The most widely used pitch control method is the addition of pitch dispersants, which can be either organic, ie, typically anionic polymers such as naphthalene sulfonates, ligninsulfonates, and polyacrylates (33,34), or inorganic, ie, typically clay or talc. The polymers maintain the pitch as a fine dispersion in the pulp, preventing agglomeration and potential deposition on the paper machine or the sheet. When talc, clay, or other adsorbent fillers are added to the furnish, moderate amounts of pitch can adsorb on these materials, producing a nontacky soHd that can be retained in the sheet. 

Other. A large variety of additives are used in paper-coatiag colors primarily to modify the physical properties of the colors (102). At high soHds concentrations in water, mineral pigment particles tend to associate and form viscous pastes. Dispersants (qv) are used to prevent this and to provide low viscosity slurries. Common dispersants include polyphosphates and sodium polyacrylate [9003-04-7]. Various water-soluble polymers are added to coatiag colors and act as water-retention agents and as rheology modifiers. 

Low molecular weight (1000—5000) polyacrylates and copolymers of acryflc acid and AMPS are used as dispersants for weighted water-base muds (64). These materials, 40—50% of which is the active polymer, are usually provided in a Hquid form. They are particularly useful where high temperatures are encountered or in muds, which derive most of their viscosity from fine drill soHds, and polymers such as xanthan gum and polyacrylamide. Another high temperature polymer, a sulfonated styrene maleic—anhydride copolymer, is provided in powdered form (65,66). AH of these materials are used in relatively low (ca 0.2—0.7 kg/m (0.5—2 lb /bbl)) concentrations in the mud. 

Acrylate and acrylamide polymers have several uses in drilling fluids, one of which is for filtration control. Sodium polyacrylates [9003-04-7] having molecular weights near 250,000 are exceUent temperature-stable filtration control agents for both fresh- and salt water muds, provided the concentration of water-soluble calcium is <400 mg/L (83). The calcium ions are precipitated using a carbonate such as soda ash, before adding the polyacrylate at concentrations up to ca 6 kg/m (3 Ib/bbl). 

Sacrificial adsorption agents such as lignosulfonates (148—151) can be used to reduce the adsorption of more expensive polymers and surfactants. Other chemicals tested include poly(vinyl alcohol) (152), sulfonated poly(vinyl alcohol) (153), sulfonatedpoly(vinylpyrrohdinone) (153), low molecular weight polyacrylates (154), and sodium carbonate (155). 

---