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VINYL ACETAL POLYMERS Introduction Vinyl acetal polymers are made by hydrolyzing poly(vinyl acetate) [9003-20-7] to poly(vinyl alcohol) [9002-89-5] and the reaction of the latter with an aldehyde in the presence of an acid catalyst. These two reactions, hydrolysis and acetalization, can be conducted either sequentially or concurrently (1). The acetalization reaction, shown in Figure 1, strongly favors complete condensation of one molecule of aldehyde with the 1,3-glycol of two vinyl alcohol units of poly(vinyl alcohol) to form the 1,3-dioxane ring of one vinyl acetal unit. The first reported vinyl acetal polymers were prepared in Germany by W. Haehnel and W. O. Herrmann in the 1920s by acetalization of poly(vinyl alcohol) (2). Commercialization of vinyl acetal polymers began during the 1930s and 1940s following development efforts by a number of companies, including Consortium ¨ Electrochemische Industrie, I.G. Farbenindustrie, Wacker, Canadian Electro fur Products, Union Carbide, General Electric, DuPont, Shawinigan Chemicals and Monsanto (both now Solutia) (3–11). Poly(vinyl butyral) [63148-65-2] (PVB, R = C3 H7 ) from butyraldehyde [123-72-8] is superior over the vinyl acetal polymers from either formaldehyde [50-00-0], acetaldehyde [75-07-0], or propionaldehyde [123-38-6] for laminated safety glass owing to its better cold temperature characteristics (1). PVB provides flexible toughness over a wide range of temperatures and at a lower cost than longer chain aldehydic carbon acetals. PVB and to a lesser extent poly(vinyl formal) [9003-33-2] (PVF, R = H) continue to be made in significant commercial quantities. Where stiffer performance at higher temperatures is required, PVF provides significant property advancement. Encyclopedia of Polymer Science and Technology. Copyright John Wiley & Sons, Inc. All rights reserved.

382

VINYL ACETAL POLYMERS

+ RCHO OH

Vol. 8 H+

+ H2O

2

Vinyl alcohol

O

O

H

R

Vinyl acetal

Aldehyde

Fig. 1. Acid-catalyzed acetalization of two vinyl alcohol units of poly(vinyl alcohol).

Vinyl acetal polymers form hard, unpliable materials that are difficult to process without using solvents or plasticizers. PVF was developed for use in lacquers and impregnating materials and for wire insulation. PVF is combined with other reactive resins and cured to form tough, chemical- and abrasion-resistant coatings. The impetus for PVB development was the discovery of the greatly improved properties of laminated safety glass made with plasticized PVB interlayer over that offered by plasticized cellulose acetate then in general use. This application was expanded to include the architectural as well as automotive fields, and is today the largest single use of vinyl acetal polymer (12). Small amounts of PVB resin are used for a variety of adhesive, printing, and surface coating applications. Applications for PVF and PVB resins make use of the toughness, resilience, optical clarity, high pigment and filler binding capacity, and high adhesion the resins can provide when appropriately formulated.

Synthesis and Structure Acetals are formed under conditions of acid catalysis by the reaction of aldehydes with alcohols (Fig. 2). The initial product of nucleophilic addition of alcohol to the carbonyl group is called a hemiacetal. In the net reaction, one molecule of aldehyde reacts with two molecules of alcohol (13). Similarly, vinyl acetal polymers are manufactured by the reaction of aldehydes with poly(vinyl alcohol) in the presence of an acid catalyst. Reaction of the aldehyde with an alcohol, in this instance the polymeric alcohol poly(vinyl alcohol), yields the unstable hemiacetal. Complete condensation with loss of water is strongly favored to form the cyclic acetal. Poly(vinyl alcohol) used to manufacture vinyl acetal polymers is produced by hydrolysis of poly(vinyl acetate) homopolymer with methanol or ethanol. Both acids and bases catalyze the reaction, but base catalysis is usually done with methanol (14). The catalyst is either acid or base, depending on the process. Poly(vinyl acetate) is polymerized from vinyl

O RCH

Aldehyde

R′OH, H+

OH

R′OH, H+

RCH

OR′ RCH + H2O

OR′

OR′

Hemiacetal

Acetal

Fig. 2. One molecule of aldehyde reacts with two molecules of alcohol under conditions of acid catalysis to make an acetal.

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VINYL ACETAL POLYMERS

O

O

H

R

x

Oy H H

O

383

z

C

O

C

H

H

Fig. 3. Generalized terpolymer structure for vinyl acetal polymers, R = C3 H7 for poly(vinyl butyral) PVB and R = H for poly(vinyl formal) PVF. Ranges for commercial grades of Butvar PVB from Solutia and Pioloform B PVB from Wacker include the following: x, vinyl butyral, is 52–74 mol% or 77–90 wt%; y, vinyl alcohol, is 26–45 mol% or 10–20 wt%; z, vinyl acetate, is 0–4 mol% or 0–3 wt% (19,20). For commercial grades of Vinylec PVF from Chisso: x, vinyl formal, is 73–79 mol% or 80–86 wt%; y, vinyl alcohol, is 10–14 mol% or 5.0–6.5 wt%; z, vinyl acetate, is 10–14 mol% or 9.5–13 wt% (21)

acetate by suspension or solution polymerization. (See VINYL ALCOHOL POLYMERS; VINYL ACETATE POLYMERS.) Hydrolysis of poly(vinyl acetate) produces a poly(vinyl alcohol) with predominantly 1,3-glycol units. The derived poly(vinyl alcohol) can contain up to 2.3 mol% 1,2-glycol units that come from head-to-head placement of vinyl acetate monomer (15). Lower vinyl acetate polymerization temperature and conversion reduces the irregularities of the polymer, such as branching and the 1,2-glycol structure (16– 18). Poly(vinyl acetate) hydrolysis is seldom complete, and for some applications, not desired. Therefore, vinyl acetal polymers are terpolymers, reflecting the three reactions that are used in their manufacture. The class can be represented by the generalized terpolymer structure (Fig. 3), with vinyl acetal, vinyl alcohol, and vinyl acetate units. A five-membered-ring acetal from acetalization of a 1,2-glycol unit is not shown. A statistical estimate of the maximum degree of acetalization or mole fraction of isolated, unreacted hydroxyl units is 0.1840 for 1,3- and 1,2-glycol containing poly(vinyl alcohol) and 0.1353 for pure 1,3-glycol containing poly(vinyl alcohol) for irreversible acetalization (22). For acetalization with butyraldehyde, assuming no vinyl acetate component, this corresponds to an unreacted vinyl alcohol weight of 12.25% in PVB for the first case and 8.84% in PVB for the second case. As acetalization is reversible, interchange to higher levels of acetalization was also modeled (23). In practice, however, quantitative conversion is accompanied by intermolecular acetalization, which effectively limits higher levels of acetalization in commercial products. The tacticity of hydroxyls in commercial poly(vinyl alcohol) is nominally atactic. However, an excess of cis-1,3-dioxane stereoisomers is formed during acetalization. Acetal formation depends strongly on process kinetics (24,25) and small quantities of other system components (26). During acetalization of poly(vinyl alcohol), for example, cis-acetalization is more rapid than trans-acetalization (27). In addition, the rate of hydrolysis of the trans-acetal is faster than for the more stable cis-acetal conformation (28). Because hydrolysis competes with acetalization during the acetalization process, a high cis/trans ratio is favored. The stereochemistry of PVF and PVB resins has been studied by proton and carbon NMR spectroscopy (29–32).

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Manufacture Although there are a number of potential methods for the manufacture of vinyl acetal polymers, in practice, only two basic processes with variants are used commercially today. By the solution process, formation of the acetal is as a solution in an organic solvent. By the aqueous process, the acetal is precipitated during the reaction of the aldehyde with an aqueous solution of poly(vinyl alcohol). These two reactions, hydrolysis and acetalization, can be conducted either sequentially or concurrently in the solvent process (1). A solvent process with concurrent hydrolysis and acetalization is used to produce PVF resin (21,33–35). The hydrolysis of poly(vinyl acetate) and acetalization of the resultant poly(vinyl alcohol) to the formal are carried out concurrently in an aqueous acetic acid solution that also contains a strong mineral acid catalyst. Final polymer composition is controlled by the ratio of acetic acid, water, and formaldehyde in the starting mixture. When the reaction is complete, the mineral acid is neutralized. As water is added to the agitated mixture, the PVF resin precipitates. Color can be improved by adding antioxidants (qv) during acetalization (36). The resin is centrifuged and dried after washing with water to remove salt and organic by-products. Figure 4 is a flow diagram for the manufacture of PVF (33). PVB resin can be produced by either a solvent process (37,38) or an aqueous process (11,39,40). The flow sheets for these processes are shown in Figures 5 and 6. In the aqueous process, poly(vinyl alcohol) is dissolved in water or an aqueous solution that contains acetic acid, then acidified with a mineral acid and reacted with butyraldehyde. During acetalization, PVB precipitates from the aqueous reaction mixture.

1

3

2

9

6 10

5

4

7 11

12 8

Fig. 4. Flow sheet for the manufacture of poly(vinyl formal) by a concurrent solvent process. 1, Poly(vinyl acetate) solution; 2, sulfuric acid tank; 3, sodium acetate tank; 4, reactor for hydrolysis and acetalization; 5, precipitator; 6, water tank; 7, wash tank; 8, liquor recovery system; 9, hold-up tank; 10, centrifuge; 11, dryer; 12, finished product (33). Courtesy of The Electrochemical Society, Inc.

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Vinyl acetate monomor

Butyraldehyde Mineral acid Poly(vinyl Mineral catalyst acid Poly(vinyl acetate) alcohol) solution catalyst

385

Ethyl alcohol

Peroxide-type initiator

Ethyl alcohol

Polymerizer Dissolver

Hydrolyzer Storage

Acetal reactor

Filter press

Centrifuge Ethyl acetate and alcohol Poly(vinyl butyral) solution Recovered ethyl alcohol Water

Water

Washer

Precipitator

Centrifuge

Water to sewer Ethyl acetate

Alcohol–water slurry of poly(vinyl Dilute alcohol butyral)

Wet poly(vinyl butyral)

Recovery still

Sifter

Drier Poly(vinyl butyral) to packing

Water

Fig. 5. Flow sheet for the manufacture of poly(vinyl butyral) by a solvent process using sequential hydrolysis and acetalization (38). Courtesy of McGraw-Hill, Inc.

In the solvent process to make PVB (Fig. 5), poly(vinyl acetate) is saponified by transesterification in the presence of ethanol and a mineral acid catalyst to produce poly(vinyl alcohol). The ethanol and ethyl acetate are separated from the precipitated poly(vinyl alcohol) by centrifugation. Because the desired properties of the final PVB require a low poly(vinyl acetate) content, concurrent hydrolysis and acetalization, employed for PVF manufacture, cannot be used. In a separate unit operation, poly(vinyl alcohol) is acetalized after being reslurried with ethanol, and heated with butyraldehyde and the acid catalyst. As the acetalization reaction proceeds in the solvent process, the slurry of poly(vinyl alcohol) dissolves as PVB in the ethanolic reaction mixture. Upon completion of the acetalization reaction in both solvent and aqueous processes, the acid catalyst is neutralized. PVB is precipitated into water during

386

VINYL ACETAL POLYMERS

Vol. 8 Sulfuric acid

Poly(vinyl alcohol)

Acetic acid

Acetic acid

Water

Butyraldehyde

Storage

Acetal reactor

Dissolver

Water

Pump

Suction filter Filter press

Diluted acetic acid Suction cell filter

Dryer

Poly(vinyl butyral)

Fig. 6. Flow sheet for the manufacture of poly(vinyl butyral) by an aqueous process (39).

aqueous neutralization in the solvent process. In both aqueous and solvent processes, resin is then separated, washed, and dried. Neutralization, typically with sodium hydroxide or potassium hydroxide, and washing stages are necessary to remove the acid catalyst, salt, and to achieve a more alkaline resin pH for improved resin thermal stability (8,10,37). For the solvent process, the ethyl acetate by-product can be recovered, refined, and sold as an additional product. This somewhat offsets the cost of sequential polymerization, hydrolysis, acetalization, and solvent recovery unit operations in one manufacturing plant. Because of the low capital investment required to produce PVB with market poly(vinyl alcohol) however, most of the recent published literature has dealt with the aqueous process. Resin from the solvent acetalization reaction has very low levels of gel from intermolecular acetalization, whereas precipitated resin in the aqueous acetalization reaction has a tendency toward high levels of intermolecular acetalization. Cross-linking can be minimized by adding emulsifiers to control particle size (40– 45), or substances like ammonium thiocyanate (46) or urea (47), to improve the solubility of PVB in the aqueous phase. To increase the average molecular weight

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and polydispersity of the resin, small quantities of a dialdehyde or trialdehyde can be added during the acetalization step (48).

Properties The properties of vinyl acetal polymers are a function of the relative amounts of the three randomly distributed units and the molecular weight. As indicated in Figure 3, manufacturers offer a variety of hydroxyl levels. Generally, PVB grades are produced commercially with either high (17–20 wt%) residual vinyl alcohol content or low (10–13 wt%) vinyl alcohol content. The acetate level for commercial PVB resins is usually low (0–3 wt%). However, comparatively higher acetate levels are produced for PVF resin grades to improve solubility at the expense of strength and dimensional stability (33). Residual vinyl acetate and vinyl alcohol contents are 9.5–13 wt% and 5.0–6.5 wt%, respectively, for commercial PVF grades available (21). Weight–average molecular weight ranges from about 25,000 to 100,000 Da for PVF resins and from 30,000 to 350,000 Da for PVB resins, depending on the grade. Table 1 lists suppliers for PVB resins, commercial trade names, and reported 1999 plant capacities (49). The only major manufacturer of PVF resins is Chisso Corp. in Japan (trade name Vinylec). Chisso purchased Monsanto’s PVF Formvar business in 1992. Wacker no longer manufactures PVF Pioloform F resins, only PVB Pioloform B resins. Table 2 lists reported properties of Vinylec PVF resins (21). The physical, mechanical, and thermal properties of various grades of Solutia’s Butvar resins are listed in Table 3 (19). In general, resin melt and solution viscosity increase with increasing molecular weight and vinyl alcohol content, whereas the tensile strength of materials made from PVB increases with vinyl alcohol content for a given molecular weight. The major use of PVB resin is for the manufacture of sheet used as an interlayer in laminated safety glass for automotive and architectural applications. PVB for laminated safety glass contains typically only 1–3 wt% of residual vinyl acetate units and 18–23 wt% vinyl alcohol units (49). The remaining hydroxyl Table 1. Major PVB Resin Producing Companies Resin plants United States Solutia DuPont Europe Solutia Kuraray Wacker Asia Sekisui a Ref. b Not

49. available.

Plant location

Trade name

1999 Annual capacitya , 103 t

Trenton, Mich, and Springfield, Mass Fayetteville, N.C., and Parkersburg, W.Va.

Butvar Butacite

57 41

Antwerp, Belgium Frankfurt, Germany Burghausen, Germany

Butvar Mowital PioloformB

20 25

Koga-gun, Shiga Prefecture, Japan

S-Lec

30

b

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Table 2. Properties of Vinylec PVF Resinsa PVF Vinyl alcohol, wt% Vinyl acetate, wt% Specific gravity Tensile strength, MPab Flexural strength, MPab Hardness, shore Flow temperature, ◦ C Heat distortion temperature, ◦ C Dielectric strength, kV/mm Dielectric constant, 60 Hz Volume resistivity, ·cm Dissipation factor, 60 Hz

5.0–6.5 9.5–13 1.1–1.3 49–78 108–127 70–80 140–150 84–93 26–39 3.0–3.7 1014 –1016 0.006–0.015

a Ref. b To

21. convert MPa to psi, multiply by 145.

groups have reacted with butyraldehyde to form acetal units. Hydroxyl level provides the prime leverage on performance in most applications. Unacetalized hydroxyls take part in both intramolecular and intermolecular hydrogen bonding. Intermolecular hydrogen bonding helps bind individual macromolecules together, making it more difficult for chains to untangle and slip by each other. Resin glasstransition temperature (T g ), viscosity, modulus, and tensile strength increase with higher residual hydroxyl levels. Simultaneously, processability and resiliency are reduced. Backbone hydroxyl groups also can form hydrogen and covalent bonds to the surface of polar substrates and are largely responsible for the adhesion. It is postulated that both hydrogen bonds and silyl alkyl ether covalent bonds are formed between resin hydroxyl groups and silanol groups at the PVB interlayer– glass interface (50). Film is made by the addition of plasticizer and other additives to the resin. Resin functionalities as well as plasticizer and moisture level of the formulation are important to PVB’s safety glass properties. A wide range of thermal performance results from the selection of aldehyde in addition to the composition of hydroxyl and acetate units in vinyl acetal polymers. The thermal glass-transition temperature (T g ) of vinyl acetal polymers of aliphatic aldehydes can be estimated from equation 1. VOH and VAC are the weight percent of residual vinyl alcohol and residual vinyl acetate units and C is the number of carbons in the chain derived from the aliphatic aldehyde (51). Tg = 65 + 1.26(VOH − 19.0) − 0.6(VAC − 1.5) + 46 ln(4/C)

(1)

The equation is set up for a typical PVB with 19% residual vinyl alcohol and 1.5% residual vinyl acetate. For this typical PVB (C = 4, VOH = 19.0, and VAC = 1.5) the equation reduces to a predicted thermal glass transition of 65◦ C. Vinyl acetal polymers of any glass-transition temperature between roughly 20 and 120◦ C can be obtained by formulating with mixed aldehydes. Glass-transition temperatures for mixed aldehyde polymers can be estimated using equation 1 by

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Table 3. Properties of Butvar PVB Resinsa Method

B-72

B-74

B-76

B-90

B-98

Vinyl alcohol, wt% 17–20 17–20 11–13 18–20 18–20 Vinyl acetate, wt% 0–2.5 0–2.5 0–1.5 0–1.5 0–2.5 Mol weight ave, 103 Da b 170–250 120–150 90–120 70–100 40–70 d Viscosity, Pa·sc 7–14 3–7 0.5–1 0.6–1.2 0.2–0.4 e Viscosity, Pa·s 1.6–2.5 0.8–1.3 0.2–0.45 0.2–0.4 0.07–0.2 f Ostwald viscosity, cP 170–260 40–50 18–28 13–17 6–9 ◦ Specific gravity at 23 C ASTM D792-50 1.100 1.100 1.083 1.100 1.100 Refractive index ASTM D542-50 1.490 1.490 1.485 1.490 1.490 Tensile strength, MPag Yield ASTM D638-58T 47–54 47–54 40–47 43–50 43–50 Break 48–55 48–55 32–39 39–46 39–46 Elongation, % Yield ASTM D638-58T 8 8 8 8 8 Break 70 75 110 100 110 Elastic modulus, GPah 2.30 2.30 1.97 2.10 2.17 Flexural strength, MPa Yield ASTM D790-59T 83–90 83–90 72–79 76–83 76–83 Rockwell hardness M ASTM D785-57 115 115 100 115 110 E 20 20 5 20 20 Impact strength, J/mi ASTM D256-56 j 58.7 58.7 42.7 48 37.4 Flow temperature, ◦ C ASTM D569-59 145–155 135–145 110–115 125–130 105–110 Heat distortion temp, ◦ C ASTM D648-56 56–60 56–60 50–54 52–56 45–55 Heat sealing temp, ◦ C k 220 220 200 205 200 l Tg , ◦ C 72–78 72–78 62–72 72–78 72–78 a Ref.

19.

b Determined

by size exclusion chromatography in tetrahydrofuran with low angle light scattering. convert Pa·s to cP, multiply by 100. d 15 wt% measured in 60:40 toluene/ethanol at 25◦ C using a Brookfield viscometer. e 10 wt% measured in 95 wt% ethanol at 25◦ C using an Ostwald–Cannon–Fenske viscometer. f B-72 in 7.5 wt% anhydrous methanol at 20◦ C; B-76 and B-79 in 5.0 wt% SD-29 ethanol at 25◦ C; B-74, B-90, and B-98 in 6.0 wt% anhydrous methanol at 20◦ C, all using an Ostwald–Cannon–Fenske viscometer. g To convert MPa to psi, multiply by 145. hTo convert GPa to psi, multiply by 145,000. i To convert J/m to (ft·lb)/in., divide by 53.38. j Notched Izod [1.27 × 1.27 cm (0.5 × 0.5 in.)]. k Dried film (0.025 mm) on paper cast from 10 wt% resin in 60:40 toluene/ethanol; heat sealer dwell time, 1.5 s at 60 psi. l By differential scanning calorimetry from 30 to 100◦ C on dried resin. c To

computing an average chain length weighted by the respective aldehyde mole fractions. Practical considerations have thus far precluded commercial manufacture of vinyl acetal polymers from higher molecular weight aldehydes or from mixed aldehydes. At an aldehyde chain length of more than four carbon atoms, the aldehyde becomes insoluble in water, with the result that washing and purification of the resin are extremely difficult. T g drops with increasing aldehyde chain length and

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Table 4. Solubility Parameter Ranges of PVF and PVB Resins Resina PVF, 9.5–13 wt% vinyl acetate PVB, 10–13 wt% vinyl alcohol PVB, 17–20 wt% vinyl alcohol a Ref.

Low hydrogenbonding solvents

Medium hydrogenbonding solvents

High hydrogenbonding solvents

9.3–10.0 9.0–9.8

9.7–10.4 8.4–12.9 9.9–12.9

9.9–11.8 9.7–12.9 9.7–14.3

b

52.

b Insoluble.

so drying and storage without agglomeration becomes impractical. In general, a reasonable compromise in properties can be reached by selection of a commercially available PVF or PVB resin combined with a suitable plasticizer. A close working relationship with the manufacturer can be helpful for applications development. Vinyl acetal polymers form hard, unpliable materials that are difficult to process without using solvents or plasticizers. The solubility parameter ranges for commercially available PVF and PVB resins are listed in Table 4. For most applications, T g is far more practically manipulated with plasticizers. However, acetalization with longer chain aldehydes (53–55) and polyoxyalkylene chains (56) provides a degree of internal plasticization to reduce T g without relying exclusively on liquid plasticizers. PVB resins are soluble in alcohols, glycol ethers, and selected mixtures of polar and nonpolar solvents. The low (10–13 wt%) vinyl alcohol content PVB resins are soluble in a wider range of solvents than are the high (17–20 wt%) vinyl alcohol content PVB resins. Solvent blends are commonly used, the exact solvent blend and resin composition dictated by the end use of the solution and the required drying properties (19,20). PVF resins are soluble in a more limited number of solvents and in certain mixtures of alcohols and aromatic hydrocarbons. Table 5 compares solvent compatibilities of PVF and PVB resins. A wide variety of plasticizers are suitable for PVB and PVF resins. For many years, the universally used plasticizer for PVB was triethylene glycol di(2ethylbutyrate) [95-08-9] (6). More recently this has been supplanted by triethylene glycol di(2-ethylhexanoate) [94-28-0], tetraethylene glycol diheptanoate [7072968-9], dihexyl adipate [110-33-8], 2-ethylhexyl diphenyl phosphate [1241-94-7], and a variety of other oligomeric ethylene glycol esters and ethers, and other adipate, phosphate, phthalate, sebacate, and ricinoleate esters (19,20,57–62). For PVF, diethyl, diphenyl, and dicyclohexyl phthalates, as well as tributyl, triphenyl, and tricresyl phosphates are useful plasticizers (21). By proper choice of plasticizer type and level, the physical–mechanical, chemical, and adhesion properties of these resins can be tailored for a wide variety of applications (see PLASTICIZERS). Vinyl acetal polymers can be formulated with other thermoplastic polymers and with a variety of multifunctional cross-linkers. Examples of polymers that are at least partially compatible with PVF or PVB resins include some types of polyurethanes, some types of celluloses, epoxies, isocyanates, phenolics, silicones, unsaturated polyesters, and melamine– and urea–formaldehyde polymers (19–21). Although vinyl acetal polymers are thermoplastic, hydroxyl groups permit cross-linking reactions with a variety of thermosetting resins, for example,

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Table 5. Solvent Compatibilities of PVF and PVB Resinsa,b

Vinyl alcohol, wt% Vinyl acetate, wt% Acetic acid (glacial) Acetone n-Butanol Butyl acetate Carbon tetrachloride Cresylic acid Cyclohexanone Diacetone alcohol Diisobutyl ketone Dioxane N,N-dimethylacetamide N,N-dimethylformamide Ethanol, 95 wt% Ethyl acetate, 99 wt% Ethyl acetate, 85 wt% Ethyl “Cellosolve” Ethylene chloride Hexane Isopropanol, 95 wt% Methyl acetate Methanol Methyl “Cellosolve” Methyl “Cellosolve” acetate 2-Methyl-3-butyn-2-ol 3-Methyl-1-pentyn-3-ol Methyl ethyl ketone Methyl isobutyl ketone N-methyl-2-pyrrolidinone Nitropropane 2-Propanol, 95 wt% Toluene Toluene/ethanol (60:40 wt%) Xylene Xylene/n-butanol (60:40 wt%)

PVF

PVB

PVB

5.0–6.5 9.5–13 S I I I I S I I I S S S I I I I S I I I I I I S S I I S I I I S I I

10–13 0–3 S S S S I S S S S S S S S S S S S I S S I S S S S S S S I S S S I S

17–20 0–3 S I S I I S S S I S S S S I S S S I S S S S I S S I I S I S I S I S

a Ref. bS

52. = completely soluble; I = insoluble or not completely soluble.

thermosets such as phenolics, ureas, melamines, and epoxies and chemicals such as dialdehydes and diisocyanates. In this manner, incorporation of even small amounts of the vinyl acetal polymer into thermosetting compositions markedly improves the toughness, flexibility, and adhesion of the cured composition. Alternatively, incorporation of smaller quantities of thermosets often gives the vinyl acetal polymer a better balance of properties. Illustrations of the mechanisms and formulation recipes for cross-linking vinyl acetal polymers can be found in the product literature (19,20).

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Vinyl acetal polymers have adequate thermal stability for many applications. Thermogravimetric analysis indicates significant rate of weight loss, starting about 240◦ C in air or about 320◦ C in nitrogen for PVF (63,64) compared to about 280◦ C in air or up to about 320◦ C in nitrogen for PVB (65). In air, significant oxidative degradation occurs at lower temperatures with longer thermal exposure as evidenced by loss of solubility, color development, and increasing T g attributed to the initial formation of unsaturated bonds and cross-linking (64,66). Mechanisms for degradation have also been studied employing combination techniques, including gas chromatography/mass spectrometry and infrared spectroscopy/thermogravimetry (65,67). For both PVF and PVB, the activation energy for degradation is much less in air than in nitrogen, suggestive of a reaction of oxygen resulting in structures more favorable for degradation (64,65). Sidegroup elimination, begun at about 280◦ C for PVB, by rupture of the acetal ring is proposed to occur by a free-radical mechanism involving hydroperoxide formation subsequent to an initial attack of molecular oxygen. This leads to the formation of carbonyl (C O) groups and liberation of small molecules, including the original aldehyde. The first stage of PVB degradation in nitrogen (ranging from 320 to 355◦ C) is mainly due to the elimination of water from the vinyl alcohol with the formation of small amounts of butyraldehyde. The second stage of PVB thermal degradation (ranging from 355 to 450◦ C) is associated with side-group elimination and main-chain scission during which most of the polymer is degraded (67).

Health and Safety The U.S. Food and Drug Administration regulates PVB resins used as indirect food additives (19,20). However, PVB resin is practically nontoxic by single-dose oral ingestion (LD50 > 10.0 g/kg for rats). Unformulated PVB and PVF resins have flash points above 370◦ C. The lower explosive limit for PVB dust in air is 20 g/m3 . Details on specific products are available with the manufacturer.

Economic Aspects During 1998, about 107,000 t of unplasticized PVB was manufactured in the United States, Western Europe, and Japan (49). Of this amount, more than 87% was plasticized and extruded into sheet for use in laminated safety glass for vehicle windshields and laminated architectural glazing. The remainder, less than 13%, was used for noninterlayer applications. The U.S. list price for PVB non-sheet grade, specialty resins was $9.48 per kg in 1998 ($6.11–11.45 per kg in Japan). 2003 PVB specialty resins prices, as surveyed by the author, remain essentially unchanged from $6.50–9.50 per kg depending on grade in the United States and Europe. 2003 PVF resins range from $15.00–20.00 per kg, a significant increase over historical values when PVF resins were available at lower prices than PVB specialty resins. The only producers of PVB non-sheet grade, specialty resins, not captive for interlayer, are Solutia (Butvar) and Wacker (Pioloform B). Major producers of interlayer for laminated glass are Solutia (Saflex), the largest producer,

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followed by DuPont (Butacite), Sekisui (S’Lec), and HT-Troplast (Trosifol). The only major manufacturer of PVF resins is Chisso Corp. (trade name Vinylec).

Applications Laminated Glass. PVB sheet is manufactured by extrusion of an intimate mixture of PVB resin, plasticizer, and trace additives. Commercial PVB sheet is available in thicknesses from 0.038 to 0.152 cm, with 0.076 cm predominant. The sheet must have a surface topography to enable optimal handling and subsequent removal of air from between sheets while laminating at elevated temperature. Laminated to glass, PVB exhibits high adhesion, optical clarity, stability to sunlight, and high tear strength and impact-absorbing characteristics. It adheres to glass fragments after a glass-breaking impact, thereby helping to reduce injury from flying glass. After the glass is broken during an impact, the interlayer’s high tear strength and resiliency acts like a safety net by absorbing enough energy to resist penetration by a projectile or a vehicle occupant’s head (12). In addition to its safety features, laminated glass in automotive and architectural applications adds sound attenuation (68,69), heat insulation, and break-in security, and also blocks ultraviolet radiation. For laminated safety glass, the strength of the adhesive bond between the glass and the interlayer is carefully controlled with additives, usually salts, to achieve the desired balance (70–80). Adhesion to clean glass is very high. If adhesion is too high, a projectile can easily penetrate the laminate because cracks made in the glass propagate through the interlayer. Group IA or IIA alkanoate salts as well as moisture are thought to reduce adhesion by competing with resin hydroxyls for bonding sites on the glass surface. If adhesion is too low, glass retention during an impact will be reduced even though the interlayer is not penetrated. Interlayer with gradient color bands are made for automobile windshields (81–83). The band is printed on the interlayer surface or tinted by coextrusion with pigmented resin. Curvature for a windshield is accomplished by differentially stretching sheet heated at about 85–100◦ C over a tapered shaping drum. Rolls of sheet or precut interlayer blanks are usually stored or shipped refrigerated at 3–10◦ C, or shipped at ambient conditions with an interleaved thin sheet of plastic such as polyethylene to prevent blocking. PVB composites layered with a film of poly(ethylene terephthalate), acrylic, or polycarbonate, or metal fabric, in addition to glass are designed for some specialty uses (84–87). Most laminated safety glazings are a trilayer composite of glass–PVB–glass, but some specialty applications can include a polymer film interlayer in the PVB to achieve decorative designs or solar reflective properties, or even a metal fabric to provide radio frequency shielding from external sources. For security applications, such as bullet- and projectile-resistant laminates, multi-ply PVB interlayer and glass composites are also designed. Surface Coatings and Primers. The first and most extensive application for PVF resins starting in 1938 was for electrical insulation and this still remains its major application (5). In these applications the PVF resin component helps provide dielectric properties, toughness, as well as abrasion and thermal resistance. PVF is combined with other ingredients, such as phenolic, epoxy,

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or melamine resins, to produce a thermoset coating solution for copper or aluminum wire. Coated wire is cured at elevated temperatures to give a cross-linked film coating with excellent uniformity, and electrical and chemical resistance (88–94). Wash primer formulations with PVB form a good foundation for various types of topcoats (19,95,96). Wash primers provide good adhesion to metal surfaces and stabilize the metal surface by continuously supplying corrosion-inhibiting ions. Phosphoric acid with zinc chromate or chromic acid can be used to make anticorrosive wash primers. However, due to toxicity concerns associated with chromates, alternative anticorrosive formulations, such as with a pigment of zinc molybdate (97) or borate and phosphate pigments (98), have been recommended. Non-solventborne wash primer formulations have been obtained with self-emulsifying waterborne PVB dispersions (99). Water-borne PVB dispersions eliminate the need for volatile organic solvents. The dispersion of plasticized PVB in water, marketed by Solutia as Butvar Dispersion BR, is used as a permanent surface size in textile applications where toughness of the butyral film lends outstanding abrasion resistance to the fabric (100). PVB dispersions can be applied to textiles by spraying, from a dilute bath by impregnation on a padder, or from a thickened dispersion by coating on spreading equipment. The dried dispersion imparts a soft, full-bodied finish to rayon, cotton, or nylon and helps prevent unraveling of filament yarns. PVB has also been used as a component of wash coats and sealers in wood finishing operations. It confers good holdout, intercoat adhesion, moisture resistance, flexibility, impact resistance, and protection against wood discoloration (19,101). Vinyl acetal polymers can also be used in coating formulations for other polymer surfaces (102,103). Adhesives and Binders. The principal adhesive uses of vinyl acetal resins are in high performance thermosetting adhesives and in thermoplastic hot-melt formulations. PVB binds the glass beads used in retroreflective films for licence plates, decals, and road signs (104–106). PVB resin is formulated with plasticizers, waxes, and other resins to make hot-melt adhesives (107). Vinyl acetal polymers are used for green strength as a fugative binder in ceramic tapes for electronics (108–110), but the largest application is as the binder in the production of ceramic substrates used primarily for electronic devices (111–117). Printing Inks and Toners. PVB resins have been used in printing ink formulations for many years. PVB resins are soluble in mild solvents, such as alcohols and esters, so can be used in solvent-based flexographic, gravure, screen, and inkjet printing formulations as a binder to improve flexibility, adhesion, and toughness (19,20,118,119). Flexographic and gravure printing are the dominant processes employed for printing flexible packaging used mainly in the food-processing industry, and to a lesser extent in the pharmaceutical and chemical industries. PVB is also used in toner formulations as a binder (19,120). PVB is added to the formulations to increase viscosity, to improve film integrity over the fuser roll, and to prevent blocking. The overall toughness of PVB enhances the integrity of the toner during the milling process and extended machine operation. This minimizes the level of fines without detracting from the flow properties.

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31. B. Lebek, K. Schlothauer, A. Krause, and H. Marschner, Acta Polym. 40, 92 (1989). 32. P. A. Berger, E. E. Remsen, G. C. Leo, and D. J. David, Macromolecules 24, 2189 (1991). 33. A. F. Fitzhugh, E. Lavin, and G. O. Morrison, J. Electrochem. Soc. 100, 351 (1953). 34. S. Matsuzawa, T. Imoto, and K. Ogasawara, Kobunshi Kagaku 25, 173 (1968). 35. S. Matsuzawa, Kobunshi Kako 18, 35 (1969). 36. Ger. Pat. 1,071,343 (Dec. 17, 1959), E. Bergmeister, J. Heckmaier, and H. Zoebelein (to Wacker Chemie GmbH). 37. U.S. Pat. 2,496,480 (Feb. 7, 1950), E. Lavin, A. T. Marinaro, and W. R. Richard (to Shawinigan Resins Corp.). 38. Chem. Eng. (N.Y.) 61, 122,123, 346–349 (Feb. 1954). 39. R. D. Dunlop, FIAT Final Report No. 1109, U.S. Government Printing Office, Washington, D.C., 1947. 40. U.S. Pat. 3,153,009 (Oct. 13, 1964), L. H. Rombach (to E. I. du Pont de Nemours & Co., Inc.). 41. Ger. Pat. Appl. 3,526,314 (Feb. 13, 1986), R. Degeilh (to Saint-Gobain Vitrage). 42. Rom. Pat. Appl. 63,627 (Apr. 30, 1978), A. Chifor, V. Dumitrascu, and I. Manu. 43. Ger. Pat. 2,838,025 (Sept. 10, 1992), P. Dauvergne (to Saint-Gobain Industries SA). 44. Jpn. Kokai 58,067,701 (Apr. 22, 1983), 57,195,706 (Dec. 1, 1982), and 57,030,706 (Feb. 19, 1982), S. Nomura, M. Miyagawa, and K. Asahina (all to Sekisui Chemical Co. Ltd.). 45. U.S. Pat. 5,349,014 (Sept. 20, 1994), R. Degeilh (to E. I. du Pont de Nemours & Co., Inc.). 46. Pol. Pat. 96,247 (Dec. 31, 1977), H. Pietkiewicz, M. Knypl, and A. Madeja. 47. L. N. Verkhotina, L. S. Gembitskii, E. N. Gubenkova, L. S. Sev’yants, and A. M. Sarkis’yan, Plast. Massy 7, 35 (1977). 48. U.S. Pats. 4,902,464 (Feb. 20, 1990), 4,874,814 (Oct. 17, 1989), 4,814,529 (Mar. 21, 1989), and 4,654,179 (Mar. 31, 1987), G. E. Cartier and P. H. Farmer (all to Monsanto Co.). 49. W. K. Johnson, G. Humphries, and K. Sakota, CEH Product Review, Polyvinyl Butyral, SRI International, Menlo Park, Calif., (Nov. 1999). 50. D. H. David, in Proceedings: Polymer–Solid Interfaces, First International Conference, Namur, Belgium, 1992, p. 133. 51. G. E. Cartier, unpublished data, Solutia, Inc., Springfield, Mass., 1987. 52. Butvar, Poly(vinyl butyral) and Formvar, Poly(vinyl fomal), Technical Bulletin No. 6070E, Monsanto Co., St. Louis, Mo., June 1980. 53. A. F. Fitzhugh and R. N. Crozier, J. Polym. Sci. 8, 225 (1952); Errata 9, 96 (1952). 54. Jpn. Kokai 62,278,148 (Dec. 3, 1987), K. Morita and T. Ii (to Sekisui Chemical Industries). 55. U.S. Pat. 5,137,954 (Aug. 11, 1992), A. M. Das Gupta, D. J. David, and R. J. Tetreault (to Monsanto Co.). 56. Eur. Pat. 394,884 (May 11, 1994), M. Gutweiler, R. K. Driscoll, and E. I. Leupold (to Hoechst AG). 57. U.S. Pat. 3,841,955 (Oct. 15, 1974), A. W. M. Coaker, J. R. Darby, and T. C. Mathis (to Monsanto Co.). 58. U.S. Pats. 3,884,865 (May 20, 1975) and 3,920,878 (Nov. 18, 1975), R. H. Fariss and J. A. Snelgrove (to Monsanto Co.). 59. U.S. Pat. 4,128,694 (Dec. 5, 1978), D. A. Fabel, J. A. Snelgrove, and R. H. Fariss (to Monsanto Co.).

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60. U.S. Pat. 4,144,217 (Mar. 13, 1979), J. A. Snelgrove and D. I. Christensen (to Monsanto Co.). 61. U.S. Pat. 4,230,771 (Oct. 28, 1980), T. R. Phillips (to E. I. du Pont de Nemours & Co., Inc.). 62. Eur. Pat. 877,665 (Aug. 23, 2000), J. J. D’Errico, B. A. Jemmott, M. S. Krach, and J. R. Moran (to Monsanto Co.). 63. M. Chandra, W. S. J. Kumar, and P. Raghavendrachar, J. Polym. Sci. 23, 755 (1979). 64. H. Aoki and T. Suzuki, J. Polym. Sci., Part A: Polym. Chem. 26, 31 (1988). 65. L. C. K. Liau, C. K. Thomas, and D. S. Viswanath, Polym. Eng. Sci. 36, 2589 (1996). 66. H. C. Beachell, P. Fotis, and J. Hucks, J. Polym. Sci. 7, 353 (1951). 67. L. C. K. Liau, C. K. Thomas, and D. S. Viswanath, Appl. Spectrosc. 50, 1058 (1996). 68. J. Lu, in International Congress and Exposition on Noise Control Engineering, Internoise 2002, Dearborn, Mich., Apr. 2002, Papers IN 02 581 and IN 2 582. 69. R. A. Esposito and G. E. Freeman, in Proceedings of the 2002 SAE International Body Engineering Conference and Automotive and Transportation Technology Conference, Paris, France, July 2002, Paper 2002-01-1993. 70. U.S. Pat. 3,262,837 (July 26, 1966), E. Lavin, G. E. Mont, and A. F. Price (to Monsanto Co.). 71. U.S. Pat. 3,249,487 (May 3, 1966), F. T. Buckley and J. S. Nelson (to Monsanto Co.). 72. Jpn. Kokai 50,121,311 (Sept. 23, 1975), I. Karasudani, T. Takashima, and Y. Honda (to Sekisui Chem. Co., Ltd.). 73. Ger. Pat. 2,410,153 (Feb. 3, 1977), R. Beckmann and W. Knackstedt (to Dynamit Nobel, AG). 74. U.S. Pats. 3,718,516 (Feb. 27, 1973) and 3,556,890 (Jan. 19, 1971), F. T. Buckley, R. F. Riek, and D. I. Christensen (both to Monsanto Co.). 75. Ger. Pat. 2,904,043 (Nov. 15, 1990), H. K. Inskip (to E. I. du Pont de Nemours & Co., Inc.). 76. Ger. Pat. 2,646,280 (Oct. 10, 1985), H. D. Hermann and J. Ebigt (to Hoechst, AG). 77. Eur. Pat. 617,078 (Feb. 25, 1998), H. Fischer (to Hoechst, AG). 78. Ger. Pat. Appl. 3,417,653 and 3,417,654 (Nov. 14, 1985), H. D. Hermann, K. Fock, K. Fabian, and J. Ebigt (to Hoechst, AG). 79. U.S. Pat. 4,292,372 (Sept. 29, 1981), R. E. Moynihan (to E. I. du Pont de Nemours and Co., Inc.). 80. U.S. Pat. 5,728,472 (Mar. 17, 1998), J. J. D’Errico (to Monsanto Co.). 81. U.S. Pat. 3,982,984 (Sept. 28, 1976), D. B. Baldridge (to Monsanto Co.). 82. U.S. Pat. 3,973,058 (Aug. 3, 1976), J. L. Grover and W. H. Power (to Monsanto Co.). 83. Ger. Pat. 2,841,287 (July 14, 1983), D. S. Postupack (to PPG Industries, Inc.). 84. Jpn. Kokai 6,155,681 (June 3, 1994), H. Yatani (to Asahi Kasei Kogyo). 85. Structural Performance of Laminated Architectural Glass, Technical Bulletin 2458043A, Solutia, Inc., St. Louis, Mo., 1999. 86. Security Glazing Design Guide, Technical Bulletin 2458104B, Solutia, Inc., St. Louis, Mo., 1999. 87. VancevaTM Advanced Solutions for Glass, Technical Bulletin 2459766, Solutia, Inc., St. Louis, Mo., 2002. 88. U.S. Pat. 2,307,588 (Jan. 5, 1943), E. H. Jackson and R. W. Hall (to General Electric Co.).

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89. U.S. Pat. 3,069,379 (Dec. 18, 1962), E. Lavin, A. F. Fitzhugh, and R. N. Crozier (to Shawinigan Resins Corp. and Phelps Dodge Copper Products Corp.). 90. U.S. Pat. 3,104,326 (Sept. 17, 1963), E. Lavin, A. H. Markhart, and R. F. Kass (to Shawinigan Resins Corp.). 91. E. Lavin, A. H. Markhart, and R. W. Ross, Insulation 8, 25 (1962). 92. U.S. Pats. 3,516,858 (June 23, 1970), A. F. Fitzhugh and J. A. Snelgrove; 3,639,330 (Feb. 1, 1972), A. F. Fitzhugh and R. M. Huck (both to Monsanto Co.). 93. U.S. Pat. 4,129,678 (Dec. 12, 1978), M. Seki, M. Sato, H. Tsukioka, E. Ohe, and A. Mitsuoka (to Hitachi Ltd.; Hitachi Cable Ltd.). 94. U.S. Pat. 4,254,007 (Mar. 3, 1981), R. G. Flowers and W. A. Fessler (to General Electric Co.). 95. J. D. Scantlebury and F. H. Karman, Corros. Sci. 35, 1305 (1993). 96. Military Specifications: DOD-P-15328D and MIL-C-8514C (ASG), Information Handling Services (HIS), Englewood, Colo. 97. J. L. Nogueira, Corros. Prot. Mater. 11, 11 (1992). 98. T. Foster, G. N. Blenkinsop, P. Blattler, and M. Szandorowski, J. Coat. Technol. 63, 91 (1991). 99. M. Gerlitz and E. Supper, Surf. Coat. Int., Part A: Coat. J. 84, 389 (2001). 100. Butvar Polyvinyl Butyral Resin Dispersion BR Resin Technical Bulletin, Publication No. 2006019F, Solutia, Inc., St. Louis, Mo., 2002. 101. U.S. Pat. 3,320,203 (May 16, 1967), M. D. Kellert (to Monsanto Co.). 102. U.S. Pat. 3,313,651 (Apr. 11, 1967), R. J. Burns (to Union Carbide Corp.). 103. Ger. Pat. 2,144,233 (Mar. 8, 1973), H. Hinrichs, J. Peter, and W. D. Schuessler (to Reichhold-Albert Chemie AG). 104. Eur. Pat. 223,564 (Aug. 28, 1991), T. R. Bailey, R. R. Kult, and L. C. Belisle (to 3M Co.). 105. Eur. Pat. 360,420 (Mar. 27, 1996), B. B. Wilson and R. E. Grunzinger (to 3M Co.). 106. U.S. Pat. 6,221,496 (Apr. 24, 2001), Y. Mori (to 3M Co.). 107. Czech. Pat. 155,587 (Dec. 15, 1974), M. Schatz, K. Salz, and J. Volek. 108. Rus. Pat. 744,741 (June 30, 1980), D. T. Kostin, I. A. Budkin, A. F. Rozov, V. N. Stazhkov, and I. V. Skvortsov. 109. Rus. Pat. 860,142 (Aug. 30, 1981), D. T. Kostin, V. N. Stazhkov, A. G. Yashenkov, I. A. Budkin, and A. F. Rozov. 110. R. E. Mistler, Am. Ceram. Soc. Bull. 77, 82 (1998). 111. Ger. Pat. 2,227,343 (Dec. 24, 1981), L. C. Anderson, R. W. Nufer, and F. G. Pugliese (to IBM Corp.). 112. Jpn. Kokai 62,046,954 (Feb. 28, 1987), K. Hoshi, S. Tosaka, and T. Yoshimi (to Taiyo Yuden Co., Ltd.). 113. Jpn. Kokai 61,266,350 (Nov. 26, 1986), N. Ushifusa, S. Ogiwara, K. Nagayama, K. Shinohara, and A. Toda (to Hitachi, Ltd.). 114. Jpn. Kokai 60,122,767 (July 1, 1985) (to NGK Spark Plug Co., Ltd.). 115. Eur. Pat. 200,484 (Feb. 5, 1992), M. S. H. Chu and C. E. Hodgkins (to TAM Ceramics, Inc.). 116. Jpn. Kokai 57,067,075 (Apr. 23, 1982) (to Nippon Kouatsu Electric Co., Ltd.). 117. U.S. Pat. 4,786,342 (Nov. 22, 1988), J. E. Zellner and R. M. Martin (to Coors Porcelain Co.). 118. U.S. Pat. 3,951,882 (Apr. 20, 1976), A. H. Markhart and D. R. Cahill (to Monsanto Co.). 119. Ger. Pat. Appl. 2,547,862 (May 6, 1976), K. Taubert (to Sandoz-Patent-GmbH). 120. Jpn. Kokai 08,328,303 (Dec. 13, 1996) and 08,292,596 (Nov. 5, 1996), H. Minamino, T. Takahashi, and K. Noguchi (both to Sekisui Chemical Co. Ltd.).

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GENERAL REFERENCES E. Lavin and J. A. Snelgrove, in M. Grayson, ed., Kirk-Othmer Encyclopedia of Chemical Technology, 3rd ed., Vol. 23, John Wiley & Sons, Inc., New York, 1983, pp. 798–816. J. W. Knapczyk, in J. I. Kroschwitz, ed., Kirk-Othmer Encyclopedia of Chemical Technology, 4th ed. (On-line), John Wiley & Sons, Inc., New York, 1997. P. H. Farmer and B. A. Jemmott, in I. Skeist, ed., Handbook of Adhesives, 3rd ed., Van Nostrand Reinhold, New York, 1990, pp. 423–436.

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