Ions in Polymers - American Chemical Society

12 Water-Soluble Polyester Adhesives

Downloaded by CALIFORNIA INST OF TECHNOLOGY on November 20, 2017 | http://pubs.acs.org Publication Date: June 1, 1980 | doi: 10.1021/ba-1980-0187.ch012

JOHN M. NOONAN and ROBERT C. McCONKEY Research Laboratories, Eastman Kodak Co., Rochester, NY 14650

Novel ionic polyesters that are soluble in water and that display very strong adhesive properties over the range 25°-120°C were synthesized using high-temperature melt-condensation polymerization. The polyester compositions contained the glycol 1,4-bis(2-hydroxyethoxy)cyclohexane and the diesters diethyl succinate and dimethylsodioimino-bis(sulfonyl-m-benzoate). Several nonionic diesters could be used in place of or in conjunction with diethyl succinate to give very strong adhesives. A UV-sensitive diester was incorporated into the polyester composition. The UV-sensitive polyester showed very strong adhesive strength; however, exposure of the adhesive to UV radiation caused a dramatic decrease in the adhesive strength.

here are many advantages i n preparing polyester resins v i a hightemperature melt condensation, for example, (a) the polyesters are easily prepared i n large-scale operations, ( b ) the desired molecular weight is easily achieved, ( c ) the monomers used are usually innocuous, and ( d ) the cost and potential pollution problems normally associated with organic solvents used during the synthesis and isolation steps of other polymerization techniques do not apply. Many functional groups can survive the high temperatures used i n melt-condensation polymerization, but only a few w i l l directly render these polyesters truly hydrophilic. I n fact, the literature reveals only two such functional groups: sulfonic acid salts (1,2) and iminosulfonyl salts ( 3 ) . Usually these groups are attached to the ring of an aromatic diester. However, the sodium salt of l,3-dicarboxycyclohexane-5-sulfonic acid (4) easily survived the polymerization conditions. W e wish to report the synthesis of water-soluble ion-containing polyesters that were prepared b y standard high-temperature melt-con0-8412-0482-9/80/33-187-185$05.00/0 © 1980 American Chemical Society

Eisenberg; Ions in Polymers Advances in Chemistry; American Chemical Society: Washington, DC, 1980.


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densation procedures. These ionic polyesters are characterized b y having a glycol component comprising one or more diols, a diester monomer that has an iminosulfonyl salt moiety, and one or more nonionic diesters. I n addition, when the correct combination and ratio of the above monomers were used, the resulting polymers displayed excellent adhesive properties. I n an attempt to increase the cohesive strength of the polyesters at high temperatures, the polyesters were cross-linked. This was accomplished by incorporating a UV-sensitive diester into the polymer backbones and then effecting cross-linking w i t h U V radiation. Unexpectedly, cross-linking caused a dramatic deterioration i n the bond strength of the adhesives. Experimental Polymerization. T h e ionic polyesters were prepared b y standard high-temperature melt-condensation procedures ( 3 ) . Viscosity Measurements. Viscosities were determined using an Ostwald—Fenske capillary viscometer. Measurements were made at 25 °C and at a concentration of 2.5 m g / m L i n 1:1 phenol-chlorobenzene. Molecular Weight Determinations. Number-average ( M ) and weightaverage ( M ) molecular weights were determined with a Waters gel-permeation chromatograph (GPC model 200) on diazomethylated polymer samples that were dissolved i n tetrahydrofuran. T h e columns were 1 0 10 À pore diameter. The molecular weights were reported as polystyrene equivalent weights. Calorimetry. The glass transition temperatures (T 's) of the ionic polyesters were determined under nitrogen on a D u Pont 990 thermoanalyzer. Heating and cooling rates were 10°C/min. Melt Viscosity. The melt viscosities were measured on a Rheometrics mechanical spectrometer with a cone-and-plate configuration under steady shear. Substrates Sealed. Aqueous polymer solutions were coated on Estar base, which had been precoated with a subbing layer ( 5 ) , to produce a 0.5-mil dry film thickness, then sealed to cellulose acetate, which h a d been precoated with another subbing layer ( 6 ) . These subbing layers were vinyl terpolymers which were synthesized from acrylonitrile, vinylidene chloride, and acrylic acid. Sample Sealing. Half-inch-wide substrate strips were sealed on a heated drum at 120°C using a roller with a 3-kg load weight ( 7 ) . Peel Force Determinations. Peel force was measured on an Instron drum apparatus (7). The Estar substrate was peeled from the cellulose acetate substrate, and a 90° angle of peel was maintained at a l l times. The peel force measurements were made over the range 2 5 ° - 1 2 0 ° C at two different rates: 0.1 in./min and 12 in./min. Monomers. The following monomers were obtained from Eastman Organic Chemicals and used as received: diethylene glycol, ethylene glycol, hexamethylene glycol, diethyl succinate, diethyl malonate, diethyl adipate, and 1,4-cyclohexane dimethanol. The following monomers were n

w

3

6

g


12.

NOONAN A N D MCCONKEY

Woter-Soluble Polyester Adhesives

187

obtained from the Tennessee Eastman Company and used as received: 1,4-bis ( 2-hydroxyethoxy ) cyclohexane, dimethyl sodioiminobis ( sulfonylra-benzoate), and diethyl p-phenylenebis(acrylate). Results and Discussion Polymer I was an amorphous water-soluble polymer w i t h an inherent viscosity of 0.33 and a T of 26°C. The M and M were 6,419 and 15,546 respectively. The ionic polyester displayed excellent adhesive properties as shown i n Figure 1. Absolute peel force values could not be obtained n


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II (35 mol %) -fC—C H —C— 2

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4-0—C H —0— 2

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-O—C H —O2

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Il y\ Il H -C— :VVT—S—N—SS- / \ —C—(15 mol %) ii _ il l o i ΊΟΠ Ο θ 0 \/

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® POLYMER I

at most temperatures, regardless of peel rate, because the bond strength was great enough to cause the Estar base to break before bond failure occurred. The adhesive strength was very dependent on the structure of the ionic polyester.

c

4000

CP

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2000 Κ

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50

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Temperature, °C Figure I . Temperature dependence of peel force for Polymer I: (O) peel rate at 0.1 in./min, (Π) peel rate at 12 in./min; (A) adhesive failure, (B) Estar base broke, (C) cohesive failure



188

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Diols. W h e n the diol l,4-bis(2-hydroxyethoxy)cyclohexane (A) was replaced with either 1,4-cyclohexanedimethanol (Polymer II) or ethylene glycol, the resulting polymers were much less soluble i n water and their adhesive strength dropped drastically. I n fact, the polymer with hexamethylene glycol was insoluble i n water. (The peel force results of Polymer II are shown i n Figure 2. ) However, if only 25 mol % of 1,4bis(2-hydroxyethoxy) cyclohexane was replaced with one of the above glycols, the resulting polymers were much more soluble i n water and displayed very high peel strengths. Figure 3 shows the peel forces when the glycol component contained 25 mol % of A and 25 mol % of hexamethylene glycol (Polymer I I I ) . W h e n D i o l A was replaced with diethylene glycol or tetramethylene glycol, the resulting polymers were readily soluble i n water and showed peel forces equal to those of Polymer I. Therefore, to ensure high adhesive peel forces at least 50 mol % of the glycol content should be a diol having ether linkages. Nonionic Diesters. The homologous series of diesters from oxalate to sebacate were individually substituted for the succinate moiety in Polymer I. W i t h the exception of the malonate- and adipate-containing polymers, the resulting polymers displayed very l o w peel strengths. The bond strengths of the malonate- and adipate-containing polymers were almost equal to that of Polymer I as shown i n Figure 4.


12.

NOONAN AND MCCONKEY


τ

Water-Soluble Polyester Adhesives

1

1

189

Γ

Temperature, °C Figure 3. Temperature dependence of peel force for Polymer III: (O) peel rate at 0.1 in./min, (D) peel rate at 12 in./min; (A) adhesive failure, (B) Estar base broke, (C) cohesive failure

4000

ο ο 2000 h-

50 100 Temperature, °C Figure 4. Temperature dependence of peel force for polymers contain ing 35 mol % malonate (Π), 35 mol % adipate (O), and 17.5 mol % adipate (V) at a peel rate of 0.1 in./min; (A) adhesive failure, (B) Estar base broke, (C) cohesive failure


190

IONS IN POLYMERS I

1

1

I

1

4000

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3000


2000

-

D

•B

B

• Β

• Β

1000 500

-

c C

1

0

25

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50

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75

100

9 τ

A

125

Temperature, °C Figure 5. Temperature dependence of peel force for Polymer I modi fied with 10 mol % ethylene glycol vs. protonated form at a peel rate of 12 in./min: (Π) Polymer I modified, (O) protonated Polymer I modified; (A) adhesive failure, (B) Estar base broke, (C) cohesive failure (T = -7°C; {η} = 0.32) g

However, when only 17.5 mol % of the succinate moiety i n Polymer I was replaced with either the malonate or adipate moiety, the bond strengths of the resulting polymers were greater than those of polymers containing 35 mol % of the malonate or adipate moieties (Figure 4 ) . Dimethyl Sodioiminobis(sulfonyl-w-benzoate). The content of the sodioiminobis(sulfonyl-m-benzate) ( 8 , 9 ) moiety ( C ) i n Polymer I was varied from 5 to 50 mol % , with the appropriate corresponding change in the succinate content. W e determined that 12-15 mol % of C was necessary to give maximum peel force values such as those shown i n Figure 1. W h e n the concentration of C was greater than 15 mol % , a semicrystalline polymer that had very low bond strength was obtained. W h e n the content of C was less than 12 mol % , the T of the resulting polymers ranged from —-10° to 10 °C, and as a result these polymers had very low peel forces above 35 °C. g

Protonation of Polymer I. T h e sodium cation associated with Polymer I was replaced with the hydrogen ion by acidifying an aqueous solution of Polymer I with I N hydrochloric acid. The protonated polymer was insoluble i n water but soluble i n organic solvents, especially chlori nated solvents. The bond strength of the protonated polymer was very poor (Figure 5 ) . W h e n the sodium cation of Polymer I was replaced with the potas sium cation, the T of the resulting polymer decreased to 8°C. In addi tion, the bond strength was very low, especially i n the range 2 5 ° - 5 0 ° C . Melt Viscosity. The steady shear viscosities of Polymer I repre senting the Newtonian flow region at four temperatures are shown i n Figure 6. The melt viscosity drops precipitously between 150° and 200°C. g


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NOONAN AND MCCONKEY

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τ

Temperature, °C Figure 6.

Steady shear viscosities representing the Newtonian flow region

Effect of Cross-Linking on Peel Force. T h e bond strength of Poly mer I was low at temperatures above 100°C (Figure 1 ) . I n an attempt to increase the bond strength, a few potentially cross-linkable sites were incorporated into the structure of Polymer I. A change i n the viscoelastic properties of the polymers should result upon cross-linking the polymer matrix with U V radiation and provide higher cohesive bond strengths. The UV-sensitive diester diethyl p-phenylenebis(acrylate) ( D ) (3) Ο Ο Il *—* Il C H —O—C—CH=CH-

Ions in Polymers - American Chemical Society

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