ba-1986-0213.ch023

23 Poly(2-ethyl-2-oxazoline): A New Water-andOrganic-Soluble Adhesive Thomas T . Chiu, Bruce P. Thill, and William J. Fairchok

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The Dow Chemical Company, Midland, M I 48674 Poly(2-ethyl-2-oxazoline) is prepared by the ring-opening polymerization of 2-ethyl-2-oxazoline with a cationic initiator. Many of the polymer's characteristics stem from its molecular structure, which has a backbone of alternating two carbon atoms and one nitrogen with a pendent propionyl group off the nitrogen. Rheologically, the behavior of poly(2-ethyl-2-oxazoline) is more Newtonian and relatively shear stable compared to that of common thermoplastics. The polymer's broad solubility, ranging from water and acetonitrile to methylene chloride, leads to applications of miscible polymeric systems. Single glass transition temperatures have been observed in a number of blends with poly(2-ethyl-2-oxazoline). The unique property of poly(2-ethyl-2oxazoline), being water soluble and hot meltable, suggests utilities such as heat sealing of disposable products, water remoistenable hot-melt adhesives, and other adhesion-enhancement applications.

A

H E BEHAVIOR

A N D PROPERTIES

OF

POLY(2-ETHYL-2-OXAZOLINE)

( P E O X , a trademark of D o w Chemical), a novel tertiary amide polymer, are described in this chapter. This polymer is prepared b y a cationic ring-opening polymerization of 2-ethyl-2-oxazoline (1-5). M a n y applications (6-11 ) of poly(2-ethyl-2-oxazoline) were reported. This chapter presents the physical property background of poly(2-ethyl-2-oxazoline); the physical factors suggest its utility as an adhesive or as a compatibilizing agent.

Experimental Section 2-Ethyl-2-oxazoline. 2-Ethyl-2-oxazoline is both a reactive intermediate for aminoethylation and a unique monomer. The synthesis of oxazolines has been extensively reviewed (3). One method of preparation for 2-ethyl-2-oxazoline is via alumina-catalyzed dehydration in the vapor phase to cyclize N-(2-hydroxyethyl)propionamide (4). 2-Ethyl-2-oxazoline is a clear, colorless liquid with a musky amine-like odor. Its boiling point and freezing point are 128 and —62 °C, respectively. 2-Ethyl-2-oxazoline is very soluble in most solvents, including acetone, methylene chloride, diethyl ether, toluene, and hexane. 0065-2393/86/0213-0425$06.00/0 © 1986 American Chemical Society

In Water-Soluble Polymers; Glass, J.; Advances in Chemistry; American Chemical Society: Washington, DC, 1986.

426

WATER-SOLUBLE POLYMERS

C H — CH 2

2

RX

O,

R

C

I

C H 2

QH

5

5

poly(2-ethyl-2-oxazoline)


2-ethyl-2-oxazoline

Polymerization. The 2-ethyl-2-oxazoline used is available from Dow Chemical. This compound was dried prior to polymerization by passage through a column containing 4 - Â molecular sieves that had been activated by drying at 170 °C/25 torr for 24 h. The dried 2-ethyl-2-oxazoline was protected from contact with moist air. The water content of 2-ethyl-2-oxazoline was determined by Karl Fischer titration. Water levels below 20 ppm were considered acceptable. Methyl tosylate (Aldrich Chemical) was used as received as the initiator throughout this study. Polymerizations were performed in sealed ampules. Ten grams (0.101 mol) of dried 2-ethyl-2-oxazoline was delivered to a carefully dried ampule, and the appropriate amount of 0.538 M methyl tosylate in dry ethyl acetate was added. Monomer-to-initiator ratios of 200-2000 were employed. The ampule was cooled in methylene chloride-dry ice, evacuated to approximately 5 torr, and sealed. After being warmed to room temperature, the ampules were placed in a 150 °C oil bath for 15 h. The ampules were removed, cooled, and opened, and the conversion was determined by percent nonvolatiles after 15 min at 225 °C/25 ton*. Conversions were typically greater than 99& Molecular Weight Determination. Poly(2-ethyl-2-oxazoline) molecular weights were determined by size-exclusion chromatography (SEC) on T S K G6000PW and G5000PW columns. A sample of polymer at a concentration of 0.25% by weight in 0.1 M sodium phosphate buffer at p H 7.0 was eluted with the same solvent at 1.0 mL/min. Detection was by U V at 214 nm. The columns were calibrated with a sample of poly(2-ethyl-2-oxazoline) polymer of broad molecular weight distribution standard that was characterized by a coupled SEC-lowangle laser light scattering (LALLS) technique. Data acquisition and reduction were computer-assisted. Number-average molecular weight__(M ), weightaverage molecular weight (M ), z-average molecular weight (M ), the ratio of M to M ( M : M ) , and integral and differential molecular weight distribution curves were obtained from the S E C analyses. n

w

w

n

w

z

n

Density. A value of 1.14 g/cm was obtained by using a density gradient column according to A S T M D-1505-79. 3

Refractive Index (no ). A flat disk of poly(2-ethyl-2-oxazoline) was prepared by using a heated Pasadena Hydraulics, Inc., platen press and 1-in. disk mold. A portion of the disk was cut out and mounted on the prism of a Bausch & Lomb Abbe refractometer. A liquid of higher refractive index was placed between the prism and disk. The sample temperature was maintained at 25 °C. 25


23.

427

Poly(2-ethyl-2-oxazoline)

C H I U E T AL.

Vicat Softening Temperature. The Vicat softening temperature was obtained according to American Society for Testing and Materials (ASTM) D-1525-82. Glass Transition Temperature (T ). T was obtained by using a Du Pont 1090B thermal analyzer and 910 differential scanning calorimeter and following A S T M D-3418-82. g

g


Thermogravimetric Analysis (TGA). An analysis was made by using a Du Pont 1090B thermal analyzer and a 951 thermogravimetric analyzer. Melt Blending. Poly(2-ethyl-2-oxazoline) was melt blended with other polymers at 190 °C for 10 min in an oil-heated Brabender mixer. The polymer blends were ground in a Wiley mill with a 16-mesh screen and stored in glass bottles.

Results and Discussion P h y s i c a l Properties. P o l y ( 2 - e t h y l - 2 - o x a z o l i n e ) is a m o r p h o u s . It has a T o f 5 5 ° C w h e n m e a s u r e d o n a q u e n c h e d s a m p l e . W i t h an u n q u e n c h e d s p e c i m e n , the T ranges f r o m 69 to 71 ° C . T h e p o l y m e r has a V i c a t t e m p e r a t u r e o f 7 0 ° C . D e p e n d i n g o n its molecular weight, poly(2-ethyl-2-oxazoline) exhibits a softening range o f 110 t o 120 ° C . T h e t h e r m a l s t a b i l i t y o f t h e p o l y m e r is e x c e p t i o n a l l y g o o d . F i g u r e 1 s h o w s a T G A o f a M 500,000 p o l y m e r . N o s u b s t a n t i a l g

g

w

500,000

M

w

PEOX

380' ^

*—400°

Air& N Atmospheres 10°C/Min. 2

Air-

%wt. Loss

1

100

-/A

350 400 Temperature, C

450

0

Weight Loss />98%,450°C

500

Figure 1. Thermal gravimetric analysis of a M 500,000 poly(2-ethyl-2oxazoline). The air and nitrogen atmospheres changed at a rate of 10 °C/min. w


428


d e g r a d a t i o n o c c u r s u n t i l 380 ° C (716 ° F ) i n a i r a n d 400 ° C i n a n i t r o g e n atmosphere. T h e p o l y m e r ' s r e f r a c t i v e i n d e x o f 1.520 ± 0.001 c o i n c i d e n t a l l y m a t c h e s that o f glass. T h i s f a c t m a y suggest utilities w h e r e a c l o s e m a t c h o f r e f r a c t i v e i n d e x e s is p r e f e r r e d i n c e r t a i n g l a s s - p o l y m e r systems. Bheology. As an amorphous linear p o l y m e r , poly(2-ethyl-2-oxazoline) e x h i b i t s a r a t h e r u n e x p e c t e d r h e o l o g i c a l b e h a v i o r . F i g u r e 2 s h o w s the v i s c o s i t y o f m o l t e n p o l y m e r p l o t t e d against v a r y i n g shear rates at 170 ° C . A p o l y s t y r e n e ( M = 275,000) c u r v e w a s i n c l u d e d f o r r e f e r e n c e o f a w e l l - k n o w n p s e u d o p l a s t i c m a t e r i a l . T h e l o w e r the m o l e c u l a r w e i g h t o f t h e p o l y m e r , the m o r e t h e b e h a v i o r o f t h e p o l y m e r a p p r o a c h e s N e w tonian behavior. U n d e r the high-shear conditions of a V i c k e r s vane p u m p , a formulated aqueous solution of M 200,000 p o l y ( 2 - e t h y l - 2 o x a z o l i n e ) r e t a i n e d t h r e e - q u a r t e r s o f its i n i t i a l v i s c o s i t y after 260 h o f test o p e r a t i o n . T h i s b e h a v i o r is g e n e r a l l y m a n i f e s t e d i n the e x c e l l e n t m e l t flow a n d r e l a t i v e shear s t a b i l i t y o f t h e p o l y m e r i n h a n d l i n g a n d processing.


w

w

T h e solution properties of poly(2-ethyl-2-oxazoline) were studied. I n t r i n s i c v i s c o s i t i e s w e r e d e t e r m i n e d f o r f o u r s a m p l e s o f the p o l y m e r w i t h m o l e c u l a r w e i g h t s o f 50,000, 100,000, 200,000, a n d 500,000 i n a q u e ous s o l u t i o n s (12). F i g u r e 3 p l o t s l o g [77] v e r s u s l o g M . T h e M a r k - H o u w i n k e q u a t i o n d e d u c e d is [η] = (6.5 X 1 0 - ) M 4

0 5 6

T h e v a l u e o f t h e e x p o n e n t o f M b e i n g 0.56 i n d i c a t e s that w a t e r is n e a r l y a Θ s o l v e n t f o r the p o l y m e r . C o n s e q u e n t l y , h i g h c o n c e n t r a t i o n s o f the p o l y m e r i n aqueous solution can be h a n d l e d w i t h o u t excessive t h i c k e n ing. A c o m p a r i s o n of viscosity versus percent concentration i n w a t e r for the p o l y m e r a n d f o u r o t h e r w a t e r - s o l u b l e p o l y m e r s is s h o w n i n F i g u r e 4.

1

Shear Rate (sec." ) Figure 2. Viscosity of poly(2-ethyl-2-oxazoline)

vs. shear rate at 170


°C.

Poly(2-ethyl-2-oxazoline )


C H I U E TA L .

20000

40000

100000 200000 Molecular Weight

429

400000

Figure 3. Intrinsic viscosity vs. the molecular weight of an aqueous solu tion of poly(2-ethyl-2-oxazoUne) at 25 °C. [η] = 6.5 X 10~ M . 4

100,000

r

056

Polyvinyl Pyrrolidone K-90 _ PEOX 350,000 M w

10,000

1,000 h Brookfield Vise, (cps) 21°C

0

1.0 20 30 40 Wt. % Concentration

Figure 4. Aqueous solution viscosity vs. the concentration of poly(2-ethyl2-oxazoline) compared to that of other water-soluble polymers. The weight-average molecular weight was 300,000 for Klucel Type G; 400,000 for Polyox N-3000; 125,000 for Gelvatol 20-90; and 350,000 for poly(2ethyl-2-oxazoline). The number-average molecular weight was 360,000 for poly( vinylpyrrolidone).


430 At


comparable

concentrations,

solutions o f

poly(2-ethyl-2-oxazoline)

a p p e a r t o b e s e v e r a l o r d e r s o f m a g n i t u d e less v i s c o u s t h a n ( h y d r o x y p r o pyl)cellulose (Klucel), poly(ethylene oxide) (Polyox), p o l y ( v i n y l alcohol) (Gelvatol), and poly(vinylpyrrolidone).


Solubility a n d C l o u d Point.

T a b l e I highlights the solubility of

p o l y ( 2 - e t h y l - 2 - o x a z o l i n e ) i n v a r i o u s solvents a r r a n g e d a c c o r d i n g t o t h e i r s o l u b i l i t y p a r a m e t e r , δ. T h e p o l y m e r has a n u n u s u a l l y b r o a d s o l u b i l i t y i n s o l v e n t s r a n g i n g f r o m c h l o r o f o r m , m e t h y l acetate, m e t h y l e n e c h l o r i d e , acetonitrile, ethanol, a n d w a t e r . W a t e r has b e e n n o t e d to b e a r o o m temperature 0 solvent f o r the p o l y m e r . A t elevated temperatures, the p o l y m e r t e n d s t o d r o p o u t o f the s o l u t i o n a n d e x h i b i t s a c l o u d p o i n t as s h o w n i n F i g u r e 5. F o r a h i g h e r w e i g h t - a v e r a g e m o l e c u l a r w e i g h t p o l y m e r o f 350,000, the c l o u d p o i n t is 62.0 ° C ; a l o w e r w e i g h t - a v e r a g e m o l e c u l a r w e i g h t p o l y m e r o f 70,000 has a c l o u d p o i n t o f a b o u t 64.5 ° C . T h e c l o u d p o i n t o f a n aqueous solution o f the p o l y m e r can b e raised b y the a d d i t i o n o f a s u r f a c t a n t o r a b e t t e r s o l v e n t , s u c h as a g l y c o l , w h i c h is miscible w i t h water. Polymer Blends. Oxazoline polymers m a y b e considered p o l y m e r i c a n a l o g u e s o f Ν , Ν - d i m e t h y l f o r m a m i d e ( D M F ) (13):

T a b l e I. Solubility o f Poly(2-ethyl-2-oxazoline)

δ

Solvent

7.0 7.4 7.8 8.5 8.9 9.3 9.3 9.3 9.3 9.5 9.6 9.7 9.9 10.0 11.9 12.7 12.7 13.3 14.5 23.4

n-pentane diethyl ether diisobutyl ketone η-butyl acetate toluene perchloroethylene dibutyl phthalate chloroform methyl ethyl ketone ethylhexanol methyl acetate methylene chloride acetone dioxane acetonitrile nitromethane ethanol propylene carbonate methanol water

Solubility pe

Ρ Ρ Ρ Ρ Ρ Ρ S S

fc

s s s s s s s s s s s

*P is less than 2% by weight. S is greater than 25% by weight. b


as

23.

431

Poly(2-ethyl-2-oxazoline)

CHIU E T AL.

CH3

-^CH

CH3

2

I

I

C

C


/ \

L.C2H5

ο

H

poly(2-ethyl-2-oxazoline) Ο This suggests that poly(2-ethyl-2-oxazoline) could be a broadly com DMF patible polymeric solvent. This suggestion was verified by the observa tion that a number of blends (14) with the polymer exhibit miscibility such that single T values resulted for the systems. Some of the polymers found to be miscible with poly(2-ethyl-2-oxazoline) polymer are styrene-acrylonitrile copolymer, acrylonitrile-butadiene-styrene copolymer, and phenoxy resin. Partial miscibility was observed with vinylidene chloride-vinyl chloride copolymer. G

Applications. Many of the novel utilities of poly(2-ethyl-2-oxazoline) stem from its polymeric-solvent nature. Compounding with poly(2-ethyl-2-oxazoline) enhances the adhesion of some polymer sys-

Temperature, °C 65

140 Molecular

2

8

weight

0 χ 10

3

Figure 5. Cloud point of poly(2-ethyl-2-oxazoline) of four different molecular weights. The concentration of poly(2-ethyl-2-oxazoline) was 1.0% in water.


432


terns to polar substrates. In some blends, the addition of poly(2-ethyl-2oxazoline) modifies the fluid permeability. A n example of this modification would be the i m p r o v e d moisture transmission through a blend of plasticized poly (vinyl chloride) and poly(2-ethyl-2-oxazoline). In other instances, controlled release of specific ingredients may be achieved via formulations with poly(2-ethyl-2-oxazoline) into a carrier matrix. T h e rheological and thermal properties of poly(2-ethyl-2-oxazoline) allow it to be applied either from solution or b y the hot-melt technique. Such an adhesive coating can be employed

directly and used in a


moisture-activatable system or in a heat-sealable construction. Poly(2-ethyl-2-oxazoline) applied from aqueous solutions adheres to aluminum foil, cellophane, nylon, poly (vinyl alcohol), poly (methyl methacrylate), and poly(ethylene terephthalate).

Poly(2-ethyl-2-oxazoline)*s

adhesion compares very favorably with that of poly(vinylpyrrolidone) or poly(vinyl alcohol) as shown in T a b l e II. In a composite

system,

chopped fiberglass sized with a formulation containing P E O X - b r a n d polymer has been used to reinforce a styrene-acrylonitrile copolymer. Outstanding tensile strength and Izod impact have been noted.

Summary Poly(2-ethyl-2-oxazoline) is unique because of the combination of its properties: • nonionic; • soluble in water and polar organic solvents; • low viscosity; • polymer compatibility; •

thermoplastic;

• high thermal stability; • adhesion enhancement; and • low hazard. Table II. Adhesion of Poly(2-ethyl-2-oxazoline), Poly(vinylpyrrolidone) and Poly(vinyl alcohol) to Plastic-Metal Films

Substrate

Poly(2-ethyl2-oxazoline), M 500,000

Poly( vinylpyrrolidone), M 360,000

Poly( vinyl alcohol), M 125,000

Aluminum foil Cellophane Nylon Poly(vinyl alcohol) Poly(methyl methacrylate) Poly(ethylene terephthalate)

pass pass pass pass pass pass

pass fail fail fail fail fail

fail pass fail

w

n

w

N O T E : The Scotch Tape test (Scotchbrand 600 tape) was used.


.—

fail fail

23.

CHIU E T AL.

Poly(2-ethyl-2-oxazoline )

433

T h e physical properties of the polymer allow it to be utilized in both hot-melt and solution adhesives for dissimilar materials. T h e adhe sion properties of the polymer may be activated b y heat or moisture. Because it is water soluble, adhesives formulated with the polymer pro vide recyclability. Many innovative applications of the polymer are sug gested b y its combination of properties.


Literature Cited 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14.

Tomalia, D . Α.; Sheetz, D . P. J. Polym. Sci. 1966, A-1, 4, 2253. Bassiri, T . G.; Levy, Α.; Litt, M . Polym. Lett. 1967, 5, 187. Frump, J. A. Chem. Rev. 1971, 71(10), 483. Seeliger, W. et. al. Angew. Chem., Int. Ed. Engl. 1966, 5(10), 875. Kem, Κ. M . J. Polym. Sci., Polym. Chem. Ed. 1979, 17, 1977. Chamberlin, Τ. Α.; Madison, N . L. U.S. Patent 4 001 160, 1977. Kelyman, J. S. U.S. Patent 4 087 413, 1978. Tomalia, D. A. et al. U.S. Patent 4 112 067, 1978. Miller, S. L.; Dickert, Y. J. U.S. Patent 4 113 674, 1978. Dickert, Y. J.; DeRoo, A. M . U.S. Patent 4 132 831, 1979. Chamberlin, Τ. Α.; Bangs, S. W. U.S. Patent 4 144 211, 1979. Buchholz, F . L. The Dow Chemical Company, private communication. Miyamoto, M . et. al. Eur. Polym. J. 1983, 19(10/11), 955. Keskkula, H . ; Paul, D. R. Proc. Div. PMSE ACS Meeting, St. Louis, MO 1984, p 11.

RECEIVED for review September 28, 1984. ACCEPTED October 10, 1985.


ba-1986-0213.ch023

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