Low-Temperature Polycondensation Processes - Advances in

14 Low-Temperature Polycondensation Processes P. W. MORGAN Pioneering Research Division, Textile Fibers Department, Ε. I. du Pont de Nemours and Co., Inc., Wilmington, Del.

Polycondensation at room temperature between Downloaded by UNIV OF ARIZONA on September 7, 2015 | http://pubs.acs.org Publication Date: January 1, 1962 | doi: 10.1021/ba-1962-0034.ch014

two or more fast-reacting intermediates is be coming widely used because of its convenience and speed.

The interfacial polycondensation sys

tem, in particular, which employs two immiscible liquids, is applicable to a wide variety of chemical structures: amides, urethanes, esters, sulfonates, sulfonamides, and ureas.

Many products can be

made at low temperature which could not be formed by melt methods because of their infusi bility or thermal instability.

The low tempera

ture procedures are subject to the effect of many variables, but these are readily controlled and acceptable conditions for use with new polymers or

intermediates

can usually

be found.

The

processes are readily scaled up in simple batch equipment or continuous reactors.

Special areas

of application are the direct formation of fibers from the reactants and polycondensation on fiber substrates.

M a n y condensation polymers are formed b y the interaction of bifunctional inter mediates with the elimination of a small by-product molecule at each point of combination. A well-known example is the commercial preparation of 6-6 nylon. F o r this preparation, a diamine and a diacid are combined to form a polymeric salt, w h i c h then is subjected to heat a n d later to heat a n d vacuum; water is e l i m i nated and a linear polyamide is formed. T h e preparation of nylon i n this way requires h i g h temperature, special pres sure a n d vacuum equipment, and a lengthy reaction period. T h e use of such processes is limited almost w h o l l y to the preparation of polymers w h i c h are fusible and thermally stable. There have come into prominence i n the past few years fast, low-temperature processes for the preparation of condensation polymers (12, 22). T h e chemistry of these processes is o l d and simple—in fact, the application of this chemistry to polymer-making is not new. M u c h work on polyurethanes was done, 20 years ago, b y Farbwerke Hoechst A . - G . i n Germany. O u t of this work 191 In POLYMERIZATION AND POLYCONDENSATION PROCESSES; PLATZER, N.; Advances in Chemistry; American Chemical Society: Washington, DC, 1962.

Downloaded by UNIV OF ARIZONA on September 7, 2015 | http://pubs.acs.org Publication Date: January 1, 1962 | doi: 10.1021/ba-1962-0034.ch014

192

ADVANCES IN CHEMISTRY SERIES

came Perlon U , made by the reaction of diisocyanates and glycols (6, 17). Both earlier and later references (12) to other polymers may be found, but many of these polymers d i d not possess h i g h molecular weight. Neither a historical review nor a complete story of this field of polymer making is presented here. Rather, this is a series of views of the chemistry a n d procedures, from w h i c h one may obtain some idea of the potential as w e l l as of the limitations of the methods. T h e discussion includes only reactions w h i c h y i e l d essentially linear polymers, bypassing polyurethane foams and phenol-formalde hyde condensates. Equation 1 shows the reaction for the preparation of 6-10 polyamide. T h e 6-10 notation stands for the number of chain carbon atoms i n the two intermedi ates, the diamine structure being designated first. In place of diacids, w h i c h ter minate i n O H groups, one uses diacid chlorides w h i c h are extremely reactive to w a r d amines even at room temperature or below. Hydrogen chloride is the by product rather than water, w h i c h is eliminated i n the conventional high-tempera ture process. T h e average polymer size, indicated by the subscript i n Equation 1, may be 25 to 100 repeat units. This is equal to the molecular weights obtained by melt processes. Ο

Ο il

H

H N-(CH ) -NH 2

2

6

C1-C-(CH ) -C-C1.

2

2

Hexamethylenediamine

8

Sebacyl chloride

Polymer precipitate

Range of Chemical Structures and Polymer Properties B y varying the structures between the functional groups, many polyamides can be made. B y changing the functional groups, other classes of polymers are obtained. T h e principal limitations result from too great a reduction i n reactivity of the intermediates or the production of intermediates or polymers w i t h insuf ficient stability for effective use. Table I shows some of the possible polymer classes. T h e change from one chemical class to another, as i n Table I, w i l l produce changes i n polymer properties such as solubility and melting point. T h e same type of change within a polymer class can be produced by varying the structures connecting the functional groups. Low-temperature polycondensation procedures are especially applicable to the formation of polymers w i t h wide property differ ences, as indicated i n T a b l e II.

Polycondensation Procedures T h e majority of the reactions listed i n Table I are best carried out b y use of two immiscible l i q u i d phases, one of w h i c h is preferably water. T h e water phase contains the diamine or diol and any added alkali. T h e other phase consists of the d i a c i d halide and an organic l i q u i d , such as carbon tetrachloride, dichloroIn POLYMERIZATION AND POLYCONDENSATION PROCESSES; PLATZER, N.; Advances in Chemistry; American Chemical Society: Washington, DC, 1962.

MORGAN

193

Low-Temperature Polycondensation Processes

Table I.

Chemical Classes of Polymers from Low-Temperature Polycondensation Processes Reacting Groups in Linking Structure in Polymer Intermediates Ο

Ο

Amide (7, 74)

—lU-C— Ο

—Ν—Η + C l — C — Ο

Urea (20)

—Ν—h—Ν—

—Ν—Η + Cl—C—Cl Ο

I

II

I


—Ν—H + Cl—C—Ν— Ο

I

II

—Ν—H + C = N — Urethane (27)

Ο —Ν—C—Ο—

Ο —Ν—H + Cl—C—Ο— Ο — N = C + H—Ο—

H O Sulfonamide (78)

—Ν—I—

A

Η Phosphonamide (5)

H

Ο Η

—Ν—Ρ—Ν—

I

Ester (3) Carbonate (76)

Sulfonate (4)

R Ο —Ο—C— Ο —Ο—C—Ο— Ο

II

«

—Ο—S—

ο

O

—Ν—H -f- Cl—I—

ι

Η

Ο

—Ν—Η + Cl—Ρ—Cl

I R Ο —Ο—Η + C l — Ι II Ο —Ο—Η + Cl—C—Cl Ο

II

ι

—Ο—Η + Cl—S—

ο

methane, xylene, or hexane. T h e polymerization takes place at or near the l i q u i d interface and therefore the process has been named interfacial polycondensation. T h e following outline shows the simplicity of the procedure: A few of the polycondensation reactions may be performed i n a single l i q u i d phase. Examples of this are the reaction of diisocyanates w i t h diols (8) or diamines (7) a n d the formation of polycarbonates from bisphenols a n d phosgene i n a solvent w i t h pyridine as the acid acceptor (15, 22). Low-temperature polycondensation reactions are best carried out w i t h h i g h speed stirring (1, 14), although there are examples of successful reactions per formed w i t h only moderate stirring. H o m e blenders are excellent reaction vessels. T h e processes may be scaled u p easily b y use of large cans or drums a n d overhead stirrers. Polymerization may be carried out continuously i n T-tubes or other devices. Figure 1 illustrates a glass laboratory apparatus for continuous poly merization. In POLYMERIZATION AND POLYCONDENSATION PROCESSES; PLATZER, N.; Advances in Chemistry; American Chemical Society: Washington, DC, 1962.

194

ADVANCES IN CHEMISTRY SERIES Table II.

Variation in Physical Properties and Order in Polymers from Low-Temperature Polycondensation Processes Property or Structural Characteristic Example /

rj\

Soluble and fusible

-N /

0 il

N - C - ( C H

2

)

0 ii

8

(74)

- C -

Ο Thermally unstable

2

J 7 Downloaded by UNIV OF ARIZONA on September 7, 2015 | http://pubs.acs.org Publication Date: January 1, 1962 | doi: 10.1021/ba-1962-0034.ch014

Infusible, but soluble

(27)

-N / N-C-0-CH -CH -0-C 2

ο

0

- Ν^1 Ν - C - / ~ V - / ~ ~ V C Η

Η

Ο

Ο

I II

I

Insoluble, network

(0

II

(10)

-Ν—(CH ) —Ν—(CH ) —Ν—C—(CH ) —C2

3

2

3

2

8

C—(CH )s—C—

Ordered and block structures

2

Il

II

ο

ο

Metered

(9)

Solutions of

Diocid

Holidt

end

Diamine

Polymer Slurry

Cooling Water

Figure I.

Continuous polymerizer

In POLYMERIZATION AND POLYCONDENSATION PROCESSES; PLATZER, N.; Advances in Chemistry; American Chemical Society: Washington, DC, 1962.

MORGAN

Low-Temperature Polycondensation Processes Table III.

195

Stirred Interfacial Polycondensation Process Steps

Polycondensation reaction 1. Make up reactant solutions 2. Mix vigorously, 1 to 5 minutes Polymer isolation 1. Polymer precipitates naturally or add a nonsolvent 2. a. Filter or centrifuge polymer precipitate b. Alternatively, steam off low-boiling solvents 3. Wash 4. D r y Use


1. Isolate polymer solution directly and cast or spin 2. Redissolve polymer and spin, cast or coat 3. Compact powder and mold or extrude

Figure 2. Continuous formation of 6-10 polyamide in an unstirred interfacial polycondensation system If the complementary phases for an interfacial polycondensation are brought together without stirring, and if the organic l i q u i d is a nonsolvent for the polymer, a thin film of polymer forms at once at the interface. U n d e r the right conditions, this film is tough and has high molecular weight. W h e n the film is grasped a n d In POLYMERIZATION AND POLYCONDENSATION PROCESSES; PLATZER, N.; Advances in Chemistry; American Chemical Society: Washington, DC, 1962.

196



pulled from the area of the interface, more polymer forms at once and a collapsed sheet or tube of polymer may be w i t h d r a w n continuously (Figures 2 and 3 ) . T h i s type of polymerization has been used as a lecture demonstration ( 1 3 ) . Since the omission of stirring decreases the number of variables, the method has also been used to study the polymerization mechanism.

Figure 3. Diagram of film formation in unstirred interfacial polycondensation system T h e yield of polymer b y this process is only 25 to 5 0 % because much unreacted material is carried away upon the film, whereas the yields from stirred p r o cedures are usually between 75 a n d 1 0 0 % . Variables Affecting Interfacial Polycondensation Reactions Polymers may often be made successfully i n a nonsystematic manner. H o w ever, higher quality polymers a n d higher yields are obtained b y attention to the effects of some of the many process variables. Several of the more important ones are listed i n Table I V . Table IV.

Important Variables in Interfacial Polycondensation Procedures 1. Chemical reaction rate 2. Precipitation rate of the polymer ( including its degree of swelling or solubility ) 3. Purity of materials 4. Hydrolysis of the acid halide 5. Stirring rate 6. Phase volume ratio and concentration of the intermediates

Stirring rate and reactant concentration are considered briefly. Figure 4 presents several plots relating the inherent viscosity of the polymer ( w h i c h is a measure of molecular weight) to the concentration of sebacyl chloride i n the preparation of 6-10 polyamide. T h e diamine concentration was held con stant for each plot. This is a polymerization system from w h i c h the polymer precipitates very rapidly. F o r the unstirred preparations ( A ) a n d those w i t h a In POLYMERIZATION AND POLYCONDENSATION PROCESSES; PLATZER, N.; Advances in Chemistry; American Chemical Society: Washington, DC, 1962.

MORGAN


197

medium stirring rate ( B ) , the peaks i n inherent viscosity occur at about the same acid chloride concentration. W i t h high-speed stirring, the highest viscosity occurs


at a

hicrhfir

arid

r h l n r i d f *

r o n r o ntra H o n .

Figure 4. Folyamide 6 - 1 0 , product solution viscosity vs. reactant concentrations in polymerization reactions A. Without stirring B. With stirring, medium speed, total liquid volume, 600 ml C. Full speed with total liquid volume, 300 ml. In all cases, diamine concentration is 0.10M T h e peaks presumably result from the attainment of conditions under w h i c h the quantities of the two reactants reaching the polymerization site i n the organic solvent are most nearly equivalent. A s the quantity of reactants i n the system as a whole is increased, stirrability decreases a n d this accounts for part of the decline in quality toward the right of the plots for the stirred reaction mixtures. T h e peaks i n inherent viscosity represent more than the conditions under w h i c h polymers w i t h the highest molecular weights m a y be made. A t such a peak point, the numbers of amine a n d carboxyl end groups per unit weight are most nearly equivalent, the molecular weight distribution is nearest to that char acteristic of a polyamide made b y the melt method, a n d the y i e l d of polymer is highest i n the stirred system (14). T h e preceding discussion applies to a polyamide w h i c h precipitates. F i g u r e 5 shows that for poly(sebacyl piperazine) (first structure, Table I I ) , w h i c h r e mains dissolved i n the organic solvent, there are likewise coincident peaks i n the plots of inherent viscosity and yield vs. the concentration of acid chloride. Some Practical Applications I n addition to the use of low-temperature polycondensation reactions as a research tool leading to new polymers, several other applications have been described. T h e unstirred, interfacial polycondensation procedure has been used to pro duce fibers w i t h dimensions useful for textiles. T h i s was accomplished b y use of very small interfaces or b y extruding a solution of one reactant into a bath of the dissolved complementary reactant (10). U n d e r some conditions the fibers m a y be ribbon-like as a result of the collapse of the initial tubular structure (11). In POLYMERIZATION AND POLYCONDENSATION PROCESSES; PLATZER, N.; Advances in Chemistry; American Chemical Society: Washington, DC, 1962.



198

0.61

1

ι

ι ι ι ι ι t

0.03 SEBACYL

ι

0.1 CHLORIDE

ι

.

ι

» • i.i 1.0

IN

ι

.

1

«—1 5.0

1 , 2 - D I C H L O R O E T H A N E , moles/liter

Figure 5. Polyamide Pip-10, stirred polymerization reactions with the polymer in metastable solution A. Product solution viscosity vs. reactant concentration B. Yield vs. reactant concentration Conditions. Diamine concentration 0.1 Μ, full speed stirring, total liquid volume, 400 ml. Whitfield, M i l l e r , and Wasley (19) have described a shrink-proofing treat ment for wool w h i c h employs interfacial poly condensation. T h e fabric is first wet out w i t h a dilute aqueous solution of hexamethylenediamine, the excess l i q u i d is squeezed out, then the fabric passes through a dilute solution of sebacyl chloride i n a water-immiscible organic solvent. Polycondensation takes place here w i t h the formation of a thin film of polyamide about the fibers. The excess l i q u i d is pressed out and the fabric is washed and dried. T h e gain in fabric weight is only a few per cent and it is said that there is no stiffening or marked change in physical properties. Yet the wool can now be put through ordinary laundry cycles and drying treatments without shrinkage. Polycarbonates from bisphenols ( E q u a t i o n 2) have reached commercial importance. T h e y may be made by several methods, including both low- and high-temperature procedures (16). A recently constructed plant for the prepara tion of the polycarbonate from Bisphenol A [2,2-bis(4-hydroxyphenyl) propane] is reported to use phosgene i n a low-temperature process ( 2 ) . T h e reaction is carried out i n a single solvent for the reactants and polymeric product. Pyridine is used as the acceptor for by-product hydrogen chloride. HO

(2)


MORGAN


199

T h e solution of polymer and pyridine salt is washed w i t h water to remove the salt, the aqueous wash liquors are decanted, a n d the polymer is isolated byuse of a precipitating l i q u i d or nonsolvent. T h e polymer is then collected, washed, dried, pelletized, and passed o n for extrusion or other forming steps. Pyridine and solvents are recovered i n additional operations. Chopey gives a detailed process diagram ( 2 ) .


Conclusion Low-temperature polycondensation processes provide polymer chemists w i t h a broadly applicable a n d fast laboratory tool, w i t h w h i c h rapid surveys of a large number of polymer structures are possible. Semiworks-scale preparations are easy and even plant-scale operations are feasible. Already one such operation has been started. O n a large scale, solvent recovery a n d waste disposal present some economic problems. T h e next five years w i l l bring forth many more publications on new research i n this field a n d further practical applications w i l l be emerging. Literature Cited (1) Beaman, R. G., Morgan, P. W., Koller, C. R., Wittbecker, E . L., Magat, Ε. E . , J. Polymer Sci. 40, 329 ( 1959 ). (2) Chopey, N. P., Chem. Eng. 67, No. 23, 174 ( 1960 ). (3) Conix, Α., Ind. Eng. Chem. 51, 147 ( 1959 ). (4) Conix, Α., Laridon, U., Angew. Chem. 72, 116 ( 1960 ). (5) Harris, D. M . , Jenkins, R. L., Nielsen, M. L.,J.Polymer Sci. 35, 540 ( 1959 ). (6) Hill, R., "Fibres from Synthetic Polymers," Elsevier, New York, 1953. (7) Katz, M. ( to Ε. I. du Pont de Nemours and Co. ), U.S. Patent 2,888,438 ( May 26, 1959 ). (8) Lyman, D. J.,J.PolymerSci.45, 49 ( 1960 ). (9) Lyman, D. J., Jung, S. L., Ibid., 40, 407 ( 1959 ). (10) Magat, E . E., Strachan, D. R. ( to Ε. I. du Pont de Nemours and Co. ), U.S. Patent 2,708,617 ( May 17, 1955 ). (11) Ibid., 2,798,283 ( July 9, 1957 ). (12) Morgan, P. W., S.P.E. Journal 15, 485 ( 1959 ). (13) Morgan, P. W., Kwolek, S. L.,J.Chem. Educ. 36, 182, 530 ( 1959 ). (14) Morgan, P. W., Kwolek, S. L., J. Polymer Sci., in press. (15) Schnell, H., Ind. Eng. Chem. 51, 157 ( 1959 ). (16) Schnell, H., Plastics Inst. ( London ) Trans. 20, No. 75, 143 ( 1960 ). (17) Smith, L . H., "Synthetic Fiber Developments in Germany," pp. 491-2, 700-10, Textile Research Institute, New York, 1946. (18) Sundet, S. Α., Murphey, W. Α., Speck, S. B., J. Polymer Sci. 40, 389 ( 1959 ). (19) Whitfield, R. E . , Miller, L. Α., Wasley, W. L., Textile Research J. 31, No. 8, 704 ( 1961 ). (20) Wittbecker, E . L. ( to Ε. I. du Pont de Nemours and Co. ), U.S. Patent 2,816,879 ( Dec. 17, 1957 ). (21) Wittbecker, E. L., Katz, M., J. Polymer Sci. 40, 367 ( 1959 ). (22) Wittbecker, E . L., Morgan, P. W., Ibid., 40, 289 ( 1959 ); and papers following. RECEIVED September 6, 1961.


Low-Temperature Polycondensation Processes - Advances in

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