TECHNICAL FIELD

This invention relates to solution polymerization of a. halogenated aromatic polyester.

Halogenated aromatic polyesters may be prepared by solution polymerization of a halogenated aromatic bisph- 5- ^' enol and a diacid halide.

BACKGROUND ART

In accordance with typical solution polymerization .procedures of the prior art, the reactants are present in a common solvent which also serves as a solvent for the polymer under the conditions of condensation. The bis--

10. phenol and the diacid halide are dissolved in separate portions of the chosen solvent. A catalyst or acid acceptor is added and the solutions are combined with agitation. Control of the molecular weight of the resulting polymer has hereto-fore _De en achieved by utili-

15. zing specific amounts of reactants in accordance with exact stoichiometric calculations. Once the required amount of reactants have been determined in this manner they are rapidly combined and allowed to polymerize until ^' a maximum inherent viscosity is achieved. Although this

20. method is capable of achieving a polymer having predet¬ ermined molecular weight such a procedure possesses many disadvantages when carried Ou"on- a.commercial scale. For example, commercial starting materials are non-uniform and they vary from batch to batch. Moreover, the start-

25. ing materials often contain impurities which, although not adversely affecting the resultant polymer, require correction in the above described calculations to account for their presence.. Thus, a non-uniform and impure starting material often leads to weighing errors which in

30. turn give rise to deviations from the predetermined

molecular weight in the final polymer product.

Typical solution polymerization procedures for preparing polyesters are outlined in the U.S. Patent Nos. Nos. 3,234,167 and 3,309,334.

DISCLOSURE OF THE INVENTION -

5. It is therefore an object of the present invention t provide an improved and relatively inexpensive process fo the preparation of high molecular weight halogenated aromatic polyesters of the type disclosed herein. The process has the advantage that it enables one to produce

10. the polymer with a predictable molecular weight range, reproducibly, and is readily controlled.

According to one aspect of the present invention there is provided a means for preparing a halogenated aromatic polyester having a predetermined molecular weigh

15. and of the following recurring structural formula:

20. where X, which.may be the same or different, is chlorine or bromine, Y, which may be the same or different, is . hydrogen, chlorine or bromine, R and R ^τ may be the same o different and represent lower alkyl groups, or hydrogen, or together constitute a cyclic hydrocarbon group, and n

25, equals at least 10, by the solution polymerization of a halogenated bisphenol and a diacid halide selected from the group consisting of isophthaloyl chloride, terephth- aloyl chloride-,and mixtures thereof which comprises pro¬ viding a solution comprising an organic solvent, a halo¬

30. genated aromatic bisphenol, and an acid acceptor, adding

the said diacid halide to the said solution under con¬ ditions such that the said diacid halide reacts with the said halogenated aromatic bisphenol to form a polymer, sensing the viscosity of the solution con aining the 5. resulting polymer, and terminating the addition of the diacid halide in response .to the sensing of a predeter¬ mined solution viscosity limit as defined herein.

In another form of the invention the said solution containing the halogenated aromatic bisphenol is sensed

10. as said diacid halide is added thereto forming the polymer and thereby causing an increase in solution viscosity, and the addition of the diacid halide is controlled in response to the sensed solution viscosity as the sensed solution viscosity approaches a predetermined solution viscosity

15. limit as defined herein, and the addition of the diacid halide is terminated in response to the sensing of the predetermined solution viscosity limit.

The addition of diacid halide is preferably con¬ trolled by gradually reducing the amount of the diacid 20. halide, which is added to the solution containing the polymer, to zero as the sensed viscosity reaches the predetermined .solution viscosity limit.

In another modification the said diacid halide is added to the solution of halogenated aromatic bisphenol

25. in an amount less than the amount necessary to achieve stoichiometric equivalence with the halogenated aromatic bisphenol, the viscosity'of the solution is sensed, an additional .amount of diacid halide is added in response to the sensed solution viscosity as the sensed solution

30. viscosity approaches a predetermined solution viscosity

limit and the addition of the diacid halide is terminate in response to the sensing of the predetermined solution viscosity limit.

Halogenated aromatic polyesters prepared in accord¬

5. ance with the process of this invention have recurring

10. where X, which may be the same or different, is chlorine or bromine, Y, which may be the same or different is hydrogen, chlorine, or bromine, R, and R ¹ may be the sam or different and represent lower alkyl groups (e. g. , of 1 to 5 carbon atoms), or hydrogen, or together constitute

15. a cyclic hydro-carbon group, and n equals at least 10 (e. g., n equals about 40 to 400). Commonly the aromatic polyester utilized in accordance with the process of this invention has a chlorine and/or bromine content of about 5% to 60^ by weight based upon the weight of the aromati

20. polyester, (e.g., a chlorine and/or bromine content of about 25% to 50% by weight). As is apparent from the structural formula, the aromatic polyester is chlorinated and/or brominated in the sense ^" that .these substituents ar directly attached to an aromatic ring. Preferably the

25. halogen substituents are all ^" bromine.

The halogenate _aromatic polyesters conforming to the above-defined formula are prepared by reacting sub¬ stantially equimolar amounts of (1) an appropriate bisphenol and (2) a diacid halide such as isophthaloyl

30, chloride, terephthaloyl chloride, ^' , or mixtures thereof by

I

solution polymerization.

Initially, the appropriate bisphenol is dissolved in a suitable solvent. A catalyst or acid acceptor is also dissolved in the solvent prior to the addition of the 5 ^' . diacid halide.

The bisphenols which are useful in the preparation of the polyesters having recurring units of the formula illustrated above have the structure:

15- where X, Y, R, and R ¹ , have the same significance as set forth hereinabove. Suitable bisphenols which are useful in the practice of this invention include 4,4'-methylene-

2 , 2 * , 6, 6 * ,-tetrabromodiphenol; 4,4'-ethylidene-2,2' ,6,6'- tetrabromodiphenol; 4,4 ^l -isopropylidene-2,2 ^: ,6,6'- 20. tetrachlorodiphenol(i.e. , tetrachlorobisphenol A);

2,2-bis(3-chloro 4-hydroxy phenyl) propane; 2,2-bis(3-bromo 4-hydroxy phenyl) propane; 1, -bis(5-bromo 4-hydroxy phenyl) ethane; 1 ,1-bis(5-chloro 4-hydroxy phenyl) ethane; 2,2-bis(3 chloro.5-hromo 4-hydroxy phenyl) 25. propane; bis(3-chloro 4-hydroxy phenyl) methane; bis(3, - dichloro 4-hydroxy phenyl) methane; 1,1-bis(3,5-dichloro 4-hydroxy phenyl) ethane; as well as their alkali metal salts.

Preferred bisphenols useful in the practice of this 30. invention are.4,4'-isopropylidene-2, '6,6'-tetrabromodi-

phenol also known as tetrabromobisphenol A and 4,4'- isopropylidene-2,2 ^τ ,6,6' tetrachlorodiphenol also known as tetrachlorobisphenol A.

Many brominated bisphenols of the above-described 5. structure are commercially available and may be prepared by the condensation of a lower alkyl ketone or aldehyde with tv/o molecules of the phenol and subsequently bro - inating and/or chlorinating the unsubstituted phenol. This reaction is usually carried out, with or without an 10. inert solvent, in the presence of an acid. This reaction is summarized in the case of X and Y being bromine in the following equations wherein R and R* have the meanings hereinabove described.

techniques are employed, the solvent in which the bi¬ sphenol and catalyst or acid acceptor are dissolved and in which the reaction takes place should be inert and incapable of reacting with any of the components present

30. therein. Furthermore, the solvent should be -a solvent

for both the starting materials as well as the resulting polymer. This allows the solvent to help maintain the forming _. polymer in a more workable form.

Those suitable solvents which may be utilized in the 5. solution .polymerization technique described herein in¬ clude chloroalkanes, aromatic and chloroaromatic compounds such as methylene chloride, chloroform, tetrachloroethane, trichloroethane, chlorobenzene, chlorotoluene, dichloroethane, benzene, toluene, xylene, or mixtures 10. thereof.

The catalyst or acid .acceptor is preferably a ter¬ tiary amine, (or a mixture of tertiary amines) which is capable of undergoing a reaction with the bisphenol to form a complex salt. Generally potential stoichiometric amounts

15. of the bisphenol and the acid acceptorare employed al¬ though a molar excess of acid acceptor of about 5 to about 10% over the stoichiometric amount is preferred. Thus the ratio of the tertiary amine to the bisphenol is about 2:1 and preferably from about 2.1:1 to about 2.2:1. A

20. bisphenol salt subsequently reacts with the diacid halide - and liberates an amine chloride.

Suitable acid acceptors include any tertiary amine or mixtures thereof.

Representative examples ..of'suitable tertiary amine 25. acid acceptors include triethylamine, diamino -2, 2, 2, bicyclo octane, tripropyl amine, dimethyl aniline, pyridine, dimethyla ine, and benzyl amine.

It will be noted ^" that halogenated aromatic polyesters of this invention are prepared by the condensation of 30. bisphenols with the diacid halides of isophthalic acid,

terephthalic acid or mixtures thereof. The- use of a diacid halide as opposed to.other corresponding derivatives is critical, the direct preparation of polymers from bisphenols and free acids being normally n

5. possible. These acid halides may be derived from a corresponding dicarboxylic acid by any one of several ^" methods well known in the art such as reacting the respective acids with thionyl chloride. Thus, the diaci halide.is preferably utilized in the form of a diacid

10. chloride.

It is generally preferred to dissolve the diacid halide in the same type of solvent utilized to prepare t solution containing the halogenated bisphenol. Although this is not critical the employment- of a solvent provide 15. for a more accurate control of the addition of the diaci halide to the bisphenol containing solution.

In preparing a preferred brominated aromatic poly¬ ester, the diacid halide will generally be utilized in t form of an aromatic acid chloride mixture of 45 to 75% 20. (e.g., 60%) by weight isophthaloyl chloride and correspo ^■ ingly 55 to 25% (e.g., 40%) by weight terephthaloyl chloride. ^'

In preparing a preferred chlorinated aromatic poly ester, the diacid halide will generally be utilized as a aromatic acid chloride mixture of ^' 90 to 40%, and prefer- 25. ably from 80 to 60% (e.g., 70%) by weight isophthaloyl chloride and correspondingly.10 to 60% and preferably form 20 to 40% (e.g., 30%) by weight terephthaloyl ^' chloride.

For smooth- operation in a stirred solution 30. polymerization, the resulting polymer product preferably

should be about 10% or less on the basis of the total weight of the solvent although percentages as high as 25% may be utilized depending upon the molecular weights of the polymer.

5. Generally substantially stoichiometric amounts of each reactant are employed; typical molar amounts of from - 1:0.8:2 to about 1:0.2:0.8, of -the ratio of bisphenol, isophthaloyl chloride and terephthaloyl chloride, respectively, are utilized.

10. In calculating the amounts of reactants which are to be utilized to achieve a predetermined molecular weight the assumption is made that the reactants are pure and any error which may be introduced into said calculation as a result of this assumption is ignored. This assumption is

15. made possible by the compensating effect of the feedback techniques described herein, which permit one to achieve a desired molecular weight in the absence of exact stoichio¬ metric calculations.

Thus, the essence of the presently claimed invention 20. lies in the ability to terminate the addition of the di¬ acid halide to the bisphenol containing solution at the precise point necessary to obtain a polymer having a pre¬ determined molecular weight without making complex pre¬ liminary calculations to determine exact stoichiometric 25. requirements. The identificatio -of this termination point or end point is achieved by a feedback mechanism wherein the viscosity of the polymer containing solution is monitored or sensed during or after the addition of the diacid halide to the bisphenol containing solution.

After the molecular weight which may be expressed a a weight average Mw and/or a-number average Mn and which is to characterize a final end product polymer-has been determined, the viscosity of a solution (herein referred

5. to as the solution .viscosity limit) utilized in, accord¬ ance with the solution polymerization reaction which is indicative of a degree of polymerization sufficient to yield the said final end product polymer of the desired molecular weight must also be determined. This is

10. achieved by relating the solution viscosity to molecular weight. Such a relationshp cannot be easily obtained directly and therefore is generally obtained indirectly expressing the molecular weight in terms of a standardiz viscosity which takes into account the variations of

15. viscosity as a result of variations in the concentration of the solution measured.

^• The preferable standardized viscosity utilized to relate molecular weight to solution viscosity is inheren viscosity. As is well known in the polymer art, the in-

20. herent viscosity is determined by measuring the relative viscosity of a 0.1% solution of the polymer at 25°C in a suitable solvent, such as chloroform or a 10/7 (w/w) mix¬ ture of phenoϊ/trichlorophenol. The viscosity of the polymer solution is measured relative to the solvent alon

25. and the inherent viscosity (I,. Vs) is determined from the following equation:

V,

In

V,

I . V. =

In the above formula, V is the efflux time of the solution, V-, is the e flux time of the solvent, and C is the concentration expressed in grams of polymer per hundered millilitres of solution. As is also known in the polymer 5. art, inherent viscosity is onotonically related to the molecular weight of the polymer.

The molecular weight of the halogenated aromatic polyesters may be determined by any method known to those skilled in the art such as illustrated by W. Sorenson and 10. T. Campbell, Preparative Methods of Polymer Chemistry (1968),

The inherent viscosity value which relates the specifi c predetermined molecular weight to the solution viscosity limit is referred to as the "inherent viscosity limit."

15. More specifically, the "inherent viscosity limit" is hereby defined as the inherent viscosity of a polymer having a particular molecular weight which molecular v/eight corresponds to- the predetermined molecular weight of a polymer sought to be prepared in accordance with the solu-

20.- tion polymerization process of the present invention.

The "solution viscosity limit" is hereby defined as the viscosity of a solution containing a polymer having a particular inherent viscosity limit (i.e., a given pre¬ determined molecular weight) measured under conditions 25. which will be present during the actual solution poly¬ merization.

Thus, a predetermined molecular weight of a given polymer can be expressed in terms of an "inherent viscosity limit" and a corresponding "solution viscosity limit."

The "inherent viscosity limit" is a standarized laboratory oriented value which can easily be empiricall related to a predetermined molecular weight of a polymer and which serves to link the solution viscosity limit t

5. said predetermined ^' molecular weight. The "solution viscosity limit" is a commercially oriented parameter which is related to the predetermined molecular v/eight o a polymer by correlation with the "inherent viscosity limit" of the polymer and which serves to identify the

10. end point at which the addition of -fche diacid halide to the bisphenol is terminated. As described above, the attainment of this end point is readily ascertained during the process of solution polymerization by directl sensing the viscosity of the solution containing the

15- reactants and polymerproduct as the diacid halide is added to the bisphenol containing solution. Thus, when the sensed solution viscosity reaches a solution viscosi limit (i.e., the solution viscosity limit as determined by any sensing means) the addition or further addition o

20. diacid halide to the bisphenol is terminated.

It is to be emphasized that although utilization of inherent viscosity to relate solution viscosity to molecular weight is preferred, any standardized viscosit index such as kinematic viscosity or intrinsic viscosity 25. can provide the required relationship to permit the determination of the "solution viscosity limit."

The sensing of the solution viscosity may be accom¬ plished by any suitable-means, such as a Brookfield viscometer on withdrawn samples or an in-line viscomete 30. Alternatively, the pressure drop of a constant volume

' .

flow- through a recycle loop may be monitored and corr¬ elated, to the solution viscosity.

The preferred method for sensing the viscosity of the solution is to. measure the change in torque of a

5. constant speed agitator which- is in contact with the polymer containing solution. Since the change in torque is a function of the change in solution viscosity the agitator can be calibrated to accurately determine the solution viscosity by any method well known to those

10. skilled in the art.

The sensing of the solution viscosity may be continuous or intermittent the only requirement being that the sensing' be sufficient to accurately indicate when the solution viscosity has reached the solution

15. viscosity limit and to provide sufficient time to terminate the addition of the diacid halide before the solution viscosity limit is exceeded. It is therefore possible to tailor the rate of addition in accordance With the duration and type of sensing employed. Thus,

20. the rate of addition may proceed in a manner similar to that utilized ina conventional titration process. In¬ itially, therefore, an amount of diacid halide which is less than the amount necessary to achieve stoichiometric equivalence v/ith the halogenated bisphenol and which is

25. insufficient to drive the ..polymerization reaction to the extent necessary to reach the solution viscosity limit is rapidly added to the bisphenol containing solution. Said amount is determined by treating the reactants as if they contained no impurities and any error which might

30. result therefrom is compensated for by the feedback mech-

.

anisrn described herein. Thus, as the purity of reactan and therefore the accuracy of the determination of such amounts ^' improves, the rate of addition during Hie initi stages of polymerization may be increased and the initi

5. sensing may be held to a minimum. When proceeding in this manner, the first feed which contains substantial amounts of diacid halide may constitute from about 60 t about 95% of the amount of diacid halide necessary to achieve the stoichiometric equivalence for the bispheno

10. After, the first feed the viscosity of the solution rapidly increases and begins to approach the solution viscosity limit. Further addition of the diacid halide therefore should proceed at a decreasingly slower rate to avoid over-shooting the solution viscosity limit. Th

15. intermittent approach to sensing an addition of the diac halide to the bisphenol solution is generally applicable to the batch type of process.

If it is desired to prepare the halogenated aromati polyester b a continuous process the addition of the

20. diacid halide. to the bisphenol containing solution as we as the sensing of the solution viscosity is more conven¬ iently carried out in a continuous manner. Thus, the viscosity of the bisphenol containing solution may be sensed from the first addition of the diacid halide unti

25. such addition is terminated. The rate of addition of th diacid halide to the bisphenol containing solution will be high during the initial stages of polymerization.and decrease to zero at the solution viscosity limit.

In a preferred embodiment, the polymerization 30. reaction may be carried out in a continuous manner, by

which the reactants are continuously introduced into the reaction, zone and the polymer product is continuously prepared and withdrawn. This may be achieved, for example by utilizing a cylindrical tube, having static

5. ^" mixers, as a reaction vessel. . The bisphenol containing solution is passed through the tube while adding the diacid halide at various points along the longitudinal axis in response to the viscosity of the polymer contain¬ ing solution as it is sensed at the outgoing portion of

10. the tube. Thus, the diacid halide is added in large amounts at the downstream portion of the tube and in gradually decreasing amounts at positions further upstream in the tube.

The final concentration of the polymer in solution 15. is about 3 to about 25%, preferably from about 5 to about 20% and most preferably from about 7 to about 1 %. At these, percentages of concentration, the solution vis¬ cosity will generally vary from about 1 to about 3000 ppise, preferabH-y from about 5 to about 2000 poise and 20. most preferably from about 10 to 1000 poise.

Polymerization is effective at temperatures which may vary from about 0 to about 200°C, preferably from about 10 to about 100°C, and most preferably from about 15 to about 50°C, and at pressures which

25. may vary from about 0.01 to ^' about- 0 atmospheres and preferably from about 0.1 to about 10 atmospheres. Agitation of the reactantswill e sufficient to evenly disperse the diacid halide throughout the bisphenol containing solution to avoid'a build-up of the concen-

30. tration of "the diacid halide in a localized area within

the reaction mixture. Such agitation may be supplied b any of the standard means of mixing such as by stirrer shaker, static mixer, spray nozzle or other flowing agitating means.

5. After polymerization the polymer is generally recovered by washing the polymer containing solution wi dilute, aqueous hydrogen chloride to neutralize the excess acid acceptor. The polymer solution is then washed with water, to remove salts and collected in any

10. suitable manner such as by evaporation of the solvent o by precipitation of the polymer in a suitable non-solven such as acetone or methanol The polymer may then be con¬ centrated to a desired spinning dope viscosity or dilute without isolation if the polymer is a solid, and there-

15. after processed for shaping, e.g., spun or cast for maki fibers or films, respectively.

Generally, the solution polymerization technique described herein is utilized to control the molecular ^' weight of the halogenated aromatic polyesters in a manne

20. sufficient to obtain a polymer having inherent viscosity (IV) limits which may vary from about 0.4 to about 1.7, preferably from about 0.6 to about 1.5, and most pref¬ erably from about 0.7 to about 1.2, which are indicative of polymers having a weight average molecular v/eight Mw

25. of about 25,000 to about 150-,000 .preferably from about 41,000 to about 127,000, and most preferably from about 50,000 to about 97,000.

^' The above described inherent viscosity ranges will generally correspond to solution viscosity limits of 30. about 1 to about 3000 poise, typically from about 5 to

about 1000 poise and preferablyfrom about 30 to about 95 poise at 'the typical final solution concentrations described above.

The halogenated aromatic polyesters prepared by the 5 ^" . - process o the presently claimed invention may be diss¬ olved in a suitable spinning or casting solvent, such as methylene chloride or tetrahydrofuran and formed into a shaped article, such as a fiber or film.

BEST MODE OF CARRYING OUT THE INVENTION

The invention may be put into practice in various 10. ways and certain specific embodiments will be given to illustrate it with reference to the accompanying examples. All parts and percentages in the examples as well as the remainder of the specification are by weight.unless other¬ wise specified.

EXAMPLE 1

15. The objective of this example is to obtain a polymer with an inherent viscosity between 0.9 and 1.1 which corresponds to a weight average molecular weight (AW) Mw of from 68,000 to about 87,000 and a solution viscosity limit of from ^" about 40 to about 71 poise. Thus, a

20. ^" brominated aromatic polyester containing bromine chem¬ ically bound to an aromatic ring and possessing the structural formula heretofore illustrated where X and Y are bromine groups, R and R' are methyl groups and n is about 100 is prepared by solution polymerization in the

25. following manner.

The amounts of reactants utilized in this example are based on theoretical stoichiometric requirements to achieve the desired molecular weight and no correction is made for other factors such as impurities in the reactants which 30. might affect the theoretical requirements. Thus,

parts by weight of 4,4' - isopropylidene - ^' 2,2'. 6,6' - tetrabromodiphenol are added to a reactionvessel con¬ taining about 1800 parts by weight of methylene chloride and 80 parts by weight of triethylamine with agitation.

5. A solution of a mixture of diacid halide comprising 44.7 parts by weight of previously distilled isophth¬ aloyl chloride and about 29.8 parts by weight of prev¬ iously distilled terephthaloyl chloride and 213.8 parts by weight of methylene chloride is then added at a rate

10. of 3«37 liters per minute to the bisphenol containing solution over a period of time of about one half hour, and at a temperature of about 30°C. The viscosity of the resulting solution is then sensed by measuring the viscosity of an in-line sample at 30°C with a Brookfield

15. viscometer (spindle no, 4 -6 ) and found to be less than 2 poise. The viscosity was found to be independent of the rate.of shear.

An additional amount of the same diacid halide solution which has been diluted to about 2.5 percent by

20. weight is then added.at a rate of 0.76 liters per minute. After a period of time ofabout 20 to 30 minutes the ^• solution viscosity increases to about 2 poise at 30°C and the flow rate is decreased to 0.26 liters per minute over a period of about 20 to 30. minutes. The viscosity

25. of the solution is then sensed in the manner described above and found to be 20 poise. The previously diluted diacid halide solution is then charged to the reaction vessel at a flow rate of about 0.11 liters per minute in progressively shorter increments until the solution

30. viscosity is sensed as being 45 poise at 30°C. This

solution viscosity corresponds to an inherent viscosity limit of about 0.95 which meets the objective. At the termination of addition of the diacid halide solution the polymer is present at a concentration of about 10% by 5. weight in the final reaction solution.

The polymer containing solution is then washed with a 5% aqueous solution of HC1 and decanted to remove the triethylamine as a salt. This procedure is repeated four times. The polymer is then washed with distilled water 10. to remove HC1 until the pH remains constant. The washed polymer is then precipated with methanol and recovered for molecular weight determination to confirm that the target molecular weight has been achieved.

The final mole ratios of the components utilized are 15. 1 part tetrabrominated bisphenol, 1.02 parts of 60:40 mixture of isophthaloyl and terephthaloyl chloride and 2.15 parts triethylamine.

The results of this example are summarized in ^S Table 1.

^' EXAMPLE II

20. Example 1 is repeated with the exception that the objective is to prepare a polymer having an inherent viscosity of about 1.1 to about 1.2 which corresponds to a weight average molecular- Weight (AW) Mw of from about 87,000 to about 97,000 and a solution viscosity

25. limit of from about 71 poise to about 95 poise. The same amounts of the reactants were used as in Example 1.

The results of this example are summarized in Table 1.

Table I. ,

5. Solution Inherent

Viscosity Viscosity

Example' Limit Limit AW (Mw)

I 45 poise ^' 0.95 73,000

II 84 poise 1.15 92,000

EXAMPLE III

10. . The objective of this example is to describe how the solution viscosity limit is determined. A target weight average molecular weight of 97,000 is determined wherein n of the structural formula is about 150 and the polymer utilized in Example 1 having said predetermined molecular

15. weight is prepar ^' ed. This is achieved by first determinin the exact stoichiometric requirements necessary to obtain a polymer of the desired molecular weight, taking into account such factors as purity of. the reactants, solvent reactivity, side reactions of the diacid chlorides and

20. amine acid acceptors and polymer hydrolysis. Thus, 201.7 parts of 4,4' - isopropylidene - 2,2', 6,6'- tetrabromodi phenol is added to a reaction vessel containing about . 1800 parts by weight ethylene chloride and 82 parts by weight triethylamine under agitation.

A solution of a diacid halide mixture comprising 25. 46.0 parts by weight of previously distilled isophthaloyl chloride, 30.8 parts by weight of ^' previously distilled terephthaloyl chloride and 320 parts by weight methylene chloride is then rapidly and completely added to the ; solution containing the bisphenol in a single increment 30. and reacted-therewith ^' at a temperature of 35 C. The

reaction vessel is cooled to terminate the reaction after a period of 1 hour when the polymer has achieved a maximum ^' inherent viscosity of 1.2 which corresponds to the desired molecular weight. This inherent viscosity is

5. then designated as the inherent viscosity limit for said target molecular weight. A sample of the resulting poly¬ mer solution, wherein the polymer is present in an amount of 10% by weight thereof, is removed, from the reaction vessel and maintained at a temperature of 30 C. The

10. solution viscosity of this sample is then determined by a Brookfield viscometer (spindle no. 4-6) and found to be 95 poise. The viscosity was found to be independent of the rate of shear. This solution viscosity is then designated as the solution viscosity limit for said target

15. molecular.weight. This procedure is repeated several times utilizing different target molecular weights. A table is then drafted which lists different target molecular weights and corresponding inherent viscosity limits and solution viscosity limits (e.g., at a typical

20. polymer concentration described herein). Such a table is provided for a polymer prepared by reacting tetrabrom- obisphenol A and a 60:40 mixture of isophthaloyl: terephthaloyl -chloride at Table II.

TABLE II

25. Target Ihher-ent'' :,, . Solution Viscoisity

Weight Average _ Viscosity ^• Limit at 10%

Molecular Weight Mw ^• Limit Polymer Cone.

50,000 0.7 19 poise

55,000 . ^' 0.8 28 poise

68,000 0.9 40 poise

77,000 1.0 52 poise _β

87,000 1.1 71 poise

97,000 1.2 95 poise

30. 107,000 1.3 140 poise

INDUSTRIAL APPLICABILITY

The presently claimed process avoids the necessity for careful and mostly weighing and analysis procedures necessitated by the raw materials used to prepare .the polymer and allows for the production of a 5. uniform product of a predictable molecular weight range.

The halogenated aromatic polyesters described here¬ in may be used to produce a number of inherently non- burning fibrous materials which offer the public a great degree of fire safety, particularly when fibrous article 10. are required for use in fire-control environments, e.g., children's sleepwear, suits for fire fighters, hospita _lι furnishings, and uniforms for military and civilian personnel.

N