CA1251879A

CA1251879A - Production of melt consistent aromatic polyester

Info

Publication number: CA1251879A
Application number: CA000455438A
Authority: CA
Inventors: Arnold B. Finestone
Original assignee: BP Corp North America Inc
Current assignee: Solvay Specialty Polymers USA LLC
Priority date: 1983-11-30
Filing date: 1984-05-30
Publication date: 1989-03-28
Also published as: GB2150580A; MA20146A1; FR2555592B1; BE899785A; SE8406043L; CH664365A5; FI842150A; SE8406043D0; ZA845247B; BR8403550A; DE3443219A1; IT1176953B; AU2894784A; PT79392A; KR850004967A; PT79392B; JPH0532415B2; NO842580L; FR2555592A1; AU572151B2

Abstract

PROCESS FOR THE PRODUCTION
OF AROMATIC POLYESTERS

ABSTRACT

The production of oxybenzoyl polyesters is facilitated by the incorporation of a salt, particularly an alkali earth metal salt, and preferably potassium sulfate, during the production enabling the consistent production from these polyesters of molded articles of improved appearance and excellent properties.

Description

1 Rc-ls70-rl026 l, PROCESS FOR THE PRODUCTION

OF AROMATIC POLYESTERS
1 , I¦ ABSTRACT

¦ The production of oxybenzoyl polyesters is facilitated l by the incorporation of a salt, particularly an alkali earth ¦Imetal salt, and preferably potassium sulfate, during the production enabling the consistent production from these polyesters of molded articles of improved appearance and excellent properties.

BACKGROUND OF THE INVENTION
_ _ I

The present invention relates to an improved process for the production of copolyesters. More particularly, it relates to a process for the production of oxybenzoyl polyesters of aromatic I dicarboxylic acids, dihydroxyphenols and p-hydroxybenzoic acid 1 compounds as the starting materials.
It is known that such polyester resins can be produced by various polymerization processes including suspension polymeri-zation and bulX polymerization. Of these, the bulk polymerization process is perhaps the most desirable process in terms of economy.

However, since the aromatic polyesters have a high melting point a~

compared with aliphatic polyesters, such as polyethylene tereph-thalate, a higher temperature is required to maintain the aromatic polyesters at their molten stateO Consequently, the polymers are often colored and deteriorated in performance.
j Further, difficulty has been experienced in obtaining lot-to-lot consistency in molding characteristics of the resin.
Obviously, variations in molding conditions are undesirable in com-mercial operations and can result in inefficiencies of operation i and unacceptable differences in the molded articles.
~ Much ef~ort has therefore been expended on the develop-ment of a process which eliminates the disadvantages discussed ' I I

above and provides a polyester molding material Erom which articles of pleasing and uniform appearance and properties can be obtained. , i ll THE INVENTION

l According to the present invention, there can be consis-¦Itently produced a poly~.er having an extremely low degree of discol-¦oration and an excellent heat stability which has hitherto not been 'obtainable by the conventional bulk polymerizat-,on.
It is an object of the present invention to provide a l process for the production of aromatic polyesters having an 1 extremely low degree of discoloration and an excellent heat stabil-ity.
It is another object of the invention to provide an improved process for the consistent, economic production of aro-Imatic polyesters of acceptable quality.
1 It is a further object of this invention to provide poly-esters having reproducible melting and crystallization tempera-tures.
Other objects and further scope of the applicability of the present invention will become apparent from the detailed des-cription given hereinafter. It should be understood, however, that the detailed description and specific examples, while indicating 1, preferred embodiments of the lnvention, are given by way of illus-tration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.
It has been found that a process overcoming the problems encountered in the practice of the prior art processes and provid-ing polyester resins whose use is not attended by the noted draw-l backs is provided by the improvement which comprises adding a salt, 1 particularly an alkaline earth metal salt or an alkali salt and preferably potassium sulfate, during the preparation of the resin ¦¦and, particularly to the prepolymer melt prior to advancement of l¦the final product to the desired degree of polymerization.

Il ~J~,53~'7~

¦~ The wholly aromatic polyes~ers towards whose production ¦,the present invention is directed consist of combinations oE
ilrepeating units of one or more of the following formulae:
~ ~o~(X)n~3 C3 ~oc ~ (X)n ~3co~

¦ I II q ~ ~ ~ (X)n ~ ~ ~ ~ CO

,1 III r IV

OC ~ ~ t ~ ~

. 10 1~ VI

where x is O, S, - U -, NH or SO2 and n is 0 or 1 and the total lof the integers p ~ q + r ~ s + t + u in the moieties present is ',Ifrom about 3 to about 800.
lll Combinations of the above units include union of the i carbonyl group of Formulae I, II, IV and V with the oxy group of Formulae 1, III, IV and Vl. ~n the most general combination all ¦units of the above formulae can be present in a single copolymer.
I¦The simplest e~odiment wo~d be homopolymers of units I or IV.
ll Other combi~tions include mixtures of units II and III, II and VI, !IIII and V, V and VI, and I and IV.

Il - 3 -5~J~

The location of the functional groups are preferably in the para (1,4) positions. They can also be located in meta (1,3) ~position to each other. With respect to the naphthalene moiety, Ithe most desirable locations o~ the functional groups are 1,4; 1,5 1 and 2,6. Such groups can also be in the meta position to each I other.
The symbols p, q, r, s, t and u are integers and indicate the number of moieties present in the polymer. The total (p + q +
r + s + t + u) can vary from 3 to 800 and, when present, the ratio of q/r, q/u, t/r, t/u, q + t , q + t , and t can vary from r r + u r + u about 10/11 to about 11/10 with the most preferably ratio being l 10/10 . I
Exemplary of materials from which the moieties of For-mula I may be obtained are p-hydroxybenzoic acid, phenyl-p-hydroxy-1 benzoate, p-acetoxybenzoic acid and isobutyl-p-acetoxybenzoate.
Those ~rom which the moiety o Formula II is derivable include terephthalic acid, isophthalic acid, diphenyl terephthalate, diethyl isophthalate, methylethyl terephthalate and the isobutyl l half ester of terephthalic acid. Among the compounds from which the moiety of Formula III results are p,p'-bisphenol; p,p'-oxybis-phenoi; 4,4'-dihydroxybenzophenone; resorcinol and hydroquinone.
Inspection will show which of these materials are also suitable for supplying the moieties of Formulae VI - VIII.
Examples of monomers represented by Formula IV are 6-hydroxy-1-naphthoic acid; 5-acetoxy-1-naphthoic acid and phenyl 5-hydroxy-1-naphthoate. Monomers representing Formula V include 1,4-naphthalenedicarboxylic acid; 1,5-naphthalenedicarboxylic acid and 2,6-naphthalenedicarboxylic acid. The diphenyl esters or dicarbonyl chlorides of these acids can also be used. Examples of, 301 monomers representative of Formula VI are 1,4-dihydroxynaphthalene;

2,6-diacetoxynaphthalene and 1,5-dihydroxynaphthalene.
Particularly preferred for use in the practice of the present invention are plastic materials based upon oxybenzoyl ,Ipolyesters.

l 4 _ `

The oxybenzoyl polyesters useful in the present invention are generally those repeating units of Formula VI:
~VII) ~ O ~ l ~

where p is an integer of from about 3 to about 600.
One preferred class of oxybenzoyl polyesters are those of Formula VII:
(VIIA) Rl~O ~C ~ oR2 i_ s wherein Rl is a member selected from the group consisting of b~n-. 15 zoyl, lower alkanoyl, or preferably hydrogen; wherein R2 is hydro-gen, benzyl, lower alkyl, or preferably phenyl; and p is an integer from 3 to 600 and preferably 30 to 200. These values of p corres--~ pond to a molecular weight of about 1,000 to 72,000 and preferably . ~

3,500 to ~5,000.
Another preferred olass of oxybenzoyl polyesters are .
-~ copolyesters of recurring units of Formulae VII, VIII and IX:
(VIII) _~_ O~ _~01 ~

_q (IX) _~ o ~(X)m ~ ~

7~

wherein X is -O or -SO2-; m is 0 or 1; n is 0 or 1; q:r = 10:15 to 15:10) p:q = 1:100 to 100:1; p + q ~ r = 3 to 600 and preferably 20 to 200. When m is O the recurring unit of Formula lX would then become (lXa) ~ 0~ 0~

The carbonyl groups of the moietv of Formula VII or VIII are linked to the oxy groups of a moiety of Formula VII or IX; the oxy groups of the moiety of Formul~ VII or IXare linked to the carbonyl groups of the moiety of Formula VII or VIII.
The preferred copolyesters are those bf recurring units of Formula X:
~X) C ~3 11 - O ~1l - o ~43 The synthesis of these ~olyesters is described in detail in U.S. Pat. No. 3,637,595, entitled "P-Oxybenzoyl Copolyesters"
In accordance with the present teachings, a melt-processable wholly aromatic Polyester having reproducible melting and crystallization temperates as provided. The polyester has been made by bulk polymerization, including heating condensing wholly aromatic precursors to form a prepolymer in the presence of an alkali or alkaline earth metal salt, and advancing the prepolymer to the required degree of polymerization. The metal salt is added in an amount effective to render the melting and crysta71ization temperatures substantially reproducible with respect to melt processing of the polyester, and the polyester is an oxybenzoyl polyester which comprises recurrent moieties of the following formula:

b~`~9 ~o43-cl [~ }
VII P VIII
~ 0 ~ 0~

o IXa where n is zero or one, q:r is 10:15 to 15:10, p:q is about 1:100 to 100:1, p + q ~ r is about 3 to 600, the carbonyl groups of the moiety of formual ~II or VIII are linked to the oxy groups of the moiety of formula VII or IXa, and the oxy groups of the moiety of formula VII or IXa are linked to the caronly groups of the moiety of formula VII or VIII.
The bulk condensation ~f aromatic polyesters is described in the patent literature and broadly considered involves an alkan-oylation step in which a suitable dicarboxylic acid, hydroxyben-zoic acid and diol are reacted with an acid anhydride, a prepoly-merization step in the reaction product of the first step is poly-condensed to prepare a prepolymer and the prepolymer is thereafter heated to produce a polycondensate of the desired degree of poly-merization.
The polyesters useful in the present invention can also be chemically modified by various means such as by inclusion in the polyester of monofunctional react~n~s such as benzoic acid or tri- or higher functional reactants such as trimesic acid or cyan-uric chlorid2. The benzene rings in these polyesters are prefer-ably u~su~stituted bu~ can be substi~uted with non-inter~ering substituents, examples of which include among other halogen such as chlorine or bromine, lower alkoxy such as methoxy and lower alkyl such as methyl.
The salt can be an organic or an inorganic salt. More - 6a -,, "3 particularly, the following sal-ts can be employed: aluminum j,acetate, calcium acetate, calcium sulfate, copper acetate, mag-~nesium acetate, magnesium terephthalate, potassium acetate, potas-isium chloride, potassium phosphate~ sodium acetate, sodium sulfate !and potassium bisulfate.
While the addition of the salt at any stage of the pro-cedure is contemplated, it has been found to be particularly effec-tive, and to provide markedly superior properties in ihe articles Imolded from the oxybenzoyl polyester resin, if the salt is added Iwith the monomer charge.
The salt can be added as solid or as a solution at a temperature above the melting point of the salt. It is also possible to add the salt in a solution when incorporation is jeffected at a lower temperature.
ll Broadly, the salt has been added over a range of from about 25.0 parts per million to about 500 parts per million.
¦ The exact mechanics by which the processability of the polyester and the appearance and properties of articles molded from llthe polyester is markedly enhanced by the addition of the defined j salts is not fully understood. However, it has been observed that the retention of peak heights in repeated endothermic transitions and the achievement of consistent exothermic transitions is signif-icantly and materially improved when the defined salts are employed j~in the processing of the polyesters.
ll The aromatic oxybenzoyl polyester polymers are known to display an endothermic transition which corresponds to a melting f the polyester. On cooling, an exothermic transition or crystal-¦~lization occurs. Where a strong exotherm is observed, the transi-I tions are described as reversible. Observations and the results Idescribed in later tables demonstrate that the addition of a salt, ¦Isuch as potassium sulfate, has greatly enhanced the reversibility of the peaks detected in the differential scanning calorimeter or DSC.
In determining the retention of peak height, the endo-thPrm fn~ thP. firs~ and the second heating cycles are recorded on ~ 5~~9 the same scale. The distances from base line to the maxima are determined and the height of the first cycle peak is divided by the height of the second cycle peak (x 100). This value is expressed l!as "Percent Retention". I' !I When the endotherms are measured on the aromatic oxyben- 1, ,jzoyl polyesters which do not contain a salt, it has been found , that in the second cycle peaks the onset of transition is difficult I to define and the breadth or broadness of the heating curve makes it difficult to determine the peak. Thus, the change in tempera-¦ture between the onset of transition and the occurrence of the ~imaximum temperature is of a gradual nature, providing a heating 'Icur~e which resembles a gently sloping or rounded hill. Such a ,!peak is referred to in this specification and particularly in the Examples thereof as a broad or diffuse peak.
1S '! The second cycle peaks obtained in those instances where I
ia salt has been incorporated in the processing of the aromatic polyesters in accordance with the present invention are sharp and ~clear with well defined temperature curves and in which the temper-llatures of the onset of transition and of peak maximum are easily Idetermined.
I~ general terms, the invention provides a melt-processable wholly aromatic polyester having reproducible melting and crystallization temperatures;
said polyester having been made ~y bulk polymerization, including heat condensing 2 5 wholly aromatic precursors to fo~n a prepolymer in the presence of an aL~ali or aL~caline earth metal salt, and advancing the prepolymer to the required degree of polymerization;
said metal salt 'oeing added in an amount effective to render said melting and crystallization temperatures substantially reproducible with respect ~o melt processing of said polyester, a~

;5~

said polyester being ar, oxybenzoyl polyester which comprises recurrent moieties of the follo~ing formulas:
5 L~ t~ ~
s VII P VIII q .
10 to~o r IX~
where n is zero or one; q:r is about 10:15 to 15:10; p:(q i r) ls greater than about 1:4; p + q ~ r is abou~ 5 to 600; the carbonyl groups of the moiety of formula VII or VIII are linked to the oxy groups of the moiety of formula VII or IXa; and the oxy groups of the moiety of formula VII or IXa are linked to the carbonyl groups of the moiety of formula VII or VIII.
The invention can also be defined, in general terms a.s a melt-processable wholly aromatic polyester having repro-ducible melting and crystallization temperatures;
said polyester having been made by buLIc polymerization, including heat condensing wholly aromatic precursors to form a prepolymer in the presencç of an aL~cali or alkaline earth metal salt, and advancing the prepolymer to the re~uired degree of polymerization;
2 5 said precursors being an aromatic dicarboxylic acid, a hydroxycarboxylic acid, and an aromatic diol;
said metal sal~ ~eing an inorganic salt of p~tassium or magnesium;
said meaa~ lit Ib~ng ~ded with the charge of precursors~ in an arnount effective to render saud melting and crystallization temperatures substantially reproducible wit}., respect to melt processing of said polyester and within the range of about 0.0025 to 0.05 % by weight; and 8a said polyester being an oxybenzoyl polyester which comprises recurrent moieties of the following formulas:
{~ ~{ ]
VII P VIII q 1~ ~0~;0~

I~

where n is zero or on~3; q:r is about 10:15 to 15:10; p:(q I r) is ~reater than about 1:4; p ~ q * r is about 5 to 600; the carbonyl groups of the moiety of formula VII or VIII are linked to the oxy groups of the moiety of formula VII or IXa; and the oxy groups of the moiety of formula ~II or IXa ar~ linked to the carbonyl groups of the moiety of formula VII or VIII.
.i q (~
Another general definition of the invention describes a melt-processable ~holly aromatic polyester having reproducible melting and crystallization temperatures;

said polyester having been made by bulk polymerization, including he.at condensing wholly arom~tic p~curscr~ r,c~ ~orm a prepolymer in the presence of an aLkali or alkaline 2 5 earth me~al s~ aE~d adva~ing the prepolymer to the required degree of polymerization;
sa~ p~ecursors being terephthalic acid, hydroxybenzoic acid and dihydroxybiphenyl;
- said metal salt being a sulfate or chloride of potassium or magnesium;

8b ~5~

said metal salt being added with thc charge of precursors, in an amount effective to render said melting and crystallization temperatures substantially reproducible with respect to injection molding of said polyester and within the range of about 0.0025 to 0.05% by weight;
said polyester having a melting temperature of at least about 378C; and said polyester being an oxybenzoyl polyester which comprises recurrent moieties of the following formulas:
10 jo~ll~ Lll~ll]
VII p VIIL~ q 1 5 L r IXC

where q:r is about 10:15 to lS:10; p:(q + r) is greater than about 1:4; p + q + r is about S to 600; the ~arbonyl groups of the moiety of formula VII or VIIIa are linked to the oxy groups of the moiety of formula VII or IXc; and the oxy groups of the moiety of formula VII or IXc are linked to the carbonyl groups of the moiety of forrnula VII or VIIIa.
In an~ther aspect~ the invention provides a process for making a melt-processable wholly aromatic polyester having reproducible melting and crystallization temperatures, comprising:
2 5 heat condensing, in buLk, wholly aromatic precursors to form a prepolymer in the presence of an aLkali or alkaline earth metal salt; and advancing the prepolymer to the required degree of polymerization;
said precursors being an aromatic dicd:boxylic acid, a hydroxycarboxylic acid, and an aromatic diol, and wherein condensation of said precursors is by aL~canoylation with an 3 0 acid anhy~ide;
said metal salt being an inorganic salt of potassium or rnagnesium;

8c said metal salt being added with the charge of precursors, in an amo~lnt effective tO
render said melting and crystallization temperatures substan~ially reproducible with respect to melt processing of said polyester and within the range of about 0.0025 to 0.05 % by weight; and said polyester being an oxybenzoyl polyester which comprises reculTent moieties of ~e following fo~nulas:
10 -E~-ll-} ~II~c~
~ VII P VIII q 5 -E ~;; ~
r~

where n is zero or one; q:r is about 10 15 to 15:10; p (q + r) is greater than about 1:4; p + q + r is about 5 to 600; the carbonyl groups of the moiety of formula VII or VIII are linked to the oxy groups of the moiety of formula VII or IXa; and the oxy groups of the moiety of formula VII or IXa are linked to the carbonyl ~ro~ps of the moiety of formula VII or VIII.

The invention is illustrated by the following examples which are not to be construed as limiting the present invention, the scope of which is defined by the appended claims.

'.

A reaction vessel was charged with 268 pounds of 4,4'-dihydroxy biphenyl, 396 pounds of p-hydroxybenzoic acid, 238 pounds jof terephthalic acid, and 690 pounds of a etic anhydride. It was !blanketed with nitrogen and heated with stirring to reflux which was continued for a minimum of three hours. Distillation with no I

jreturn was then initiated and continued for about 5 l/2 hours while the temperature of the reaction mixture was increased to 315C.
'At this point, 0.71 pounds of distearyl pentaerythritol diphosphite 8d y9 was added and after 10 minutes the thick melt (93.3~ conversion based on distillate yield) was poured into an insulated stainless steel tray and allowed to cool under a nitrogen blanket. It was !Ithen removed and ground (size ~ 1.2 mm, 80% ~ 0.5 mm). The yield of prepolymer after grinding is 90~.
The prepolymer was advanced by tumbling under nitrogen in a rotating oven. The prepolymer is heated from ambient tempera-ture to 365C at a rate of 23C/hr and cooled immediately. The resulting polymer is obtained as a free flowing powder.

¦ The procedure of Example 1 was repeated exactly using the same materials and procedures with the single exception of the laddition of 57 g of potassium sulfate to the reaction vessel with jithe monomers charge.
ll The DSC (Differential Scanning Calorimeter) endothermic and exothermic peaks for the first and second heating cycles were determined and are listed below in Table I.

! ¦ TABLE I

¦ DSC Endotherm Peak DSC Exotherm Onset I Heating Cycle Cooling Cycle _lst 2nd lst 2nd Example 1 410 weak* 366 355 Example 2 421 419 381 381 ~* The peak recorded here is of a broad and diffuse nature and does I~not represent a sharp, clear-cut peak.

I EXA~lPLE 3 l l A reaction vessel was charged with 204.0 g (1.095 mole) of 4,4'-dihydroxy biphenyl, 301.1 g (2.18 moles) of p-hydroxy-l~benzoic acid, 181.1 g (1.09 mole) of terephthalic acid, and 526.6 g ¦1 (5.158 moles) of acetic anhydride, was blanketed with nitrogen and;

_ g _ `'heated with stirring to reflux which was continued for a minimum of three hours. Distillation with no return was then initiated and continued for about 5 1/2 hours while the temperature of the reaction mixture was increased to 315C. At this point, 0.76 g of 'distearyl pentaerythritol diphosphite was added and after 10 min-'utes the thick melt (93.3% conversion based on distillate yield) was poured into a stainless steel beaker lined with aluminum foil 'land maintained at 300C. The prepolymer was kept under a nitrogen 'blanket at 300C for 20 hours, then removed, allowed to cool and ground (size ~ 1.2 mm, 80~ C 0.5 mm). The yield of prepolymer after grinding is 90~. 1 The prepolymer was advanced by tumbling under nitrogen iin an aluminum drum which is rotated in an oven. The prepolymer l'is heated from 204 to 354C and maintained at the higher tempera-'Iture for one hour. On cooling, the resulting polymer is obtained las a free flowing powder.
.j . I
,I EXAMPLE 4 "

The procedure of Example 1 was repeated exactly using the I same materials and procedures with the single exception of the lladdition of 0.067 g of potassium sulfate to the reaction vessel jwith the monomers charge.
The DSC (Differential Scanning Calorimeter) endothermic peaks for the first and second heating cycles were determined and are listed below, together with the percent retention of the endo-1l thermic peak height, in Table II.

T~BLE II
¦ PercentDSC Endotherm Peak Retention of Heating Cycle I Endo Peak Ht 1st 2nd 1l Example 3 34 422 417*
Example 4 107 416 429 *The peak recorded here is of a broad and diffuse nature and does ~not represent a sharp, clear-cut peak.

i11 - 10 -i ll ~
1'l Similar comparisons were made for several other polyes- j ters, the control being prepared in accordance with the procedure ~of Example 1 and the potassium sulfate-containing polyester being `prepared in accordance with the procedure of Example 2. The ¦Iresults are listed in Table III below.

¦ TABLE III
K2SO4 PercentDSC Endotherm Peak Added Retention ofHeating Cycle p~m Endo Peak Ht ls~ 2nd Example 5 0 27 414 412*
Example 6 110 71 414 422 Example 7 0 40 418 417*
Example 8 110 75 422 426 ¦I*The peak recorded here is of a broad and diffuse nature and does 1 not represent a sharp, clear-cut peak.
As demonstrated, the salt-containing polyester showed a significantly improved percent retention of endothermic peak height.
. I
Comparisons are provided in Table IV between controls Iprepared in accordance with Example 1 and salt-containing poly-esters prepared in accordance with Example 2. The same control was used in Examples 10, 12, 16, 20 and 22 but is set forth sep-arately in order to provide more immediate comparison with the Ipolyesters oE Examples 9, 11, 15, 19 and 21.

! PPM of Percent l Salt Cation Retention l _ !
I Ex. 9Aluminum Acetate 98 50 Ex. 10 Control 0 22 ¦ Ex. 11 Calcium Acetate 152 35 Ex. 12 Control 0 22 Ex. 13 Copper Acetate 84 84 Ex. 14 Control 0 32 ¦ Ex. 15 Magnesium Acetate 126 86 Ex. 16 Control 0 22 Ex. 17 Potassium Chloride 100 70 Ex. 18 Control 0 18 Ex. 19 Sodium Acetate 73 38 Ex 20 Control 0 22 ¦ Ex 21 Sodium Sulfate 73 38 Ex. 22 Control 0 22 Similar significant improvements in the percent retention as compared to controls having broad or diffuse second cyclic peak~

were obtained when the following salts were employed in lieu of those salts specifically recited in Table III; calcium sulfate, magnesium terephthalate, potassium acetate, potassium phosphate ~and potassium bisulfate.

`
, EXAMPLE 23 A reaction vessel was charged with 344.5 pounds of 4,4'-dihydroxy biphenyl, 514.0 pounds of p-hydroxyben~oic acid, 309.0 pounds of terephthalic acid, 896.0 pounds of acetic anhydride, and 57.0 grams of potassium sulfate. It was blanketed with nitrogen il ' and heated with stirring to reflux which was continued for a mini- I
l i l mum of three hours. Distillation with no return was then initiated and continued for about 5 1/2 hours while the temperature of the reaction mixture was increased to 315C. At this point, 416.0 grams of distearyl pentaerythritol diphosphite was added and after 10 minutes the thick melt (93.3% conversion based on distillate yield) was poured into an insulated stainless steel tray, blanketed with nitrogen and allowed to cool. It was then remo~ed and ground (size ~ 1.2 mm, ~0~ ~ 0.5 mm).
The prepolymer was advanced by tumbling under nitrogen in a rotating oven. The prepolymer is heated from ambient temper-ature to 365C and cooled immediately. The resulting polymer is obtained as a free flowing powder. The polymer is characterized by first and second endotherm peaks of 416 and 418 and by first and second exotherm points of 377 and 379.

A series of 65 runs was made in which polyesters were prepared according to the procedure of Example 33, employing 93 par-ts per million of potassium sulfate based on the final polymer. The mean average exotherm onset on first cycle was deter-t~

,, .

mined to be 377.8 and the mean average exotherm onset for second cycle was determined to be 378.4~. The closeness of these points is extremely significant in relation to consistency and reproduc-ibility in injection molding operations. The products obtained on 5 ~ the injection molding of the polyesters were of high quality.
In the Tables set forth above the amount of salt used is based upon parts per million in the finished polymer.
In the above Examples and in the appended claims, the term "advancing" is to be understood as polymerization in the solid I state.

/
/
/

I
I

Il, - 13 -' I .

Claims

The embodiments of the invention in which an exclusive right or privilege is claimed are defined as follows:

1. A melt-processable wholly aromatic polyester having reproducible meltng and crystallization temperatures;
said polyester having been made by bulk polymerization, including heat condensing wholly aromatic precursors to form a prepolymer in the presence of an alkali or alkaline earth metal salt, and advancing the prepolymer to the required degree of polymerization;
said metal salt being added in an amount effective to render said melting and crystallization temperatures substantially reproducible with respect to melt processing of said polyester, and said polyester being an oxybenzoyl polyester which comprises recurrent moieties of the following formulas:

VII p VIII q IXA r where n is zero or one; q:r is about 10:15 to 15:10; p:(q + r) is greater than about 1:4; p + q + r is about 5 to 600; the carbonyl groups of the moiety of formula VII or VIII are linked to the oxy groups of the moiety of formula VII or IXa; and the oxy groups of the moiety of formula VII or IXa are linked to the carbonyl groups of the moiety of formula VII or VIII.

2. An injection molded article comprising the aromatic polyester of claim 1.

3. The polyester of claim 1 wherein the precursors comprise an aromatic dicarboxylic acid, a hydroxycarboxylic acid and an aromatic diol.

4. The polyester of claim 3 wherein said precursors comprise terephthalic acid, hydroxybenzoic acid and dihydroxybiphenyl.

5. The polyester of claim 3 wherein condensation of said precursors is by alkanoylation with an acid anhydride.

6. The polyester of claim 4 wherein the molar ratios of said precursors are about 1:2:1, respectively.

7. The polyester of claim 1 wherein said melting temperature is at least about 378°C.

8. The polyester of claim 1 wherein said metal salt is added in the amount of about 0.0025 to 0.05% % by weight.

9. The polyester of claim 1 wherein said metal salt is added with the precursor charge.

10. The polyester of claim 1 wherein said metal salt is an inorganic salt of potassium or magnesium.

11. The polyester of claim 10 wherein said metal salt is a sulfate or chloride.

12. The polyester of claim 11 wherein said metal salt is potassium sulfate.

13. A melt-processable wholly aromatic polyester having reproducible melting and crystallization temperatures;
said polyester having been made by bulk polymerization, including heat condensing wholly aromatic precursors to form a prepolymer in the presence of an alkali or alkaline earth metal salt, and advancing the prepolymer to the required degree of polymerization;
said precursors being an aromatic dicarboxylic acid, a hydroxycarboxylic acid, and an aromatic diol;
said metal salt being an inorganic salt of potassium or magnesium;
said metal salt being added with the charge of precursors, in an amount effective to render said melting and crystallization temperatures substantially reproducible with respect to melt processing of said polyester and within the range of about 0.0025 to 0.05% by weight; and said polyester being an oxybenzoyl polyester which comprises recurrent moieties of the following formulas:

VII p VIII q IXA r where n is zero or one; q:r is about 10:15 to 15:10; p:(q + r) is greater than about 1:4; p + + q + r is about 5 to 600; the carbonyl groups of the moiety of formula VII or VIII are linked to the oxy groups of the moiety of formula VII or IXa; and the oxy groups of the moiety of formula VII or IXa are linked to the carbonyl groups of the moiety of formula VII or VIII.

14 A melt-processable wholly aromatic polyester having reproducible melting and crystallization temperatures;
said polyester having been made by bulk polymerization, including heat condensing wholly aromatic precursors to form a prepolymer in the presence of an alkali or alkaline earth metal salt, and advancing the prepolymer to be required degree of polymerization;

said precursors being terephthalic acid, hydroxybenzoic acid and dihydroxybiphenyl;
said metal salt being a sulfate or chloride of potassium or magnesium;
said metal salt being added with the charge of precursors, in an amount effective to render said melting and crystallization temperatures substantially reproducible with respect to injection molding of said polyester and within the range of about 0.0025 to 0.05% by weight;
said polyester having a melting temperature of at least about 378°C; and said polyester being an oxybenzoyl polyester which comprises recurrent moieties of the following formulas:

VII p VIIIA q IXC r where q:r is about 10:15 to 15:10; p:(q + r) is greater than about 1:4; p + q + r is about 5 to 600; the carbonyl groups of the moiety of formula VII or VIIIa are linked to the oxy groups of the moiety of formula VII or IXc; and the oxy groups of the moiety of formula VII or IXc are linked to the carbonyl groups of the moiety of formula VII or VIIIa.

15. An injection molded article comprising the aromatic polyester of claim 14.

16. The polyester of claim 14 wherein the molar ratios of said precursors are about 1:2:1, respectively.

17. The polyester of claim 14 wherein condensation of said precursors is by alkanoylation with an acid anhydride.

18. The polyester of claim 13 wherein condensation of said precursors is by alkanoylation with an acid anhydride.

19. A process for making a melt-processable wholly aromatic polyester having reproducible melting and crystallization temperatures, comprising:
heat condensing, in bulk, wholly aromatic precursors to form a prepolymer in the presence of an alkali or alkaline earth metal salt; and advancing the prepolymer to the required degree of polymerization;
said precursors being an aromatic dicarboxylic acid, a hydroxycarboxylic acid, and an aromatic diol, and wherein condensation of said precursors is by alkanoylation with an acid anhydride;
said metal salt being an inorganic salt of potassium of magnesium;
said metal salt being added with the charge of precursors, in an amount effective to render said melting and crystallization temperatures substantially reproducible with respect to melt processing of said polyester and with the range of about 0.0025 to 0.05 % by weight; and said polyester being an oxybenzoyl polyester which comprises recurrent moieties of the following formulas:

VII p VIII q IXA r where n is zero or one; q:r is about 10:15 to 15:10; p:(q + r) is greater than about 1:4; p + q + r is about 5 to 600; the carbonyl groups of the moiety of formula VII or VIII are linked to the oxy groups of the moiety of formula VII or IXa; and the oxy groups of the. moiety of formula VII or IXa are linked to the carbonyl groups of the moiety of formula VII or VIII.