Cyclic tin catalysts are employed for the preparation of branched polyesters from macrocyclic polyester oligomers. They are less susceptible than previously known catalysts to the presence of acidic impurities in the oligomer compositions.

BACKGROUND OF THE INVENTION 
This invention relates to the polymerization of macrocyclic polyester 
oligomer compositions. More particularly, it relates to an improved method 
for such polymerization which is capable of producing novel branched 
polyesters. 
The preparation of macrocyclic poly(alkylene dicarboxylate) oligomers and 
their polymerization to linear polyesters is described in U.S. Pat. Nos. 
5,039,783, 5,214,158 and 5,231,161 and in copending, commonly owned 
applications Ser. Nos. 07/702,577 and 07/978,583. The catalysts employed 
for such polymerization include various organotin compounds and titanate 
esters. 
Polymerization using these Catalysts is quite successful and affords 
polyesters having excellent properties and a wide variety of potential 
applications. However, the catalysts are somewhat sensitive to impurities 
present in the macrocyclic polyesters, particularly acidic impurities 
which can include water, hydroxy compounds and carboxylic acids and their 
anhydrides. 
In the presence of such impurities, the catalyst may be partially 
deactivated and polymerization may be incomplete or may yield polymers 
with low weight average molecular weights. Attempts to increase polymer 
yield by increasing the proportion of catalyst in the polymerization 
mixture cause significant further reductions in the molecular weight of 
the linear polymer, since the catalyst becomes part of the polymer end 
group and increased amounts of catalyst compete for the same proportions 
of structural units in the macrocyclic oligomers. 
Another problem sometimes encountered with linear polyesters prepared from 
macrocyclic oligomers, particularly when employed in fiber-reinforced 
composites, is a tendency to flow or "creep" under high load. This 
property is detrimental to the use of such polyesters under high load 
conditions, such as for the fabrication of automobile frames which must 
carry large weights and be extremely rigid and dimensionally stable. 
It would be desirable, therefore, to develop improved catalysts with high 
activity for the polymerization of macrocyclic oligomers containing 
increased proportions of impurities, especially acidic impurities. It 
would be further desirable to convert macrocyclic oligomer compositions to 
branched polyesters having improved dimensional stability, for use as 
load-bearing members in automobiles and the like. 
SUMMARY OF INVENTION 
The present invention provides a novel class of branched polyesters with 
high dimensional stability which may be produced from macrocyclic 
oligomers. Said oligomers and polyesters may be employed in the 
fabrication of fiber-reinforced composites and the like. 
The invention includes branched poly(alkylene dicarboxylates) having the 
formula 
##STR1## 
wherein R.sup.1 is an alkylene or mono- or polyoxyalkylene radical 
containing a straight chain of about 2-8 atoms, R.sup.2 is a C.sub.1-4 
primary alkyl radical, A is a m- or p-linked monocyclic aromatic or 
alicyclic radical, X is a linear or branched organic end group, y has an 
average value of at least about 10 and m is 0 or 1.

DETAILED DESCRIPTION; PREFERRED EMBODIMENTS 
In formula I, the R.sup.2 radicals may be methyl, ethyl, n-propyl or 
n-butyl and are preferably methyl or ethyl. The X radicals are organic end 
groups and may themselves be polymeric. For example, they may have 
structures similar to the portion of formula I to the left of the tin 
atom, bound through oxygen to additional tin atoms. The precise nature of 
the end groups will be apparent to those skilled in the art but is not 
critical for the purposes of the invention. 
The branched polyesters of this invention may be prepared from macrocyclic 
polyester oligomers comprising structural units of the formula 
##STR2## 
wherein R.sup.1 and A are as previously defined. Said macrocyclic 
polyester oligomers may themselves be prepared by contacting at least one 
diol of the formula HO-R.sup.1 -OH and at least one diacid chloride of the 
formula 
##STR3## 
under substantially anhydrous conditions and in the presence of a 
substantially water-immiscible organic solvent, with at least one 
unhindered tertiary amine; said contact being conducted at a temperature 
from about -25.degree. to about +25.degree. C. This procedure is described 
in detail in the aforementioned patents and applications, and it is 
therefore deemed unnecessary to provide a detailed explanation herein. In 
most instances, the products are mixtures of macrocyclic oligomers having 
differing degrees of polymerization. 
To prepare the branched polyesters, the macrocyclic polyester oligomers are 
contacted with a macrocyclic polyester oligomer polymerization catalyst 
having the formula 
##STR4## 
wherein each R.sup.3 is a C.sub.1-10 alkyl radical, preferably a primary 
radical such as methyl, ethyl, n-butyl, n-hexyl, n-octyl, 2-ethylhexyl or 
n-decyl, and most preferably a C.sub.3-10 radical, and Z is 
##STR5## 
The Z value may be a single carbon atom or a tetravalent radical of formula 
IV. The catalysts wherein Z is a single carbon atom are known compounds, 
being disclosed, for example, in U.S. Pat. No. 3,969,319 and in Lin et 
al., ACS Polymer Preprints, 33 (1), 1111-1112 (1993). Their use affords 
branched polyesters having formula I in which m is 0. 
The catalysts in which Z has formula IV are novel trisstannoxanes; they are 
disclosed and claimed in copending, commonly owned application Ser. No. 
08/262,793. They afford branched polyesters in which m is 1. Said novel 
trisstannoxanes may be prepared by the reaction of a dialkyltin oxide of 
the formula (R.sup.3).sub.2 SnO with a triol of the formula R.sup.2 
(CH.sub.2 OH).sub.3, such as 1,1,1-tris(hydroxymethyl)ethane or 
1,1,1-tris(hydroxymethyl)propane, in a molar ratio of at least about 1.2:1 
and preferably about 1.25-1.75:1. The reaction is preferably conducted in 
solution in a substantially non-polar solvent such as toluene and at a 
temperature in the range of about 100.degree.-150.degree. C. An inert 
atmosphere such as nitrogen is usually employed and water is removed as it 
is formed, preferably as an azeotropic mixture with the solvent employed. 
The preparation of the novel catalysts is illustrated by the following 
example. 
Example 1 
A mixture of 2.68 grams (20 mmol.) of 1,1,1-tris(hydroxymethyl)propane, 
10.83 grams (30 mmol.) of dioctyltin(IV) oxide and 25 mi. of toluene was 
heated under reflux in a nitrogen atmosphere in a 3-necked flask equipped 
with a Dean-Stark trap, with removal of water as an azeotropic mixture 
with toluene. After refluxing for 1 hour, the trap was replaced with 
another trap filled with 3A molecular sieves and refluxing was continued 
for 4 hours. The resulting solution was filtered under nitrogen while hot 
and the solvent was removed by distillation. The residue was dried under 
vacuum at 100.degree. C. Upon cooling, the desired 
bis[(5-ethyl-2,2-dioctyl-2-stanna-1,3-dioxacyclohexane 
)-5-methyleneoxy]dioctyltin in impure form solidified to a waxy solid 
having a melting point of 78.degree.-83.degree. C. The crude yield was 
12.5 grams (96.3% of theoretical). A portion of the product, upon 
recrystallization from hexane, melted at 91.degree.-93.degree. C. 
The macrocyclic polyester oligomers are converted to the branched 
polyesters of this invention by contact with said catalyst at a 
temperature in the range of about 160.degree.-300.degree. C., preferably 
160.degree.-250.degree. C. The latter is typically employed in the amount 
of about 0.01-2.0 and preferably about 0.05-1.0 mole percent based on 
structural units in the oligomers. This method of polymerizing macrocyclic 
polyester oligomers is disclosed and claimed in copending, commonly owned 
application Ser. No. 08/262,795. 
The branched polyesters of this invention have advantageous properties in 
addition to their branched structure. For example, they have high 
molecular weights even when prepared from oligomer mixtures with a 
relatively high proportion of acidic impurities. 
The previously disclosed catalysts, including those described in the 
aforementioned patent and application, produce linear polyesters. It is 
within the scope of the invention to employ a mixture of such a catalyst 
with one of formula II to produce a mixture of branched polyesters of this 
invention and linear polyesters. The proportions of the two types of 
catalysts may be varied to afford the desired degree of branching. 
The preparation of the branched polyesters of this invention is illustrated 
by the following examples. 
Examples 2-5 
The macrocyclic oligomers employed were prepared by the reaction of 5 
millimoles of ethylene glycol and 95 millimoles of 1,4-butanediol with 100 
millimoles of terephthaloyl chloride, substantially as described in the 
aforementioned patents and applications. Solutions in methylene chloride 
of the macrocyclic oligomers were divided into two samples; Sample A was 
washed first with aqueous acid, then with aqueous base and finally with 
deionized water, and Sample B with aqueous acid and water only. The 
methylene chloride was then removed by vacuum stripping and the products 
were pre-dried for 15 minutes at 100.degree. C. under vacuum and then 
heated to 190.degree. C. for 15 minutes with magnetic stirring, to form 
melts. 
The molten oligomer melts were returned to atmospheric pressure by addition 
of nitrogen, polymerization catalysts in the desired proportion were added 
by injection and the mixtures were maintained at 190.degree. C. for 20 or 
30 minutes. During polymerization the products crystallized. The yields 
and molecular weights of the polyesters obtained were determined by gel 
permeation chromatography relative to standard polystyrene. The results 
are given in the following table, in comparison with controls employing 
two catalysts not part of the invention. The catalysts are identified in 
Table VII as follows: 
______________________________________ 
I: Formula II, R.sup.3 = octyl, Z = C. 
II: Formula II, R.sup.2 = ethyl, R.sup.3 = octyl, Z has formula III. 
III: Formula II, R.sup.2 = ethyl, R.sup.3 = n-butyl, Z has formula III. 
IV: Dioctyltin bis(2-ethylhexoxide). 
V: Tetra-2-ethylhexyl titanate. 
Catalyst Time, % Mw/ 
Example Identity Mole % min. yield Mw Mn 
______________________________________ 
2B I 0.5 30 100 227,000 
3.73 
3A II 0.5 30 98 517,600 
6.76 
3B II 0.5 20 96 162,600 
2.90 
4A III 0.25 30 100 227,000 
2.93 
4B III 0.25 30 71 99,600 
2.10 
5A III 0.5 30 100 384,000 
6.84 
5B III 0.5 30 98 117,600 
3.04 
Control 1A 
IV 0.5 30 100 115,300 
2.07 
Control 1B 
IV 0.5 30 100 76,600 
1.93 
Control 2A 
V 0.25 30 100 97,100 
1.87 
Control 2B 
V 0.25 30 58 49,200 
1.94 
Control 3A 
V 0.5 30 100 62,700 
2.54 
Control 3B 
V 0.5 30 86 45,800 
2.20 
______________________________________ 
The results in the table show that the branched polymers of the invention 
have uniformly high weight average molecular weights, even when the 
relatively impure B oligomer samples were employed. By contrast, the 
controls when employed with B samples afforded polymers of relatively low 
molecular weight. The higher molecular weight dispersities (Mw/Mn) of the 
polymers formed by the method of this invention are believed to be the 
result of their highly branched structures.