Branched polyesters prepared from hydroxyfunctional components with functionality in excess of two and their use in physiological separation vehicles

Polyesters are described which are substantially the condensation products of at least one dicarboxylic acid, at least one volatile diol and at least one hydroxyl-functional component with functionality greater than 2 which controls ultimate viscosity. The products are suitable vehicles for the formulated thixotropic gels for centrifugal separation of fluids such as serum into high and low density components of, for example, separation of mixtures of cells on the basis of density.

FIELD OF THE INVENTION 
The present invention relates to polyester fluids useful for preparing 
physiological separation vehicles, which are useful for facilitating 
separations such as of blood serum or plasma from the cellular portion of 
blood. 
BACKGROUND OF THE INVENTION 
The polyester fluids of the invention are conveniently formulated into a 
partitioning composition for use in a blood collection vessel in which the 
blood sample is subjected to centrifugation until the cellular portion and 
serum or plasma are completely separated. 
Note that while blood is the most usual candidate for physiological 
separation, conceivably urine, milk, sputum, stool solutions, meconium, 
pus, semen, spinal fluid and the like could all be subject to 
physiological separation and assay for therapeutic agents and the 
subsequent discussion, while focusing on blood for clarity, is not meant 
to be limited to blood. 
The physical and chemical properties of the partitioning composition are 
such that a continuous, integral seal is provided between the separated 
blood phases, thereby maintaining separation of the phases after 
centrifugation and simplifying removal of the serum or plasma from the 
blood collection vessel. The high volume testing of blood components in 
hospitals and clinics has led to the development of various devices to 
simplify the collection of blood samples and preparation of the samples 
for analysis. Typically, whole blood is collected in an evacuated, 
elongated glass tube that is permanently closed at one end and sealed at 
the other end by a rubber stopper having a diaphragm which is penetrated 
by the double-tipped cannula used to draw the patient's blood. After the 
desired quantity of blood is collected, the collection vessel is subjected 
to centrifugation to yield two distinct phases comprising the cellular 
portion of the blood (heavy phase) and the blood serum or plasma (light 
phase). The light phase is typically removed from the collection vessel, 
e.g., via pipette or decantation, for testing. 
It has been proposed heretofore to provide manufactured, seal-forming 
members, e.g., resilient pistons, spools, discs and the like, in blood 
collection vessels to serve as mechanical barriers between the two 
separated phases. Because of the high cost of manufacturing such devices 
to the close tolerances required to provide a functional seal, they have 
been supplanted by fluid sealant compositions. Fluid sealant compositions 
are formulated to have a specific gravity intermediate that of the two 
blood phases sought to be separated, so as to provide a partition at the 
interface between the cellular and serum phases. Such compositions 
typically include a polymer base material, one or more additives for 
adjusting the specific gravity and viscosity of the resultant composition, 
and optionally, a network former. Representative fluid sealant 
compositions developed in the past include: styrene beads coated with an 
anti-coagulant; silicone fluid having silica dispersed therein; a 
homogenous, hydrophobic copolyester including a suitable filler, e.g., 
silica; a liquid .alpha.-olefin-dialkylmaleate, together with an aliphatic 
amine derivative of smectite clay or powdered silica; the reaction product 
of a silicone fluid with a silica filler and a network former; and a 
mixture of compatible viscous liquids, e.g., epoxidized vegetable oil and 
chlorinated polybutene, and a thixotropy-imparting agent, e.g., powdered 
silica, and liquid polyesters. Also, random copolymers have been made of a 
diol and large quantities of a dicarboxylic acid with pendent, long 
(C.sub.9 to C.sub.13) olefin groups as well as random copolymers of a diol 
and large quantities of a dicarboxylic with a long olefin along its 
backbone, such as a C.sub.36 dimerized fatty acid. Such polyester 
compositions have proved useful as functional blood partitioning 
compositions having reduced affinity for therapeutic agents present in 
blood such as phenobarbital and imipramine. See, for example, W. L. 
O'Brien, U.S. Pat. No. 5,124,434, the entire disclosure of which is 
incorporated by reference in the present specification, as if set forth 
herein in full. 
Ideally, a commercially useful blood partitioning composition should 
maintain uniform physical and chemical properties for extended time 
periods prior to use, as well as during transportation and processing of 
blood samples, readily form a stable partition under normal centrifugation 
conditions and be relatively inert or unreactive toward the substance(s)in 
the blood, therapeutic and otherwise, whose presence or concentration is 
to be determined. 
SUMMARY OF THE INVENTION 
The invention is a viscous liquid branched polyester, which comprises the 
reaction product of at least one hydroxyl-functional initiator with 
functionality greater than 2, at least one dicarboxylic acid chain 
extender, at least one diol chain extender and at least one monocarboxylic 
acid chain terminator. The invention includes process for making the 
polymer and its use in physiological separation vehicles. 
The polyester fluids of the invention are readily formulated together with 
other ingredients, typically a suitable filler, such as silica, and 
compatible surfactant or other coupling agent, into functional blood 
partitioning compositions, as is well known in the art. The density of the 
finished blood partitioning composition is controlled within prescribed 
limits, so that during centrifugation the composition becomes stably 
positioned at the interface between the serum or plasma phase and heavier 
cellular phase and, when centrifugation is terminated, forms a continuous 
integral barrier within the blood collection vessel to prevent the two 
phases from recombining or mixing, especially when decanting or pipetting 
the serum or plasma. The blood partitioning compositions of the invention 
are advantageously employed in small amounts, on the order of 1-5 g., in a 
10 ml blood collection vessel of the type previously described which are 
then ready for use in blood sampling and analysis in the usual way. The 
polyester-based physiological separation vehicles of the present invention 
are especially suited for use in blood separation procedures. 
Principle advantages of the invention include: 1) Relatively high purity, 
highly reactive components produced inexpensively in high tonnages are 
employed. 2) Procedures are simple and self-limiting to a large extent. 3) 
Residual monomer content is extremely low. 4) A useful density range for 
use with or without fillers is readily available. 5) Metallic catalyst 
residues are absent since no ester interchange procedure is necessary to 
achieve target viscosity. Note that, except in the examples, all 
quantities found hereinafter shall be understood to be modified by the 
term "about."

DETAILED DESCRIPTION OF THE INVENTION 
The polyester is made by condensation reaction of the ingredients, the 
hydroxyl-functional initiator, the diol, the dicarboxylic acid and the 
monocarboxylic acid. 
The best results in terms of progress toward the target viscosities were 
obtained using reactor charges comprising a triol-diol mixture, a mixture 
of two dicarboxylic acids in equivalent ratios appropriate to provide the 
desired density and a monocarboxylic acid to control functionality and 
limit molecular growth. The small amount of organic distillates which 
accompany the water of reaction are not recaptured. Table 1 and the 
equation following are believed to describe preferred embodiments of the 
invention. Table 1 is in the form of a matrix, the equivalents (e) of each 
reactant being multiplied and summed with the functionality (f) of each 
reactant to arrive at the theoretical gel point desired. 
TABLE 1 
______________________________________ 
Typical 
Reactants, equivalents of which 
Equivalent 
Functionality 
n are "e" Weight "f" 
______________________________________ 
1 isostearic acid 286 1 
2 pelargonic acid 125 1 
3 adipic acid 73 2 
4 dodecanedioc acid 115 2 
5 phthalic anhydride 74 2 
6 mother liquor acid.about.C.sub.8 acid 
91 2 
7 azelaic acid 95 2 
8 dimer acid 288 2 
9 propylene glycol 38 2 
10 1,3-butylene glycol 
45 2 
11 1,4-butanediol 45 2 
12 ethylene glycol 31 2 
13 neopentyl glycol 52 2 
14 trimethylolpropane 43.3 3 
15 glycerol 31 3 
16 APG-12 94.3 5.25 
______________________________________ 
The critical gel point (.alpha..sub.c), equals 1/(f.sub.avg -1), which in 
turn can be calculated for each embodiment via the relationship: 
.alpha..sub.c =1/((.SIGMA.(e.sub.1-16 
.multidot.f.sub.1-16)/.SIGMA.e.sub.1-16)-1). Adjustment of the formulas to 
provide a critical gel point (.alpha..sub.c) of 0.83 or slightly higher, 
to 0.93, permits viscosities between 2500 and 10,000 cSt at 99.degree. C. 
to be obtained without gelation. 
The viscosity target is .gtoreq.3000 cSt/99.degree. C. and the density 
target is .rho..sub.25 =1.02-1.045 g/cc (preferably 1.02-1.035 g/cc) and 
.gtoreq.1.05 g/cc, using adipic-dimer and phthalic dimer, respectively. 
The presence of one volatile diol is advantageous for reasons other than 
the facilitation of ester interchange, since interchange is not necessary 
for viscosity development in the instances described. Where a relatively 
common low equivalent weight diol is shown, it is used for economic 
reasons and convenience in adjusting total functionality of the mixture. 
Branched formulations given as examples of the types of materials we are 
hoping to establish as functional fluids for physiological separations are 
formulated on the following principles: 
1. A framework of diol (usually, but not necessarily, propylene glycol) and 
triol (such as glycerine), with a monobasic terminator to permit 
achievement of high degrees of condensation without gelation, is 
established. The framework permits introduction of 0.7 additional 
equivalents of acid to bring it into balance. 
2. An equivalents excess of hydroxyl is allowed for, in this case 4%, which 
avoids stalling and favors fluidity; the remaining acid component is then 
0.66 eq. 
3. The dibasic acid parents of the repeating units are charged at 
equivalent fractions defined as: equivalents used/total eq. dibasic acids. 
At least four different ratios are used to determine the 
composition-density relationship within the framework of para. 1. 
4. The critical gel point is calculated as shown in table 1. Experience has 
taught that when glycerine is used as the source of branch units, the 
reaction can be carried to a degree of completion which substantially 
exceeds the calculated value (F. W. Billmeyer, Jr., Textbook of Polymer 
Science, 2nd Ed., New York, Wiley, 1971, pp. 272-274). The acid and 
hydroxyl values reported generally represent .gtoreq.90% conversion of 
functional groups. 
Working examples in the adipic-dimer range were successfully condensed to 
3000-4000 cSt/99.degree. C., exhibiting .rho..sub.25 1.024 and 1.044 g/cc, 
and presumably feasible from 1.01 to 1.055 g/cc; for higher density 
requirements, it is necessary to change the framework of 
pelargonic-glycerol-PG within which the ratios of dibasic acids have been 
varied to achieve the required properties. 
An embodiment of the invention is the conversion of a small part of the 
product to a soap of a monovalent or multivalent ion, using the residual 
acid value as a reactive site. The pseudopolymeric characteristics of such 
a soap or ionomer would be expected to confer characteristics of a 
reinforced polyester fluid to the base material at low loading. 
The details of the viscous polyester fluids, ingredients and process will 
now be discussed. 
The polyesters according to the invention are produced in the form of 
viscous liquids, having a density at room temperature in the range of 
1.015-1.09 g/cc and preferably from 1.02 to 1.035 g/cc. 
The physical and chemical properties of these polyesters are uniformly 
maintained over extended periods prior to use, as well as during 
transportation and processing of blood samples. 
The branched polyesters of the invention are characterized by having an 
acid value of 2 to 15, preferably 6 to 9 and a hydroxyl value of 10 to 70, 
preferably 38 to 54. The finished branched polyesters of the invention 
will typically have a viscosity greater than, or equal to, 1700 cSt, and 
preferably greater than, or equal to, 3000 cSt, when measured at 
99.degree. C. 
Fluids having the above-described properties are especially useful as blood 
partitioning agents in blood collection vessels where they provide a 
continuous integral barrier or seal between the serum and clot portions of 
blood. In other words, the fluid completely partitions the separated 
phases so that the serum and cellular or clot portions are no longer in 
contact at any point, forming a unitary seal which firmly adheres to the 
inner surface of the blood collection vessel. By forming a continuous, 
integral barrier in this way, it is possible to easily remove the serum or 
plasma portion by decanting or pipetting, with the clot portion remaining 
undisturbed in the collection vessel. 
The hydroxyl-functional initiator has a functionality greater than 2. 
Examples include trimethylolpropane, trimethylolethane, glycerol, 
1,2,6-hexanetriol, pentaerythritol, alkyl polyglycosides such as the 
lauryl ether of mixed glucose dimer-trimer, sorbitol, castor oil, and 
their alkoxylates and the like. 
The dicarboxylic acid member of the polyesters of the invention is 
primarily selected for economy in achieving the selected properties and 
the optimal choice may depend on market value. However, typical candidate 
diacids include: adipic acid, phthalic anhydride, dodecanedioic acid, 
dodecenylsuccinic acid, succinic acid, glutaric acid, pimelic acid, 
suberic acid, azelaic acid, sebacic acid, undecanedioic acid, terephthalic 
acid, isophthalic acid, dimerized fatty acids and mixtures thereof. 
Dimerized fatty acids are also known as polymerized fatty acids, which 
include aliphatic dicarboxylic acids having from 32-40 carbon atoms 
obtained by the polymerization of olefinically unsaturated monocarboxylic 
acids having from 16-20 carbon atoms, such as palmitoleic acid, oleic 
acid, linoleic acid, linolenic acid and the like. Polymeric fatty acids 
and processes for their production are well known. See, for example, U.S. 
Pat. Nos. 2,793,219 and 2,955,121. Polymeric fatty acids particularly 
useful in the practice of this invention preferably will have as their 
principal component C-36 dimer acid. Such C-36 dicarboxylic acids are 
obtained by the dimerization of two moles of a C-18 unsaturated 
monocarboxylic acid, such as oleic acid or linoleic acid, or mixtures 
thereof, e.g., tall oil fatty acids. These products typically contain 75% 
by weight or more of C-36 dimer acid and have an acid value in the range 
of 180-215, saponification value in the range of 190-215 and neutral 
equivalent from 265-310. Examples of commercial dimer acids of this type 
are EMPOL.RTM. 1008, EMPOL.RTM. 1015, EMPOL.RTM. 1061, EMPOL.RTM. 1016, 
EMPOL.RTM. 1018, EMPOL.RTM. 1022 and EMPOL.RTM. 1024, all trademarked 
products of the Henkel Corporation, and identified hereinafter as a class 
as "C-36 dimer acid." The dimer acids may be hydrogenated prior to use. To 
increase the C-36 dimer content and reduce the amount of by-product acids, 
including unreacted monobasic acid, trimer and higher polymer acids, the 
polymeric fatty acid may be molecularly distilled or otherwise 
fractionated. EMPOL.RTM. 1016, used in the examples below, is a typical 
C-36 dimer acid and has an acid value in the range from 190 to 198 and a 
saponification value of 197. 
It will be apparent to those skilled in the art that the various 
art-recognized equivalents of the aforementioned dicarboxylic acids, 
including anhydrides thereof, may be employed in preparing the polyesters 
of the invention. Accordingly, as used herein, the term "acid" is intended 
to encompass such acid derivatives. Mixtures of acids and anhydrides may 
also be reacted to obtain the desired product. Also, the acid residues of 
the polyester may originate from acid chlorides or other acid precursors. 
Suitable diols which may be reacted with the above described dicarboxylic 
acid(s) to yield the polyesters of the invention include diols of the 
formula: 
##STR1## 
in which R.sub.1, R.sub.2, R.sub.3, R.sub.4, R.sub.5 and R.sub.6 are 
independently selected from the group consisting of hydrogen and an alkyl 
group having 1-4 carbon atoms, n =1-4 and x=0-4. Representative diols 
falling within the foregoing formula include ethylene glycol, 
neopentylglycol, 1,3-butanediol, 1,4-butanediol, propylene glycol, 
diethylene glycol, triethylene glycol, 1,2-butanediol, 
3-methyl-1,5-pentanediol, 1,2-pentanediol, 1,3-pentanediol, 
1,4-pentanediol, 1,5-pentanediol, hexylene glycol, 1,6-hexanediol, 
polytetramethylene ether diol, cyclohexanedimethanol, benzenedimethanol, 
polyoxypropylene diol, dipropylene glycol, trimethylpentanediol, 
propoxylated bisphenol A, 1,4-Bis(2-hydroxyethoxy)benzene, tetramethylene 
adipate glycol, polycaprolactone glycol, polyhexamethylenecarbonate 
glycol, 1,6-hexanediol and hydrogenated bisphenol A and the like and 
mixtures thereof. The preferred diols contain from 3-5 carbon atoms, with 
particularly useful polyester products being obtained using neopentyl 
glycol, propylene glycol, triethylene glycol, or mixtures thereof. In a 
particularly preferred embodiment of the invention, in which a mixture of 
neopentyl glycol and propylene glycol is used, the amount of neopentyl 
glycol comprises 70 to 95 equivalent percent, and the amount of propylene 
glycol comprises 5 to 30 equivalent percent of the total diol component 
equivalents. The diol and triol residues of the polyesters of the 
invention may originate from sodium alcoholates or other alcohol 
precursors. 
The monocarboxylic acid chain terminator can be any organic acid, but 
aliphatic fatty acids are preferred. Examples include isostearic acid, 
coconut fatty acids, oleic acid, linoleic acid, tallow fatty acids, 
stearic acid, caprylic acid, capric acid, lauric acid, myristic acid, 
palmitic acid, soya fatty acid, pelargonic acid, heptanoic acid and the 
like. 
If an improvement in color is desired, the polyester may be bleached by any 
of the well known and acceptable bleaching methods, e.g., using hydrogen 
peroxide or chlorite. Alternatively, the polyester may be decolorized by 
filtering through a filter aid, charcoal or bleaching clay. 
To prepare the polyesters, a small excess (based on the equivalents of acid 
present) of a volatile diol may used. The excess diol also serves as the 
reaction medium and reduces the viscosity of the reaction mixture. The 
excess diol is distilled off as the esterification is carried to 
completion and may be recycled to the reactor if desired. Generally, 20% 
by weight excess volatile diol, based on the total weight of the diol 
component, will suffice. Where a volatile and a relatively involatile diol 
are present together, any excess is supplied as additional volatile diol. 
The more volatile glycols are commonly used for this purpose. Among them 
are propylene glycol, ethylene glycol, 1,3-butanediol, 1,4-butanediol, 
1,2- butanediol, 3-methyl-1,5-pentanediol, 2-methyl-1,3-propanediol and 
the like. 
The source of the acids or acid derivatives and the manner by which the 
dicarboxylic acid blends are prepared, in those embodiments where such 
blends are used, is of no consequence so long as the resulting blend 
contains the specified acids or acid derivatives in the required ratios. 
Thus, dicarboxylic acid or acid derivative blends may be obtained by 
mixing the individual acid components. On the other hand, mixtures of acid 
obtained as by-products from various manufacturing operations and which 
contain one or more of the necessary acid components may be advantageously 
utilized. For example, mixed succinic, glutaric and adipic acids may be 
obtained as a co-product from the manufacture of adipic acid and may be 
conveniently blended with any other acid, e.g. oleic dimer acid, selected 
for inclusion in the polyester of the invention. 
Preparation of blood partitioning compositions using the polyesters of the 
invention may be carried out in the manner described in commonly owned 
U.S. Pat. Nos. 4,101,422 and 4,148,764, the entire disclosures of which 
are incorporated by reference in the present specification, as if set 
forth herein in full. 
The following examples are presented to illustrate the invention more 
fully, and are not intended, nor are they to be construed, as a limitation 
of the scope of the invention. 
EXAMPLE 1 
A 5 liter reactant charge was prepared for a one-pot synthesis, the 
ingredients were in the following ratio: 0.518 equivalent adipic acid, 0.3 
eq. pelargonic acid, 0.142 equivalent EMPOL.RTM. 1016, 0.3 equivalent 
propylene glycol, and 0.7 equivalent glycerol. It was heated to a final 
temperature of 200.degree. C. until esterification was complete as 
indicated by a cessation in the reduction of the acid value of the 
reaction product. The polyester recovered had an acid value equal to 8.2 
mg KOH/g, a hydroxyl value of 53.6, 99.degree. C. kinematic viscosity of 
3890 cSt and a specific gravity at 25.degree. C. of 1.024. This 
corresponds in FIG. 1 to a density 3 of 1.024 g/cc. 
EXAMPLE 2 
A 5 liter reactant charge was prepared for a one-pot synthesis, the 
ingredients were in the following ratio: 0.585 equivalent adipic acid, 0.3 
eq. pelargonic acid, 0.075 equivalent EMPOL.RTM. 1016, 0.3 equivalent 
propylene glycol, and 0.7 equivalent glycerol. It was heated to a final 
temperature of 210.degree. C., followed by low-vacuum stripping. The 
polyester recovered had an acid value of 6.5 mg KOH/g, a hydroxyl value of 
38.4, 99.degree. C. kinematic viscosity of 3870 cSt and a specific gravity 
at 25.degree. C. of 1.0444. This corresponds in FIG. 1 to a density 11 of 
1.044 g/cc. 
EXAMPLES 3-7 
Additional experiments were done with pelargonic acid, propylene glycol and 
glycerol equivalents as above, but varying the adipic acid within 0.515 to 
0.634 equivalents, while varying the EMPOL 1016 from within 0.145 to 0.026 
equivalents. The results are shown in FIG. 1 as densities 5, 7, 9, 13 and 
15. When the results of each example are fitted to a curve 1, the density 
of the polyester resulting from the reaction equals 
1.7474-1.9297X+1.2848X.sup.2 g/cc, wherein X equals the equivalents 
fraction of adipic acid. The goodness of fit, r.sup.2, is 0.9922. 
While the present invention has been described and exemplified above in 
terms of certain preferred embodiments, various other embodiments may be 
apparent to those skilled in the art. Accordingly, the invention is not 
limited to the embodiments specifically described and exemplified, but 
variations and modifications may be made therein and thereto without 
departing from the spirit of the invention, the full scope of which is 
delineated by the following claims.