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The present invention relates to polyesters
useful for facilitating the separation of blood serum 5 or plasma from the cellular portion of blood. The
polyesters 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 centri ugation until the cellular portion 10 and serum or plasma are completely separated. 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 15 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 20 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
25 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 30 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 the two blood phases sought to be separated, so as to provide a partition a 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 prior art fluid sealant compositions include: styrene beads coated with an anti-coagulent (U.S. Patent 3,464,890); silicone fluid having silica dispersed therein (U.S. Patent 3,780,935); a
homogenous, hydrophobic copolyester including a
suitable filler, e.g., silica (U.S. Patents 4,101,422 and 4,148,764); a liquid -olefin-dialkylmaleate, together with an aliphatic amine derivative of
smectite clay or powdered silica (U.S. Patent
4,310,430); the reaction product of a silicone fluid with a silica filler and a network former (U.S. Patent 4,386,003); and a mixture of compatible viscous
liquids, e.g., epoxidized vegetable oil and
chlorinated polybutene, and a thixotropy- imparting agent, e.g., powdered silica (U.S. Patent 4,534,798).
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 whose presence or concentration is to be determined.
Inertness to substances sought to be determined is a particular concern when blood collection vessels are used for therapeutic drug monitoring (TDM) , which is assuming an increasingly important role in drug treatment strategies. TDM enables the administration of drugs in the appropriate therapeutic ranges, established through the accumulated experience of clinicians, and consequently reduces the number of patients receiving dosage levels that are either below detection limits or toxic. Administration of drugs under TDM allows one to take into account such factors as drug tolerance developed with passage of time, presence of multiple physical disorders and
synergistic or antagonistic interactions with other therapeutic agents. Among the drugs recommended for administration under TDM are those having dangerous toxicity with poorly defined clinical endpoint, steep dose-response curve, narrow therapeutic range,
considerable inter-individual pharmacokinetic
variability or non-linear pharmacokinetics, as well as those used in long term therapy or in the treatment of life-threatening diseases. By way of example, the evaluation of blood levels of a number of tricyclic antidepressant compounds, such as imipramine or desipra ine, in relation to an empirically
established therapeutic range is reported to be particularly useful in the treatment of seemingly drug-refractive depression. TDM is likewise used to monitor the dosage of anticonvulsant drugs, such as phenytoin and phenobarbital which are administered in the treatment of epilepsy, antitumor drugs, such as methotrexate, and other more commonly prescribed drugs, including, but not limited to digoxin,
lidocaine, pentobarbital and theophylline.

Reports of recent studies on the effect of blood partitioning compositions on drug concentrations in serum and plasma indicate that care must be taken in the selection of polymeric materials which come into contact with the blood samples obtained for drug assay. See, for example, P. Orsulak et al.,
Therapeutic Drug Monitoring, 6:444-48 (1984) and Y. Bergqvist et al. Clin. Chem. , 30:465-66 (1984). The results of these studies show that the blood
partitioning compositions provided in blood collection vessels may account for reduced serum or plasma values, as a result of drug absorption by one or more components of the composition. The reported decreases in measured drug concentrations appears to be
time-dependent. One report concludes that the
observed decreases in drug concentrations may
effectively be reduced by minimizing the interval between collection and processing. Another report recommends that blood samples be transported to the laboratory as soon as possible, with processing occurring within 4 hours. A commercially useful blood collection vessel, however, must produce accurate test results, taking into account routine clinical
practices in large institutions, where collection, transportation and processing of blood samples may realistically take anywhere from about 1-72 hours.

In accordance with the present invention, it has been discovered that certain highly hydrophobic polyesters satisfy the above-noted criteria for incorporation in a clinically useful blood
partitioning composition. The polyesters of the invention comprise, as their reactive components, at least one diol and at least one dicarboxylic acid, including a first dicarboxylic acid containing from 15-36 carbom atoms, which comprises from 10-100 equivalent percent of the total acid component equivalents, and a second dicarboxylic acid, selected from the group of short chain dicarboxylic acids and polymeric fatty acids, which comprises up to 90 equivalent percent of the total acid component
equivalents. The resultant polyester product is a viscous liquid having a density at room temperature (25°C) in the range of 1.01-1.09.
Particularly useful polyester products have been obtained from the reaction of dodecenylsuccinic acid with propylene glycol and from the reaction of
linoleic acid-acrylic acid adduct, as the first dicarboxylic acid, and an acid selected from the group of succinic acid, glutaric, adipic acid, azelaic acid, oleic dimer acid, or a mixture thereof, as the second dicarboxylic acid, with a mixture of neopentyl glycol, and propylene glycol.
The polyesters of the invention are readily formulated together with other ingredients, typically a suitable filler and compatible surfactant, into functional blood partitioning compositions. 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 gm. , 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 blood partitioning compositions of the invention are especially suited for use in TDM procedures,
displaying negligible interaction with commonly monitored therapeutic agents.

The present invention relates to polyesters derived from one or more relatively long-chain
dicarboxylic acids, having 15-36 carbon atoms, optionally, a second dicarboxylic acid, selected from the group of short chain dicarboxylic acids and polymer fatty acids, and a diol. When the reactive components of the polyesters are combined in the prescribed ratios and esterified using conventional esterification techniques, polyester products are obtained having molecular weights from about 3,000 to about 12,000 (number average, as determined by gel permeation chromatography) . The polyesters of the invention are produced in the form of viscous liquids, having a density at room temperature in the range of 1.01-1.09. Particularly notable among the properties of these polyesters is their inertness, making them especially useful in TDM programs. The polyesters of the invention are also highly hydrophobic, exhibiting neglible water solubility. 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. Among the other notable characteristics of these polyesters is the ability to undergo
ultracentrifugation for up to 1 hour at up to 1500 G (G being the ratio of centrifugal acceleration to acceleration of gravity) , without any detectable adverse effect.
The polyesters of the invention are further characterized by having an acid value of 2 or less, an hydroxyl value of 23 or less and a 210°F kinematic viscosity of about 1700-4000 centistokes.

_ ? _

Polyesters 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 polyester 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 reactive components of the polyesters of the invention include at least one dicarboxylic acid, including a first dicarboxylic acid containing 15-36 carbon atoms, a second dicarboxylic acid, selected from the group of short-chain dicarboxylic acids and polymeric fatty acids, and at least one diol. The first dicarboxylic acid is preferably selected from the group of polyalkenylsuccinic acids, adducts of unsaturated monocarboxylic acids or a mixture thereof. The first dicarboxylic acid may be the exclusive constituent of the acid component of the polyester. Alternatively, the second dicarboxylic acid may optionally be added to the acid component.
Short-chain dicarboxylic acids suitable for preparing the polyesters of the invention are
saturated aliphatic acids having 4-12 carbon atoms. More preferably, these acids have from 4-9 carbon atoms and are essentially straight-chain acids.
Representative short chain dicarboxylic acids include succinic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid, sebacic acid, undecanedoic acid and dodecanedoic acid. Mixtures of _ fl _

two or more of such short-chain dicarboxylic acids may be used, if desired.
The polymeric fatty acids which may be used to prepare the polyesters of the invention are obtained by the polymerization of olefinically unsaturated monocarboxylic acids having from 16-20 carbon atoms, such as pal itoleic 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. Patent Nos. 2,793,219 and
2,955,121. Polymeric fatty acids 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. 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, tri er and higher polymer acids, the polymeric fatty acid may be molecularly distilled or otherwise fractionated.
The first dicarboxylic acid comprises from 10-100 equivalent percent of the total acid component
equivalents; whereas the second dicarboxylic acid, when used, may comprise up to 90 equivalent percent of the total acid component equivalents. The equivalent percent of short-chain dicarboxylic acid(s) in the second dicarboxylic acid component will generally range from about 80 to about 100 equivalent percent of the total acid components provided by the second dicarboxylic acid. The polymeric fatty acid, when used, will generally comprise up to about 20 6 . Q .

equivalent percent of the total acid component
equivalents provided by the second dicarboxylic acid. It will be apparent to those skilled in the art that the various art-recognized equivalents of the aforementioned dicarboxylic acids, including
anhydrides and lower alkyl esters 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. Methyl esters are particularly advantageous for the
preparation of the polyesters described herein.
Mixtures of acids, anhydrides and esters may also be reacted to obtain the desired product.
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:

HO(- "Cf-(CR5R6)x-C-0-)nH
R2 R
in which R^, R2, R3 and R are independently selected from the group consisting of hydrogen and an alkyl having 1-4 carbon atoms, n = 1-4 and x = 0-4.
Representative diols falling within the foregoing formula include neopentyl glycol, propylene glycol, diethylene glycol, triethylene glycol, 3-methyl-l,5-pentane diol, 1,2 propane diol, 1,3-butane diol,
1,2-butane diol, 1,2-pentane diol, 1,3-pentane diol, 1,4-pentane diol and the like. The preferred diols contain from 3-5 carbon atoms, with particularly useful polyesters 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 about 70 to about 95 equivalent percent, and the amount of propylene glycol comprises about 5 to about 30 equivalent percent of the total diol component equivalents.
Conventional esterification procedures and equipment are used to obtain the polyester of the invention. The reactive components are normally added to the reaction vessel as a unit charge and the reaction mixture is then heated with agitation at a temperature from about 150-250°C for a period of time sufficient to substantially complete the
esterification reaction. The reaction may be driven to completion by application of vacuum (typically 1-5 mm Hg absolute at 200-250°C) until the desired properties are obtained. Vacuum distillation removes the final traces of water, any excess reactants and small amounts of other volatile materials present in the reaction mixture.
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.
The rate of esterification may be enhanced by the use of known esterification catalysts. Suitable esterification catalysts for enhancing the rate of esterification of free carboxyl groups include phosphoric acid, sulfuric acid, toluenesulfonic acid, methane sulfonic acid, and the like. The amount of such catalyst may vary widely, but most often will be in an amount from about 0.1% to about 0.5% by weight, based on the total reactant charge. Catalysts useful for effecting ester interchange include dibutyltin diacetate, stannous oxalate, dibutyltin oxide, tetrabutyl titanate, zinc acetate and the like. These catalysts are generally employed in an amount ranging from about .01% to .05% by weight, based on the total resistant charge. When such catalysts are used, it is not necessary that the catalyst be present throughout the entire reaction. It is sometimes advantageous in order to obtain products having good color and
relatively low acid value, on the order of 2 mg
KOH/gm, or less, to add the catalyst during the final stages of the reaction. Upon completion of the reaction, the catalyst may be deactivated and removed by filtering or other conventional means.
Inert diluents, such as benzene, toluene, xylene and the like may be employed for the reaction,
however, the use of diluents is not necessary. It is generally considered desirable to conduct the reaction without diluents since the resultant polyester can be directly used as it is obtained from the reaction vessel. A small excess (based on the equivalents of acid present) of the diol component may be used if desired. The excess diol 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, about 20% by weight excess diol, based on the total weight of the diol component, will suffice. The more
volatile glycols are commonly used for this purpose.
A particularly useful blood partitioning agent is obtained by reacting substantially stoichiometric amounts of (i) linoleic acid-acrylic acid adduct, having 21 carbon atoms, as the first dicarboxylic acid component, a second dicarboxylic acid comprising (ii) oleic dimer acid and (iii) a mixture of dimethyl succinate, dimethyl glutarate, and dimethyl adipate, with a diol component comprising neopentyl glycol and propylene glycol. The equivalents ratio of the three dicarboxylic acid components is 1:1:3.55, with the relative approximate weight percentages of the esters in the ester mixture being 1% dimethyl
succinate, 75% dimethyl glutarate and 24% dimethyl adipate. The equivalents ratio of neopentyl glycol to propylene glycol ranges from about 0.75:0.25 to about 0.90:0.10.
Another particularly useful polyester product is obtained from the reaction of essentially
stoichiometric amounts of dodecenylsuccinic acid and propylene glycol.
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 dimethyl esters of 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.
Patents 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.
Determination of the extent of interaction between the polyesters of the invention and commonly monitored drugs may be carried out using well known recovery experiments and drug measurement techniques, such as, gas chromatography , gas-liquid
chromatography , high-performance liquid
chromatography, thin layer chromatography or
immunoassay techniques, including radioimmunoassay, enzyme immunoassay, fluorescence polarization
immunoassay, nephelometric assay, and the like. A variety of suitable procedures are reported in the literature. See, for example, Bergqvist et al., supra Such determinations may be carried out using human serum, or commercially available bovine serum, if desired.
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. In the examples, all percentages are on a weight basis unless otherwise indicated.
Example 1
A reactant charge was prepared, including 558 g . of dodecenylsuccinic anhydride and 192 gm. of
propylene glycol (which includes a 20% excess over the stoichometric requirement for the reaction, to serve as the reaction medium), placed in a one liter
reaction vessel equipped with a stirrer, fused and heated gradually to a final temperature of 225-230°C. Water of reaction was collected from a temperature of approximately 190°C. The diol component was retained in the reaction mixture by the action of a Vigreaux fractionating column. The rate of temperature
increase was regulated so that the still head
temperature did not exceed 110°C during the initial condensation. When the rate of water evolution
diminished sharply, i.e., when about 85% of the
expected distillate had been collected, a partial vacuum was applied to complete the conversion of acid groups present to esters (about 28 inches vacuum at 225°C) . The vacuum esterification stage required about 3-4 hours. At this point, an interchange catalyst was introduced (0.02% dibutyltin diacetate (DBTDA) based on the total reactant charge), the fractionating column was removed, and relatively high vacuum applied (approximately 1-2 mm Hg).
Distillation of volatile diol proceeded slowly until the target viscosity was achieved, which required approximately 6 hours. The product was filtered through a coarse screen. The polyester recovered had an acid value of 3.0, an hydroxyl value of 22.4, 210°F kinematic viscosity of 1978.

Example 2
The same general procedure described in Example 1 was followed in preparing a polyester from a reactant charge comprising 314 gm. of dodecenylsuccinic
anhydride, 221 gm. of azelaic acid and 215 gm. of propylene glycol, except that one half the amount of the DBTDA catalyst was used and vacuum distillation proceeded for an additional 2 hours. The resultant product had an acid value of 1.8, a hydroxyl value of 9.5, 210°F kinematic viscosity of 2554.

Example 3
A polyester was prepared from a reactant charge comprising 335 gm. linoleic acid-acrylic acid adduct, 661 gm. azelaic acid, 405 gm. neopentyl glycol and 99 gm. propylene glycol. The reaction was carried out in a 2 liter reaction vessel equipped with a stirrer and a Vigreaux fractionating column, following the same general reaction conditions set forth in Example 1, above, except that vacuum distillation was performed for approximately 10 hrs. overall. The polyester obtained from this reaction had an acid value of 0.73, an hydroxyl value of 18.6, 210°F kinematic viscosity of 1912 and density at room temperature of 1.0348.

Example 4
A polyester was prepared from a reactant charge including 229 gm. linoleic acid-acrylic acid adduct, 393 gm. of a mixture of dicarboxylic acid dimethyl esters, including 75% dimethyl glutarate, 24% dimethyl adipate and 1% dimethyl succinate, 390 gm. oleic dimer acid, 352 gm. neopentyl glycol and 86 gm. propylene glycol. The reaction was run in a 2 liter reaction vessel equipped as described in Example 3. The reaction conditions described in Example 1 were followed for the most part with certain variations. Specifically, the catalyst (DBTDA) was introduced at the outset of the reaction, and in an amount of 0.02%, based on the total weight of the reactant charge. In addition, the heating rate was adjusted so that the head temperature did not exceed 90°C until an amount of distillate corresponding approximately to the predicted weight of ethanol was collected. The upper limit of the reaction temperature was approximately 225°C. Stripping of the reaction medium to the
desired viscosity was carried out essentially as described in Example 1, above. The polyester obtained from the reaction had an acid value of 1.1, an
hydroxyl value of 14.1, 210°F kinematic viscosity of 1972 and density at room temperature of 1.0202.

Example 5
A reactant charge was prepared including 508 gm . dodecenylsuccinic anhydride 1116 gm. oleic acid dimer , 1123 gm. of the ester mixture described in Example 4 , 1008 gm. neopentyl glycol and 245 gm. propylene glycol . This charge , together with 0.02% of DBTDA, was placed in a 5 liter reaction vessel equipped as described in Example 3 , and reacted following the general procedure of Example 4. The reaction yielded a polyester having an acid value of 0.3, an hydroxyl value of 14.1, 210°F kinematic viscosity of 2510 and density at room
temperature of 1.0226.

Example 6
A polyester was prepared from a reactant charge, including 196 gm. linoleic acid-acrylic acid adduct, 193 gm. dimethyl azelate, 558 gm. of the ester mixture described in Example 4, 445 gm. neopentyl glycol and 108 gm. propylene glycol, together with 0.02% DBTDA, following the general procedure of Example 4, with the exception that the usual vacuum esterification stage to reduce free acidity proved unnecessary in this case. The product of the reaction had an acid value of 0.4, an hydroxyl value of 8.3, 210°F kinematic viscosity of 2256 and density at room temperature of 1.082.
Polyesters prepared as described in the foregoing examples were evaluated for interaction with the antidepressant, imipramine (IM) and the
anticonvulsant, phenobarbital (PB) , two drugs which are commonly administered under TDM. A recovery of 90% was established as a benchmark for utilization of the polyesters of the invention in TDM programs. The results of these evaluations are set forth below in Table I.

All of the recovery values reported above were
obtained using commercially available bovine serum. Experience has shown that higher recovery values (up to about 2% higher) are obtainable with human serum.
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.