US20030096940A1 - Copolymers of monocyclic esters and carbonates and methods for making same - Google Patents

Copolymers of monocyclic esters and carbonates and methods for making same Download PDF

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US20030096940A1
US20030096940A1 US10/165,241 US16524102A US2003096940A1 US 20030096940 A1 US20030096940 A1 US 20030096940A1 US 16524102 A US16524102 A US 16524102A US 2003096940 A1 US2003096940 A1 US 2003096940A1
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copolymer
carbonate
units derived
bicyclic
monocyclic
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Ray Drumright
Mark Hartmann
Richard Wolf
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    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08L—COMPOSITIONS OF MACROMOLECULAR COMPOUNDS
    • C08L67/00—Compositions of polyesters obtained by reactions forming a carboxylic ester link in the main chain; Compositions of derivatives of such polymers
    • C08L67/04—Polyesters derived from hydroxycarboxylic acids, e.g. lactones
    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08G—MACROMOLECULAR COMPOUNDS OBTAINED OTHERWISE THAN BY REACTIONS ONLY INVOLVING UNSATURATED CARBON-TO-CARBON BONDS
    • C08G63/00—Macromolecular compounds obtained by reactions forming a carboxylic ester link in the main chain of the macromolecule
    • C08G63/02—Polyesters derived from hydroxycarboxylic acids or from polycarboxylic acids and polyhydroxy compounds
    • C08G63/06—Polyesters derived from hydroxycarboxylic acids or from polycarboxylic acids and polyhydroxy compounds derived from hydroxycarboxylic acids
    • C08G63/08—Lactones or lactides
    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08G—MACROMOLECULAR COMPOUNDS OBTAINED OTHERWISE THAN BY REACTIONS ONLY INVOLVING UNSATURATED CARBON-TO-CARBON BONDS
    • C08G63/00—Macromolecular compounds obtained by reactions forming a carboxylic ester link in the main chain of the macromolecule
    • C08G63/64—Polyesters containing both carboxylic ester groups and carbonate groups
    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08G—MACROMOLECULAR COMPOUNDS OBTAINED OTHERWISE THAN BY REACTIONS ONLY INVOLVING UNSATURATED CARBON-TO-CARBON BONDS
    • C08G64/00—Macromolecular compounds obtained by reactions forming a carbonic ester link in the main chain of the macromolecule
    • C08G64/02—Aliphatic polycarbonates
    • C08G64/0208—Aliphatic polycarbonates saturated
    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08L—COMPOSITIONS OF MACROMOLECULAR COMPOUNDS
    • C08L69/00—Compositions of polycarbonates; Compositions of derivatives of polycarbonates
    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08L—COMPOSITIONS OF MACROMOLECULAR COMPOUNDS
    • C08L69/00—Compositions of polycarbonates; Compositions of derivatives of polycarbonates
    • C08L69/005—Polyester-carbonates
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
    • Y10T—TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION
    • Y10T428/00—Stock material or miscellaneous articles
    • Y10T428/31504—Composite [nonstructural laminate]

Definitions

  • This invention relates to polyesters and/or carbonates that have modified rheological properties and methods for making those polyester and/or polycarbonates.
  • Certain monocyclic compounds can be polymerized to form polyesters or polycarbonates.
  • monocyclic esters include dioxanones (such as p-dioxanone), lactones (such as ⁇ -caprolactone or 4-valerolactone), dioxan(dione)s (such as glycolide, lactide or tetramethyl-1,4-dioxan-2,5-dione), carbonates such as ethylene carbonate and trimethylene carbonate, and ester-amides (such as morpholine-2,5-dione).
  • polylactide polymers also known as polylactic acid, or PLA
  • these polyesters are linear molecules and therefore thermoplastic materials. They are useful for making a variety of films, fibers and other products.
  • these polymers offer the significant advantages of being derived from renewable resources (lactic acid can be prepared from plant carbohydrates such as dextrose) and of being biodegradable.
  • lactic acid can be prepared from plant carbohydrates such as dextrose
  • biodegradable the rheological properties of these polymers are such that they can be difficult to process in certain applications. This difficulty in processing has so far limited the applications for which these polymers can be used. For example, in extrusion coating, poor rheological properties lead to phenomena such as neck-in and draw instability (draw resonance and edge weave). Poor rheological properties make it very difficult to make blow molded articles at all, and cause extruded foams to collapse because operating windows are extremely narrow.
  • melt strength The rheological property of primary interest is often melt elasticity, which is often expressed as “melt strength”.
  • a thermoplastic polymer forms a melt having a reasonably low shear viscosity so that it can be processed readily, but at the same time the molten polymer must possess enough strength that, once formed into a desired shape, it can hold that shape and in some instances even be worked with until it has time to cool and harden.
  • melt strength can be increased in a thermoplastic resin by increasing the molecular weight. However, this also increases the shear viscosity so that the benefits of improved melt strength are offset by the increased force that is needed to shape the polymer in the first place.
  • this invention is a copolymer having, in polymerized form, units derived from (a) a monocyclic ester or corresponding hydroxy acid or (b) a monocyclic carbonate, or both (a) and (b), and units derived from a bicyclic diester and/or carbonate.
  • the copolymer may range from slightly branched to densely crosslinked. Branching in these copolymers tends to be long-chain type branching, as described more below.
  • the proportion of bicyclic monomer units is such that the copolymer is a thermoplastic that exhibits excellent melt strength yet is readily melt processable.
  • the preferred copolymers exhibit, for example, reduced neck-in and improved web stability when processed in extrusion coating, compared to the corresponding linear polyesters or polycarbonates, and are more easily processed in blow molding and extrusion foaming operations.
  • this invention is a method comprising subjecting a mixture including a monocyclic ester and/or carbonate and a bicyclic diester and/or carbonate to conditions sufficient to polymerize the mixture to form a copolymer having, in polymerized form, units derived from the monocyclic ester and/or carbonate and units derived from the bicyclic monomer.
  • This method provides a convenient, reproducible way to make copolymers that have a controlled amount of branching, as the extent of branching increases with increasing proportions of the bicyclic diester and/or carbonate.
  • the monocyclic monomer is lactide
  • the polymerization reaction proceeds predictably, controllably and at nearly the same rates as lactide homopolymerizations under the same conditions.
  • the process permits such a copolymer to be prepared with excellent control over its rheological properties and with minimal gelling.
  • FIG. 1 is a graph showing the relationship between intrinsic viscosity and molecular weight for certain embodiments of copolymers of the invention.
  • FIG. 2 is a graph showing dynamic mechanical spectroscopy data for certain embodiments of copolymers of the invention.
  • polylactide polylactic acid
  • PLA polylactic acid
  • the copolymer contains polymerized units derived from (a) a monocyclic ester or the corresponding hydroxy acid or (b) a monocyclic carbonate.
  • monocyclic esters include any monocyclic molecules that contain one or more ester linkages incorporated into the ring structure, and which are polymerizable.
  • monocyclic carbonates are any monocyclic molecules that contain one or more carbonate linkages incorporated into the ring structure, and which are polymerizable.
  • Monocyclic esters (and the corresponding hydroxy acids) and monocyclic carbonates are referred to herein collectively as “monocyclic monomers”.
  • Suitable monocyclic esters and carbonates include lactones such as ⁇ -caprolactone or 4-valerolactone; dioxanones such as p-dioxanone; dioxan(dione)s such as glycolide, lactide or tetramethyl 1,4-dioxan-2,5-dione; carbonates such as ethylene carbonate and trimethylene carbonate; and ester-amides such as morpholine-2,5-dione.
  • lactones such as ⁇ -caprolactone or 4-valerolactone
  • dioxanones such as p-dioxanone
  • dioxan(dione)s such as glycolide, lactide or tetramethyl 1,4-dioxan-2,5-dione
  • carbonates such as ethylene carbonate and trimethylene carbonate
  • ester-amides such as morpholine-2,5-dione.
  • the hydroxy acids are hydroxyl-sub
  • the hydroxy acids include alpha-, beta-, gamma, and epsilon-hydroxy carboxylic acids such as glycolic acid, dimethyl glycolic acid, lactic acid, epsilon-hydroxycaproic acid, alpha-hydroxy valeric acid, and the like.
  • the copolymer may contain polymerized residues of two or more of these monomers, in block and/or random arrangement. Polylactide (PLA) copolymers are most preferred.
  • the copolymer also contains units derived from a bicyclic diester and/or dicarbonate (sometimes referred to herein collectively as “bicyclic monomers”).
  • the units derived from the bicyclic monomer introduce branching sites into at least some of the copolymer molecules.
  • the structure of the polymerized bicyclic monomer units is derived from that of the bicyclic monomer, which is a bridged cyclic compound having two ester and/or carbonate groups in a ring structure and at least one atom in the bridge.
  • the bicyclic monomer can be represented as:
  • each R is independently hydrogen, alkyl or inertly substituted alkyl, each n and each o is independently zero or a positive integer, and Y is a bridging group.
  • Z is a covalent bond in the case of an ester group and —O— in the case of a carbonate group.
  • R is preferably lower (C 1-4 ) alkyl and is most preferably hydrogen.
  • Y is suitably —CR 2 ) m —, where m is a positive integer, —O—, —S—, —NR 1 — (in which R 1 is alkyl or substituted alkyl) and the like or a combination of two or more of these groups.
  • Each n is preferably no greater than 1.
  • Each o is preferably zero.
  • the values of each n and o, taken together, are more preferably so that the main ring (including the two ester and/or carbonate groups but excluding the —Y— bridge) contains 6 or 7 members in the case of esters and 8 or 9 members in the case of carbonates.
  • each n is zero and each o is zero.
  • Y is preferably —(CR 2 ) m — where m is at least one, preferably 1, 2 or 3, and most preferably 2.
  • Each Z is preferably a covalent bond, making the bicyclic monomer a diester. The most preferred bicyclic monomer is 2,5-dioxa-bicyclo[2.2.2]octane-3,6-dione.
  • n, o, Y and m impart to the bicyclic monomer a reactivity similar to that of lactide, and thus enhance the ability of the bicyclic monomer to copolymerize with lactide.
  • Bicyclic monomers in which o is zero and Y is —(CR 2 ) m — can be formed from substituted dicarboxylic acids of the form
  • R, Z, m and n are as defined before, and X is a group that will react with a carboxylic acid group to form a covalent bond to the carbonyl carbon, or a group that is displaced by the carboxylic acid group.
  • X is preferably hydroxyl, halogen or —NO 2 , and is more preferably chlorine or bromine.
  • Substituted dicarboxylic acids of structure II can be prepared from the corresponding unsubstituted diacid chloride by reacting it with an agent that will introduce the X groups, and then reacting the resulting substituted diacid chloride with water if necessary to convert the acid chloride groups to free acid form.
  • the bicyclic diester is then generated by heating the substituted dicarboxylic acid in the presence of a weak base such as sodium carbonate.
  • a weak base such as sodium carbonate.
  • the bicyclic monomer reacts during polymerization conditions to open one of the ester or carbonate groups in the main ring to form a polymer containing a cyclic ester or carbonate group in the polymer chain, represented by the structure:
  • O—M—C(O)— represents a polymerized unit of a monocyclic ester (or corresponding hydroxy acid) or carbonate monomer and p represents a positive number.
  • the cyclic ester or carbonate group in the polymer chain can then undergo a further ring-opening reaction with additional monocyclic monomer (or hydroxy acid) to form a branch point having the structure
  • each unit of bicyclic monomer that undergoes this full sequence of reactions becomes incorporated into a copolymer molecule and creates a branch point where four polymer “arms” are joined.
  • a more highly branched polymer molecule can be formed if more than one bicyclic monomer molecule is polymerized into the polymer chain.
  • not all polymer molecules may contain a bicyclic monomer unit incorporated into them.
  • the copolymer is in fact a mixture of linear polymers of the monocyclic monomer and branched copolymers that contain branch points derived from the bicyclic monomer. The latter case is generally true with the preferred thermoplastic copolymers.
  • the degree of branching in the copolymer depends on the amount of bicyclic monomer that is incorporated into it and the molecular weight of the copolymer. At a given molecular weight, increased bicyclic monomer use increases branching and can lead to crosslinking. The effect of lowering molecular weight is to permit the use of higher proportions of the bicyclic monomer without causing crosslinking.
  • branching can be controlled so that copolymers are produced having very light branching, heavier branching or even crosslinking. In this way, the rheological properties of the copolymer can be “tailored” to meet the processing demands of specific applications.
  • the incorporated bicyclic monomer advantageously constitutes from about 0.05 to about 1.5 percent by weight of the polymer, although these amounts may increase or decrease, respectively, as the copolymer molecular weight is decreased or increased. Preferred amounts of the incorporated bicyclic monomer will vary according to the processing demands of particular applications. When light branching is desirable, the incorporated bicyclic monomer preferably constitutes from about 0.1 to about 0.3 percent of the weight of the polymer. To further modify the rheological properties of the copolymer, from about 0.3 to about 1.0 percent of the bicyclic monomer is incorporated into it, on the same basis.
  • thermoplastic PLA copolymers containing 0.3 weight percent or more incorporated bicyclic monomer often exhibit melt tensions exceeding 4 cN and even in the range of 6-16 cN, as determined by the method described in the Examples below. Values such as these are quite high for a PLA resin, and correlate to substantially improved processability in many applications.
  • a copolymer containing more than about 1.5% of incorporated bicyclic monomer will typically be crosslinked, although the precise amount of bicyclic monomer needed to induce crosslinking will depend somewhat on copolymer molecular weight.
  • the amount of incorporated bicyclic monomer may be as high as 99% by weight, but is more preferably no greater than about 50% by weight, more preferably no greater than about 15% by weight, and most preferably no greater than about 10% by weight.
  • the copolymer may also contain residues from one or more initiator compounds. These initiator compounds may be intentionally added to further refine the molecular weight and/or rheological properties of the copolymer or, as is particularly true in the case of lactide, are present as impurities in the monocyclic monomer, and react during the copolymerization process to initiate polymer molecules.
  • the bicyclic monomer contains impurities, those impurities may also act as initiator compounds. Thus, it is preferred to either purify the bicyclic monomer (such as to reduce the level of impurities to ⁇ 5 wt. %, preferably ⁇ 2 wt. %, especially ⁇ 1 wt. %), or to determine the number and type of impurities and take those impurities into account in manufacturing the copolymer.
  • the copolymer may further contain repeating units derived from other monomers that are copolymerizable with the monocyclic monomer, such as alkylene oxides (including ethylene oxide, propylene oxide, butylene oxide, tetramethylene oxide, and the like). Repeating units derived from these other monomers can be present in block and/or random arrangements. It is preferred that any such comonomer does not introduce branching points into the copolymer, as this makes it more difficult to control its rheological properties.
  • alkylene oxides including ethylene oxide, propylene oxide, butylene oxide, tetramethylene oxide, and the like.
  • the thermoplastic copolymers advantageously have a number average molecular weight of from about 10,000, preferably from about 30,000, more preferably from about 40,000 to about 500,000, preferably to about 300,000, more preferably to about 250,000, as measured by the GPC/DV technique described in the Examples.
  • the thermoplastic copolymers advantageously exhibit a polydispersity index (PDI, defined as the ratio of weight average molecular weight to number average molecular weight per the GPC/DV technique) of at least about 1.9, preferably at least about 2.1, more preferably at least about 2.5, to about 5, preferably to about 4, more preferably to about 3.5.
  • PDI polydispersity index
  • They advantageously exhibit a die swell of at least about 1.05, preferably at least about 1.2, more preferably at least about 1.4 and especially from about 1.5, to about 2.0, preferably to about 1.8, when measured under the conditions described in the Examples.
  • Preferred copolymers exhibit a melt tension, measured as described in the Examples, of at least about 0.8 cN, preferably at least about 2 cN, more preferably at least about 4 cN, even more preferably at least about 6 cN, and most preferably at least about 12 cN, to about 16 cN or more. It is especially preferred that the copolymers have melt tensions within the foregoing ranges while simultaneously exhibiting melt flow rates, measured as described in the Examples, in the range of 1 to about 15 g/10 min, especially 4-12 g/10 min.
  • a preferred non-crosslinked copolymer will exhibit a die swell of at least about 1.1, preferably at least about 1.5, measured as described in the examples below.
  • the preferred non-crosslinked copolymer will have a ratio of M z+1 /M n (measured as described in the following examples) of at least about 8, more preferably at least about 10, even more preferably at least about 15.
  • a preferred method of making the copolymers of the invention is through a copolymerization of the bicyclic monomer and a monocyclic ester and/or carbonate.
  • polymerization methods and conditions suitable for homopolymerizing the monocyclic esters and monocyclic carbonates can be used without significant modification, other than the inclusion of the bicyclic monomer into the reaction mixture.
  • Suitable lactide polymerization processes are described in U.S. Pat. Nos. 5,247,059, 5,258,488 and 5,274,073 to Gruber et al; U.S. Pat. No. 5,288,841 to Bellis et al.; U.S. Pat. No. 2,951,828; and U.S. Pat. No.
  • a particularly suitable process for preparing PLA is described in U.S. Pat. Nos. 5,247,059, 5,258,488 and 5,274,073. This process is easily adapted to make the copolymers of this invention.
  • lactide is fed as a liquid directly to a polymerization system, where it is polymerized at elevated temperature in the presence of a catalyst.
  • a catalyst As molecular weight increases, an equilibrium is established between the polymer and free lactide, thus limiting the build-up of molecular weight and producing a polymer containing a certain amount of free lactide.
  • the free lactide provides some plasticizing effect that is often undesirable, and also tends to coat the surfaces of polymer processing equipment.
  • the polymerization process typically includes a devolatilization step during which the free lactide content of the polymer is reduced, preferably to less than 1% by weight, and more preferably less than 0.5% by weight.
  • the polymerization can be conducted batch-wise, semi-continuously or continuously.
  • Continuous stirred-tank reactors and tube or pipe reactors are suitable types of polymerization vessels.
  • a series of CSTRs or tube or pipe reactors may be used to conduct the polymerization in stages. This permits additives to be introduced at specific stages in the polymerization process if desired, and also allows for different reaction conditions to be used at different stages of the polymerization.
  • Suitable polymerization temperatures preferably are, for solventless processes, above the melting temperature of the monomer or monomer mixture and above the melting temperature of the product copolymer, but below the temperature at which significant polymer degradation occurs.
  • a preferred temperature range is from about 100° C. to about 220° C.
  • a more preferred temperature range is from 120° C. to about 200° C. and especially from about 160° C. to about 200° C.
  • Residence times at polymerization temperatures are selected to produce a copolymer of the desired molecular weight and/or desired conversion of monomers.
  • Molecular weight and conversion are controlled by polymerization time and temperature, the equilibrium between free lactide and the polymer, and by the use of initiator compounds. In general, increasing quantities of initiator compounds on a molar basis will tend to decrease the molecular weight of the product polymer. Unless they are stringently purified, monocyclic monomers such as lactide tend to contain hydroxy-functional and/or acid-functional impurities that act as initiators during the polymerization process. If desired, additional initiator compounds can be added to provide additional control over molecular weight.
  • Suitable such initiators include, for example, water, alcohols, glycol ethers, and polyhydroxy compounds of various types, such as ethylene glycol, propylene glycol, polyethylene glycol, poly propylene glycol, glycerine, trimethylolpropane, pentaerythritol, hydroxyl-terminated butadiene polymers and the like.
  • a wide variety of polymerization catalysts can be used, including various tin compounds such as SnCl 2 , SnBr 2 , SnCl 4 , SnBr 4 , SnO, organotin compounds such as tin (II) bis(2-ethyl hexanoate), butyltin tris(2-ethyl hexanoate), hydrated monobutyltin oxide, dibutyltin dilaurate, tetraphenyltin and the like; PbO, zinc alkoxides, zinc stearate, organoaluminum compounds such as aluminum alkoxides, organoantimony compounds such as antimony triacetate and antimony (2-ethyl hexanoate), organobismuth compounds such as bismuth (2-ethyl hexanoate), calcium stearate, magnesium stearate, certain yttrium and rare earth compounds such as are described in U.S
  • Catalysts are used in catalytically effective amounts, which depend somewhat on the particular catalyst, but are usually in the range of from about 1 mole catalyst to about 3000-50,000 moles monomers. Preferred catalyst concentrations are in excess of 5000 moles monomers per mole catalyst, and especially in excess of 10,000 moles monomers per mole catalyst.
  • the catalyst may be supported if desired to facilitate its removal.
  • Suitable deactivating agents include carboxylic acids, of which polyacrylic acid is preferred; hindered alkyl, aryl and phenolic hydrazides; amides of aliphatic and aromatic mono-and dicarboxylic acids; cyclic amides, hydrazones and bishydrazones of aliphatic and aromatic aldehydes, hydrazides of aliphatic and aromatic mono- and dicarboxylic acids, bis-acylated hydrazine derivatives, phosphite compounds and heterocyclic compounds.
  • Certain hydroxy acids particularly ⁇ -hydroxy acids such as lactic acid, exist in two optical isomers, which are generally referred to as the “D” and “L” isomers.
  • D- or L-lactic acid can be produced in synthetic processes, whereas fermentation processes usually tend to favor production of the L isomer.
  • Lactide similarly exists in a variety of isomeric forms, i.e., “L-lactide”, which is a dimer of two L-lactic acid molecules, “D-lactide”, which is a dimer of two D-lactic acid molecules and “meso-lactide”, which is a dimer formed from one L-lactic acid molecule and one D-lactic acid molecule.
  • D,L-lactide 50/50 mixtures of L-lactide and D-lactide that have a melting temperature of about 126° C.
  • D,L-lactide 50/50 mixtures of L-lactide and D-lactide that have a melting temperature of about 126° C.
  • Any of these forms of lactide, or mixtures thereof, can be copolymerized in accordance with this invention.
  • Increased optical purity i.e., higher concentrations of D- or L-isomer
  • the polymer contains either L- or D-lactic acid units alone or else contains a mixture of both L- and D-lactic acid units in which one of the isomers (either L- or D-) constitutes at most about 3 mole %, preferably up to about 2 mole %, more preferably up to about 1.6 mole %, and especially up to about 1.2 mole percent of the isomeric units in polymerized form.
  • Particularly preferred semi-crystalline copolymers contain from 98.4 to 100% L isomer and from 0 to 1.6% D isomer (based on total moles of lactic acid repeating units).
  • the ratio of L- and D-isomer repeating units in the copolymer is suitably from about 98:2-2:98, preferably from 90:10 to 10:90, especially from about 70-90% L-isomers and 10-30% D isomers (based on total moles of lactic acid repeating units).
  • the selection of stereoisomer ratios will depend on the particular application and/or desired copolymer properties. In general, the higher the crystallinity, the higher are the thermal performance and the modulus of the copolymer.
  • bicyclic monomers may also exist as two or more stereoisomers.
  • An example of this is the 2,5-dioxa-bicyclo[2.2.2]octane-3,6-dione described in the examples below.
  • the ratio of stereoisomers may affect crystallinity, and should be taken into account, together with the stereoisomer content of the monomers (i.e., the monocyclic ester(or corresponding hydroxy acid) and a monocyclic carbonate), in the manufacture of the copolymer, so that desired properties are obtained.
  • a preferred lactide is produced by polymerizing lactic acid to form a prepolymer, and then depolymerizing the prepolymer and simultaneously distilling off the lactide that is generated. Such a process is described in U.S. Pat. No. 5,274,073 to Gruber et al., which is incorporated herein by reference.
  • the comonomer is introduced into the polymerization apparatus. This can be done by blending the comonomer with the monocyclic ester, by adding the comonomer neat as a separate stream, or by adding the comonomer as a solution in a suitable solvent. Comonomers can be copolymerized randomly or sequentially to form random and/or block copolymers.
  • Another method of preparing the copolymer is to blend the bicyclic monomer with a previously-formed polymer of monocyclic esters and/or carbonate, and then subject the mixture to transesterification conditions.
  • Thermoplastic copolymers of the invention are useful in a variety of applications, such as fibers (including staple fibers, monofilament fibers, blended fibers, textured fibers, bicomponent fibers, yarns and the like), films such as cast film, blown film, oriented film (including biaxially oriented film where stretching is performed in two directions either simultaneously or sequentially), extruded foam, blow molding, compression molding, sheet molding, injection molding, extrusion coating, paper coating and other applications.
  • the copolymer of the invention can be used in the same applications as the corresponding homopolymers are used, plus additional applications where better rheological properties are desirable.
  • the copolymer is particularly useful in applications where excellent shear thinning and/or high melt tension are desirable.
  • the copolymers of this invention exhibit improved shear thinning and melt tension compared to linear polymers of the same monocyclic monomer (at equivalent M w ). It is therefore possible to obtain good processing at an equivalent or lower molecular weight than is needed for the corresponding linear polymers to be processable. This gives the processor the option of using lower processing temperatures and/or pressures, thus reducing polymer degradation (monomer reformation, molecular weight loss and color generation), reducing energy consumption, and in some instances permitting the use of smaller, less expensive equipment.
  • the copolymer of the invention can be compounded with additives of all types, including antioxidants, preservatives, catalyst deactivators, stabilizers, plasticizers, fillers, nucleating agents, colorants of all types and blowing agents.
  • the copolymer may be blended with other resins, and laminated or coextruded to other materials to form complex structures.
  • the copolymer of this invention can also be blended with additional amounts of linear polylactic acid polymers to produce a blended polymer having tailored rheological properties. It can also be blended with other polymers, such as polyesters, polyhydroxyalkanoates, polycarbonates, polystyrenics, polyolefins and the like.
  • Freshly distilled adipic acid dichloride (100.65 parts) is loaded into a 3-necked flask equipped with a reflux condenser, dropping funnel and stirrer.
  • the adipic acid dichloride is heated to 100° C., and 193.6 parts bromine (Br2) is added over about 48 hours with stirring. Volatiles are removed by applying vacuum (20 Torr, 0.5 hour) to yield 187 parts of a mixture of meso and d,l-forms of ⁇ , ⁇ ′-dibromoadipic acid dichloride.
  • ⁇ , ⁇ ′-dibromoadipic acid dichloride is added slowly with vigorous stirring to 1750 parts ground ice, so that an emulsion of highly-dispersed oil droplets in water is formed. Stirring is continued for about 10 hours, during which time the oil droplets form into soft pieces and then into a hard powder. The emulsion is then filtered, washed with water and dried in open air. One hundred fifteen parts of a mixture of meso and d,l-forms ( ⁇ 2.0 ratio) of ⁇ , ⁇ ′-dibromoadipic acid having a melting point of 185-188° C. are recovered. The water phase is extracted twice with 500 ml diethyl ether.
  • the ether extracts are dried over CaCl 2 and concentrated to yield an additional 46 parts of a mixture of meso and d,l-forms ( ⁇ 1.4 ratio) of ⁇ , ⁇ ′-dibromoadipic acid having a melting point of 135-149° C.
  • the separate portions of product ⁇ , ⁇ ′-dibromoadipic acid are combined.
  • Copolymers of ⁇ , ⁇ ′-2,5-dioxa-bicyclo[2.2.2]octane-3,6,dione and L-lactide (1.08% D isomer) are prepared using a polymerization system including three tube reactors and a devolatilizer. Each of the tube reactors is a stainless steel tube 18.5 inches long with an internal diameter of 2.5 inches containing internal static mixing elements. Each of the tube reactors is divided into three heated zones. During the copolymerizations, the tube reactor is heated at 130° C., the second at 180° C. and the third at 185° C. The first and second tube reactors are connected by a transfer line that is held at 180° C.
  • the second and third tube reactors are connected by a transfer line that is held at 200° C.
  • the lactide is introduced into the bottom of the first tube reactor, is transferred from top of the first tube reactor to the bottom of the second tube reactor, is transferred from the top of the second tube reactor to the bottom of the third tube reactor, and is transferred from the top of the third tube reactor to the devolatilizer through a heated transfer line equipped with a divert valve.
  • the devolatilizer consists of an electrically heated flat plate heater followed by a 15′′ ⁇ 1′′ diameter single-screw extruder which pumps the polymer melt out of a die.
  • the flat plate heater is operated at 250° C. and the extruder is operated at 190-200° C.
  • the unreacted monomers that are removed in the devolatilizer are trapped in a traced and insulated carbon steel 37′′ ⁇ 4′′ diameter column at 20° C.
  • the entire polymerization system is computer controlled.
  • the lactide used if homopolymerized, would be predicted to form a polymer having a M n of 101,000 daltons.
  • the lactide is melted, held in a feed tank, and fed to the bottom of the first tube reactor using a mass flowmeter at a rate of 454 grams/hour.
  • a separate feed of 25% tin octoate in toluene is pumped into the bottom of the second tube reactor at a rate of 4.38 microliters/minute.
  • the ⁇ , ⁇ ′-2,5-dioxa-bicyclo[2.2.2]octane-3,6,dione is fed on demand as a 15% solution in gamma-butyrolactone to the bottom of the first tube reactor with a diaphragm pump using a shot tube.
  • a 25% polyacrylic acid solution in N-methylpyrrolidinone is pumped into the center zone of the third tube reactor at a rate of 13 microliters/minute, in order to kill the catalyst.
  • Control Sample A and Examples 1-5 are made by varying the amount of ⁇ , ⁇ ′-2,5-dioxa-bicyclo[2.2.2]octane-3,6,dione that is fed into the polymerization system.
  • the amount of ⁇ , ⁇ ′-2,5-dioxa-bicyclo[2.2.2]octane-3,6,dione added is 0.1%, 0.2%, 0.4%, 0.4% and 0.6%, respectively, based on the total weight of monomers fed.
  • the separation is performed on three Waters Styragel HR columns that are connected in series (5 micron particle size, 300 mm ⁇ 7.8 mm columns with pore sizes of 10 5 ⁇ , 10 4 ⁇ and 10 1 ⁇ ).
  • the temperature of the column set and detector is 35°C.
  • the detector is a Waters model 410 differential refractometer. Data is analyzed with Millenium 32 software. # The injection volume is 0.050 mL. Three PL-gel mixed-B columns (300 ⁇ 25 mm, part #1210-6100) are used.
  • the detector is a Viscotek Model 250 Differential Viscometer/Refractometer.
  • the data is collected and analyzed on a personal computer running TriSEC GPC software, using universal calibration with a 3 rd order curve fit.
  • Narrow fraction polystyrene standards from American Polymer Standards Corporation are used to establish the universal calibration plot. # An average of at least three measurements of 1 minute each are used to calculate the melt flow rate. Samples for die swell measurements are collected during the melt flow runs. Approximately 1 inch lengths of molten polymer strand are cut off at the die and cooled. The diameter of the strands is measured and divided by the known diameter of the die to give melt swell. Reported results are an average of at least 5 measurements.
  • branches can be inferred from chromatographic measurements such as polydispersity.
  • branching can be qualitatively and quantitatively determined from size exclusion chromatography with multiple detectors. Plotting the log of dilute solution viscosity against the log of molecular weight (Mark-Houwink plot) is another appropriate tool for determining branching.
  • Mark-Houwink plot is another appropriate tool for determining branching.
  • polymers having branches will tend to have a lower dilute solution viscosity, at a given molecular weight, than an otherwise similar linear polymer. Mark-Houwink plots for copolymer Examples 1, 3 and 5 are given in FIG. 1.
  • FIG. 1 Mark-Houwink plots for copolymer Examples 1, 3 and 5 are given in FIG. 1.
  • the length of the branches is often inferred from rheological measurements, and increases in characteristics such as die swell and melt strength indicate the presence of long-chain branches.
  • Yet another suitable method of inferring the existence of long chain branches is dynamic mechanical spectroscopy.
  • Copolymer Examples 1, 2 and 3 are each dried overnight at 100° C. in a vacuum oven, and placed in a dessicator containing phosphorous pentoxide drying agent. Dynamic mechanical spectroscopy testing is performed within 8 hours of removing the samples from the oven, using a Rheometrics RDS-2 spectrometer running under Rhios 4.4.4 software for machine control and data collection. Specimens are heated to 210° C. and immediately cooled to 180° C. for testing.
  • melt tension of copolymer Examples 1, 2, 3 and 5 is evaluated on a Goettfert test frame.
  • the sample is packed into the capillary rheometer and extruded at 190° C. at a shear rate of 33 sec ⁇ 1 through a die 30 mm long and 2 mm in diameter.
  • Melt tension is measured with a wheel sensitivity in the range of 1-1000 cN.
  • the wheels of the melt tension apparatus are located 110 mm below the capillary die. Results are: Example No. % Bicyclic diester Melt Tension (cN) 1 0.1 ⁇ 0.8 2 0.2 ⁇ 2.0 3 0.4 ⁇ 8.5 5 0.6 ⁇ 13.5
  • melt tension also increases with increasing bicyclic diester content, and demonstrates how copolymer properties can be tailored through adjustments in bicyclic diester level.
  • Examples 3 and 5 in particular exhibit excellent melt tension values for a PLA resin.
  • Copolymer Example 4 is selected for processing into blown film.
  • the sample is dried in a desiccant drier for 11 ⁇ 2 days at 40° C., ⁇ 40° C. dew point. It is processed into monolayer blown film on a 1′′ Killion three-zone extruder with a 40/80/40 mesh screen pack, through a 3′′ diameter die with a 0.035′′ die gap at a rate of 13 pounds/hour.
  • Extruder temperatures are 300° F. in zone 1, 345° F. in zone 2 and 365° F. in zone 3, at the clamp and at the die.
  • Haul-off rates are 22 feet/minute.
  • the line is started up and run for a period with PLA homopolymer to purge the system, and film is then produced with Copolymer Example 4 for about 15 minutes. Bubble stability is excellent and the film has very few gels. The film has little to no crystallinity as measured by DSC, but is easily crystallized when oriented by stretching.

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US20090311937A1 (en) * 2006-07-14 2009-12-17 Kimberly-Clark Worldwide, Inc. Biodegradable polylactic acid for use in nonwoven webs

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WO2013184014A1 (en) 2012-06-06 2013-12-12 Universidade De Coimbra Process for preparing high molecular weight poly(lactic acid) by melt polycondensation
KR102241623B1 (ko) 2016-04-28 2021-04-19 네이쳐웍스 엘엘씨 폴리락티드 수지의 외장 층을 갖는 폴리머 발포체 단열 구조물
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