HK1110273B - Branched polylactic acid polymers and method of preparing same - Google Patents

Description

Branched polylactic acid polymer and preparation method thereof

Technical Field

The benefit of U.S. provisional application 60/582,156 filed in this application, 2004-06-23.

The present invention relates to lactide polymers with improved rheological properties and to a process for the preparation of such polylactide polymers.

Background

Commercial interest in polylactide polymers (also known as polylactic acid or PLA) is rapidly growing. Unless modified in some way, the PLA polymer will be a linear molecule and the properties belong to the thermoplastic material. They can be used to make a variety of different films, fibers, and other products. PLA offers the important advantages of being derivable from renewable resources (lactic acid can be made from plant carbohydrates such as glucose) and biodegradable. However, the rheological properties of such polymers make them potentially difficult to process in certain applications. Such production difficulties have heretofore restricted the fields of application in which such polymers can be used. For example, in extrusion coating, poor rheology causes phenomena such as necking and draw instability (draw resonance and wavy edges). Poor rheological properties result in blow molded articles that are very difficult, if not impossible, to manufacture and result in collapse of the extruded foam due to the extremely narrow operating window.

The rheological property of primary interest is usually melt elasticity, often expressed as "melt strength". In general, it is desirable that the thermoplastic polymer form a melt with a reasonably low shear viscosity in order to make it easy to process. At the same time, the molten polymer must possess sufficient strength and/or dimensional stability so that once formed into the desired shape, it will be able to retain that shape and in some cases even handle it before it has time to cool and harden. Generally, the melt strength of thermoplastic resins can be increased by increasing the molecular weight. However, this will also increase the shear viscosity so that the benefit of improving melt strength is sometimes offset by an increase in the force required to shape the polymer. The increased force requirement requires at least higher power consumption to process the polymer. In some cases this means that heavier, more expensive equipment is required, otherwise the processing speed must be reduced. In addition, increasing the molecular weight tends to increase the processing temperature required, which necessarily exacerbates polymer degradation.

For this reason, a great deal of research has been undertaken to improve the processing characteristics of PLA, focusing on the introduction of long chain branching by some mechanism. For example, attempts have been made to polymerize lactide with epoxidized fats or oils, as in U.S. patent 5,359,026, or with bicyclic lactone comonomers, as described in WO 02/100921a 1. It has been proposed to treat PLA with peroxide, as described in us patents 5,594,095 and 5,798,435, and to use specific polyfunctional initiators in the polymerization thereof, as described in us patents 5,210,108 and 5,225,521, to Spinu, GB 2277324 and EP 632081.

Unfortunately, none of these approaches is entirely satisfactory. In some cases, the rheological properties of the polymer are improved as much as desired. In other conditions, good rheological improvements are achieved, but it is difficult to manufacture the desired product in a reproducible manner. Sometimes, the different reactivity of the branching agent and the monocyclic ester or carbonate results in systems that do not copolymerize well. This is especially the case with lactide. In other cases, the steps required to induce branching can interfere with the polymerization reaction. This may lead to prolonged polymerization times, non-uniform product quality and other problems.

While good properties can be obtained when lactide is copolymerized with a bicyclic lactone comonomer, the comonomer is expensive and care must be taken to avoid gelation. In such cases, the copolymer properties are very sensitive to the amount of comonomer used, and therefore careful control is required in order to obtain the desired rheological properties. In addition, this method is not well suited to the modification of separately prepared polymers, since the copolymerization is carried out using a bicyclic lactone and lactide. In most cases, the copolymers have to be prepared according to the particular product.

It would be desirable to provide a melt processable PLA polymer having improved rheological properties over linear PLA resins, yet which can be conveniently made to have predictable and repeatable rheological properties.

In one aspect, the present invention is a melt-processable polylactide resin containing long chain branching comprising the reaction product of a polylactide resin having terminal hydroxyl or carboxylic acid groups, or both terminal hydroxyl and carboxylic acid groups, and an acrylate polymer or copolymer containing an average of from about 2 to about 15 free epoxy groups per molecule.

In a second aspect, the present invention is a method of introducing long chain branching into a melt-processable polylactide resin, comprising heating a mixture of a polylactide resin having a glass transition temperature of at least 40 ℃ and terminal hydroxyl or carboxylic acid groups, or both terminal hydroxyl and carboxylic acid groups, and an acrylate polymer or copolymer having an average of from about 2 to about 15 free epoxy groups per molecule to a temperature above the glass transition temperature of the polylactide resin. The method of the second aspect may be used to produce the resin of the first aspect.

The present invention provides a surprisingly flexible and efficient process for producing branched PLA resins. This branching reaction can be incorporated into standard hot melt processing procedures, if desired.

By virtue of the present invention, excellent control of the denaturation properties of the product stream, with little or no gelation, is obtained when high amounts of acrylate polymer or copolymer are employed. The branched PLA resin has improved rheological properties compared to the corresponding unbranched resin and is easier to melt process in a wide variety of applications. The branched polymers exhibit, for example, reduced necking and greater base stock stability when processed in extrusion coating as compared to corresponding linear PLA resins, and are more easily processed in film and sheet extrusion, foaming, blow molding, and extrusion foaming operations.

In another aspect, the invention is a dry blend of: (1) a melt-processable polylactide resin having terminal hydroxyl groups or carboxylic acid groups, or both terminal hydroxyl groups and carboxylic acid groups, and (2) a solid acrylate polymer or copolymer containing an average of from about 2 to about 15 free epoxy groups per molecule. The dry blend can be processed in a wide variety of melt processing operations to introduce long chain branching into the polylactide resin during the melt processing operation, thereby avoiding separate branching and melt processing operations. The use of dry blends also eliminates or simplifies the metering step during melt processing operations and helps to form a uniform product.

In a fourth aspect, the present invention is a PLA resin containing free epoxy groups. The PLA resin conveniently comprises the reaction product of a PLA resin with from about 0.5 to about 20 moles per mole of PLA resin, an acrylate polymer or copolymer having an average of from about 2 to about 15 free epoxy groups per molecule. The epoxy-containing PLA resin in this aspect is particularly useful as a "masterbatch" material that can be prepared in a melt processing step and blended with an unbranched polymer to obtain the desired degree of branching. In addition, the epoxy-containing PLA resins are useful as reactive compatibilizers or as reactive "tie" layers in coextrusion and similar applications.

For the purposes of the present invention, the terms "polylactide", "polylactic acid" and "PLA" are used interchangeably to denote a polymer having the structure-OC (O) CH (CH)₃) -a polymer of repeating units, regardless of how the repeating units constitute the polymer. The PLA resin preferably contains at least 50%, e.g., at least 80%, at least 90%, at least 95%, or at least 98% by weight of those repeat units.

The preferred PLA resin is a polymer or copolymer of lactide. Certain hydroxy acids, particularly alpha-hydroxy acids, e.g., lactic acid, exist in the form of 2 optical isomers, commonly referred to as the "D" and "L" enantiomers. Either D-or L-lactic acid can be produced synthetically, whereas fermentation processes generally (but not always) tend to produce the L-enantiomer preferentially. Lactide similarly exists in a wide variety of enantiomeric forms, i.e., "L-lactide" as a dimer of 2L-lactic acid molecules; "D-lactide", i.e., a dimer of 2D-lactic acid molecules; and "meso-lactide," a dimer consisting of 1L-lactic acid molecule and 1D-lactic acid molecule. Additionally, 50/50 mixtures of L-lactide and D-lactide with melting points of about 126 ℃ are commonly referred to as "D, L-lactide". Polymers of any of these forms of lactide or mixtures thereof may be used in the present invention. The increase in optical purity (i.e., higher concentration of the main enantiomer, either the D-or L-enantiomer) tends to result in the formation of polymers with higher crystallinity. When a semi-crystalline polymer is desired, it is preferred that the polymer comprises only L-or D-lactic acid enantiomer units or a mixture of L-and D-lactic acid units, but wherein one of the enantiomers (either L-or D-) comprises up to about 5 mol%, preferably up to about 3 mol%, more preferably up to about 2 mol%, especially up to about 1.6 mol% of the polymeric repeat units. Particularly preferred semi-crystalline copolymers comprise 98.4 to 100% L isomer and 0 to 1.6% D enantiomer (based on total moles of lactic acid repeating units). When a preference for amorphous polymers is desired, the ratio of the predominant enantiomeric repeat units to the remaining enantiomeric repeat units in the copolymer is suitably from about 80: 20 to about 98: 2, preferably from 88: 12 to 98: 2, especially from about 90 to about 98% of the L-enantiomer, and correspondingly from about 10 to about 2% of the D enantiomer (based on the total moles of lactic acid enantiomer repeat units). In general, the choice of the enantiomeric ratio will depend on the particular application and/or the desired properties of the copolymer. In general, the higher the crystallinity of the copolymer, the higher the thermal properties, dimensional stability and modulus.

Preferred lactides are produced by: lactic acid is polymerized to form a prepolymer, which is subsequently depolymerized while distilling off the lactide formed. Such a process is described in U.S. Pat. No. 5,274,073 to Gruber et al, which is incorporated herein by reference.

The PLA resin may also contain repeating units derived from other monomers that can be copolymerized with lactide or lactic acid, such as alkylene oxides (including ethylene oxide, propylene oxide, butylene oxide, trimethylene oxide, etc.) or cyclic lactones or carbonates. The repeating units derived from these other monomers may be present in block and/or random arrangements. These other repeat units suitably comprise from about 10 wt% of the weight of the PLA resin, preferably from about 0 to about 5 wt% of the weight of the PLA. Preferably, any such comonomer does not introduce branching points into the PLA, as this would make control of its rheological properties more difficult.

The PLA resin may also contain residues of initiator compounds that are commonly used to control molecular weight during polymerization. Suitable such initiators include, for example, water, alcohols, glycol ethers, various types of polyols (e.g., ethylene glycol, propylene glycol, polyethylene glycol, polypropylene glycol, glycerol, trimethylolpropane, pentaerythritol, hydroxyl-terminated butadiene polymers, and the like).

However, the PLA resin preferably contains, on average, from about 0.5 to about 2.0 terminal carboxyl groups per molecule. Such PLA resins are conveniently made using initiator compounds containing 1 or more carboxyl groups, or 1 or more carboxyl groups and 1 or more of their hydroxyl groups. Lactic acid, or dimeric or oligomeric forms of lactic acid, are particularly suitable initiators. It is believed that the terminal carboxyl groups on the PLA resin preferentially react with the epoxy groups on the copolymer to form the desired branched PLA resin. On the other hand, PLA resins with an average of much more than 1 carboxyl group per molecule tend to become cross-linked to form gels. The balance between promoting crosslinking and avoiding gelation can be readily achieved where the PLA resin contains from about 0.8 to about 1.5, more preferably from about 0.9 to about 1.25, and especially from about 0.95 to about 1.1, terminal carboxyl groups per molecule. Such PLA resins will also contain non-carboxyl end groups, typically hydroxyl end groups. These hydroxyl end groups are less reactive with epoxide groups than carboxyl groups. The reaction conditions can be readily selected such that the carboxyl end groups react with the copolymer while the hydroxyl end groups remain substantially unreacted. This will enable both branching to be achieved but also avoid cross-linking and gel formation.

The number average molecular weight of the PLA resin before branching by reaction with the acrylate polymer or copolymer is advantageously from about 10,000, preferably 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 determined by GPC techniques described below.

One process particularly suitable for the preparation of PLA by lactide polymerization is described in U.S. Pat. nos. 5,247,059, 5,258,488 and 5,274,073. Such preferred polymerization processes typically include a devolatilization step during which the free lactide content of the polymer is reduced, preferably to less than 1 wt%, more preferably to less than 0.5 wt%. To produce melt stable lactide polymers, it is preferred to remove or deactivate the catalyst at the end of the polymerization process. This can be achieved by precipitating the catalyst or, preferably, by adding an effective amount of a deactivation agent to the polymer. The deactivation of the catalyst is suitably carried out by adding a deactivating agent to the polymerization vessel, preferably before the devolatilization step. Suitable phlegmatising 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 dihydrazones of aliphatic and aromatic aldehydes, hydrazides of aliphatic and aromatic mono-and dicarboxylic acids, derivatives of bis-acylated hydrazines, phosphite compounds and heterocyclic compounds.

The acrylate polymer or copolymer is characterized as a solid at 23 ℃, contains an average of from about 2 to about 15 free epoxy groups per molecule (e.g., from about 3 to about 10 or from about 4 to about 8 free epoxy groups per molecule), and is the polymerization product of at least one epoxy-functional acrylate or methacrylate monomer, preferably copolymerized with at least one additional monomer.

The acrylate polymer or copolymer suitably has a molecular weight per epoxy group of from about 150 to about 700, for example from about 200 to 500 or from about 200 to 400. The acrylate polymer or copolymer suitably has a number average molecular weight of from about 1000 to about 6000, for example from about 1500 to about 5000 or from about 1800 to about 3000.

The epoxy-functional monomer contains an epoxy group and at least one acryloyl (CH)₂CH-C (0) -) or methacryl (CH)₂＝C(CH₃) -a C (0) -) group. Glycidyl acrylate and glycidyl methacrylate are examples of such epoxy functional monomers. The additional monomer may be, for example, a methacrylic monomer, an acrylic monomer, a vinyl aromatic monomer, or a mixture of 2 or more thereof. The additional monomer is "non-functional," that is, the additional monomer does not have groups that will react with the PLA resin, particularly groups that can react with hydroxyl or carboxyl end groups on the resin. The additional monomer may be, for example, acrylic acid, methacrylic acid, methyl methacrylate, ethyl methacrylate, butyl methacrylate, methyl acrylate, ethyl acrylate, butyl acrylate, isobutyl methacrylate, isobutyl acrylate, cyclohexyl methacrylate, cyclohexyl acrylate, isobornyl methacrylate, hydroxyethyl acrylate, hydroxybutyl methacrylate, hydroxybutyl acrylate, styrene, vinyl naphthalene, or the like, or a mixture of two or more of the above. Preferred copolymers are copolymers of an epoxy-functional acrylic or methacrylic monomer, at least one additional acrylate or methacrylate monomer, and a vinyl aromatic monomer such as styrene.

The acrylate polymer or copolymer is conveniently prepared according to the polymerization process described in U.S. Pat. No. 6,552,144.

Suitable acrylate copolymers are available under the trade name Johnson Polymer companyAnd (5) selling. Particularly preferred products include4300、4348 and4349A polymer.

To generate long chain branching, up to about 0.5 moles of acrylate polymer or copolymer per mole of PLA resin is used. An average of 2 PLA resin molecules will be coupled by each acrylate polymer or copolymer molecule (assuming that on average each PLA resin molecule is monofunctional via a terminal carboxyl group to react with the copolymer) in an amount up to about 0.5mol/mol, in practical cases there will be a distribution of reaction products including unconjugated PLA resin molecules, adducts of single PLA resin molecules with one acrylate polymer or copolymer molecule, and conjugates containing 2 conjugated PLA resin molecules up to a number of conjugated PLA resin molecules equal to the number of epoxy functionalities of the acrylate polymer or copolymer, when the number of acrylate polymers or copolymers is reduced from about 0.5mol per mole of PLA resin (further) there will tend to be a less homogeneous mixture containing more highly branched species and less unbranched species, preferably from about 0.02 to about 0.45mol of acrylate polymer or copolymer per mole of PLA resin, when a long chain branched PLA resin product is desired. Another suitable range for making long chain branched products is from about 0.05 to about 0.4 moles of acrylate polymer or copolymer per mole of PLA resin. The number of equivalents of epoxy groups on the acrylate polymer or copolymer per mole of PLA resin is advantageously from about 0.1 to about 4, especially from about 0.3 to about 2.7. When more than 1 equivalent of epoxy is employed per mole of PLA resin, the branched product will contain some free epoxy groups.

When the amount of the acrylate polymer or copolymer is more than 0.5mol per mol of the PLA resin, the degree of branching tends not to increase any more. Alternatively, an increasing proportion of linear reaction products of 1mol PLA resin to 1mol acrylate polymer or copolymer will tend to form. This tendency prevents gel formation, which is a problem for many other branching mechanisms. The resulting adduct contains free epoxy groups, making it suitable for a variety of uses as set out below.

The ability to form an epoxy-containing PLA resin adduct can be quite advantageous because it will allow us to easily prepare a masterbatch using a high proportion of acrylate polymer or copolymer. Such masterbatches can be prepared from about 0.5, 1.0, or 2.0 moles of acrylate polymer or copolymer per mole of PLA resin, up to about 20, especially about 8, especially up to about 3 moles of acrylate polymer per mole of PLA resin. The resulting masterbatch contains predominantly 1: 1 linear reaction product, with a small amount of higher branching material. The masterbatch will also contain free epoxy groups that can react with other PLA resin molecules during subsequent melt processing operations to produce additional branching. When more than 1 mole of acrylate polymer or copolymer is used per mole of PLA resin, the masterbatch will also contain unreacted acrylate polymer or copolymer.

These masterbatch materials have the advantage of being melt flowable at temperatures suitable for melt processing of PLA resins. The masterbatch material can then be melt blended with additional PLA resin during melt processing to form a modified PLA resin having desirable rheological properties. Such masterbatch methods have several advantages, including metering accuracy of modification, avoidance of localized high concentrations of acrylate polymers or copolymers (and thus the formation of localized high concentrations of highly branched reaction products), and easier and more uniform blending into the PLA resin. The PLA added will react with unreacted epoxy groups in the masterbatch to introduce additional branching.

The epoxy-functional PLA resin may also be used as a reactive compatibilizer. It can be melt blended with 2 or more different resins that are generally incompatible but each contain functional groups that can react with epoxy groups. The functional group reacts with the epoxy group on the masterbatch under melt processing conditions (or simply, at elevated temperature) to form a residue of an epoxy-functional PLA resinLinking the constituent graft polymers. Resins containing carboxylic acid and amino groups are of particular interest. These resins include carboxyl-or amino-functional polyolefins (e.g., modified to impart such groups: high density polyethylene, low density polyethylene, linear low density polyethylene, substantially linear polyethylene, polypropylene, polyisobutylene, ethylene-propylene copolymers, ethylene-styrene copolymers, and the like), ethylene-acrylic acid copolymers, polyacrylic acid, amine-terminated polyethers (e.g.,materials supplied by Huntsman chemical company), carboxy-terminated polycarbonates and polyesters, and polylactic acid.

Similarly, epoxy-functional PLA resins can be used as tie layers to promote adhesion of incompatible resins together, for example, in a coextrusion process. As above, the resin should have epoxy-reactive functional groups that provide sites for bonding to the epoxy-functional PLA resin. The resins described in the preceding paragraph may adhere together in this manner.

The reaction of the acrylate polymer or copolymer with the PLA resin is generally conducted at an elevated temperature above the glass transition temperature of the PLA resin. Reaction temperatures of about 100 to 250 ℃ are generally suitable, with temperatures of about 140 to 220 ℃ being preferred in order to obtain good reaction rates with minimal thermal degradation of the PLA resin. The reaction rate will vary with temperature. At the above range of processing temperatures, a reaction time of about 0.1 to 20min, in particular 0.2 to 10min, is generally sufficient. One convenient way to make the branched product is to feed the PLA resin and the acrylate polymer or copolymer to an extruder with a mixing temperature in the above range. The operating rate is generally chosen such that the residence time of the mixture in the extruder is within the above-mentioned range.

This branching step can be incorporated into the ordinary melt processing for making PLA resins into, for example, fibers, films, sheets, foams, thermoformed articles, or molded articles. The acrylate polymer or copolymer should be added to the melt processing at a point where it has sufficient time to react with the PLA resin to form the desired degree of branching. The acrylate polymer or copolymer can be added in several ways-either as a separate feed, as a masterbatch as described above, or as a dry blend with the PLA resin. As long as the processing temperature and residence time are sufficient, branching reactions will occur during the melt processing step. The newly formed branched PLA resin is then extruded through a suitable die or injection molded into a suitable mold to form the desired article of manufacture, e.g., a fiber, film, sheet, foam, thermoformed article, or molded article. If the conditions are such that the branching reaction is not complete during melt processing, the PLA article may then be subjected to a thermal curing treatment to complete the branching reaction.

Another branching agent may be used in conjunction with the acrylate polymer or copolymer to further increase branching or for other purposes. The simultaneous use of peroxide branching agents is of particular interest because peroxide branching agents can react with monomeric or oligomeric species that may generate impurities in the acrylate polymer or copolymer and fix these impurities to the polymer. This will reduce volatiles in the production and help prevent the formation of undesirable low molecular weight chemical species.

The branched PLA resin advantageously exhibits a polydispersity index (PDI, defined as the ratio of weight average molecular weight to number average molecular weight, as determined by GPC as described below) 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. The branched PLA resin advantageously exhibits a die swell ratio of at least about 1.05, preferably at least about 1.2, more preferably at least about 1.4, especially about 1.5, to about 2.0, preferably to about 1.8, as determined under the conditions described below.

The branched PLA resin of the present invention can be used in a wide variety of applications, for example, fibers (including staple fibers, monofilament fibers, blend fibers, textured fibers, bicomponent fibers, yarns, etc.), films such as cast films, blown films, oriented films (including biaxially oriented films where stretching is performed in 2 directions simultaneously or sequentially), extruded foams, blow molding, compression molding, sheet molding, injection molding, extrusion coating, paper coating, and other applications. In general, the branched PLA resins of the present invention can be used in the same applications as the corresponding linear PLA resins, plus additional applications that require better rheological properties. Branched PLA resins are particularly useful where excellent shear thinning and/or high melt tension are required.

The branched PLA resin of the present invention can be compounded with all types of additives, including antioxidants, preservatives, catalyst deactivators, stabilizers, plasticizers, fillers, nucleating agents, all types of colorants, and blowing agents. The branched PLA resin may be blended with other resins and laminated or coextruded onto other materials to form complex structures.

The branched PLA of the present invention can also be blended with additional amounts of linear polylactic acid polymer to produce a polymer blend with tailored rheological properties. It may also be blended with other polymers, for example, polyesters, polyhydroxyalkanoates, polycarbonates, polystyrenes, polyolefins, and the like.

The following examples are given to illustrate the invention but are not intended to limit its scope. All parts and percentages are by weight homogenous unless otherwise indicated.

Examples 1-4 and comparative example A

PLA resin A was a copolymer of 88.6% L-and 11.4% D lactide with a relative viscosity of 4.05 as measured as a 1% solution in chloroform at 30 ℃. PLA resin a contains about 1 carboxyl-terminal group per molecule and 1 hydroxyl-terminal group per molecule. M thereof_wIs about 218,000. In these examples, the molecular weight is determined according to gel permeation chromatography: 1.0g of the sample was dissolved in 10mL of dichloromethane. An aliquot of 0.25mL of the formulation solution was transferred to a 20mL vial and diluted with 5mL of tetrahydrofuran. The sample was filtered through a 0.45 μm syringe filter into an autosampler vial. With Waters Alliance 2690Liquid ChroThe chromatography system acts as a pump and sampler. The diluent was tetrahydrofuran, the flow rate was 1mL/min, and the temperature was 35 ℃. The injection volume was 50 μ L. 3 Waters gel permeation columns (7.8X 300mm, Stryragel HR5, HR4 and HR1) were used. The detector was a Waters model 410 differential refractometer. Data were collected and analyzed on a personal computer running a waters empowersoftware (software) using a 3 rd order calibration curve generated from narrow-cut polystyrene standards supplied by american polymer standards corporation.

Branched PLA resin examples 1-4 were prepared by separately combining PLA resin A and4368 acrylic acid copolymer was fed to a 50mm co-rotating twin screw extruder.4368 the acrylic copolymer has a number average molecular weight of about 2000, a molecular weight per epoxy group of about 285, and an average of about 7 epoxy groups per molecule. The temperature settings of the heating zones of the extruder were: zone 1, 120 ℃; zone 2, 170 ℃; zone 3, 220 ℃; zone 4-10, 240 ℃; and zone 11, 236 ℃. The component ratios were varied as given in table 1. The feed rate was varied as follows to vary the residence time of the reactants in the extruder. The obtained branched PLA resin was extruded and pelletized. For comparison, PLA resin a was melt processed under the same conditions but without the addition of the acrylate copolymer. The results are shown in Table 1.

TABLE 1

^＊And are not embodiments of the present invention.¹Based on the weight of blend A.²The approximate equivalent number of acrylate copolymers per mole of PLA resin. These numbersThe values are M obtained by gel permeation chromatography of polystyrene standards_nThe measured value was calculated. At M, a chemical species having a molecular weight of 4000 or less_nThe measurement was ignored. Will M_nThe measurements were multiplied by 0.6 to correct for the difference in swelling between PLA and polystyrene standards.³Pounds of blend extruded per hour.⁴The sections were dried overnight at 100 deg.C under vacuum and the vacuum oven was purged with 100cc/min of nitrogen. The dried sample was removed from the oven, capped and immediately tested. The melt flow rate was measured in a TiniusOlsen Extrusion Plastometer (Extrusion Plastometer) at 210 ℃ under a load of 2.16kg and a die diameter of about 0.0825 inches. The sample slices were loaded into the barrel of the instrument and held there for 5min before the load was applied. The melt flow rate was calculated from the average value of at least 3 measurements taken for 1min for each sample. Samples for die swell ratio determination were collected during melt flow rate determination. About 1 inch long strands of molten polymer were cut at the die. The diameter of the strands was measured and divided by the known die diameter to obtain the die swell ratio. The results given are the average of at least 5 measurements.⁵Relative to polystyrene standards.

Melt flow rate, die swell ratio, relative viscosity, molecular weight, and polydispersity measurements all indicate that significant branching of the PLA resin occurs under these conditions.

Examples 5 to 7 and comparative example B

PLA resin B was a copolymer of 90.5% L-and 9.5% D lactide with a relative viscosity of 3.04, measured as a 1% solution in chloroform at 30 ℃. M thereof_wAbout 170,000. PLA resin B contains about 1 carboxyl-and 1 hydroxyl-terminal group/molecule.

Branched PLA resin samples of examples 5-7 were prepared and evaluated in the same manner as described in examples 1-4. For comparison, PLA resin B was melt processed under the same conditions but without the addition of the acrylate copolymer. The results are shown in Table 2.

TABLE 2

^＊And are not embodiments of the present invention.^1-5See comments 1-5 of Table 1.

As noted above, melt flow rate, die swell ratio, relative viscosity, molecular weight, and polydispersity measurements all indicate that significant branching of the PLA resin occurs under these conditions.

Examples 8 to 10 and comparative example C

PLA resin C was a copolymer of 93.1% L-and 6.9% D lactide with a relative viscosity of 2.60, measured as a 1% solution in chloroform at 30 ℃. M thereof_wIs about 124,000. PLA resin C contains about 1 carboxyl-terminal group per molecule and 1 hydroxyl-terminal group per molecule.

Branched PLA resin samples of examples 8-10 were prepared and evaluated in the same manner as described in examples 1-4. For comparison, PLA resin C was melt processed under the same conditions but without the addition of the acrylate copolymer. The results are shown in Table 3.

TABLE 3

^＊And are not embodiments of the present invention.^1～4See comments 1, 2, 4 and 5 of table 1.

As noted above, both molecular weight and polydispersity measurements indicate that significant branching of the PLA resin occurs under these conditions.

Examples 11 to 14 and comparative example D

PLA resin D was a copolymer of 95% L-and 5% D lactide with a relative viscosity of 2.52, measured as a 1% solution in chloroform at 30 ℃. M thereof_wIs about 108,000. PLA resin D contains about 1 carboxyl-and 1 hydroxyl-terminal group per molecule.

Branched PLA resins the samples of examples 11-14 were prepared and evaluated in the same manner as described in examples 8-10. For comparison, PLA resin D was melt processed under the same conditions but without the addition of the acrylate copolymer. The results are shown in Table 4.

TABLE 4

^＊And are not embodiments of the present invention.^1-3See comments 1, 2, 4 and 5 of table 1.

As noted above, both molecular weight and polydispersity measurements indicate that significant branching of the PLA resin occurs under these conditions.

Example 15

A certain amount of PLA resin B and4368 the acrylate polymers were dried overnight in a vacuum oven at 45 deg.C, respectively. The dried material was compounded using a Brabender plastograph PL2100 mixer equipped with a 60cc 3-zone mixing roll with a roll scraper. The speed of the roll blade was set at 60rpm, which corresponds to a maximum shear rate of about 150/s. 99.5 parts by weight of PLA resin B were added to the mixing bowl and heated at 210 ℃ for 6 min. Subsequently, 0.5 part by weight of an acrylate polymer was added and further kneaded for 9 min. The torque measured during the mixing was used asAn indirect measure of the progress of the reaction between the PLA resin and the acrylate polymer. The torque reached a maximum 4.7min after the acrylate polymer addition.

When the experiment was repeated at a mixing temperature of 225 ℃, the torque reached a maximum 3.3min after the addition of the acrylate polymer. When repeated again at 240 ℃, the torque reached its maximum value about 2.1min after the acrylate polymer addition.

Examples 16 to 20 and comparative example E

From a batch M using a 34-mm, 11-heating zone extruder_nApproximately 90,000 and M_wPLA resin B of approximately 170,000, and4368 acrylate polymer a masterbatch was prepared. In the case of example 16, the heating zone temperatures were: 170 ℃, zone 1; 180 ℃, zone 2; the temperature is 200 ℃, and the temperature is 3-11 ℃; and 220 deg.C, zone 11. The heating zones of example 17 were the same temperature except that the last zone temperature was 225 ℃. In example 16, the PLA resin was fed at about 20 lbs/hr and the acrylate resin was fed at about 2 lbs/hr. In example 17, the feed rates were 18 and 2 lbs/hr, respectively. This corresponds to about 19.64 equivalents epoxy groups per mole of PLA resin.

Both materials can be easily processed through an extruder despite the high amount of branching agent.

Masterbatch example 17 was used to dilute the samples of run examples 18-20 made by blending an additional amount of PLA resin B. To prepare the sample of example 18, masterbatch example 17 and PLA resin B were compounded in a 4: 96 weight ratio in the same 34-mm extruder. The heating zone temperature is 150 ℃, zone 1; 170 ℃, zone 2; the temperature of 210 ℃ is 3-10; and 235 deg.C, zone 11. Examples 19 and 20 were prepared in the same manner except that the ratios were 8: 92 and 15: 85, respectively. Examples 19 and 20, which differ in the degree of branching due to the different mixing ratios. For comparison, a portion of virgin PLA resin B was processed through an extruder under similar conditions. The molecular weights and polydispersities are shown in Table 5.

TABLE 5

Samples of each of examples 18-19 were extruded through a cast film die to produce about 1 mil sheet and then visually inspected for signs of sheet gelation. Example 20 was extruded into about 15 mil sheet. Example 20, due to the molecular weight is too high, can not be calendered to a thin thickness. None of the sheet materials showed significant gelation.

It will be appreciated that various modifications can be made to the invention herein described without departing from the spirit thereof, the scope of which is defined by the appended claims.

Claims (23)

1. A melt-processable polylactide resin containing long chain branching comprising the reaction product of a starting polylactide resin having terminal hydroxyl or carboxylic acid groups, or having terminal hydroxyl and carboxylic acid groups, and an acrylate polymer containing an average of 2 to 15 free epoxide groups per molecule, the acrylate polymer having a number average molecular weight of 1000 to 6000 and a molecular weight per epoxide group of 150 to 700,

wherein the molar ratio of acrylate polymer to starting polylactide resin is at most 0.5.

2. The polylactide resin of claim 1 which is the reaction product of 0.05 to 0.4mol of an acrylate polymer per mole of starting polylactide resin.

3. The polylactide resin of claim 1 wherein the starting polylactide resin contains an average of 0.8 to 1.5 carboxyl groups per molecule.

4. A polylactide resin according to claim 3 wherein the number average molecular weight of the starting polylactide resin is from 30,000 to 250,000 as determined by gel permeation chromatography using polystyrene standards.

5. The polylactide resin of claim 1 wherein the starting polylactide resin has an average of from 0.8 to 1.25 terminal carboxylic acid groups per molecule and the acrylate polymer contains an average of from 2 to 10 free epoxy groups per molecule.

6. A method of introducing long chain branching into a melt processable polylactide resin, comprising heating a mixture of a melt processable polylactide resin having a glass transition temperature of at least 40 ℃ and terminal hydroxyl or carboxylic acid groups, or terminal hydroxyl and carboxylic acid groups, and an acrylate polymer containing an average of from 2 to 15 free epoxy groups per molecule to a temperature above the glass transition temperature of the polylactide resin, wherein the acrylate polymer has a number average molecular weight of from 1000 to 6000 and a molecular weight per epoxy group of from 150 to 700, wherein the molar ratio of acrylate polymer to starting polylactide resin is at most 0.5.

7. The method of claim 6, wherein the molar ratio of acrylate polymer to starting polylactide resin is from 0.05 to 0.4.

8. The method of claim 6, wherein the starting polylactide resin contains an average of 0.8 to 1.5 carboxyl groups per molecule.

9. The method of claim 8, wherein the starting polylactide resin has a number average molecular weight of 30,000 to 250,000 as determined by gel permeation chromatography using polystyrene standards.

10. The process of claim 6, wherein the starting polylactide resin has an average of from 0.8 to 1.25 terminal carboxylic acid groups per molecule and the acrylate polymer contains an average of from 2 to 10 free epoxy groups per molecule.

11. A polylactide resin containing free epoxy groups which is the reaction product of 0.5 to 20mol per mole of starting polylactide resin of an acrylate polymer containing an average of 2 to 10 free epoxy groups per molecule, the acrylate polymer having a number average molecular weight of 1000 to 6000 and a molecular weight per epoxy group of 150 to 700.

12. The polylactide resin of claim 11 wherein the starting polylactide resin contains an average of 0.8 to 1.5 carboxyl groups per molecule.

13. The polylactide resin of claim 12 wherein the starting polylactide resin has a number average molecular weight of from 30,000 to 250,000 as determined by gel permeation chromatography using polystyrene standards.

14. The polylactide resin of claim 13 wherein the starting polylactide resin has an average of from 0.8 to 1.25 terminal carboxylic acid groups per molecule and the acrylate polymer contains an average of from 2 to 10 free epoxy groups per molecule.

15. A dry blend comprising a melt processable polylactide resin having terminal hydroxyl or carboxylic acid groups and a solid acrylate polymer containing an average of from 2 to 15 free epoxide groups per molecule, the acrylate polymer having a number average molecular weight of from 1000 to 6000 and a molecular weight per epoxide group of from 150 to 700,

wherein the molar ratio of acrylate polymer to starting polylactide resin is at most 0.5.

16. The dry blend of claim 15, wherein the molar ratio of acrylate polymer to polylactide resin is from 0.05 to 0.4.

17. The dry blend of claim 15, wherein the polylactide resin has an average of from 0.8 to 1.5 terminal carboxylic acid groups per molecule and the acrylate polymer contains an average of from 2 to 10 free epoxy groups per molecule.

18. A method comprising melt processing the dry blend of any of claims 15 to 17 to form a long chain branched polylactide.

19. A process comprising melt processing a mixture of a polylactide resin of any one of claims 11-14 and at least one other resin having an epoxy-reactive functional group.

20. The method of claim 19, wherein the at least one other resin is another polylactide resin having carboxyl groups.

21. The method of claim 19, wherein the polylactide resin is melt processed with at least 2 other resins that are different from each other.

22. The method of claim 21, wherein the melt processed product of the method is a compatible mixture of polylactide resin and at least 2 other resins.

23. A multilayer structure having at least one tie layer which is an intermediary of 2 other layers, the 2 other layers being composed of resins which are different from each other and each of which contains an epoxy functional group, wherein the tie layer is a polylactide resin of any one of claims 11 to 14.