Title of Invention

IMPACT RESISTANT POLYOLEFIN COMPOSITIONS

Abstract

Olefin polymer composition comprising (by weight, unless otherwise specified): A) 60 - 95% of a propylene homopolymer or copoloymer having a Polydispersity Index (P.I.) value of from 4.6 to 10 and a content of isotactic pentads (mmmm), measured by 13C NMR on the fraction insoluble in xylene at 25 °C, higher than 98 molar; B) 5 - 40% of a copolymer of ethylene containing from 40% to 70% of propylene or C4-C10 α-olefins) or of combinations thereof, and optionally minor proportions of a diene; said composition having a Temperature Rising Elution Fractionation (TREF) profile, obtained by fractionation in xylene and collection of fractions at temperatures of 40 °C, 80°C and 90 °C, in which the ethylene content Y of the fracti...

Full Text

IMACT RESISTANT POLYOLEFIN COMPOSITIONS The present invention concerns impact resistant polyolefin compositions and the process for As is known, isotactic polypropylene, though being endowed with an exceptional combination of excellent properties, is affected by the drawback of insufficient impact resistance at relatively low temperatures. According to the teachings of the prior art, it is possible to obviate this drawback, without sensibly affecting the other polymer properties, by modifying the synthesis process or by blending with rubbers. The modification of the synthesis process comprises, after polymerizing propylene to isotactic polymer, copolymerizing ethylene and propylene mixtures in the presence of the isotactic polymer. Processes and compositions representative of the prior art are described in U.S. Pat. Nos. 3,200,173, 3,629,368, and 3,670,053, European patent application No. 0077532, and U.S. Pat No. 6,313,227. It has now been found that it is possible to obtain polypropylene compositions with a particularly advantageous balance of properties, in particular of high rigidity and good impact resistance, by operating in two polymerization stages. In the first stage propylene is polymerized or copolymerized with minor amounts of comonomer(s), and in the second stage ethylene/α-olefin(s) mixtures are copolymerized in the presence of the propylene polymer obtained in the first step. Thus the present invention relates to an olefin polymer composition comprising (by weight, unless otherwise specified): A) 60 - 95%, preferably 65- 90%, of a propylene homopolymer, or a copoloymer of propylene containing 3% or less of ethylene or C4-C10 a-olefin(s) or of combinations thereof, said homopolymer or copolymer having a Polydispersity Index (P.I.) value of from 4,6 to 10, preferably from 5.1 to 8 and a content of isotactic pentads (mmmm), measured by l3C NMR on the fraction insoluble in xylene at 25 °C, higher than 98 molar %, preferably from 98.5 to 99.5 molar %; B) 5 - 40%, preferably 10 - 35%, of a copolymer of ethylene containing from 40% to 70%, preferably from 47 to 62%, of propylene or C4-C10 a-olefin(s) or of combinations thereof and optionally minor proportions of a diene; said composition having a Temperature Rising Elution Fractionation (TREF) profile, obtained by fractionation in xylene and collection of fractions at temperatures of 40 °C, 80°C and 90 °C, m winch the ethylene content Y of the fraction collected at 90 °C satisfies the following rotation (I): Y a molecular weight distribution in component (A), expressed by the Mw/Mn ratio, measured by GPC, equal to or higher than 7, in particular from 7 to 20; a value of Mz/Mw ratio in component (A), measured by GPC, equal to or higher than 3.6, in particular from 3.6 to 7; Flexural Modulus from 900 to 2000 MPa, more preferably from 1100 to 1700 MPa; Melt Flow Rate (MFR) from 0.5 to 45 g/10 min, more preferably from 2 to 35 g/10 min. (measured under condition L, namely 230 °C, 2.16 kg load); The total quantity of copolymerized ethylene is preferably from 1.5 to 24% by weight As previously said, the compositions of the present invention can be prepared with a polymerization process comprising at least two stages, where in the first stage the relevant monomer(s) are polymerized to form component (A) and in the following stage(s) the mixtures ethylene-propylene,ethylene-propylene and one or more C4-C10 α-olefin(sX ethylene and one or more C4-C10 α-olefin(s) and, optionally, a diene, are polymerized to form component (B). Thus the present invention relates also to a process for preparing the previously said compositions by a sequential polymerization comprising at least two sequential steps, wherein components (A) and (B) are prepared in separate subsequent steps, operating in each step, except the first step, in the presence of the polymer formed and the catalyst used in the preceding step. The catalyst is added only in the first step, however its activity is such that it is still active for all the subsequent steps. The component (A) is preferably prepared in a single polymerization stage. The order of the polymerization stages is not a critical process feature, however component (A) is preferably prepared before component (B). Tbe polymerization can occur in liquid phase, gas phase or liquid-gas phase. For example, k is possible to carry out the propylene polymerization stage using liquid propylene as diluent, and the following copolymerization stage in gas phase, without inermediate stages except for the partial degassing of the propylene. Examples of suitable reactors are continuously operated stirred reactors, loop reactors, fluidized-bed reactors or horizontally or vertically stirred powder bed reactors. Of course, the reaction can also be carried out in a plurality of reactors connected in series. It is possible to carry out the polymerization in a cascade of stirred gas-phase reactors which are connected in series and in which the pulverulent reaction bed is kept in motion by means of a vertical stirrer. The reaction bed generally comprises the polymer which is polymerized in the respective reactor. Propylene polymerization to form component (A) can be done in the presence of ethylene and/or one or more C4-C10 α-olefin(s), such as for example butene-1, pentene-1, 4- methylpentene-1, hexene-1 and octene-1, or combinations thereof. As previously said, the copolymerization of ethylene with propylene (preferred) and/or other C4-C10 α-olefin(s) to form component (B) can occur in the presence of a diene, conjugated or not, such as butadiene, 1,4-hexadiene, 1,5-hexadiene and ethylidene-norbornene-1. The diene, when present, is typically in an amount of from 0.5 to 10% by weight with respect to the weight of (B). Reaction time, pressure and temperature relative to the polymerization steps are not critical, however it is test if the temperature is from 20 to 150 °C, in particular from 50 to 100 °C. The pressure can be atmospheric or higher. The regulation of the molecular weight is carried out by using known regulators, hydrogen in particular. The compositions of the present invention can also be produced by a gas-phase polymerisation process carried out in at least two interconnected polymerisation zones. The said type of process is illustrated in European patent application 782 587. In detail, the above-mentioned process comprises feeding one or more monomer(s) to said polymerisation zones in the presence of catalyst under reaction conditions and collecting the polymer product from the said polymerisation zones. In the said process the growing polymer particles flow upward through one (first) of the said polymerisation zones (riser) under fast fluidisation conditions, leave the said riser and enter another (second) polymerisation. zone (downcomer) through which they Sow downward in a densified form under the action of gravity, leave the said downcomer and are reintroduced into the riser, thus establishing a circulation of polymer between the riser and the downcomer. In the downcomer high values of density of the solid are reached, which approach the bulk density of the polymer. A positive gain in pressure can thus be obtained along the direction of flow, so that it becomes possible to reintroduce the polymer into the riser without the help of special mechanical means. In this way, a "loop" circulation is set up, which is defined by the balance of pressures between the two polymerisation zones and by the head loss introduced into the system. Generally, the condition of fast fluidization in the riser is established by feeding a gas mixture comprising the relevant monomers to the said riser. It is preferable that the feeding of the gas mixture is effected below the point of reintroduction of the polymer into the said riser by the use, where appropriate, of gas distributor means. The velocity of transport gas into the riser is higher than the transport velocity under the operating conditions, preferably from 2 to 15m/s. Generally, the polymer and the gaseous mixture leaving the riser are conveyed to a solid/gas separation zone. The solid/gas separation can be effected by using conventional separation means. From the separation zone, the polymer enters the downcomer. The gaseous mixture leaving the separation zone is compressed, cooled and transferred, if appropriate with the addition of make-up monomers and/or molecular weight regulators, to the riser. The transfer can be effected by means of a recycle line for the gaseous mixture. The control of the polymer circulating between the two polymerisation zones can be effected by metering the amount of polymer leaving the down comer using means suitable for controlling the flow of solids, such as mechanical valves. The operating parameters, such as the temperature, are those that are usual in gas-phase olefin polymerisation process, for example from 50 to 120 °C. This process can be carried out under operating pressures of between 0.5 and 10 MPa, preferably from 1.5 to 6 MPa. Advantageously, one or more inert gases are maintained in the polymerisation zones, in such quantities that the sum of the partial pressure of the inert gases is preferably between 5 and 80S of the total pressure of the gases. The inert gas can be nitrogen or propane, for example. THE various catalysts are fed up to the riser m. any point of the said riser. However, they can also be fed A any point of the down comer. The catalyst can be in any physical state, therefore catalysts in either solid or liquid state can be used Preferably die polymerization catalyst is a Ziegler -Natta catalyst comprising a solid catalyst component comprising: a) Mg, Ti and halogen and an electron donor selected from succinates, preferably from succinates of formula (I) below: wherein the radicals R1 and R2, equal to, or different from, each other are a C1-C20 linear or branched alkyl, alkenyl, cycloalkyl, aryl, arylalkyl or alkylaryl group, optionally containing heteroatoms; the radicals R3 to R6 equal to, or different from, each other, are hydrogen or a C1-C20 linear or branched alkyl, alkenyl, cycloalkyl, aiyl, arylalkyl or alkylaryl group, optionally containing heteroatoms, and the radicals R3 to R6 which are joined to the same carbon atom can be linked together to form a cycle; with the proviso that when R3 to R5 are contemporaneously hydrogen R6 is a radical selected from primary branched, secondary or tertiary alkyl groups, cycloalkyl, aryl, arylalkyl or alkylaryl groups having from 3 to 20 carbon atoms, or a linear alkyl group having at least four carbon atoms optionally a interning heteroatoms; b) an alkylaluminum compound and, optionally (but preferably), c) one or more electron-donor compounds (external donor). Other preferred catalysts are Ziegler-Natta catalysts as above defined, wherein however the solid catalyst component (a) comprises, in addition to the said Mg, Ti and halogen, at least two electron donor compounds, said catalyst component being characterized by the fact that at least one of the electron donor compounds, which is present in an amount from 15 to 50% by mol with respect to the total amount of donors, is selected from esters of succinic acids which are not extractable, under the conditions described below, for more than 20% by mol and at least another electron donor compound which is extractable, under the same conditions, for more than 30% by mol. The esters of succinic acids not extractable for more than 20% by mol are defined as non-extraciable succinates. The electron donor compounds extractable for more than 30% by mol are defined as extractable electron donor compounds. Preferably, the amount of non-extractable succinates is between 20 and 45 and more preferably from 22 to 40% by mol with respect to the total amount of the electron donor compounds. Among the non-extractable succinates mentioned above, particularly preferred are the succinates of formula (II) below : in which the radicals R1 and R2, equal to, or different from, each other are a C1-C2o linear or branched alkyl, alkenyl, cycloalkyl, aryl, arylalkyl or alkylaryl group, optionally containing heteroatoms; and the radicals R3 and R4 equal to, or different from, each other, are C1-C2o alkyl, cycloalkyl, aryl, arylalkyl or alkylaryl group, optionally containing heteroatoms with the proviso that at least one of them is a branched alkyl; said compounds being, with respect to the two asymmetric carbon atoms identified in the structure of formula (II), stereoisomers of the type (S,R) or (R,S) that are present in pure forms or in mixtures. Among the extractable electron donor compounds particularly preferred are the esters of mono or dicarboxylic organic acids such as benzoates, malonates, phthalates and succinates. Preferred are alkylphthalates. The extractability test is carried out as follows. A Preparation of the solid catalyst component Into a 500ml four-necked round flask, purged with nitrogen, 250 ml of T1CI4 are introduced at 0°C. While stirring, 10.0 g of mkrospheroidal MgCl2*2.8C2H5OH (prepared according to the method described in ex.2 of USP 4,399,054 but operating at 3,000 rpm instead of 10,000) are introduced. 4.4 mMols of the selected electron donor compound are also added. in particular. the addition of nucleating agents brings about a considerable improvement in important physical-mechanical properties, such as Flexural Modulus, Heat Distortion Temperature (HDT), tensile strength at yield and transparency. Typical examples of nucleating agents are the p-tert-butyl benzoate and the 1,3- and 2,4- dibenzylidenesorbitols. The nucleating agents are preferably added to the compositions of the present invention in quantities ranging from 0.05 to 2% by weight, more preferably from 0.1 to 1% by weight with respect to the total weight. The addition of inorganic fillers, such as talc, calcium carbonate and mineral fibers, also brings about an improvement to some mechanical properties, such as Flexural Modulus and HDT. Talc can also have a nucleating effect The particulars are given in the following examples, which are given to illustrate, without limiting, the present invention. The data relating to the polymeric materials of the examples are determined by way of the methods reported below. MFR: ASTM D 1238, condition L, 230 °C, 2.16 Kg; intrinsic viscosity [r\]: measured in tetrahydronaphthalene at 135° C; Mn (number average molecular weight X Mw (weight average molecular weight) and Mz (z average molecular weight): measured by way of gel permeation chromatography (GPC) in 1,2,4-trichlorobenzene; in detail, the samples are prepared at a concentration of 70 mg/50 ml of stabilized 1,2,4 trichlorobenzene (250μg/ml BHT (CAS REGISTRY NUMBER 128-37-0); the samples are then heated to 170°C for 2.5 hours to solubilize; the measurements are run on a Waters GPCV2000 at 145°C at a flow rate of 1.0 ml/min. using the same stabilized solvent; three Polymer Lab columns are used in series (Plgel, 20μm mixed ALS, 300 X 7.5 mm); ethylene content by IR spectroscopy; Flexural Modulus: ISO 178; Izod: measured according to the ISO 180/1A method; Break energy: Basell method 17324 (see below); the same test specimens and testing method as for the determination of the Ductile/Brittle transition temperature (hereinafter described) are used, but in the present case the energy required to break the sample at -20 °C is determined. Determined according to internal method MA 17324, available upon request. According to tins method, the bi-axial impact resistance is determined through impact with an automatic, computerised striking hammer. The circular test specimens are obtained by cutting with circular hand punch (38 mm diameter). They are conditioned for at least 12 hours at 23 °C and 50 RH and then placed in a thermostatic bath at testing temperature for 1 hour. The force-time curve is detected during impact of a striking hammer (5.3 kg, hemispheric punch with a 1/2" diameter) on a circular specimen resting on a ring support. The machine used is a CEAST 6758/000 type model no. 2. D/B transition temperature means the temperature at which 50% of the samples undergoes fragile break when submitted to the said impact test The Plaques for D/B measurement, having dimensions of 127x127x1.5 mm are prepared according to the following method. The injection press is a Negri Bossi™ type (NB 90) with a clamping force of 90 tons. The mould is a rectangular plaque (127x127x1.5mm). The main process parameters are reported below: Back pressure (bar): 20 Injection time (s): 3 Maximum Injection pressure (MPa): 14 Hydraulic injection pressure (MPa): 6-3 First holding hydraulic pressure (MPa): 4±2 First holding time (s): 3 Second holding hydraulic pressure (MPa): 3±2 Second holding time (s): 7 Cooling time (s): 20 Mould temperature (°C): 60 The melt temperature is between 220 and 280 °C. Determination of isotactic pentads content 50 mg of each xylene insoluble fraction were dissolved in 0.5 mL of C2D2CI4. The 13CNMR spectra were acquired on a Bruker DPX-400(100.61 Mhz, 90° pulse, 12s delay between poises). About 3000 transients were stored for each spectrum; mmmm pentad peak (21.8 ppm) was used as reference. The microstructure analysis was carried out as described in literature (Polymer, 1984, 25, 1640, bylnoue Y. etAl and Polymer, 1994, 35, 339, byChnjoR. etAl). Polydispersity Index (PI): measurement of molecular weight distribution of the polymer. To detnnine the PI value, the modulus separation at low modulus value, e.g. 500 Pa, is determined at a temperature of 200 °C by using a RMS-800 parallel plates rheometer model marketed by Rheometrics (USA), operating at an oscillation frequency which increases from 0.01 rad/second to 100 rad/second. From the modulus separation value, the PI can be derived using the following equation: PI = 54.6 x (modulus separation)-1.76 wherein the modulus separation (MS) is defined as: MS = (frequency at G' = 500 Pa)/(frequency at G" = 500 Pa) wherein G' is the storage modulus and G" is the loss modulus. Fractions soluble and insoluble in xylene at 25 °C: 2.5 g of polymer are dissolved in 250 ml of xylene at 135 °C under agitation. After 20 minutes the solution is allowed to cool to 25 °C, still under agitation, and then allowed to settle for 30 minutes. The precipitate is filtered with filter paper, the solution evaporated in nitrogen flow, and the residue dried under vacuum a 80 °C until constant weight is reached. Thus one calculates the percent by weight of polymer soluble and insoluble at room temperature (25 °C). Temperature Raising Elution Fractionation (TREF) Determined in xylene by using the following method. The main fractionation vessel consists of a 500ml double wall reactor. A vibro mixer is intoduced from above. The preheated solvent for the extraction process can enter the reactor through a tubing which is situated at the lower outlet of the vessel The TREF procedure is started by dissolving 5g of the polymer in 400 ml boiling xylene, stabilized with 5g/l 2,6-di-tert-butyl-4-methylphenoL To precipitate the polymer, the solution is cooled down linearly to 25°C controlled by a thermostat at a cooling rate of 10 0C/h First Step. The suspension of the crystals is then heated to the first elution temperature (40°C), the polymer crystals in the apparatus are agitated by the vibromixer and extracted for 15 minutes. Then the polymer in solution is discharged through the lower valve, whereas the remaining polypropylene crystals stay in the extractor. The solution is poured into 800ml of cold Acetone (Temperature Next Step. The temperature of the extractor is increased to the desired temperature and 400 ml of xylene of the same temperature are introduced into the fractionation vessel. The remaining polymer crystals in the apparatus are then extracted again for 15 minutes.The polymer solution is again discharged, the dissolved polymer precipitated and filtered. Then this step is repeated again at the following temperature and so on, until approaching 125°C, the boiling point of the solvent At this temperature the whole polymer should have been extracted. Example 1 and Comparative Examples 1 and 2 Preparation of the solid catalyst component Into a 500 mL four-necked round flask, purged with nitrogen, 250 mL of TiCU were introduced at 0 °C. While stirring, 10.0 g of microspheroidal MgCl2*2.SC2H5OH (prepared according to the method described in ex.2 of USP 4,399,054 but operating at 3000 rpm instead of 10000 rpm) and 7.4 mmol of diethyl 2,3-diisopropylsuccinate were added. The temperature was raised to 100 °C and maintained for 120 min. Then, the stirring was discontinued, the solid product was allowed to settle and the supernatant liquid was siphoned off. Then 250 mL of fresh TiCl4 were added. The mixture was reacted at 120 °C for 60 min and, then, the supernatant liquid was siphoned off. The solid was washed six times with anhydrous hexane (6 x 100 mL) at 60 °C. Catalyst system and prepolymerization treatment Before introducing it into the polymerization reactors., the solid catalyst component described above is contacted at 12 °C for 24 minutes with aluminum triethyl (TEAL) and dicyclopentyldimethoxysilane (DCPMS) in such quantity that the weight ratio of TEAL to the solid catalyst component be equal to 11, and the weight ratio TEAL/DCPMS be equal to 4.4. The catalyst system is then subjected to prepolymerization by maintaining it in suspension in liquid propylene at 20 °C for about 5 minutes before introducing it into the first polymerization reactor. Polymerization The polymerization run is conducted in continuous mode in a series of three reactors equipped with devices to transfer the product from one reactor to the one immediately next to it The first two reactors are liquid phase reactors, and the third is a fluid bed gas phase reactor. Component (A) is prepared in the first and second reactor, while component (B) is prepared in the third. Hydrogen is used as molecular weight regulator. The gas phase (propylene, ethylene and hydrogen) is continuously analyzed via gas-chromatography. At the end of the run the powder is discharged and dried under a nitrogen flow. The main polymerization conditions and the analytical data relating to the polymers produced in the three reactors are reported in Table 1. Then the polymer particles are introduced in a rotating drum, wherein they are mixed with 0.2% by weight of Irganox B 225 (made of about 50% Irganox 1010 and 50% Irgafos 168), 0.3% by weight of GMS90 (glycerin monostearate) and 0.09% by weight of Na benzoate, to obtain a nucleated composition.The previously said Irganox 1010 is pentaerytrityl tetrakis 3-(3,5-di-tert-butyl-4-hydroxyphenyI) propanoate, while Irgafos 168 is tris (2,4-di-tert-butylphenyl) phosphite. Then the polymer particles are extruded under nitrogen atmosphere in a twin screw extruder, at a rotation speed of 250 rpm and a melt temperature of 200-250 °C The properties of the so obtained polymer are reported in Table 2. In the same table are also reported the properties of two comparison nucleated polymer compositions (Comp. Examples 1 and 2), having closely comparable MFR, heterophasic structure and composition. The comparison polymer composition of Comp. Example 1 is made of (all amounts by weight): A) 83.5% of a propylene homopolymer having MFRL of 33 g/10min., xylene insoluble content of 98.8% and PI of 43; B) 16.5% of a propylene/ethylene copolymer containing 45% of ethylene; and contains 0.3% of GMS90,0.12% of Irganox B225 and 0.09% of Na benzoate. Moreover, the said comparison composition contains 15.3% by weight of fraction soluble in xylene, having an intrinsic viscosity value of 2, and has the following features: (mmmm) of the xylene-insoluble portion of (A): 99.1% molar; Mw /Mn of (A): 10.1; Mz/Mw of (A);3.5; Y: 15.1 wt%; X:37.7wt%. The comparison polymer composition of Comp. Example 2 is made of (all amounts by weight): A) 82% of a propylene homopolymer having PI of 4.3; B) 18% of a propylene/ethylene copolymer containing 50% of ethylene; and contains 0.3% of GMS90,0.12% of Irganox B225 and 0.09% of Na benzoate. Moreover, the said comparison composition contains 16% by weight of fraction soluble in xylene, having an intrinsic viscosity value of 2.58 dl/g, and has the following features: (mmmm) of the xylene-insoluble portion of (A): 99.1% molar, Mw/Mn of(A): 10.1; Mz/Mw of(A):3.5. Claims Olefin polymer composition comprising (by weight, unless otherwise specified): A) 60 - 95% of a propylene homopolymer, or a copoloymer of propylene containing 3% or less of ethylene or C4-C10 α-olefin(s) or of combinations thereof said homopolymer or copolymer having a Polydispersity Index (P.I.) value of from 4.6 to 10 and a content of isotactic pentads (mmmm), measured by 13C NMR on the fraction insoluble in xylene at 25 °C, higher than 98 molar, B) 5 - 40% of a copolymer of ethylene containing from 40% to 70% of propylene or C4-C10 a-olefin(s) or of combinations thereof, and optionally minor proportions of a diene; said composition having a Temperature Rising Elution Fractionation (TREF) profile, obtained by fractionation in xylene and collection of fractions at temperatures of 40 °C, 80°C and 90 °C, in which the ethylene content Y of the fraction collected at 90 °C satisfies the following relation (I): Y The composition of claim 1, wherein component (A) has a molecular weight distribution, expressed by the Mw/Mn ratio, measured by GPC, equal to or higher than 7 and a value of Mz/Mw ratio, measured by GPC, equal to or higher than 3.6. Polymerization process for preparing the olefin polymer composition of claim 1, comprising at least two sequential steps, wherein components (A) and (B) are prepared in separate subsequent steps, operating in each step, except the first step, in the presence of the polymer formed and the catalyst used in the preceding step. The polymerization process of claim 3, wherein the polymerization catalyst is a Ziegler -Natta catalyst comprising a solid catalyst component comprising: a) Mg, Ti and halogen and an election donor selected from succinates, preferably from succinates of formula (I) below: wherein the radicals R1 and R2, equal to, or different from, each other are a C1-C20 linear or branched alkyl, alkenyl, cycloalkyl, aryl, arylalkyl or alkylaryl group, optionally containing heteroatoms; the radicals R3 to R6 equal to, or different from, each other, are hydrogen or a C1-C20 linear or branched alkyl, alkenyL, cycloalkyl, aryl, alylalkyl or alkylaryl group, optionally containing heteroatoms, and the radicals R3 to R6 which are joined to the same carbon atom can be linked together to form a cycle; with the proviso that when R3 to R5 are contemporaneously hydrogen R6 is a radical selected from primary branched, secondary or tertiary alkyl groups, cycloalkyl, aryl, aiylalkyl or alkylaryl groups having from 3 to 20 carbon atoms, or a linear alkyl group having at least four carbon atoms optionally containing heteroatoms; b) an alkylaluminum compound and, optionally, c) one or more electron-donor compounds (external donor).

Documents:

2509-chenp-2005 abstract-duplicate.pdf

2509-chenp-2005 claims-dupliate.pdf

2509-chenp-2005 description(complete)-duplicate.pdf

2509-chenp-2005-abstract.pdf

2509-chenp-2005-claims.pdf

2509-chenp-2005-correspondnece-others.pdf

2509-chenp-2005-correspondnece-po.pdf

2509-chenp-2005-description(complete).pdf

2509-chenp-2005-form 1.pdf

2509-chenp-2005-form 18.pdf

2509-chenp-2005-form 3.pdf

2509-chenp-2005-form 5.pdf

2509-chenp-2005-pct.pdf