i-PP/EPR REACTOR ALLOY PREPARED THROUGH ETHYLENE/PROPYLENE SLURRY COPOLYMERIZATION CATALYZED BY META

Chinese Joumal of Polymer Science Vol. 26, No. 5, (2008), 597- -604Chinese Journal ofPolymer Science⑥2008 World Scientifici-PP/EPR REACTOR ALLOY PREPARED THROUGH ETHYLENE/PROPYLENESLURRY COPOLYMERIZATION CATALYZED BY METALLOCENESUPPORTED iPP PARTICLES*Lie Lu, Hong Fan*, Bo-geng Li*" and Shi-ping Zhu’State Key Laboratory of Chemical Engineering, Deparment of Chemical and Biochemical Engineering,Zhejiang University Hangzhou 310027, China"Department of Chemical Engineering, McMaster University, Hamilton, L8S 4L7, Canadametallocene (rac-E(Ind)2ZrCl2) supported on porous iPP particles. Polar monomer (dihydromyrcene alcohol) treated withtriethyaluminum was added in the preparation of porous iPP particles to introduce hydroxy1 groups and thus enhance theability for chermically supporting the meallocene catalyst. The efects of MAO/Zr ratio and monomer composition in feed onthe reaction activity and property of polymer were invesigated. DSC analysis results imply that EPR prepared bymeallocene supported PP particles showed much more obvious features of random copolymer compared with that preparedwith conventional Z.N catalyst. Under appropriate reaction conditions, well separated spherical particles of iPP/m-EPRreactor alloy containing up to about 40 wI% m-EPR were obtained. SEM analysis results showed that m- EPR microphasessmaller than 2 um in size were uniformly distributed in PP matrix after blending the iPP/m-EPR reactor aloy.Keywords: Reactor aloy; Ethylene/propylene copolymerization; Metallocene.INTRODUCTIONPolypropylene (PP) had been widely used in a variety of applications because of is advantages, such as low cost,low density, high softening point, easy processing, as well as outstanding tensile properties. However, its poorimpact strength, especially at low temperature, hindered its application as an engineering thermoplasticl.21. Aconventional way to cover the shortage was to blend the polymer with its compatible elastomer. To producetoughened PP, various elastomers had been applied, such as ethylene -propylene rubber (EPR)3-5), styrene-butadiene styrene (SBS) copolymer', butyl rubber'", and ethylene-propylene diene rubber (EPDM)8. 9]. Amongthese rubbers, EPR and EPDM were considered as the most effective impact modifiers. However, it has beenfound in our recent work that the ethylene-propylene diene rubbers polymerized by metallocene catalyst(m-EPDM) is much better than conventional EPDM for toughening Ppl I01. The PP/m- EPDM blended polymerhad a lower critical rubber content when the britle-ductile transition occurred and the bitle-ductile transitioninterval of PP/m-EPDM blends is much narrower. And also, the elongation at break of PP/m-EPDM blends waslonger than PP/EPDM blends.It was well known that conventional Ziegler-Natta (Z-N) catalysts had multiple active sites exhibiting arange of reactivity and producing a spectrum of composition and molecular weight. Ethylene-propylenecopolymers synthesized by Z-N catalyst contained a large portion of blocky copolymers, which were not as'This work was supported by National Basic Research Program of China (No.2005CB623804) and the National NaturalScience Foundation of China (No.20476090).“Corresponding authors: Hong Fan (范宏), E-mail: hfan@ zju.edu.cn中国煤化工Bo-geng Li (李伯耿), E-mai: bgli@ zju.edu.Invited lecture presented at the Asian Polyolefin Workshop 2007, 2007.MYHCNMHGReceived March 17, 2008; Revised April 15, 2008; Accepted April 16, 20U8598LLuetal.effective as random copolymers on improving low temperature impact strength of PP. In contrast, meallcenecatalysts were generally single site catalysts, meaning that all catalytic sites were identical. This feature yieldedproducts with extremely uniform composition and molecular weight. And also, the metallocene catalysts weregenerally more effective than conventional Z-N catalysts in incorporating high levels of a wide variety of olefincomonomerslI-l3].On the other hand, it has been proved that the iPP/rubber alloys prepared by in situ or reactor granuletechnology were much better than that formned by mechanical blending both on mechanical properties andproduction costsl14-18, since there were strong interaction between PP and rubber and the rubber could reach ahigh content in the reactor aloy. In order to prepare the iPP/m-EPR reactor aly, Galli et al!9! devised amulticatalyst process in which the metallocene was impregnated onto PP particles. However, the physicalabsorption of metallocene resulted in a poor linking between PP and rubber. Up to now, the preparation andcommercialization of iPP/m-EPR reactor alloy through muli-steps with combination of Z-N and metallocenetype catalyst are still faced with many challenges.In thepresent work, functional polypropylene granules were synthesized through propylenecopolymerization with protected dihydromyrcene alcohol by a spherical Z-N catalyst (TiCI/MgCI:/SiO2). Thefunctional polypropylenes performed efectively as supports in anchoring the metallocene catalysts (rac-Et(Ind)ZrCl2), and then were applied in the slurry copolymerization of ethylene and propylene to produceiPP/m-EPR reactor alloy.EXPERIMENTALMaterialsSpherical TiCL/MgCl2/SiO2-ID (where ID was an internal donor) catalyst, in which Ti content is 2.22 w% andMg/Si weight ratio is 0.67, was donated by Beijing Research Institute of Chemical Industry, Beiing, China.Triethyaluminium (TEA) and cyclohexylmethyldimethoxysilane (CHMDMS) were selected as a cocatalyst andexternal donor respectively in propylene polymerization reactions. Metallocene catalyst rac-E(Ind)zZrCl2 ispurchased from Sterm Chemicals Company. Methylaluminoxane (MAO) from J&K Chemical Company was usedas received. Polymerization- grade ethylene and propylene from Yangzi Petrochemical Chemical EngineeringCompany, China were purifed by passing through CuO and 0.5 nm molecular sieves. Toluene (anhydrous grade,from Hangzhou Chemical Reagents Factory, China) was refluxed over potassium for 24 h prior to use.Preparation of Functional PP ParticlesCopolymerization of propylene with dihydromyrcene alcohol treated by TEA was conducted to preparefunctional PP particles. Toluene (600 mL) was introduced to a nitrogen-purged autoclave equipped with amechanical sirrer and a temperature probe. The toluene was sirred vigorously (100 r/min) and kept at thepolymerization temperature, and then trialkylaluminum and dihydromyrcene alcohol were added. After 20 min,Z-N catalyst, TEA and external donon (CHMDMS) were introduced into the reactor, and immediately the feedingof propylene gas was started. The polymerization was conducted at 50°C for 6 h. Finally, the polymer waswashed several times with toluene and dried under vacuum at 60°C. 'H-NMR was used to determine the polarmonomer content in the obtained polymer.The above polymer was immersed in acidic methanol solution for 5 h with strring for alcoholysis, thenwashed several times with methanol and dried under vacuum al 60°C.Supporting Metallocene Catalyst on Functional PP PariclesThe flask was added with 20 g of functional PP paricles, 80 mL of toluene and 20 mL of MAO in sccession.The temperature was brought up to 60PC and the reaction proceeded for 3 h, then filered and washed 3 timeswith toluene. Then 80 mg of rac Et(Ind),ZrCl2 in toluene solution was added, and the supprting reaction wasconducted at 60°C for 5 h. The resulting slury was washed中国煤化工fnally dried undervacuum.TYHCNMHGi-PP/EPR Reactor Alloy Prepared by Metallocene Supported iPP Paricles599Copolymerization of Ethylene and PropyleneQuantitative toluene, metallocene supported PP particles and MAO were introduced into autoclave equipped witha magnetic stirer under a flow of nitrogen. After evacuating the nitrogen in the reactor by a vacuum pump, thecopolymerization was initiated by introducing the mixture of ethylene and propylene with an appointedcomposition, and conducted at 45°C at a constant pressure. The copolymerization was finally terminated byadding excess amount of hydrochloric acid solution diluted with ethanol.CharacterizationHigh temperature 'H-NMR spectra were recorded on a Bruker AMX400 NMR spectrometer ino-dichlorobenzene-d4 at 1209C. The concentration of Zr (in rac-Et(Ind)zZrCl2) on the PP supports weredetermined by inductively coupled plasma atomic emission spectroscopy using a IRIS Intrepid II XSP type ICP.The intrinsic viscosity of polypropylene and EPR was measured with an Ubbelohde in decalin solution at135°C. Viscosity-average molecular weights (M,) of PP and EPR were estimated from the intrinsic viscosity datausing the Mark Houwink equation. Isotacticity (1.I) of polypropylene was determined as the weight fraction ofpolymer insoluble in boiling heptane. The iPP/m-EPR reactor alloy was extracted by boiling heptane for 24 h,and EPR dissolved in boiling heptane was obtained by removing the solvent. Apparent morphology of sampleswas examined by scanning electron microscopy (model Hitachi S-4800). Differential scanning calorimetryanalysis of the samples was made on a DSC Q100 V9.5 Build 288. The sample was heated from -100C to180°C at a heating rate of I0 K/min, and kept at 180°C for 5 min, then cooled to -100°C at 10 K/min forrecrysallization; this was followed by reheating from -1009C to 180°C at 10 K/min.RESULTS AND DISCUSSIONThe Functional PP ParticlesFigure I ilustrated the process for preparation of functional PP particles. Copolymerization of propylene anddihydromyrcene alcohol treated by triethylaluminium was conducted with Z-N catalyst system, followed byhydroxylation with acidic methanol, leading to the production of functional PP particles containing hydroxyl inside chains (B in Fig. 1).、"+ A(Eo)一个ou个o-a(TiC1/MgC)/SiO;HCIMethanolCopolymerizationtthrttBFig. 1 Scheme for synthesis of functional polypropylene particlesIt was seen from Table 1 that the addition of dihydromyrcene alcohol treated by triethylaluminium inthe polymerization of propylene increased the activity of Z-N catalyst slightly as compared with the propylenehomo-polymerization case and the polar monomer reached a high conversion level of 66.3%. The functionalpolypropylene particles showed almost the same basic properties as neat PP.Figure 2 showed the 'H-NMR spectra of neat PP and copolymer A. For the copolymer A, in addition to thethree major peaks at δ= 0.86, 1.26, and 1.57 corresponding to the CH, CH2, and CH protons in the PPbackbone, there was a minor peak at δ= 0.1 (marked by arrows) corresponding to the protons of methylene in一Al- CH2- CH; on the side group of PP backbone. The polar monomer content in copolymer A was thencalculated by comparing the integrated intensity of the peak at δ= 0.1 with that of the sum of the peaks atδ= 0.86, 1.26, 1.57 based on the number of protons each ch中国煤化工omer content incopolymer A was 1.33 mol%, indicating the satisfactory insertionMHCN M H Gbones.600L. Lu et al.Table 1. Preparation and characterization of neat PP and functional Pp*Run°AlcoholfYield (g)ActivityConv' cceMn.TmAH{ I.1(mmol)(kg PP/(molTih))___ (%)_ (mol%)(x 10)(C_ (J/g)__ (%)_84.3151.964.5161.888.9 98.089.0160.41.3363.3160.8Conditions: Z-N cat. = 100 mg, TEATi = 300, Si/Ti = 30,1=6 h, T= 50°C, pressure = 0.202 MPa, amount of toluene =600 mL; "Run 1 is neat PP, run 2 is copolymer A in Fig. I; 'Dihydromyrcene alcohol was treated with TEA (TEAValcoholmol ratio = 1.2) before Z-N catalyst system was added; “Conversion of dihydromyrcene alcohol; “Comonomer(dihydromyrcene alcohol) content in the polymer determined by 'H-NMR; 'Determined by DSC measurement_L.I~b1.6 1.20.0Fig. 2 'H-NMR spectra of (a) neat PP and (b) copolymer ACopolymeriation of Ethylene and PropyleneThe obtained functional polypropylene granules with porous structure were used as supports to chemically bondrac-E(Ind)2ZrClz as mentioned in the experimental section. Inductively coupled plasma (ICP) results showedthat the content of Zr in the thus-prepared metallocene supported PP particles was 110 ug per gram of PP. Thismetallocene supported PP particles were then applied for ethylene and propylene slurry copolymerization toproduce iPP/m-EPR reactor alloys.The effects of MAO/Zr ratio on the copolymerization activity and property of the obtained polymer wasinvestigated. As shown in Table 2, the reaction activity rapidly increased from 1.29 to 12.28 g of EPR/(mol Zr hPa) when increasing MAO/Zr ratio from 1000 to 3000 (run 1-3), since more potential active sites of metalloceneanchoring on PP particles were activated by more amount of MAO. As a result, the amount of m-EPR in alloyincreased from 9.55% to 49.93%. Figure 3 showed that the melting peak attributing to EPR component graduallybecame stronger as MAO/Zr ratio increased. Furthermore, Tm of EPR gradually shifted to higher temperaturewith increasing MAO/Zr ratio.Table 2. Copolymerization of ethylene and propylene with melallocene supported PP particles*PressureEthyleneTimeEPRM, of EPRRunAIZr(g of EPR/(MPa)in feed (mol%)(min) content (Wt%)(mol Zr h Pa))0.101501000101.292520004036.687.13300049.9312.287.821.094)053.036.046:56.7616.140.6062065.715(88.2928.6194.1940.40762.48 _2.1Conditions: T = 45°C, mtllocene supported PP particles=2 g.| 中国煤化工alymerizationof ethylene and propylene with homogeneous rac-E(nd)zZrCI2 C:00 mL of toluene:MYHCNMHGi-PP/EPR Reactor Alloy Prepared by Metallocene Supported iPP Paricles601The copolymerization activity was also greatly influenced by the monomers composition in feed (run 3-6perfomned at 0.101 MPa) as shown in Table 2. The activity increased grealy from 1.09 to 16.14 g of EPR/(molZr h Pa) as ethylene content in fee increased from 30% to 65%, which resulted from the higher reactivity ofethylene compared with propylene in copolymerization catalyzed by mlallocene catalyst. The content of EPR inalloy also increased with increasing ethylene content in feed. The situation was analogous for run 7-9 whichwere performed with different feed composition at 0.606 MPa. Figures 4 and 5 showed the DSC profiles ofPP/m-EPR aloys produced with variable monomer composition at 0.101 MPa and 0.606 MPa respectively. Themelting peak of m-EPR prepared by the mallocene catalyst shifed to higher termperature with increasingethylene content in monomer feed due to the increasing content of ethylene in EPR. Therefore, high ethylenecontent in feed was propitious to the production of blocky EPR, while low ethylene content in feed waspropitious to the production of EPR with random microstructure.-100-60-202060100140180Temperature (C)Fig. 3 DSC curves of PP/m-EPR alys prepared at diferent MAO/Zra) 1000 (run 1); b) 2000 (run 2); c) 3000 (run 3)-100 -60-202060100140 180Fig.4 DSC curves of PP/m- EPR aloys prepared at dfferenet feed composition a 0.101 MPaEthylene content in feed: a) 30% (run 4); b) 40% (run 5); c) 50% (run 3); d) 65% (run 6)-100 -60 -20 20 60100 140 18Temperaure (C)中国煤化工Fig. 5 DSC curves of PP/m EPR alys prepared at diffEthylene content in feed: a) 30% (run 7); b) 50% (run 8)|YHCNMHG602L. Lu et al.The m-EPR in reactor aloy prepared by melallocene supported on PP particles was compared with thatprepared by the homogeneous maeallocene catalyst. As shown in Table 2, the molecular weight of m-EPRproduced by meallocene supported on PP particles (run 8) was much higher than that produced by homogeneousmetallocene (run 10) due to the steric hindrance in catalyst suppoting. As shown in Fig. 6, m-EPR in the reactoralloy presented more intensive and broader melting peak comparing with the neat m-EPR prepared withhomogeneous metallocene catalyst. The intensive melting peak (i.e. high value of melting enthalpy) of run 8indicated that the copolymer prepared with the supported metallocene was less random than that prepared withhomogeneous one. The broad melting peak of m-EPR in the reactor alloy was believed to be related to the broaddistribution of monomer composition from the surface to inner of PP particle, which resulted from monomerdiffusion limitations.-100 -60 -2140 180Temperature (C)Fig.6 DSC curves of PP/EPR aloys prepared by (a) homogeneous metallocenecatalyst (run10) and (b) PP -supported metallocene catalyst (run 8)Figure 7 showed the DSC curves of PP/EPR alloy prepared by sole Z-N catalyst and PP/m.EPR alloyprepared from melallocene supported PP particles. Comparing with the PP/EPR, m-EPR in PP/m-EPR alyshowed much lower melting temperature, indicating that ethylene propylene copolymers synthesized frommetallocene supported PP particles had much more random features in microstructure. Therefore, it is possible tooptimize the structure of EPR in reactor alloy by integrating the advantage of metallocene catalyst incopolymerization of ethylene and a-olefin.-100 -60 -20 20 60 100 140 180Fig. 7 DSC curves of PP/EPR aloys prepared by (a) Z-N catalyst (EPR = 19 w%)and (b) maeallocene supported PP particles (run 2 in Table 2)MorphologyWith the aid in morphological replication of Z-N catalyst particles under mild polymerization, the functional PPparticles were spherical and porous with diameter of 300- -500 μm as observed in Fig. 8. PP/m-EPR reactor alloywith 37 wt% copolymer prepared from matallocene supported PP particles maintained the spherical shape of PPparticles and were well scattered. However, the pores of original PP particles were flled with copolymer phaseresulting in smooth surface of alloy. The active sites of metllocene catalvst. which were immobilized on thesurface of pores or in the amorphous phase, conducted cop中国煤化工propylene, and theproduced copolymer phase would fil gradually in the pores.YCNMHGi-PP/EPR Reactor Alloy Prepared by Metallocene Supported iPP Particles603200 um ._200 um_100md_ 200umFig. 8 Surface morphologies of particlesa, b) Functional polypropylene particles; C, d) PP/m EPR aloy containing 37 wt%copolymer (run 2 in Table 2)To investigate the m-EPR phase distribution in PP matrix, the obtained iPPEPR reactor alloy with 37 w%m-EPR was melt-blended in a mixer, and then heat molded into sheet which was subsequently extracted byboiling heptane for 24 h. Finally, the m-EPR on the surface of sheet was removed away by the solvent. Figure 9showed that the m-EPR separated phases were finely and uniformly dispersed in PP matrix, and the domains ofm-EPR micro phase were mostly less than 2 μm in size.Fig.9 Distribution of m-EPR phase in PP matrix after meltblending of iPP/EPR reactor alloyCONCLUSIONSSpherical isotactic polypropylene porous particles containing a certain amount of hydroxyl groups wereprepared with the copolymerization of propylene and triethyaluminum treated dihydromyrcene alcohol byZieger-Natta catalyst. These particles were eficient in supporting rac-Et(nd)zZrCh2 by chemical anchoring andwere applied to ethylene and propylene slury copolymerization to produce PP/m-EPR reactor alloys. It wasfound that the copolymerization activity of metallocene supported PP particles increased with the increase ofMAO/Zr ratios and ethylene content in feed, and the composition of m-EPR formed could be adjusted bymonomer composition in feed. 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