Search

A new class of melt blend material was prepared by extruding a mixture of 3-aminopropyltriethoxysilane (APTES), maleic anhydride-grafted poly(propylene) (PP-g-MA) with different molecular weight and MA content and poly(propylene) powder produced with a TiCl 3 -based catalyst (PP-A). A suitable selection of PP-g-MA provided extremely high melt strength (MS) of resultant blend materials. Such a superior melt property was caused by the synergy between the present melt reaction and the higher molecular weight portion containing PP-A. The gel content measurements of typical blend materials and PP-g-MA/ APTES blends indicated that an excessive amount of inert PP suppresses the formation of gels. The reaction between PP-g-MA and APTES was then investigated by analyzing crystalline polymer fractions separated from the atactic PP/PP-g-MA/APTES and atactic PP/PP-g-MA blends. The FT-IR analysis of the fractions revealed that the NH 2 group in APTES readily reacts with MA grafted on PP and the reaction leads to the formation of imide linkage. Moreover, the GPC analysis of the fraction showed that higher molecular weight polymers were formed in the presence of APTES. Since a trace amount of water surely produces in the vicinity of active silyltriethoxy groups during the reactive extrusion, such polymers were formed by the condensation between hydrolyzed APTES-grafted polymer chains. These results led us to the conclusion that long-chain-branched PP (LCB-PP) was certainly produced and its formation is essential for the increase in MS of the present blend materials.

Ethylene polymerization was conducted with a catalyst prepared by mixing 2,6-bis{1-[2,6-(diisopropylphenyl)imino]ethyl}pyridine iron dichloride, Mg(C2H5)(n-C4H9) and Al(C2H5)1.5Cl1.5 in the presence of common alkylaluminium as cocatalyst. Both the activity and the molecular weight of polymers produced were markedly dependent upon the polymerization temperature. The end-group analysis of polymers showed that the molecular weight of polymers produced at higher temperature was reduced by chain transfer with Al(C2H5)3 in addition to β-hydrogen elimination.

Summary: Stopped-flow polymerization of propene was first conducted at 40 °C using the TiCl4/DBP/MgCl2 catalyst (DBP = dibutyl phthalate) combined with Al(C2H5)3. An induction period was observed at the beginning of polymerization, and the resulted polymer contained a considerable amount of the isolated ethylene unit. The formation of such unusual structures was concluded to be the result of copolymerization with ethylene originating from the ethylated Ti4+ species. Catalyst washing with toluene and stopped-flow polymerization at 70 °C brought about a drastic decrease in the contents of both Ti and DBP as well as a disappearance of both the induction period and isolated ethylene unit. The microstructures of polymers revealed that the highly stereoregular polymers are produced at the initial stage of polymerization. Changes in yield and molecular weight of polymers with polymerization time showed that the addition of tert-butyl methyl ether (TBME) brought about an increase in the concentration of active sites, but did not affect the propagation rate of propene polymerization. Such an increase in the active site concentration caused by an external donor has hardly been reported so far in kinetic studies using the stopped-flow method; thus, the present result is believed to be a unique example. Kinetic curves of propene polymerization with the Cat. IV-Al(i-C4H9)3 catalyst. (•): with TBME/Al = 0.1 and hydrogen, (♦): with TBME/Al = 0.1 and without hydrogen, (○): without TBME and with hydrogen, (⋄): without TBME and hydrogen.

The article discusses two subjects : (a) temperature effects on the molecular weight, molecular weight distribution and stereoregularity of crystalline fractions of propylene polymers prepared with a supported TiC1 4 /dibutyl phtalate/MgC1 2 - A1 (i-Bu) 3 catalyst system, and (b) effects of different modifiers (components of cocatalyst mixtures that either greatly increase or decrease the content of the crystalline material) on the structures of the crystalline and the amorphous fraction. The principal approach of the research is the combination of GPC data for a series of polypropylene samples prepared under different conditions, the data on the distributional stereoregularity of the polymers (from analytical temperature-rising elution fractionation (Tref) and DSC), and the 13 C NMR analysis in order to produce a coherent picture of functioning of active centers. The combination of the experimental results shows that the crystalline fractions of polypropylene are produced by several families of active centers. The centers significantly differ in the average molecular weights of the polymer components they produce and in stereospecificity. The steric control exerted by the active centers of the highest isospecificity slightly decreases with temperature. In contrast, average isotacticity parameters of the crystalline fractions (estimated by NMR) increase with temperature. The latter effects is mainly the outcome of the variation in the relative contents of polymer components of low isotacticity in the crystalline fractions prepared at different temperatures. When a silane is used as a part of a cocatalyst, it not only poisons aspecific centers but poisons the centers of reduced isospecificity as well. This effect results in the increase of the average molecular weight of the crystalline fraction, narrowing of its molecular weight distribution and the increase of its average isotacticity.

Glass-fiber (GF) reinforced polypropylene (PP) is a very important industrial material. However, as PP is a non-polar polymer, the interfacial adhesion strength between PP and GF is very weak. In order to resolve this problem, maleic acid grafted PP (MA-PP) is generally used. In this way the tensile strength of GFPP can be improved remarkably. Moreover long glass-fiber reinforced PP pellets for injection molding have been recently developed. In spite of these improvements, the strength of GFPP still lags those of other GF reinforced engineering plastics. In order to improve the strength of GFPP, it is necessary to reinforce the weakest of the many interfaces and interphases in the GFPP system. It was found that the interface between the malefic acid grafted PP and the neat matrix PP is the weakest layer. Thus, to reinforce this interface, it is important to increase the entanglement between the MA-PP and PP molecules. It was found that the strength of GFPP could be improved by using high molecular weight MA-PP.

Copolymerization of propene and small amount of ethylene was conducted with the TiCl 4 /DBP/MgCl 2 -Al( i-C4H9)3 catalyst in the presence and absence of 1-allyl-3,4-dimethoxybenzene( ADMB ). Addition of ADMB caused a decrease in the ethylene content in copolymer with an increase in the activity. From a detailed analysis of the copolymers fractionated with boiling diethylether, it was found that the ADMB-containing system gives ether-soluble polymers with higher molecular weight and narrower molecular weight distribution as well as less content of regioirregular sequences of propene. The microstructures of the ether-soluble parts suggested that ADMB might accelerate the propene polymerization at the aspecific sites formed.

Influence de la nature et de la concentration de l'ether ajoute (Et 2 O, n−BuOMe, t−BuOMe) sur l'activite et la stereospecificite du catalyseur supporte TiCl 4 (phtalate de dibutyle/MgCl 2 −Al(i−Bu) 3 dans la polymerisation du propene. L'ether t−BuOMe montrant l'augmentation de l'activite la plus importante, l'influence de la nature et de la concentration de l'ester (benzoate d'ethyle, phtalate de dibutyle, phtalate de dicyclohexyle) sur l'activite du catalyseur contenant cet ether est etudiee

Propene polymerization was first carried out at 70 °C using the TiCl 4 /DBP/MgCl 2 catalyst in combina- tion with a mixture of ADMB and various alkylaluminium compounds. Both the activity and the molecular weight of the polymer were strongly dependent on the kinds of alkylaluminiums. However, the isotactic index (I.I.) of the polymer was hardly affected by them. In order to control the I.I. value, the propene polymerization was then conducted with the TiCl 4 /DBP/MgCl 2 -Al(i-C 4 H 9 ) 3 /ADMB catalyst by changing the polymerization temperature. A suitable selection of polymerization temperatures gave a higher molecular weight PP containing various amounts of APP, i.e., I.I. 4-59%. Mechanical testing indicated that the obtained polymers exhibited a wide range of physical properties from a low modulus thermoplastic elastomer to flexible plastics depending on their stereoregularities. The improved elastic recovery of the obtained PP in the present study could be simply interpreted by the decrease in the [mmmm] or crystallinity of the polymer. Thus, the polymer having the lowest such values was found to have an excellent elastic recovery, which was comparable to that of ELPP as previously reported. The present result is the first example of the synthesis of an elastomeric poly- (propylene) using a highly active MgCl 2 -supported Ti catalyst.

Homo- and copolymerization of ethylene and propylene was carried out using a heterogeneous Cr(Ch 3 COO) 3 AlEt 2 Cl catalytic system in toluene at 40°C. Homopolymerization was studied at atmospheric pressure and followed by measuring the volume of monomer consumed. Copolymerization was carried out at low pressure in a closed system and the progress of the reaction was studied by monitoring the change in monomer pressure. Random copolymers were obtained despite the catalytic system being heterogeneous.

The copolymerization of propylene with 1-butene was carried out in presence of the catalytic system TiCl4/Mg[(CH2)5CH3]2 in heptane. A transparent copolymer with a random distribution (r1 · r2 = 1,0) was obtained. The catalyst shows a considerably high activity. The rate of monomer addition was found to be independent of the chemical structure of the growing polymer chain end, which is quite different for the copolymerization of ethylene with propylene.

Both the homopolymerization of ethylene, propylene, 1-hexene and 1,3-butadiene and the copolymerization of ethylene with these monomers were conducted over the SiO2-supported TiCl4 catalyst using AlEt2Cl or AlEt3 as a reducing reagent. With an increase in the concentration of AlEt3, the polymerization activities except for ethylene markedly decreased and the structures of the copolymers drastically changed to polyethylene. From these results, a correlation was established between the oxidation states of titanium and the polymerization activities for these monomers.

The SiO2-supported MgCl2/TiCl3 catalyst was prepared by treating the mixture of TiCl3· 3C5H5N, MgCl2·(THF) and SiO2 with AlEt2Cl in n-heptane solvent. The catalyst combined with AlEt3 showed a very high activity for the copolymerization of ethylene and propylene and gave a moderately random copolymer. A plausible model for the copolymerization was proposed from the kinetic study of the copolymerization.

The SiO2-supported TiCl4 catalyst was prepared by allowing SiO2 to react with TiCl4 in n-heptane. Then MgCl2 was supported onto this catalyst by treating a mixture of this catalyst and MgCl2·(THF)2 with AlEt2Cl in n-heptane. The SiO2-supported MgCl2/TiCl2 catalyst thus prepared showed a very high activity for the copolymerization of ethylene and propylene and gave a moderately random copolymer. A plausible model for the active species was proposed from the analytical results of the catalytic system.

Based on the theory of catalyst design, which we established, we developed an efficient Ti-based catalyst for the production of an EP rubber. The catalyst was prepared by milling the Ti (OBu)4/MgCl2 mixture in heptane, followed by treatment with AlEt2Cl. The catalyst combined with Al(i-Bu)3 showed a markedly high activity for ethylene-propylene copolymerization and gave quality EP rubber. Addition of hydrogen to the system controlled molecular weight without diminishing polymerization activity. The optimum conditions of the copolymerization were also investigated.

Copolymerization of ethylene with propylene was conducted over the thermally-reduced γ-Al2O3-supported TiCl4 catalyst both in the absence or presence of AlEt3 (or AlEt2Cl). It was found that the structure of the polymer drastically changed from a random copolymer to polyethylene with an increase in the concentration of AlEt3. A plausible mechanism was proposed for the copolymerization.