Elsevier

Polymer

Volume 42, Issue 13, June 2001, Pages 5763-5769
Polymer

Structure and viscoelastic properties of amorphous ethylene/1-hexene copolymers obtained with metallocene catalyst

https://doi.org/10.1016/S0032-3861(00)00936-8Get rights and content

Abstract

Copolymerization of ethylene and 1-hexene was performed with diphenylmethylidene (cyclopentadienyl-fluorenyl) zirconium dichloride (Ph2C(Cp)(Flu)ZrCl2) in combination with dimethylanilinium tetrakis-(pentafluorophenyl)borate ((Me2PhNH)(B(C6F5)4))/triisobutylaluminum (i-Bu3Al) catalyst. This catalyst system produced ethylene/1-hexene random copolymers (EHRs) with high molecular weight and narrow molecular weight distribution. The rheological properties of the rubbery EHRs were compared with those of the rubbery ethylene/propylene copolymer (EPR). It was found that the rubbery plateau modulus GN0 of the EHR is much lower than that of the EPR.

Introduction

After the frontier works by Kaminsky [1], great interest has arisen in the field of metallocene catalyst technology. In particular, there have been many reports on the copolymerization of ethylene and α-olefins [2], [3], [4], [5]. Kaminsky and Miri [2] showed that dicyclopentadienyl zirconium dimethyl (Cp2ZrMe2)/methylaluminoxane (MAO) has high activity for the copolymerization of ethylene and propylene and the terpolymerization of ethylene, propylene, and 5-ethylidene-2-norbornene. Moreover, the catalyst system was found to produce the random polymers having narrow molecular weight distribution. Further, Ewen [3] studied the reactivity ratio for several metallocene catalysts. Chien and He [4] investigated the relation between metal centers of the metallocene compounds and the characteristics of the copolymers obtained. Uozumi and Soga [5] discussed the effect of the catalyst stereospecifity on the copolymerization reactivity for the ethylene/propylene and ethylene/1-hexene copolymerization.

Their intensive studies make it possible to produce various kinds of rubbery ethylene/α-olefin copolymers commercially. Thus, much attention has been focused on the application of the vulcanized rubber. Mäder et al. [6] studied the thermal properties of the rubbery ethylene/α-olefin copolymers produced by the metallocene catalyst, in which the copolymers having below 50 mol% of α-olefin were used. According to them, glass transition temperature Tg takes the lowest value when the α-olefin content in the copolymer is about 50–60 wt% for both rubbery ethylene/propylene copolymer (EPR) and ethylene/1-butene copolymer (EBR). The results agree well with those obtained by the model EBR produced by the hydrogenation of polybutadienes with various vinyl contents [7]. Moreover, the rheological properties of the model EBRs were investigated by Carella et al. [7]. According to them, the rubbery plateau modulus GN0 decreases with increasing 1-butene content in the EBR, whereas the product of Je0GN0 is constant, where Je0 represents the steady-state compliance. The rheological properties of rubbery ethylene/1-hexene copolymer (EHR) and ethylene/1-octene copolymer (EOR), however, have not been clarified yet, although both EBR and EOR can be produced by the metallocene catalyst. Furthermore, it is important for the industrial application because the rheological properties greatly affect the processability as well as the mechanical properties of the vulcanized rubbers.

The aim of this study is to clarify the characteristics of the rubbery EHR produced by the metallocene catalyst system composed of diphenylmethylidene (cyclopentadienyl-fluorenyl) zirconium dichloride (Ph2C(Cp)(Flu)ZrCl2) in combination with dimethylanilinium tetrakis-(pentafluorophenyl) borate ([Me2PhNH][B(C6F5)4])/triisobutylaluminum (i-Bu3Al). In this paper, we will discuss the relation between molecular characteristics of the EHR and mechanical properties of the vulcanized EHR.

Section snippets

Materials

Ph2C(Cp)(Flu)ZrCl2 was synthesized according to the literature [8]. [Me2PhNH][B(C6F5)4] and i-Bu3Al from Tosoh Akzo Co. were used without purification. Ethylene, 1-hexene, and toluene as a solvent were obtained commercially and purified according to the usual procedures.

Copolymerization procedure

The copolymerization was carried out in a 5-l stainless steel autoclave equipped with a temperature controller and a magnetic stirrer. The autoclave was filled with 2.5 l of toluene containing 1-hexene and heated up to 313 K. Then

Characteristics of polymers

The composition and the molecular weights of the copolymers used are shown in Table 1. As seen in the table, the 1-hexene content in EHR25 is as much as the propylene content in EPR37 by weight ratio. Moreover, the α-olefin content in EPR37 is between those in EHR33 and EHR40 by molar ratio. Furthermore, all samples used have a high molecular weight and a narrow molecular weight distribution.

Fig. 1 exemplifies the result of the GPC-IR measurement of EHR33. As seen in the figure, the 1-hexene

Conclusions

In the present study, the copolymerization of ethylene and 1-hexene was performed with diphenylmethylidene (cyclopentadienyl-fluorenyl) zirconium dichloride (Ph2C(Cp)(Flu)ZrCl2) in combination with dimethylanilinium tetrakis-(pentafluorophenyl)borate ((Me2PhNH)(B(C6F5)4))/triisobutylaluminum (i-Bu3Al) catalyst. It was found that the catalyst system produced ethylene/1-hexene random copolymers (EHRs) with high molecular weight and narrow molecular weight distribution. Moreover, the 1-hexene

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