$MgCl_2$/THF/$TiCl_4$ bimetallic complex catalyst showing high catalytic activity in ethylene polymerization when combined with aluminum alkyl cocatalyst was prepared. Temperature programmed decomposition of $MgCl_2$/THF/$TiCl_4$ bimetallic complex catalysts and its effect on ethylene polymerization rate were investigated. And also a study on the possibility of propylene polymerization by using this catalyst was performed.
The products formed during the thermal treatment of $MgCl_2$/THF/$TiCl_4$ bimetallic complex catalyst were THF and 1,4-dichlorobutane as identified by MS, FTIR and $^{13}C-NMR$ spectroscopy. The amount of 1,4-dichlorobutane formed during thermal treatment decreased with the increase of Mg/Ti ratio. Ethylene polymerization was performed at 70℃ with bimetallic complex catalysts thermally pretreated at various temperatures. When the temperature of the thermal treatment of $MgCl_2$/THF/$TiCl_4$ bimetallic complex catalyst (Mg/Ti=5.2) was below 108℃, the catalytic activity increased, while the activity decreased above 140℃. However, the catalytic activity of $MgCl_2$/THF/$TiCl_4$ bimetallic complex catalyst (Mg/Ti=16.5) heated above 80℃ decreased. This indicated that the thermal stability of the catalyst decreased with the increase of Mg/Ti ratio. $MgCl_2$./THF/$TiCl_4$ bimetallic complex catalyst (Mg/Ti=5.2) was activated with excess amount of $AlEt_2Cl$(Al/Ti=5). The thermal stability of this preactivated catalyst was less than that of non-activated catalyst.
When $MgCl_2$/THF/$TiCl_4$ bimetallic complex catalyst was combined with aluminum alkyl cocatalyst, propylene was not polymerized. The catalyst was characterized by ESR and the chemical titration in order to investigate the reason why propylene was not polymerized in this catalytic system. Titanium oxidation state in the catalyst was observed to be mostly in state of $Ti^{4+}$. ESR band at g (spectroscopic splitting factor)=1.968 due to $Ti^{3+}$ associated with adjacent $Ti^{2+}$ appeared when the catalyst was treated with $AlEt_3$ ([$AlEt_3$]/[$TiCl_4$]=128). $Ti^{3+}$ denoted by ESR band at g=1.968 was suggested to be inactive site for porpylene polymerization, because propylene was not polymerized in this catalytic system. The ESR band at g=1.968 was weak because most of $Ti^{3+}$ present in the catalyst formed $Ti^{3+}-Ti^{3+}$ cluster. Model catalyst ($MgCl_2$/$AlEt_2Cl$/THF/$TiCl_4$ catalyst) was prepared and characterized to compare with $MgCl_2$/THF/$TiCl_4$ bimetallic complex catalyst. ESR band at g=1.886 disappeared and the intensity of ESR band at g=1.94 became stronger when model catalyst was treated by $AlEt_3$ ([$AlEt_3$]/[$TiCl_4$]=128). Propylene was polymerized in model catalyst (($MgCl_2$/$AlEt_2Cl$/THF/$TiCl_4$) while not in $MgCl_2$/THF/$TiCl_4$ bimetallic complex catalyst. These results suggested that $Ti^{3+}$ denoted by ESR band at g=1.94 might be active site for propylene polymerization.
Methylaluminoxane (MAO) which has been known to increase activity and stereospecificity by using organometallic complex catlysts was synthesized and the analysis of the prepared MAO was performed. A study on ethylene polymerization with $Cp_2ZrCl_2$ and the prepared MAO was carried out. $rac-Et(Ind)_2ZrCl_2$ which is a typical stereospecific catalyst was synthesized and analyzed by mass spectroscopy and $^1H-NMR$ spectroscopy. Polymerization of propylene with $rac-Et(Ind)_2ZrCl_2$ and the prepared MAO (II) was carried out. The microstructure of polypropylene was analyzed to investigate the stereoand regiospecificity, resulting from polymerization condition by using the $^{13}C-NMR$ spectrometer.
The activity of ethylene polymerization was above 1.000 Kg-PE/g-Zr.hr.atm by using $Cp_2ZrCl_2$ and the prepared MAO. The catalytic activity of the prepared MAO was very high. The viscosity average molecular weight of the produced polymer was in the range between 60,000 and 370,000. The density was in the range between 0.94 and $0.98 g/cm^3$. The melting temperature was in the range between 135 and 139℃. The overall activation energy for ethylene polymerization was 5.9 ± 07 kcal/mol.
When propylene polymerization was performed by using $rac-Et(Ind)_2ZrCl_2$ and the prepared MAO (II) with [Al]=210 mmol/L at 50℃, the activity was 3,000 kg-PP/mol-Zr.hr.atm. As the concentration of MAO increased, the intrinsic viscosity and the molecular weight of polypropylene did not change much. However, the density and the melting point increased. The molecular weight was more affected by the polymerization temperature than the concentration of MAO. As the polymerization temperature increased, the activity increased, and the molecular weight and the density and the melting point of polypropylene decreased, and the area of the resonances of mmmm sterochemical pentads decreased. The overall activation energy for propylene polymerization was 11.6 ± 0.4 kcal/mol. Polypropylene produced by high pressure polymerization has more stereoregularity and regioirregularity than by atmospheric pressure polymerization. In high pressure polymerization, the n-propyl chain end group was shown. In the case of atmospheric pressure polymerization, various peaks having the vinylidene, n-propyl and isobutyl chain end group was shown. As the concentration of monomer increased, the molecular weight and the melting point of polypropylene increased.
에틸렌 중합에 고활성을 나타내는 $MgCl_2/THF/TiCl_4$ 촉매를 제조하였다. 이 촉매의 열처리가 촉매상태의 변화 및 에틸렌 중합 속도에 미치는 영향을 조사하였다. 또한, 이 촉매로 프로필렌 중합이 되지않는 원인에 관한 연구도 수행하였다. $MgCl_2/THF/TiCl_4$ 촉매를 열처리하면 THF와 1,4-dichlorobutane이 생성됨을 MS, FTIR 및 $^{13}C-NMR$을 사용하여 확인하였다. Mg/Ti 비가 증가하면 촉매를 열처리하는 동안에 생성되는 1,4-dichlorobutane의 양이 감소하였다.
$MgCl_2/THF/TiCl_4$ (Mg/Ti=5.2) 촉매의 열처리 온도가 108 ℃ 이하일때 촉매 활성이 증가하였지만, 140 ℃ 이상으로 열처리하면 활성은 감소하였다. 그러나, $MgCl_2/THF/TiCl_4$ (Mg/Ti=16.5) 촉매는 80 ℃ 이상으로 열처리하면 활성은 감소하였다. 이것은 Mg/Ti의 비가 증가함에 따라서 촉매의 열안정성이 감소하는 것을 나타낸다. $AlEt_2Cl$로 활성화시킨 $MgCl_2/THF/TiCl_4$ 촉매 (Mg/Ti=5.2, Al/Ti=5.0)의 열안정성은 활성화시키지 않은 촉매의 열안정성보다 더 낮았다.
$MgCl_2/THF/TiCl_4$ 촉매는 프로필렌을 중합하지 못하였다. 따라서, 그 원인을 조사하기 위하여 Ti의 산화상태와 그 분포를 ESR과 적정법을 이용하여 분석하였다. 이촉매의 산화상태는 대부분 $Ti^{4+}$의 상태이었다. 이촉매를 $AlEt_3$ ($[AlEt_3]/[TiCl_4]$ = 128)로 처리하면 g=1.986에서 ESR band가 나타나는데, 이것은 $Ti^{2+}$와 결합하고 있는 $Ti^{3+}$에 의한 것이며, 이 g=1.968에서 나타나는 $Ti^{3+}$가 프로필렌 중합에 비활성점인 것으로 추정된다. 또한, 이 band의 강도가 약한데, 이것은 대부분의 $Ti^{3+}$가 $Ti^{3+}-Ti^{3+}$ cluster를 형성하기 때문인 것으로 생각된다. 프로필렌 중합이 가능한 모델 촉매 ($MgCl_2/AlEt_2Cl/THF/TiCl_4$ 촉매)를 $AlEt_3$($[AlEt_3]/[TiCl_4]$ = 128)로 처리하면 g=1.886에서의 ESR band는 사라지고, g=1.94에서의 ESR band의 강도는 더 증가하였다. 따라서, g=1.94에서 나타나는 $Ti^{3+}$가 프로필렌 중합의 활성점인 것으로 생각된다.
유기금속 화합물 촉매와 함께 사용하여 활성 및 입체 규칙성을 증가시키는 MAO (methylaluminoxane)을 $H_2O$와 TMA (trimethylauminum)를 직접 반응시켜서 합성하였으며, $Cp_2ZrCl_2$와 함께 사용하여 에틸렌 중합을 수행하였다. $rac-Et(Ind)_2ZrCl_2$ 유기금속화합물 촉매를 제조하여 MAO와 함께 프로필렌 중합을 수행하였으며, 생성된 폴리프로필렌의 미세구조에 관한 연구도 수행하였다.
제조한 MAO와 $Cp_2ZrCl_2$에 의한 에틸렌 중합 활성은 1,000 kg-PE/g-Zrㆍhrㆍatm 이상이었다. 따라서, 제조한 MAO의 촉매활성은 매우 높았다. 생성된 중합체의 점도 평균 분자량은 60,000-370,000이며, 밀도는 $0.94-0.98 g/cm^3$ 이고, 녹는점은 135-139 ℃ 이었다. 또한, 에틸렌 중합의 전체 활성화 에너지는 5.9 ± 0.7 kcal/mol 이었다.
$rac-Et(Ind)_2ZrCl_2$와 MAO를 사용하여 50 ℃ [AT]=210 mmol/L의 중합조건으로 프로필렌을 중합하였을때 활성은 3,000 kg-PP/mol-Zrㆍhrㆍatm 이었다. MAO의 농도가 증가함에 따라 생성된 폴리프로필렌의 고유점도 및 분자량은 크게 변하지 않았지만 밀도와 녹는 점은 증가하였다. 중합온도가 증가함에따라 활성이 증가하며, 생성된 중합체의 분자량, 밀도, 녹는점 및 입체규칙성은 감소하였다. 이상의 실험으로부터 분자량은 MAO의 농도보다 온도에 더 영향을 받는다는 것을 알수 있었다. 프로필렌 중합에 대한 전체 활성화 에너지는 11.6±0.4 kcal/mol 이었다. 고압 중합에 의해서 생성된 폴리프로필렌은 상압 중합으로 생성된 폴리프로필렌보다 입체규칙성이 더 높으며, 위치불규칙성도 더 높았다. 또한, 고압중합에 의해 생성된 폴리프로필렌에서는 n-프로필 사슬 말단기만 나타나며, 상압 중합으로 생성된 폴리프로필렌에서는 비닐리덴, n-프로필 및 아이소부틸 사슬 말단기가 나타났다. 또한, 프로필렌 농도가 증가함에 따라서 생성된 폴리프로필렌의 분자량 및 녹는점이 증가하였다.
