Theoretical Studies on The Cationic Polymerization Mechanism of Oxetanes 


Vol. 35,  No. 6, pp. 636-644, Dec.  1991


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  Abstract

에너지기인 methoxy기(-CH2OCH3), azido기(-CH2N3) 그리고 nitrato기(-CH2ONO2)로 치환된 옥세탄(oxetane)의 단량체를 산촉매하의 중합반응에 관해서 반경험적인 MINDO/3, MNDO, AMI 방법 등을 사용하여 이론적으로 고찰하였다. 치환체 옥세탄의 친핵성 및 염기성은 옥세탄 산소원자의 음전하 크기로 설명할 수 있으며, 공중합하의 성장단계에서 옥세탄의 반응성은 옥세탄의 반응 중심 탄소의 양전하 크기와 친전자체의 낮은 LUMO 에너지에 좌우됨이 예측된다. 에너지화기 고리형 oxenium 이온형이 열린 carbenium 이온형으로 전환되는 과정은 oxonium 이온과 carbenium 이온 사이의 계산된 안정화에너지(약 10~20 kcal/mole)에 의하면 carbenium 이온이 더 유리함을 예측할 수 있다. 평형상태의 고리형 oxonium 이온과 열린 carbenium 이온의 농도크기가 반응메카니즘의 결정단계이며, 산촉매하의 형태와 계산을 기초로 하여 빠른 평형을 예상하여 볼 때 선폴리머 성장단계에서 SN1 메카니즘이 SN@ 메카니즘보다 빠르게 반응할 것으로 예측된다. The cationic polymerization of substituted oxethanes which have pendant energetic groups such as methoxy, azido, and nitrato are investigated theoretically using the semiempirical MINDO/3, MNDO, and AM1 methods. The nucleophilicity and basicity of substituted oxethanes can be explained by the negative charge on oxygen atom of oxetanes. The reactivity of propagation in the polymerization of oxetanes can be represented by the positive charge on carbon atom and the low LUMO energy of active species of oxetanes. The reaction of the energetic cyclic oxonium ion forms to the open chain carbenium ion forms is expected by computational stability energy of the oxonium and carbenium ion (about 10~20 kcal/mole) favoring the carbenium ion. The relative equilibrium concentration of cyclic oxonium and open carbenium ions is found to be a major determinant of mechanism, owing to the rapid equilibrium of these cation forms and the expectation based on clauclation the the prepolymer propagation step SN1 mechanism will be at least as fast as that for SN2 mechanism.

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  Cite this article

[IEEE Style]

Y. Cheun, J. Kim, S. Park, "Theoretical Studies on The Cationic Polymerization Mechanism of Oxetanes," Journal of the Korean Chemical Society, vol. 35, no. 6, pp. 636-644, 1991. DOI: .

[ACM Style]

Young-Gu Cheun, Joon-Tae Kim, and Seong-Kyu Park. 1991. Theoretical Studies on The Cationic Polymerization Mechanism of Oxetanes. Journal of the Korean Chemical Society, 35, 6, (1991), 636-644. DOI: .

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