Rational Approaches to Regulating Polymer Properties in Ring-Opening Metathesis Polymerization

Xn, chain transfer, degree of polymerization, living polymerization, ruthenium, microstructure, double bond migration

Benedicto, Alto D. ; Grubbs, Robert H.

University:California Institute of Technology

Department:Chemistry and Chemical Engineering

关键词: Xn, chain transfer, degree of polymerization, living polymerization, ruthenium, microstructure, double bond migration;   

Others  :  https://thesis.library.caltech.edu/3471/3/Benedicto_ad_1995.pdf

美国|英语

来源: Caltech THESIS

【 摘 要 】

The molecular weight distribution of a living polymerization when chain-transfer agents are intentionally added were computed numerically. Results showed that traditional expressions for number-average degree of polymerization (X̅_n) and polydispersity index (PDI) of chain-growth polymerization cannot be used. The well-known Mayo equation fails even when the system has achieved steady-state polymerization. Although the behavior of the system is complex, an analytical expression for X̅_n was derived. Plots based on the analytical expression showed excellent agreement with that from numerical solutions. The implications of the calculations were discussed. The kinetics of living ring-opening metathesis polymerization (ROMP) of norbornene in the presence of neohexene catalyzed by Mo was investigated.

The living ROMP of norbornene (n̲) and bicyclo[3.2.0]hept-2-ene (c̲) by Cl₂(PPh₃)₂Ru(=CHCHCPh₂) was demonstrated. The molecular weight varied linearly with conversion. Discrete propagating species showed that PPh₃ ligand dissociated during polymerization of c̲, and that CuCl (abstracts PPh₃) enhanced the rate of polymerization of n̲. The specific propagation rate constants (k_n̲n̲ and k_c̲c̲, respectively) of homopolymerization of n̲ and c̲ were measured, respectively. Block copolymers were easily prepared. From reactivity ratio studies, the ordering of the specific propagation rate constants are k_n̲c̲ >> kk_n̲n̲ > k_c̲c̲ > k_c̲n̲. The effect of styrene as chain-transfer agent on the molecular weight was examined.

The hitherto unassigned (and unknown) microstructure of polymers prepared from 7-oxabicyclo[2.2.1]hept-2-ene derivatives have finally been unambiguously assigned. Polymers catalyzed by W(CH-_t-Bu)(NAr)(OCMe(CF₃)₂)₂ have all cis double bonds and highly syndiotactic, while those from RuCl₃•3H₂0 and [RuCl(μ-Cl)(μ³:μ³-C₁₀H₁₆)]₂ {C₁₀H₁₆= 2,7-dimethyloctadienediyl} have high trans double bond content and highly isotactic.

Studies on the olefin isomerization catalyzed by Ru(H₂O)₆tos₂ revealed that the presence of hydroxyl functionality on the terminal olefin resulted in formation of 1:1 ratio of cis : trans double bonds on the isomerized internal olefin product, in contrast with near exclusive isomerization of double bond to trans when no hydroxyl group was present.

A numerical algorithm was developed for the evaluation of a chirality function for triangles on a plane, showing that such algorithm may be easily extended into the case of tetrahedron in 3-dimensional space.