Living Alternating Ring-Opening Metathesis Polymerization Based on Single Monomer Additions

Abstract

By judiciously modulating the ring strain and sterics, we developed a class of disubstituted cyclopropenes that selectively underwent single monomer addition in ring-opening metathesis but readily underwent alternating ring-opening metathesis polymerization with low-strain cyclic olefins in a living fashion. The substituents on cyclopropenes effectively inhibited homoaddition and prevented secondary metathesis on the polymer backbone. The resulting polymers had controllable molecular weights and end groups, very low dispersities, and high regularity in microstructure under optimized conditions. (1)H and (13)C NMR spectroscopy and MALDI-TOF MS showed a rigorously alternating sequence. Interestingly, disubstituted cyclopropenes were found to present zero-order kinetics, indicating their rapid single addition and the rate-determining ring opening of the low-strain olefin.

Degradable precision polynorbornenes via ring‐opening metathesis polymerization

“…Kinetic control of the monomer sequence has also been shown in anionic polymerization, and ring‐opening metathesis polymerization (ROMP). A few examples in the literature involve the synthesis of alternating copolymers using ROMP, as a result of the catalyst‐monomers pairing, such as in the case of dienes and diacrylates . We previously studied the use of exo norbornenes as functional monomers that when added to the ROMP of the slower endo norbornenes, were rapidly incorporated in the growing polymer chain, thus resulting in copolymers with some control over the monomer sequence .…”

“…A few examples in the literature involve the synthesis of alternating copolymers using ROMP, as a result of the catalyst-monomers pairing, such as in the case of dienes and diacrylates. [16][17][18][19][20][21][22][23][24][25][26][27][28][29][30] We previously studied the use of exo norbornenes as functional monomers that when added to the ROMP of the slower endo norbornenes, were rapidly incorporated in the growing polymer chain, thus resulting in copolymers with some control over the monomer sequence. 31 Nevertheless, when attempting the introduction of a single exo norbornene moiety, the precision was limited.…”

Evidence for Dynamic Chemical Kinetics at Individual Molecular Ruthenium Catalysts

“…Employing this estimation with examination of 75 unique linear growth portions of 0.29 μm 2 regions, each within a distinct aggregate and from three experimental replicates, provided polymerization rates of 0.52×10 5 –20×10 5 monomers s −1 with an average of 6.1×10 5 monomers s −1 , wherein the range reflected the distribution of kinetics in the sample (for linear fits see the Supporting Information, Figure S5). The pseudo‐zero‐order kinetics implied by these linear regions indicated the possibility of a monomer concentration independence on the observed rates. This feature may arise from diffusion‐limited access of the monomer to the ruthenium or from the measurement of the kinetics for short durations over which the effective concentration of monomer is constant.…”

Tuning the Reactivity of Cyclopropenes from Living Ring‐Opening Metathesis Polymerization (ROMP) to Single‐Addition and Alternating ROMP

“…Monomers that undergo single addition are extremely rare for chain‐growth polymerizations and are particularly useful for manipulating the monomer sequence in a polymer. After a single turnover with G3 , these 1,1‐CPE monomers yielded a Ru carbene complex which could not react with a second equivalent of CPE but reacted with unhindered low‐strain cyclic olefins in an alternating fashion to produce alternating copolymers with controlled MWs and narrow MW distributions . AROMP is a unique method to produce polymers with functional groups at defined, long distances,– but it has been challenging to achieve MW control– until recent examples involving 1,1‐CPE monomers from our group and isomerizing bicyclo[4.2.0]octene‐8‐carboxamide monomers from Sampson and co‐workers .…”