Monitoring ROMP Crossover Chemistry via ESI-TOF MS

We report on the ESI-TOF MS investigation of oligomerization and co-oligomerization reactions via ring-opening metathesis polymerization of noncharged monomers. Thus, the monomers <b>1</b>–<b>4</b> ((±)<i>endo</i>,<i>exo</i>-bicyclo­[2,2,1]­hept-5-ene-2,3-dicarboxylic acid-bis-<i>O</i>-methyl ester (<b>1</b>), <i>exo</i>-<i>N</i>-(4,4,5,5,6,6,7,7,7-nonafluoroheptyl)-10-oxa-4-azatricyclodec-8-ene-3,5-dione (<b>2</b>), 3-methyl-3-phenylcyclopropene (<b>3</b>), and (±)<i>endo</i>,<i>exo</i>-bicyclo­[2,2,1]­hept-5-ene-2,3-dicarboxylic acid-bis-<i>O</i>-2,2,6,6-tetramethylpiperidinoxyl ester (<b>4</b>)) were investigated with the catalysts <b>5</b>–<b>8</b> (Grubbs catalyst first generation (<b>5</b>), Grubbs catalyst third generation (<b>6</b>), Umicore M1 (<b>7</b>), and Umicore M3 (<b>8</b>)) with respect to their crossover chemistries. Monomers <b>1</b>–<b>4</b> differ in ring size and substitution patterns and allow to study the monomer reactivities in the order of increasing reactivity for monomer <b>3</b> < <b>4</b> ≈ <b>1</b> < <b>2</b>. The measured spectra display a significant difference between the reactions conducted with first- and third-generation catalysts with the main fraction being unreacted catalyst species for the first-generation catalysts <b>5</b> and <b>7</b>, while just a small fraction is composed of oligomer and co-oligomer species. A significant reduction of the amount of the catalyst species and an increase in the fractions of oligomer and co-oligomer species are observed for the third-generation catalysts <b>6</b> and <b>8</b>, in accordance with their higher reactivity as compared to the first-generation catalysts. The highest fraction of co-oligomer species is observed for the crossover reactions <b>1/3</b> and <b>1</b>/<b>4</b>. Propagation of the second monomer, however, is only observed in the combinations <b>1</b>/<b>2</b> and <b>1</b>/<b>4</b> indicative of the higher reactivity of the norbornenes <b>2</b> and <b>4</b> when compared to the cyclopropene <b>3</b>, the latter requiring the addition of hydrochloric acid

Influence of Grafted Block Copolymer Structure on Thermoresponsiveness of Superparamagnetic Core–Shell Nanoparticles

The morphology and topology of thermoresponsive polymers have a strong impact on their responsive properties. Grafting onto spherical particles has been shown to reduce responsiveness and transition temperatures; grafting of block copolymers has shown that switchable or retained wettability of a surface or particle during desolvation of one block can take place. Here, doubly thermoresponsive block copolymers were grafted onto spherical, monodisperse, and superparamagnetic iron oxide nanoparticles to investigate the effect of thermal desolvation on spherical brushes of block copolymers. By inverting the block order, the influence of core proximity on the responsive properties of the individual blocks could be studied as well as their relative influence on the nanoparticle colloidal stability. The inner block was shown to experience a stronger reduction in transition temperature and transition enthalpy compared to the outer block. Still, the outer block also experiences a significant reduction in responsiveness due to the restricted environment in the nanoparticle shell compared to that of the free polymer state. The demonstrated pronounced distance dependence importantly implies the possibility, but also the necessity, to radially tailor polymer hydration transitions for applications such as drug delivery, hyperthermia, and biotechnological separation for which thermally responsive nanoparticles are being developed