The efficient and selective introduction of functional
groups to
hydrocarbon polymers enables facile access to new polymer materials
with various physical properties. In the present study, we have focused
on cyclopropane-containing norbornadiene dimers (NBDDs) as bifunctional
monomers and post-polymerization modification (PPM) for the synthesis
of functionalized cyclic olefin polymers (COPs). The ring-opening
metathesis polymerization (ROMP) of the four NBDD stereoisomers (exo-exo, exo-endo, endo-exo, and endo-endo) and the subsequent hydrogenation
proceeded selectively to give the corresponding COPs (H-poly(NBDD)s)
with reactive cyclopropane moieties. There are distinct differences
between the four isomers in terms of polymerization rate and the physical
properties of the resultant polymers. The endo-exo- and endo-endo-NBDDs show lower ROMP reactivities
than the exo-exo- and exo-endo-NBDDs
due to steric hindrance. All of the polymers before and after hydrogenation
are amorphous, regardless of annealing (with the exception for the
unannealed H-poly(exo-endo-NBDD)). Compared with
the polymers of the exo-norbornenyl isomers, their endo-counterparts show lower solubilities, higher glass
transition temperatures, sharper X-ray diffraction peaks, and larger d-spacings. The highly soluble H-poly(exo-exo-NBDD) was employed for the PPM via protic acid-catalyzed cyclopropane
ring-opening to produce six new COPs bearing acyloxy, alkoxy, or aryl
groups. Although rearrangements occur during ring-opening presumably
through nonclassical carbocations, the polymer structures were determined
with reference to the reactions of their corresponding monomeric model
compounds. The PPM with m-xylene, for example, proceeds
regioselectively while maintaining a narrow molecular weight distribution
to produce a xylyl-substituted COP with good solubility and high thermal
stability.
In relationship to a solid target cooling system of an accelerator-driven system (ADS), wettability effect on boiling heat transfer has been experimentally investigated by irradiation with ultraviolet and gamma rays (γ-rays). The experimental apparatus consists of a copper heater block, a rectangular container, and a thermostat bath. Two copper heater blocks were fabricated: one is for radiationinduced surface activation (RISA) and the other is for photoelectric reaction by ultraviolet whose heat transfer surface is coated by a TiO 2 film. These copper heater blocks were irradiated by ultraviolet or by γ-rays to change the surface wettability. Boiling heat transfer under subcooling conditions was measured before and after the irradiations to study the wettability effect. Experimental results show that nucleate boiling curves are shifted to the higher wall superheated side with the irradiated surface because of the decrease of the active nucleation sites. Heat transfer enhancement was found in both the critical heat flux and microbubble emission boiling (MEB) regions under these experimental conditions.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.