2 research outputs found
Catalytic Chain Transfer Mediated Autopolymerization of Divinylbenzene: Toward Facile Synthesis of High Alkene Functional Group Density Hyperbranched Materials
A facile and highly reproducible autopolymerization method,
mediated
by catalytic chain transfer, for the synthesis of hyperbranched materials
with high alkene functional group density is reported. The rapid autopolymerization
of divinylbenzene at 150 °C in the absence of any catalytic chain
transfer agent was demonstrated to result in the formation of highly
cross-linked networks/gels in less than 10 min. Exploitation of the
extremely high chain transfer coefficient of bis[(difluoroboryl)diphenylglyoximato]cobalt(II)
delayed gelation and produced good yields of high molecular weight
hyperbranched divinylbenzene in under 1 h on a multigram scale. Gas
chromatography was employed to monitor the levels of conversion over
the course of the reaction. The materials produced were characterized
by GPC, MALLS, and viscometry
Mechanistic Investigation into the Accelerated Synthesis of Methacrylate Oligomers via the Application of Catalytic Chain Transfer Polymerization and Selective Microwave Heating
The
synthesis of methyl methacrylate (MMA) oligomers by catalytic chain
transfer polymerization (CCTP) is demonstrated to be significantly
accelerated by the use of microwave heating. The CCTP reactions, which
use a cobalt-based catalyst to very efficiently control the molecular
weight of the final polymer, were conducted in both a conventional
oil bath and a CEM Discover microwave reactor with a target set point
of 80 °C. The required reaction time was shown to be reduced
from 300 to 3 min, while also retaining control over the polymerization.
Additionally, for the first time the bulk temperature of these catalyzed
polymerizations was monitored in both heating methods by the use of
internal optical fiber sensors. It was demonstrated that, to monitor
the temperature of the reaction correctly, it is essential to use
an optical fiber sensor rather than the external IR sensor supplied
with the reactor. The acceleration in the synthesis during microwave
heating was attributed to selective heating of the radical and oligomeric
species within the reaction, which lead to both rapid heating of the
reaction bulk to reaction temperature and average reaction temperatures
that were higher than the chosen set point. However, comparative reactions
carried out under conventional heating (CH) conditions at the true
reaction temperature of the microwave experiments (MWH) showed that
MWH was able to produce significantly greater yields than the CH experiments
after only 3 min, indicating the existence of a real selective heating
effect during the reaction. Three methods have been investigated to
optimize the acceleration achieved in the MWH experiments while retaining
control and yield levels within the MWH experiments. These were varying
the; solvent concentration, initiator concentration and chain transfer
agent concentration. It was demonstrated that by understanding the
influence of the microwave heating that it was possible to retain
control over the molecular structure of the product polymer at the
accelerated rate