2 research outputs found
Photoassisted Radical Depolymerization
Controlled radical polymerization
techniques enable the
synthesis
of polymers with predetermined molecular weights, narrow molecular
weight distributions, and controlled architectures. Moreover, these
polymerization approaches have been routinely shown to result in retained
end-group functionality that can be reactivated to continue polymerization.
However, reactivation of these end groups under conditions that instead
promote depropagation is a viable route to initiate depolymerization
and potentially enable closed-loop recycling from polymer to monomer.
In this report, we investigate light as a trigger for thermal depolymerization
of polymers prepared by reversible-addition–fragmentation chain-transfer
(RAFT) polymerization. We study the role of irradiation wavelength
by targeting the n → π* and π
→ π* electronic transitions of the thiocarbonylthio end-groups
of RAFT-generated polymers to enhance depolymerization via terminal
bond homolysis. Specifically, we explore depolymerization of polymers
with trithiocarbonate, dithiocarbamate, and p-substituted
dithiobenzoate end groups with the purpose of increasing depolymerization
efficiency with light. As the wavelength decreases from the visible
range to the UV range, the rate of depolymerization is dramatically
increased. This method of photoassisted depolymerization allows up
to 87% depolymerization efficiency within 1 h, results that may further
the advancement of recyclable materials and life-cycle circularity
Comparison of Polypentenamer and Polynorbornene Bottlebrushes in Dilute Solution
Bottlebrush (BB)
polymers were synthesized via grafting-from-atom
transfer radical polymerization (ATRP) of styrene on polypentenamer
and polynorbornene macroinitiators with matched grafting density (ng = 4) and backbone degrees of polymerization
(122 ≥ Nbb ≥ 61) to produce
a comparative study on their respective dilute solution properties
as a function of increasing side chain degree of polymerization (116
≥ Nsc ≥ 5). The grafting-from
technique produced near quantitative grafting efficiency and narrow
dispersity Nsc as evidenced by spectroscopic
analysis and ring closing metathesis depolymerization of the polypentenamer
BBs. The versatility of this synthetic approach permitted a comprehensive
survey of power law expressions that arise from monitoring intrinsic
viscosity, hydrodynamic radius, and radius of gyration as a function
of increasing the molar mass of the BBs by increasing Nsc. These values were compared to a series of linear (nongrafted, Nsc = 0) macroinitiators in addition to linear
grafts. This unique study allowed elucidation of the onset of bottlebrush
behavior for two different types of bottlebrush backbones with identical
grafting density but inherently different flexibility. In addition,
grafting-from ATRP of methyl acrylate on a polypentenamer macroinitiator
allowed the observation of the effects of graft chemistry in comparison
to polystyrene. Differences in the observed scaling relationships
in dilute solution as a function of each of these synthetic variants
are discussed