Silica
particles with grafted poly(methyl methacrylate) brushes,
SiO2-g-PMMA, were prepared via activator
regeneration by electron transfer (ARGET) atom transfer radical polymerization
(ATRP). The grafting density and dispersity of the polymer brushes
was tuned by the initial ATRP catalyst concentration ([CuII/L]0). Sparsely grafted particle brushes, which also displayed
an anisotropic string-like structure in TEM images, were obtained
at very low catalyst concentrations, [CuII/L]0 < 1 ppm. The effect of the initial catalyst concentration on
dispersity and initiation efficiency in the particle brush system
was similar to that observed in the synthesis of linear PMMA homopolymers.
The kinetic study revealed a transition from controlled radical polymerization
to a less controlled process at low monomer conversion, when the [CuII/L]0 decreased below about 10 ppm.
Linear and bottlebrush polyacrylates were prepared by
photomediated
atom transfer radical polymerization (photoATRP) catalyzed by either
CuBr2/TPMA (tris(2-pyridylmethyl)amine) or the more active
CuBr2/TPMA*3 (tris([(4-methoxy-2,5-dimethyl)-2-pyridyl]
methyl)amine). The latter had a lower rate constant of photoreduction
(k
red) but unexpectedly enabled faster
polymerization. Kinetic simulations showed that the equilibrium concentration
of a Br–CuII/L deactivator was larger for CuBr2/TPMA*3, resulting in a faster reduction rate (R
red ∝ k
red[Br–CuII/L]) and higher radical concentration.
At the same time, the low [CuI/TPMA*3] counterweighed
its high tendency to promote catalyzed radical termination (CRT),
and the CRT rate was similar for the two catalytic systems. Kinetic
simulations proved that (i) relative reaction rates cannot be predicted
by the rate constant alone as exhibited by the relative amount of
CuI and CuII species mediated by catalyst activity
and termination selectivity and (ii) the polymerization steady state
is reached faster with more active catalysts. With this understanding,
polyacrylate bottlebrushes were synthesized at moderately high conversion
by photoATRP.
Copolymers of n-butyl acrylate/methyl methacrylate (BA/MMA) with certain compositions were recently proposed as self-healing materials due to "key-and-lock" interchain interactions of alternating sequences. This inspired us to analyze by numerical simulations the formation of heterosequences in BA/MMA copolymers prepared by atom transfer radical polymerization (ATRP). Stochastic Monte Carlo and deterministic simulations using numerical integration of differential equations showed that the highest contribution of alternating sequences is present in a statistical copolymer with 1:1 BA/MMA composition. However, batch ATRP of a 1:1 BA/MMA mixture generates a gradient copolymer with a diminished fraction of alternating sequences. Therefore, a method for preparing a statistical BA/MMA copolymer with the highest fraction of alternating sequences is proposed through normal ATRP copolymerization with feeding of MMA. The contribution of heterosequences was analyzed for both batch ATRP systems and in the presence of feeding, to identify the conditions that maximize the amount of alternating sequences in the copolymers.
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.