ma6b01974_si_001.pdf (14.24 MB)
Nanocrystal Formation in Aqueous Insertion Polymerization
journal contribution
posted on 2016-12-02, 20:14 authored by Alexandra Godin, Inigo Göttker-Schnetmann, Stefan MeckingHigh molecular weight
linear polyethylene, in the form of 7 nm
thin single-lamella nanocrystals with a diameter of up to 200 nm,
is generated via aqueous catalytic polymerization using the water-soluble
catalyst precursor [κ2-N,O-{2,6-(3′,5′-(F3C)2C6H3)2C6H3-NC(H)-(3,5-I2-2-O-C6H2)}NiCH3{P(3-C6H4SO3Na)3}] (1-TPPTS). Studies under true pressure reactor
conditions using a 13C-labeled catalyst precursor 1-13C-TPPTS show that
in the first 30 s, 21–28% of the catalyst precursor initiates
polymer chains. Catalyst deactivation occurs preferentially by hydrolysis,
resulting in the formation of fully saturated polyethylene chains.
The catalyst lifetime can be extended for more than 10 h upon addition
of weakly coordinating compounds like N,N-dimethylformamide. Alternatively, at strongly basic conditions
(pH 12.5) nanoparticle dispersions consisting of polyethylene with
molecular weight of up to Mn = 7 ×
105 g mol–1 and Mw/Mn = 1.2 are accessible after
60 min polymerization time. “Living”-type polymerization
also can be performed by substituting water with deuterium oxide as
the reaction medium. Here, catalyst lifetimes of more than 24 h are
observed, and dispersions with more than 20 wt % nanocrystals are
accessible at turnover frequencies (TOF) of ∼4000 ethylene
(catalyst precursor)−1 h–1. A
pressurizable sampling chamber was used to draw samples at high pressure
and enabled the in-depth analysis and monitoring of the polymerization
reaction and the particle formation in a time range of 30 s–24
h. It was shown that under most reaction conditions studied each nickel
center produces one single-chain polyethylene particle, and the diameter
of the resulting nanoplatelet is determined by the molecular weight
of the polyethylene chain.