Ideal polyethylene nanocrystals

Article abstract of DOI:10.1021/ja4052334

The water-soluble catalyst precursor [[(2,4,6-(3,5-(CF₃) ₂C₆H₃)₃-C₆H ₂)-N-C(H)-(3-(9-anthryl)-2-O-C₆H₃)- κ²-N,O]Ni(CH₃)(TPPTS)] (TPPTS = tri(sodiumphenylsulfonate)phosphine) polymerizes ethylene to aqueous dispersions of highly ordered nanoscale crystals (crystallinity χ(DSC) ≥ 90%) of strictly linear polyethylene (<0.7 methyl-branches/1000 carbon atoms, M _n = 4.2 × 10⁵ g mol^-1). SAXS in combination with cryo-TEM confirms this unusually high degree of order (χ(SAXS) = 82%) and shows the nanoparticles to possess a very thin amorphous layer on the crystalline lamella, just sufficient to accommodate a loop, but likely no entanglements. This ideal chain-folded structure is corroborated by annealing studies on the aqueous-dispersed nanoparticles, which show that the chain can move through the crystal as evidenced by lamella thickening without disturbing the crystalline order as concluded from an unaltered low thickness of the amorphous layers. These ideal chain-folded polyethylene nanocrystals arise from the crystallization in the confined environment of a nanoparticle and a deposition of the growing polymer chain on the crystal growth front as the chain is formed by the catalyst.

Full text of DOI:10.1021/ja4052334

Article
pubs.acs.org/JACS
Ideal Polyethylene Nanocrystals
Anna Osichow,† Christian Rabe,‡ Karsten Vogtt,‡ Theyencheri Narayanan,§ Ludger Harnau,∥,⊥
Markus Drechsler,# Matthias Ballauff,*,‡,¶ and Stefan Mecking*,†
†Chair of Chemical Materials Science, Department of Chemistry, University of Konstanz, Universitatsstr. 10, D-78457 Konstanz,
̈
Germany
‡Helmholtz-Zentrum Berlin for Materials and Energy, Hahn Meitner-Platz 1, D-14109 Berlin, Germany
§European Synchrotron Radiation Facility, F-38043 Grenoble, France
∥Max Planck Institute for Intelligent Systems, D-70569 Stuttgart, Germany
⊥Institute for Theoretical Physics IV, University of Stuttgart, D-70550 Stuttgart, Germany
#Bayreuth Institute of Macromolecular Research (BIMF), University of Bayreuth, D-95440 Bayreuth, Germany
¶Department of Physics, Humboldt University Berlin, Newtonstr. 15, D-12489 Berlin, Germany
S
* Supporting Information
ABSTRACT: The water-soluble catalyst precursor [[(2,4,6-
(3,5-(CF3)2C6H3)3-C6H2)-NC(H)-(3-(9-anthryl)-2-O-
C6H3)-κ2-N,O]Ni(CH3)(TPPTS)] (TPPTS = tri-
(sodiumphenylsulfonate)phosphine) polymerizes ethylene to
aqueous dispersions of highly ordered nanoscale crystals
(crystallinity χ(DSC) ≥ 90%) of strictly linear polyethylene
(<0.7 methyl-branches/1000 carbon atoms, Mn = 4.2 × 105 g
mol−1). SAXS in combination with cryo-TEM confirms this
unusually high degree of order (χ(SAXS) = 82%) and shows
the nanoparticles to possess a very thin amorphous layer on
the crystalline lamella, just sufficient to accommodate a loop, but likely no entanglements. This ideal chain-folded structure is
corroborated by annealing studies on the aqueous-dispersed nanoparticles, which show that the chain can move through the
crystal as evidenced by lamella thickening without disturbing the crystalline order as concluded from an unaltered low thickness
of the amorphous layers. These ideal chain-folded polyethylene nanocrystals arise from the crystallization in the confined
environment of a nanoparticle and a deposition of the growing polymer chain on the crystal growth front as the chain is formed
by the catalyst.
most) as provided by the individual nanoparticles. The
dispersed nanocrystals formed consist of a single crystalline
lamella covered by thin amorphous polymer layers which
contain all defects such as branches and entanglements.3
Annealing of such crystals below the melting temperature leads
to a thickening of the crystalline lamella that can be studied
with high precision.4 This thickening of the crystalline lamella
can be understood in terms of an unlooping of polymer chains
within a single nanoparticle. However, the role of short chain
branches and entanglements remained unclear in all studies
done so far, and consequently the realization of this concept to
’perfect’ polymer nanocrystals had remained elusive.
We now report how unusually high degrees of order can be
obtained by crystallization during ethylene polymerization in
the compartmented space of nanoparticles in aqueous systems.
A key to these findings is a new water-soluble catalyst, which
produces high molecular weight polyethylene particles virtually
devoid of any branches. The degree of crystallinity and thus the
INTRODUCTION
■
Crystalline order is ubiquitous in condensed phases. Practically,
it is decisive for the mechanical properties of many materials. In
high molecular weight polymeric materials the degree of
crystalline order is limited. Even for linear polymers devoid of
any branches that disturb crystallization, a substantial portion of
the material is present as an amorphous phase containing loops
and entanglements. This results from intertwined chains not
being able to unravel during crystal formation. Such
entanglements improve the mechanical properties and hinder
the processing strongly. To overcome this problem, it is
desirable to access nonentangled ’nascent’ polymers from the
polymerization process.1 A possible approach is a compartmen-
talization during polymerization, and furthermore a ’perfect’
ordered deposition of the forming chain on a nanocrystal
growth front.
Such a compartmentalization scenario can be put into
practice by catalytic ethylene polymerization in aqueous
systems to polyethylene nanoparticle dispersions.2 The
crystallization of the polymer occurs in a limited volume
containing very little material (a few polymer chains at the
Received: May 24, 2013
Published: July 15, 2013
© 2013 American Chemical Society
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high degree of order of these dispersed nanoparticles are
revealed by SAXS in combination with cryo-TEM.5 Based on
careful annealing studies of the particles we argue that the PE-
nanocrystals thus generated represent ideal polymer crystals.
Concerning the origin of this unusually high order, one must
consider the crystal formation process. The polymer is formed
at a polymerization temperature of 10 °C. Both crystal growth
and crystal formation rates, that is, the rate at which stems add
to an existing growth front, and rates of nucleation of crystals
are difficult to estimate: this temperature regime has not been
accessible for studies of such a process, as traditional
experimental approaches employ rapid quenching from the
melt which is difficult to perform practically to such low
temperatures as 10 °C. Observed initial rates of polymerization
with 1 point to a chain growth rate on the order of 10 repeat
units per second. Extrapolation of nucleation rate data6 and
crystallization rate data7 suggests that crystallization occurs
faster than this chain growth. This would correspond to
incorporation of the chain as it grows by catalytic insertion
steps directly into the crystal (Figure 2), and thus minimize the
possibility to form larger chain segments with conformations
unfavorable for the generation of crystalline order, like
entanglements.
RESULTS AND DISCUSSION
■
In the catalytic polymerization in aqueous emulsion employ-
ed,2b an aqueous surfactant solution of a water-soluble catalyst
precursor is exposed to ethylene. Upon activation for
polymerization the catalyst becomes lipophilic, and poly-
ethylene chain growth will result in immediate formation of a
surfactant-stabilized particle in which further polymerization
occurs, to yield nanoscale single-crystals (Figure 1).3
Figure 1. Particle formation by catalytic polymerization in an aqueous
system.
From ongoing screening of a large number of new catalysts,
the novel complex 1 was found to be exceptional in that it
reproducibly affords highly ordered ideal polyethylene nano-
crystals (for synthesis and characterization of the precatalyst cf.
Supporting Information, SI). This catalyst produces highly
linear polyethylene (Mn = 4.2 × 105 g mol−1 and Mw/Mn = 1.4;
see SI) virtually devoid of any branches within experimental
error of the 13C NMR microstructure analysis (<0.7 methyl-
branches/1000 carbon atoms, Figure S2). An unusually high
crystallinity of χ ≥ 90% and also a high melting point of Tm =
144 °C was concluded from the DSC traces of nascent powders
obtained from precipitation of the aqueous particle dispersions
(Figure S3). Thus, the present synthetic method leads to a
virtually perfect chain and crystallization is not disturbed by
branching.
Figure 2. Polymer chain incorporation during formation of ideal PE-
nanocrystals by catalytic insertion polymerization with a water-soluble
Ni(II) catalyst.
Cryogenic transmission electron microscopy (cryo-TEM) of
the dispersions shows well-defined nanocrystals with relatively
narrow size distribution and a faceted shape (Figure 3). In
particular, most of the crystals have a rectangular shape. This
shape may be due to the fact that the crystals exhibit a
monoclinic fraction as revealed by wide-angle X-ray scattering
Chart 1. Chemical Structure of the New Water-Soluble κ2-
(N,O)-Salicylaldiminato Nickel(II) Methyl TPPTS
Precatalyst
Figure 3. Cryo-TEM micrograph of the PE-nanocrystals in aqueous
dispersion.
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qxL
⎛
⎜
⎝
(see the discussion of Figures S4 and S5 in the SI). Note that
the amorphous layers are not visualized by cryo-TEM due to
the small electron density contrast of the amorphous polymer
layers compared with the vitrified water.
The micrograph shows a slightly bimodal size distribution
which is corroborated by analysis by analytical ultracentrifuga-
tion (Figure S6). Attempted electron diffraction on single PE-
nanocrystals failed to provide further information on the crystal
structure, due to a rapid degradation of the crystals under the
electron beam at room temperature.
Small-angle X-ray scattering (SAXS) was used for the
comprehensive analysis of the PE-nanoparticle. SAXS also
complements TEM in that it captures the entire ensemble of
particles in the sample under study.
The platelet model used for the evaluation of these scattering
data (Figure S7) consists of a crystalline lamella which is
enclosed by two amorphous layers (Figure 4). Two additional
J (qR 1 − x2 )
( )
sin
2
1
F(q) = 2πR
ΔbSDS/PEG
⎜
⎜
qx
q 1 − x2
( 2 )
(3)
qx(La + Lc)
qxLc
⎞
sin
sin
(
)
(
)
2
2
⎟
+ Δb
+ Δb
a
c
⎟
⎟
qx
( 2 )
qx
( 2 )
⎠
Here R is the radius of a circular platelet consisting of a
crystalline layer of the height Lc sandwiched between layers of
amorphous PE and adsorbed SDS as well as PEG as is shown in
Figure 4. The faceted nanocrystals can be treated in good
approximation as circular platelets for the SAXS analysis.3,4 The
heights of the amorphous PE regions are given by La/2, while L
denotes the total height of the platelet. The electron contrasts
are defined as ΔbSDS = bSDS − bs, Δba = ba − bSDS, and Δbc = bc
− ba, where ba, bc, bs, and bSDS are the electron densities of the
amorphous PE layers, the crystalline PE layer, the solvent, and
the SDS/PEG layers, respectively. Here the hydrocarbon tails
of the SDS molecules contribute to the amorphous PE layers.
The value of the electron density of the solvent bs is determined
by the concentrations of water and added glucose acting as
contrast agent. Moreover, J1(x) denotes the cylindrical Bessel
function of first order.
The overall PE-nanoparticle dimensions following from the
fit of the scattering intensities are the average height of the
crystalline layer Lc = 8.8 1 nm, the average total height of the
amorphous layer La = 2.1 0.5 nm, and the height of the SDS
and PEG layers LSDS/PEG = 1.0 nm (Figure 4). The results of the
contrast variation show that the PE-nanocrystals obtained with
catalyst precursor 1 are characterized by a crystalline fraction of
82%. This significantly exceeds the degree of order found
previously for nanocrystals of PE with remaining chain
branches (χ(SAXS) = 70%).4 The height La/2 ≈ 1 nm of
each of the two amorphous PE-layers is reasonably close to the
theoretical minimum height of about 0.5 nm of tight loops
found in recent computer simulation studies of adsorbed PE
chains.8,9
The high crystallinity of the particles found by X-ray
diffraction supports the assumption (vide supra) that
crystallization occurs faster than the chain growth. The chain
produced by a catalyst will be attached immediately to the
growing crystal and no amorphous intermediate state
intervenes. The consequences of this mechanism are
immediately evident: The amorphous layer will be very small
and will just assume the minimum size to accommodate a tight
folding of the PE-chains. To this end, thermal annealing is also
instructive. Annealing is not expected to increase the thickness
of the amorphous layer considerably if no branches are present
and no entanglements were formed during polymerization. The
chains may diffuse through the crystal and the amorphous
layers on top and below the lamella act as the wheels in a pulley
by just changing the direction of the chains by 180°. We term
this state ’ideal polyethylene nanocrystal’ since the polymer
chains are arranged in an ordered fashion without defects or
entanglements. If, on the other hand, crystallization after
polymerization proceeds through an intermediate state with
little order, entanglements will be formed immediately which in
turn will lead to a much thicker amorphous phase.
Figure 4. Scheme of the platelet-like structure of the nanoparticles.
layers on top and below describe adsorbed polyethylene glycol
(PEG) together with the surfactant SDS that stabilizes the
particles. Note that the addition of polyethylene glycol and
ethylene glycol was necessary to avoid the formation of
clathrates from water and ethylene at typical polymerization
conditions (10 °C and 40 atm of ethylene). In general, the
SAXS intensity can be described by
N
V
I(q, ϕ) = I0(q)S(q) = ϕVP(Δb)2P(q)S(q)
(1)
where q is the magnitude of the scattering vector (q = (4π/λ)
sin(θ/2), λ: wavelength, θ: scattering angle), N/V is the
number density of the dispersed particles, and I0(q) is the
scattering intensity deriving from single particle scattering. The
particle volume fraction is expressed by ϕ, whereas VP is the
particle volume. The contrast is denoted by Δb. It describes the
difference between the local scattering length densities to the
surrounding medium. The form factor P(q) describes the shape
and the size of the particles whereas S(q) is the structure factor
describing the particle interactions. The scattering intensity of
such a particle I0(q) can be calculated according to
I (q) = 1 F2(q, x) dx
∫
(2)
0
SAXS-investigations on annealed dispersions were conducted
using samples in neat water having a slightly higher
concentration vs the aforementioned studies (ωPE = 2.6 wt
0
with
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%; see SI). Higher concentrations were used in order to obtain
a good signal-to-noise ratio even at low contrast. For annealing,
the dispersion of the nanocrystals was kept at a given
temperature for 10 min. Typically, dispersions were stable
under these conditions (T = 100−130 °C). During annealing at
150 °C, which is significantly above the melting temperature
(Figure S3), small amounts of precipitate of the polymer were
formed which were filtered off. Analysis was performed after
cooling down to room temperature.
Table 1. Structural Parameters of Annealed PE-
Nanocrystals.
a
T [°C]
Lc[nm]
La[nm]
bc[nm−3
]
25
100
115
125
130
150
8.8
11.5
13.7
7.8
2.1
2.1
340
340
340
346
346
340
2.1
3.2
8.5
4.4
9.8
16.0
The SAXS intensities of the original sample together with the
measured scattering intensities after annealing at 100, 115, 125,
130, and 150 °C are shown in Figure 5a (from bottom to top).
a
Main parameters derived from the model fits to the scattering
intensities shown in Figure 5a. The heights of the crystalline and
amorphous PE layers are denoted as Lc and La, respectively, while bc is
the electron density of the crystalline PE layer. The standard deviation
of the Gaussian size distribution is 1 nm for Lc and 0.5 nm for La,
whereas bc is considered a constant. The electron densities of the
amorphous PE-layers ba = 302 nm−3 and the SDS layers bSDS = 397
nm−3 are independent of the annealing temperature.
The height Lc of the crystalline lamellae obtained by
annealing at a given temperature demonstrates that annealing
at 100 and 115 °C increases Lc markedly while the height La of
the amorphous region remains constant (Table 1). Thus,
crystallinity is increasing and after annealing at 115 °C the
crystalline fraction is 88%. This finding supports the notion of
an ’ideal PE-nanocrystal’: The absence of branches allows the
chains to diffuse through the crystal. The amorphous layers act
as the wheels of a pulley as shown schematically in Figure 6; no
entanglements within these layers impede the motion of the
chains.
Figure 5. SAXS measurements of the polyethylene nanoparticles
dispersed in pure water. (a) Measured scattering intensity I(q, ϕ) of
polyethylene nanoparticles at 25 °C and after annealing at 100, 115,
125, 130 and 150 °C. For clarity, the five uppermost scattering
intensities are shifted up by a factor of 10, 102,103, 104, and 105. The
dashed lines represent the results of the modeling of the SAXS data for
a dispersion of noninteracting particles and the solid lines of
interacting particles, respectively. (b) Annealing temperatures
(triangles: 100 °C, 115 °C, diamonds: 125 °C, 130 °C, square: 150
°C) as a function of the inverse height of the crystalline layer Lc
together with the data obtained using PE with significant chain
branches (circles).4 The stars represent experimentally determined
initial crystalline lamellar thicknesses of PE crystallized from the
melt,12 while the dotted line denotes the melting line.13
Figure 6. Mechanism of thermal annealing in an ideal PE-nanocrystal:
The amorphous layers covering both platelets act as the wheels of a
pulley just changing the direction of the chains. A moderate raise of
the temperature induces sufficient mobility that allows the chains to
move within the crystal. Hence, the thickness Lc of the crystalline
phase is increased while the thickness La of the amorphous layers
remains constant.
The surface free energy of the crystal is proportional to the
slope of the annealing temperature T as a function of 1/Lc
(Figure 5b) as suggested by the Gibbs−Thomson equation (see
ref 10 and references therein) T = T∞ (1 − α/Lc) with α = 2σ/
Δh, where Δh is the heat of fusion, σ the surface free energy of
the lamellae, and T∞ the temperature limit referring to fully
crystalline samples. In the limit of a large lateral size of the PE-
nanocrystals (R ≫ L), σ is the solvent−amorphous layer
interfacial tension, while finite crystal size effects have been
discussed in ref 11. The surface free energy of the ’ideal PE-
nanocrystal’ under consideration here is higher in comparison
to the literature known crystals with branches.4 Both molecular
stiffness and the free energy needed to stabilize an amorphous
loop increase with increasing branching ratio due to restriction
of rotation and bending of the backbone chains by the side
chains. Hence, crystals from perfect PE-chains should exhibit a
higher surface energy as is found here.
The lines in Figure 5a show the calculated results for
noninteracting particles (dashed lines) and for interacting
particles (solid lines) using the model parameters according to
eq 3 as listed in Table 1.
Moreover, the radius R of the particles is chosen such that
the number of PE-repeating units is independent of the
annealing temperature as expected on physical grounds. For
small magnitudes of the scattering vector q the calculated
scattering intensities for noninteracting particles (dashed lines)
and for interacting particles (solid lines) deviate due to strong
repulsive electrostatic interaction between the particles due to
the adsorbed SDS molecules (see the discussion in refs 3 and 4,
and the SI).
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For comparison the stars represent experimentally deter-
mined initial crystalline lamellar thicknesses of PE crystallized
from the melt,12 while the dotted line denotes the melting line
T = 141.1 °C − 259.7 nm/Lc according to ref 13. Evidently, the
temperatures T∞ = 182 °C obtained by extrapolation of the
three data sets below the melting line agree within experimental
accuracy. This is to be expected since the influence of the
amorphous regions on the crystallization (stars) and recrystal-
lization (triangles, circles) processes is vanishing in the limit of
infinitely long polymer chains.
EXPERIMENTAL SECTION
■
Cryogenic Transmission Electron Microscopy. Studies were
carried out using a Zeiss EM922 Omega transmission electron
microscope (TEM) equipped with a cryo sample stage. Thin films of a
diluted PE-nanocrystal dispersion supported on a copper grid were
vitrified in liquid ethane at −183 °C.14
Small Angle X-ray Scattering. Experiments were carried out at
the ID02 beamline at the European Synchrotron Radiation Facility
(ESRF) in Grenoble (France). Scattering intensities were measured
with the FReLoN 2D CCD detector at 1 and 2 m detector position.
This setup covers a q-range of 0.05 < q < 2.9 nm−1 and 0.09 < q < 4.9
nm−1, respectively. A photon energy of 12.46 keV was selected,
corresponding to a wavelength of λ = 1 Å. The samples were measured
in a tempered 2 mm polycarbonate capillary at 25 °C. The obtained
2D scattering patterns were normalized to an absolute intensity scale
and azimuthally averaged following the standard procedure to obtain
the one-dimensional scattering profiles which were further averaged
among the ten measurements. The sample was automatically pushed
through the capillary to prevent radiation damage. The obtained
scattering intensities were averaged during the data reduction process.
Wide Angle X-ray Diffraction. This was measured with a Bruker
AXS D8 Advance diffractometer using the Cu-α line at λ = 1.5406 Å.
The samples were measured as precipitated polymer powder in the
range 10° < 2θ < 80°. Additionally, wide angle diffraction was
measured during the SAXS experiments at ID02 beamline by operating
the AVIEX PCCD-detector simultaneously. This option covers a q-
range between 5 < q < 30 nm−1.
Sample Preparation. The samples were prepared from a dialyzed
stock dispersion of the polyethylene nanoparticles with a polymer
weight fraction of 2.6 wt %. As additives the dispersion contained 0.13
wt % SDS for stabilization and 0.37 wt % of PEG that could not be
removed by dialysis. Under these conditions the dispersion was stable
over month.
For the contrast variation series the samples were diluted with a
SDS solution to keep the surfactant concentration constant. In the
following the PE-nanocrystal samples and the corresponding scattering
background solutions were prepared by the addition of glucose.
Glucose was purchased from Sigma Aldrich and used as received.
Polyethylene nanocrystals were annealed in dispersion at 100, 115,
125, 130 and 150 °C in a sealed glass vial for 10 min. The respective
polymer weight fraction of the annealed samples was ωPE = 2.6 wt %.
The density of the polyethylene nanoparticles including the
adsorbed additives was determined by densiometric measurements
in a concentration series. A density of ρ = 1.0024 0.001 g cm−3 was
determined for the nanoparticles including the adsorbed surfactant and
PEG.
The decrease of the crystalline height of PE-nanocrystals
upon increasing the annealing temperature from 115 to 125 °C
is rather unexpected. In the case of bulk PE this increase of
temperature leads to further increase of Lc. For the nanocrystals
under consideration here, this is not observed, but Lc decreases
markedly while La is increasing. Further annealing leads to an
increase of Lc again as expected from previous experiments.4
However, the slope of the annealing temperature as a function
of the inverse height of the crystalline layer is smaller (α = 2.46
nm, upper red line in Figure 5b) as compared to the one in the
lower annealing temperature regime (α = 5.20 nm, lower red
line in Figure 5b). Moreover, the increase of the amorphous
part of the crystals is not only evident from La measured by
SAXS but also from WAXS-measurements performed simulta-
neously with the SAXS measurements (see the discussion of
Figure S5 in the SI). The small monoclinic fraction vanishes
after annealing at 100 °C and the amorphous halo underneath
the remaining reflections related to the orthorhombic
modification is increasing. Thus, a crossing of the melting
line (dashed line in Figure 5b) leads to a drastic change of the
overall structure of the PE-nanocrystals. The increased mobility
of the PE-chains at these temperatures has apparently affected
the order in the crystals. Under these conditions, the shape of
the nanocrystals seems to be mainly determined by the surface
tension as discussed previously.4 Hence, the dependence of Lc
on T does not present a general phenomenon anymore but
depends on the stabilizing agents used herein.
SUMMARY AND CONCLUSIONS
■
The novel water-soluble salicylaldiminato Ni(II)-methyl
complex 1 produces highly ordered high molecular weight
polyethylene nanocrystals devoid of branches at a low
polymerization temperature of 10 °C in an aqueous medium.
The particles formed are single ’perfect’ ordered nanocrystals
consisting of a single crystalline lamella covered by very thin
amorphous layers, as revealed by combination of cryo-TEM
and SAXS analysis. The unusually high degree of order found
independently by SAXS and DSC results from crystallization
during polymerization in the compartmented space of nano-
particles. An ordered deposition of the growing polymer chain
on the nanocrystal growth front occurs as the chain is formed
by the catalyst. This leaves no opportunity for entanglements to
form, and an ideal nanoscale polymer crystal is formed under
these conditions. This highly ordered structure is further
corroborated by annealing studies, which show that below the
melting point the chains can slip through the crystal in a well-
behaved undisturbed fashion without increasing the size of the
very thin amorphous layer.
ASSOCIATED CONTENT
■
S
* Supporting Information
Detailed experimental procedures, characterization data, and
data analysis. This material is available free of charge via the
Internet at http://pubs.acs.org.
AUTHOR INFORMATION
■
Corresponding Author
*E-mail: stefan.mecking@uni-konstanz.de and matthias.
ballauff@helmholtz-berlin.de.
Author Contributions
The manuscript was written through contributions of all
authors. All authors have given approval to the final version of
the manuscript.
The generic synthetic approach to highly ordered nanoscale
polymer crystals by chain growth polymerization in nanoscopic
confinement appears of future interest to address, among
others, problems associated with entanglements in the
processing of ultra high molecular weight polymers.
Notes
The authors declare no competing financial interest.
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ACKNOWLEDGMENTS
We thank ESRF for the provision of synchrotron beam time.
A.O. and S.M. thank the Stiftung Baden-Wurttemberg for
financial support. We thank Antje Volkel and Helmut Colfen
■
̈
̈
̈
for analytical ultracentrifugation analysis.
ABBREVIATIONS
■
DSC, differential scanning calorimetry; SAXS, small-angle X-ray
scattering; WAXS, wide-angle X-ray scattering; TEM, trans-
mission electron microscopy
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