To actively manipulate ROMP activity, we de-
creased the norbornene concentration to 0.1 M
while maintaining the ~17 pN pulling force. Ex-
pectedly, the average polymerization rate decreases
by ~29% (Fig. 3G). The average jump length de-
creases by ~25% (Fig. 3E), reflecting smaller hair-
balls due to slower polymerization rates. The
average waiting time increases by ~36% (Fig. 3D),
reflecting slower unraveling kinetics and more
stable hairballs, even though the hairballs are
smaller. We speculate that the slower polymeri-
zation rate here might allow the newly incor-
porated monomers to form better nonbonded
interactions within the hairball; consistently,
the average slope decreases by ~38% (Fig. 3F),
reflecting tighter hairballs.
We further manipulated the ROMP activity by
using a less active monomer cis-cyclooctene (29).
Under the same ~17-pN pulling force and 1 M
monomer concentration, the average polymerization rate slows down expectedly (Fig. 3G). The average waiting time, jump length, and slope when
using cis-cyclooctene monomer all show similar
trends to those using a lower norbornene concentration (Fig. 3, D to F).
We then examined how the microscopic properties of hairballs relate to the polymerization
rate of each polymer. Under any attempted reaction condition, the polymerization rates V of
individual polymers differ greatly, up to a factor of ~50 (Fig. 4A and fig. S38, A, E, and I),
even though the associated polydispersity index is 1.5 ± 0.4 (supplementary text 5.5). V of
individual polymers shows strong correlations
with their average jump length, waiting time,
and waiting-period-slope, under all reaction
conditions (Fig. 4, B to D, and fig. S38). Because
the jump length, waiting time, and waiting-time-slope reflect, respectively, the size, kinetic
stability, and structural looseness of the hairballs, these correlations indicate that faster
polymerizations are associated with larger, less
stable, and looser hairballs. Therefore, the microscopic configurations of the hairballs play
key roles in each polymer’s growth, perhaps
by controlling access to the catalyst, and the
dispersion of the hairball’s microscopic configuration likely contributes substantially to
the dispersion of polymerization rate among
individual polymers under identical growth
In typical solution synthesis of polymers, no
stretching force exists, and the quality of solvent
could be poorer. In such conditions, conformationally entangled hairballs could be more prevalent (supplementary text 4.8 and 5.7) (10, 30)
and thus play a bigger role in altering polymerization kinetics.
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The research is mainly supported by the Army Research
Office (grant W911NF-14-1-0620), and in part by the
Army Research Office (grants W911NF-13-1-0043
and W911NF-14-1-0377), U.S. Department of Energy
(grant DE-SC0004911), Petroleum Research Foundation
(grant 54289-ND7), and National Science Foundation
(grant CMMI-1435852). The research uses Cornell
Chemistry nuclear magnetic resonance facility,
Extreme Science and Engineering Discovery Environment
(XSEDE), and Cornell Center for Materials Research
Shared Facilities supported by NSF (grants CHE-1531632,
ACI-1053575, and DMR-1120296). We thank R. Khurana
and A. DiCiccio for advice on synthesis; M. D. Wang,
J. Ma, and J. Lin for advice on magnetic tweezers;
and R. F. Loring for discussions. C.L. constructed
instrument, performed measurements, coded software,
and analyzed data; K.K. performed syntheses and
measurements and contributed to instrument
construction and data analyses; E. W. performed
simulations; K.-S.H., F. Y., and G.C. contributed to
experiments; F.A.E. supervised simulations; G. W.C.
supervised syntheses; P.C. and G. W.C. designed
experiments; P.C. conceived and oversaw research; C.L.,
K.K., E. W., F.A.E., G. W.C., and P.C. wrote the manuscript.
Materials and Methods
Figs. S1 to S40
Equations S1 to S15
Tables S1 to S4
19 May 2017; accepted 11 September 2017
Fig. 4. Origin of kinetic dispersion in polymerization among individual polymers. (A) Histogram of the average polymerization rate V of
individual polynorbornene molecules. Red line,
lognormal fit. The polydispersity index of V is 1.5 ±
0.4. (B to D) Correlation plots between the
average polymerization rate V of each polymer
molecule and its average jump length, waiting
time, and waiting-period-slope, and the respective Pearson’s correlation coefficients. Each
solid black square indicates a single polymer.
Open red squares indicate binned and averaged
results. All data are from 1 M norbornene and
17 pN pulling force condition. x and y error
bars are SD.