Cooperative Soft-Cluster Glass in Giant Molecular ClustersYuchu Liu,†,‡,§,# GengXin Liu,*,†,# Wei Zhang,‡ Chen Du,‡ Chrys Wesdemiotis,‡

and Stephen Z. D. Cheng*,†,‡,§

†Center for Advanced Low-Dimension Materials, State Key Laboratory for Modification of Chemical Fibers and Polymer Materials,College of Material Science and Engineering, Donghua University, Shanghai 201620, China‡South China Advanced Institute for Soft Matter Science and Technology, School of Molecular Science and Engineering, SouthChina University of Technology, Guangzhou 510640, China§College of Polymer Science and Polymer Engineering, Department of Polymer Science, The University of Akron, Akron, Ohio44325, United States

*S Supporting Information

ABSTRACT: Three-dimensional giant molecular clusters, OPOSS16 andOPOSS24, have been designed and precisely synthesized. They have 16 or 24octyl polyhedral oligomeric silsesquioxane (OPOSS) building blockschemically linked by short, flexible chains. Despite the small difference intheir molecular weight, 25 and 38 kg/mol respectively, they show differentdynamics above the conventional glass transition temperature (Tg). OPOSS16in the bulk quickly turns to viscous. In contrast, OPOSS24 shows a long-lastingelastic plateau even far above the Tg, corresponding to confinements onindividual OPOSS. To achieve any confinements, clusters have to be immobile, although individual OPOSS possesses mobility.It directly confirms that in the bulk giant molecular clusters possess a cooperative soft-cluster glass in addition to conventionalglass if they are larger than the critical diameter. This critical diameter is close to the estimated diameter of cooperativerearranging regions during glass transition. Giant molecular clusters present unique dynamics different from colloidal caging insolution or polymer entanglements.

■ INTRODUCTION

Chainlike polymers possess a distinct one-dimensional (1D)curvilinear dynamics as “reptation” within “tubes” formed byconfining surrounding chains.1 One effective way to alter thedynamics of polymers is to deviate from the linear architecture,e.g., by using multiarm star,2 long-chain branching,3 and so on.Molecular nanoparticles, such as polyhedral oligomericsilsesquioxane (POSS), fullerene, polyoxometalates, andothers, have also been incorporated within or dangling onthe polymer linear backbone.4,5 However, the fundamentaldynamics is still dominated by entanglement. Without chainends, a topologically driven glass has also been proposed forinfinitely long ring polymers.6,7

The extreme deviation from linear architecture could beachieved when the connectivity leads to a three-dimensional(3D) cluster instead of a 1D chain.2 Modularly synthesizedgiant molecular clusters containing rigid molecular nano-particles as building blocks are a new class of unconventionalmacromolecules.8−14 Unlike polydisperse polymers, they haveexact molecular weights, chemical compositions, sequences,and topological structures. They possess virtual shapepersistency and fulfill the requirement of forming soft-clusters.They are named “soft-cluster” to emphasize that they are not arigid aggregate,15 thus different from colloidal hard spheres.The model 3D soft-clusters contain many chemically linked

molecular nanoparticles. It is realized as a cluster by usingPOSS with bulky octyl side groups (OPOSS) as the building

blocks and linking them to a central core POSS (Figure 1).This approach achieves the noncrystalline nature and relativelylow Tg of the clusters. Only weak van der Waals forces existamong clusters. Within one cluster, short and flexible chemicallinkers constrain molecular nanoparticles not to move far apartfrom each other, as a cooperative soft-cluster.Soft colloids,16−28 notably dendrimers, multiarm stars, and

cross-linked nanogels in the bulk states, were developed inrecent years. With varying elasticity, they are a unique modelsystem. Soft-clusters with well-defined chemical structures areorders of magnitude smaller than typical soft colloids and arenot interfered by entanglements or cross-linking. We ask whatdynamics these soft-clusters can be. Because there is noentanglement, the dynamics should be different from thebehavior of reptation. Because they are smaller and softer andcontain well-defined building blocks, the dynamics in the bulkmight be different from colloidal caging.Indirectly supported by our previous experimental results,10

we hypothesized that above the conventional glass transitiongiant molecular clusters might have dynamics analogous to thecooperative rearrangement in glasses.29−34 Conventional glasstransition can be revealed by differential scanning calorimetry(DSC), dynamic mechanical analysis (DMA), and so on. If this

Received: March 18, 2019Revised: May 4, 2019

Article

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© XXXX American Chemical Society A DOI: 10.1021/acs.macromol.9b00549Macromolecules XXXX, XXX, XXX−XXX

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speculation is correct, the study of giant molecular clusters mayreveal a new cooperative soft-cluster glass and lead tounexplored material properties. Thus, the question is at whatsize of these clusters this new glass behavior appears.To achieve large enough clusters, we carefully design and

synthesize the two giant molecular clusters OPOSS16 and

OPOSS24 (containing 16 or 24 OPOSS, respectively) as shownin Figure 1. They are different from our previous work inwhich no specific interactions (such as hydrogen bonding orcrystallization) are involved. After verification of their chemicalstructures and molecular characters, their dynamics will berevealed by rheological measurements and analysis.

Figure 1. Scheme of the modular synthesis of OPOSS16 and OPOSS24.

Figure 2. (a) Modular synthesis routes of OPOSS16 and OPOSS24 and chemical structure of OPOSS. (b) Chemical structure of OPOSS16. (c)1H

NMR spectrum. (d) 29Si NMR spectrum. (e) MALDI-TOF-MS. (f) GPC trace of OPOSS16. (g) Chemical structure of OPOSS24. (h)1H NMR

spectrum. (i) 29Si NMR spectrum. (j) MALDI-TOF-MS. (k) GPC trace of OPOSS24.

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■ RESULTS AND DISCUSSIONSynthesis and Characterization of Giant Molecular

Clusters. The modular syntheses of OPOSS16 and OPOSS24by two chemical reactions are shown in Figure 2a and FigureS3. During the first reaction, all eight hydroxyl groups onhydroxyl-functionalized POSS are converted by esterificationwith mono- or triple-alkyne groups. The results are POSScores surrounded by 8 or 24 alkyne groups. The structures ofPOSS-8yne and POSS-24yne are confirmed by 1H, 13C, and29Si NMR as well as MALDI-TOF MS (Figures S14−S22).During the second reaction, N3-2OPOSS and N3-OPOSS, as

shown in Figure 2a and Figure S1 are “clicked” onto POSS-8yne and POSS-24yne, respectively.11−13 The results are giantmolecular clusters with 16 or 24 OPOSS building blocks. Theiranalyses and characterizations are summarized in Figure 2b−k.In 1H NMR spectra (Figures S22 and S27, comparing to

Figures S14 and S18), the disappearance of the chemical shiftaround 4.7−4.8 ppm confirms the full conversion of triplebonds and the completion of “click” reactions. All protons canbe clearly assigned, and the integration ratio matches well withdesigned structures. In 29Si NMR spectra, four chemical shiftsare found in both molecules and assigned (Figures S24 andS29).The major m/z peaks in MALDI-TOF-MS (Figure 2e,j,

Figures S25 and S30, and Table 1) agree with the theoretically

calculated molecule masses. Traces given by gel permeationchromatography (GPC) show narrow peaks, indicating eachsample is one substance (Figure 2f,k and Figures S26 and S31).From all of the experimental evidence collected, we canconclude that OPOSS16 and OPOSS24 are obtained asdesigned with no traceable impurities.Structures and Diameters of Giant Molecular

Clusters. The two samples have identical chemical linkersbetween the core POSS and peripheral OPOSS buildingblocks. With eight more peripheral OPOSS building blocks,OPOSS24 should be larger than OPOSS16 as illustrated inFigure 3a. For the ease of analysis, we estimated a characteristicdiameter dM of giant molecular clusters in the bulk via

M N(6 )/( )w A3 πρ , assuming they are densely packed spheres.Although they may not be truly spherical, this governing factorhelps to quantify their dynamics. With densities measured tobe around 1.07 g/cm3, dM would be approximately 1.5, 4.2, and4.8 nm for OPOSS01 (single OPOSS as a cluster), OPOSS16,and OPOSS24, respectively.Scattering results corroborate these characteristic diameter

sizes. In agreement with the estimated dM of OPOSS01, onebroad correlation scattering peaks (dS) at a center of 1.26 nmcan be observed in a small-angle X-ray scattering (SAXS)pattern in the bulk (Figure S32). It has also been observed at1.45 nm in the solution and at 1.21 nm in the bulk of SAXSpatterns of OPOSS16 or OPOSS24 (Figure 3b and Figure S32).In agreement with the estimated dM of OPOSS16 and

OPOSS24, the characteristic diameters dS of OPOSS16 andOPOSS24 in the solution can be observed from Iq4 in SAXS

patterns at 4.8 and 6.2 nm, respectively, as shown in Figure 3b.These values are slightly larger than dM values estimated in thebulk. It is reasonable considering the inclusion of solventmolecules within the clusters. SAXS patterns in the bulk(Figure S32) show almost identical broad correlationscattering peak at low q around 4.4 nm. From a dendrimerpoint of view, OPOSS16 and OPOSS24 are of the same firstgeneration. The conformation of OPOSS16 in the bulk is notan ideal sphere-like one. The characteristic scattering may bean average of many different detecting angles and resulted inthis observation.26

Table 2 summarizes the molecular and cluster parametersthat are important for following discussions, including the

exact molecular weight (Mw), estimated diameters in the bulk(dM), and diameters obtained by SAXS in the solution (dS).The concepts of boundary ζ and bead diameter will be definedin the following section.

Cooperative Glass: A Long-Lasting Elastic Plateauand a Drastic Viscous-to-Elastic Transition. DSCthermodiagrams in Figure 4a show that the conventionalglass transition temperatures Tg of OPOSS16 and OPOSS24 arealmost identical at around −8 °C; that is about 20 °C higherthan the Tg of OPOSS01. We measure linear viscoelasticity at10 rad/s during temperature ramp and plot storage G′ and lossG″ modulus against temperature as in Figure 4b. Master curvesof G′ and G″ in the frequency domain are given in Figure 5a atthe reference temperature of 30 °C and complementary to thetemperature ramp. They are constructed by time−temperaturesuperposition of the small-amplitude oscillatory shear (SAOS)data as shown in Figures S34 and S35. The horizontal shiftingfactor aT is given in Figure 5b.

Table 1. Molecular Weights of OPOSS16 and OPOSS24 (MAg= 107.9 g/mol)

Mn (calcd) Mn (MALDI-TOF-MS)

OPOSS16 24922.8 25030.7 (24922.8 + MAg)OPOSS24 38416.9 38525.3 (38417.4 + MAg)

Figure 3. (a) Space-filling models show that OPOSS24 is larger thanOPOSS16. (b) SAXS patterns of OPOSS16 and OPOSS24 in solutionsshow the characteristic diameters of OPOSS16 and OPOSS24 as wellas individual OPOSS. Lines correspond to scattering intensity I on theleft vertical axis; dotted lines correspond to Iq4 on the right verticalaxis.

Table 2. Summary of Parameters from Characterizationsand Analysis

Mw[g/mol]

dM[nm]

dS[nm] dM/rb Gpl [Pa]

d0[nm]

OPOSS01 1326 1.5 1.5 N.A. N.A. N.A.OPOSS16 24923 4.2 4.8 5.6 N.A. N.A.boundary, ζ ∼4.5 ∼6OPOSS24 38417 4.8 6.2 6.4 4.2 × 105 1.9

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Above 30 °C or below 10 rad/s, the rheological behavior ofOPOSS16 is dominated by its viscous component. In contrast,with only eight more OPOSS (13 kg/mol), OPOSS24 shows anelastic plateau even above 50 °C or below 0.01 rad/s.Evidently, this plateau would not end anytime soon, so we stopat 140 °C and do not go to higher temperatures riskingdegradation of the sample. Figure 5a does not reach lowerfrequencies because it is hard to determine aT as SAOS givesplateau at temperatures higher than 70 °C. If we extrapolate aTto 140 °C (Figure 5b) by the WLF equat ion

( a Clog TC T T

T T C

( )

( )1 g

g 2= +

−− + ), the elastic plateau in Figure 5a

would extend to at least 10−9 rad/s. That is 15 orders ofmagnitude lower than the high-frequency crossover.These giant molecular clusters do not have any entangle-

ment or specific association (such as hydrogen bonding). Theinteractions between OPOSS and clusters are only weak vander Waals force. At temperatures far above Tg (50−140 °C) orfrequencies (below 0.1 rad/s at 30 °C), individual OPOSSshould have sufficient mobility. Yet, we observe this distinctlong-lasting elastic plateau far above Tg.With a molecular weight of 38 kg/mol, OPOSS24 in the bulk

cannot relax even a small perturbation at ∼150 °C above its Tg.In other words, OPOSS24 remains immobile to preventrelaxation. If thousands of POSS are arranged in chain-likemanner,5 such polymers can still reptate and relax. Althoughsoft colloids may also reach colloidal glass state with an elastic

plateau, their typical molecular weight ranges from a fewthousand kg/mol to 10000 kg/mol.18−22 Giant molecularclusters are quite different from typical soft colloids in theabsent of solvent and in their much smaller molecular weightand diameter.This drastic transition from viscous to elastic behaviors

happens within a window of only eight OPOSS or 13 kg/mol.This dynamics slowdown of giant molecular clusters withrespect to the diameter of clusters has to be of cooperativenature, like a glass transition. To differentiate from conven-tional glasses, such state of soft-clusters is named “cooperativeglass”. We observe it experimentally, evidenced by the long-lasting elastic plateau for a molecular weight of 38 kg/mol andthe drastic viscous to elastic transition over a difference of only13 kg/mol.This viscous-to-elastic transition occurs, with respect to the

diameter of clusters, somewhere between 4.2 and 4.8 nm (thediameter dM of OPOSS24 and OPOSS16). We propose that acritical diameter ζ governs the dynamics of giant molecularclusters. Within this region of eight OPOSS, 0.6 nm and 13 kg/mol, the exact value of ζ is less important than the existence ofsuch divergent dynamics slowdown. When clusters contain alarge number of OPOSS building blocks and have a largediameter, the mobility of each cluster requires many clusters tomove cooperatively to clear a path, which becomes impossibleunder thermal fluctuation.

Figure 4. (a) DSC thermodiagrams show OPOSS16 and OPOSS24 have almost identical glass transition temperature. (b) Linear viscoelasticity ofOPOSS16 and OPOSS24 during temperature ramp shows storage G′ and loss G″ modulus at different temperatures. (c) Enlarged plot of G′ vstemperature of OPOSS24 and linear fit using data between 100 and 140 °C.

Figure 5. (a) Master curves of G′ and G″ in the frequency domain at a reference temperature of 30 °C constructed from SAOS data, between 0 and70 °C for OPOSS24 and between 0 and 50 °C for OPOSS16. (b) The shifting factor aT between 0 and 70 °C for OPOSS24 and between 0 and 50 °Cfor OPOSS16. WLF fitting of OPOSS24 extrapolates to 140 °C shows aT between 140 and 70 °C for OPOSS24 is 10

−4.

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A minor issue is that although we made OPOSS24 andOPOSS16 with identical linker from core POSS and peripheralOPOSS, the intrabranch distance between adjacent OPOSShas not been the same. This will be perfected in future workand may minor influence the exact boundary.Confined Dynamics. The long-lasting elastic plateau

suggests confined dynamics and that the cluster as a whole isnot diffusing. Yet it is already 150 °C above Tg; logically, thegiant molecular cluster should not be a hard sphere at suchcondition. In other words, different OPOSS within a clustershould have quasi-independent motion, given that they arelinked by short and flexible chains.In the plateau region, G′ increases linearly with temperatures

as enlarged in Figure 4c. The slope from 100 to 140 °C is 3.82× 103 Pa/°C. The elastic plateau modulus might reveal therattling unit in confinement agitated by thermal energy,35−41

with the characteristic massM0 of 2328 g/mol via Gpl/T ≈ ρR/

M0 and the diameter d0 of 1.9 nm via M N(6 )/( )0 A3 πρ .

Numerically, those values suggest that this elastic plateauoriginates from confinement on the level of individual OPOSS,not on the level of the whole cluster.Would such confinement on individual OPOSS break at a

finite or an infinite time? We hypothesize it should be finite,but the breaking might not cause relaxation because not allconfinements break at the same time. Thus, it does notinterrupt the elastic plateau. Future experiments likely withlabeled samples would provide a definite answer. Nonetheless,the clusters must be immobile for confinements to be effective.There are two levels of structures and dynamics: the level of

cluster and the level of constituting OPOSS building block.This feature is different from colloidal glass, which dominatedby one level of mobility−the colloidal particles, in hard or softcolloids.2,28

In the previous section, we have discussed the low-frequency, long-time, high-temperature behaviors of the twogiant molecular clusters. Between the low-frequency region andhigh-frequency (conventional glass) region, there is anintermediate region. OPOSS24 shows a plateau-like behaviorat those intermediate frequencies (Figure 5a, between 0.1 and105 rad/s) or temperatures (Figure 4b, between 5 and 45 °C).A characteristic value Gh of 6.35 × 106 Pa can be taken fromthe local minimum of G″/G′.39As a comparison, OPOSS16 shows no plateau in this narrow

intermediate region, and its G′ and G″ values are very closedwith scaling exponent around 0.5. This is also different fromthe previous Zimm-like behavior on a smaller giant molecular

cluster. We now observe that giant molecular clusters that aresmaller but close to the boundary ζ have this intermediateregion and then turn to viscous. The chemistry of the linkermay also be a contributing factor besides diameter alone,especially in this intermediate region, and will be examined inthe future.

Cooperative Glass under Large Perturbation. Largeclusters, for instance OPOSS24, are in a cooperative soft-clusterglass state, with a long-lasting elastic plateau Gpl. Thermalenergy (before reaching degradation) is not enough tocooperatively activate more than the critical number ofmolecular nanoparticles. However, external activations, suchas large strain or stress, should be able to drive them into afluid state.The strain sweep in Figure 6a shows linear responses end at

a strain amplitude of 20%. The crossover from elastic toviscous response, critical strain γc, is at 60%, above whichOPOSS24 becomes a fluid. Figure 6b shows, upon largerstrains, for instance 100%, relaxation happens immediately, andthe stress can fully relax.After a sudden step strain of 10 or 30%, relaxation does not

take place until a few seconds later. A characteristic relaxationtime on the order of 20 s is revealed. It equals to10−5 rad/s inFigure 5a (aT from 30 to 70 °C is 2.3 × 10−4). We suspect thisis the breaking of confinement on individual OPOSS. Finally,after thousands of seconds, 8% of the stress still remainsunrelaxed.In Figure 6c, constant stress is applied instead of strain. A

stress of 20 kPa is not enough to activate OPOSS24 into flow,while 40 kPa is sufficient. If we take the critical stress σc asaround 30 kPa, then σc ≈ Gpl × γc. To further study thedynamics of cooperative soft-cluster glass, such nonlinearrheological measurements, as widely used in soft glassymaterials in general, would provide more information besideslinear rheology.20,42−44

Theoretical Connections of Soft-Cluster. Claiming as anew glass state, we provide the following analysis to rationalizeour findings. The smallest mobile unit in glassy state iscommonly referred to as the “bead”.45,46 It would also be thebasic mobile unit at higher temperatures. For giant molecularclusters, we can roughly estimate the bead diameter rb to be0.75 nm based on πrb

3/6 = 35.6kBTg/G (G is the glassy stateshear modulus of ∼6 × 108 Pa).10,46 Assuming Gh ∼ kBT/(dh)

3, the characteristic modulus at high frequency Gh ofOPOSS24 might correlate to a mobile unit with Mh of 420 g/mol and dh of 1 nm, roughly corresponding to the size of theestimated bead. With rb, the giant molecular cluster can then

Figure 6. Nonlinear rheological measurements on OPOSS24 at 70 °C. (a) Strain sweep experiments with increasing oscillatory strain amplitude at10 rad/s. (b) Stress relaxations after different amounts of step strains. (c) Creep test under different amounts of stress; the increase of strain ismonitored.

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be abstracted as a physical model of soft cluster withoutchemical details.According to experimental measurements and simulation on

the cooperative rearranging region, as well as random first-order transition (RFOT) theory, the critical diameter ζ ofcooperative rearranging regions to reach glassy state would beζ ∼ 6rb.

29−34 This value may not be exact but at least veryclose. For the soft-clusters here, 6rb is thus 4.5 nm, between thediameter dM of OPOSS24, 4.8 nm, and dM of OPOSS16, 4.2 nm.Therefore, the experimental boundary seems in agreementwith the critical diameter of cooperative rearranging regions atthe conventional glass transition, hinting a connection to itsglassy nature.Glassy dynamics diverges quickly, so does the viscous-to-

elastic transition with respect to cluster diameter. Thisboundary would be in the range, if not numerically exact.The numerical coincidence would be supportive to analogizesoft clusters as the cooperative rearranging cluster, thusrevealing a new glass state: cooperative glass.As of the difference between OPOSS16 and previous T10M

in the intermediate region, we hypothesize if two clusters aretoo large to move together cooperatively, confinement andimmobility would be effective in a narrow temperature windowabove Tg. If the diameter of two clusters combined equals ζ,the boundary would be 2−1/3ζ/rb = 4.7. T10M contains 11POSS, and dM/rb is 3.9, while dM/rb of OPOSS16 is 5.6. Itagrees with current experimental results and will be examinedin the future.Of course, there may be other ways to interpret the results,

for instance in the framework of soft colloids23,25 or in theframework of mode coupling theory.47−49 Similarities anddifferences with soft colloids have been illustrated in previoussections. Figure 7 makes a summary: (1) the gray dashed circledepicts the confinement on individual OPOSS and its rattling;(2) the cluster of OPOSS building blocks as a whole isimmobile, i.e., the center of mass of the cluster should notmove. Giant molecular clusters indeed exhibit dynamicsdifferent from colloidal suspensions or chains of nanoparticles.5

■ CONCLUSION

Giant molecular clusters used in this study are chemicallylinked multiple OPOSS in three dimensions. They do notpossess entanglement or strong interaction/association. Acritical diameter ζ divides the dynamics of clusters based ontheir diameters. This ζ can approximate to the cooperativerearranging length scale at glass transition.Clusters larger than ζ exhibit a long-lasting elastic plateau

Gpl, even at far above Tg. For instance, OPOSS24 has amolecular weight of 38 kg/mol, much lower than the typicalsoft colloids. The value of Gpl correlates with individualOPOSS in confinement. Such confinement is possible becauselarge giant molecular clusters are still immobile. Thus, there aretwo levels of structures and dynamics: cluster and constitutingOPOSS building block.The 3D correlation of molecular nanoparticles within

clusters causes this immobilitya new kind of dynamicsdifferent from polymer entanglement or colloidal caging. Theviscous-to-elastic transition happens at a narrow region of nomore than 8 OPOSS, 0.6 nm, and 13 kg/mol. It has to be ofcooperative nature. Thus, we claim it as a cooperative glass. Wealso find that large strain or stress can drive cooperative soft-cluster glass into flow and the critical strain and stress is linkedby Gpl.We expect this phenomenon to be general and not specific

to any particular type of nanoparticles to form the cluster.Detailed mapping of diameters, conformations, and mixtures aswell as examining the rigidity and length of linkers are onschedule as future work.

■ MATERIALS AND METHODSSynthesis. Details are provided in the Supporting Information.Density. The density was measured by adjusting the density of KI

solution so that a small piece of sample can be suspended in thesolution. The density of the solution was then measured by weightingits weight in a 5 mL volumetric flask.

Thermal Analysis. Differential scanning calorimetry (DSC) wasperformed on a TA Instruments Q200, with the heating/cooling rateof 10 °C/min.

SAXS. Measurements were taken on a Rigaku MicroMax 002+instrument with a voltage of 50 kV and a current of 0.6 mA. Thedetector was a Dectris Pilatus 300K at 2 by 2 movable configurations.The samples in the bulk were self-adhered to thin aluminum foil.Scattering patterns in the bulk are shown in Figure S32. The samplesin THF solutions at 10 mg/mL were flame-sealed in 1.5 mm quartzcapillary. The raw data of the solution were presented in Figure S33and smoothed by the LOWESS method with a span of 0.1 to reducenoise (Figure 3b).

Rheology. The samples were dissolved in THF and dropwise caston polyimide film to form a dome larger than 8 mm and higher than 1mm. The solvent, THF, was slowly evaporated first at ambientconditions, then low vacuum, and finally high vacuum at elevatedtemperature (∼60 °C). The samples were detached from the film andtransferred to 8 mm parallel plates on an ARES-G2 (TA Instruments).The linear viscoelasticity was measured under an oscillatory straintypically of 0.1 or 0.3%. Autostrain adjustment and axial forceadjustment were active for temperature ramp experiments withcalibrated thermal expansion of the fixture. Control stress experimentsin Figure 6c was performed with 15 mm 2° cone and plate on aMCR301 (Anton-Paar).

Figure 7. Scheme of giant molecular clusters (d > ζ) in the bulk. Thecenter of each cluster would not move. The long-lasting Gpl originatesfrom the confinement, as shown by the gray dashed circle, onindividual OPOSS.

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■ ASSOCIATED CONTENT*S Supporting InformationThe Supporting Information is available free of charge on theACS Publications website at DOI: 10.1021/acs.macro-mol.9b00549.

Materials and characterizations of synthesis, syntheticprocedures; Figures S1−S35 (PDF)

■ AUTHOR INFORMATIONCorresponding Authors*(S.Z.D.C.) E-mail: scheng@uakron.edu.*(G.L.) E-mail: gl15@zips.uakron.edu; lgx@dhu.edu.cn.ORCIDYuchu Liu: 0000-0001-9780-8724GengXin Liu: 0000-0002-2998-8572Wei Zhang: 0000-0002-9321-6411Chrys Wesdemiotis: 0000-0002-7916-4782Stephen Z. D. Cheng: 0000-0003-1448-0546Author Contributions#Y.L. and G.L. contributed equally. G.L., Y.L., and S.Z.D.Cdesigned the research; Y.L. and W.Z. (synthesis), C.D. andC.W. (mass spectroscopy), and G.L. (structure and rheology)performed the research; G.L. and Y.L. analyzed data; and G.L.,Y.L., and S.Z.D.C wrote the paper.NotesThe authors declare no competing financial interest.

■ ACKNOWLEDGMENTSG.L. is supported by Donghua University. This work is alsosupported by NSF DMR-1408872.

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