segmental dynamics of poly(styrene-b-2-vinylpyridine) in bulk and at the surface/air interface

Segmental Dynamics of Poly(styrene-b-2-vinylpyridine)in Bulk and at the Surface/Air Interface

MING XIE,* FRANK D. BLUM

Department of Chemistry and Materials Research Center, University of Missouri–Rolla, 142 Schrenk Hall,Rolla, Missouri 65409-0010

Received 28 December 1995; revised 1 December 1997; accepted 15 January 1998

ABSTRACT: Anionically polymerized poly(a-deuterostyrene) and poly(b-deuterostyr-ene-b-2-vinylpyridine) (DSVP), selectively deuterated on the styrene backbone, werestudied using deuterium wide-line NMR in bulk and adsorbed on silica and alumina.Changes in the segmental dynamics of the bulk and adsorbed polymers were inferredvia changes in the NMR line shape with temperature. The DSVP bulk sample, whichconsisted of micellar aggregrates with a 2-vinylpyridine core, was more rigid than thehomopolystyrene of a similar molecular weight. A significant change in mobility oc-curred at 207C higher in the DSVP bulk sample than it did in homopolystyrene. TheDSVP-adsorbed sample showed more restrictive mobility than bulk DSVP. The spectraof the adsorbed samples contained ‘‘rigid’’ Pake patterns with considerable intensityat temperatures where the collapse of the Pake pattern for the DSVP bulk sample wasobserved. DSVP bound to the silica surface was found to have a mobility similar to thesame copolymer on alumina. q 1998 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 36:1609–1616, 1998Keywords: polymer–surface interactions; deuterium NMR; block copolymers; polymermicelles

INTRODUCTION face.3,4 The adsorbing block serves as the ‘‘anchor’’and the tethered chain as the ‘‘buoy.’’ 5 These can

Polymer–solid interfaces are present in a number be used to modify the surface of a solid andof technologically important materials systems, thereby to manipulate surface properties.including composites, adhesives, and colloidal dis- Investigations into the properties of interfacialpersions. The widespread use of adsorbed poly- regions are made difficult by the complex mor-mers has motivated extensive studies of these sys- phology that characterizes these materials. NMRtems.1,2 The adsorption behavior of copolymers is methods have provided considerable insight intonaturally richer than that of homopolymers be- the behavior of bulk polymers, especially in thecause more than one kind of affinity can be built determination of molecular motions and variousinto different parts of the same macromolecule. morphological domains.6,7 These, in turn, influ-In the case of a diblock copolymer, selective ad- ence the overall macroscopic properties of the ma-sorption from selective solvents can create poly- terials. The sensitivity of NMR to different nu-mer ‘‘brushes’’ or ‘‘mushrooms’’ when polymer clear environments is reflected in a number of dif-chains are tethered by their ends at an inter- ferent phenomena. It is particularly well

established in its effect on NMR line shapes.6,8,9

Correspondence to: F. D. Blum Line shape analyses provide a convenient way to*Current address: Department of Chemical Engineering, study dynamic processes with correlation times

Michigan State University, East Lansing, MI 48824between 1004 to 1006 . The presence of motion

Journal of Polymer Science: Part B: Polymer Physics, Vol. 36, 1609–1616 (1998)q 1998 John Wiley & Sons, Inc. CCC 0887-6266/98/101609-08 leads to partially narrowed spectra, with the re-

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8q5d 9512008/ 8q5d$$2008 04-17-98 12:52:35 polpa W: Poly Physics

1610 XIE AND BLUM

Table I. Molecular Weights of Polymers from GPC

wt % wt % Mw

Styrene 2-Vinylpyridine kg/mol Mw/Md

SVP-11 77 23 11.2 2.00DS-4 100 0 10.0 1.15DSVP-B1 77 23 9.8 1.76

sultant line shapes depending on the type and the along with their composition and polydispersities.The structures of the polymers are shown below:time scale of the motion.

The study of adsorbed polymers requires addi-tional effort over bulk or solution polymers chieflybecause the amounts adsorbed are typically smallin comparison to bulk. This is particularly prob-lematic for NMR studies. Nevertheless, signifi-

©(CH¤©CD)©

DS-4 DSVP

n©(CHD©CH)©(CH¤©CH)©

x y

N

cant gains in these areas have been made.10,11

Carbon-1312 NMR showed that for poly(iso-propyl Samples with monolayer coverage of surface-acrylate), where there was an attraction to the adsorbed DSVP were prepared for NMR solidsurface, segmental mobility of the surface-bound wide-line studies. The two model surfaces thatpolymer was reduced. More recent work with deu- were chosen for adsorption studies were amor-terium NMR on poly(vinyl acetate)13 and poly- phous fumed silica, Cab-O-Sil grade M-5 (Cabot(methyl acrylate)14 showed that the situation was Corporation. Tuscola, IL) and g-Al2O3 (Johnsonmore complicated. A small fraction of segments, Matthey Electronics, Ward Hill, MA). The Cab-assigned to those at the air–polymer interface, O-Sil M-5 consisted of fumed silica beads withwere more mobile than those of the bulk–poly- diameters of about 140 A each and a surface areamer. Most segments, especially those near the of 200 { 25 m2/g.20 The alumina contained 90%polymer silica interface, were less mobile than g-Al2O3 and 10% a-Al2O3. The surface area of thebulk. The interfacial polymer layer was proposed alumina was 79 m2/g, with a particle size of aboutto be graded in terms of mobility. Gradation, in 0.01 micron. Monolayer coverage of DSVP on sil-terms of mobility, was also found in layers of si- ica and alumina was determined from adsorp-lane coupling agents in composite materials.15

tion isotherms measured for an unlabeled sampleIn this article, we report studies of a low molec- of poly(styrene-b-2-vinylpyridine) (SVP-11) on

ular-weight bulk homopolystyrene, a bulk block Cab-O-Sil M-5 and g-Al2O3. The SVP-11 copoly-copolymer poly(deuterostyrene-b-2-vinylpyridine) mer had a molecular weight that was similar to(DSVP), and the block copolymer adsorbed on sil- that of the deuterated copolymers.ica and alumina. We have previously reported the Adsorption isotherms for SVP-11 on both sub-segmental dynamics of DSVP adsorbed on sur- strates were measured in toluene at 257C.18

faces swollen in toluene and other solvents.16–18The substrates were heated for at least 24 h

The focus of this work is on the behavior of the before use, and g-Al2O3 was dried at 4007C in andry adsorbed polymer using the deuterium solid oven for 1 day. Toluene solutions of varying con-wide-line NMR to study segmental mobility. centrations were added to known amounts of sub-

strates in centrifuge tubes. They were thenshaken in a water bath for approximately 48 h

EXPERIMENTAL at 257C and centrifuged. A measured volume ofsupernatant liquid was drawn off and placed inan aluminum weighing pan. Toluene was evapo-The diblock copolymers poly(b-deuterostyrene-b-

2-vinylpyridine) (DSVP) and homo-poly(a-deu- rated at 1057C and the weight of the polymer resi-due determined. The amount of SVP adsorbed perterostyrene) (DS-4) were synthesized by anionic

polymerization. The experimental procedure for m2 of substrate was then calculated based onknowledge of the initial and final concentrationsboth deutero-styrene monomer preparation and

copolymer synthesis have been reported.19 Table of SVP and the amount of substrate used. Theadsorption isotherms were obtained by plottingI lists the diblock copolymers used in this work


SEGMENTAL DYNAMICS OF POLY(STYRENE-b-2-VINYLPYRIDINE) 1611

shown for comparison in Figure 1.18 Although theadsorption of polymers is complex and, strictlyspeaking, a Langmuir isotherm would not neces-sarily be expected, we found that the adsorptionisotherms for DSVP on either surface could ade-quately be described by it.23

A Å ac / (1 / bc ) (1)

where A is the amount adsorbed, mg polymer/m2

surface, a , b are constants, and c is equilibriumconcentration, mg/mL. The ratio of a /b representsthe limiting monolayer coverage. The monolayeramount of material on each surface was similar.The adsorption plateau (a /b ) was approximately2.95 mg polymer/m2 on alumina and 2.89 mg poly-mer/m2 on silica. The polymers had a higher af-

Figure 1. Adsorption isotherms for SVP-11 on silica and finity for alumina as observed from the isotherm.alumina for (A) alumina and (B) silica (after ref. 18). To study the segmental motion in the DS and

DSVP samples, a series of deuterium wide-linethe amount of SVP adsorbed per m2 of surface spectra was collected as a function of tempera-against the equilibrium concentration of the poly- ture. Figures 2 to 5 show the NMR powder patternmer in solution. spectra of DS (bulk), DSVP (bulk), and DSVP

Deuterium solid wide-line NMR has been usedto explore the styrene segmental motions. Themeasurements were carried out at 61.4 MHz on aVarian VXR-400/S NMR spectrometer at severaldifferent temperatures. The quadrupole echo21

pulse sequence ‘‘SSECHO’’ was used with a typi-cal 907 pulse length 2.7 ms. The relaxation delaytime was 6 s. A 2-kHz line broadening was appliedbefore Fourier transformation. Data were ac-quired with a sweep width of 2 MHz and an acqui-sition size of 4096 points. Fourier transformationwas performed on the half-echo, which was left-shifted to the top of the echo. The number of ech-oes accumulated varied between 5000 and 10,000,depending on the sample.

Transmission electron microscopy (TEM) wasperformed on a DSVP sample that was dissolvedin toluene and cast from solution into a shapeconvenient for microtoming at room temperature.The approximately 70 nm-thick sections weresupported on lacey carbon grids (200 mesh). Thesections were stained with I2 , which selectivelystains the VP groups.22 A Philips CM120 Bio-TWIN Cryo, operated at 120 kV, was used to ex-amine the sections, and images were recordedwith a Gatan multiscan CCD camera.

RESULTS

The adsorption isotherms for the SVP-11 block Figure 2. 2H wide-line spectra of DS-4 bulk as a func-tion of temperature.copolymer on Cab-O-Sil M-5 and g-Al2O3 are


1612 XIE AND BLUM

nent was apparent even at 847C, although its in-tensity was very small. The majority of theintensity of the Pake pattern was gone at 120.57C,where only a weak narrow resonance was ob-served.

Both surface-bound samples (Figs. 4 and 5) fallinto the same pattern as the bulk block copolymersample. The threshold temperatures, at which thenarrow components in the spectra started toevolve, were higher than that for the bulk sample.However, once they were evident, their intensitywas greater than in the corresponding bulk sam-ple. At the highest temperature studied (1207C),evidence of significant amounts of the ‘‘rigid’’ com-ponent was still apparent. The composition of thesurface (silica vs. alumina) did not seem to havea significant influence on the line shapes. Finally,we note that there was a significant reduction insignal-to-noise as the progression from styreneú DSVP(bulk) ú DSVP(silica) ú DSVP(alum-ina). This is the obvious result of a dilution in

Figure 3. 2H wide-line spectra of DSVP bulk as afunction of temperature.

(surface-bound) samples, respectively. The fea-tures of each set of these are similar, but thechanges occur at different temperatures for each.To observe the major spectral features of each,each spectrum was increased in a vertical scale sothat a similar peak height for each was observed.

For the homopolymer, DS-4, rigid powder(Pake) pattern spectra were observed at lowertemperatures. The splitting between the hornswas 123.37 kHz. This pattern was observed to bemostly collapsed at 1007C, with a small amount ofpowder pattern remaining. At 1007C a significantreduction in intensity of the resonance was notedcorresponding to motion in the intermediate re-gime. Above 1007C, the spectra showed a single,relatively narrow resonance.

The bulk block copolymer sample exhibited aPake powder pattern spectrum below about 1107C(Fig. 3). At 1107C the Pake pattern was distorted,but still present. As the temperature was in-creased, a second component (more mobile) ap- Figure 4. 2H wide-line spectra of DSVP adsorbed on

silica as a function of temperature.peared as a narrow central peak. A narrow compo-



v Å v0 { 38 (e2qQ /h ) (3 cos2u 0 1

0 h sin2u cos22f ) (2)

where e2qQ /h is the quadrupole coupling con-stant, u and f are polar angles specifying the ori-entation of the magnetic field with respect to theprincipal axis system of the electric field gradienttensor, and h is the asymmetry parameter. Foraliphatic C{D bonds, h is usually zero, becausethe electric field gradient tensor is usually axiallysymmetric. Therefore, eq. (2) can be rewritten as:

v Å v0 { 38(e2qQ /h ) (3 cos2u 0 1) (3)

The frequencies of the NMR transitions dependupon the angle, u, that the C{D bond makes withthe external magnetic field. In a powder sample,all possible orientations of the C{D vector wouldexist if the C{D bonds were ‘‘rigid’’ on the deute-rium NMR time scale, meaning the motion of thebond vector was very slow. For deuterium wide-line NMR line shapes, slow motions are classifiedby Dyqtc @ 1, where Dyq is the quadrupole split-ting and tc is the correlation time.

For an aliphatic deuteron, the splitting for astatic pattern is approximately 125 kHz due to aquadrupole coupling constant of typically 165Figure 5. 2H wide-line spectra of DSVP adsorbed onkHz. A spectrum with these characteristics isalumina as a function of temperature.called a ‘‘Pake’’ powder pattern. This was approx-imately what was observed in Figures 2 (257C,

the numbers of labeled styrene segments in the 847C), 3 (257C), 4 (257C, 847C, 1007C), and 5samples.

The TEM picture of the solid polymer from thedrying of a toluene solution is shown in Figure 6.In the picture small dark dots, on the order ofabout 5 nm, were observed. The small size andcontrast made it difficult to get a precise measure-ment of the dimensions of the cores. No definitelonger range structure was observed. Based onthe sample preparation procedures employed, thismay not be an ‘‘equilibrium’’ structure.

DISCUSSION

The deuterium nucleus has a spin of I Å 1, whichmeans that in the presence of a strong magneticfield there are three quantized energy levels. TheNMR experiment is sensitive to the two transi-tions between these levels. Because deuterium Figure 6. Transmission electron micrograph of thesolid-state NMR spectra are dominated by the DSVP copolymer obtained from the drying of a toluenequadrupole coupling, the NMR frequencies of the solution. The small dots appear to be the micelle cores

from the VP segments that were stained with I2 .two transitions are given by:24,25


1614 XIE AND BLUM

(257C, 847C, 1007C), which is indicative of slow ture of DS-4 and DSVP will not be significant fac-tors affecting the segmental motions.motions with correlation times longer than 1005

The DS-4 homopolymer (Fig. 2) showed Pakes. Our experimentally measured quadrupole cou-patterns indicative of the polymer being essen-pling constant for these spectra was 164.5 kHz.tially ‘‘rigid’’ on the NMR time scale at 847C andIn solids, interactions such as electric quadru-below. The spectrum at 1007C showed the pres-polar couplings for deuterium depend on orienta-ence of a second narrow component, and signifi-tion with respect to the magnetic field axis. Re-cant loss in the intensity of the Pake powder pat-stricted molecular motions in the solid state maytern. The loss of intensity of the Pake pattern atcause partial averaging of the orientation depen-1007C was likely due to motion in the intermedi-dent anisotropic line shape. For powder samples,ate time range.33 Only a relatively small amountcertain line-shape features are often characteris-of this intensity was transformed into the narrowtic of a particular type of motion. Variable temper-component at this temperature. The spectrum atature line-shape experiments can provide a sensi-1107C only gave a single sharp peak, indicatingtive means to quantify the characteristics of themore isotropic motion of styrene segments. Themotion over a wide range.line shape for DS-4 changed from an essentiallyIf there is appreciable reorientation of C{Drigid solid (847C) to a motionally narrowed singlevector during the experiment, then, u and the linepeak (1107C). DSC measurements on our DS-4shape will be motionally averaged. The line shapesample showed a glass transition around 807C.that arises would then be dependent upon howThe NMR measurements suggested a significanteffectively the motion averages the quadrupolarchange in mobility that appeared to be completeinteraction. The line shape is generally dependentby 1107C. This is significantly above the DSC Tg ,not only on the rate of motion, but also the typeand is to be expected, as the NMR time scale isof motion. For certain types of motion, the shapemuch faster than that for DSC. In this case, theof the resonance is well know.26 However, some-NMR time scale is given by the reciprocal of thetimes the shape of the spectrum arising for a givensplitting for the rigid pattern.system may be difficult to predict. Then some sort Spectra similar to ours have been observed for

of motional model would be needed to help deter- polystyrene27,28 and other polymers.13,14,34 Spiessmine the motional mode. Initial examination of et al.28 reported polystyrene segmental motion be-our spectra indicates that there were basically low and above Tg . For a high molecular weighttwo components contributing to the overall exper- sample (Mw Å 141,000) of backbone deuteratedimental line shapes. One is essentially ‘‘rigid’’ on polystyrene, they observed the line shape changethe NMR time scale, and the other is indicative from a Pake powder pattern to a Lorentzianof significant motional narrowing resulting in a within what they termed a narrow temperaturemotionally narrowed resonance. Based on the na- range (from 130 to 1607C). They concluded thatture of our spectra, detailed simulations were not in polystyrene, the segmental motion became es-necessary for understanding the causes of the line sentially isotropic in a single process. Gradualshape. The spectra and changes observed are sim- narrowing, characteristic of highly restricted mo-ilar to those previously observed27,28 for polysty- tion, was not observed. Henrichs and Long27 re-rene. We also note that both the homopolymer ported similar results for the segmental motion ofand copolymer had similar molecular weights, but backbone-labeled partially deuterated polysty-they were deuterated at different positions. Hen- rene when above the glass transition tempera-richs and Long27 have indicated that the behavior ture. Below 1177C, there was no motional averag-of both the a- and b-deuterated positions yield the ing of the deuterium spectrum. Above 1577C, thesame motional information so the position of the spectrum was averaged into a Lorentzian linelabel is not an important consideration. Because that narrowed as the temperature was raised. Thethe DS-4 and DSVP were synthesized by anionic amplitudes of ring- and main-chain motions of apolymerization in different solvents, we have variety of polystyrenes have been studied bystudied the tacticity of the two polymers. Our 13C- Schaefer et al.35 from the 13C-NMR magic-angleNMR spectra and previous reports of others29,30 spinning sideband patterns of dipolar and chemi-showed similar tacticity in the resulting poly- cal shift tensors. The most prevalent motion inmers. Even so, polystyrene with different tacticity these polymers that they found was restrictedhas been reported to have very similar Tgs.31,32 phenyl rotation with a sizable average jump

angle. Low-frequency (kilohertz) main-chain mo-Thus, the position of the label and the microstruc-



tion was assigned to a cooperative main-chain mo- upon evaporation from a toluene solution, it ap-pears that the micellar structure from solutiontion in which the rings undergo limited transla-

tions but no rotations. More recently, Chin et al.36 was retained by our DSVP copolymer as shown inthe TEM photo (Fig. 6). The size of the micellesreported on the behavior of deuterated polysty-

rene in a glassy blend at the glass transition by were quite small, roughly 5 nm, but consistentwith the much lower molecular weight (VP/STY:two-dimensional solid-state deuteron NMR. They

found that the segmental motion of the deute- 2.3 k/7.5 k) of our copolymer.One plausible explanation for the effect on dy-rium-labeled polymer exhibited the characteris-

tics of rotational Brownian diffusion with an asso- namics would be that if the micelle core were morerigid than the styrene segments due to packingciated broad distribution of correlation times that

was considerably broader than that typical for and stronger segmental interactions, it wouldtend to make the styrene segments more rigid.the single-component polymer. These prior re-

sults27,28 are similar to our observations except This would result from one end, that near theVP segments, being effectively tied in the micellethat, for our lower molecular weight polymer, we

observed this behavior (the NMR glass transi- core. One way to think of this is that the SVPpolymer has a much greater effective moleculartion) at a much lower temperature.

For the DSVP bulk sample (Fig. 3), little mo- weight.The surface-bound copolymer exhibited mobil-tion of the backbone was observed at ambient

temperature. As the temperature was raised, the ity that was different from either the bulk copoly-mer or homopolymer. The spectral intensity of themobility of the polymer increased. The presence

of a small amount of mobile component appeared surface bound resonance was lower than that inbulk because of the dilution effect of the solid sup-in the spectrum taken at 847C. This component

at the center of the spectrum was indicative of a port. The spectra still showed the presence of thePake powder pattern with considerable intensityvery small amount of material with considerable

freedom of backbone segmental motions. The in- even at 1207C, although there was also a narrowcomponent seen at 1107C. The results confirmedtensity of the mobile component grew slowly as

the temperature increased. At 1207C, the Pake that the surface had the effect of further re-stricting the motion of the polymer. This restric-pattern was mostly eliminated and the presence

of the motionally narrowed component was more tion is in stark contrast to the behavior of thesame polymer when swollen with toluene18 whereprominent, although most of the intensity was

missing due to motion in the intermediate re- the mobility of the surface-bound polymer wassimilar to that in solution. Clearly, the interactiongime.33 A comparison of Figures 2 and 3 indicated

that the styrene segments were more mobile in between the VP anchor and surface greatly hin-dered the mobility of the styrene block.the low molecular-weight homopolymer than in

the DSVP block copolymer in bulk. This was ap- Finally, the spectra of DSVP on alumina (Fig.5) were similar to those on silica (Fig. 4). Theparent in the higher temperature spectra where

the collapse and loss of the Pake pattern for the intensities, and hence, signal-to-noise ratios, fromthe alumina sample were lower because its lowerblock copolymer occurred at about 207C higher

than for the homopolymer. specific area. The features, however, are almostidentical. Even the loss of intensity in the PakeThe differences in the mobility of the DSVP

and DS-4 are undoubtedly due to differences in pattern at 1107C for both surface-bound sampleswas similar; only about 40% of the intensity re-structure between the two species. DSVP is

known to form micelles at moderate concentra- mained compared to that at 1007C. Similar reduc-tions in intensities are expected for similar mo-tions of the polymer in toluene.19 These have a

core of VP with the styrene on the outside. TEM tions.33 The similarity of the behavior on both sur-faces was an indication that neither the detailedphotographs of higher molecular-weight SVP

(VP/STY: 102 k/75 k and 32 k/75 k) have also nature of the surface structure nor the size playeda significant role in the styrene dynamics at simi-shown the presence of micelles in toluene solu-

tion.37,38 These had micelle cores of VP around 48 lar adsorbed amounts.and 30 nm, respectively. It was suggested thatthe cores were ‘‘dense.’’ The morphology of the CONCLUSIONSSVP polymers can be quite rich, and a wide vari-ety of structures may be formed under various The dynamics of bulk and surface-bound block

copolymer poly(styrene-b-2-vinylpyridine) wereconditions and thermal treatments.22 However,


1616 XIE AND BLUM

State NMR of Polymers, L. J. Mathias, Ed., Plenumstudied by deuterium wide-line NMR. Variable-Press, New York, 1991, p. 271.temperature studies of the bulk homopolymer,

13. W.-Y. Lin and F. D. Blum, Macromolecules, 30,block copolymer, and adsorbed copolymer of simi-5331 (1997).lar molecular weights showed that the dynamics

14. F. D. Blum, G. Xu, M. Liang, and C. G. Wade, Mac-of each were different. Motion around the deute- romolecules, 29, 8740 (1996).rium NMR time scale (roughly the reciprocal of 15. F. D. Blum, Macromol. Symp., 86, 161 (1994).100 kHz in this case) caused the collapse of the 16. F. D. Blum, B. R. Sinha, and F. C. Schwab, Macro-Pake powder pattern. The onset of significant sty- molecules, 23, 3592 (1990).rene backbone motions in homopolystyrene oc- 17. B. R. Sinha, F. D. Blum, and F. C. Schwab, Macro-

molecules, 26, 7053 (1993).curred at roughly 1007C, which was roughly 207C18. M. Xie and F. D. Blum, Langmuir, 12, 5669 (1996).lower than a similar onset in the bulk copolymer19. M. Xie and F. D. Blum, Macromolecules, 29, 3862(1207C) of similar molecular weight. The bulk co-

(1996).polymer had a micellar structure with the dense20. Cab-O-Sil Untreated Fumed Silica Properties andVP core responsible for decreasing the mobility of Functions, Cabot Corporation, Tuscola, IL, 1993.

the styrene segments. Both silica- and alumina- 21. M. Bloom, J. H. Davis, and M. I. Valic, Can. J.bound DSVP samples showed even more reduced Phys., 58, 1510 (1980).mobility due to their surface attachment. The on- 22. M. F. Schulz, Ashish K. Khandpur, F. S. Bates, K.set of significant backbone motion did not occur Almdal, K. Mortensen, D. A. Hajduk, and S. M.

Gruner, Macromolecules, 29, 2857 (1996).until 1207C for the surface-bound samples.23. A. W. Adamson, Physical Chemistry of Surfaces,

4th ed., John Wiley & Sons, New York, 1982, p.The authors would like to acknowledge Gunnell Karls- 152.son of the Biomicroscopy Unit at the Chemical Center, 24. A. Abragam, The Principles of Nuclear Magnetism,Lund University, Sweden, for assistance with the TEM Oxford University Press, Oxford, 1961.work, and National Science Foundation for its financial 25. H. W. Spiess, NMR-Basic Principles and Progress,support. Vol. 15, P. Diehl, E. Fluck, R. Kosfeld, Eds.,

Springer Verlag, New York, 1978.26. L. W. Jelinski, Annu. Rev. Mater. Sci., 15, 359

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segmental dynamics of poly(styrene-b-2-vinylpyridine) in bulk and at the surface/air interface

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