Chemical composition effects on the fracture of polystyrene-block-poly(methyl methacrylate)block copolymers

$Page 1: Chemical composition effects on the fracture of polystyrene-block-poly(methyl methacrylate)block copolymers$
Chemical Composition Effects on the Fractureof Polystyrene-block-Poly(methyl methacrylate)Block Copolymers

WON KIM,1,2 JUNWON HAN,1,2 CHANG Y. RYU,1,2 HOICHANG YANG3

1Department of Chemistry and Chemical Biology, Rensselaer Polytechnic Institute,110 8th Street, Troy, New York 12180

2Department of Chemical and Biological Engineering, Rensselaer Polytechnic Institute,110 8th Street, Troy, New York 12180

3Rensselaer Nanotechnology Center, Rensselaer Polytechnic Institute, 110 8th Street, Troy, New York 12180

Received 26 June 2006; revised 8 September 2006; accepted 8 September 2006DOI: 10.1002/polb.21019Published online in Wiley InterScience (www.interscience.wiley.com).

ABSTRACT: The crazing and fracture behaviors of glassy–glassy block copolymerswere investigated for polystyrene-block-poly(methyl methacrylate) (PS-b-PMMA)diblock copolymers that had similar overall molecular weights but different poly(methyl methacrylate) (PMMA) molar fractions. A liquid chromatography techniquewas applied to separate as-synthesized PS-b-PMMA [(1) weight-average molecularweight (Mw) ¼ 94,000 g/mol and PMMA molar fraction ¼ 0.35 and (2) Mw ¼ 65,000 g/mol and PMMA molar fraction ¼ 0.28] into three fractions with different chemicalcompositions. With a copper-grid technique, the fracture behaviors of 0.5-lm-thickPS-b-PMMA films were studied as a function of the applied strain. For the higherMw PS-b-PMMA samples, the median strains at crazing and fibril breakdownincreased with an increase in the PMMA molar fraction from 0.24 to 0.46, corre-sponding to an increase in the chain entanglements in the PMMA domains. In con-trast, for the lower Mw samples, the two values were not significantly changed evenwhen the PMMA molar fraction was varied from 0.16 to 0.35. Mw of the minor com-ponent in PS-b-PMMA played a critical role in controlling the fracture behaviors ofthe block copolymers. Specifically, Mw/Me of the minor component (where Me is themolecular weight between entanglements) had to be roughly larger than 2 for theblock copolymers to sustain sufficient strains before fracture. VVC 2006 Wiley Periodicals,

Inc. J Polym Sci Part B: Polym Phys 44: 3612–3620, 2006

Keywords: block copolymers; crazing; fractionation of polymers; fracture; liquidchromatography

INTRODUCTION

To design polymeric materials with enhanced me-chanical properties, it is important to understandthe fracture behavior of polymers in terms of the

molecular parameters.1–3 In glassy homopolymers,the entanglements and crosslinks determine whethercrazing or shear deformation governs the plasticdeformation before the fibril breakdown.4 Thatthis physical and chemical crosslinking effect gov-erns fracture behavior was clearly demonstratedby Henkee and Kramer,4 who used polystyrene(PS) films crosslinked by electron radiation to pro-duce various strand crosslinking densities beyond

Correspondence to: C. Y. Ryu (E-mail: [email protected])

Journal of Polymer Science: Part B: Polymer Physics, Vol. 44, 3612–3620 (2006)VVC 2006 Wiley Periodicals, Inc.

3612

the physical crosslinking via entanglement. Twodifferent modes of deformation, crazing and sheardeformation, exist, depending on the entangle-ment density for linear glassy polymers. The ef-fects of other parameters, such as the rate of crazeinitiation5 and molecular heterogeneity, on thegrowth and breakdown of crazes6–8 have also beenstudied for homopolymers that exhibit crazing.However, understanding the fracture behaviors ofblock copolymers (BCPs) in terms of the molecularparameters could be more complicated thanunderstanding the fracture behaviors of homopoly-mers. BCPs have a wide range of tailorable prop-erties that are strongly affected by microphaseseparation, chemical composition, and chain ori-entation. Therefore, the fracture properties ofBCPs depend not only on the molecular weight,9

ordered structure,10,11 and chain architecture12

but also on the macroscopic alignment10,13 andthermal aging.14

Recent developments in high-performance liq-uid chromatography (HPLC) for BCPs have en-abled the separation of BCPs by chemical compo-sition differences.15,16 For example, it has beenshown that the chemical composition differencesof HPLC-fractionated polystyrene-b-polyisoprenes(PS-b-PIs) are as high as 9 wt %.17 HPLC has beensuccessfully applied to fractionate different BCPssuch as polystyrene-block-poly(methyl methacry-late) (PS-b-PMMA),18 PS-b-PI,17,19 and polystyrene-b-poly-2-vinylpyridine.20 In addition to separatingBCPs in terms of the chemical composition differ-ence, HPLC fractionation provides a unique op-portunity to prepare BCP samples that have nar-rower chemical composition distributions than themother BCP samples. Because the overall BCPchain length is very similar for HPLC-fractionatedsamples, we can focus on two primary factors, (1)the average chemical composition and (2) the chem-ical composition broadness, for the fracture behav-iors of BCPs that have similar molecular weightdistributions.

Here we have studied the crazing and fracturebehaviors of PS-b-PMMAwith similar chain lengthsbut different average chemical compositions (Fig. 1).We have used a liquid chromatography fractiona-tion technique to fractionate PS-b-PMMA sampleswith different average chemical compositions withsilica gel. Specifically, we have fractionated as-synthesized mother PS-b-PMMA into three frac-tions with different compositions, including asmuch as 20 mol % poly(methyl methacrylate)(PMMA). This fractionation technique allows usto elucidate the effect of the chemical composition

difference on PS-b-PMMA crazing while keepingthe average molecular weight of each fraction con-stant. Because fractionated PS-b-PMMA has anarrower chemical composition distribution thanthe corresponding mother sample, we can alsostudy the effect of the chemical composition broad-ness on the fracture behaviors of PS-b-PMMABCPs.

EXPERIMENTAL

Materials

PS-b-PMMA was synthesized by anionic polymer-ization. Styrene and methyl methacrylate wereadded sequentially after the initiation of the poly-mer with sec-butyl lithium in tetrahydrofuran(THF) at �78 8C. To reduce the reactivity of thepolystyryl anion in THF, diphenyl ethylene wasadded before the addition of methyl methacrylate.Degassed 1-butanol was used to terminate thereaction.21 Two PS-b-PMMAs were synthesizedand fractionated by liquid chromatography, andtheir average molecular weights and chemicalcompositions are summarized in Table 1.

Fractionation of PS-b-PMMA by theChemical Composition Difference

PS-b-PMMA solution samples were prepared in asolvent mixture of THF and iso-octane (IO) with55 vol % THF at a concentration of 3% (w/v). Thesolution was added to a bare silica gel column (60-A pore size; Aldrich) to selectively adsorb PS-b-PMMA over PS homopolymer precursors. The

Figure 1. Illustrations representing AB diblockcopolymers that have the same molecular weight butdifferent chemical compositions.

CHEMICAL COMPOSITION EFFECTS ON FRACTURE 3613

Journal of Polymer Science: Part B: Polymer PhysicsDOI 10.1002/polb

adsorbed PS-b-PMMA on the silica surface wasseparated into three fractions (F1, F2, and F3 inTable 1) by the following procedure. First, fractionF1 was obtained by the rinsing of the PS-b-PMMA-adsorbed silica column with a mixed THF/IO solvent with 58 vol % THF. Then, F2 and F3were subsequently fractionated via rinsing with61 and 64 vol % THF, respectively. The molecularweight distributions of the fractionated PS-b-PMMAs were characterized by size exclusionchromatography (SEC) with a LabAlliance model500 ultraviolet–visible detector. 1H NMR (Varian500 Unity) was used to characterize the averagechemical composition of PMMA in the mother andfractionated PS-b-PMMA samples.

Craze Characterization and Sample Preparation

To quantify the crazing process for polymer thinfilms, the copper-grid technique22 was employed.Thin films of PS-b-PMMA (�0.5 lm thick) werespin-cast onto a glass substrate at 1000 rpm from5.0 wt % toluene and floated on a water surface.Then, the polymer film was picked up by a coppergrid, which was previously coated with the samePS-b-PMMA BCP. Finally, the sample polymerfilm and copper grid were bonded by a short expo-sure (several seconds) to the solvent toluene anddried at room temperature for 20 h. Figure 4(shown later) presents a schematic diagram repre-senting uniaxial tensile deformation. By takingadvantage of the plastic deformation of the coppergrid (annealed at 600 8C for 10 min in vacuo), thistechnique allowed us to examine many samples ineach grid for the statistical analysis of the fracturebehavior under uniaxial strains. At strain regularintervals, the strained films on the copper grid

were examined with reflective optical microscopy(OM) and atomic force microscopy (AFM). ForAFM, a Digital Instrument Multimode atomicforce microscope was used in the tapping mode.Transmission electron microscopy (TEM) was alsoperformed to characterize the craze formation andfibril breakdown with a JEOL CM-12 operating atan accelerating voltage of 120 kV.

RESULTS AND DISCUSSION

Chemical Composition Distribution in the BCPs

Because of the polydispersity of each block, as-synthesized AB diblock copolymers should exist asmixtures of polymer chains with different chemi-cal compositions. Experimentally, Tanaka et al.23

showed an approximately 30 mol % compositionaldistribution of PS-b-PMMA BCP with prepara-tive-scale thin-layer chromatography. Podesvaet al.24 also showed divergence in the distribution ofchemical heterogeneity in PS-b-PI BCPs synthe-sized by a modified anionic polymerization proce-dure. For an AB diblock copolymer, when B is thecompositionally minor block, the maximum andminimum chemical compositions in the as-synthe-sized AB diblock copolymers due to the polydisper-sity of the molecular weights can be estimated bythe calculation of the compositions of a chain withthe shortest A blocks and longest B blocks andthen a chain with the longest A blocks and short-est B blocks for a given polydispersity index (PDI)of A and B. Figure 2 shows the calculated maxi-mum and minimum chemical compositions (molarfractions) of the B block in AB diblock copolymerscontaining 700 A units and 300 B units on average(A700–B300) at different PDIs of A and B. For

Table 1. Polymer Properties of the PS-b-PMMA Mothersand Fractionated PS-b-PMMAs

Sample Mw (g/mol) Mw/Mn xPMMA

Mn/Me

PS PMMA

BCP1 Mother 94,000 1.09 0.35 3.6 2.5BCP1 F1 94,000 1.08 0.24 4.2 1.7BCP1 F2 94,000 1.09 0.31 3.9 2.2BCP1 F3 94,000 1.08 0.46 3.0 3.3BCP2 Mother 65,000 1.06 0.28 2.8 1.4BCP2 F1 65,000 1.05 0.16 3.2 0.8BCP2 F2 65,000 1.05 0.30 2.7 1.5BCP2 F3 65,000 1.05 0.35 2.5 1.7

3614 KIM ET AL.


example, when the PDI of A700 and B300 is 1.05,the actual number of repeating units in A and B is700 6 50 and 300 6 35, respectively. Therefore,the maximum and minimum molar fractions of Bhave been calculated to be 335/(335 þ 650) ¼ 0.26and 265/(265 þ 750) ¼ 0.34, respectively. This sug-gests that the polydispersity of each block will sig-nificantly contribute to the broadness of the chem-ical composition distribution in the as-synthesizedBCPs. The polydispersity of each block alone atPDI ¼ 1.1, for example, will produce about a10 mol % compositional difference in A700–B300

diblock copolymers.Table 1 summarizes the average chemical com-

positions of three PS-b-PMMA BCPs fractionatedfrom as-synthesized mother PS-b-PMMAs withliquid chromatography. PS-b-PMMA BCP1 [weight-average molecular weight (Mw) ¼ 94,000 g/mol,weight-average molecular weight/number-averagemolecular weight (Mw/Mn) ¼ 1.09, and molar frac-tion of PMMA (xPMMA) ¼ 0.35] was separated intothree fractions: xPMMA ¼ 0.24, xPMMA ¼ 0.31, andxPMMA ¼ 0.46. Sample BCP2 (Mw ¼ 65,000 g/mol,Mw/Mn ¼ 1.06, and xPMMA ¼ 0.28) was fractionatedinto three samples: xPMMA ¼ 0.16, xPMMA ¼ 0.30, andxPMMA ¼ 0.35. Therefore, we were able to experi-mentally fractionate PS-b-PMMA BCP samples,with the PMMA composition differing by about20 mol %. In addition, the chemical compositionaldistribution in each fraction must be narrowerthan that in the mother BCP samples because theliquid chromatography separation was achieved

in terms of the chemical composition difference.Although the chemical compositions of the fractio-nated BCPs are significantly different, SEC pro-files (Fig. 3) suggest that the molecular weightdistribution of each fraction remains relativelyunchanged from that of the mother BCP samples.Therefore, by employing a sample set of a BCPmother, F1, F2, and F3, we can study the effects ofthe chemical composition difference and broad-ness on the fracture behavior of PS-b-PMMAwhile maintaining a similar average molecularweight for each BCP sample.

Fracture Studies of the PS-b-PMMA BCPs

The fracture behavior of BCPs is generally affectednot only by molecular factors, such as the homo-polymer molecular weight,25 copolymer composi-Figure 2. Maximum and minimum chemical compo-

sitions in A700–B300 BCPs as functions of the PDI ofeach block. Each block is assumed to have the samePDI.

Figure 3. (a) SEC profiles showing absorbance at260 nm (A260) with respect to retention times, and (b)xPMMA values of BCP1 samples. [Color figure can beviewed in the online issue, which is available atwww.interscience.wiley.com.]



tion,26 and chain architecture,12,27 but also by pro-cessing parameters, such as the shear alignment13

and thermal aging.14 In particular, the mechanicalbehavior of BCPs with anisotropic ordered struc-tures is further complicated13,28 because it de-pends on the extent of long-range ordering andthe direction of macroscopic deformation. Becauseof such morphological complexity, it is difficult tounderstand the fracture properties of BCPs interms of their molecular factors. To avoid suchmorphological complications originating from pro-cessing conditions, we have deliberately limitedthe ordering of BCPs to a short range by spin-coating BCP films without further thermal an-nealing.

The copper-grid technique, developed by Lau-terwasser and Kramer,22 has been employed todetermine the strains for developing crazes or cat-astrophic failure. Figure 4(b) shows reflective OMimages of 0.5-lm-thick PS-b-PMMA BCP filmsbonded onto copper grids as a function of theapplied tensile strain. As shown in Figure 4(c),the development of crazes is identified as darklines perpendicular to the extension direction withreflective OM. When the sample films are stretchedfurther after the development of crazes, a shadowin the reflective OM images starts to appear, andthis is attributed to the catastrophic failures ofthe film [Fig. 4(d)].22

As shown in Figure 5, both AFM and TEM sup-port the formation of fibril-like structures in thecraze region. However, the typical width of thecrazed region in BCP1 films does not exceed0.5 lm, indicating that the films are quite brittleeven at Mw ¼ 94,000 g/mol. When BCP2 films (Mw

¼ 65,000 g/mol) were examined, the samples wereso brittle that fibril breakdown occurred immedi-ately after the formation of crazes. Therefore,craze-depth characterization of BCP2 films couldnot be performed by AFM. Because each coppergrid contained many polymer films bonded to thecopper-grid frame, many sample films were exam-ined at once for the statistical analysis of craze de-velopment or fibril breakdown at various strainsfrom a single copper-grid extension experiment.Specifically, the fractions of crazed or failed filmswere statistically analyzed and plotted as a func-tion of the applied strains (Fig. 6).

Chemical Composition Effects on Crazeand Fibril Breakdown

The median strains for crazing and fibril break-down were determined when the fraction ofsquare films exhibiting crazing or fibril break-down reached 0.5. Figure 7(a,b) shows the medianstrains of crazing and fibril breakdown from sev-

Figure 4. (a) Schematic diagram of the copper-grid setup used to study the fractureof polymer films, (b) OM image representing a BCP1 F3 film with no strain applied,(c) OM image representing a BCP1 F3 film with crazes at e ¼ 2.4%, and (d) OMimage representing a BCP1 F3 film with fibril breakdown at e ¼ 2.9%.

3616 KIM ET AL.


eral copper-grid experiments for a set of motherand fractionated samples of BCP1 and BCP2,respectively. These sample sets are ideal for us tounderstand the effects of the average chemicalcomposition difference on the fracture behaviorswhile keeping the same average molecular weightwithin each set. As the chemical composition(xPMMA) increases from 0.24 to 0.46 in a series ofBCP1 fractionated samples (Mw ¼ 94,000 g/mol),the average median strain for crazing increasesfrom 1 to 2.6%. Such chemical composition de-pendence can be similarly observed for the fibrilbreakdown, which increases from 1.1 to 3.3% inthe BCP1 fractionated samples. The BCP1 mothersample (xPMMA ¼ 0.35) exhibits median strains forcrazing and fibril breakdown at 2.0 and 3.0%,

respectively. This suggests that the average chem-ical composition plays a major role in determiningthe median strains for crazing and fibril break-down, regardless of whether the mother or fractio-nated BCP1 samples (i.e., whether composition-ally broader mother or narrower fractionated sam-ples) are used.

The chemical composition broadness, however,seems to affect the reproducibility of the fraction–strain curves from the repeated copper-gridexperiments. We took advantage of the statisticalanalysis nature of the copper-grid experiment tocharacterize the fracture behavior, and the frac-tional curves in Figure 6 show the statistical de-velopment of crazes as a function of the appliedstrain for the BCP1 mother and BCP1 F2 fraction.

Figure 5. (a) AFM phase image of the crazed region in a BCP F2 film, (b) surfaceplot of a height image of the same region (height scale ¼ 100 nm), and (c) TEMimage of the crazed region in a BCP F2 film.



From 14 copper-grid experiments of the BCP1mother sample [xPMMA ¼ 0.35; Fig. 6(a)], thestandard deviations of the median strains for craz-ing and fibril breakdown are 1 and 1.5%, respec-tively. On the contrary, the fractionated F2 sample(xPMMA ¼ 0.31), which has a chemical compositionand molecular weight similar to those of themother sample, exhibits very reproducible medianstrain values for crazing and fibril-breakdownbehavior [Fig. 6(b)]. The standard deviations of

the median strains for crazing and fibril break-down for F2 from several copper-grid experimentsare 0.01 and 0.17%, respectively.

Figure 7(b) shows the median strains for craz-ing and fibril breakdown in a series of BCP2mother and fractionated samples (Mw ¼ 65,000 g/mol) that have a lower molecular weight than theBCP1 samples (Mw ¼ 94,000 g/mol). Unlike theBCP1 samples, these BCP2 samples have shownlittle chemical composition dependence on their

Figure 6. Fraction of copper grids as a function ofextension, e, exhibiting crazing: (a) BCP1 mother (Mw

¼ 94,000 g/mol and xPMMA ¼ 0.35) and (b) BCP1 F2fraction (Mw ¼ 94,000 g/mol and xPMMA ¼ 0.31). Thefractional curves represent more than 10 copper-gridexperiments repeated to characterize the statisticaldevelopment of crazes and catastrophic failure.

Figure 7. Median strains for (l) crazing and (n)fibril breakdown for mother and fractionated (F1, F2,and F3) samples of (a) BCP1 and (b) BCP2. The errorbars stand for the standard deviation from severalcopper-grid experiments. The solid lines of the insetfigures represent the median strain for the fibrilbreakdown as a function of Mn/Me from Yang et al.31

using monodisperse homopolymers. The solid squaresin the insets indicate the median strain data as afunction of Mn/Me of the minor domains in the fractio-nated samples.

3618 KIM ET AL.


fracture behaviors. Because the molecular weightof BCP2 is very low, all the samples are alreadyquite brittle, exhibiting fibril breakdown as soonas the craze occurs at a strain of about 1%. It isimportant to understand why the BCP1 samplesshow a composition-dependent fracture behavior,whereas the fracture behaviors of the BCP2 sam-ples display little dependence on the chemicalcomposition. Such a contrasting difference in thefracture behaviors of the BCP1 and BCP2 samplesshould be attributed to the molecular weight dif-ferences, which eventually affect chain entangle-ments in BCPs. Specifically, we have found thatthe molecular weights of less entangled PMMAdomains in the PS-b-PMMA samples play a cru-cial role in determining the fracture behavior ofthe BCPs.

As the minor PMMA molecular weight in-creases for a given molecular weight of a BCP, notonly is there an increase in the chemical composi-tion (xPMMA), but there is also an enhancement ofthe entanglement density within the PMMAdomains. Because the molecular weight betweenentanglements (Me)

29,30 is 17,000 for PS and13,000 g/mol for PMMA, Mn/Me is lower for thePMMA block, except for BCP1 F3, in our study(see Table 1). From the molecular weight depend-ence on the fracture behaviors of monodispersePS, Yang et al.31,32 have shown that there exists amolecular weight window of Mn/Me (2 � Mn/Me

�12) in which the fracture properties stronglydepend on the molecular weight. In the case ofhigher molecular weight BCP1 samples, Mn/Me ofthe PMMA block changes from 1.7 to 3.3 [inset ofFig. 7(a)] when xPMMA increases from 0.24 to 0.46.Therefore, the observed chemical composition de-pendence on the fracture properties in the BCP1samples is attributed to the enhancement of Mn/Me in the minor PMMA domains, which arelocated within the window of 2 � Mn/Me �12. Onthe contrary, Mn/Me of the PMMA block for lowermolecular weight BCP2 samples varies from 0.8 to1.7 [inset of Fig. 7(b)]. Because these ratios arelocated outside the window, the fracture proper-ties of the PMMA domains in BCP2 do not dependon the molecular weight change of the PMMAblocks.

CONCLUSIONS

The effects of the chemical composition and itsbroadness on the fracture properties of PS-b-PMMA BCPs have been studied. By the use of a

liquid chromatography technique, as-synthesizedPS-b-PMMA BCPs [(1) Mw ¼ 94,000 g/mol, PDI¼ 1.09, and xPMMA ¼ 0.35 and (2) Mw ¼ 65,000 g/mol, PDI ¼ 1.06, and xPMMA ¼ 0.28] have beenseparated into three fractions with differentxPMMA values (as much as 22 mol %) but with thesame molecular weight distribution.

The strains for crazing and fibril breakdownhave been evaluated by the copper-grid techniquefor mother and fractionated samples of PS-b-PMMA. For the samples of 94,000 g/mol, the me-dian strain for crazing and fibril breakdownincreases from 1 to 2.5% and from 1 to 3.2%,respectively, as xPMMA increase from 0.24 to 0.46.However, for the lower molecular weight PS-b-PMMA with 65,000 g/mol, the fracture behaviorsshow little compositional dependence. The compo-sitional dependence in the PS-b-PMMA sampleswith 94,000 g/mol may be attributed to the entan-glement density difference of PMMA domains asMn/Me of the PMMA block, which increases from1.7 to 3.3. As for PS-b-PMMA samples with 64,000g/mol, Me of the PMMA blocks is already too low(Mn/Me ¼ 0.8–1.7) to show any significant depend-ence on the compositional difference. Therefore,we have concluded that the molecular weight ofthe minor block in the BCPs has to be Mn/Me > 2to exhibit the compositional dependence on theirfracture behaviors. For a given molecular weightand average xPMMA value, the chemical composi-tion broadness of PS-b-PMMA BCPs significantlyaffects the reproducibility of the fracture behav-iors. The fractionated samples exhibit more repro-ducible fracture behaviors than the mother sam-ple during repeated copper-grid experiments. Thisis due to the fact that the fractionated sampleshave a chemical composition distribution nar-rower than that of the as-synthesized mother BCPsample.

This work was gratefully supported by grants fromNational Science Foundation DMR CAREER (NSF-0449736) and Nanoscale Science and EngineeringCenter for Directed Assembly of Nanostructures(NSF-0117792).

REFERENCES AND NOTES

1. Kramer, E. J. Adv Polym Sci 1983, 52, 1.2. Kramer, E. J. J Polym Sci Part B: Polym Phys

2005, 43, 3369.3. Kramer, E. J. Plast Rubber Compos 1997, 26, 241.4. Henkee, C. S.; Kramer, E. J. J Polym Sci Polym

Phys Ed 1984, 22, 721.



5. Argon, A. S.; Hannoosh, J. G. Philos Mag 1977,36, 1195.

6. Donald, A. M.; Kramer, E. J. J Polym Sci PolymPhys Ed 1982, 20, 899.

7. Donald, A. M.; Kramer, E. J.; Bubeck, R. A. JPolym Sci Polym Phys Ed 1982, 20, 1129.

8. Michler, G. H. Colloid Polym Sci 1986, 264, 522.9. Giraud, Y.; Goletto, J. Makromol Chem Makromol

Symp 1989, 23, 225.10. Lee, J.-Y.; Crosby, A. J. Macromolecules 2005, 38,

9711.11. Weidisch, R.; Ensslen, M.; Michler, G. H.; Fischer, H.

Macromolecules 1999, 32, 5375.12. Ryu, C. Y.; Ruokolainen, J.; Fredrickson, G. H.;

Kramer, E. J.; Hahn, S. F. Macromolecules 2002,35, 2157.

13. Hermel, T. J.; Wu, L.; Hahn, S. F.; Lodge, T. P.;Bates, F. S. Macromolecules 2002, 35, 4685.

14. Ruokolainen, J.; Fredrickson, G. H.; Kramer, E.J.; Ryu, C. Y.; Hahn, S. F.; Magonov, S. N. Macro-molecules 2002, 35, 9391.

15. Chang, T. J Polym Sci Part B: Polym Phys 2005,43, 1591.

16. Chang, T. Adv Polym Sci 2003, 163, 1.17. Park, S.; Cho, D.; Ryu, J.; Kwon, K.; Lee, W.;

Chang, T. Macromolecules 2002, 35, 5974.18. Park, S.; Park, I.; Chang, T.; Ryu, C. Y. J Am

Chem Soc 2004, 126, 8906.19. Lee, W.; Cho, D.; Chun, B. O.; Chang, T.; Ree, M.

J Chromatogr A 2001, 910, 51.20. Cho, D.; Noro, A.; Takano, A.; Matsushita, Y.

Macromolecules 2005, 38, 3033.

21. Anderson, B. C.; Andrews, G. D.; Arthur, P., Jr.;Jacobson, H. W.; Melby, L. R.; Playtis, A. J.; Shar-key, W. H. Macromolecules 1981, 14, 1599.

22. Lauterwasser, B. D.; Kramer, E. J. Philos Mag1979, 39, 469.

23. Tanaka, T.; Omoto, M.; Donkai, N.; Inagaki, H. JMacromol Sci Phys 1980, 17, 211.

24. Podesva, J.; Stejskal, J.; Kratochvil, P. Macromo-lecules 1987, 20, 2195.

25. Dai, C.-A.; Kramer, E. J.; Washiyama, J.; Hui, C.-Y. Macromolecules 1996, 29, 7536.

26. Rogovina, L. Z.; Chalykh, A. E.; Valetsky, P. M.;Nekhaenko, E. A.; Genin, Y. V.; Zakharova, N. I.;Levin, E. I.; Dolgoploski, S. B.; Vinogradova, S.V.; Slonimsky, G. I.; Korshak, V. V. Soedin Ser A1979, 21, 393.

27. Hermel, T. J.; Hahn, S. F.; Chaffin, K. A.; Gerber-ich, W. W.; Bates, F. S. Macromolecules 2003, 36,2190.

28. Cohen, Y.; Albalak, R. J.; Dair, B. J.; Capel, M. S.;Thomas, E. L. Macromolecules 2000, 33, 6502.

29. Fetters, L. J.; Lohse, D. J.; Richter, D.; Witten, T.A.; Zirkel, A. Macromolecules 1994, 27, 4639.

30. Fetters et al. (Ref. 29) used the following formulafor Me: Me ¼ (4/5)qRT/GN

0 , where GN0 is the pla-

teau modulus, R is the ideal gas constant, T isthe temperature, and q is the density. Our calcu-lation of Me here used Me ¼ qRT/GN

0 .31. Yang, A. C. M.; Kramer, E. J.; Kuo, C. C.; Phoe-

nix, S. L. Macromolecules 1986, 19, 2010.32. Yang, A. C. M.; Kramer, E. J.; Kuo, C. C.; Phoe-

nix, S. L. Macromolecules 1986, 19, 2020.

3620 KIM ET AL.


Documents

Chemical composition effects on the fracture of polystyrene-block-poly(methyl methacrylate)block copolymers