UNCORRECTED PROOF
ABA triblock copolymers containing polyhedral oligomeric
silsesquioxane pendant groups: synthesis and unique properties
Jeffrey Pyuna,*, Krzysztof Matyjaszewskia, Jian Wub, Gyeong-Man Kimb,Seung B. Chunb,1, Patrick T. Matherb
aDepartment of Chemistry, Center for Macromolecular Engineering, Carnegie Mellon University, 4400 Fifth Avenue, Pittsburgh, PA 15213, USAbPolymer Program, Institute of Materials Science, University of Connecticut, Storrs, CT 06269-3136, USA
Received 4 November 2002; received in revised form 26 December 2002; accepted 9 January 2003
Abstract
The synthesis and characterization of POSS containing ABA triblock copolymers is reported. The use of atom transfer radical
polymerization (ATRP) enabled the preparation of well-defined model copolymers possessing a rubbery poly(n-butyl acrylate)(pBA) middle
segment and glassy poly(3-(3,5,7,9,11,13,15-heptaisobutyl-pentacyclo[9.5.1.13,9.15,15.17,13]-octasiloxane-1-yl)propyl methacrylate(p(MA-
POSS)) outer segments. By tuning the relative composition and degree of polymerization (DP) of the two segments, phase separated
microstructures were formed in thin films of the copolymer. Specifically, dynamic mechanical analysis and transmission electron microscopy
(TEM) observations reveal that for a small molar ratio of p(MA-POSS)/pBA (DP ¼ 6/481/6) no evidence of microphase separation is evident
while a large ratio (10/201/10) reveals strong microphase separation. Surprisingly, the microphase-separated material exhibits a tensile
modulus larger than expected (ca. 2 £ 108 Pa) for a continuous rubber phase for temperatures between a pBA-related Tg and a softening point
for the p(MA-POSS)-rich phase. Transmission electron microscopy (TEM) images with selective staining for POSS revealed the formation
of a morphology consisting of pBA cylinders in a continuous p(MA-POSS) phase. Thermal studies have revealed the existence of two clear
glass transitions in the microphase-separated system with strong physical aging evident for annealing temperatures near the Tg of the higher
Tg phase (p(MA-POSS). The observed aging is reflected in wide-angle X-ray scattering as the strengthening of a low-angle POSS-dominated
scattering peak, suggesting some level of ordering during physical aging. The Tg of the POSS-rich phase observed in the microphase
separated triblock copolymer was nearly 25 8C higher than that of a POSS-homopolymer of the same molecular weight, suggesting a strong
confinement-based enhancement of Tg in this system.
q 2003 Published by Elsevier Science Ltd.
Keywords: POSS-homopolymer; polyhedral oligomeric silsesquioxane; ring-opening metathesis polymerization
1. Introduction
The synthesis of linear organic/inorganic hybrid poly-
mers containing polyhedral oligomeric silsesquioxane
(POSS) groups has recently gained attention as a route to
prepare novel nanocomposite materials [1]. In the pursuit to
understand the effect of POSS inclusions in polymeric
hybrids, the synthesis of well-defined model copolymers of
precise molar mass, composition and architecture is
required [2]. Numerous approaches have been reported in
the preparation of POSS containing copolymers, namely,
condensation polymerization [3–5], ring-opening metath-
esis polymerization (ROMP) [6–8], metallocene-mediated
processes [9] and free radical polymerization [10,11]
techniques. Additionally, recent advances in controlled/
living radical polymerization [12,13] have offered a
versatile tool to prepare model copolymers from a wide
range of monomers (e.g. styrenes, (meth)acrylates),
enabling investigation of structure-property relationships
[14]. Our group demonstrated the ability to introduce
methacrylate functional POSS monomers into polyacrylate
materials for the synthesis of well-defined star diblock and
ABA triblock copolymers using atom transfer radical
polymerization (ATRP) [15–18]. In these block copoly-
mers, POSS moieties are attached to the copolymer
backbone as pendant side chain groups.
Several studies reported the presence of POSS groups
to effect both thermal and rheological properties of
0032-3861/03/$ - see front matter q 2003 Published by Elsevier Science Ltd.
doi:10.1016/S0032-3861(03)00027-2
Polymer xx (0000) 1–12
www.elsevier.com/locate/polymer
1 Present address: Rogers Corporation, Rogers, CT, USA.
* Corresponding author. Present address: IBM, Almaden, CA, USA.
JPOL 7176—23/1/2003—16:50—AWINDOW—62636— MODEL 5 – br,ed
ARTICLE IN PRESS
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
UNCORRECTED PROOF
polystyrene [19], polyurethane [4,20], polynorbornene [6,7]
and polypropylene-based blends and copolymers [9,21].
Limited findings on POSS-methacrylate copolymers have
shown that high molecular weight POSS containing
homopolymers (Mw , 200 kDa, DP , 100) do not reveal
a glass transition below thermal decomposition around
T ¼ 400 8C [11]. However, systematic investigation of
POSS-containing block copolymers based on poly(meth)a-
crylates has not been conducted. In particular, an ABA
triblock copolymer composed of a soft polyacrylate middle
segment and hard POSS based outer segments was of
interest, as phase separation would yield sequestered
domains of POSS groups on nanometer length scales.
Such a system would allow examination of bulk mor-
phology and properties due to POSS segments, but also may
provide insight into the ordering of POSS groups within
phase separated domains.
The effect of nano-confinement on organization within
microphase separated domains of POSS-based copolymers
is a phenomenon gaining increasing attention. While
substantial work has been conducted on copolymers
containing crystalline polymers with POSS segments, very
limited attention has been given to the structure and
morphology in block copolymers composed of amorphous
segments with POSS groups [22]. Of particular interest is
whether phase separated domains of POSS are crystalline,
or glassy in nature. The POSS-rich phase may serve as
physical crosslinks due to phase separation of glassy, or
crystalline domains. There are rare investigations on the
physical aging behavior in ‘pseudo’ network systems [23].
We were prompted to question whether the glassy phase in
our ABA block copolymer would exhibit the same behavior
and properties relative to the analogous POSS containing
homopolymers.
Herein, we report the synthesis and characterization of
ABA triblock copolymers possessing a soft middle poly-
acrylate segment and POSS containing outer blocks. By the
use of ATRP we demonstrate the ability to prepare
microphase separated structures by tuning composition
and molar mass of each polymeric segment. Thermal
analysis of the bulk copolymer using Differential Scanning
Calorimetry (DSC) was conducted to also demonstrate how
the presence of POSS domains affected morphology and
properties of the hybrid material.
2. Experimental
2.1. Materials
n-Butyl acrylate (Acros) was stirred over calcium hydride
overnight and distilled before use. Copper(I) bromide
(Aldrich) and 4,40-(di-5-nonyl)-2,20-bipyridine (dNbpy) were
purified and prepared according to previously reported
procedures [24]. Copper(II) bromide, N;N;N 0;N 00;N 00-penta-
methyldiethylenetriamine (PMDETA), dimethyl-2,7-dibro-
moheptanedioate were purchased from Aldrich and used as
received. 3-(3,5,7,9,11,13,15-heptacyclopentyl-pentacy-
clo[9.5.1.13,9.15,15.17,13]octasiloxane-1-yl)propyl methacry-
late (cyclopentyl MA-POSS) and 3-(3,5,7,9,11,13,15-
heptaisobutyl-pentacyclo[9.5.1.13,9.15,15.17,13]octasiloxane-
1-yl)propyl methacrylate (isobutyl MA-POSS) were
purchased from Hybrid Plastics and used as received.
2.2. Characterization
(i) Size exclusion chromatography (SEC). Was performed
in tetrahydrofuran using a Waters 510 pump, 3 Styragel
columns (Polymer Standards Service, pore sizes 105 A,
103 A, 102 A) and a Waters 2410 refractive index
detector. Calculations of apparent molar mass were
determined using the PSS software from a calibration
based on linear polystyrene standards (from PSS). 1H
NMR analysis was done on a 300 MHz Bruker
spectrometer using the Tecmag software.
(ii) Dynamic Mechanical Analysis. A TA Instruments
2980 DMA was run in tensile mode at an oscillation
frequency of 1 Hz with a static force of 0.010 N, an
oscillation amplitude of 5.0 mm and an automatic
tension of 125%. Samples were heated from T ¼ 50 8C
(below Tg for pBA) to T ¼ 100 8C (above p(MA-
POSS) softening) with a heating rate of 4 8C/min. The
sample geometry was a thin film in tension.
(iii) Thermal Analysis. The thermal properties of both
POSS homopolymer and triblock copolymers were
investigated using DSC with variation in thermal
history so as to age the samples to varying degrees.
For this purpose, a TA Instruments DSC 2920 was
employed with samples (5–15 mg) prepared from
powders and sealed in aluminum pans. Heating
experiments were conducted with a nitrogen atmos-
phere and using a heating rate of 20 8C/min. For
isolated cases a slower heating rate of 10 8C/min was
employed with negligible differences observed. As our
annealing periods extended to several days, annealing
was performed on a custom-built hot-stage with
temperature control to ^0.2 8C.
(iv) Wide-Angle X-ray Scattering. In order to assess
microstructure and aging-induced microstructural
changes in the POSS-triblock polymer, we have
used wide-angle X-ray scattering (WAXS). For this
purpose, we have employed a Bruker D5005 X-ray
diffractometer with angular range 5 , 2u , 408 and
using Cu Ka radiation with wavelength,
l ¼ 1.5418 A. Samples were prepared as fine
powders (after aging treatment) prior to WAXS
data collection.
(v) Microscopy. Investigations of morphology were per-
formed using a Philips EM300 transmission electron
microscope operated at 80 kV. Samples were cast from
chloroform and the ultrathin sections for TEM with a
thickness of about 50 nm were cryo-microtomed at
JPOL 7176—23/1/2003—16:50—AWINDOW—62636— MODEL 5 – br,ed
J. Pyun et al. / Polymer xx (0000) 1–122
ARTICLE IN PRESS
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
UNCORRECTED PROOF
280 8C. In order to increase the phase contrast the
ultrathin sections were chemically selective vapor
stained with RuO4. Specifically, the ultra-thin sections
of our triblock copolymer samples were transferred to
200 mesh copper grids and the sections placed in a
glass jar containing 0.5% RuO4 aqueous solution. The
sections were exposed to RuO4 vapor for 1–5 min,
selectively stainining the p(POSS-MA) block, believed
to be easily stained owing to the high concentration of
cyclopentyl groups. Selective staining of the POSS
phase was determined by applying the same process to
an immiscible blend of MA-POSS homopolymer and
pMMA, with minor p(MA-POSS) content, and observ-
ing staining of the minor component with TEM. We
assume that selectivity observed in this blend is the
same for p(MA-POSS) and pBA, given compositional
similarity.
(vi) Melt Rheology. Investigations of linear viscoelastic
behavior for a triblock copolymer showing micro-
phase-separation was conducted using rotational rheo-
metry (Rheometric Scientific ARES) for temperatures
above the second softening (observed using DMA) to
better understand the nature of this peak and the fluid
properties. Samples were prepared by compression
molding at T ¼ 100 8C with care taken to remove
voids. The parallel plate geometry was adopted and
frequency sweeps from v ¼ 0:1 rad/s to v ¼ 100 rad/s
were conducted for temperatures spanning
80 8C , T , 170 8C. Time-temperature superposition
(TTS) was found to work moderately well over this
temperature range without the use of vertical data
shifting.
2.3. Synthesis of difunctional poly(n-butyl acrylate)
macroinitiator (Mn61,700 g/mol)
To a 25 ml round bottom flask with magnetic stir bar was
added Cu(I)Br (25 mg, 0.178 mmol), Cu(II)Br2 (2.0 mg,
0.009 mmol) and then the flask was fitted. The reaction flask
was then evacuated (1–5 mm Hg) and backfilled with
nitrogen for three cycles. n-Butyl acrylate (20 ml,
139 mmol) was bubbled with nitrogen for 1 h before use
and then added via syringe to the reaction vessel, followed
by PMDETA (39 ml, 0. 187 mmol). To a separate 4 ml vial
with magnetic stir bar was added dimethyl-2,6-dibromo-
heptanedioate (60 mg, 0.173 mmol). The vial was then fitted
with a rubber septum and evacuated/backfilled with
nitrogen (3 cycles). Nitrogen purged n-butyl acrylate
(1 ml, 8.7 mmol) was then added via syringe to the vial to
dissolve the initiator. The initiator solution was then
transferred to the 25 ml round bottom flask containing the
catalyst solution and the reaction vessel was placed in a
70 8C oil bath. The reaction was allowed to proceed for 16
hrs and 16 min. 1H NMR analysis of the polymerization
mixture revealed that a monomer conversion of 57% was
obtained. The polymer solution was diluted in THF and
filtered through neutral alumina to remove the catalyst. The
polymer solution was then concentrated via distillation of
THF in vacuo and precipitated into a ten-fold excess of
methanol/water (4:1 by volume). SEC against linear pS
standards indicated a molar mass of Mn ¼ 61,700;
Mw/Mn ¼ 1.31.
2.4. Synthesis of p(MA-POSS)-b-pBA-b-p(MA-POSS) from
cyclopentyl functional POSS methacrylate monomer
To a 4 ml vial with magnetic stir bar was added 1 g of
difunctional pBA macroinitiator (Mn ¼ 61,700), cyclopen-
tyl MA-POSS (0.32 g, 0.3 mmol) and Cu(I)Cl (2.96 mg,
0.03 mmol). The vial was fitted with a rubber septum and
deoxygenated by evacuation (1–5 mm Hg) and backfilling
with nitrogen (3 cycles). PMDETA (6.26 ml, 0.03 mmol)
was then added via syringe and the reaction vessel was place
in an oil bath set at 60 8C. Polymerization allowed to
proceed for 14 h and 32 min and 1H NMR analysis of the
reaction mixture indicated that a monomer conversion of
90% was achieved. The polymer was then diluted in THF
and passed through neutral alumina to remove catalyst.
Following concentration of the polymer solution by in
vacuo removal of THF, precipitation into a 10-fold excess of
methanol/water (4:1 by volume) was conducted. Using this
procedure, residual cyclopentyl MA-POSS could not be
separated from the p(MA-POSS)-b-pBA-b-p(MA-POSS)
triblock copolymer. Trituration of the crude product in
20 ml of nonane overnight at room temperature quantitat-
ively removed MA-POSS monomer as confirmed by SEC.
2.5. Synthesis of poly(3-(3,5,7,9,11,13,15-heptaisobutyl-
pentacyclo[9.5.1.13,9.15,15.17,13]-octasiloxane-1-yl)propyl
methacrylate (isobutyl MA-POSS) homopolymer
Isobutyl MA-POSS (1 g, 1.06 mmol) and AIBN
(1.74 mg, 0.0106 mmol) were weighed into a 5 ml round
bottom flask with magnetic stir bar. The flask was then fitted
with a septum and was evacuated (1–5 mm Hg) and
backfilled with nitrogen (3-cycles). Nitrogen sparged
(30 min) toluene (2 ml) was then added to the flask via
syringe, and the flask was put into a 60 8C oil bath. Polymers
were recovered by precipitation into methanol. The
presence of residual monomer required fractionation of
the higher molar mass homopolymer. Fractionation was
conducted by dissolving 1 g of the p(MA-POSS)/MA-POSS
crude mixture in 20 ml of THF, followed by the gradual
addition of methanol. The first fraction was collected after
the addition of 5 g of methanol. SEC analysis of the
fractionated polymer revealed a molecular weight of
Mn ¼ 12,000 g/mol and a polydispersity of Mw/Mn ¼ 1.8.
2.6. Synthesis of difunctional poly(n-butyl acrylate)
macroinitiator (Mn ¼ 25,800 g/mol)
To a 100 ml round bottom flask with magnetic stir bar
JPOL 7176—23/1/2003—16:50—AWINDOW—62636— MODEL 5 – br,ed
J. Pyun et al. / Polymer xx (0000) 1–12 3
ARTICLE IN PRESS
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
UNCORRECTED PROOF
was added Cu(I)Br (50 mg, 0.35 mmol) and 1,4-dimethoxy-
benzene (1 g) and then the flask was fitted with a rubber
septum. The reaction flask was then evacuated (1–5 mm
Hg) and backfilled with nitrogen for three cycles. n-Butyl
acrylate (50 ml, 349 mmol) was bubbled with nitrogen for
1 h before use and then added via syringe to the reaction
vessel, followed by PMDETA (60 mg, 0.35 mmol) and
dimethyl-2,6-dibromoheptanedioate (603 mg, 1.745 mmol).
The reaction vessel was placed in an 80 8C oil bath. The
reaction was allowed to proceed for 3 hrs and 39 min. 1H
NMR analysis of the polymerization mixture revealed that a
monomer conversion of 91% was obtained. The polymer
solution was diluted in THF and filtered through neutral
alumina to remove the catalyst. The polymer solution was
then concentrated via distillation of THF under vacuum and
precipitated into a ten-fold excess of methanol/water (4:1 by
volume). SEC against linear polystyrene standards indicated
a molar mass of Mn ¼ 25,800; Mw/Mn ¼ 1.20.
2.7. Synthesis of p(MA-POSS)-b-pBA-b-p(MA-POSS) from
isobutyl functional POSS methacrylate monomer
To a 10 ml Schlenk flask with magnetic stir bar was
added isobutyl MA-POSS (1.27 g, 1.34 mmol) and Cu(I)Cl
(1.4 mg, 0.014 mmol). The flask was then fitted with a
rubber septum and deoxygenated by evacuation (1–5 mm
Hg) and backfilling with nitrogen (3 cycles). To a separate
vial was added difunctional pBA macroinitiator
(Mn ¼ 25,800 g/mol) (1 g, 0.03 mmol Br) and then a rubber
septum was fitted over the vial. Deoxygenation of the vial
was performed by evacuation (1–5 mm Hg) and backfilling
with nitrogen (3 cycles). o-Xylene (2.5 ml) was bubbled
with nitrogen for 1 hr before use and then added to the vial
via syringe. The pBA macroinitiator solution was then
transferred to the 10 ml Schlenk flask via syringe. PMDETA
(3.6 ml, 0.014 mmol) was added to reaction vessel via
microliter syringe and the flask was placed in an oil bath set
to 60 8C for 22 h and 54 min. Monomer conversion was
determined via 1H NMR and proceeded to 90%. The
product was then diluted in 5 ml of THF and precipitated
into 100 ml of methanol. To remove residual isobutyl MA-
POSS monomer, ultrafiltration was employed using the
Millipore Solvent Resistant Stirred Cell (XFUF 07601). The
crude triblock copolymer of p(MA-POSS)-b-p(BA)-p(MA-
POSS) was dissolved in toluene (120 ml) and methanol
(60 ml). Ultrafiltration at 15–20 psi of nitrogen using RC
filters (MWCO 100,000, Millipore, PLGC07610) was done
for 60 min until approximately 50 ml of the solution
remained. The solution from the cell was decanted and
allowed to dry first in air, then under vacuum. After drying,
750 mg of the triblock copolymer was recovered. SEC
against linear pS standards was used to determine molar
mass (Mn ¼ 43,010 g/mol; Mw/Mn ¼ 1.20) of the triblock
copolymer and confirmed quantitative removal of the POSS
monomer.
3. Results and discussion
3.1. Synthesis of ABA triblock copolymers using ATRP
The synthesis of ABA triblock copolymers possessing a
central segment of poly(n-butyl acrylate)(pBA) and outer
blocks of poly(methacryate-POSS)(p(MA-POSS)) was con-
ducted using a two-step ATRP strategy [16]. Compositions
of approximately 10 – 20 wt% of p(MA-POSS) were
targeted for the design of a spherical morphology of phase
separated p(MA-POSS) domains in a matrix of pBA. In the
first stage of the synthesis, the ATRP of n-butyl acrylate
(BA) was conducted using dimethyl-2,6-dibromoheptane-
dioate as the initiator for the preparation of a difunctional
pBA macroinitiator (Scheme 1). To retain high chain end
functionality, the polymerization was stopped at 57%
monomer conversion (1H NMR) while targeting a high
degree of polymerization ([M]o/[I]o ¼ 800). SEC of the
macroinitiator relative to linear pS standards was used to
calculate molar mass (Mn ¼ 61,700 g/mol; Mw/Mn ¼ 1.31).
Comparison of theoretical molar mass values based on
conversion and the ratio of monomer to initiator (i.e.
Mn theoretical ¼ conversion £ ð½M�o=½I�oÞ £ MWBA ¼ 58; 400
g=mol) versus those from SEC ðMn SEC ¼ 61; 700 g=molÞ
indicated that an initiation efficiency in the polymerization
was 94%.
Chain extension of the pBA macroinitiator was then
conducted by the ATRP of 3-(3,5,7,9,11,13,15-heptacyclo-
pentyl-pentacyclo[9.5.1.13,9.15,15.17,13]octasiloxane-1-
yl)propyl methacrylate (cyclopentyl MA-POSS). In the
ATRP reaction, a monomer conversion of 92% was
achieved, as determined from 1H NMR. SEC of the triblock
copolymer against linear pS standards confirmed a small
increase in molar mass (Mn ¼ 64,010; Mw/Mn ¼ 1.39) after
the ATRP of cyclopentyl MA-POSS. Composition of the
triblock copolymer and DPn of each segment was
determined via 1H NMR in conjunction with corrected Mn
SEC values of the pBA macroinitiator (2.5 mol%; 16 wt% of
p(MA-POSS)). The overall molar composition of the
triblock copolymer was determined to be p(MA-POSS)6-
b-pBA481-b-p(MA-POSS)6.
Initial morphological investigations of thin films pre-
pared from the p(MA-POSS)6-b-pBA481-b-p(MA-POSS)6
triblock copolymer was conducted using small angle X-ray
scattering (SAXS) and (TEM). Both techniques confirmed
that morphology of triblock copolymer thin films were
featureless, indicating that phase separation was not induced
at this composition and molar mass. Efforts to prepare
phase-separated structures by increasing the DPn of the
p(MA-POSS) were not successful, as limiting degrees of
polymerization were observed in the ATRP of MA-POSS
monomers (DPn , 15) [16]. This observation is consistent
with similar reports of limiting DP in the ROMP of dendritic
macromonomers, presumably due to inaccessibility of the
ruthenium complexed chain-ends shielded by bulky
dendron side chain groups [25]. Thus, in the ATRP of
JPOL 7176—23/1/2003—16:50—AWINDOW—62636— MODEL 5 – br,ed
J. Pyun et al. / Polymer xx (0000) 1–124
ARTICLE IN PRESS
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
UNCORRECTED PROOFMA-POSS monomers, bromine-end groups from growing
p(MA-POSS) chains may also be inaccessible to copper(I)
complexes after a certain DP is reached in the
polymerization.
An alternative approach to preparing phase-separated
microstructures was devised by preparing a difunctional
pBA macroinitiator of lower molar mass. While the overall
DPn of the block copolymer was reduced, increasing the
relative composition (i.e. volume fraction, f a) of pBA to
p(MA-POSS) segments was anticipitated to yield phase-
separated morphologies assuming large values for the
interaction parameter (x) [26]. Additionally, the isobutyl
MA-POSS monomer was chosen in this case over the
cyclopentyl MA-POSS due to observation of a glass
transition in isobutyl p(MA-POSS) homopolymer, as will
be discussed in later sections.
The synthetic route to prepare phase separated materials
was similar to that used for the higher molar mass POSS
triblock, except a lower monomer to initiator ratio ([M]o/[I])
was employed in the ATRP of BA for the synthesis of the
difunctional macroinitiator. The polymerization of BA
reached a conversion of 90% and SEC relative to pS
standards confirmed the synthesis of lower molar mass pBA
(Mn ¼ 25,800; Mw/Mn ¼ 1.20). A high initiation efficiency
(.90%) was also observed in the polymerization as for the
higher molar mass pBA macroinitiator. Chain extension of
the macroinitiator with 3-(3,5,7,9,11,13,15-heptaisobutyl-
pentacyclo-[9.5.1.13,9.15,15.17,13]octasiloxane-1-yl)propyl
methacrylate (isobutyl MA-POSS) was then conducted and
proceeded to high conversion (92%) as measured using 1H
NMR. Monomer conversion was determined by monitoring
consumption of vinyl protons (d ¼ 6.10, 5.50 ppm) from
isobutyl MA-POSS relative to resonances from pBA
macroinitiator protons.1H NMR of the p(MA-POSS)-b-pBA-b-p(MA-POSS)
triblock copolymer purified by ultrafiltration indicated the
presence of protons from both n-butyl and POSS side chain
groups. Resonances from the poly(meth)acrylate backbone
(d ¼ 0.7–2 ppm) were poorly resolved due to the abun-
dance of protons from side chain groups, with the exception
of methine protons (d ¼ 2.35 ppm, 6, Fig. 1) from the pBA
segment. Resonances observed at d ¼ 0.60 ppm (1 and 4,
Fig. 1) were clearly assigned to methylene protons from
p(MA-POSS) segments. Methyl protons (d ¼ 1:0 ppm, 2,
Fig. 1) and methine protons (d ¼ 1.95 ppm, 2, Fig. 1) from
isobutyl groups in p(MA-POSS) were distinguishable in
addition to methyl protons (d ¼ 1.0 ppm, 10, Fig. 1) and
methylene groups from n-butyl groups in the pBA
macroinitiator (d ¼ 1.5 and 1.8 ppm, 9 and 10 Fig. 1). At
higher chemical shift, methylene protons from both pBA
(d ¼ 4.0 ppm, 7, Fig. 1) and p(MA-POSS) (d ¼ 3.8 ppm, 5,
Fig. 1) were observed indicating successful chain extension
had occurred. Calculations of molar composition of each
component was conducted by comparison of integration
from p(MA-POSS) methylene protons (d ¼ 0.60 ppm, 1 and
4, Fig. 1) and pBA methine protons (d ¼ 2.35 ppm, 6, Fig.
1). Overall, the composition of p(MA-POSS) from 1H NMR
was determined to be 9.7 mol%, corresponding to 44 wt%.
The DPn was also calculated, beginning from Mn SEC
values of the pBA macroinitiator (Mn ¼ 25,800 g/mol)
yielding molar ratios, of p(MA-POSS)10-b-pBA201-b-
p(MA-POSS)10 for the final triblock copolymer. This
corresponds to a SEC-determined composition of
9.1 mol% and 42.4 wt% of p(MA-POSS). Thus, both
estimations of the triblock copolymer composition (1H
NMR and SEC) yield a substantial POSS weight fraction
that we expected to strongly modify morphological and
rheological properties relative to the lower POSS-content
triblock with 16 wt% p(MA-POSS).
SEC of the triblock copolymer against linear pS
standards confirmed the incorporation of p(MA-POSS) as
a small but clear increase in molar mass (Mn ¼ 43,010;
Scheme 1. Synthetic methodology for the preparation of ABA triblocks containing a poly(n-butyl acrylate) middle segments and outer segments of p(MA-
POSS). In the first step, difunctional pBA macroinitiator is prepared by the ATRP of BA from a dimethyl 2,6-dibromoheptanedioate initiator. Subsequent chain
extension of the pBA macroinitiator with MA-POSS yielded the ABA triblock copolymer.
JPOL 7176—23/1/2003—16:50—AWINDOW—62636— MODEL 5 – br,ed
J. Pyun et al. / Polymer xx (0000) 1–12 5
ARTICLE IN PRESS
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
UNCORRECTED PROOFMw/Mn ¼ 1.20) relative to the macroinitiator was obtained
(Fig. 2). Importantly, no change in polydispersity was
observed for ATRP chain extension of the pBA macro-
initiator with MA-POSS.
3.2. DMA observation of melt-pressed triblocks of varying
PBA molecular weight
To begin our characterization comparison of the two
triblocks, we conducted DMA temperature sweeps on
tensile specimens, the results being shown in Fig. 3. Such
measurements are sensitive to changes in thermal tran-
sitions, observed through loss tangent peaks, and are
connected to morphology differences through storage
modulus magnitude. Comparison of the DMA spectra
between the higher molar mass p(MA-POSS)6-b-pBA481-
b-p(MA-POSS)6 (trace (i)) and the p(MA-POSS)10-b-
pBA201-b-p(MA-POSS)10 (trace (ii)) copolymers also
provided greater insight into the organization of p(MA-
POSS) segments in the microphase separated system. For
the homogeneous p(MA-POSS)6b-pBA481-b-p(MA-POSS)6
system, a plateau tensile modulus above the Tg of pBA of
Fig. 1. 1H NMR spectrum of p(MA-POSS)10-b-pBA201-b-p(POSS-MA)10 with peak assignments as shown.
Fig. 2. Representative size exclusion chromatogram (SEC) of pBA
macromonomer (solid line) and p(MA-POSS)10-b-pBA201-b-p(POSS-
MA)10 (dashed line). Molar mass scale is computed from elution volume
using polystyrene calibration standards and solution refractive index was
used as the detection scheme.
Fig. 3. Dynamic Mechanical Analysis (DMA) comparing POSS-triblocks
of varying poly(butyl acrylate) central block molecular weight: (i) p(MA-
POSS)6-b-pBA481-b-p(MA-POSS)6 and (ii) p(MA-POSS)10-b-pBA201-b-
p(POSS-MA)10. Tensile films were prepared be solvent casting and
temperature sweeps conducted at a heating rate of 4 8C/min while applying
oscillatory strain of approximate magnitude 0.1% and with a frequency of
1 Hz.
JPOL 7176—23/1/2003—16:50—AWINDOW—62636— MODEL 5 – br,ed
J. Pyun et al. / Polymer xx (0000) 1–126
ARTICLE IN PRESS
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
UNCORRECTED PROOF
approximately 0.4 MPa was observed. Taking the glass
transition temperature to be the onset of tensile modulus
decrease (for comparison with DSC) we measure a value of
Tg ¼ 248 8C for the high molecular weight sample (trace
(i)) and Tg ¼ 242 8C for the lower molecular weight (trace
(ii)). We note that the entanglement molecular weight for
pure pBA has been reported [27] to be 28,000 g/mol
(substantially larger than the 8,800 value for pMA [28,29]),
from which we have estimated the plateau modulus in shear,
GoN; to 0.1 MPa or 0.3 MPa in tension. By comparing our
observed value with that estimated from Me measurements
of others [27], we reason that this material behaves as an
ordinary entangled poly(n-butyl acrylate).
For the phase separated p(MA-POSS)10-b-pBA201-b-
p(MA-POSS)10 sample, however, a significantly higher
plateau modulus was observed (200 MPa) in the same
temperature range as for the homogeneous system. The
large difference in the plateau moduli of the two copolymer
systems cannot be solely attributed to an increase in the
physical crosslink density due to microphase separation of
p(MA-POSS) domains in a matrix of pBA. Instead, the
enhanced value of the plateau modulus suggests the
formation of a microphase separated structure (to be
clarified by TEM) composed, surprisingly, of a continuous
phase of solid p(MA-POSS) -glassy or semicrystalline - and
dispersed domains of pBA. The inverse morphology would
be expected to yield a much lower tensile modulus
,1 MPa. This assessment is further supported by the larger
magnitude of the loss tangent transition at 70 8C relative to
the value at 230 8C. Assignments of these transitions
correspond to the Tg of the pBA phase at 230 8C and
softening of the p(MA-POSS) phase at 50 8C. Furthermore,
the effect of a larger weight fraction of POSS in the p(MA-
POSS)10-b-pBA201-b-p(MA-POSS)10 copolymer was also
seen in the DMA by doubling of the cryogenic modulus
(below Tg of pBA) relative to the p(MA-POSS)6-b-pBA481-
b-p(MA-POSS)6 sample, which is consistent with previous
reports for random copolymer systems containing POSS [6].
Finally, no significant difference in the pBA-rich Tg is
observed for the two block copolymers, indicating a
negligible influence of POSS on pBA softening in either
the single or two phase systems.
As we will show below, these results are consistent with
TEM analysis and limited SAXS observations (data not
shown) for the two triblock copolymer systems. Collec-
tively, these characterization data reveal that microphase
separated structures can be formed by optimizing the length
of central pBA block provided the DP of p(MA-POSS)
block is constant.
3.3. Morphology of POSS triblock copolymer thin films
Morphological investigations of p(MA-POSS)6-b-
pBA481-b-p(MA-POSS)6 triblock copolymer thin films
prepared with pBA macroinitiator of higher molar mass
(Mn SEC ¼ 64,010; Mw/Mn ¼ 1.39) by using SAXS and
TEM indicated that no microphase separation was induced
during sample preparation; i.e. the resulting morphology
and SAXS scattering patterns were completely featureless.
However, the morphology of p(MA-POSS)10-b-pBA201-b-
p(MA-POSS)10 triblock copolymer thin films prepared with
a difunctional pBA macroinitiator of lower molar mass (Mn
SEC ¼ 25,800 g/mol; Mw/Mn ¼ 1.20) show remarkably
well-defined microphase separated structures. In Fig. 4,
we show typical microphase separated block copolymer
structures imaged by TEM by employing ultrathin sections
of thickness ,50 nm that were stained with RuO4 vapor. In
a relatively low magnification TEM image (Fig. 4a), well-
defined white cylinders are clearly discernable ordered both
in and out of the sample plane. In our previous TEM studies
on POSS incorporated thermosets, we found that the POSS
moiety can be selectively stained with RuO4, although the
chemical details of this staining have not been revealed [30].
On this basis, we are confident that the continuous dark
phase consists of the p(MA-POSS) block, whereas the
bright cylinders consist of pBA. The micrographs of Fig.
4(b) and (c) show higher magnification imaging of local
areas in Fig. 4(a). The bright domains originating from pBA
are locally well ordered in dark continuous p(MA-POSS)
matrix phase, but macroscopically disordered. The fast
Fourier transform (FFT) power spectrum was computed
Fig. 4. Transmission electron microscopy (TEM) of thin sections of POSS-
triblocks prepared with cryomicrotomy at T ¼ 280 8C to yield samples of
thickness ,50 nm. The microtomed sections were chemically treated with
RuO4, an agent selective for POSS. (a) Low magnification micrograph
showing overall morphology, (b)–(c) Higher magnification micrographs
revealing cylindrical morphology, (d) Fourier transform of selected area
from micrograph (a) revealing symmetry consistent with local hexagonal
packing of the cylinders.
JPOL 7176—23/1/2003—16:50—AWINDOW—62636— MODEL 5 – br,ed
J. Pyun et al. / Polymer xx (0000) 1–12 7
ARTICLE IN PRESS
673
674
675
676
677
678
679
680
681
682
683
684
685
686
687
688
689
690
691
692
693
694
695
696
697
698
699
700
701
702
703
704
705
706
707
708
709
710
711
712
713
714
715
716
717
718
719
720
721
722
723
724
725
726
727
728
729
730
731
732
733
734
735
736
737
738
739
740
741
742
743
744
745
746
747
748
749
750
751
752
753
754
755
756
757
758
759
760
761
762
763
764
765
766
767
768
769
770
771
772
773
774
775
776
777
778
779
780
781
782
783
784
UNCORRECTED PROOF
(Fig. 4(d)) for a portion of Fig. 4(a) showing cylinders
aligned normal to the sample plane, revealing six strong
spots due to a three-fold symmetrical arrangement of pBA
domains within the p(MA-POSS) matrix phase. Thus it
appears that pBA cylinders are dispersed in a p(MA-POSS)
matrix despite the latter being a slightly minor component
on a weight fraction basis, thus favoring lamellae formation.
In particular, 1H NMR characterization revealed that the
overall fraction p(MA-POSS) within the triblock was
9.7 mol%, but 44 wt%. This surprising observation is
perhaps attributed to unique excluded volume effects of
p(MA-POSS) phase in this type of ABA block copolymer.
3.4. Thermal analysis of POSS homopolymers and triblock
copolymers
Previous studies in the DSC of cyclopentyl- and
cyclohexyl-substituted POSS homopolymers reported
onset of decomposition occurring before observation of
the glass transition (Tg) [10,11]. This phenomenon was
ascribed to retardation of segmental motion of polymer
chains due to presence of bulky side chain groups at each
repeat unit of the backbone [19]. In addition, a previous
study [22] on diblock copolymers of polynorbornene and
poly(norbornene-POSS) showed that increasing the length
of the PN-POSS block had no effect on the polynorbornene-
rich phase Tg, with Tg , 55 8C, while the morphologies
traverse the usual sequence of spheres-cylinders-lamellae.
However, a Tg was not detected for the POSS-PN phase for
temperature below decomposition. In the present study, we
have found that for the single-phase system, p(MA-POSS)6-
b-pBA481-b-p(MA-POSS)6, a single Tg , 2 50 8C is
observed (data not shown), essentially unmodified from
pure pBA homopolymer. Above this temperature, the
p(MA-POSS)6-b-pBA481-b-p(MA-POSS)6 copolymer
behaves as an entangled polyacrylate (Fig. 3). Thus, in the
single phase case, we observe simple glass-rubber transition
behavior. In contrast, for the p(MA-POSS)10-b-pBA201-b-
p(MA-POSS)10 triblock copolymer, we observed remark-
ably different phase behavior that is reflected in the DMA
response (Fig. 3) and in DSC results we now present.
By comparison, the thermal transition behavior of p(MA-
POSS)10-b-pBA201-p(MA-POSS)10 is quite sensitive to
thermal history, but generally shows two strong transitions.
As shown in Fig. 5, trace (i), near T ¼ 248 8C (onset), we
observe a strong Tg signal indicated by a dramatic step in
heat capacity at that temperature. This temperature is to be
compared with the Tg for pure pBA of T ¼ 254 8C [31].
Less obvious is a second transition with an onset of
T ¼ 65 8C (DH ¼ 0.71 J/g) that appears to be first order
melting during the first heating of the as-synthesized (and
precipitated) powder. However, we were surprised to find a
melting transition for a p(MA-POSS) rich phase at such a
low temperature, or even at all, based on prior reports on
POSS containing homopolymers showing the absence of
crystallization. Therefore, we sought to determine whether
or not this observation was a true melting point, a first
heating artifact, or the manifestation of significant physical
aging present in the POSS phase. If the latent heat feature of
Fig. 5(i) could be enhanced via thermal treatment at
T , 65 8C or removed by quenching to leave a strictly
second-order transition, then physical aging would be
implicated. Thus, following the first heating scan, the
triblock copolymer sample was cooled to T ¼ 45 8C and
annealed at that temperature for 40 hours under nitrogen and
then re-scanned from T ¼ 2100 8C to 100 8C as shown in
Fig. 5(ii). We observed that this thermal history enhanced
the latent heat endotherm while maintaining the transition
temperature beginning near 65 8C. However, the DSC trace
of this annealed sample has further revealed a significant
heat capacity offset above and below the thermal transition,
an aspect discussed further below.2 In light of this
annealing-induced enhancement of the latent endotherm at
Tg, we consider the endotherm itself as a reflection of
enthalpy relaxation that occurred during significant physical
aging at T ¼ 45 8C.
Fig. 5. Differential Scanning Calorimetry (DSC) characterization of
triblock copolymer p(MA-POSS)10-b-pBA201-b-p(MA-POSS)10 using a
heating rate of 20 8C/min for the following thermal history: (i) The first scan
(after cooling to T ¼ 2100 8C); (ii) Heating scan following (i) and direct
cooling to T ¼ 45 8C for 40 hours of annealing and subsequent cooling at
20 8C/min to T ¼ 2100 8C; (iii) heating scan after (ii); (iv) Heating scan
following (iii) and direct cooling to T ¼ 45 8C for 7 days of annealing and
subsequent cooling at 20 8C/min to T ¼ 2100 8C for reheating.
2 We note that the slight fluctuation in the DSC thermogram at T ¼ 0 8C
was an artifact of our DSC for those runs.
JPOL 7176—23/1/2003—16:50—AWINDOW—62636— MODEL 5 – br,ed
J. Pyun et al. / Polymer xx (0000) 1–128
ARTICLE IN PRESS
785
786
787
788
789
790
791
792
793
794
795
796
797
798
799
800
801
802
803
804
805
806
807
808
809
810
811
812
813
814
815
816
817
818
819
820
821
822
823
824
825
826
827
828
829
830
831
832
833
834
835
836
837
838
839
840
841
842
843
844
845
846
847
848
849
850
851
852
853
854
855
856
857
858
859
860
861
862
863
864
865
866
867
868
869
870
871
872
873
874
875
876
877
878
879
880
881
882
883
884
885
886
887
888
889
890
891
892
893
894
895
896
UNCORRECTED PROOF
Following this heating run, the sample was again cooled
to T ¼ 2100 8C, this time without intermediate aging. In
this case, trace (iii), two clear Tg transitions are observed
with the following onset temperatures: TpBAg ¼ 252 8C and
TpMA-POSSg ¼ 75 8C: T
pBAg ; associated with the softening of
the pBA-rich phase is about 3–4 8C lower than the value
measured in trace (i) (virgin sample) and features a larger
step change in heat capacity, although we have not
investigated this change quantitatively. More importantly,
no latent heat endotherm is observed at TpMA-POSSg in this
case, revealing the lack of enthalpy relaxation during prior
cooling to T ¼ 2100 8C. Finally, the triblock copolymer
was cooled to T ¼ 45 8C for long duration annealing (7
days) to see if the physical aging associated with trace 5 (ii)
could be reproduced. The resulting heating scan (trace iv)
revealed pBA glass transition as before and a latent heat
endotherm at the pMA-POSS Tg with an onset at T ¼ 65 8C
and a peak at T ¼ 82.3 8C (DH ¼ 1:64 J/g), but with an
obvious step in heat capacity across the transition. We note
that DMA experiments (Fig. 3) were performed on unaged
specimens so that comparison between Fig. 3, trace (ii)
should be made with Fig. 5, trace (i). We further note that
the DMA data show a slightly lower temperature for the
second transition.
To our knowledge, the phenomena observed in Fig. 5 are
thus far unique for POSS-based systems in revealing a
clearly detectable glass transition for a POSS homopolymer
phase, albeit within a microphase morphology. Thus, we
were prompted to examine the thermal response of a p(MA-
POSS) homopolymer of similar molecular weight to that of
the block contained in the p(MA-POSS)10-b-pBA201-b-
p(MA-POSS)10 triblock. Does such a polymer reveal an
accessible glass transition in contrast to p(MA-POSS)
homopolymers with cyclopentyl or cyclohexyl [11] corner
groups? The DSC results for such a p(MA-POSS) homo-
polymer with Mn ¼ 12; 000 g/mol are shown in Fig. 6, this
time focusing on a single transition observed near
T ¼ 60 8C. Specifically, the first scan of the precipitated
polymer sample, trace a (i), reveals a strong endotherm at
T ¼ 63:6 8C with DH ¼ 1:76 J/g. A second scan taken
immediately after cooling to T ¼ 0 8C (trace a (ii)) shows
reduction of this complex transition to a simple glass
transition with a low onset Tg ¼ 40:5 8C. We immediately
see that Tg of the POSS homopolymer is significantly lower
(DTg , 25 8C) than that of the POSS-rich phase in the
p(MA-POSS)10-b-pBA201-b-p(MA-POSS)10 triblock copo-
lymer. Following this thermal history, enthalpy relaxation
was attempted by annealing the sample at T ¼ 45 8C (like
for the triblocks in Fig. 5), for four days, the resulting
heating scan being shown as trace b (i) in Fig. 6. Clearly, no
latent heat endotherm is observed to indicate enthalpy
relaxation, but instead a simple Tg is observed at 47 8C. A
second heat with no intervening heat treatment (trace b (ii))
shows no alteration of the thermal behavior. Annealing at a
temperature closer to Tg, however, does result in the
appearance of a slight endotherm at Tg, as shown in trace c
(i) of Fig. 6. Here, annealing was conducted at T ¼ 55 8C for
seven days, resulting in a peak after Tg (onset Tg ¼ 46.5 8C)
at T ¼ 58 8C. This feature is largely erased on cooling and
reheating without annealing (trace c (ii)), but not entirely.
By comparison of Figs. 5 and 6, we make the following
salient observations: (i) the Tg for p(MA-POSS) homo-
polymer is 20–25 8C lower than that observed in a triblock
copolymer bearing the same MA-POSS repeating unit
(isobutyl corner groups), (ii) in both cases, enthalpy
relaxation is indicated for thermal annealing at T , Tg;
and (iii) enthalpy relaxation for p(MA-POSS) homopolymer
is rapid only quite close to Tg in contrast to the triblock
copolymer, where relaxation was indicated for annealing
40 8C below Tg. While we do not have a definitive
explanation for this large Tg difference in aging behavior,
recent studies by Zhu et al. [32] revealed an analogous
sensitivity of PEO crystal stability on the matrix Tg of PEO/
PS cylindrical diblocks. Specifically, it was observed on the
basis of DSC, WAXS, and SAXS analyses that PEO
crystallization was enhanced for ‘soft confinement’; i.e.
when the PS matrix was plasticized to a Tg , Tcryst:; relative
Fig. 6. Differential Scanning Calorimetry (DSC) characterization of POSS
homopolymer, p(MA-POSS) using a heating rate of 20 8C/min and with
systematically varied thermal histories: a(i) the first scan, followed by a(ii),
a second scan after directly cooling to 0 8C; b(i) a heating scan following
a(ii) and subsequent annealing at T ¼ 45 8C for 4 days, followed by b(ii), a
heating scan after directly cooling to T ¼ 210 8C; c(i) a heating scan
following b(ii) and subsequent annealing at T ¼ 55 8C for seven days,
followed by c(ii), a heating scan after directly heating to T ¼ 210 8C.
Traces are vertically displaced for clarity, but preserving the inset scale bar
of 2 W/g.
JPOL 7176—23/1/2003—16:50—AWINDOW—62636— MODEL 5 – br,ed
J. Pyun et al. / Polymer xx (0000) 1–12 9
ARTICLE IN PRESS
897
898
899
900
901
902
903
904
905
906
907
908
909
910
911
912
913
914
915
916
917
918
919
920
921
922
923
924
925
926
927
928
929
930
931
932
933
934
935
936
937
938
939
940
941
942
943
944
945
946
947
948
949
950
951
952
953
954
955
956
957
958
959
960
961
962
963
964
965
966
967
968
969
970
971
972
973
974
975
976
977
978
979
980
981
982
983
984
985
986
987
988
989
990
991
992
993
994
995
996
997
998
999
1000
1001
1002
1003
1004
1005
1006
1007
1008
UNCORRECTED PROOF
to crystallization within glassy PS confinement. It was
argued that the enhanced stability for soft confinement is
related to increased dimensionality (in the Avrami sense) of
the crystals perhaps afforded by a mechanically compliant
environment. We suggest an analogous explanation for the
contrasting physical aging behavior between the p(MA-
POSS) homopolymer (slow aging) and p(MA-POSS)10-b-
pBA201-b-p(MA-POSS)10 triblock (faster aging). While
aging in the p(MA-POSS) homopolymer sample transpires
in a rigid environment relatively devoid of surface or
interface, the triblock copolymer ages with proximity to an
interface with compliant pBA (Tg , 255 8C). Recall from
Fig. 4 that we observe a cylindrical morphology of
continuous p(MA-POSS) and pBA cylinders; apparently,
such a ‘soft confinement’ enhances the physical aging
process while raising Tg significantly.
3.5. WAXS studies of triblock copolymers
To further elucidate the aging of the POSS containing
homopolymer samples, we have examined the local
structure of our polymers using WAXS and compare the
results with scattering patterns of the POSS monomer and a
triblock copolymer (p(MA-POSS)6-b-pBA481-b-p(MA-
POSS)6) sample. The results are shown in Fig. 7. For
reference, we show in trace (iv) the WAXS pattern for a
representative MA-POSS monomer (R ¼ cyclopentyl,
others are virtually identical) revealing a rhombohedral
unit cell by comparison with a previous report [4].
Polymerization yielding the p(MA-POSS) homopolymer,
destroys crystallinity to leave four broad scattering peaks in
the WAXS patterns (trace (ii)), one of which is sensitive to
aging. In particular, the unaged sample (ii) shows very
strong scattering at angles, 2u ¼ 9.12, 18.768, weak
scattering at 2u ¼ 23.22 deg, and very weak scattering
near 2u ¼ 12 deg. These peaks correspond grossly to the
101, 030, 312, and 110 hkl reflections of the rhombohedral
unit cell of the POSS monomer [4], but with significant shift
in the 101 and 110 reflections. We note that such
comparison is not meant to suggest that this polymer is
crystalline, nor that it would have the same unit cell as the
monomer. Upon aging at T ¼ 55 8C for seven days, as for
the case of trace c (i) in Fig. 6, we observe near-doubling of
the peak at 11.27 deg (110,7.85 A) from 6.2% of the total
wide-angle scattering to 12.4 % (trace (i)), indicating some
enhanced alignment of POSS ‘faces’ with respect to each
other. Meanwhile, peaks 1 and 4 are observed to reduce in
size while peak 4 also shifts to smaller d-spacing. Table 1
summarizes the WAXS data for the p(MA-POSS) homo-
polymer sample, with area-% being calculated using
deconvolution with Peakfite software and assuming a
Lorentzian form for each peak.
While beyond the scope of the present study, preliminary
investigation of triblock microstructure by WAXS of both
triblock copolymers has shown behavior intermediate
between the high level of ordering in POSS monomer and
low ordering of POSS homopolymer, but very similar to
previously reported observations on POSS-based multi-
block polyurethanes (Fig. 6) [4]. Trace (iii) of Fig. 7 shows a
WAXS pattern typical of the triblocks, but in this case for
p(MA-POSS)6-b-pBA481-b-p(MA-POSS)6.
3.6. Rheological behavior of triblock copolymers
Finally, we have characterized the rheological behavior
of the microphase separated p(MA-POSS)10-b-pBA201-b-
p(MA-POSS)10 triblock copolymer using dynamic
oscillatory shear for temperatures spanning
80 8C , T , 170 8C; i.e. above the softening points of
both phases: T . TpMA-POSSg q T
pBAg : Thus, Fig. 8 shows a
master curve for shear storage and loss moduli where a
Fig. 7. Powder patterns of wide-angle X-ray scattering (WAXS) using
Cu Ka radiation (l ¼ 1.5418 A) for (i) p(MA-POSS) homopolymer
following annealing at T ¼ 55 8C for seven days (same as DSC trace c(i)
for Fig. 5); (ii) p(MA-POSS) homopolymer as isolated after fractionation;
(iii) POSS triblock copolymer, p(MA-POSS)6-b-pBA481-b-p(MA-POSS)6;
and (iv) MA-POSS (cyclopentyl) monomer.
Table 1
Analysis of WAXS patterns from Fig. 7
Original Sample Annealing at 55 8C for one
week
Peak 2u
(deg), d spacing
(A)
Area
(%)a
2u
(deg), d spacing
(A)
Area(%)a
1 9.12 (9.71) 32.4 9.10 (9.72) 27.9
2 11.27 (7.85) 6.2 11.93 (7.42) 12.4
3 18.76 (4.73) 15.3 18.52 (4.79) 17.9
4 23.22 (3.83) 46.1 23.60 (3.77) 41.8
a Obtained by Lorentzian deconvolution.
JPOL 7176—23/1/2003—16:50—AWINDOW—62636— MODEL 5 – br,ed
J. Pyun et al. / Polymer xx (0000) 1–1210
ARTICLE IN PRESS
1009
1010
1011
1012
1013
1014
1015
1016
1017
1018
1019
1020
1021
1022
1023
1024
1025
1026
1027
1028
1029
1030
1031
1032
1033
1034
1035
1036
1037
1038
1039
1040
1041
1042
1043
1044
1045
1046
1047
1048
1049
1050
1051
1052
1053
1054
1055
1056
1057
1058
1059
1060
1061
1062
1063
1064
1065
1066
1067
1068
1069
1070
1071
1072
1073
1074
1075
1076
1077
1078
1079
1080
1081
1082
1083
1084
1085
1086
1087
1088
1089
1090
1091
1092
1093
1094
1095
1096
1097
1098
1099
1100
1101
1102
1103
1104
1105
1106
1107
1108
1109
1110
1111
1112
1113
1114
1115
1116
1117
1118
1119
1120
UNCORRECTED PROOF
reference temperature of T ¼ 80 8C was used and frequency
sweeps spanning 0.1 , v , 100 rad/s were collected over
the stated temperature range. With reference to Fig. 3, the
viscoelastic properties of the material beyond the sensitive
range of DMA (i.e. at higher temperature) were examined
by shear rather than tensile deformation, noting E0 , 3G0:
We observe modest applicability of TTS for our data,
although this is not expected for microphase separated
morphologies, with a lack of fluidity at even the highest
temperatures and lowest frequencies probed. This can be
seen clearly by comparison of the storage and loss modulus
traces with the expected fluid scalings of G0 , v2 and G00 ,v shown as reference lines on the plot. Indeed, a slope near
1=2 is observed for the low frequency regions of both the
storage and loss shear moduli. Such a response is consistent
with other rheological observations for ordered block
copolymers (Fig. 4) and implicates elasticity derived from
the microphase separated morphology of a strongly
segregated system [33]. We have observed no indication
of an order-disorder transition in this system for
T , 170 8C, the highest temperature probed in our exper-
iments, but expect that TODT may be quite high due to the
large incompatibility between the p(POSS-methacrylate)
and p(butyl acrylate) phases.
4. Conclusions
The synthesis and characterization of POSS containing
homopolymers and ABA triblock copolymers was con-
ducted. ABA triblock copolymers possessing a soft middle
pBA segment and outer p(MA-POSS) segments were
prepared using ATRP. We demonstrate that optimization
of composition and DP of each segment enabled the
preparation of microphase separated structures, but with
surprising morphologies. In particular, thin films of ABA
triblock copolymers of p(MA-POSS)10-b-pBA201-b-p(MA-
POSS)10 were characterized using TEM to reveal the
formation of a pBA cylinders in a p(MA-POSS) matrix.
Thermal analysis indicated the presence of two clear glass
transitions in the microphase-separated system with strong
physical aging observed in samples annealed at tempera-
tures near the Tg of the p(MA-POSS) phase. The occurrence
of physical aging was further supported by wide-angle X-
ray scattering indicating that rearrangement of POSS
moieties was observed in glassy domains. It was found
that the Tg of the p(MA-POSS) phase from triblock
copolymers sequestered in microphase separated domains
was nearly 25 8C higher relative to a p(MA-POSS)-
homopolymer of the comparable molar mass, suggesting a
strong confinement-based enhancement of Tg in this system.
Acknowledgements
PTM acknowledges preliminary WAXS analysis per-
formed by Dr Hong G. Jeon and financial support of
AFOSR, Grant F49620-00-1-0100. The National Science
Foundation under Grant No. PHY99-07949 (PTM), DMR
9871450 (KM) and Dr John Harrison (JP) are gratefully
acknowledged for funding of this research.
References
[1] Pyun J, Matyjaszewski K. Chemistry of Materials 2001;13:3436–48.
[2] Phillips SH, Blanski RL, Svejda SA, Haddad TS, Lee A, Lichtenhan
JD, Feher FJ, Mather PT, Hsiao BS. Mater Res Soc Symp Proc 2001;
628:CC461–CC4610.
[3] Haddad TS, Lee A, Phillips SH. Polym Prepr (Am Chem Soc, Div
Polym Chem) 2001;42:88–9.
[4] Fu BX, Hsiao BS, Pagola S, Stephens P, White H, Rafailovich M,
Sokolov J, Mather PT, Jeon HG, Phillips S, Lichtenhan J, Schwab J.
Polymer 2000;42:599–611.
[5] Fu BX, Zhang W, Hsiao BS, Johansson G, Sauer BB, Phillips S,
Blanski R, Rafailovich M, Sokolov J. Polym Prepr (Am Chem Soc,
Div Polym Chem) 2000;41:587–8.
[6] Mather PT, Jeon HG, Romo-Uribe A, Haddad TS, Lichtenhan JD.
Macromolecules 1999;32:1194–203.
[7] Jeon HG, Mather PT, Haddad TS. Polym Int 2000;49:453–7.
[8] Zheng L, Farris RJ, Coughlin EB. J Polym Sci, Part A: Polym Chem
2001;39:2920–8.
[9] Zheng L, Farris RJ, Coughlin EB. Macromolecules 2001;34:8034–9.
[10] Haddad TS, Choe E, Lichtenhan JD. Mater Res Soc Symp Proc 1996;
435:25–32.
[11] Lichtenhan JD, Otonari YA, Carr MJ. Macromolecules 1995;28:
8435–7.
[12] Matyjaszewski K, editor. Controlled Radical Polymerization. Pro-
ceedings of a Symposium at the 213th National Meeting of the
American Chemical Society, held 13–17 April 1997; San Francisco,
California. ACS Symp Ser, 1998; 685: 1998; p. 483.
Fig. 8. Dynamic oscillatory shear data in the form of G0 and G00 master
curves for tri-block copolymer p(MA-POSS)10-b-p(BA)201-b-p(MA-
POSS)10; The reference temperature for time-temperature superposition
shifting was T ¼ 80 8C.
JPOL 7176—23/1/2003—16:50—AWINDOW—62636— MODEL 5 – br,ed
J. Pyun et al. / Polymer xx (0000) 1–12 11
ARTICLE IN PRESS
1121
1122
1123
1124
1125
1126
1127
1128
1129
1130
1131
1132
1133
1134
1135
1136
1137
1138
1139
1140
1141
1142
1143
1144
1145
1146
1147
1148
1149
1150
1151
1152
1153
1154
1155
1156
1157
1158
1159
1160
1161
1162
1163
1164
1165
1166
1167
1168
1169
1170
1171
1172
1173
1174
1175
1176
1177
1178
1179
1180
1181
1182
1183
1184
1185
1186
1187
1188
1189
1190
1191
1192
1193
1194
1195
1196
1197
1198
1199
1200
1201
1202
1203
1204
1205
1206
1207
1208
1209
1210
1211
1212
1213
1214
1215
1216
1217
1218
1219
1220
1221
1222
1223
1224
1225
1226
1227
1228
1229
1230
1231
1232
UNCORRECTED PROOF
[13] Matyjaszewski K, editor. Controlled/Living Radical Polymerization.
Progress in ATRP, NMP, and RAFT. Proceedings of a Symposium on
Controlled Radical Polymerization held on 22–24 August 1999; New
Orleans. ACS Symp Ser, 2000; 768: 2000; p. 484.
[14] Matyjaszewski K. Macromol Symp 2001;174:51–67.
[15] Wang J-S, Matyjaszewski K. J Am Chem Soc 1995;117:5614–5.
[16] Pyun J, Matyjaszewski K. Macromolecules 2000;33:217–20.
[17] Matyjaszewski K, Xia J. Chem Rev (Washington, DC) 2001;101:
2921–90.
[18] Patten TE, Matyjaszewski K. Accounts Chem Res 1999;32:895–903.
[19] Romo-Uribe A, Mather PT, Haddad TS, Lichtenhan JD. J Polym Sci,
Part B: Polym Phys 1998;36:1857–72.
[20] Fu BX, Hsiao BS, White H, Rafailovich M, Mather PT, Jeon HG,
Phillips S, Lichtenhan J, Schwab J. Polym Int 2000;49:437–40.
[21] Fu BX, Yang L, Somani RH, Zong SX, Hsiao BS, Phillips S, Blanski
R, Ruth P. J Polym Sci, Part B: Polym Phys 2001;39:2727–39.
[22] Haddad TS, Mather PT, Jeon HG, Chun SB, Phillips SH. Mater Res
Soc Symp Proc 2001;628:CC2.6.1–CC2.6.7.
[23] Tant MR, Wilkes GL. Polym Engng Sci 1981;21:325–30.
[24] Matyjaszewski K, Patten TE, Xia J. J Am Chem Soc 1997;119:
674–80.
[25] Buchowicz W, Holerca MN, Percec V. Macromolecules 2001;34:
3842–8.
[26] Bharadwaj RK, Berry RJ, Farmer BL. Polymer 2000;41:7209–21.
[27] Tong J-D, Jerome R. Macromolecules 2000;33:1479–81.
[28] Fujino K, Senshu K, Kawai H. J Colloid Sci 1961;16:262.
[29] Wu S. J Polym Sci Polym Phys Ed 1989;27:723.
[30] Kim GM, Sun F, Fang X, Qin H, Mather PT, In preparation. 2002.
[31] Brandrup J, Immergut EH, Grulke EA. Polymer Handbook, 4. New
York: Wiley Interscience; 1999.
[32] Zhu L, Mimnaugh BR, Ge Q, Quirk RP, Cheng SZD, Thomas EL,
Lotz B, Hsiao BS, Yeh F, Liu L. Polymer 2001;42:9121–31.
[33] Larson RG. The Structure and Rheology of Complex Fluids. New
York: Oxford University Press; 1999. Chapter 13.
JPOL 7176—23/1/2003—16:50—AWINDOW—62636— MODEL 5 – br,ed
J. Pyun et al. / Polymer xx (0000) 1–1212
ARTICLE IN PRESS
1233
1234
1235
1236
1237
1238
1239
1240
1241
1242
1243
1244
1245
1246
1247
1248
1249
1250
1251
1252
1253
1254
1255
1256
1257
1258
1259
1260
1261
1262
1263
1264
1265
1266
1267
1268
1269
1270
1271
1272
1273
1274
1275
1276
1277
1278
1279
1280
1281
1282
1283
1284
1285
1286
1287
1288
1289
1290
1291
1292
1293
1294
1295
1296
1297
1298
1299
1300
1301
1302
1303
1304
1305
1306
1307
1308
1309
1310
1311
1312
1313
1314
1315
1316
1317
1318
1319
1320
1321
1322
1323
1324
1325
1326
1327
1328
1329
1330
1331
1332
1333
1334
1335
1336
1337
1338
1339
1340
1341
1342
1343
1344