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.

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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

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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

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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

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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.

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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.

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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.

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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.

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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.

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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.

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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.

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