1
Mo phological s udy and pho o-add essing in poly(s y ene-b-
bu adiene-b-s y ene) block copolyme s wi h azobenzene g oups and
polys y ene ma ix: in luence o chemical bonding
Raquel Fe nández, Iñaki Zalakain, José Angel Ramos, Loli Ma in,
Iñaki Mond agon*
‘Ma e ials + Technologies’ G oup, Depa men o Chemical & En i onmen al
Enginee ing, Poly echnic School, Uni e sidad País Vasco/Euskal He iko
Unibe si a ea, Plaza Eu opa 1, 20018 Donos ia-San Sebas ián, Spain.
* Co esponding au ho . Tel.: +34 943 017 177; ax: +34 943 017 130.
E-mail add ess: [email p o ec ed] (I. Mond agon)
This is he accep ed manusc ip o he a icle ha appea ed in inal o m in Eu opean Polyme Jou nal 47 : 1176-1185 (2011),
which has been published in inal o m a h ps://doi.o g/10.1016/j.eu polymj.2011.01.010. © 2011 Else ie unde CC BY-NC-
ND license (h p://c ea i ecommons.o g/licenses/by-nc-nd/4.0/)
2
ABSTRACT
The main goal o his wo k was he syn hesis o new azo- unc ionalized block
copolyme s (BCP) om epoxidized poly(s y ene-b-bu adiene-b-s y ene) modi ied wi h
azobenzene g oups by one-s ep acile eac ion be ween he epoxy g oups and an azo-
amine. The epoxy/amine eac ion was e i ied by Fou ie ans o m in a ed
spec oscopy. Addi ionally, we s udied he e ec o co alen a achmen o he
azobenzene moie ies by analyzing he mo phology and he op ical aniso opic esponse
o he esul ing azo-con aining BCP, wi h espec o solu ion mixing o he azobenzene
as a gues in he BCP hos wi hou chemical bonding. Sel -assembly o all modi ied
BCP esul ed in phase-sepa a ed mo phologies on he nanome e scale. None heless,
seg ega ion o azobenzene agg ega es on o he BCP su ace was obse ed in gues -hos
sys ems. In ela ion o he op ical aniso opic beha iou o he esul ing ma e ials, wo
dis inc op ical esponses we e obse ed depending on he exis ence o no o co alen
a achmen o he azo-ch omopho es o he BCP.
Keywo ds: block-copolyme ; epoxy; azobenzene; mic os uc u e; bi e ingence
3
INTRODUCTION
The in oduc ion o pho o-ch omic g oups in polyme s is e y a ac i e as i
o e s he oppo uni y o gene a ing new ligh -sensi i e ma e ials and op ical de ices
[1]. In pa icula , polyme s wi h azobenzene uni s o azo-polyme s ha e been widely
in es iga ed because o hei po en ial applica ions in op ical eco ding p ocesses based
on he pho o-o ien a ion o he azo-ch omopho es h ough pola ised ligh induced ans-
cis- ans isome isa ion cycles [2-8]. Mos s udies on his subjec ha e been pe o med
wi h amo phous and liquid c ys alline azo-con aining homopolyme s and andom
copolyme s. Howe e , ecen ly, he de elopmen o block copolyme s (BCP)
con aining azobenzene uni s has gained impo ance [9-25]. I is well-known ha BCP
can o m mic ophase sepa a ed nanos uc u es wi h cylind ical, lamella , sphe ical o
bicon inuous mo phologies [26-32]. The con inemen o pho o- esponsi e uni s in
nanosized block copolyme domains gi es hese ma e ials unique p ope ies, because o
he possibili y o al e ing hei sel -assembly beha iou , while allowing he
inco po a ion o molecules wi h op ical ea u es. Addi ionally, he eo ien a ion o
nanosized domains hemsel es, induced by he i adia ion o his ype o polyme s, has
also been epo ed. In pa icula , Ikeda and co-wo ke s [33] demons a ed a molecula
coope a i e mo ion be ween azobenzene moie ies and o he pho o-ine g oups in azo-
con aining BCP wi h speci ically designed s uc u es. The azo-ch omopho es became
aligned, igge ed by he i adia ion wi h a pola ized lase beam a 488 nm, and he
pho o-ine g oups we e o ien ed oge he wi h he azobenzenes by sup amolecula
coope a i e mo ions, al hough hey did no abso b he ac inic ligh .
The applica ions ela ed o holog aphic op ical s o age a e o he mos in e es ing
o esea che s [34, 35]. To ully exploi he ad an ages o holog aphy, hick ilms o
ens o hund eds o mic ons a e needed. Ne e heless, i is no mally limi ed o azo-
4
polyme hin ilms since, due o he op ical abso p ion o azobenzene moie ies in he
wa eleng h egion o he eco ding ligh , hick ilms o azo-homopolyme s canno be
illumina ed h ough he comple e ilm hickness. To dec ease he op ical abso p ion, he
azobenzene con en has o be dilu ed. This can be achie ed by copolyme isa ion o he
azo-ch omopho e wi h o he monome ha does no abso b a he exci a ion
wa eleng h. Howe e , i has been e i ied ha andom azo-copolyme s show a lowe
pho o-induced esponse wi h espec o ha o he co esponding azo-homopolyme s.
This ac has been associa ed wi h a dec ease o in e ac ions among azobenzene
moie ies, as a consequence o hei s a is ical dis ibu ion in he polyme ic chain. In an
a emp o ob ain an azobenzene dilu ion while keeping hose in e ac ions among
azobenzenes, BCP wi h an azo-block ha ing he same composi ion as he homopolyme
and ano he block ha does no abso b ligh in he pho o-exci a ion egion can be used.
Depending on molecula weigh and composi ion, block seg ega ion appea s in such a
way ha a mic os uc u e o azobenzene domains in he dilu ing polyme can be
induced. Thus, a dec ease o he azobenzene con en is achie ed while a pho o-induced
esponse o he azo-block simila o ha o he homopolyme can be expec ed [36].
Mo eo e , one o he mos impo an pa ame e s o holog aphic g a ings is he
di ac ion e iciency (DE). Azo-block copolyme s a e good candida es o con ol he
DE by su ace elie g a ing enhancemen upon mic ophase sepa a ion. Compa ed wi h
o he me hods o con ol he DE, such as mechanical s e ch, elec ical swi ch, ..., he
mic ophase sepa a ion me hod has he ad an age o being simple and con enien . Tha
is o say, holog aphic g a ings can be insc ibed a oom empe a u e and subsequen
annealing imp o es he DE by almos wo o de s o magni ude [37, 38]. These
holog aphic g a ings wi h enhanced e ec migh be applied o secu e in o ma ion
s o age since he in o ma ion can be easily ead ou by he he mally induced
5
mic ophase sepa a ion [39].
Based on ha knowledge, combining he excellen p ope ies o azo-polyme s
wi h mic ophase sepa a ion, azo-block copolyme s migh ind di e se uses in ad anced
echnology as well as newly p omising nano echnology. Howe e , he de elopmen o
well-de ined nanos uc u es in ol es he syn hesis o BCP wi h con olled
mac omolecula a chi ec u e, molecula weigh dis ibu ion, and composi ion. Se e al
polyme iza ion me hods, such as anionic, ca ionic, ee adical and me al-ca alyzed
polyme iza ions, ha e been explo ed o build azo-con aining BCP ha mee hese
equi emen s [39]. Al e na i ely, we p esen he e he unc ionaliza ion ia epoxida ion
o comme cial BCP, based on poly(s y ene-b-bu adiene-b-s y ene) (SBS), modi ied
wi h azobenzene moie ies by one-s ep acile eac ion be ween he epoxy and azo-amine
g oups. This is a no el and simple way o p epa ing azo- unc ionalized block
copolyme s as well as e y e sa ile conside ing ha he epoxy g oup is ecep i e o a
wide ange o eagen s. The e o e, his unc ional g oup can eac wi h di e en kinds o
ch omopho es wi h elec on-dono g oups con aining hyd ogen, such as amines,
amides, acids, anhyd ides, phenols, ..., gi ing ise o a la ge a ie y o azo-con aining
BCP, aking in o accoun also he g ea di e si y o comme cial a ailable SBS ype
copolyme s. In addi ion, we in es iga e he in luence o co alen a achmen o he
azobenzenes by s udying he mo phology and pho o-add essing beha iou o he
esul ing azo-con aining BCP, wi h espec o solu ion mixing o he azo-ch omopho es
wi hou chemical bonding as gues -hos sys ems.
6
EXPERIMENTAL
Ma e ials
An azo-ch omopho e, 4-(4-ni ophenylazo)aniline
(O2N)(C6H4)N=N(C6H4)(NH2), Dispe se O ange 3 (DO3), wi h a mel ing empe a u e
o 200 ºC, was supplied by Ald ich. Two SBS linea iblock copolyme s, C500 and
C540, wi h 30 and 40 w % o polys y ene (PS), espec i ely, we e kindly supplied by
Repsol-YPF. Gel pe mea ion ch oma og aphy (GPC) was pe o med wi h a Pe kin-
Elme LC-295 ch oma og aph. The mobile phase was e ahyd o u an (THF) a low
a e o 1 mL∙min-1. The numbe -a e age mola masses (Mn) we e 102,000 g∙mol-1 o
C500 and 75,000 g∙mol-1 o C540 as calcula ed using a uni e sal calib a ion me hod
wi h polys y ene s anda ds. PS homopolyme was pu chased om Polyme Sou ce and
had a Mn o 20,800 g∙mol-1 as gi en by he manu ac u e . All ma e ials we e used as
ecei ed wi hou u he pu i ica ion.
Syn hesis o pho o-add essable block copolyme s
Di e en epoxidized SBS iblock copolyme s, C500epX o C540epX (X being
he deg ee o epoxida ion (mol %) wi h espec o PB double bonds), we e ob ained by
epoxida ion o PB-blocks. This eac ion was ca ied ou using hyd ogen pe oxide in he
p esence o an in si u p epa ed ca alys sys em in a wa e /dichlo oe hane biphasic
mix u e, ollowing a p ocedu e desc ibed elsewhe e [40]. Then, he esul ing epoxidized
copolyme s we e eac ed wi h he azo-amine, DO3, in s oichiome ic a ios, be ween
epoxy g oups and ac i e hyd ogens o he amine, a 110 ºC du ing 24 h unde acuum
condi ions. Figu e 1 shows an schema ic illus a ion o he syn hesis p ocedu e
ollowed. In addi ion, gues -hos sys ems o C500 and C540 con aining DO3 (C500-
DO3 and C540-DO3) and PS (C500-DO3-PS and C540-DO3-PS) we e also p epa ed.
7
All samples ha e simila amoun s o azo-ch omopho e on he o de o 15 (± 2) w %.
Films p epa a ion
Films o he azo-block copolyme s and he gues -hos sys ems we e p epa ed by
spin-coa ing om 5 w % solu ions in THF:dichlo oe hane 0.15:0.85 using a P6700
spin-coa e om Cookson Elec onics. The spinne p og am was 1000 pm o 60 s.
Residual sol en was emo ed by e apo a ion a oom empe a u e. Then, ilms we e
annealed a 110 °C du ing di e en imes, 24 and 48 h, unde acuum. The ilms
hicknesses we e de e mined by ellipsome y using a Semilab Sop a GES-5E
ellipsome e om Tels a .
Techniques
High esolu ion 1H NMR spec a, eco ded in deu e a ed chlo o o m solu ion
wi h a B uke 300 MHz spec ome e a 25 ºC, we e used o de e mine he deg ee o
epoxida ion. 1H NMR chemical shi s we e measu ed wi h espec o e ame hylsilane
(TMS) as in e nal s anda d.
Di e en ial scanning calo ime y (DSC) was pe o med using a Me le Toledo
DSC 192 822 di e en ial scanning calo ime e equipped wi h a sample obo 193 TSO
801 RO. Ni ogen was used as pu ge gas (10 mL∙min-1). The eac ion empe a u e and
he glass ansi ion empe a u e (Tg), de ined as he onse o he change in speci ic hea ,
we e de e mined om he he mog ams ob ained in hea ing scans a 10 ºC∙min-1.
In a ed spec a we e aken using a Nicole Nexus 670 Fou ie ans o m
in a ed (FTIR) spec ome e equipped wi h a single ho izon al golden ga e a enua ed
o al e lec ance (ATR) cell. Spec a we e eco ded using a spec al wid h anging om
600 o 4000 cm-1, wi h 2 cm-1 esolu ion and an accumula ion o 20 scans.
8
The mo phology o he samples was s udied by a omic o ce mic oscopy (AFM).
AFM images we e ob ained wi h a Nanoscope IIIa scanning p obe mic oscope
(Mul imode™, Digi al Ins umen s). Tapping mode (TM) in ai was employed using an
in eg a ed ip/can ile e (125 µm in leng h wi h ca 300 kHz esonan equency).
Typical scan a es du ing eco ding we e 0.7-1 line∙s-1 using a scan head wi h a
maximum ange o 16 x 16 µm.
Op ical s o age expe imen s we e ca ied ou a oom empe a u e and unde
ambien condi ions. The expe imen al se up used was simila o ha p e iously
epo ed [41]. Op ical bi e ingence was induced in ilms o he azo-block copolyme s
and he gues -hos sys ems using a linea ly pola ized a gon lase ope a ing a 488 nm
(w i ing beam) wi h a pola isa ion angle o 45º wi h espec o he pola isa ion di ec ion
o a low powe He-Ne lase ope a ing a 632.8 nm ( eading beam). The powe o he
w i ing beam used in he expe imen s was a ied be ween 6 and 20 mW on a spo o 0.4
mm2 and he change in he ansmission o he eading beam, which passed h ough he
sample be ween wo c ossed pola ise s, was measu ed wi h a pho odiode. The induced
bi e ingence (Δn) was de e mined by measu ing he eading beam ansmission
(T = I/I0) acco ding o:
Δn = (λ/π d) sin-1 (I/I0)1/2
whe e λ is he wa eleng h o he eading beam, d is he ilm hickness, I is he in ensi y
o he eading beam a e he second pola ise and I0 is he ansmi ed in ensi y o he
eading beam be ween pa allel pola ise s in absence o aniso opy.
RESULTS AND DISCUSSION
A b ie accoun o he cha ac e is ics o he modi ied copolyme s can be ound
in Table 1. 1H NMR spec a p o ided e idence o he exis ence o eac i e epoxy
9
g oups in PB-block chains. Figu es 2a-d show 1H NMR spec a o he pa en
copolyme s, C500 and C540, and he epoxidized copolyme s, C500ep11 and C540ep14.
C500 and C540 showed wo signals a 5.03 and 5.45 ppm, co esponding o he ole inic
p o ons o 1,2- and 1,4-bu adiene uni s. The co esponding epoxidized copolyme s
showed likewise wo new signals a ibu ed o he p o ons a ached o ans- and cis-
epoxy g oups a 2.70 and 2.96 ppm, espec i ely. The deg ee o epoxida ion was
calcula ed by he in eg a ion o hese new signals compa ed o he sum o he in ensi ies
o double bond p o on peaks.
Fi s ly, he eac ion be ween he epoxy g oups and he azo-amine was
in es iga ed. The mal beha iou o C500ep11-DO3 and C540ep14-DO3 was s udied by
di e en ial scanning calo ime y. Dynamic DSC scans (no shown he e) we e u ilized o
es ima e eac ion empe a u es and Tg alues o samples. Acco ding o his s udy,
110 ºC du ing 24 h was selec ed as eac ion condi ion o bo h sys ems. In o de o
e i y he comple e eac ion o eac an s, iso he mal DSC scans (no shown he e) we e
ob ained a ha expe imen al condi ion (110 ºC, 24 h). In a subsequen DSC scan in
dynamic mode no esidual hea o eac ion was seen, p o ing o al eac ion. In addi ion,
he syn hesis o bo h azo-block copolyme s, C500ep11-DO3 and C540ep14-DO3, was
ca ied ou unde acuum o a oid possible oxida ion eac ions.
To co obo a e he epoxy g oups eac ion, FTIR spec a in he mid IR egion o
he samples we e also ob ained. In Figu es 3a-b he spec a o DO3, C500ep11-DO3
and C500ep11 wi h and wi hou annealing, a 110 ºC o 24 h unde acuum, a e
plo ed. The main in a ed abso p ion bands o hese samples a e lis ed in Table 2. The
bands associa ed wi h C-O-C g oups o ans- and cis-1,4-epoxidized copolyme
appea ed a 890 and 814 cm-1, espec i ely. The co esponding band o 1,2-epoxidized
uni s should appea a ound 911 cm-1. I is wo h no ing ha PS and 1,2-PB ha e a
16
ACKNOWLEDGEMENTS
Financial suppo om he Basque Coun y Go e nmen in he ame o G upos
Consolidados (IT-365-07), ETORTEK/inanoGUNE (IE08-225 and IE09-243) p ojec s,
and he Minis y o Educa ion and Science o MAT2009-06331 p ojec is g a e ully
acknowledged. The au ho s also hank he echnical and human suppo p o ided by
SGIke (Mac obeha iou -Mesos uc u e-Nano echnology uni ) (UPV/EHU, MICINN,
GV/EJ, ESF).
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22
TABLE CAPTIONS
Table 1. Cha ac e is ics o he block copolyme s used.
Table 2. FTIR assignmen s o he ele an abso p ion bands o he ma e ials used.
23
Sample
Epoxida ion deg ee
(mol %)
PS
(w %)
PB
(w %)
Epoxidized PB
(w %)
AZO
(w %)
T
g
PB
(ºC)
SBS-DO3
C500-DO3-PS
C500ep11-DO3
0
0
11
25
38
25
60
49
50
0
0
10
15
13
15
-80a
-80a
-55
a Glass ansi ion empe a u e alues o PB/epPB blocks o SBS de e mined elsewhe e [42].
Table 1
Wa enumbe (cm-1)
Band assignmen
3500-3400
3400
3080-3005
2920-2840
1712
NH2 and NH s e ching
OH s e ching
C-H s e ching o a oma ic ings
C-H s e ching o alipha ic bonds
C=O s e ching
24
1640
1600
1640-1600
1510
1390
1340
1140
990-910
890
855-835
NH
2
in-plane bending
NH in-plane bending
C=C s e ching
NO2 asymme ic s e ching
N=N s e ching
NO2 symme ic s e ching
C-H s e ching
C=C ou -o -plane bending
C-O-C asymme ic s e ching
C-H ou -o -plane bending o a oma ic ings
Table 2
FIGURE CAPTIONS
Figu e 1. Syn hesis o azo-con aining block copolyme s.
Figu e 2. 1H NMR spec a o pa en copolyme s, (a) C500 and (b)C540, and epoxidized
copolyme s, (c) C500ep11 and (d) C540ep14.
Figu e 3. FTIR spec a o DO3, C500ep11, and C500ep11 and C500ep11-DO3 a e
annealing a 110 ºC o 24 h wi hin he ange: (a) 3600-800 cm-1 and (b) 1700-800 cm-1.
25
Figu e 4. TM-AFM phase image (le ) and p o ile ( igh ) o C500-DO3 a e annealing
a 110 ºC o 24 h (3 μm × 3 μm). The s aigh line on he image indica es he posi ion
whe e he p o ile was measu ed.
Figu e 5. TM-AFM phase image (le ) and p o ile ( igh ) o C500-DO3-PS a e
annealing a 110 ºC o 24 h and 210 ºC o 4 min (3 μm × 3 μm). The s aigh line on
he image indica es he posi ion whe e he p o ile was measu ed.
Figu e 6. TM-AFM phase images o (a) C500ep11-DO3 and (b) C540ep14-DO3 a e
annealing a 110 ºC o 24 h, and (c) C500ep11-DO3 and (d) C540ep14-DO3 a e
annealing a 110 ºC o 48 h (2 μm × 2 μm).
Figu e 7. W i ing- elaxing cu es o (a) C500-DO3, (b) C540-DO3, (c) C540-DO3-PS,
(d) C500ep11-DO3, and (e) C500ep11-DO3 and ( ) C540ep14-DO3 a e annealing a
110 ºC o 24 h. The w i ing beam is on a poin A and o a B.
32
Figu e 3b
33
Figu e 4
34
Figu e 5
35
Figu e 6a
36
Figu e 6b
37
Figu e 6c
38
Figu e 6d
39
Figu e 7a
40
Figu e 7b
41
Figu e 7c
