1
Syn hesis and cha ac e iza ion o epoxy polyme s con aining
azobenzene g oups ha exhibi op ical bi e ingence
Raquel FERNÁNDEZ 1, Iñaki MONDRAGON 1, Pa icia A. OYANGUREN 2,
Ma ía J. GALANTE 2 *
1 ‘Ma e ials + Technologies’ G oup. Dep o Chemical & En i onmen al Enginee ing.
Uni e sidad País Vasco/Euskal He iko Unibe si a ea, Pza Eu opa 1, 20018 Donos ia-
San Sebas ián, Spain.
2 INTEMA Uni . Nac. de Ma del Pla a-CONICET, JB Jus o 4302 Ma del Pla a,
A gen ina.
*Co esponding au ho : Tel.: +54 223 4816600; ax: + 54 223 4810046
e-mail add ess: [email p o ec ed]
This is he accep ed manusc ip o he a icle ha appea ed in inal o m in Reac i e and Func ional Polyme s 68 : 70-76
(2008) , which has been published in inal o m a h ps://doi.o g/10.1016/j. eac unc polym.2007.10.016. © 2007 Else ie unde
CC BY-NC-ND license (h p://c ea i ecommons.o g/licenses/by-nc-nd/4.0/)
2
Abs ac
A push-pull azo dye (DO3) was used as pho osensi i e subs ance o sa is ac o ily
syn hesize new epoxy polyme s con aining azo g oups co alen ly linked. Th ee
di e en amines BA, TA and MXDA we e used as ha dene s. Ma e ials wi h di e en
chemical s uc u e and azo g oup concen a ion we e p epa ed. The polyme iza ion
kine ics was ollowed using SEC, FTIR and DSC. I was obse ed ha polyme iza ion
a e inc eases wi h he azo ch omopho e inco po a ion and wi h he pho osensi i e
componen concen a ion in he eac ion p ecu so s. The pho oinduced bi e ingence o
he ob ained ilms has been analyzed. A comple ely e e sible op ical o ien a ion was
eached.
Keywo ds: Azobenzene ch omopho e, epoxy, bi e ingence.
3
1. In oduc ion
Many yea s ago, Todo o e al. [1] demons a ed ha azo dyes in polyme ic ma ices
could gi e ise o op ical bi e ingence when exci ed by pola ized ligh . The mechanism
o his p ocess in ol es epea ed ans-cis pho oisome iza ion o azobenzene g oups and
he mal cis- ans elaxa ion, esul ing in he alignmen o azobenzene g oups in he
di ec ion pe pendicula o he pola iza ion o he inciden ligh , when ligh in he blue o
g een egion is employed [2-3]. This pho oinduced ans-cis isome iza ion o
azobenzene and i s de i a i e has been s udied in solu ion and in doped and
unc ionalized glassy polyme s [4] in o de o p oduce ma e ials ha could be used o
elec oop ical de ices, pola iza ion holog aphic g a ing, and nonlinea op ics [5].
This ype o pho oinduced isome iza ion p ocess is also o pa icula in e es
because he induced changes in molecula o ien a ion can be ans e ed o he
su ounding molecules [6]. The kine ic s udies o he ans-cis isome iza ion o he azo
g oups ha e p o ided in o ma ion on he s uc u e mo phology and segmen al mobili y
o he azo polyme s. Fo example, he azo labels on di e en si es o polyme s we e
used as molecula p obes o de ec he ee olume dis ibu ion and physical aging o
he polyme s. The in luence o he polyme p ope ies on he pho ochemical and
he mal isome iza ion has been demons a ed by kine ic s udies on di e en azo
polyme s and he a e o isome iza ion o he azo g oups a ached co alen ly o he
polyme s depends on he s uc u al p ope ies o he polyme ma ix [7]. As he
elaxa ion o he o ien a ion is ela ed o he ee olume in he polyme , i is in e es ing
o inc ease he Tg o eeze almos all molecula mo emen o polyme segmen s a
oom empe a u e. The p oblem is ha pho oisome iza ion can also be hinde ed and
become so slow ha any pho oinduced aniso opy is p e en ed [8].
New azo polyme s including polyme s con aining alipha ic azo g oups and
c osslinked polyme s we e syn hesized [9-10]. In his las g oup, epoxy composi es ind
new and new possibili ies o applica ions, when azobenzene ch omopho es a e
in oduced in epoxy sys ems [11].
Based on ha knowledge, he p incipal objec i e o his wo k is o syn hesize
and cha ac e ize epoxy polyme s wi h di e se chemical s uc u e ha con ain azo
g oups co alen ly linked and could exhibi op ical aniso opy when a e exci ed wi h
4
pola ized lase ligh in he blue egion. Thei op ical beha iou will be analyzed in de ail
in a subsequen publica ion.
2. Expe imen al
2.1. Ma e ials and samples p epa a ion
A push-pull azo dye, NO2-C6H4-N=N-C6H4-NH2 (Dispe se O ange 3, DO3,
Ald ich, AZ), Tm= 200°C was selec ed as pho osensi i e molecule. An azo p epolyme
(TAZ) was syn hesized by eac ion be ween DO3 and a diglycidyl e he o bisphenol A
(DGEBA, De 332 Dow), wi h an epoxy equi alen o 174 g eq-1. I was p epa ed in a
s oichiome ic ela ion = eq AZ/eq DGEBA= 0.5, o gene a e eac ion p oduc s wi h
epoxy g oups in he ex eme o chains. The samples we e p epa ed mixing DGEBA and
he equi ed amoun o DO3 a 200°C, in an oil ba h du ing 2 min in o de o ob ain a
homogeneous solu ion. Then, polyme iza ion was ca ied ou in an oil ba h a 180°C.
The esul ing TAZ was blended wi h DGEBA and wo di e en monoamines
(MA), one alipha ic and one a oma ic, benzylamine (BA, Ald ich) and m- oluidine (TA,
Ald ich), o p epa e azo modi ied he moplas ics. TAZ, MA and he quan i y o
DGEBA necessa y o ha e a s oichiome ic a io ´=eq MA/eq epoxy (TAZ+DGEBA) =
1 we e mixed a oom empe a u e adding some e ahyd o u an (THF) d ops o
homogenize he sample. A e ha , THF was emo ed by e apo a ion a oom
empe a u e. Reac ions we e pe o med du ing 120 min a 60 °C o BA and 140 min a
100°C o TA.
Along wi h he monoamines, an alipha ic diamine (m-xylilendiamine, MXDA,
Ald ich) was u ilized as ha dene wi h he aim o de eloping c osslinked polyme . In
his case, eac ion was ca ied ou a 100°C o abou 60 min.
2.2. Measu emen s
AZ/DGEBA eac ion was ollowed in an oil ba h a 180°C, using a se o
acuum sealed ubes. Each ube was emo ed a di e en imes and quenched in ice.
Then, Size Exclusion Ch oma og aphy (SEC) was un. A Pe king-Elme
ch oma og aph equipped wi h a bina y pump and a e ac i e index
de ec o (RI) was used. The mobile phase was THF wi h an elu ion a e o 1 mL/min;
5
he sepa a ion was ca ied ou wi h h ee s y agel columns packed wi h 5 μm pa icle gel
wi h nominal po e sizes o 100 Å, 500 Å, 104Å.
Nea In a ed Spec oscopy (NIR) was used o de e mine he polyme iza ion
kine ics. An FITR Ins umen , Nicole Nexus 670/870 was employed. NIR da a ha e
been ob ained using a calcium luo ide beam spli e , a whi e ligh sou ce and a MCT/A
de ec o cooled wi h liquid ni ogen. The epoxy and p ima y amine g oup con e sions
we e calcula ed ollowing he a ea o he abso p ions band a 4530 cm-1 and 5078 cm-1
wi h espec o he a ea o he e e ence band a 4623 cm-1.
Di e en ial Scanning Calo ime y (DSC) was pe o med using a DSC Me le
Toledo 822 de ice. The eac ion hea (a ea unde he eac ion peak) and 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 1 °C/min and 10 ºC/min,
espec i ely.
Films o sys ems polyme ized using MA we e ob ained by spin-coa ing THF
solu ions o he esul ing polyme s on o clean glass slides. In he case o sys ems cu ed
wi h MXDA, he app op ia e amoun o p ecu so s was di ec ly cu ed o e clean glass
slides. Homogeneous ilms o simila hickness we e ob ained by hese p ocedu es.
Pho oinduced bi e ingence o he esul ing ilms was de e mined using he
expe imen al se up desc ibed in Figu e 1. Bi e ingence was measu ed by placing he
sample be ween wo c ossed linea pola ize s (P2 and P3). An A + lase was used as
w i ing beam o induce op ical aniso opy in he polyme ilm, and a He-Ne lase a 633
nm was used as eading beam o measu e he powe ha is ansmi ed h ough his
op ical se up. To achie e maximum signal, he pola iza ion ec o o he w i ing beam
was se o 45° wi h espec o he pola iza ion ec o o he eading beam. All
measu emen s we e pe o med a oom empe a u e and all he ilms we e i adia ed
wi h 20 mW/mm2 o he w i ing lase .
3. Resul s and discussion
Reac ions aking place du ing he azo dye-epoxy polyme iza ion ca ied ou a
180°C we e analyzed. Figu e 2 shows SEC ch oma og ams o he eagen s, DGEBA
and AZ, and a DGEBA/AZ blend, =0.5, p io o eac ion ( =0). SEC ch oma og ams
ob ained o samples eac ed up o di e en imes a e shown in Figu e 3. The
ch oma og ams ook a di e en in e als show, oge he wi h he dec ease in he main
6
peak a 28 min ha is assigned o he o e lapped peaks o DGEBA and AZ, he
appea ance and e olu ion o highe mola mass peaks a ising om DGEBA/AZ eac ion
p oduc s.
FTIR spec a in he NIR egion (4000-10000 cm-1) we e also ob ained. The
e olu ion o he abso bance peaks du ing eac ion is plo ed in Figu e 4. The 4530 cm-1
band, assigned o he combined ension and o sion ib a ions o epoxy g oups,
dec eased p og essi ely du ing eac ion. The peak a 5078 cm-1 a ising om he
combined ension and o sion ib a ions o p ima y amine also diminished, indica ing
ha he p ima y amine eac ed wi h epoxy o be comple ely con e ed in a seconda y
amine. The de elopmen o he peak a 7000 cm-1 co esponding o he hid oxile g oups
gene a ed as p oduc o he epoxy-amine eac ion also con i med ha condensa ion ook
place.
Con e sion s. ime cu es ob ained by NIR o epoxy and p ima y amine
g oups a e plo ed in Figu e 5. As he samples we e p epa ed mixing DGEBA and AZ a
high empe a u e, a NIR spec um o DGEBA a 180 ºC was ca ied ou o de e mine
how much hey eac ed du ing mixing. I was conside ed ha he a ea o he peak a
4530 cm-1 o he DGEBA spec um co esponded o con e sion X=0. Acco ding o his,
i was de e mined ha a he beginning o he kine ic s udy (0 min), he epoxy
con e sion was X=0.16. The p ima y amine is comple ely con e ed in seconda y
amine a e app oxima ely 50 min. The epoxy con e sion a e 1 h is X=0.50, which is
he maximum heo e ical alue conside ing ha he e we e used wo epoxy equi alen s
pe equi alen o amine. In consequence, 1 h was selec ed as polyme iza ion ime wi h
he pu pose o ob aining a p epolyme (TAZ) ha subsequen ly will be dissol ed in he
epoxy-amine mix u es in o de o p epa e inal ma e ials.
The esul ing TAZ was, hen, eac ed wi h wo di e en MA, BA and TA, and
DGEBA. The samples we e p epa ed wi h di e en TAZ concen a ions (10, 20 and 50
w %) and DGEBA was added in he p opo ion necessa y o ob ain a s oichiome ic
a io be ween o al epoxy (i.e. un eac ed epoxy in TAZ plus DGEBA) and amine, as
was explained abo e. TAZ was also eac ed in a simila manne wi h an alipha ic
diamine (MXDA) o ob ain a c osslinked azo modi ied polyme .
Dynamic DSC scans we e u ilized o calcula e eac ion hea s (∆H ) and glass
ansi ion empe a u es (Tg) o samples wi h di e en TAZ composi ion. ∆H was in he
o de o 100 kJ/eq o all he p ecu so s. This is he expec ed eac ion en halpy alue o
a ypical epoxy/amine blend. Tg alues a e lis ed in Table 1. In addi ion, 20 w % azo
7
he mog ams (TAZ20) we e compa ed o he pu e DGEBA/amine sys ems, o bo h,
eac ion a es and Tg (Figu e 6-8). F om he p e ious esul s, i is clea ly deduced ha
e en hough he e is no signi ican in luence o TAZ o e ∆H and Tg alues, he
eac ion is accele a ed when TAZ pa icipa es in he eac ion, as i is demons a ed by
he shi o he exo he mic peak o lowe empe a u es in he TAZ20 sample o all he
amines. Mo eo e , he eac ion a e inc eased wi h he inc ease in he TAZ con en in
he ini ial mix u e as is exempli ied in Figu e 9 o TAZ/DGEBA/TA. I is also
obse ed a b oadening o hese exo he mic peaks when he TAZ con en is inc eased.
This ac can be due o a iscosi y inc ease o he eac i e mix u es wi h he inc ease in
TAZ con en , which migh delay he di usion p ocess o eac i e chains.
Iso he mal polyme iza ion kine ics was e alua ed ollowing he e olu ion o
epoxy con e sion wi h ime o azo modi ied sys ems using FTIR. Con e sion s. ime
cu es o samples con aining 20 w % AZ we e compa ed o he nea sys ems (Figu e
10 a, b and c). As we p e iously showed o he samples analyzed in dynamic scans,
polyme iza ion a e inc eases wi h AZ addi ion.
The op ical beha iou o he ob ained ilms has been analyzed o he moplas ic
ilms syn hesized wi h BA and TA and he mose ilms ob ained wi h MXDA. Typical
w i ing sequences a e p esen ed in Figu e 11. When he expe imen s a s, no ligh is
ansmi ed h ough he analyze , due o he azo compounds a e andomly o ien ed. As
he pola ized A + lase adia ion is in oduced (ma ked A in Figu e 11), an aniso opic
o ien a ion dis ibu ion is c ea ed as consequence o he accumula ion o cis and ans
isome s ha a e o ien ed pe pendicula o he pola iza ion ec o o he w i ing beam.
Ligh is hus ansmi ed h ough he analyze due o he onse o bi e ingence. When
he exci a ion ligh is u ned o (B in Figu e 11), he signal s a s o dec ease. Pa o
his dec ease has been associa ed o he he mal eo ien a ion o some azobenzene
g oups. This he mal eo ien a ion ends o es o e he he modynamically a ou ed
diso de ed s a e and is p obably made possible by some local hea associa ed wi h he
lase ligh which is dissipa ed h ough he ilm when he lase is u ned o . A a hi d
s age in he w i ing sequence (C in Figu e 11), he op ically induced bi e ingence is
“e ased” by o e w i ing he es spo wi h ci cula ly pola ized A + beam. I s e ec is o
andomize back he o ien a ions o he azobenzene g oups. Finally, when he w i ing
beam is u ned on again (D in Figu e 11), eo ien a ion occu s. This is he as es
p ocess in all he cases. I seems like samples would ha e “memo y” and “ emembe ”
hei p e ious o ien a ion. Howe e , i is necessa y o ake in o accoun , i s ly ha
8
be o e pe o ming he expe imen s, he ilms we e no hea ed up o a empe a u e abo e
Tg o elimina e possible p e ious o ien a ions ha could be one esponsible o he
decele a ion in he eco ding in he i s cycle. And second, a pho o-induced
plas iciza ion is assumed.
Figu e 11 shows ha he maximum le el o bi e ingence is eached by he
he mose polyme indica ing ha he op ical beha iou o azo-modi ied epoxy
polyme s depends on he en i onmen in which azo moie y exis s. Samples wi h he
same TAZ concen a ion ha e been i adia ed wi h he same powe o he pump lase .
Thus, o accoun o hese esul s, a chi ec u e pa ame e s o he polyme ma ix ha e o
be analyzed. Fo he moplas ic polyme s he maximum le el o bi e ingence ob ainable
dec eases g ea ly when he a oma ic amine (TA) is employed ins ead o he alipha ic
one (BA). Howe e , when he w i ing lase is swi ched o he e is a ce ain elaxa ion
p ocess which e en ually lea es abou 37 and 50 % o he signal in ac in abou 10 min
o sys ems polyme ized wi h BA and TA, espec i ely. The e o e, in he epoxy ma ix
ob ained wi h BA i is much easie o azo compounds o mo e on he isome iza ion
p ocesses han in he epoxy ma ix ob ained wi h TA. Conce ning he azo he mose
p epa ed wi h an alipha ic diamine (MXDA), expe imen al esul s indica e ha azo
compounds ha e good mobili y in o he ne wo k, which also con ibu es o each high
induced op ical bi e ingence.
The in luence o he azo dye concen a ion, ilm hickness and lase powe o e
he op ical aniso opy o he esul ing ma e ials as well as a mo e deeply analysis o he
chemical s uc u e o he polyme is he objec o a manusc ip in p epa a ion.
4. Conclusions
Se e al azo- unc ionalized he moplas ics and he mose s wi h a iable azo
con en we e sa is ac o ily syn hesized and cha ac e ized. Reac ion a e is accele a ed
by he p esence o he azo compound. A wholly e e sible op ical aniso opy was
de eloped. Bi e ingence measu emen s indica ed ha hese polyme s a e p omising
ma e ials o be employed in op ical in o ma ion s o age, in o ma ion p ocessing, op ical
swi ching de ices, among o he s.
9
Acknowledgemen s
This wo k was suppo ed by a g an om Uni e si y o Basque Coun y
(UPV/EHU) and E o ek-Nano on p ojec inanced by he Basque Go e nmen . The
au ho s also hank he inancial suppo o UNMDP, CONICET and ANPCyT
(A gen ina).
Re e ences
[1] T. Todo o , L. Nikolo a, N.Tomo a, Appl. Op . 23 (1984) 4309.
[2].C. Kempe, M. Ru loh, J. S umpe, J. Phys.: Condens. Ma e . 15 (2003) 813.
[3] Ch. Kulinna, I. Zebge , S.H ils ed, PS. Ramanujam, HW. Siesle , Mac omol. Symp.
83 (1994) 169.
[4] O.K. Song, C.H.Wang, M.A. Pauley, Mac omolecules 30 (1997) 6913.
[5] M. Eich, J. Wendo , J. Op . Soc. Am. B. 7 (1990) 1428.
[6] W.M.Gibbsons, P.T. Shanon, S.T. Sun, B.J. Swe lin, Na u e 352 (1991) 47.
[7] S.Xie, A. Na ansohn, P. Rochon, Chem. Ma e . 5 (1993) 403-411.
[8] A. Na ansohn, S. Xie, P. Rochon, Mac omolecules 25 (1992) 5531-5532.
[9] H. Fuji-i, A. Kaji awa, A. Ha ada, Y. Mo ishima, M. Kamachi, Mac omolecules 25
(1992) 4224.
[10] Y. Mo ishima, M. Tsuji, M. Kamachi, K. Ha ada, Mac omolecules 25 (1992)
4406.
[11] J. Rod íguez, C. Sánchez, B. Villacampa, R. Alcalá, R. Cases, M. Milla uelo, L.
O iol, Polyme 45 (2004) 2341.
16
050 100 150 200
050 100 150 200
EXO
mW
T (ºC)
TAZ20/DGEBA/TA
EXO
mW
T (ºC)
DGEBA/TA
Figu e 7, Fe nández e al.
17
050 100 150 200
050 100 150 200
EXO
mW
T (ºC)
EXO
mW
T (ºC)
TAZ20/DGEBA/MXDA
DGEBA/MXDA
Figu e 8, Fe nández e al.
18
020 40 60 80 100 120 140 160 180
EXO
mW
T (ºC)
DGEBA/TA
TAZ10/DGEBA/TA
TAZ20/DGEBA/TA
TAZ50/DGEBA/MT
Figu e 9, Fe nández e al.
19
020 40 60 80 100 120 140
0,0
0,2
0,4
0,6
0,8
1,0
TAZ20/DGEBA/BA
DGEBA/BA
Epoxy con e sion
Time (min)
Figu e 10 a, Fe nández e al.
20
020 40 60 80 100 120 140
0,0
0,2
0,4
0,6
0,8
1,0
TAZ20/DGEBA/TA
DGEBA/TA
Epoxy con e sion
Time (min)
Figu e 10 b, Fe nández e al.
21
010 20 30 40 50 60
0,0
0,2
0,4
0,6
0,8
1,0
TAZ20/DGEBA/MXDA
DGEBA/MXDA
Epoxy con e sion
Time (min)
Figu e 10 c, Fe nández e al.
22
510 15 20 25 30 35 40 45 50
0,0000
0,0002
0,0004
0,0006
0,0008
0,0010
0,0012
A
B
C
D
TAZ20/DGEBA/MXDA
TAZ20/DGEBA/TA
TAZ20/DGEBA/BA
Signal (a bi a y uni s)
Time (min)
Figu e 11, Fe nández e al.
23
Figu e Cap ion
Figu e 1: Schema ic illus a ion o he expe imen al se up o he measu emen o he
pho oinduced o ien a ion o azo compounds. Op ical componen s: P, pola ize ; L,
qua e wa e pla e; M, mi o .
Figu e 2: SEC ch oma og ams o DGEBA, AZ and a DGEBA/AZ blend, =0.5 ( =0).
Figu e 3: SEC ch oma og ams as a unc ion o eac ion ime o a DGEBA/AZ blend,
=0.5, polyme ized a T=180 °C.
Figu e 4: NIR spec a o a DGEBA/AZ o mula ion wi h = 0.5, du ing polyme iza ion
a T= 180 ºC a di e en eac ion imes.
Figu e 5: Con e sion as a unc ion o ime o DGEBA/AZ a 180 °C, de e mined by
NIR: epoxy con e sion (●); p ima y amine con e sion (○).
Figu e 6: DSC esponse in dynamic mode o DGEBA/BA and TAZ20/DGEBA/BA.
Fi s scan hea ing a e: 1 °C/min; second scan (inne g aph) hea ing a e: 10 °C/min.
Figu e 7: DSC esponse in dynamic mode o DGEBA/TA and TAZ20/DGEBA/TA.
Fi s scan hea ing a e: 1 °C/min; second scan (inne g aph) hea ing a e: 10 °C/min.
Figu e 8: DSC esponse in dynamic mode o DGEBA/MXDA and
TAZ20/DGEBA/MXDA. Fi s scan hea ing a e: 1 °C/min; second scan (inne g aph)
hea ing a e: 10 °C/min.
Figu e 9: DSC esponse in dynamic mode o DGEBA/TA and TAZ/DGEBA/TA
samples wi h se e al TAZ con en s. Hea ing a e: 1 °C/min.
Figu e 10: Con e sion as a unc ion o ime de e mined by NIR: a) DGEBA/BA (○),
TAZ20/DGEBA/BA (●); b) DGEBA/TA (○), TAZ20/DGEBA/TA (●); c)
DGEBA/MXDA (○), TAZ20/DGEBA/MXDA (●).
24
Figu e 11: W i ing and e asing es s on azo- unc ionalized polyme s con aining 20 w %
TAZ: A) w i ing beam is u ned on. B) w i ing beam is u ned o . C) e asing beam is
u ned on. D) w i ing beam is u ned on again on he same spo o he ilm.
25
Table Cap ions
Table 1: Glass ansi ion empe a u es o he di e en samples used.
