Couma in based ligh esponsi e healable wa e bo ne
polyu e hanes
Robe H. Agui esa obe, Loli Ma in*, No a A ambu u, Lou des I us a and
Ma ia Jose Fe nandez-Be idi
POLYMAT, Polyme Science and Technology Depa men , Facul y o
Chemis y, Uni e si y o he Basque Coun y, UPV/EHU, Spain.
* Mac obeha io -Mesos uc u e-Nano echnology and NMR SGike se ice o
UPV/EHU. Poly echnic School, UPV/EHU. Spain.
Email add ess: mj. e nandezbe [email protected]
Abs ac
Wa e bo ne polyu e hanes con aining couma in as chain ex ende s we e
success ully syn hesized. Taking ad an age o he pho oinduced [2+2]
cycloaddi ion eac ion o couma in moie ies, his wo k e alua ed he healing
abili ies o hese ma e ials. The pho ochemical p ocess was analyzed by UV
spec oscopy and he cycloaddi ion eac ion kine ics was s udied. In addi ion,
he healing abili ies o he syn hesized wa e bo ne polyu e hanes we e
de e mined by means o sc a ch e illing s udies and s ain-s ess es s. The
i adia ion condi ions as well as he polyme ic chain mobili y on he ac u e and
he capaci y o gene a e polyme ne wo ks by couma in linkages we e
demons a ed o be he main ac o s a ec ing he healing p ocess.
The beha io o hese sys ems was also de e mined unde he di ec i adia ion
o sunligh .
Keywo ds
Couma in, wa e bo ne polyu e hanes, sunligh , ligh esponsi e, healing.
2
Highligh s
Syn hesis o healable wa e bo ne polyu e hanes wi h couma in moie ies
inco po a ed in he polyme ic backbone.
E alua ion o couma in e e sible pho odime iza ion eac ion by UV
spec oscopy and de e mina ion o he cycloaddi ion eac ion kine ics.
Dependence o he adia ion condi ions on he sc a ch illing abili ies o he
polyme ic coa ings.
In luence o he polyu e hane physical p ope ies on he healing e iciency o he
polyme ic sys ems.
S udy o couma in cycloaddi ion eac ion unde sunligh condi ions
3
1. In oduc ion
Polyu e hanes a e polyme s ha can be easily modi ied by he in oduc ion o
di e en monome s uc u es. As a consequence, hei physical p ope ies can
be ailo ed o hose equi ed in he inal p oduc . Hence, hey ha e been widely
used in he de elopmen o in insic healable ma e ials [1–3]. The in insic
healing s a egy is based on he inco po a ion o healing ac i e elemen s in
polyme backbones so ha he chemical na u e o hese elemen s de e mines
he au onomic o non-au onomic na u e o he healing p ocess.
Howe e , he in oduc ion o ac i e monome s in o he polyu e hane s uc u e is
no easy. On he one hand, hese elemen s should be capable o eac ing wi h
isocyana e g oups and consequen ly he selec ed ac i e monome s should
ha e hyd ogen-con aining nucleophiles in hei s uc u e. On he o he hand,
he e should be a su icien amoun o ac i e elemen s on he su ace o he
damage wi hou comp omising he physical p ope ies o he polyu e hane.
The e o e, i is necessa y o each a balance be ween he healing abili ies and
he desi ed physical p ope ies o he inal p oduc .
I is well known ha couma in de i a i es show he e e sible pho oinduced
[2+2] cycloaddi ion eac ion [4,5], which enables he joining o sepa a ion o he
couma in molecules in a con olled way, selec ing he app op ia e i adia ion
condi ions. Thus, acco ding o Scheme 1, when i adia ing couma in molecules
wi h UV ligh below 300 nm, he [2+2] cycloaddi ion eac ion akes place and a
cyclobu ane is o med be ween wo molecules. In con as , he i adia ion o
hese dime s wi h UV ligh a wa eleng hs highe han 300 nm p o okes he
up u e o he cyclobu ane ing, leading o he es o a ion o he o iginal
couma in s uc u es.
Scheme 1. Couma in pho oinduced eac ions
4
As epo ed in li e a u e, couma in monome s ha e been inco po a ed in o
polyu e hane chains bo h as chain ends and/o chain ex ende s, gi ing he
possibili y o e e sibly inc easing he molecula weigh o he polyme chains o
c osslinking samples [6–8].
Taking ad an age o his p ocess, in his wo k he inco po a ion o couma in
monome s as chain ex ende s in wa e bo ne polyu e hanes is desc ibed. Ligh -
esponsi e p ope ies o couma in monome s ha e demons a ed o p o ide
epai ing abili ies o polyme s uc u es [9–12]. Howe e , o he bes o ou
knowledge, his is he i s ime ha polyu e hanes wi h op ically healable
abili ies ha e been syn hesized using a me hodology which leads o s able
wa e based dispe sions. This s a egy o e s he possibili y o using
en i onmen ally iendly ma e ials wi h healing p ope ies in a wide ange o
applica ions such as coa ings o au omobiles, ex iles, u ni u e and wood.
2. Expe imen al
2.1. Ma e ials
Isopho one diisocyana e (IPDI), 2-bis(hyd oxyme hyl) p opionic acid (DMPA),
1,4-bu anediol (BD), polyp opylene glycol (PPG) (Mn 1000 g mol-1),
ie hylamine (TEA), dibu yl in diace a e (DBTDA), ace one, phlo oglucinol, e hyl
ace ona e, 1,4 dioxane, concen a ed sul u ic acid, po assium ca bona e,
dime hyl o mamide and 2-b omoe hanol we e pu chased om Sigma-Ald ich
Chemical Co po a ion. All ma e ials we e used as ecei ed.
2.2. Syn hesis o 5, 7-bis(2-hyd oxye hoxy)-4-me hylcouma in (DHEMC)
The syn hesis o DHEMC was ca ied ou in wo sepa a e eac ions, ollowing
he p ocedu e desc ibed in li e a u e [13,12]. In he i s one, 5,7-dihyd oxy-4-
me hylcouma in (DHMC) was ob ained om he eac ion be ween
phlo oglucinol and e hyl ace oace a e in acid condi ions. In he second s ep, he
inal p oduc was ob ained by he modi ica ion o he phenolic g oups o DHMC
wi h b omoe hanol.
2.3. Syn hesis o wa e bo ne polyu e hane
The syn he ic way o ob ain PPGDHEMC polyme is shown in Scheme 2.
5
Polyol, In e nal emulsi ie (DMPA) and TEA we e pou ed oge he wi h DBTDA
(800 ppm) and ace one (36 g) in o a lask eac o . When he eac ion
empe a u e eached 56 ºC, IPDI was added and he eac ion was main ained
o 3 h. In a u he s ep, he polyme chains we e ex ended using he
app op ia e BD amoun , lea ing some ee isocyana e g oups. This eac ion
was ca ied ou o one addi ional hou . A e wa ds, DHEMC was added o he
eac ion mix u e in o de o ob ain s oichiome ic a io o NCO/OH g oups. The
eac ion was s opped when he in a ed abso bance o he NCO g oups (a ound
2200 cm-1) was negligible. Table 1 summa izes he o mula ions used in he
di e en eac ions.
Scheme 2. Syn he ic pa hway o ob ain wa e bo ne PPGDHEMC polyu e hanes
Table 1
Amoun o eagen s used in he syn hesis o di e en PPGDHEMC
Sample
Polyol
DMPA
IPD
TEA
BD
Couma in monome
mmol
mmol
mol(%)
(w %)
PPG1DHEMC
22.5
11
56.5
15
21.5
1.5
1.32
1.08
PPG5DHEMC
22.5
11
56.5
15
14.5
8.5
7.52
5.91
PPG10DHEMC
22.5
11
56.5
15
6
17
15.04
11.38
PPG15DHEMC
22.5
11
56.5
15
0
23
20.35
14.98
In o de o ob ain he wa e bo ne polyu e hane dispe sion, he solid con en o
he eac ion mix u e was adjus ed o 60% using ace one. The emulsi ica ion
6
p ocess was ca ied ou a oom empe a u e and he mechanical s i ing was
aised o 400 pm o help he dispe sion p ocess. 25 g o he eac ion mix u e
was inco po a ed in o he eac o and wa e (60 g) was added d op-wise a 1
mL/min. A e wa e addi ion, he s i ing was kep a he same a e o an
addi ional 30 min. Finally ace one was emo ed using dis illa ion equipmen a
30 ºC. The solid con en o he esul ing dispe sion was 20%.
2.4. E alua ion o healing p ope ies
The e alua ion o he healing p ope ies was de e mined aking in o accoun wo
di e en applica ions o hese ma e ials, polyme coa ings and ilms. Fo
polyme coa ings, c ack e illing expe imen s we e pe o med using op ical
mic oscopy o di e en i adia ion condi ions. The quan i ica ion o he healing
p ocess o polyme ilms was es ablished by s ess-s ain es s i adia ing die-
cu samples a 365 nm o 24 hou s, 12 hou s in each side o he ilm, in o de o
maximize he c osslinking deg ee and o p o ide hem wi h s uc u al in eg i y.
Th ee di e en independen healing e en s we e pe o med cu ing he
specimens pe pendicula ly o he applied s ess and subsequen ac u es we e
cu a 45º deg ees wi h espec o he i s . A e each ac u e he specimens
we e epai ed unde he app op ia e healing condi ions.
2.5. Ins umen a ion
1H liquid Nuclea Magne ic Resonance (NMR) spec a we e ob ained in a
Fou ie T ans o m B uke 300 MHz spec ome e (model A ance 300 DPX).
Dynamic Ligh Sca e ing (DLS) measu emen s we e ca ied ou using 90Plus
(B ookha en) Pa icle Size Analyze in o de o ob ain he diame e o he
pa icles, Dp, as an a e age o eigh measu emen s. The e e sible
pho o eac ion was moni o ed by UV- is spec ome y in a Helios Omega UV-Vis
spec ome e (The mo Scien i ic). The measu emen s we e made om ilms
ob ained by cas ing a 0.1w % ace one solu ion on o he ou side wall o a qua z
cell. The samples we e i adia ed bo h a 365 nm (0.8 mWcm-2) and 254 nm
(0.16 mWcm-2), using a Vilbe Lou ma VL-6LC lamp and he UV-Vis spec a
we e eco ded a di e en imes. Tensile es s we e ca ied ou on a uni e sal
Ins on 5569 ensile es machine. A load cell o 100 N was used, he ini ial
dis ance be ween clamps was ixed a 30 mm and he expe imen s we e
7
pe o med using a c osshead-speed o 20 mm/min. The illing abili ies o
di e en healable sys ems we e e alua ed in a Nikon Eclipse E6000 op ical
mic oscope equipped wi h a empe a u e con olle uni Me le Toledo FP90.
AFM images we e ob ained in a Dimension ICON Nanoscope V (B uke )
de ice, using TESP-V2 ips ( =320 kHz, k=40 N/m). The images we e ob ained
in 1 μm x 1 μm ames.
3. Resul s and Discussion
3.1. Cha ac e iza ion
1H NMR was used o cha ac e ize he inal p oduc (Figu e 1). As can be seen,
all signals ha e been co ec ly assigned o he co esponding p o ons. The
egion be ween 3.5 and 4.5 ppm is pa icula ly signi ican as i con i ms he
inco po a ion o he couma in g oup in he polyu e hane chain.
Table 2 summa izes he pa icle size alues o all o mula ions, whe e i can be
seen ha he pa icle size inc eases wi h couma in con en . In addi ion, all
o mula ions we e s able o a leas one week.
Figu e 1. 1H NMR o PPG10DHME sys em
8
Table 2
Pa icle size o PPGDHEMC
Couma in % w
1.5
5
10
15
Dp (nm)
50
49
77
115
3.2. Re e sible pho oinduced cycloaddi ion eac ion
UV isible spec ome y was used o ollow he [2+2] cycloaddi ion eac ion o
couma in moie ies and he dime iza ion deg ee (p) was calcula ed om he
abso bance a 320 nm as a unc ion o ime, using he me hodology epo ed
elsewhe e [9,12,14], and desc ibed by equa ion 1, whe e A co esponds o he
abso bance a 320 nm a ime and A0 he o iginal abso bance a 320 nm
be o e i adia ion a 365 nm.
Dime iza ion deg ee = 1-A /A0 ( 1 )
Figu e 2 shows he dime iza ion deg ee as a unc ion o ime o di e en
couma in con en PPGDHEMC samples o he i s i adia ion cycle.
Figu e 2. Fi s cycle kine ic plo s o PPGDHEMC samples con aining di e en
amoun s o couma in.
As can be seen he eac ion p og esses a he same eloci y independen ly o
he DHEMC con en du ing he i s 45 minu es. Howe e , a longe imes a
9
sligh dependence o he eac ion e olu ion on he couma in concen a ion is
obse ed. These esul s clea ly di e om hose ob ained p e iously o
PPGHEMC sys ems whe e he couma in moie ies we e inse ed a he
polyme ic chain ends [15]. The di e ence o he phase-sepa a ed mo phology
o bo h sys ems can be esponsible o he obse ed beha io . Figu e 3 shows
he AFM phase images o PPGHEMC and PPGDHEMC samples con aining
di e en amoun s o couma in, be o e being exposed o 365 nm UV ligh .
Figu e 3. AFM Phase images o polyu e hanes con aining di e en amoun s o
couma in as chain ends (PPGHEMC) and chain ex ende s (PPGDHEMC)
As can be seen, PPGDHEMC sys ems p esen a less homogeneous
mo phology compa ed o PPGHEMC samples, wi h b igh e and da ke egions
a ibu able o polyu e hane ha d and so domains [16,17]. Taking in o accoun
ha couma in moie ies end o agg ega e in he ha d domains, he
pho ochemical p ocess occu s p e e ably in hese domains, al hough he
p esence o couma in ou side hese domains should no be dismissed.
In o de o be e unde s and he in luence o he couma in concen a ion, a
quan i a i e analysis o he eac ion kine cs was pe o med, ollowing he same
p ocedu e ca ied ou o couma in end-capped polyu e hanes (PPGHEMC)
[15]. In con as o PPGHEMC sys ems, which i ed o a pseudo-second o de
kine ics, couma in chain ex ended polyu e hanes did no app op ia ely i any
simple kine ics laws. Howe e , aking in o conside a ion he phase sepa a ed
16
The e olu ion o he cycloaddi ion eac ion was ollowed by UV spec oscopy
and Figu e 8 shows he eac ion kine ics plo s. The cycloaddi ion eac ion in
Ma ch ook place in 3 hou s whe eas nea ly 80 pe cen o con e sion was
eached in 30 minu es when he sample was exposed in July. This ac is
di ec ly ela ed o he UV-A ligh in ensi y measu ed in bo h expe imen s: 0.59
mW/cm2 (Ma ch) and 3.1 mW/cm2 (July). Howe e he maximum con e sion
was simila in bo h cases.
4. Conclusions
Couma in moie ies we e success ully in oduced as a chain ex ende in o
wa e bo ne polyu e hane backbones (WPUs) a h ee di e en concen a ions.
The e e sible pho odime iza ion eac ion o hese moie ies was analyzed by
UV spec oscopy and he kine ics o he cycloaddi ion eac ion was de e mined.
Due o he phase-sepa a ed mo phology o he sys ems, he eac ion kine ics
was independen o couma in con en a leas du ing he i s s ages.
The inco po a ion o he couma in monome p o ides healing abili y o WPUs.
The healing e iciency shown by hese sys ems depends on hei physical
p ope ies. Thus, he chain mobili y on ac u ed su aces, oge he wi h he
sys em capaci y o o m polyme ne wo ks by means o couma in linkages, a e
he main ac o s a ec ing he healing e iciency.
The complex me hodology equi ed o ob ain WPUS does no a ec he healing
p ope ies o he inal p oduc s.
Acknowledgmen s
The au ho s acknowledge he Uni e si y o he Basque Coun y UPV/EHU (UFI
11/56), he Basque Go e nmen (Ayuda a g upos de in es igación del sis ema
uni e si a io asco IT 618/13 and PhD schola ship) and he Minis e io de
Economía y Compe i i idad (CTQ2013-4113-R) o he unding ecei ed o
de elop his wo k.
Technical and Human suppo p o ided by Mac obeha io -Mesos uc u e-
Nano echnology and NMR SGike se ice o UPV/EHU is also g a e ully
acknowledged.
17
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