1
Syn hesis and cha ac e iza ion o pho o-c osslinkable linea segmen ed polyu e hanes
based on couma in
Rubén Seoane Ri e o1, Rod igo Na a o2, Pila Bilbao Solagu en1, Koldo Gond a Zubie a1,
José Ma ía Cue as1, Angel. Ma cos-Fe nández2*
1 Gaike Cen o Tecnológico, Pa que Tecnológico Edi icio 202, 48170 Zamudio, Spain, Tel.:
+34 94 6002323, Fax: +34 94 6002324
2 Ins i u o de Ciencia y Tecnología de Políme os (CSIC), Juan de la Cie a 3, 28006 Mad id,
Spain, Tel.: +34 915622900, Fax: +34 915644853
*Co esponding au ho : [email p o ec ed]
Abs ac
Linea segmen ed polyu e hanes wi h 10% weigh o couma in g oups wi hin he so
segmen , he ha d segmen o equally dis ibu ed be ween bo h segmen s we e success ully
p epa ed. These polyu e hanes, based on polycap olac ones, isopho one diisocyana e,
bu anediol and a dihyd oxyla ed couma in monome , we e comple ely amo phous and
homogeneous wi h a single phase mo phology. In non-i adia ed polyu e hanes Tg alue
a ied linea ly wi h ha d segmen con en ha in u n was he main ac o in luencing he
mechanical p ope ies. Pho o-dime iza ion a 354 nm p oduced c osslinked ma e ials wi h
li le change on he Tg and ou s anding mechanical p ope ies, as high as 54 MPa, be e han
ha o any o he couma in-con aining polyme desc ibed.
Keywo ds
Couma in; ing-opening polyme iza ion; polycap olac one; segmen ed polyu e hanes; pho o-
dime iza ion
This is he accep ed manusc ip o he a icle ha appea ed in inal o m in Eu opean Polyme Jou nal 92 : 263-274 (2017),
which has been published in inal o m a h ps://doi.o g/10.1016/j.eu polymj.2017.05.016. © 2017 Else ie unde CC BY-NC-ND
license (h p://c ea i ecommons.o g/licenses/by-nc-nd/4.0/)
2
INTRODUCTION
The e a e many s udies in which ligh has been u ilized as a igge o he p epa a ion o
sma ma e ials.[1-4] Ligh has he ad an age ha ligh - igge ed p ocesses can be hal ed and
esumed “on demand” by u ning o and on he exci a ion ligh .[5] Se e al ligh -sensi i e
g oups o ch omopho es ha can unde go a e e sible pho o-induced eac ion can be used in
hese ma e ials such as an acenes,[6] couma ins,[7] o cinnamic acid de i a i es.[8] These
ligh -sensi i e ma e ials ha e been p oposed o many applica ions among hem shape
memo y polyme s,[8] hyd ogels,[9] su ace pa e ning,[10] d ug elease,[11,12] ligh
s abiliza ion and su ace sizing o pape ,[13] cellula imaging,[14] pho o ol aics,[15] oil
eco e y,[16] mic o-phase s abiliza ion o block copolyme s[17] and in aocula lenses.[18].
These pho o- eac i e g oups should be pa o he polyme s uc u e wi hou comp omising
he desi ed p ope ies, which o en means a limi ed con en . [19,20]
Couma in molecules can unde go e e sible pho o-induced eac ions; hus, when i adia ed a
>300 nm a [2+2] cycloaddi ion eac ion o gi e ise o a cyclobu ane ing akes place, and
when i adia ed a 254 nm a pho o-scission eac ion ende s he o iginal couma in s uc u es
as shown in Figu e 1.[7,21-23]
Figu e 1. Pho o-dime iza ion/pho o-clea age eac ions o couma in molecules
3
Couma in monome s ha e been included in he backbone o di e en ypes o polyme s,
including polye he s,[21] poly(me h)ac yla es,[23,24] polyes e s,[25] silicones[26,27] and
polyu e hanes.[19]
Polyu e hanes a e conside ed excellen ma e ials because o hei good physical p ope ies.
This is he eason why his ma e ial is widely used in di e en and nume ous applica ions.
When linea polyu e hanes a e p epa ed, usually hey a e composed o a di unc ional lexible
mac oglycol o ela i ely long chain, a diisocyana e and a sho chain diol e e ed as chain
ex ende . The inal linea polyu e hane has a segmen ed s uc u e whe e he lexible chains o
he mac oglycol cons i u e he so-called so segmen s and he ela i ely igid and pola chains
p oduced by he eac ion o he diisocyana e and he chain ex ende cons i u e he so-called
ha d segmen s.[28,29] When inco po a ed in a polyu e hane chain, he couma in monome
has been in oduced as a chain end [20,30,31] o as a chain ex ende .[19], in bo h cases wi h
he couma in moie y linked o he isocyana e monome by a pola u e hane g oup, and
he e o e wi h he couma in uni s we e wi hin he ha d segmen s, and only ecen ly we
desc ibed o he i s ime a polyu e hane wi h he couma in wi hin he so segmen .[32]
This linea polyu e hane, o mula ed wi hou chain ex ende , p oduced a e couma in
dime iza ion a ough elas ome ic ma e ial wi h he bes mechanical p ope ies o all he
couma in-con aining polyme s desc ibed in li e a u e o ha da e.
In his wo k we epo he p epa a ion o linea segmen ed polyu e hanes wi h couma in
molecules wi hin he so segmen , wi hin he ha d segmen o equally dis ibu ed in be ween
bo h segmen s. These polyu e hanes we e o mula ed wi h chain ex ende s and he e o e,
di e en om ou p e ious wo k [32], he esul ing polyu e hanes ha e a (AB)n segmen ed
s uc u e wi h al e na ing so segmen s (A: lexible chains o he mac oglycol) and ha d
4
segmen s (B: pola chains p oduced by he eac ion o diisocyana e+chain ex ende ). In his
way, he e ec o ha ing he couma in molecules wi hin he so segmen , wi hin he ha d
segmen o dis ibu ed in bo h segmen s, on he eac i i y o he couma in molecules when
i adia ed and he di e ence in he esul ing physical p ope ies a e i adia ion, can be
s udied. I is expec ed ha depending on he loca ion o couma in molecules he e ec will be
e y di e en . A couma in diol monome was used as ini ia o o he ing opening
polyme iza ion o ε-cap olac one o ob ain a couma in-con aining polycap olac one (PCL)
diol o app oxima ely 1000 g·mol-1 molecula weigh o a oid PCL c ys alliza ion. This PCL
diol was combined wi h ano he sho PCL diol, isopho one diisocyana e, bu anediol and he
couma in diol monome in he app op ia e a ios o p oduce he segmen ed polyu e hanes
wi h a 10% weigh o couma in in hei s uc u e. The pho ochemical, he mal and mechanical
p ope ies o hese polyu e hanes we e e alua ed.
EXPERIMENTAL SECTION
Ma e ials
Polycap olac one diol o nominal molecula weigh 530 g·mol-1 (PCL527, molecula weigh
527 g·mol-1 as calcula ed by 1H-NMR[33]) was supplied by Sigma Ald ich Química S.L
(Mad id, Spain). PCL527 was acuum d ied a 90 °C o 3 h and s o ed in a desicca o un il
used.
2,2-Bis(hyd oxyme hyl)p opionic acid, 2,2-dime hoxyp opane, p- oluenesul onic acid
monohyd a e, 1,3-dicyclohexylca bodiimide, eso cinol, e hyl ace oace a e, 2-b omoe hanol,
anhyd ous py idine, 1,4-dioxane, e hyl ace a e, sodium bisul i e, Dowex H+ esin, -
cap olac one, and s annous oc oa e (SnOc 2) we e supplied by Sigma Ald ich Química S.L
(Mad id, Spain) and used as ecei ed.
Ace one, dichlo ome hane, concen a ed sulphu ic acid, e hanol, N,N-dime hyl o mamide,
po assium ca bona e, magnesium sul a e and 1,2-dichlo oe hane we e supplied by Scha lau
(Ba celona, Spain) and used as ecei ed.
5
1,4-bu anediol (BD) was pu chased om Sigma Ald ich Química S.L (Mad id, Spain). BD
was d ied o e magnesium sul a e, dis illed and s o ed blanke ed wi h ni ogen un il use.
Isopho one diisocyana e (IPDI) was a gi by E onik Indus ies.
Expe imen al echniques
Solu ion NMR spec a we e eco ded a oom empe a u e in a Va ian Uni y Plus 400
ins umen (Palo Al o, CA, USA) using deu e a ed chlo o o m (CDCl3) o deu e a ed
dime hylsul oxide (DMSO-d6) as sol en . Spec a we e e e enced o he esidual sol en
signals a 7.26 ppm and 2.50 ppm o p o on spec a and 77.0 ppm and 39.5 ppm o ca bon
spec a, espec i ely.
I adia ions we e ca ied ou in a c osslinke supplied by Ul a-Viole P oduc s (Upland, CA,
USA) equipped wi h wo se s o 5 x 8 wa s lamps wi h emission maxima a 354 nm and 254
nm.
UV expe imen s we e pe o med in a Pe kin Elme Lambda 35 UV/Vis spec ome e
(Wal ham, MA, USA). Abso bance o he hin ilms was measu ed om 450 o 210 nm.
Raman spec oscopy measu emen s we e ca ied ou by a Renishaw inVia Lase mic o-
Raman Spec ome e (Wo on-unde -Edge, UK). A lase beam wi h wa eleng h o 785 nm
se ed as he exci a ion ligh . The es ing a ea on he ilm was abou 1 µm2.
The he mal ansi ions o he samples we e analyzed by DSC on a Me le Toledo DSC 822e
calo ime e (Schwe zenbach, Swi ze land) equipped wi h a liquid ni ogen accesso y. Disc
samples cu om ilms weighing app oxima ely 6 mg we e sealed in aluminium pans.
Samples we e hea ed, om 25 °C o 120 °C a a a e o 10 °C min−1, cooled o -90 °C a he
maximum cooling a e o he ins umen , main ained o 10 minu es a his empe a u e and
e-hea ed om −90 °C o 120 °C a a a e o 10 °C min−1. Glass ansi ion empe a u es (Tg)
we e aken as he midpoin o he ansi ion.
Tensile p ope ies we e measu ed in a MTS Syne gie 200 es ing machine (Eden P ai ie, MN,
USA) equipped wi h a 100 N load cell. Type 4 dumbbell es pieces (acco ding o ISO 37)
we e cu om he samples. A c oss-head speed o 5 mm min-1 was used. S ain was measu ed
om c oss-head sepa a ion and e e ed o 10 mm ini ial leng h. A minimum o 5 samples
we e es ed o each ma e ial.
Syn hesis o 2,2-bis(hyd oxyme hyl)p opiona e o 7-hyd oxye hoxy-4-me hyl-couma in
(DHEOMC diol)
6
The syn hesis o his couma in diol has al eady been epo ed by ou g oup.[32] I s s uc u e
can be seen in Figu e 2.
Figu e 2. Chemical s uc u e o he monome DHEOMC diol.
Syn hesis o 2,2-bis(hyd oxyme hyl)p opiona e o 7-hyd oxy-4-me hyl-couma in (HMC
diol)
The syn hesis o he HMC diol ollowed he same p ocedu e han he syn hesis o he
DHEOMC diol (Supplemen a y in o ma ion in e e ence 32) and i is shown in Figu e 3.
De ails on he syn hesis and cha ac e iza ion can be ound in he Supplemen a y Da a ile.
Figu e 3. Syn hesis p ocedu e o HMC diol
7
The chemical s uc u e o he HMC diol was con i med by nuclea magne ic esonance
(NMR) analysis.
Syn hesis o couma in-polycap olac one diols
Polyme iza ion was ca ied ou ollowing a gene al p ocedu e o he ing opening
polyme iza ion o -cap olac one.[34] As an example, he syn hesis o he couma in-
con aining polycap olac one diol o app oxima ely 1000 g·mol-1 molecula weigh based on
DHEOMC diol is desc ibed.
In a 25 mL ound-bo omed lask p e iously d ied, -cap olac one (CL, 78.9 mmol, 7.9 g),
DHEOMC diol (9.57 mmol, 3.22 g) and SnOc 2 (0.1% weigh espec o he monome weigh )
we e cha ged and hea ed wi h magne ic s i ing a 120 °C o 24 h. When ho , a acuum pump
was connec ed ( inal p essu e app oxima ely 100 mba ) o emo e un eac ed -cap olac one
o 2 hou s. Pump was disconnec ed and he p oduc le o cool a oom empe a u e. A solid
was ob ained wi h almos quan i a i e yield. The molecula weigh o his couma in-
con aining polycap olac one diol (PCLcoum) was calcula ed by 1H-NMR ollowing he
me hodology al eady desc ibed [32] and a alue o 1231 g·mol-1 was ob ained. Wi h his
calcula ed molecula weigh , he amoun o couma in (DHEOMC) in he couma in-con aining
polycap olac one diol (PCLcoum) is 27.3% weigh DHEOMC/weigh PCLcoum.
Syn hesis o couma in-polycap olac one polyu e hanes
The syn hesis o all polyu e hanes was ca ied ou using 1,2-dichlo oe hane as sol en , wi h
app oxima ely a 5% mola excess o diisocyana e espec o he o al mola con en o diols in
he eac ion.
As i will be discussed la e , i was no possible o p epa e a polycap olac one diol om HMC
diol, and only polyu e hanes wi h HMC diol wi hin he ha d segmen we e p epa ed. Six
polyu e hanes de i ed om HMC diol wi h 5, 10 and 15% weigh o HMC diol in he inal
polyu e hane and 1:3 o 1.1 mola a io o BD:PCL527 we e syn hesized by eac ing PCL527,
IPDI, BD and HMC diol. In Table 1, he a io o he eac an s used in he syn hesis is lis ed.
In he case o DHEOMC diol, h ee polyu e hanes we e p epa ed wi h a 10% weigh o
DHEOMC diol in he inal polyu e hane and a 1:1 mola a io o BD:PCL (PCL being
PCL527, PCLcoum o PCL527+PCLcoum) by eac ing PCL527 and/o PCLcoum, IPDI, BD
and DHEOMC diol. In hese polyu e hanes, he couma in molecules we e included in he so
segmen (PCLcoum), in he ha d segmen (DHEOMC diol) o equally dis ibu ed in bo h
8
segmen s (PCLcoum+DHEOMC diol). In Figu e 4, he h ee DHEOMC con aining
polyu e hanes wi h he loca ion o he couma in molecules wi hin he s uc u e a e
schema ically ep esen ed.
Figu e 4. Syn hesis p ocedu e o polyu e hanes wi h HEOMC wi hin he so segmen
(PU DHEOMC 10% SS), wi hin he ha d segmen (PU DHEOMC 10% HS) and equally
dis ibu ed in bo h segmen s (PU DHEOMC 5+5% SS+HS)
In Table 2, he a io o he eac an s used in he syn hesis is lis ed.
As an example, he syn hesis o he polyu e hane wi h he couma in wi hin he so segmen is
desc ibed. In a 25 mL ound-bo omed lask, 1.140 g (2.16 mmol) o PCL527, 1.83 g (1.49
mmol) o PCLcoum (con aining 0.50 g o DHEOMC), 0.332 g (3.68 mmol) o BD and 1.70 g
(7.65 mmol) o IPDI we e dissol ed in 20 mL o 1,2-dichlo oe hane. Two d ops o SnOc 2
ca alys we e added and he s i ed solu ion hea ed a 80 °C o 3 h, ollowed by 24 h s i ing
a ambien empe a u e. The esul ing polyme ic solu ion was cas ed in o a le eled glass and
he sol en e apo a ed a oom empe a u e o 48 h. Polyme ic ilms o di e en hickness
we e p epa ed om his ma e ial.
9
Table 1. Amoun s o eac an s (g) in he syn hesis o HMC diol con aining polyu e hanes
(calcula ed o 100 g o inal polyme )
POLYURETHANE
PCL527 diol
IPDI
BD
HMC diol
BD(1:3)HMC 5%
55.2
36.6
3.20
5.00
BD(1:3)HMC 10%
50.0
37.2
2.80
10.0
BD(1:3)HMC 15%
44.25
38.2
2.55
15.0
BD(1:1)HMC 5%
44.8
42.5
7.70
5.00
BD(1:1)HMC 10%
40.3
42.8
6.90
10.0
BD(1:1)HMC 15%
35.5
43.4
6.10
15.0
Table 2. Amoun s o eac an s (g) in he syn hesis o DHEOMC diol con aining
polyu e hanes (calcula ed o 100 g o inal polyme )
POLYURETHANE
PCL527
diol
PCLcoum
diol
IPDI
BD
DHEOMC
diol
PU DHEOMC 10% SS
22.8
36.6*
33.95
6.65
-
PU DHEOMC 5+5%
SS+HS
31.6
18.3**
38.3
6.8
5.00
PU DHEOMC 10% HS
40.6
-
42.5
6.9
10.0
* Con ains 10.0 g o DHEOMC diol
** Con ains 5.00 g o DHEOMC diol
Syn hesis o model polycap olac one polyu e hanes wi hou couma in
A se ies o model polyu e hanes based on PCL527, IPDI and BD we e p epa ed wi h di e en
BD:PCL527 a ios ollowing he same p ocedu e used o he couma in con aining
polyu e hanes. De ails on he syn hesis can be ound in he Supplemen a y Da a ile.
16
The esul s o he measu emen o he mechanical p ope ies in ension o he segmen ed
polyu e hanes can be ound in Table S3 in he Supplemen a y Da a ile.
Mechanical p ope ies depend mainly on he Tg o he ma e ial. When he ma e ial has a low
Tg, ensile s eng h is e y low and s ain is e y high, and when Tg is abo e ambien
empe a u e, he ma e ial eaches good ensile s eng h alues and s ain is educed. When he
ensile s eng h and ensile s ain o all polyme s a e plo ed s Tg alue, Figu es 7 and 8, i is
clea ha a ce ain Tg alue he change om a e y so ma e ial o a ough ma e ial akes
place. In he igu es, he change akes place in be ween 15 and 20 °C ( he discon inuous
e ical line ma ks he alue o 18 °C).
0
10
20
30
40
50
020 40 60 80 100
S ess / MPa
Tg / ºC
Figu e 7. Tg s ensile s ess o he segmen ed polyu e hanes: non-couma in
polyu e hanes (emp y ci cles), HMC diol de i ed polyu e hanes ( illed squa es) and
DHEOMC diol de i ed polyu e hanes (c ossed squa es)
17
0
500
1000
1500
2000
2500
3000
020 40 60 80 100
S ain / %
Tg / ºC
Figu e 8. Tg s ensile s ain o he segmen ed polyu e hanes: non-couma in
polyu e hanes (emp y ci cles), HMC diol de i ed polyu e hanes ( illed squa es) and
DHEOMC diol de i ed polyu e hanes (c ossed squa es)
This end is consis en wi h he expec ed beha io o homogeneous single-phase linea
ma e ials o which he mechanical p ope ies a e dic a ed by he igidi y o he chain ha is
de e mined by he Tg.
E ec o pho o-dime iza ion/pho o-clea age o couma in uni s in he physical p ope ies
Pho o-dime iza ion/pho o-clea age o couma in uni s
Pho o-dime iza ion/pho o-clea age o he couma in molecules we e measu ed in he
DHEOMC de i ed segmen ed polyu e hanes wi h he couma in wi hin he so segmen (PU
DHEOMC 10% SS), wi hin he ha d segmen (PU DHEOMC 10% HS) o equally dis ibu ed
be ween bo h segmen s (PU DHEOMC 5+5% SS+HS).
18
A hin polyu e hane ilm o less han 2 mic ons hickness was cas om a chlo o o m solu ion
on o he ex e nal wall o a qua z cell o s udy he eac ion kine ics o he couma in
i adia ion, and a hick polyu e hane ilm o app oxima ely 150 mic ons was cas on o a
le elled silila ed glass and used o he es o he s udies. Films we e exhaus i ely d ied
unde acuum o comple e sol en emo al. The ilms we e i adia ed wi h a se o 354 nm
lamps o p oduce couma in pho o-dime iza ion, and wi h a se o 254 nm lamps o p oduce
he pho o-clea age eac ion. The pho o- e e sibili y o he syn hesized polyu e hane was
cha ac e ized in he hin ilms by UV. In Figu e S11 in he Supplemen a y Da a ile, he UV
spec a o he pho o-dime iza ion and pho o-clea age eac ions can be seen o he polyme
PU DHEOMC 5+5% SS+HS. Du ing dime iza ion, he UV peak wi h maximum in
abso bance a 319 nm in he polyu e hane UV spec um ela ed o he conjuga ed π-sys em
dec eased due o he disappea ance o he double bond in he couma in wi h o ma ion o a
cyclobu ane ing by [2+2] cycloaddi ion ( igu e in he le side), and du ing pho o-clea age
( igu e in he igh side), double bond es o ed and abso p ion peak wi h he maximum a 319
nm eco e ed.
No signi ican di e ences in pho o-dime iza ion/pho oclea age we e ound in be ween he
couma in-con aining polyu e hanes. The kine ics was simila i espec i e o he loca ion o
he couma in molecules. When he pho o-dime iza ion/pho o-clea age cycles we e epea ed a
he op imum imes ob ained (90 minu es o pho o-dime iza ion and 90 seconds o pho o-
clea age), Figu e S12 in he Supplemen a y Da a ile, a ce ain hys e esis was ound. Pho o-
con e sion and pho o-clea age los e iciency om cycle o cycle, as al eady ound by o he
au ho s and was a ibu ed o he equilib ium be ween he dime and clea ed
moie ies.[11,19,21,24,25] and o he o ma ion o i e e sible s uc u es.[20] I can be no ed
ha he loss o e iciency was qui e signi ican o pho o-clea age and i was much lowe o
pho o-dime iza ion, as al eady obse ed by o he au ho s.[21,37] We ha e ound he same
beha io o o he polycap olac one based polyu e hanes con aining couma in uni s.[30,32]
Pho o-dime iza ion/pho o-clea age con e sions in he hick ilms could no be measu ed by
UV due o sa u a ion, and Raman spec oscopy was used.[20] I has al eady been p o ed o
simila polycap olac one based polyu e hanes con aining couma in uni s ha con e sion
measu ed by UV and by Raman is he same.[30] Quan i ica ion was done by a ioing he peak
ela ed o he double bond a 1617 cm-1 and he peak a 1442 cm-1 ela ed o me hylene
g oups.[32] Pho o-dime iza ion con e sion a e 240 minu es i adia ion a 354 nm was
app oxima ely 75% o he h ee polyu e hanes, con e sion simila o he con e sion ob ained
o a linea polyu e hane wi hou chain ex ende ;[32] a e 10 minu es i adia ion a 254 nm
19
dime iza ion con e sion lowe ed o app oxima ely 50% o he h ee polyu e hanes, hus
pho o-clea age was no e y e icien a he expe imen al condi ions used; and a e 240
minu es i adia ion a 354 nm, pho o-dime iza ion con e sion inc eased again o 71-74%,
almos he alue o he i s i adia ion. As o he hin ilms, he kine ics o
pho odime iza ion/pho oclea age is simila o he h ee polyu e hanes in hick ilms and
again no signi ican di e ences a e ound due o he loca ion o he couma in molecules
wi hin one segmen o he o he .
E ec on he he mal p ope ies
A e i adia ion, a single Tg was again ob ained. In able 4, he Tg alues o he h ee
segmen ed polyu e hanes a e consecu i e i adia ion a 354 nm, 254 nm and 354 nm a e
shown.
Table 4. Tg alue o he DHEOMC diol con aining polyu e hanes a e i adia ion a
354 nm, 354 nm + 254 nm and 354 nm + 254 nm + 354 nm
Tg / °C
POLYURETHANE
Non-
i adia ed
I adia ed
a 354 nm
I adia ed a 354
nm + 254 nm
I adia ed a 354 nm
+254 nm + 354 nm
PU DHEOMC 10% SS
1.1
(0)
4.9
(77)
4.1
(51)
5.1
(73)
PU DHEOMC 5+5%
SS+HS
14.6
(0)
20.7
(73)
15.8
(51)
20.8
(71)
PU DHEOMC 10% HS
20.0
(0)
24.2
(75)
23.8
(46)
25.1
(74)
In pa en hesis, pho o-dime iza ion con e sions (in %) measu ed by Raman
C osslinking p oduced by he dime iza ion o he couma in uni s inc eased he Tg alue o all
he segmen ed polyu e hanes, bu he inc ease was ela i ely low (6.1 °C a mos ) aking in o
accoun ha app oxima ely 75% o he couma in uni s ha e eac ed. Pho o-clea age a 254
nm educed Tg as a consequence o he educ ion o c osslinking, and e-i adia ion a 354 nm
inc eased again Tg due o he inc ease in c osslinking, eaching almos he same alue
ob ained a e he i s pho o-dime iza ion eac ion. Al hough in he second i adia ion a 354
nm he con e sion eached o dime iza ion was sligh ly lowe espec o he i s i adia ion,
he Tg alue ob ained was sys ema ically sligh ly highe . This could be explained i i is
20
assumed ha he seconda y eac ions leading o he i e e sible s uc u es ha limi he pho o-
clea age con e sion p oduce some ex a c osslinking. F om he alues in Table 4, i can be
deduced ha polyu e hane wi h he couma in uni s wi hin he so segmen PU DHEOMC
10% SS will emain a so ma e ial because Tg is always well below ambien empe a u e,
polyu e hane wi h he couma in uni s wi hin he ha d segmen PU DHEOMC 10% HS will
emain a ela i ely igid ma e ial because Tg is always abo e he c i ical alue ep esen ed in
Figu es 6 and 7, and polyu e hane wi h he couma in uni s wi hin bo h segmen s PU
DHEOMC 5+5% SS+HS has a Tg below he limi ha goes jus abo e he limi a e pho o-
dime iza ion hus will be a so ma e ial ha could inc ease i s igidi y signi ican ly.
E ec on he mechanical p ope ies
The non-i adia ed ma e ial was soluble in chlo o o m whe eas he i adia ed ma e ials we e
only swelled in chlo o o m, showing he c osslinking p oduced by couma in dime iza ion. .
Table 5. Mechanical p ope ies o he DHEOMC diol con aining polyu e hanes a e
i adia ion a 354 nm, 354 nm + 254 nm and 354 nm + 254 nm + 354 nm
S ess / MPa
S ain / %
Tensile Toughness / kJ·m-3
POLYURETHANE
Non-
i adia ed
I adia ed
a 354 nm
I adia ed a 354
nm + 254 nm
I adia ed a 354 nm
+254 nm + 354 nm
PU DHEOMC 10% SS
0.64 ± 0.11
>2500
≈ 10 ± 3
53 ± 11
1190 ± 110
148 ± 18
37 ± 8
1320 ± 80
134 ± 19
51 ± 10
1240 ± 120
160 ± 20
PU DHEOMC 5+5%
SS+HS
1.1 ± 0.3
2500 ± 600
19 ± 3
30 ± 3
1040 ± 50
111 ± 13
29 ± 3
1330 ± 20
120 ± 10
29 ± 6
1180 ± 120
119 ± 7
PU DHEOMC 10% HS
17 ± 2
580 ± 80
59 ± 12
54 ± 3
700 ± 50
210 ± 20
33 ± 4
530 ± 140
120 ± 30
43 ± 5
600 ± 200
160 ± 60
As i can be seen on Table 5, non-i adia ed PU DHEOMC 10% SS and PU DHEOMC 5+5%
SS+HS, wi h Tg alues below 15 °C, we e so and p esen ed e y low mechanical p ope ies.
Non-i adia ed PU DHEOMC 10% HS, wi h a Tg alue o 20.0 °C was mo e igid and showed
good mechanical p ope ies. C osslinking due o pho o-dime iza ion p oduced ough ma e ials
(see Figu es 9 and 10 and Figu e S13 in he Supplemen a y Da a ile), elas ome ic-like in he
21
case o he so e polyu e hanes. This imp o emen on he mechanical p ope ies canno be
due o he inc ease in he Tg ha is e y limi ed.
0
10
20
30
40
50
60
0500 1000 1500
Non i adia ed
354 nm
354+254 nm
354+254+354 nm
S ess / MPa
S ain / %
Figu e 9. S ess-s ain cu es o he segmen ed polyu e hane wi h he couma in wi hin
he so segmen (PU DHEOMC 10% SS) be o e i adia ion ( hin con inuous line), a e
i adia ion a 354 nm ( hick con inuous line), a e i adia ion a 354+254 nm (do ed
line) and a e i adia ion a 354+254+354 nm (discon inuous line)
22
0
10
20
30
40
50
60
0 100 200 300 400 500 600 700 800
Non i adia ed
354 nm
354+254 nm
354+254+354 nm
S ess / MPa
S ain / %
Figu e 10. S ess-s ain cu es o he segmen ed polyu e hane wi h he couma in
wi hin he ha d segmen (PU DHEOMC 10% HS) be o e i adia ion ( hin con inuous
line), a e i adia ion a 354 nm ( hick con inuous line), a e i adia ion a 354+254 nm
(do ed line) and a e i adia ion a 354+254+354 nm (discon inuous line)
The inc ease in mechanical p ope ies due o couma in dime iza ion (see Table 5) was
ou s anding, especially o he polyu e hane wi h he couma in wi hin he so segmen , PU
DHEOMC 10% SS, ha inc eased i s ensile s eng h by a ac o o 82, om 0.64 o 53 MPa,
and i s ensile oughness by a ac o o app oxima ely 15. Fo he polyme wi h he couma in
wi hin he ha d segmen , PU DHEOMC 10% HS, ensile s eng h and ensile ougness
inc eased app oxima ely h ee- old, and o he polyme wi h he couma in wi hin bo h
23
segmen s, PU DHEOMC 5+5% SS+HS, ensile s eng h inc eased by a ac o o 27 and
ensile oughness by a ac o o app oxima ely 6. And in all polyu e hanes, ensile s ain
inc ease was achie ed main aining a high ensile s ain, 700 o 1190 %. These excellen
mechanical p ope ies o he dime ized ma e ials a e much be e han he p ope ies
desc ibed in li e a u e o any couma in-based polyme . P ope ies o couma in con aining
polyme s based on PEG [19,20] o silicone [26] wi h a couma in con en highe han 10%
weigh and con e sion on he dime iza ion eac ion highe han 77% eached a maximum
alue o ensile s ess o 3.6 MPa and 3.8 MPa espec i ely. Polyu e hane dispe sions based
on PPG diol, IPDI, BD and a couma in diol, wi h 10% weigh o couma in, eached a
maximum o 2 MPa ensile s eng h.[37] Couma in-con aining polyu e hanes based on
polycap olac one p e iously desc ibed by ou g oup,[30,32] wi h a 10% weigh o couma in
con en in he polyme s, eached ensile s ess alues o 5.4 MPa o he b anched ma e ials
and 8 MPa o he linea ma e ial, and ecen ly desc ibed polyu e hanes based on PCL530 o
PCL2000, HDI and DHEOMC diol as chain ex ende , ga e a maximum ensile s eng h o
app oxima ely 43 MPa o PCL530 wi h a 15% weigh con en o couma in,[38] s ill below
he alues achie ed by wo o he new segmen ed polyu e hanes p esen ed he e. The so
elas ome ic polyu e hane wi h he couma in wi hin he so segmen , PU DHEOMC 10% SS,
has e en be e mechanical p ope ies han un illed c osslinked na u al ubbe , ha p esen s
ensile s ess alues up o app oxima ely 30 MPa wi h ensile s ain alues up o
app oxima ely 900%.[39,40] F om hese esul s i is di icul o s a e i he loca ion o he
couma in wi hin one segmen o he o he is ad an ageous. Due o he di e ence in ha d
segmen con en o he polyu e hanes he mechanical p ope ies o he non i adia ed ma e ials
a e e y di e en . I would be necessa y o p epa e a polyu e hane wi h he same ha d
segmen con en han PU DHEOMC 10% HS bu wi h he couma in wi hin he so segmen
o a polyu e hane wi h he same ha d segmen con en han PU DHEOMC 10% SS bu wi h
he couma in wi hin he ha d segmen o di ec ly compa e he e ec o he loca ion o he
couma in. Wha is ue is ha despi e he loca ion o he couma in molecules, he i adia ed
ma e ials ha e an ou s anding imp o emen in he mechanical p ope ies p oduced by he
chemical c osslinking.
Fo all he i adia ed b anched ma e ials, when i adia ed a 254 nm mechanical p ope ies
dec eased as a consequence o pho o-clea age o couma in uni s, which dec eased he
c osslink densi y o he ma e ial. Howe e he dime iza ion e iciency a he expe imen al
condi ions used was limi ed as shown by Raman measu emen s (dime iza ion con e sion
dec eased om app oxima ely 75% o 50%) hus he mechanical p ope ies a e pho o-
24
clea age we e s ill good and a om he ini ial p ope ies o he non-i adia ed ma e ials. Re-
i adia ion a 354 nm inc eased again he c osslink densi y by pho o-dime iza ion o couma in
uni s and mechanical p ope ies eco e ed.
CONCLUSIONS
Two couma in diols we e used as ini ia o s in he ing opening polyme iza ion o ε-
cap olac one o ob ain sho chain couma in-con aining polycap olac one diols. The
couma in diol wi h alipha ic-a oma ic es e g oup, HMC diol, was no s able in he
polyme iza ion condi ions and p oduced b anched and mono- unc ional species
whe eas he couma in diol wi h alipha ic es e g oup, DHEOMC diol, p oduced
polycap olac one diols wi h he expec ed s uc u e.
Th ee linea segmen ed polyu e hanes wi h 10% weigh couma in molecules wi hin he
so segmen , wi hin he ha d segmen and equally dis ibu ed be ween bo h segmen s,
we e success ully p epa ed wi h high molecula weigh . These polyu e hanes, based on
sho chain PCL, sho chain couma in-con aining PCL, isopho one diisocyana e,
bu anediol and DHEOMC diol, p esen ed an amo phous homogeneous single-phase
mo phology wi h a single T
g
. Mechanical p ope ies o he non-i adia ed
polyu e hanes depended mainly on he T
g
alue hus he wo polyu e hanes wi h a T
g
below 20 °C we e so and weak and he polyu e hane wi h a T
g
o 20 °C was mo e
igid wi h good ensile s ess and high ensile s ain.
Pho o-dime iza ion o he couma in molecules by i adia ion a 354 nm p oduced c osslinked
ma e ials and pho o-clea age a 254 nm dec eased c osslinking. E iciency was los om
pho o-dime iza ion/pho o-clea age cycle o cycle, mo e signi ican ly in he pho o-clea age
han in he pho o-dime iza ion. No signi ican di e ence in he kine ics o pho o-
dime iza ion/pho o-clea age due o couma in molecules loca ion was ound
Pho o-dime iza ion ans o med he weak and so linea polyu e hanes wi h he couma in
wi hin he so segmen o equally dis ibu ed be ween bo h segmen s in c osslinked ough
elas ome ic ma e ials, and inc eased almos h ee imes he ensile s eng h o he
polyu e hane wi h he couma in wi hin he ha d segmen . The mechanical p ope ies
imp o emen was due o he chemical c osslinking p oduced by pho o-dime iza ion and no o
he inc ease in Tg ha was small. Pho o-clea age dec eased he mechanical p ope ies as a
consequence o he dec ease in c osslinks and e-pho o-dime iza ion inc eased again he
25
p ope ies by es o a ion o he c osslinks. Mechanical p ope ies o he i adia ed ma e ials
we e supe io o couma in con aining ma e ials desc ibed in li e a u e.
Acknowledgemen s
The au ho s would like o hank he Minis y o Economy and Compe i i eness (MINECO)
o he inancial suppo o his wo k wi hin he amewo k o he Plan Nacional de I+D+I
h ough he esea ch p ojec s MAT2013-48059-C2 and MAT2014-52644-R and he
INNPACTO p ojec IPT-2012-0324-420000. Also, his wo k has been suppo ed by
p og amme Technology Cen es Founda ion Iñaki Goenaga and he Regional Go e nmen o
Mad id, Spain (S2013/MIT-2862).
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