Eu opean Polyme Jou nal 174 (2022) 111337
A ailable online 8 June 2022
0014-3057/© 2022 The Au ho (s). Published by Else ie L d. This is an open access a icle unde he CC BY license (h p://c ea i ecommons.o g/licenses/by/4.0/).
No el hyb id o ganic/ino ganic poly( hiou e hane) co alen
adap able ne wo ks
Fede ico Gue e o
a
, Sil ia De la Flo
b
,
*
, Xa ie Ramis
c
, Jos´
e-Ignacio San os
d
, Angels Se a
a
,
*
a
Dep . o Analy ical and O ganic Chemis y, Uni e si a Ro i a i Vi gili, C/ Ma cel⋅lí Domingo, Edi . N4., 43007 Ta agona, Spain
b
Dep . o Mechanical Enginee ing, Uni e si a Ro i a i Vi gili, A . Països Ca alans, 26, 43007 Ta agona, Spain
c
The modynamics Labo a o y, ETSEIB Uni e si a Poli `
ecnica de Ca alunya, A . Diagonal, 08028 Ba celona, Spain
d
Joxe Ma i Ko a Cen e , NMR Facili y, SGIKER-UPV/EHU, C/ Tolosa Hi ibidea, 72, 20018 Donos ia, Spain
ARTICLE INFO
Keywo ds:
Vi ime s
Poly( hiou e hane)
The mose s
POSS
Click eac ion
ABSTRACT
O ganic-ino ganic hyb id ma e ials combine he ad an ages o bo h phases: ha dness and s eng h o ino ganic
phase and elas ici y and oughness o he o ganic ma ix. In he p esen s udy, we ha e p epa ed nanocomposi es
wi h a poly( hiou e hane) polyme ic ma ix and silsesquioxane- ype s uc u es, wi h hiols as eac i e g oups
(POSS-A o POSS-B, syn hesized in di e en p essu e condi ions), looking o a co alen in e ac ion be ween bo h
phases, and good dispe sion. Due o he click beha io o he eac ion be ween he isocyana e and he hiol
g oups, highly homogeneous ma e ials a e ob ained. Bo h monome s, ca alys (dibu yl in dilau a e, DBTDL), and
he POSS p ecu so (3-me cap op opyl ime hoxysilane, MPTMS), a e comme cially a ailable, which p esen
he ad an age o being indus ially scalable. The inco po a ion o POSS leads o an inc ease in glassy and ubbe y
s o age moduli and he empe a u e o he maximum o an δ cu e. The i ime ic beha io o he poly( hio-
u e hanes) imp o ed wi h he POSS inco po a ion, ge ing lowe elaxa ion imes. Wi h a highe p opo ion o
closed cages, POSS-B leads o he mos signi ican imp o emen s. All he ma e ials p epa ed showed high
anspa ency and he ac u e o POSS modi ied ma e ials indica es an imp o ed oughness.
1. In oduc ion
In his cen u y, he need o ecycle he mose s esidues o imp o e
he sus ainabili y o ou plane has led a la ge numbe o esea che s o
de elop new ma e ials wi h hese capabili ies. As ea ly as 1946,
Tobolsky e al. [1] epo ed an unexpec ed beha io o some ypes o
c oss-linked polyme s when changing he empe a u e, which allows
hese ma e ials o main ain hei mechanical and he mal pe o mance
bu acqui e he p ocessabili y o he moplas ics. These ma e ials, whose
opology can be changed by he mally ac i a ed e e sible chemical
p ocesses, a e nowadays known as co alen adap able ne wo ks (CANs)
[2,3], being i ime s included in he CANs g oup. These e e sible e-
ac ions allow he ep ocessing and ecycling o c oss-linked polyme s
and can exhibi o he cha ac e is ics as sel -healing o sel -welding
p ope ies [4].
Among he he mose s ha can be included in he g oup o CANs,
poly(u e hane)s ha e been deeply s udied [5,6]. Polyu e hanes (PUs)
a e o g ea economic impo ance since hey a e one o he mos
consumed he mose s (a ound 5 % o polyme s o al p oduc ion in he
wo ld) wi h applica ions such as coa ings, adhesi es, oams, and elas-
ome s [7,8]. Thei hiol analogous, poly( hiou e hane)s o poly( hio-
ca bama e)s (PTUs), can p esen se e al ad an ages o e hem. Fo
example, hey can be p epa ed by a click- eac ion be ween isocyana es
and hiols, wi h high con e sions and wi hou by-p oduc s as allopha-
na es, o med du ing PU p epa a ion, c ea ing homogeneous ne wo ks
[9]. In addi ion, poly( hiou e hane)s a e biocompa ible and ha e
excellen op ical p ope ies [10,11]. Recen ly, we ha e de eloped poly
( hiou e hane) ma e ials wi h i ime -like p ope ies and demons a ed
hei easiness o ecycling and eshaping [12,13,14]. CANs based on
PTUs ha e also been epo ed by o he esea ch eams in low T
g
c oss-
linked ma e ials [15,16].
Hyb id o ganic–ino ganic ma e ials we e in oduced as one o he
s a egies o imp o e mechanical p ope ies and ob ain new high-
pe o mance polyme ic ma e ials. Hyb id ma e ials p esen a syne -
gism ha mee s he ad an ages o bo h o ganic and ino ganic phases:
ha dness and s eng h o ino ganic phase, and elas ici y and oughness
o he o ganic ma ix [17]. The e a e wo di e en ways o p epa ing
his ype o ma e ial. The i s one is h ough he sol–gel p ocess, which
* Co esponding au ho s.
E-mail add esses: [email p o ec ed] (S. De la Flo ), [email p o ec ed] (A. Se a).
Con en s lis s a ailable a ScienceDi ec
Eu opean Polyme Jou nal
jou nal homepage: www.else ie .com/loca e/eu opolj
h ps://doi.o g/10.1016/j.eu polymj.2022.111337
Recei ed 24 Ma ch 2022; Recei ed in e ised o m 2 June 2022; Accep ed 5 June 2022
Eu opean Polyme Jou nal 174 (2022) 111337
2
allows he in-si u o ma ion o he ino ganic phase by he so-called
bo om-up app oach [18,19,20]. The second sys em is he addi ion o
nano blocks o he ma ix o he ini ial o mula ion [21], also known as
he op-down app oach. Ino ganic nanoscale building blocks include
g aphene, nano ubes, laye ed silica es, me al nanopa icles, e c., among
which silica s uc u es and silsesquioxanes (POSS) a e iewed as one o
he mos exci ing nano ille s [22]. I nano blocks ha e eac i e g oups,
hey can become co alen ly linked o he polyme ic ma ix, which helps
o imp o e he dispe sion o hese s uc u es and inc ease he in e phase
in e ac ion, imp o ing some cha ac e is ics o he nanocomposi es,
especially hei mechanical pe o mance. Because o he nanoscale di-
mensions o POSS and se e al silica s uc u es, he ligh sca e ing o
homogeneous ma e ials can be a oided, and he op ical anspa en
nanocomposi e ma e ials a e sui able o op ical applica ions. The
addi ion o nano blocks o eac i e o mula ions is much easie han he
in-si u sol–gel p ocess since in he la e , small amoun s o wa e a e
needed o pe o m he eac ion, and alcohol molecules a e always
o med, which some imes leads o he appea ance o bubbles in he
he mose . In addi ion, hyd olyzable monome s like isocyana es can
lead o undesi able side eac ions i wa e is added o he ini ial
o mula ion.
In he p esen s udy, we ha e in es iga ed he e ec o ein o cing
poly( hiou e hane) CANs wi h hiol- unc ionalized silica nano-
s uc u es. The aim is o achie e a good dispe sion o he ino ganic
s uc u es in he polyme ic ma ix while imp o ing he momechanical
cha ac e is ics. The e o e, hiol-isocyana e o mula ions wi h inc easing
amoun s o hiol e mina ed ino ganic SiO
2
s uc u es ha e been cu ed,
and he cu ing p ocess has been ollowed by calo ime ic and FTIR
s udies. The o mula ions a e o med by hexame hylene diisocyana e
(HDI), he hiol- unc ionalized silica nanos uc u e (named POSS), and
ime hylolp opane is(3-me cap o p opiona e) (S3) in s oichiome ic
isocyana e/ hiol a io, using dibu yl in dilau a e (DBTDL) as he ca a-
lys . We ha e syn hesized wo di e en nanosilica s uc u es by
condensa ion o 3-me cap op opyl ime hoxysilane (MPTMS) in
ace one/acidic wa e solu ions a a mosphe ic p essu e (POSS-A) and
unde au ogenic p essu e (POSS-B). Bo h oligome ic silica s uc u es
ha e hiols as eac i e g oups, bu he use o p essu e a o s he o -
ma ion o a highe p opo ion o POSS cages, and he e o e, he silica
ein o cemen s ha e di e en mo phology.
Va ious a icles desc ibe he beha io o silica- ein o ced elas o-
me ic CANs. Leg and e al. [23] epo ed he e ec o eac i e and non-
eac i e silica nanopa icles in epoxy composi es. They obse ed an
inc eased modulus in he glassy and ubbe y s a e bu a slowdown in
s ess elaxa ion. Su ace exchangeable bonds speed up he elaxa ion o
composi es compa ed o non unc ionalized ille and allow be e
dispe sion in he ma ix. Ba abano a e al. [24] demons a ed ha silica
nanopa icles enhance he welding abili y o epoxy-anhyd ide i ime s
and inc ease he opology eezing empe a u es. Yang e al. [25] added
epoxy unc ionalized POSS o an epoxy-acid o mula ion. The i ime ic
composi es imp o ed hei mechanical cha ac e is ics compa ed wi h
he i gin ma e ial and we e easily ecycled. Howe e , hey elaxed he
s ess mo e slowly. To kelson and co. [26] epo ed elas ome ic
ep ocessable poly(hyd oxyu e hane) composi es. Whe eas when non-
eac i e silica nanopa icles a e used, he ma e ial is able o eco e
i s c oss-link densi y comple ely a e a ep ocessing s ep. Con a ily,
unc ionalized nanopa icles wi h g oups ha can pa icipa e in dy-
namic chemis ies lead o losses in mechanical p ope ies associa ed
wi h he c oss-link densi y a wo king empe a u es, along wi h as e
a es and lowe appa en ac i a ion ene gies o s ess elaxa ion a
highe empe a u es. Elas ome ic i ime s wi h mechanical obus ness,
malleabili y, and ecyclabili y we e desc ibed by Guo e al. [27] based
on he e ec o su ace silanol moie ies. Silica played he ole o ein-
o cemen and c oss-linke o endow he ne wo ks wi h chemical and
mechanical obus ness. Mo eo e , hese pe manen ne wo ks can
eshu le he opological s uc u e upon empe a u e-induced ans-
oxyalkyla ion eac ions in he elas ome -silica in e phase.
As a as we know, he p esen s udy is he i s o add ess he ole o
wo di e en oligome ic silica s uc u es, wi h mo e o less con en in
POSS boxes, as nano ille s in he i ime ic-like beha io o poly( hio-
u e hane)s wi h high T
g
and excellen cha ac e is ics as he mose ing
ma e ials. The nanocomposi es ob ained on a ying he p opo ion o
bo h ypes o hiol- unc ionalized silica nano ille s ha e been cha ac-
e ized om he he mal and mechanical poin o iew and he elaxa-
ion beha io s udied by he momechanical analysis.
2. Expe imen al pa
2.1. Ma e ials
3-Me cap op opyl ime hoxysilane (MPTMS) om Al a Aesa . T i-
me hylolp opane is(3-me cap o p opiona e) (S3), hexame hylene dii-
socyana e (HDI), and dibu yl in dilau a e (DBTDL) om Sigma-Ald ich.
Hyd ochlo ic acid, ace one, and chlo o o m om Scha lab. All he
p oduc s we e used as ecei ed.
2.2. P epa a ion o oc a hiol silsesquioxane (POSS)
2.2.1. A a mosphe ic p essu e (POSS-A)
Oc a hiol silsesquioxane (POSS-SH) was p epa ed acco ding o a
epo ed me hodology [28] 13.4 g (68 mmol) o MPTMS p ecu so and
100 mL o ace one we e placed in a lask equipped wi h e lux and a
magne ic s i e . Then, 17.3 mL o conc. hyd ochlo ic acid and 21 mL o
deionized wa e we e added. The mola a io HCl:MPTMS was 3:1. A e
48 h a e lux, a whi e solid was o med. The solid was washed wi h cold
ace one se e al imes and d ied a 60 ◦C o e nigh . The esul ing
p oduc was a whi e powde wi h a 92 % o yield. This whi e powde was
g ound and sie ed h ough a 0.05 mm sie e.
2.2.2. A au ogenic p essu e (POSS-B)
The same mix u e as in Sec ion 2.2.1 was eac ed in a 150 mL
au ocla e eac o , and a e 48 h a 90 ◦C, an o ange solu ion was
o med. This solu ion was added o cold deionized wa e , o ming a
yellowish p ecipi a e. The p ecipi a e was sepa a ed by cen i uga ion
(2000 pm o 10 min). Then, i was sol ed again in ace one, d ied using
anhyd ous magnesium sul a e, il e ed, and he sol en was elimina ed
using educed p essu e. The p oduc was an o ange oil wi h a 36 % o
yield.
2.3. P epa a ion o he o mula ions
Fo mula ions we e p epa ed by mixing s oichiome ic amoun s o
isocyana e and hiol g oups, and he amoun o POSS was calcula ed in
pe cen age in weigh o e he mass o S3. Fi s ly, POSS and S3 a e
mixed, and hen HDI is added and s i ed. Finally, he co esponding
amoun o DBTDL is added. Due o he ca alys ’s eac i i y, e en a oom
empe a u e, o mula ions canno be s o ed o a long ime and we e
always main ained a cold. The composi ion o he o mula ions es ed is
de ailed in Table 1. To 1.58 g (9.4 mmol) o HDI 0.025 g (0.04 mmol) o
DBTDL we e added in all o mula ions.
2.4. Sample p epa a ion
The samples we e p epa ed by pou ing he o mula ions on Pe i
dishes co e ed wi h adhesi e Te lon o a oid s icking o he glass. The
o mula ions we e hea ed a 140 ◦C o 30 min o ob ain a lexible
ma e ial able o be emo ed om he mold, and ully cu ed in a ho -
p ess a 170 ◦C o 60 min unde a p essu e o 15 MPa. The cu ed
samples we e die-cu o ob ain ec angula specimens o 20 ×5 ×0.5
mm
3
.
F. Gue e o e al.
Eu opean Polyme Jou nal 174 (2022) 111337
3
2.5. Cha ac e iza ion echniques
Solid-s a e
29
Si NMR spec a (
29
Si CPMAS-NMR) we e eco ded a
25 ◦C o he syn hesized POSS A and B on a B uke Ad ance III 400 MHz
a a equency o 79.5 MHz on a 4 mm MAS DVT TRIPLE Resonance HYX
p obe. NMR spec a we e ob ained wi h 4000 scans using he ollowing
pa ame e s: o o spin a e 10000 Hz, ecycling ime 5 s, con ac ime
2.0 ms, and acquisi ion ime 43 ms. Exponen ial apodiza ion wi h a line
b oadening 30 Hz, FT and manual phasing, and baseline co ec ion was
used when p ocessing he da a.
The he mal s abili y o he cu ed samples was e alua ed by he -
mog a ime ic analysis (TGA), using a Me le TGA 2 STAR Sys em
he mo-balance. All expe imen s we e pe o med unde syn he ic ai
( low 50 mL/min). Pieces o 10–15 mg cu ed samples we e deg aded
be ween 30 and 600 ◦C a a hea ing a e o 10 ◦C/min.
FTIR spec a we e eco ded wi h a spec ome e Jasco FT/IR 6700,
wi h a esolu ion o 4 cm
−1
, in an in e al om 650 o 4000 cm
−1,
and
32 scans o each spec um. The spec ome e was equipped wi h an
accesso y Specac Golden Ga e ATR Tecknok oma. All spec a we e
egis e ed a oom empe a u e.
The iscoelas ic and he momechanical p ope ies we e e alua ed
wi h a DMA Q800 analyze om TA Ins umen s and using a ilm ension
clamp. The dependence o an δ and s o age modulus on he empe a u e
was in es iga ed in he ini ial ma e ials and a e se e al s ess e-
laxa ions expe imen s. The samples we e es ed a a hea ing a e o 2 ◦C/
min om −25 o 125 ◦C, wi h a equency o 1 Hz and 0.1 % o s ain.
Tensile s ess elaxa ion es s we e conduc ed using a ilm ension clamp
on samples wi h he same dimensions as p e iously de ined. The sam-
ples we e equilib a ed a 165 ◦C and le a his empe a u e o 5 min.
Then, a cons an s ain o 1.5 % ( o ensu e he ma e ials a e wi hin he
linea ange) was applied, and he consequen s ess le el was measu ed
as a unc ion o ime o 90 min. Then, he empe a u e was inc eased o
5 ◦C, and he p ocess was epea ed un il a inal empe a u e o 195 ◦C
was eached. Relaxa ion s ess
σ
( ) was no malized by he ini ial s ess
(
σ
o
), and he elaxa ion ime (
τ
) was de e mined as he ime necessa y o
elax 0.37⋅
σ
o
.
Wi h he elaxa ion imes ob ained a each empe a u e, he ac i a-
ion ene gy alues, E
a
, we e calcula ed using an A henius- ype
equa ion:
ln(
τ
) = Ea
RT −ln A(1)
Whe e
τ
is he ime needed o a ain a s ess- elaxa ion alue
(0.37
σ
0
), A is a p e-exponen ial ac o , and R is he gas cons an . The
empe a u e o opology eezing (T
) was ob ained om he A henius
ela ion as he empe a u e a which he ma e ial eaches a iscosi y o
10
12
Pa⋅s. Using Maxwell’s ela ion and E’ de e mined om DMA
(assuming E’ is ela i ely in a ian in he ubbe y s a e),
τ
* was de e -
mined o each sample. The A henius ela ionship was hen ex apo-
la ed o he co esponding alue o
τ
* o de e mine T
o each sample.
En i onmen al scanning elec on mic oscopy (ESEM) was used o
examine he su aces o he b oken ma e ials p epa ed. A Quan a 600
en i onmen al scanning elec on mic oscopy (FEI Company, Hillsbo o,
OR, USA) allows collec ing mic og aphs a 10–20 kV and low acuum
mode wi hou he need o coa he samples.
3. Resul s and discussion
3.1. P epa a ion and cha ac e iza ion o hiol- unc ionalized silica
nanos uc u es
Se e al au ho s epo ed he addi ion o POSS (silsesquioxane)
s uc u es as nano blocks o ein o ce he mose s [29]. POSS is a h ee-
dimensional nanos uc u e wi h he gene ic o mula {RSiO
3/2
}
n
, whe e
R is an o ganic moie y. The mos ex ended use o POSS in he mose s has
been epo ed in epoxy ma e ials. In ha case, POSS has been unc-
ionalized wi h epoxy [30], amine [31], and hyd oxyl g oups [32], and
he he mose s ob ained p esen ed imp o ed oughness, s i ness, he -
mal s abili y, and lame e a dancy. In addi ion, polyimides [33],
phenolic esins [34], and poly(u e hane)s [35,36] ha e been modi ied
by hese s uc u es o imp o e he mal and mechanical cha ac e is ics,
among o he s.
In he p esen wo k, we ha e syn hesized oligome ic s uc u es
con aining POSS cages wi h hiol g oups ha a e eac i e in on o
isocyana es p oducing hiou e hane bonds. Thus, he hiol- eac i e
g oups in he POSS nanos uc u es no only con ibu e o he misci-
bili y in he o ganic phase bu also lead o c osslinking poin s due o he
high unc ionali y o he POSS s uc u e (eigh o pe ec POSS cages).
The idealized s uc u e o he hiol- unc ionalized POSS syn hesized in
his wo k is depic ed in Scheme 1.
The p epa a ion o POSS de i a i es can be summa ized in a wo-
s ep p ocess: he i s one is he hyd olysis o a ialkoxysilane, o m-
ing silanols, ollowed by hei condensa ion, which elimina es wa e .
Some ac o s ha mus be con olled a e he sol en , ca alys , p ecu so ,
dilu ion, ime, and empe a u e [37]. Fo ming pe ec ly closed POSS
cages is no an easy ask and usually coexis s wi h o he pa ially closed
s uc u es o e en andomly o de ed [38].
The syn hesis o he wo di e en me cap op opyl POSS (POSS-A and
POSS-B) was pe o med acco ding o he p ocedu e p e iously epo ed
[28] and explained in Sec ion 2.2. To imp o e he o ma ion o POSS
cages, POSS-B was syn hesized in an au ocla e which allows eaching a
highe empe a u e and p essu e, which p edic ably leads o a highe
hyd olysis p opo ion o alkoxysilane g oups and a be e condensa ion
Table 1
Composi ion o he o mula ions s udied in g am and he weigh pe cen age.
Fo mula ion S3 POSS HDI DBTDL
g % g % g % g %
0POSS 2.50 60.90 0.00 0 1.58 38.49 0.025 0.61
5POSS 2.38 57.98 0.12 2.92 1.58 38.49 0.025 0.61
10POSS 2.27 55.30 0.23 5.60 1.58 38.49 0.025 0.61
15POSS 2.17 52.86 0.33 8.04 1.58 38.49 0.025 0.61
Scheme 1. Idealized s uc u e o he cages o he oc a hiol POSS syn hesized.
F. Gue e o e al.
Eu opean Polyme Jou nal 174 (2022) 111337
4
o he silanols.
The cha ac e iza ion o POSS s uc u es is usually pe o med by
29
Si-
CPMAS NMR spec oscopy. As he MPTMPS p ecu so has h ee hy-
d olyzable g oups, di e en signals a ibu able o T
n
s uc u es can be
expec ed (T
0
, T
1
, T
2,
and T
3
) o isilanols o comple ely condensed
silicon s uc u es. As a gene al end, he signals appea a highe
chemical shi s on inc easing he condensa ion deg ee ( om T
0
o T
3
).
This is because cubic cage-like s uc u es educe he alence angles o Si
a oms, and he densi y o posi i e cha ge is educed. In linea s uc u es
o bigge cages, he in e nal ension is less, and consequen ly, he signal
would be high ield shi ed. The spec a in Fig. 1 show he p esence, o
POSS-A and POSS-B samples, o wo pa ially o e lapped peaks ha
co espond o wo di e en chemical en i onmen s o he silicon a oms
in POSS s uc u es.
Acco ding o he alues epo ed in he li e a u e, we assigned he
signals a −67 ppm o T
3
ha co espond o [Si(OSi)
3
R] and he signals
a −58 ppm o T
2
ha co espond o [Si(OSi)
2
R(OH)] [18,39]. The
b oadness o bo h peaks wi h a pa ial spli ing accoun s o a no well-
de ined oligome ic s uc u e. Al hough his ype o spec a is no
quan i a i e, i is e iden in he spec a he di e ences in bo h POSS
samples p epa ed by he wo di e en p ocedu es ha , in any case, lead
o a comple ely closed s uc u e. The ma e ial ob ained a au ogenic
p essu e (POSS-B) p esen s a highe a ea a io T
3
/T
2
han POSS-A ob-
ained a a mosphe ic p essu e, indica ing a mo e closed s uc u e o
POSS-B. In none o he spec a, i was possible o obse e signals a
chemical shi s in he T
1
and T
0
egion, so i can be concluded ha he
deg ee o condensa ion eached has been ela i ely high.
FTIR spec a can also p o ide in o ma ion abou he s uc u e o he
POSS ma e ials p epa ed. In Fig. 2, he FTIR spec a show some di e -
ences in he abso p ion bands a 1100 cm
−1
(s e ching o Si-O-Si in he
cage s uc u e) and a a ound 1010 cm
−1
(s e ching o he Si-O-Si bond
o silica ne wo k), being he o me mo e in ense in POSS-B [40].
In he spec um o POSS-B (au ogenic p essu e), he ela i e in ensi y
o he Si-O-Si band is highe han in he case o POSS-A (a mosphe ic
p essu e). The e o e, by his echnique, a highe p opo ion o cage
POSS s uc u es can be con i med in POSS-B han in POSS-A, as i was
obse ed by
29
Si-CPMAS NMR spec oscopy.
3.2. S udy o he cu ing p ocess
The cu ing p ocess o he o mula ions wi h he highes amoun o
bo h POSS syn hesized was ollowed by di e en ial scanning calo im-
e y (DSC) and compa ed wi h he e olu ion o he nea o mula ion.
Calo ime ic cu es a e shown in Fig. 3, and he mos ele an da a a e
p esen ed in Table 2. As we can see, he inco po a ion o POSS delays he
cu ing p ocess, inc easing he empe a u e a which he cu e eaches
he maximum. This e ec is mo e p onounced in he case o o mula ion
con aining POSS-B. F om he alues o en halpy measu ed, i is
con i med ha he co alen union be ween he ino ganic phase and he
polyme ic ma ix has aken place, a o ing he in e phase in e ac ions
and helping he dispe sion o he ino ganic ille in he PTU ma ix.
A e he cu ing p ocess, he FTIR-ATR spec a o cu ed samples o all
h ee o mula ions we e egis e ed o con i m ha he comple e cu ing
was eached. The spec a o hese samples a e shown in Fig. 4. In he
spec a, i is possible o obse e ha he abso p ion band o isocyana e
s e ching a 2250 cm
−1
has p ac ically disappea ed and he small
emaining abso p ion could be explained by he opological es ic ions
p oduced on cu ing ha hinde he eac ion be ween hiol and isocya-
na e g oups. The weakness o he hiol abso p ions does no allow o
ollow i s e olu ion. We can also obse e, ha he abso p ion bands o
hiou e hane s e ching a 1650 cm
−1
and N-H s e ching a 3330 cm
−1
ha e been o med. F om his echnique, no di e ences a e obse ed
among nea and modi ied o mula ions, con i ming ha a ully cu ed
ma e ial is ob ained and ha he di e ences obse ed by calo ime ic
s udies a e oo small o be conside ed. The main di e ences obse ed a e
Fig. 1.
29
Si-CPMAS NMR spec a o he wo POSS-A (black) and POSS-B ( ed)
syn hesized.
Fig. 2. FTIR spec a o he di e en hiol- unc ionalized POSS syn hesized.
Fig. 3. Calo ime ic cu es o nea and illed o mula ions wi h a 15 % o
POSS added.
Table 2
Main calo ime ic da a o he cu ing p ocess o nea and modi ied o mula ions.
Fo mula ion T
maxa
(◦C) ΔH
b
(J/g) ΔH
c
(kJ/eq)
Nea 131 353 76
15POSS-A 154 307 67
15POSS-B 164 330 72
a
Tempe a u e o he maximum o he cu ing exo he mic cu e.
b
En halpy eleased on cu ing by a g am o o mula ion.
c
En halpy eleased on cu ing by an equi alen o isocyana e o hiol.
F. Gue e o e al.
Eu opean Polyme Jou nal 174 (2022) 111337
5
ela ed o he O-Si-O egion wi h peaks a 1030 and 1100 cm
−1
due o
he p esence o POSS in he illed ma e ials.
3.3. The mal cha ac e iza ion o he nanocomposi es
The he mal s abili y o he ma e ials p epa ed was e alua ed by
he mog a ime y (TGA). Fig. 5 shows he i s de i a i e o he weigh
loss and he mos in e es ing da a a e p esen ed in Table 3.
As shown in Fig. 5, he deg ada ion occu s in h ee s eps, as p e i-
ously epo ed by us [13] o PTUs wi h di e en chemical s uc u es.
The addi ion o POSS o he o mula ion does no change he deg ada-
ion mechanism, and he h ee peaks (mo e o less o e lapped) a e s ill
p esen . The i s peak can be a ibu ed o he hiou e hane g oup
decomposi ion and he second peak o he β-elimina ion p ocess o he
es e g oups in he S3 s uc u e, being he peak a he highes empe -
a u e p oduced by he comple e deg ada ion o he ne wo k. F om he
able alues, we can see ha on inc easing he p opo ion o POSS in he
ma e ial he ini ial weigh loss s a s a a lowe empe a u e. This
beha io is mo e e iden in POSS-A due o he p esence o e minal
g oups in he mo e open silica ne wo k. As expec ed, he cha yield a
600 ◦C de e mined in he ai a mosphe e inc eases wi h he amoun o
silicon in he ma e ial.
3.4. Mo phological cha ac e is ics
The samples’ anspa ency was obse ed o analyze he dispe sion o
bo h POSS s uc u es in he polyme ic ma ix. Fig. 6 p esen s he
pho og aph o he nea ma e ial and wi h he highes POSS p opo ions
con i ming a p ope dispe sion.
To analyze he e ec o he addi ion o POSS in he mic os uc u e,
he ac u e su ace o he nea , 15% POSS A, and 15% POSS B we e
obse ed a e being b oken in liquid ni ogen. Fig. 7 p esen s he SEM
images aken a 800 magni ica ions. I can be seen ha he nea sample
p esen s a smoo h and uni o m su ace wi h ew signs o oughness
ypical o a b i le ac u e. Con a ily, he ac u e su aces o bo h
POSS nanocomposi es show signi ican inc eases in oughness wi h
nume ous ac u e pa hs and i e -line c ack p opaga ion lines dis ib-
u ed uni o mly, indica ing a mo e duc ile beha io . This su ace
mo phology implies ha , in POSS ma e ials, highe ene gy should be
Fig. 4. FTIR spec a o he nea cu ed ma e ial and he nanocomposi es wi h
he maximum amoun o POSS added.
Fig. 5. TGA and DTG cu es o he nea cu ed ma e ial and he nanocomposi es wi h he maximum amoun o bo h POSS added.
Table 3
Main da a ob ained om TGA e alua ion o he nea ma e ial and o he nano-
composi es p epa ed in ai a mosphe e.
Sample T
5%a
(◦C)
Residue
b
(%)
T
peak1 c
(◦C)
T
peak2c
(◦C)
T
peak3c
(◦C)
0POSS 283 2.1 301 327 443
5POSS-A 271 3.8 294 310 454
5POSS-B 282 3.3 301 330 447
10POSS-A 255 5.2 285 310 455
10POSS-B 279 4.8 302 329 454
15POSS-A 247 6.2 279 308 456
15POSS-B 276 5.7 301 330 456
a
Tempe a u e o 5% o weigh loss.
b
Cha esidue a 600 ◦C.
c
Tempe a u e o he maximum a e o deg ada ion o h ee main s eps.
Fig. 6. Pho og aphs o he nea ma e ial and wi h he highes p opo ion o
POSS-A and POSS-B.
F. Gue e o e al.
Eu opean Polyme Jou nal 174 (2022) 111337
6
consumed o he p og ess o he c acks, hus p esen ing highe
oughness.
3.5. The momechanical p ope ies o he nanocomposi es
Dynamic mechanical he mal analysis (DMTA o simply DMA) has
been pe o med o e alua e he ma e ials p epa ed and he in luence o
he POSS p opo ion on hei he momechanical p ope ies. The an δ
cu es o all he ma e ials p epa ed a e shown in Fig. 8, and he p ima y
da a ex ac ed om he DMA analysis a e collec ed in Table 4.
Looking a he an δ plo s o he nea sample and he nanocomposi es
p epa ed wi h inc easing amoun s o POSS, i can be obse ed ha he
an δ peaks shi o highe empe a u es when ising he p opo ion o
POSS in he ma e ial inc easing a ound 20 ◦C o he highes p opo ion
o POSS added and due o he highe c osslinking densi y achie ed. A
he same ime, he cu es become b oade and lowe , leading o lowe
alues o an δ and highe alues o FWHM ( ull wid h a hal
maximum), indica ing a less homogeneous ma e ial wi h lowe damping
p ope ies. I is e iden ha he p esence o POSS in he ma e ial educes
he mobili y o he polyme chains, due o he co alen bonding o he
POSS, wi h a high unc ionali y, o he ma ix. This e ec is mo e
e iden in POSS-A samples, p obably due o he mo e he e ogeneous
s uc u e o his POSS.
Conce ning he alues o he s o age modulus p esen ed in Table 4,
he inco po a ion o POSS posi i ely a ec s he s i ness o he ma e ials,
inc easing bo h he glassy and ubbe y moduli. This inc ease in s i ness
is also due o he inc ease in he c osslinking densi y, due o he co alen
inco po a ion o he POSS (wi h unc ionali y o eigh ) in o he ma ix.
In gene al, POSS-B a ec s mo e posi i ely due o i s mo e closed
s uc u e.
To de e mine he i ime ic-like cha ac e is ics and o analyze he
e ec o he p opo ion o POSS in hese nanocomposi es, he elaxa ion
beha io was e alua ed by DMA s ess elaxa ion es s a di e en
empe a u es om 170 ◦C o 190 ◦C du ing 90 min. Fig. 9 shows he
no malized s ess elaxa ion o he p epa ed ma e ials a 180 ◦C.
As obse ed in Fig. 9, he inco po a ion o POSS o he ne wo k
posi i ely a ec s he elaxa ion ime, educing i . Mo eo e , POSS-B has
a mo e signi ican e ec on he elaxa ion phenomena han POSS-A. The
same endency was obse ed in all he empe a u es es ed. As demon-
s a ed by ou esea ch eam, he elaxa ion o PTUs is due o he ans-
hioca bamoyla ion eac ion be ween hiou e hane bonds [12,13,14].
This mechanism goes h ough he decomposi ion o hiou e hanes o
isocyana e and hiol, which ins an aneously eac o o m again he
hiou e hane g oup. The e o e, he mechanism is dissocia i e, bu wi h a
elaxa ion beha io ypical o i ime s in ol ing an A henius- ype
dec ease in iscosi y as i he deg ee o c osslinking emained un-
changed. These ma e ials wi h hose cha ac e is ics can be quali ied as
i ime ic-like.
I has been desc ibed ha an inc ease in he ubbe y modulus e-
duces he elaxa ion ime because o he dec eased abili y o eac i e
g oups o di use wi hin a highe c osslinked ne wo k [41]. Howe e , in
he p esen s udy, he addi ion o POSS sho ens he elaxa ion imes
Fig. 7. SEM mic og aphs o he ac u e su aces o he nea sample and wi h he highes p opo ions o POSS es ed a 800 magni ica ions.
Fig. 8. E olu ion o an δ wi h he empe a u e o he nea ma e ial and nanocomposi es p epa ed.
Table 4
P ima y da a ob ained om DMA analysis o he nea ma e ial and o all he
nanocomposi es p epa ed.
Sample T
anδ a
(◦C) FWHM
b
(◦C) E’
glassyc
(MPa) E’
ubbe yd
(MPa)
0POSS 55 11 2087 10
5POSS-A 59 13 2120 17
5POSS-B 58 13 2195 15
10POSS-A 64 16 2203 23
10POSS-B 67 14 2380 18
15POSS-A 72 26 2295 28
15POSS-B 73 16 2637 23
a
Tempe a u e a he maximum o he an δ peak a 1 Hz.
b
Full wid h a hal maximum o he an δ peak.
c
Glassy s o age modulus de e mined by DMA a T
g
−50 ◦C.
d
Rubbe y s o age modulus de e mined by DMA a T
g
+50 ◦C.
F. Gue e o e al.
Eu opean Polyme Jou nal 174 (2022) 111337
7
while p oducing a signi ican inc ease in he ubbe y modulus. Silyl
e he me a hesis has been epo ed as a mechanism o ne wo k elaxa-
ion ca alyzed by B ¨
ons ed o Lewis acids [42]. Mo e ecen ly [43],
POSS nanocomposi es ob ained om polye hylene ha e been p epa ed,
and i was demons a ed ha hese he moplas ics could be con e ed
in o i ime s h ough he in oduc ion o POSS s uc u es and u he
c osslinking by silyl e he me a hesis ca alyzed by zinc i la e. Mo e-
o e , by measu es o e ac i e index and dielec ic p ope ies he
s uc u al change on hea ing poly(silsesquioxane) ilms has been p o ed
[40]. Thus, in ou wo k, inco po a ing silsesquioxane s uc u es can
p o ide a second mechanism o elaxa ion ha can po en ia e he ans-
hioca bamoyla ion mechanism o he hiou e hane g oups in he
o ganic ma ix sho ening he imes needed o elaxa ion.
In p e ious s udies, o he esea ch eams ha e also inco po a ed wo
di e en ypes o co alen dynamic c osslinking mechanisms [44] such
as anses e i ica ion and disul ide me a hesis [45] and ans-
ca bamoyla ion and disul ide me a hesis [46]. They obse ed a signi i-
can accele a ion o he s ess elaxa ion and a dec ease in he
empe a u e a which he i ime s a s o be malleable compa ed o a
simila ne wo k wi h only one exchange mechanism.
F om he elaxa ion s ess es s pe o med a di e en empe a u es
be ween 165 ◦C and 195 ◦C, he ime o each a elaxed s ess s a e o
σ
/
σ
o
=0.37 (
τ
0.37
) can be ex ac ed, plo ed e sus 1/T, and i ed o he
A henius ela ionship (Eq. (1)). F om he A henius equa ion and he
elaxa ion ime needed o a ain a iscosi y o 10
12
Pa⋅s, T
is also
calcula ed o each ma e ial. The main pa ame e s om he A henius
equa ion a e p esen ed in Table 5 as well as T
and
τ
0.37
a 180 ◦C o
each ma e ial.
As we can see, he e is a no iceable dec ease in he
τ
0.37
alues on
adding inc easing p opo ions o POSS, leading o he addi ion o POSS-
B o sho e imes han POSS-A. The addi ion o 15 % o POSS-B leads o
a elaxa ion a e a ound en imes as e han in he case o he nea poly
( hiou e hane) ma ix. I should be conside ed ha he amoun o hi-
ou e hane bonds in ou sys em is he same despi e he composi ion.
Howe e , he ac i a ion ene gies inc ease on adding POSS o he
o mula ion, al hough POSS-B ends lowe alues han POSS-A. The
ac i a ion ene gy in chemical exchange eac ions indica es he sensi-
i i y o he eac ion a e ( elaxa ion imes) o empe a u e. Thus, he
p esence o POSS aises he sensi i i y o hese nano compounds o
empe a u e a ia ions in he elaxa ion phenomena, inc easing his
dependence wi h inc easing he p opo ion o he ino ganic s uc u e in
he ma e ial. Mo eo e , as e elaxa ions can be achie ed by a p ope
combina ion o low E
a
and high lnA, as in POSS B nanocomposi es.
I is impo an o highligh ha in he li e a u e he e a e no e e -
ences on he e ec o he ino ganic ne wo k s uc u es in he elaxa ion
p ocess, bu i seems e iden om he esul s ha he highe p opo ion
o cages in POSS-B a o s his elaxa ion phenomenon.
Rega ding he opology eezing empe a u e (T
), i can be deduced
ha inc easing he p opo ion o POSS ba ely a ec s his pa ame e in
any POSS s uc u e. Howe e , POSS B p esen s sligh ly lowe T
alues
han POSS A, p obably due o i s mo e closed s uc u e, leading o lowe
moduli and, consequen ly, lowe elaxa ion imes, as explained be o e
[39]. In all he POSS samples, T
is well abo e T
g
, ensu ing excellen
c eep esis ance o e a wide empe a u e ange, especially a se ice
( oom) empe a u e.
In a p e ious s udy, we could p o e how on inc easing he p opo ion
o DBTDL, a no able enhancemen o he elaxa ion a e could be
obse ed [12]. As he p esen s udy aimed o de e mine he e ec o he
addi ion o POSS o a poly( hiou e ane) ma ix, we ha e only es ed
o mula ions wi h 1 ph o DBTDL since he di e ences will be mo e
p onounced. Howe e , i is o eseeable ha on inc easing he p opo ion
o DBTDL in he o mula ion he elaxa ion imes will be highly educed
in he nanocomposi es.
To con i m ha he ne wo k s uc u e emains unal e ed a e he
elaxa ion p ocess, we pe o med a he momechanical analysis o
compa e hei anδ e olu ion wi h empe a u e. Fig. 10 p esen s hese
compa isons o he nea sample and he highe p opo ion o bo h POSS
a e a elaxa ion es a 180 ◦C.
To ea i m ha no changes in he chemical ne wo k s uc u e ha e
occu ed du ing he elaxa ion phenomenon, FTIR spec a we e eco -
ded be o e and a e a elaxa ion es a 180 ◦C. Fig. 11 compa es bo h
spec a o he ma e ials wi h he highes p opo ion o POSS-A and
POSS-B. As we can see, he e a e no di e ences when compa ing hese
spec a, con i ming ha he chemical s uc u e o he ne wo k emains
unal e ed.
F om hese es s we can assu e ha he nanocomposi e ma e ials can
Fig. 9. No malized s ess elaxa ion plo s as a unc ion o ime o he di e en samples ob ained wi h POSS-A (le ) and POSS-B ( igh ) a 180
◦C.
Table 5
Main da a om DMA analysis o he nea ma e ial and o he nanocomposi es
p epa ed.
Sample
τ
0.37a
(min) E
a
(kJ/mol) lnA
2
T
b
(◦C)
0POSS 51 137 28.3 0.995 140
5POSS-A 44 162 35.1 0.997 149
5POSS-B 17 159 35.2 0.997 139
10POSS-A 37 181 40.6 0.990 151
10POSS-B 10 179 41.1 0.994 142
15POSS-A 29 187 42.5 0.993 150
15POSS-B 5 192 44.9 0.997 141
a
Time o each a alue ela i e elaxed s ess o
σ
/
σ
o
=0.37 a 180 ◦C.
b
Topology eezing empe a u e.
F. Gue e o e al.
Eu opean Polyme Jou nal 174 (2022) 111337
8
be ep ocessed wi hou impo an damage o he ne wo k s uc u e and
ha he p esence o silsequioxanes acili a es his p ocess, sho ening
he ime needed.
4. Conclusions
In he p esen s udy, hyb id o ganic–ino ganic poly( hiou e hane)
nanocomposi es we e p epa ed om a mix u e o a comme cial i hiol,
di e en p opo ions o oc a hiol unc ionalized POSS, and hexam-
e hylene diisocyana e. Two POSS de i a i es we e i s ly syn hesized by
a sol–gel p ocess pe o med a di e en condi ions: a no mal p essu e
(POSS-A), and in an au ogenic au ocla e (POSS-B).
29
Si NMR spec a
showed ha POSS-B had a highe p opo ion o closed oc ahed al cages.
The ma e ials p epa ed showed good anspa ency, con i ming he
excellen dispe sion o he ino ganic s uc u es in he polyme ic ma ix.
The p esence o POSS in he ma e ial led o an inc ease in he he -
momechanical pa ame e s (T
g
and s o age moduli), al hough he addi-
ion o POSS-A inc eases he he e ogenei y o he ma e ial, b oadening
he an δ cu e. The SEM images o ac u e su aces demons a ed ha
he addi ion o POSS makes hese nanocomposi es mo e duc ile,
inc easing hei oughness.
The addi ion o POSS leads o a signi ican ly as e elaxa ion,
Fig. 10. Compa ison o an δ e olu ion wi h empe a u e be o e and a e a elaxa ion p ocess a 180
◦C o he nea ma e ial and wi h he highe p opo ion o
bo h POSS.
Fig. 11. FTIR spec a o he nea ma e ial and he ma e ial a e elaxa ion a 180
◦C.
F. Gue e o e al.
Eu opean Polyme Jou nal 174 (2022) 111337
9
especially wi h a highe p opo ion o POSS-B, aising he sensi i i y o
empe a u e a ia ions in he elaxa ion phenomena. Con a ily,
inc easing he p opo ion o POSS ba ely a ec s he opology eezing
empe a u e in any POSS s uc u e, being T
, in all he cases, well abo e
T
g
, ensu ing excellen c eep esis ance o e a wide empe a u e ange,
especially a se ice ( oom) empe a u e. Compa ing he he mo-
mechanical and FTIR cha ac e is ics be o e and a e a elaxa ion p o-
cess a 180 ◦C, i has been con i med ha he chemical and ne wo k
s uc u es emain unal e ed.
Da a a ailabili y
The aw da a equi ed o ep oduce hese indings canno be sha ed
a his ime due o echnical limi a ions. Please, con ac us in case you
need some speci ic da a.
Decla a ion o Compe ing In e es
The au ho s decla e he ollowing inancial in e es s/pe sonal e-
la ionships which may be conside ed as po en ial compe ing in e es s:
‘Angels Se a epo s inancial suppo was p o ided by Spain Minis y
o Science and Inno a ion.’
Acknowledgmen s
This wo k is pa o he R&D p ojec s PID2020-115102RB-C21 and
PID2020-115102RB-C22 unded by MCINAEI/ 10.13039/
501100011033. We acknowledge hese g an s and he Gene ali a de
Ca alunya (2017-SGR-77 and BASE3D).
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