Disappea ance o Mel Memo y E ec wi h Comonome
Inco po a ion in Isodimo phic Random Copolyes e s
Lei e Sang oniz,*Ma yam Sa a i, An xon Ma ínez de Ila duya, Ha i z Sa don, Da io Ca allo,
and Alejand o J. Mulle *
Ci e This: Mac omolecules 2023, 56, 7879−7888
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sı Suppo ing In o ma ion
ABSTRACT: Mel memo y e ec s in polyme c ys alliza ion ha e
a ac ed much a en ion in he pas ew yea s. Al hough p og ess
has been made in unde s anding how he chemical s uc u e o
polyme s can a ec mel memo y, he e a e s ill some knowledge
gaps. In his wo k, we s udy how inco po a ing a second
comonome uni ha is pa ially included in he c ys alline uni
cell a ec s he mel memo y e ec o he majo componen in a
andom isodimo phic copolyme o he i s ime. This second
comonome uni dep esses he mel ing empe a u e o he
homopolyme , educes he c ys allini y, and dis o s he c ys alline
uni cell. Howe e , i s e ec on he s abili y o sel -nuclei and he
p oduc ion o mel memo y has no been s udied so a . To his aim, we ha e selec ed poly[(bu ylene succina e)- an-(ε-
cap olac one)] andom copolyes e s PBS- an-PCL ha a e isodimo phic, i.e., hey exhibi a pseudoeu ec ic poin . This poin
sepa a es he o ma ion o BS- ich c ys als om CL- ich c ys als as a unc ion o composi ion. The esul s e eal ha he mel
memo y e ec o hese isodimo phic copolyme s is s ongly educed wi h he inco po a ion o e en e y small amoun s o
comonome uni (i.e., 1 mola %). This indica es ha he inco po a ion o a second comonome uni in he polyme chain dis up s
he in e molecula in e ac ions p esen be ween he chain segmen s in he c ys al la ice o he majo componen and educes he
capaci y o he ma e ial o p oduce sel -nuclei. This educ ion is mo e d as ic o copolyme s in which he second comonome uni is
mos ly ejec ed om he c ys alline phase. Con a y o ole in-based copolyme s, o copolyes e s, he second comonome uni eases
he p ocess o each an iso opic mel s a e upon mel ing. This wo k e eals he impac o in oducing comonome uni s on he mel
memo y e ec in isodimo phic andom copolyes e s.
1. INTRODUCTION
Polyme s a e widely used in a ious a eas, including packaging,
he au omo i e indus y, cons uc ion, medicine, and e e yday
p oduc s like u ni u e o oys. The success o polyme s esul s
om hei e sa ili y, low densi y, easy p ocessabili y, and low
cos . Howe e , he du abili y and high esis ance o en i on-
men al ac o s ha e led o plas ic was e pollu ion. Polyme s a e
employed in single-used applica ions such as packaging, in
which hey a e exploi ed only o a sho pe iod o ime. Once
hey a e disposed, hey a e incine a ed, deposi ed in land ills,
o ecycled. Howe e , some o he plas ic was e escapes he
collec ion and so ing p ocess, leading o plas ic was e
accumula ion in he en i onmen .
1,2
Due o he g owing conce n abou plas ic was e pollu ion, in
he las decades, biodeg adable polyme s ha can be deg aded
in bioac i e en i onmen s ha e gained much a en ion. Unde
app op ia e condi ions, biodeg adable polyme s can be
con e ed in o ca bon dioxide, me hane, wa e , and biomass,
among o he subs ances.
3
One o he mos p omising
biodeg adable polyme s a e polyes e s, which can be ob ained
om enewable sou ces and a e e y e sa ile, wi h
applica ions in se e al a eas such as ibe s, ilms, o bo les.
4
Among biodeg adable polyes e s, polybu ylene succina e
(PBS) has in e es ing p ope ies, such as good chemical
esis ance, biodeg adabili y, and biocompa ibili y. I has a high
mel ing empe a u e, abo e 100 °C, high hea de lec ion
empe a u e, and can be ob ained om enewable sou ces.
4−6
Howe e , due o he high c ys allini y deg ee, i shows a b i le
beha io as has been shown by some o us.
7
One s a egy o imp o e he physical pe o mance o PBS in
o de o widen i s possible applica ions is o copolyme ize i
wi h a second comonome uni ha has complemen a y
p ope ies. This is he case o polycap olac one (PCL) ha has
in e es ing p ope ies such as biocompa ibili y, good solubili y,
Recei ed: July 12, 2023
Re ised: Augus 31, 2023
Published: Sep embe 21, 2023
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and excellen mechanical p ope ies.
8
In ac , PCL has a duc ile
beha io wi h elonga ion a b eak alues
7
abo e 100%.
The physical p ope ies o poly[(bu ylene succina e)- an-(ε-
cap olac one)] copolyme s PBS- an-PCL ha e been in ensely
s udied by some o he au ho s.
7−12
The inco po a ion o he
second comonome uni s inc eases he duc ili y o he
ma e ials. On he con a y, he elas ic modulus is educed
due o he lowe c ys allini y deg ee o he copolyme s.
7
The
copolyme s a e able o c ys allize o all composi ions showing
a educ ion o mel ing and c ys alliza ion empe a u e wi h he
inco po a ion o he second comonome uni s.
9,10
A a ce ain
composi ion, wo c ys alline phases coexis , i.e., BS- ich and
CL- ich phases. This composi ion is known as he
pseudoeu ec ic poin . The dimensions o he c ys alline uni
cell depend on he composi ion, showing a ia ions wi h he
p esence o he second comonome uni s. This beha io
co esponds o isodimo phic copolyme s in which he second
comonome uni s a e pa ially included in he c ys al la ice.
13
The inco po a ion o he second comonome uni s inc eases
he nuclea ion a e and nuclea ion densi y o he ma e ial,
al hough he sphe uli ic g ow h a e is educed.
11
I is well-known ha he he mal p ope ies o polyme s
depend on hei he mal his o y. Howe e , he e ec o he
empe a u e on he mel s a e has no been in es iga ed o
isodimo phic copolyme s. When he he mal his o y o he
polyme is comple ely emo ed by hea ing i o empe a u es
ha a e 25−30 °C highe han he mel ing empe a u e, an
iso opic mel s a e is ob ained. The polyme will c ys allize a
a s anda d c ys alliza ion empe a u e when i is cooled om
his mel s a e. Howe e , when he empe a u e is no enough
o emo e he he mal his o y, e.g., jus abo e he mel ing
empe a u e o he ma e ial, some sel -nuclei can emain.
14,15
In he subsequen cooling, he c ys alliza ion o he ma e ial
will be shi ed o highe empe a u es han he s anda d alue
since hose sel -nuclei inc ease he nuclea ion densi y, which is
p opo ional o he Tc. When he polyme is hea ed o a
empe a u e wi hin he mel ing ange, some c ys als can
su i e ha can ac as sel -seeds and could also anneal (i he
empe a u e is low enough), his esul s in a ise in he
c ys alliza ion empe a u e and in he ollowing hea ing scan,
pa o he ma e ial could mel a highe empe a u es (i
annealing ook place).
The men ioned sel -nuclei ha e a ac ed much a en ion
o e he las yea s, and hei exac na u e is s ill unde
deba e.
14,15
Acco ding o di e en ial scanning calo ime y
(DSC) expe imen s, when he empe a u e is abo e he
mel ing ange o he polyme (i.e., abo e i s end mel ing
empe a u e, whe e no mo e endo he mic hea is de ec ed) bu
below he empe a u e needed o e ase he he mal his o y, no
c ys al agmen s emain. O he echniques, o ins ance, X- ay
o op ical mic oscopy, a e no able o de ec any di e ences
be ween an iso opic mel s a e and mel s con aining sel -
nuclei. The e ec o inc easing he c ys alliza ion empe a u e
p oduced by he gene a ion o sel -nuclei has been deno ed he
mel memo y e ec .
14,15
Recen ly, he impac o he chemical s uc u e o polyme s
on mel memo y has been elucida ed in a se ies o wo ks
co e ing polyamides, polyes e s, polyca bona es, polye he s, o
polyes e s ha con ain se e al unc ional g oups.
16−19
These
s udies showed ha mel memo y is di ec ly ela ed o he
s eng h o in e molecula in e ac ions. The s onge he
in e ac ions, he mo e p onounced he mel memo y e ec ,
i.e., he inc ease o he c ys alliza ion empe a u e in
compa ison wi h he s anda d c ys alliza ion empe a u e will
expand o e a wide empe a u e ange.
16,17,19
The e ec o inco po a ing a second comonome uni on
mel memo y has been in es iga ed in he case o polyole ins.
Alamo e al. s udied polye hylene-based copolyme s.
20−24
Thei ex ensi e s udies show ha he inco po a ion o a
second comonome uni , such as bu ene, esul s in s ong mel
memo y e ec s ha do no anish e en abo e he equilib ium
mel ing empe a u e. This e ec has been ela ed o he
o ma ion o complex mel opologies due o he c ys allizable
sequence leng h selec ion du ing he c ys alliza ion p ocess.
Since he app op ia e sequence has o di use o he c ys al
g ow h on , complex mel opologies a e o med in he
p ocess. This impedes eaching an iso opic mel s a e, and
hus, highe empe a u es a e equi ed o each his s a e in
compa ison wi h he homopolyme .
20−24
Al hough he e ha e been many p e ious s udies on he mel
memo y e ec , he impac o inco po a ing a second
comonome uni ha can be pa ially inco po a ed wi hin
he c ys alline uni cell o he homopolyme has ne e been
in es iga ed, as a as he au ho s a e awa e. The wo king
hypo hesis he e is ha aking in o accoun ha he
comonome uni s dep ess he mel ing empe a u e and modi y
he c ys alline uni cell, i can modi y he he mal s abili y o
sel -nuclei and hus al e he mel memo y e ec . I is ele an
o s udy his e ec since a s onge mel memo y will equi e
highe empe a u es o emo e he he mal his o y and hus a
highe ene gy consump ion du ing p ocessing. In his wo k, we
p opose o in es iga e how small amoun s o a second
comonome uni ha can be pa ially inco po a ed wi hin
he c ys alline uni cell o he homopolyme a ec he mel
memo y e ec in poly[(bu ylene succina e)- an-(ε-cap olac-
one)] copolyme s PBS- an-PCL. This sys em has been
selec ed because PBS and PCL homopolyme s exhibi he
wides mel memo y e ec s among homopolyme s,
15
which
allows o analyze p ecisely he impac o a second comonome .
2. EXPERIMENTAL PART
2.1. Ma e ials. PBS- an-PCL copolyme s ich in BS and CL we e
syn hesized ollowing he me hod desc ibed in a p e ious wo k.
10
In
b ie , a wo-s age mel polycondensa ion eac ion was employed. Fi s ,
a anses e i ica ion/ROP eac ion was ca ied ou wi h dime hyl
succina e (DMS), 1,4-bu anediol (BS), and ε-cap olac one (CL) a
160 °C unde ni ogen o 4 h. A e his s ep, polycondensa ion was
conduc ed a 210 °C unde educed p essu e o 4 h. The chemical
s uc u e o he copolyme s ob ained is shown in Figu e 1.1H NMR
was pe o med o de e mine he composi ion and he numbe -a e age
mola mass, see Table 1.Figu e S1a,b shows 1H NMR o BS-phase
and CL-phase, espec i ely. Based on ou p e ious wo ks wi h simila
copolyme s
10,11
and he 13C NMR analysis ca ied ou on selec ed
composi ions (Figu e S2 and Table S1), he p epa ed copolyme s can
be conside ed andom in he en i e composi ion ange. A commen
abou he mola mass is included in Suppo ing In o ma ion.
2.2. Di e en ial Scanning Calo ime y. The he mal p ope ies
we e in es iga ed employing a Pe kinElme 8500 DSC connec ed o
an In acoole III. The DSC was calib a ed employing indium and in,
and he measu emen s we e pe o med unde ul apu e ni ogen low.
Figu e 1. Chemical s uc u e o PBS- an-PCL copolyme s.
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2.2.1. Noniso he mal Expe imen s. The ma e ial was hea ed o he
app op ia e empe a u e: 90 °C o CL- ich copolyme s and 150 °C
o BS- ich copolyme s. The sample was held a his empe a u e o 3
min, and hen, i was cooled o −60 °C. A e holding he sample a
−60 °C o 1 min, he sample was inally hea ed again. Hea ing and
cooling a es o 20 °C min−1we e employed.
2.2.2. Sel -Nuclea ion Expe imen s. Mel memo y e ec was
in es iga ed applying he sel -nuclea ion p ocedu e de eloped by
Fillon e al.
14,15,25
The polyme sample was i s hea ed o
empe a u es ha a e 25−30 °C abo e he end o he mel ing
empe a u e o emo e he he mal his o y. The sample was hen
cooled o −60 °C a 20 °C min−1, ob aining a s anda d c ys alline
s a e, and i was held o 1 min a −60 °C. Subsequen ly, i was hea ed
o he selec ed Ts empe a u e and kep a his empe a u e o 5 min.
A e his s ep, he sample was cooled o −60 °C and hen hea ed
again a 20 °C min−1. Wi h his p ocedu e (Figu e S3) and employing
se e al Ts empe a u es, he ma e ial can each se e al sel -nuclea ion
Domains. Those a e de e mined conside ing he c ys alliza ion
empe a u e when cooling om Ts empe a u e and he mel ing
empe a u e o a subsequen hea ing scan.
14,15,25
2.3. X- ay Di ac ion. The c ys alline s uc u e o he copolyme s
was analyzed by simul aneous wide-angle/small-angle X- ay sca e ing
(WAXS/SAXS) a he ALBA Synch o on adia ion acili y
(Ba celona, Spain). The samples we e p epa ed in DSC, emo ing
he he mal his o y and c ea ing a s anda d c ys alline s a e. Then, he
ob ained DSC pans we e measu ed in an X- ay acili y. Fo he
samples wi h a mel ing empe a u e close o oom empe a u e, he
s anda d c ys alline s a e was c ea ed in si u in a Linkam THMS600
ho s age ollowing he p ocedu e employed in he DSC. In WAXS
measu emen s, a Rayonix LX255-HS de ec o was employed (sample
o de ec o dis ance = 99.25 mm, il angle = 30.04°). Du ing SAXS
expe imen s, a Pila us 1 M de ec o was used (sample o de ec o
dis ance = 6590 mm, il angle = 0°).
3. RESULTS AND DISCUSSION
3.1. Noniso he mal DSC Expe imen s. Figu e 2 shows
he cooling and subsequen hea ing scans ob ained o PBS-
an-PCL copolyme s ich in BS and CL. Fi s , he he mal
his o y was emo ed by hea ing he ma e ial o he app op ia e
empe a u e a 20 °C min−1. The he mal p ope ies ex ac ed
om he hea ing/cooling scans o he homopolyme s and
copolyme s a e collec ed in Table S2. All o he copolyme s
ich in PCL o PBS can c ys allize and show one c ys alliza ion
peak, excep BS80CL20, which shows wo c ys alliza ion peaks.
This copolyme only o ms one c ys alline phase, as i will be
discussed in he nex sec ion (C ys alline S uc u e: X- ay
Di ac ion). Fo BS- ich copolyme s, in oducing CL como-
nome uni s b oadens he c ys alliza ion peak.
The subsequen hea ing scans (Figu e 2c,d) show ha PCL
displays only one mel ing peak, whe eas PBS shows an
exo he m ha a ises om he ec ys alliza ion o impe ec /
hinne c ys als and a bimodal mel ing peak ha p obably
co esponds o a mel ing ec ys alliza ion p ocess du ing he
hea ing scan.
10,26
The copolyme s show he same end as ha
obse ed wi h he homopolyme s: CL- ich copolyme s show
only one mel ing peak, whe eas BS- ich copolyme s show cold
c ys alliza ion and bimodal mel ing peaks.
10
Figu e 3 shows he mel ing empe a u e (Tm) and
c ys alliza ion empe a u e (Tc) as a unc ion o BS con en ,
including he esul s om p e ious s udies co e ing he en i e
composi ion ange. The esul s indica e ha he copolyme s
c ys allize unde he condi ions s udied in his wo k in he
whole composi ion ange, wi h he Tmand Tcbeing a s ong
unc ion o he composi ion o he comonome uni s. In he
plo s o Figu e 3, he cha ac e is ic pseudoeu ec ic beha io o
isodimo phic andom copolyme s can be obse ed: a educ ion
o he ansi ion empe a u es wi h he inco po a ion o a
second comonone uni eaching a minimum a an
in e media e BS con en .
10,13
In andom copolyme s, Tmand
Tcdepend on he con en and dis ibu ion o he comonome
uni s, wi h Tmbeing Tmcon olled by lamella hickness. The
second comonome uni s educe he c ys allizable chain leng h
Table 1. Composi ion and Mola Mass o he Syn hesized
Copolyme s
sample code BS eed (% mol) copolyme (% mol) Mn(g mol−1)
BS0CL100 0 0.0 31,000
BS1CL99 1 1.3 12,100
BS3CL97 3 3.1 7950
BS4CL96 4 4.0 8880
BS6CL94 6 6.2 11,300
BS12CL88 10 11.8 18,100
BS20CL80 20 20.0 5900
BS25CL75 25 25.0 8700
BS75CL25 75 75.0 12,200
BS80CL20 80 79.4 15,350
BS87CL13 90 87.1 8980
BS95CL595 94.5 12,560
BS97CL3 97 96.4 14,000
BS99CL199 98.6 14,600
BS100CL0100 100.0 32,700
Figu e 2. Cooling scans om he mel o (a) CL- ich and (b) BS- ich
copolyme s and subsequen hea ing scans o (c) CL- ich and (d) BS-
ich copolyme s a a a e o 20 °C min−1.
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when i is excluded om he c ys al la ice. Isodimo phic
copolyme s a e capable o c ys allizing in he whole
composi ion ange in uni cells ha esemble he ones o he
co esponding homopolyme s wi h a small inclusion o he
mino comonome uni s. In hese copolyme s, an equilib ium
exis s be ween exclusion and inclusion o he comonome
uni s, whe e exclusion is usually mo e impo an .
13
In ac , he
educ ion o he ansi ion empe a u es indica es ha
al hough some inco po a ion o he mino comonome uni s
occu s, he excluded amoun o comonome uni s om he
c ys alline phase is much highe han he inclusion, as has been
p o ed o simila copolyme s wi h X- ay and NMR
echniques.
27
Howe e , he amoun o inclusion depends on
how di e en he chemical s uc u es o he wo monome s
unde conside a ion a e. The mo e simila he chemical
epea ing uni s, he highe he inclusion amoun . I he
chemical s uc u es a e e y simila , he copolyme s can be
isomo phic; in ha case, o al inclusion occu s.
13
A he pseudoeu ec ic poin , wo c ys alline phases coexis ,
as e lec ed by he wo mel ing empe a u es, co esponding o
he BS- and CL- ich phases.
10,13
Those c ys alline phases can
inco po a e some uni s om he second comonome . As
shown in Figu e 3, only one Tcis ob ained a he
pseudoeu ec ic composi ion, e lec ing a coinciden c ys al-
liza ion o bo h phases.
In Figu e 3b, a line has been d awn by conside ing a simple
law o mix u es ega ding he mel ing empe a u e o
homopolyme s. This line co esponds o he comple e
inclusion o he comonome uni s; he e o e, he beha io
indica ed by his s aigh line co esponds o he end
displayed by hypo he ical isomo phic copolyme s.
13
In he
plo , we can obse e ha o CL- ich copolyme s, he e is a
signi ican de ia ion om his line since he e is a educ ion in
Tmins ead o an inc ease wi h he BS con en . This means ha
he e is a signi ican exclusion o BS uni s om he CL
c ys alline phase. Howe e , o BS- ich copolyme s, he
mel ing empe a u e does no de ia e as much om he
isomo phic line, which means ha he e should be a highe
inclusion o CL comonome uni s in he BS- ich c ys als. As i
has been epo ed in he li e a u e, small comonome s uni s
can accommoda e mo e easily in he c ys alline uni cell o
bigge monome s, so his esul could be expec ed.
Figu e 3c shows he c ys allini y deg ee calcula ed om he
no malized mel ing en halpy employing a alue o 110.3 J g−1
as he equilib ium mel ing en halpy
28
(ΔHm
0) o PBS and
139.5 J g−1 o PCL.
29
A pseudoeu ec ic beha io simila o
ha obse ed o Tmis ob ained wi h he composi ion o he
copolyme . The educ ion o Xcwi h he inco po a ion o he
second comonome uni s a ises om he exclusion o he
comonome uni s ha in e up he c ys allizable sequence
segmen .
10,13
3.2. C ys alline S uc u e: X- ay Di ac ion. The
c ys alline s uc u e o he copolyme s was s udied by
WAXS. Figu e 4 shows he WAXS pa e ns ob ained a −50
°C a e c ys allizing he samples om he mel a 20 °C/min.
The main e lec ions o BS- ich copolyme s appea a 14, 15,
and 16 nm−1and co espond o he (020), (021), and (110)
planes o he monoclinic uni cell o PBS. The esul s show
ha BS- ich copolyme s o m only BS-like c ys als.
30,31
Simila ly, CL- ich copolyme s show only CL-like c ys als
wi h p ima y e lec ions a ound 15.5 and 17.2 nm−1 ha a ise
om he (110) and (200) planes o he o ho hombic uni
cell
32−35
o PCL. As has been epo ed p e iously by some o
us,
9,10
he PBS- an-PCL copolyme s a he pseudoeu ec ic
poin show e lec ions co esponding o bo h PCL and PBS
c ys als, con i ming he exis ence o bo h c ys alline phases.
The d-spacing om WAXS pa e ns has been calcula ed by
employing B agg′s law. The (110) and (020) planes o BS-like
c ys als and (100) o he CL-like c ys als show changes in
magni ude wi h comonome con en , which esul s om he
Figu e 3. (a) C ys alliza ion empe a u e, (b) mel ing empe a u e, and (c) c ys allini y deg ee as a unc ion o BS con en . Da a om Sa a i e al.
10
has been included o compa ison pu poses.
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modi ica ions in he c ys alline uni cell size (Figu e 4c)
needed o inco po a ion o comonome uni s. These esul s
indica e ha some inclusion o comonome uni s occu s in
acco dance wi h p e ious wo ks on isodimo phic copoly-
me s.
10,13
SAXS expe imen s (Figu e 5) we e pe o med o de e mine
he long pe iod and lamella hickness o he BS- ich and CL-
ich copolyme s. A single peak is obse ed o all o he
copolyme s, which a ises om he X- ay sca e ing due o he
lamella s acks in he sample. Fo some o he samples, he peak
can no be obse ed (BS80), o he maximum is e y weak; his
could be due o he low c ys allini y deg ee o he sample o o
he ac ha he e a e no enough lamella s acks ul illing
B agg′s condi ion.
The long pe iod can be ob ained om he q alue o he
maxima o he peak. The long pe iod as a unc ion o
composi ion is shown in Figu e 5c. PBS has a long pe iod close
o 8 nm, whe eas PCL shows a la ge d* alue o 12.5 nm. Fo
BS- ich copolyme s, he inco po a ion o CL inc eases he long
pe iod since PCL has a la ge long pe iod. Also, he p esence o
BS uni s in CL- ich copolyme s inc eases sligh ly he long
pe iod. I should be conside ed ha he long pe iod depends
on he c ys allini y, so he esul s ha e o be conside ed
cau iously.
Conside ing he long pe iod and he c ys allini y deg ee
ob ained by DSC, i is possible o es ima e he c ys alline
lamella hickness by employing he equa ion lc=d*Xc. In
Figu e 5d, he lamella hickness as a unc ion o copolyme
composi ion is shown. The inco po a ion o he second
comonome uni s educes he lamella hickness. A pseudoeu-
ec ic beha io is obse ed simila o wha has been ob ained
wi h mel ing and c ys alliza ion empe a u e o he c ys allini y
deg ee.
10,13
The educ ion o he lamella hickness a ises om
excluding he comonome uni s ha de e mine he leng h o
he c ys allizable chain sequence.
3.3. Sel -Nuclea ion Expe imen s. Figu e 6 shows he
DSC cooling cu es om Ts empe a u e and pos e io hea ing
cu es ob ained a se e al sel -nuclea ion empe a u es o he
BS95CL5copolyme , as an example. When his copolyme is
cooled om sel -nuclea ion empe a u es equal o o abo e
117 °C, i c ys allizes a he same empe a u e. Thus, hea ing
he ma e ial o 117 °C o abo e makes he ma e ial lose i s
he mal his o y and achie e an iso opic mel s a e. In he
subsequen cooling, he ma e ial c ys allizes a he s anda d
c ys alliza ion empe a u e. So, a Tsequal o 117 °C o abo e,
he polyme is in Domain I o he iso opic mel Domain.
14,15
Fo Ts empe a u es below 116 °C, he polyme c ys allizes
a highe empe a u es du ing subsequen cooling compa ed o
he s anda d Tc alue. The inc ease in Tcis p opo ional o he
inc emen in he nuclea ion densi y, which a ises om he
exis ence o sel -nuclei. So, he 116−107 °C empe a u e ange
co esponds o he sel -nuclea ion Domain o Domain II.
Figu e 4. WAXS pa e ns o (a) BS- ich and (b) CL- ich copolyme s.
(c) d-Spacing o copolyme s, including da a om Sa a i e al.
10
(ci cle symbols)
Figu e 5. Lo en z-co ec ed SAXS p o iles (Iq2as a unc ion o he
sca e ing ec o ) o (a) BS- ich and (b) CL- ich copolyme s. (c)
Long pe iod and (d) c ys alline lamella hickness o he copolyme s,
including he da a co e ing he en i e composi ion and epo ed
be o e.
10
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Finally, when Tsis low enough, some c ys al agmen s a e
le ha a e able o anneal. This occu s a empe a u es equal
o 106 °C o below. When cooling om he men ioned Ts
egion an inc ease in Tcis obse ed, and in he nex hea ing
scan, a second mel ing peak appea s a highe empe a u es
due o he mel ing o annealed c ys als. This addi ional mel ing
peak ma ks he ansi ion om Domain II o Domain III. This
occu s a empe a u es equal o 106 °C o below; a his
empe a u e egion, he ma e ial is in Domain III o he
annealing and sel -nuclea ion Domain.
The esul s ob ained by applying he sel -nuclea ion
p ocedu e a e summa ized in Figu e 6c, in which a s anda d
mel ing endo he m is supe imposed wi h he c ys alliza ion
empe a u es ob ained when cooling om se e al Ts empe -
Figu e 6. (a) DSC cooling cu es ob ained om se e al Ts alues and (b) subsequen hea ing cu es o BS95CL5copolyme . (c) S anda d hea ing
endo he m supe imposed o c ys alliza ion empe a u es ob ained a se e al Ts alues. Ve ical solid lines ma k he ansi ion be ween domains,
whe eas he dashed line indica es he end o he mel ing peak.
Figu e 7. T ansi ion empe a u es be ween Domain I,Domain II, and Domain III and equilib ium mel ing empe a u es (Tm
0) o (a) CL- ich
copolyme s and (b) BS- ich copolyme s as a unc ion o he end mel ing empe a u e. (c) T ansi ion empe a u es o he Domains as a unc ion o
BS con en .
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a u es. The e ical lines indica e he empe a u e ange ha
comp ises each sel -nuclea ion Domain: A empe a u es equal
o o abo e 117 °C, he polyme is in Domain I; in he ange
116−107 °C, he ma e ial is in Domain II and inally below 106
°C in Domain III.
Mulle e al. p oposed he spli o Domain II in o 2 sub-
Domains conside ing he end o he mel ing empe -
a u e.
14,15,36
The idea behind his di ision is o dis inguish
be ween he egion in Domain II a high empe a u es (i.e.,
Domain IIa o mel memo y Domain), whe e acco ding o he
DSC da a, all c ys als a e mol en as no endo he mic hea is
de ec ed, om ha in Domain II a lowe empe a u es
(Domain IIb o sel -seeding Domain). In Domain IIb (o DIIb),
he ma e ial is no ully mol en, and he e a e some c ys al
agmen s ha beha e as excellen sel -seeds o nuclea ion.
Fo his BS95CL5copolyme , he DSC inal baseline a e
mel ing is eached a 112 °C, which means ha , abo e his
empe a u e, he e a e no c ys al agmen s ha can be
de ec ed by DSC. Thus, in he 112−116 °C empe a u e
egion, he inc emen in he c ys alliza ion empe a u e comes
om sel -nuclei, and he e o e, his egion belongs o Domain
IIa o o he mel memo y Domain. Below 112 °C, DSC esul s
indica e ha he e a e some c ys al agmen s p esen since he
baseline o he hea low has no been eached. These c ys al
agmen s a e no able o anneal, and he sample is s ill
conside ed o be in Domain II. So, his empe a u e egion
co esponds o DIIb, and he inc ease in Tca ises om he
p esence o sel -seeds, and hus,DIIb is deno ed by he sel -
seeding Domain.
14,15
The esul s co esponding o all o he copolyme s and
homopolyme s a e displayed in he Suppo ing In o ma ion
(Figu e S4). The ansi ion om DII o DIII occu s inside he
mel ing endo he m o all o he copolyme s, as could be
expec ed. Rega ding he ansi ion om DI o DII, his is
shi ed o lowe empe a u es, ge ing close o he mel ing
empe a u e as he amoun o he second comonome uni s is
inc eased. Thus, when a comonome uni is inco po a ed, i is
necessa y o educe he empe a u e mo e in compa ison wi h
he homopolyme o lea e sel -seeds ha can e icien ly
inc ease he nuclea ion densi y, which esul s in an inc ease
o Tc. In o he wo ds, he inco po a ion o a comonome uni
acili a es he emo al o he mel memo y e ec since lowe
supe hea ings a e needed o ob ain an iso opic mel s a e.
The ansi ion empe a u es ha ma k he limi s o he sel -
nuclea ion domains a e displayed as a unc ion o he end
mel ing empe a u e in Figu e 7. The inco po a ion o a
second comonome uni educes he mel ing empe a u e;
he e o e, in he plo s o Figu e 7a,b, he ansi ion empe a u e
be ween Domains o he nea homopolyme can be ound a
he highes Tm,end alues o each plo . As he comonome
con en inc eases, he ansi ion empe a u es co esponding o
he copolyme s p og essi ely dec ease as Tm,end alues
dec ease.
Fo CL- ich copolyme s, he empe a u e limi s be ween
DII/DI and DIII/DII lay e y close o each o he (Figu e 7a),
which e lec s a na ow Domain II. Only he homopolyme and
he copolyme wi h a small amoun o comonome uni s show
some Domain II. The e is a dep ession o he ansi ion
empe a u es as Tm,end dec eases o as he he mal s abili y o
he s anda d c ys alline s a e dec eases, which could be
expec ed conside ing ha comonome uni inco po a ion
dep esses he mel ing empe a u e. The slopes o bo h lines
o ansi ion empe a u es e sus Tm,end a e close o one,
e lec ing a linea p opo ional beha io be ween he ansi ion
alues and he he mal s abili y o he c ys als.
On he con a y, o BS- ich copolyme s (Figu e 7b), a
signi ican gap be ween he DII/DI and DIII/DII ansi ion
empe a u es can be obse ed. Also in his case, he
homopolyme and copolyme s wi h a small amoun o
comonome uni s show he mos impo an Domain II wid h.
The slope o he DII/DI ansi ion is highe han 1 (1.1),
whe eas he one co esponding o DIII/DII is below 1 (0.94),
Figu e 8. (a) Domain II wid h, (b) Domain IIa wid h, and (c) Domain IIb wid h as a unc ion o BS con en .
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which implies a as e dep ession o he mel memo y e ec
wi h Tm,end dec ease in compa ison wi h he empe a u e
equi ed o anneal he c ys als. Fo all copolyme s, an iso opic
mel s a e is eached well below he equilib ium mel ing
empe a u e (Tm
0), as depic ed in Figu e 7a,b. The Tm
0was
aken om a p e ious wo k,
11
and he alues co esponding o
he cu en composi ions we e es ima ed i ing he Tm
0as a
unc ion o composi ion.
The esul s p esen ed in Figu e 7 indica e ha he lowe he
mel ing empe a u e o he copolyme s, he lowe he inc ease
in empe a u e o e ase he mel memo y e ec is. A clea
impac o he composi ion on he ansi ion empe a u es can
be obse ed in Figu e 7c, in which he ansi ion empe a u es
a e depic ed along wi h he composi ion. The inco po a ion o
a second comonome uni educes he ansi ion empe a u es
o BS- ich and CL- ich copolyme s.
To conside he e ec o he comonome uni s inco po-
a ion on Domain II,Figu e 8 shows Domain II,Domain IIa,
and Domain IIb empe a u e wid hs as a unc ion o copolyme
composi ion. Inco po a ing a second comonome uni educes
he wid h o Domain II p og essi ely o copolyme s ich in BS
and CL.
I Domain IIa o he mel memo y Domain is analyzed, he
esul s a e qui e in e es ing (Figu e 8b). PCL has a mel
memo y e ec o 7 °C, which is close o he esul s epo ed in
he li e a u e.
37
A sligh inco po a ion o BS in PCL- ich
copolyme s (only 1.3%, acco ding o Table 1) anishes he
en i e mel memo y e ec . Howe e , his is no he case o BS-
ich copolyme s. In his case, a p og essi e educ ion in he
wid h o DIIa is obse ed, and mel memo y anishes a a CL
con en o 20%. Fo mos o he copolyme s, he e is some DII
due o sel -seeds, i.e., he magni ude o DIIb is always oughly
cons an (see Figu e 8c). This means ha he e is only an
inc ease o Tcin compa ison wi h he s anda d Tcwhen he
polyme is hea ed close o he end o he mel ing eno he m,
lea ing some small c ys al agmen s ha canno anneal.
15
As men ioned p e iously, he mel memo y o CL- ich
copolyme s is educed wi h he inco po a ion o iny amoun s
o BS (1.3%) comonome uni s. Howe e , in he case o BS-
ich copolyme s, highe amoun s o CL (20%) a e needed o
e ase he mel memo y. A possible explana ion o hese
di e ences lies in he exclusion/inclusion a io o he second
comonome uni s. As men ioned be o e, conside ing he
mel ing empe a u e beha io , he e is a signi ican exclusion
o BS uni s om he CL- ich c ys alline phase, whe eas CL
uni s a e included in a highe amoun wi hin he BS- ich
c ys alline phase. This is p obably due o he la ge size o BS
monome s in compa ison wi h CL monome s (see Figu e 1).
The esul s indica e ha he inclusion o he CL monome
in BS- ich c ys als allows holding some mel memo y e ec , a
leas un il 20% o CL inco po a ion. On he con a y, o CL-
ich copolyme s, BS is mainly ejec ed om he c ys alline
phase, and in his case, e en a small p esence o BS in he
copolyme is enough o e ase he mel memo y e ec . Thus,
BS uni s educe he he mal s abili y o sel -nuclei and ac as
diluen s, educing he empe a u e needed o each an
iso opic mel s a e.
The esul s can also be explained by conside ing he
in e molecula in e ac ions. PBS shows a s onge mel
memo y e ec ha may a ise om s onge in e ac ions in
compa ison wi h PCL. The s udies ca ied ou wi h Raman
spec oscopy, in a ed spec oscopy, and quan um chemical
calcula ions (QCCs) show ha PBS and PCL ha e 3 ypes o
hyd ogen bonds comp ising in e molecula and in amolecula
in e ac ions.
38,39
Those hyd ogen bonds a e o med be ween
he oxygen a oms om he es e g oups and hyd ogen a oms
om me hylene g oups o PBS and PCL. These bonds ha e a
simila bond leng h. Howe e , i should be conside ed ha o
PCL, he e a e 5 me hylene g oups pe each es e g oup,
whe eas o PBS, he e a e 6 me hylene g oups pe 2 es e
g oups. This could explain why PBS shows a s onge mel
memo y e ec han PCL since he in e molecula in e ac ions
a e mo e dilu ed o PCL as i con ains mo e me hylene g oups
pe unc ional g oup compa ed wi h PBS.
Fo he PBS- ich composi ions, when he second como-
nome uni s a e in oduced in he polyme chain and pa ially
included in he c ys al, hese couni s dis up he men ioned
in e ac ions, which esul s in a educ ion o he mel memo y
e ec . In he case o PCL- ich composi ions, he BS couni s a e
la gely excluded om he c ys al, as judged by he mel ing
poin dec ease. Ne e heless, he inco po a ion o only 1 mol
% comple ely e ased he mel memo y. This unexpec ed esul
sugges s ha BS uni s, e en i mos ly ejec ed om he c ys als,
could s ill be loca ed a he c ys al su ace, weakening he
in e molecula in e ac ions be ween CL segmen s. Scha e e
al.
27
demons a ed by solid-s a e NMR s udies ha in PBS- an-
PBA isodimo phic copolyme s, up o 9% PBS could be
included wi hin he c ys al la ice o PBA in a 20:80 PBS- an-
PBA andom copolyme . Howe e , in he case o a 60:40 PBS-
an-PBA andom copolyme , PBA epea ing uni s we e loca ed
on he c ys alline su ace, p esumably in pocke -like s uc u es
(app oxima ely 7 o 9% o BA uni s).
Despi e he quan i a i e di e ences obse ed on he wo
sides o he composi ion diag am, he new and impo an
inding is he educ ion o he mel memo y e ec wi h small
amoun s o comonome uni inco po a ion, which holds o
bo h ypes o c ys als and is hus ela ed o an in e play
be ween in e molecula in e ac ions and comonome uni
inclusion/exclusion balance in he c ys alline la ice.
This beha io di e s comple ely om ha o polyole in-
based copolyme s in which he second comonome uni s
induce complex mel opologies, leading o a s ong mel
memo y e ec .
20−24,40
Ex ensi e wo ks wi h e hylene-based
copolyme s ha e shown ha inco po a ion o bu ene
comonome uni s
20,23,24
esul s in a s ong mel memo y
e ec ha pe sis s e en abo e he calcula ed equilib ium
mel ing empe a u e. This mel memo y o igina es om he
sequence pa i ioning ha occu s du ing he c ys alliza ion
p ocess. The comonome uni s a e excluded om he
c ys alline phase, and du ing c ys alliza ion, he e is a selec ion
o he sequence leng h; i s , he longe sequences a e selec ed,
which ha e o di use o he c ys al on . This p ocess leads o
a complex mel opology, esul ing in a s ong mel memo y
e ec since highe empe a u es a e equi ed o each an
iso opic mel s a e s a ing om he “he e ogeneous”
mel .
20−24
Fo p opylene/e hylene andom copolyme s, i has also been
shown ha he inco po a ion o e hylene comonome uni s
widens he mel memo y e ec , i.e., he mel memo y e ec is
displayed on a b oade empe a u e ange.
39
The esul s a e
explained conside ing he opological cons ain s b ough by
inco po a ing a second comonome uni pa ially ejec ed om
he c ys alline phase, as o PE-based copolyme s. Howe e , o
polyp opylene-based copolyme s, mel memo y disappea s a
empe a u es much lowe han he equilib ium mel ing
empe a u e.
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The opposi e ends be ween ole in-based copolyme s and
polyes e -based copolyme s could a ise om he ac ha he
mechanisms o mel memo y a e di e en . In ole in-based
copolyme s, he e a e only weak an de Waals in e ac ions.
The mel memo y e ec in hose ma e ials a ises om he
complex mel opology ha is gene a ed due o sequence
selec ion du ing c ys alliza ion and di usion o he chain
segmen s o he c ys al g ow h on . Howe e , in polyes e
and se e al polyme s ha con ain unc ional g oups such as
polyamides, polye he s, and polyca bona es, mel memo y is
di ec ly ela ed o he in e molecula in e ac ion s eng h. The
s onge he in e ac ions a e, he s onge he mel memo y
e ec .
16−19
The inco po a ion o a second comonome uni
migh educe o dis up he in e molecula in e ac ions wi hin
he c ys als on bo h sides o he pseudoeu ec ic poin .
4. CONCLUSIONS
In his wo k, he mel memo y e ec o PBS- an-PCL
isodimo phic copolyes e s was in es iga ed o he i s ime.
The copolyme s wi h small amoun s o a second comonome
uni show only one c ys alline phase, simila o he one o he
homopolyme . The s udy e eals ha he inco po a ion o a
second comonome uni s s ongly educes he mel memo y
e ec due o a dis up ion o he in e molecula in e ac ions
be ween he chain segmen s, easing he p ocess o each he
iso opic mel s a e. The comonome wi h a highe exclusion
a io, bu ylene succina e, shows a mo e se e e educ ion in he
mel memo y e ec o polycap olac one, which e lec s a
highe e ec i eness in educing in e molecula in e ac ions
wi hin CL chain segmen s. This beha io is comple ely
di e en om he beha io shown by ole in-based copolyme s,
which sugges s ha he mechanism o mel memo y is di e en
o hose ma e ials. In he case o polyes e s, mel memo y
a ises om in e molecula in e ac ions p esen in polyes e s.
The second comonome uni s dilu e hese in e ac ions and
esul in mel opologies upon c ys alliza ion ha a e less
seg ega ed han hose o ole in-based copolyme s.
■ASSOCIATED CONTENT
*
sı Suppo ing In o ma ion
The Suppo ing In o ma ion is a ailable ee o cha ge a
h ps://pubs.acs.o g/doi/10.1021/acs.mac omol.3c01389.
1H NMR o all he copolyme s and 13C NMR o selec ed
copolyme s; able wi h he andomness o selec ed
copolyme s; he he mal SN p ocedu e employed; he
he mal p ope ies ob ained by noniso he mal DSC
expe imen s and SN esul s o all he copolyme s and
homopolyme s (PDF)
■AUTHOR INFORMATION
Co esponding Au ho s
Lei e Sang oniz −POLYMAT and Depa men o Polyme s
and Ad anced Ma e ials: Physics, Chemis y, and
Technology, Facul y o Chemis y, Uni e si y o he Basque
Coun y UPV/EHU, 20018 Donos ia-San Sebas ián, Spain;
o cid.o g/0000-0003-0714-3154;
Email: [email p o ec ed]
Alejand o J. Mulle −POLYMAT and Depa men o
Polyme s and Ad anced Ma e ials: Physics, Chemis y, and
Technology, Facul y o Chemis y, Uni e si y o he Basque
Coun y UPV/EHU, 20018 Donos ia-San Sebas ián, Spain;
IKERBASQUE, Basque Founda ion o Science, 48009
Bilbao, Spain; o cid.o g/0000-0001-7009-7715;
Email: [email p o ec ed]
Au ho s
Ma yam Sa a i −POLYMAT and Depa men o Polyme s
and Ad anced Ma e ials: Physics, Chemis y, and
Technology, Facul y o Chemis y, Uni e si y o he Basque
Coun y UPV/EHU, 20018 Donos ia-San Sebas ián, Spain;
Physical Chemis y and So Ma e , Wageningen Uni e si y
&Resea ch, Wageningen 6708 WE, The Ne he lands
An xon Ma ínez de Ila duya −Depa men d’Enginye ia
Química, Uni e si a Poli ecnica de Ca alunya, ETSEIB,
08028 Ba celona, Spain; o cid.o g/0000-0001-8105-
2168
Ha i z Sa don −POLYMAT and Depa men o Polyme s
and Ad anced Ma e ials: Physics, Chemis y, and
Technology, Facul y o Chemis y, Uni e si y o he Basque
Coun y UPV/EHU, 20018 Donos ia-San Sebas ián, Spain;
o cid.o g/0000-0002-6268-0916
Da io Ca allo −Depa men o Chemis y and Indus ial
Chemis y, Uni e si y o Geno a, 16146 Geno a, I aly;
o cid.o g/0000-0002-3274-7067
Comple e con ac in o ma ion is a ailable a :
h ps://pubs.acs.o g/10.1021/acs.mac omol.3c01389
No es
The au ho s decla e no compe ing inancial in e es .
■ACKNOWLEDGMENTS
The au ho s acknowledge he p ojec PID2020-113045GB-
C21 unded by MCINN/AEI/10.13039/501100011033 and
g an IT1503-22 unded by he Basque Go e nmen . L.S.
acknowledges Ma ga i a Salas ellowship om he Uni e si y o
he Basque Coun y (UPV/EHU), which is unded by he
Eu opean Union-Nex Gene a ion EU and he Spanish
Go e nmen .
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