Polyme 307 (2024) 127285
A ailable online 11 June 2024
0032-3861/© 2024 The Au ho s. Published by Else ie L d. This is an open access a icle unde he CC BY-NC license (h p://c ea i ecommons.o g/licenses/by-
nc/4.0/).
Emulsion copolyme iza ion o 2-me hylene-1,3-dioxepane (MDO) and
ac yla e monome s: Inco po a ion s hyd olysis
Fabian Wenzel
1
, Mi en Agui e
**
, Jose R. Leiza
*
POLYMAT and Kimika Aplika ua Saila, Kimika Fakul a ea, Uni e si y o he Basque Coun y UPV/EHU, Joxe Ma i Ko a Zen oa, Tolosa Hi ibidea 72, 20018,
Donos ia-San Sebas ian, Spain
ARTICLE INFO
Keywo ds:
2-Me hylene-1,3-dioxepane (MDO)
Ac yla e monome s
Emulsion copolyme iza ion
Hyd olysis o MDO
ABSTRACT
The inco po a ion o polyes e moie ies o he backbone o wa e bo ne polyme dispe sions by he emulsion
copolyme iza ion o 2-me hylene-1,3-dioxepane (MDO) and ac yla e monome s (n-bu yl ac yla e and 2-oc yl
ac yla e) is explo ed in his wo k. Due o he compe i ion be ween he consump ion o MDO by hyd olysis
(MDO is e y sensi i e o wa e ) and by copolyme iza ion eac ions, seeded semiba ch emulsion co-
polyme iza ions we e ca ied ou a ying he empe a u e o he eac ion, he eeding a es o he comonome s,
and main aining a basic pH (~pH =8) ha dec eases no ably he a e o hyd olysis o he MDO. In e es ingly, we
ound ha he lowe he empe a u e o he eac ion (T =20 ◦C) and he highe he monome addi ion low a e,
allowed he highes inco po a ion o MDO in he copolyme (up o 86 mol %). Un o una ely, he MDO inco -
po a ed in he closed o med (i.e., in he ace al o m) and he e o e, he ac yla e copolyme s p oduced did no
con ain es e g oups in he backbone. Fu he mo e, inc easing he MDO composi ion in he copolyme s unde he
same polyme iza ion condi ions a o ed mo e hyd olysis han copolyme iza ion and hence, inco po a ion con-
en dec eased. On he o he hand, he es e size (2-oc yl s n-bu yl) o he ac yla e did no ha e any no iceable
e ec in he MDO inco po a ion con en .
1. In oduc ion
The global en i onmen al c isis, oge he wi h he deple ion o ossil
esou ces and he go e nmen al policies owa ds ca bon neu ali y has
gi en ise o an inc easing a en ion owa ds deg adable and/o bio-
based polyme s. The emulsion copolyme iza ion o cyclic ke ene ace-
als (e.g., MDO) wi h o he inyl monome s is a e y appealing ou e o
p oduce deg adable polyme dispe sions ha migh ind applica ion in
ma e ials o liquid polyme o mula ions whe e he e m o use is sho
and hei ecyclabili y is no iable [1]. The e o e, he e is a s ong in-
e es in indus y and academia o syn hesize la ices wi h backbone
deg adable polyme pa icles [2]. Howe e , he polyme iza ion o cyclic
ke ene ace als in wa e bo ne sys ems is challenging due o hei high
wa e sensi i i y, which leads o apid hyd olysis [3–6]. Fu he mo e,
MDO polyme izes ollowing wo di e en ou es, ei he by ing opening
o by ing e en ion (see Scheme 1). The MDO uni ha unde goes ing
opening is inco po a ed in o he polyme backbone wi h an es e uni ,
p o iding a deg adable uni o he polyme ic chain. Howe e , when he
MDO uni is inco po a ed as ing e en ion, an ace al uni is added o he
polyme chain wi hou adding any deg adable uni . The a io o ing
opening o ing e en ion is s ongly in luenced by he polyme iza ion
pa ame e s, mainly by he empe a u e [7–9].
I is epo ed in li e a u e ha inc easing he empe a u e inc eases
he a io o ing opening o ing e en ion [8]. Fo ins ance, a 70 ◦C 28 %
o he MDO was inco po a ed in o a nBA/MDO-copolyme (by solu ion
polyme iza ion in cyclohexane) as ing opened uni s, whe eas a 90 ◦C
34 % we e inco po a ed as ing opened uni s. Fu he mo e, i is also
s a ed ha la ge alkyl ac yla es also a o he ing opening o he MDO
[8].
The li e a u e epo s abou he inco po a ion o MDO (o o he
CKAs o monome s like cyclic inyl ace als [5], and biphenilic cyclic
hionolac ones [10,11]) in o wa e bo ne polyme ic dispe sions a e
eally sca ce. Land es e e al. [12] we e he i s ones copolyme izing
he cyclic ke ene ace al 5,6-benzo-2-me hylene-1,3-dioxepane (BMDO)
wi h me hyl me hac yla e (MMA) and s y ene by miniemulsion poly-
me iza ion o ob ain biodeg adable d ug ca ie s. They showed ha
* Co esponding au ho .
** Co esponding au ho .
E-mail add esses: [email p o ec ed] (M. Agui e), [email p o ec ed] (J.R. Leiza).
1
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Polyme 307 (2024) 127285
2
depending on he amoun o BMDO in he copolyme , a signi ican
dec ease o he weigh a e age mola mass o he copolyme a e
ea men wi h ei he he enzyme Lipase PS o concen a ed po assium
hyd oxide solu ion (50 %–5 % esidual Mw a e 48 h) was obse ed.
Fu he mo e, he easibili y o he nanopa icles o ac as d ug ca ie s
was p o en by he inco po a ion and elease o he cy os a ic d ug
pacli axel.
Apa om he medical applica ion as d ug ca ie , la ices wi h
backbone deg adable pa icles a e also o in e es in o he ields [13].
One o hem is he usage as coa ings o single use pape p oduc s, which
a e o en used o he packaging o ood, such as pape boxes, w appe s,
e c. These a e in many cases coa ed o inc ease he mechanical p op-
e ies and he oil/g ease esis ance. Howe e , when hese
ood-packaging p oduc s a e con amina ed, i becomes di icul o
eco e and ecycle he unde lying ibe s, p e en ing po en ial pa h-
ways o deg ada ion. Sus ainabili y could be inc eased by coa ings
made o (bio)deg adable la ices [14]. Wi h his mo i a ion Ca e e al.
desc ibed he emulsion copolyme iza ion o MDO wi h inyl ace a e
[15,16]. They epo ed ha mildly basic condi ions (pH =8) and low
empe a u es (40 ◦C) a e essen ial o p e en he apid hyd olysis o
MDO. Fu he mo e, hey demons a ed he deg adabili y o he MDO
uni s con aining co-polyme s by hyd olysis o he es e g oups in a basic
aqueous solu ion wi h a bica bona e bu e and a pH alue o 10. Wi hin
50 days, hey obse ed a mass loss o ⁓50 % o d ied ilms o
VAc-co-MDO copolyme . Recen ly, Ko des e al. [5] p esen ed an
ex ensi e analysis o he hyd olysis kine ics o MDO in wa e , pa icu-
la ly a s anda d condi ions du ing an emulsion polyme iza ion p ocess.
Fu he mo e, based on he op imal empe a u e and pH condi ions
ound o educe he hyd olysis o MDO, hey conduc ed emulsion
copolyme iza ion o MDO and VAc and concluded, con a y o wha i
was epo ed by Ca e e al. [15], ha only small amoun s o MDO we e
inco po a ed in he copolyme and ha he majo i y was hyd olyzed.
They also poin ed ou ha he agmen s o he deg ada ion o he
polyme s unde basic pH we e oo la ge o be me abolized by mic oo -
ganisms. Recen ly, Ca e e al. [17] in iew o he disc epancies ound
by Ko des e al. [5] o ep oduce hei expe imen s, conduc ed a se ies o
expe imen s o p oo ha he op imal expe imen al condi ions desc ibed
in hei o iginal manusc ip (i.e., T =40 ◦C, pH =8 (o highe ) and high
ins an aneous con e sions o VAc and MDO), i con olled ca e ully
du ing he emulsion polyme iza ion p ocess, do gua an ee a e y limi ed
hyd olysis o MDO (o inco po a ion o MDO highe han 85 %).
Fu he mo e, hey ca ied ou expe imen s mimicking poo con ol o
empe a u e and pH and he mode o educ an addi ion on he inco -
po a ion amoun o MDO. They ound ha small de ia ions in pH,
empe a u e and he addi ion o he educ an yield lowe inco po a ion
o he MDO, emphasizing he necessi y o a igh con ol o hese a i-
ables o a success ul inco po a ion o es e moie ies in he backbone and
hence, he p oduc ion o deg adable copolyme s by emulsion polyme -
iza ion. On he o he hand, Galanopoulo e al. [18] ecen ly epo ed he
ab-ini io emulsion polyme iza ion o BMDO and MMA ca ied ou a
70 ◦C and basic pH (a ound 8). They ound ha basic condi ions a e
necessa y o inco po a e BMDO in o he copolyme , and he highe he
ini ial ac ion o BMDO he lowe i s inco po a ion (be ween 64 % and
100 % o ac ions be ween 10 mol% and 2 mol% o BMDO in he
o mula ion). Accele a ed deg ada ion expe imen s o he poly(MMA--
co-BMDO) copolyme s showed ha deg ada ion o a leas 80 % o he
chains con aining BMDO occu ed.
All wo ks discussed abo e [5,12,15–17,19] ha e a emp ed o
inco po a e MDO in o wa e bo ne polyme dispe sions using s a egies
o o e come he hyd olysis o MDO (low empe a u es, alkaline pH, high
ins an aneous con e sions, hyd ophobic comononome s and mini-
emulsion polyme iza ion among o he s). Howe e , e y ecen ly, Mo he
e al. [20] ha e epo ed ha by means o ba ch emulsion copolyme i-
za ion o MMA and MDO using alkaline pH (highe han 10), empe a-
u es o 70 ◦C, neu al (i.e., non-ionic) su ac an s, and 5 mol% o a
hyd oxy- unc ional cos abilizing monome (Hyd oxy e hyl ac yla e,
HEA), deg adable la exes can be p oduced. The au ho s claim ha i is
essen ial o use neu al emulsi ie s o inco po a e MDO in emulsion
polyme iza ion oge he wi h alkaline pH. The high pH’s used (pH =10)
educed u he he a e o hyd olysis o MDO al hough his pH can be
ha sh o some monome s ha also su e hyd olysis in alkaline condi-
ions like VAc. None heless, i is wo h no ing ha mo e han 50 % o he
MDO hyd olysed in hei ba ch emulsion polyme iza ions, likely due o
he ela i ely high empe a u es (T =70 ◦C) employed.
On he o he hand, D’Agos o e al. epo ed he emulsion copoly-
me iza ion o he hionolac one monome dibenzo[c,e]oxepane-5-
hione (DOT) [21], which was i s p oposed by Ro h e al. [22] and
Gu ekuns e al. [23], wi h bu yl ac yla e and/o s y ene. DOT, simila o
MDO, also unde goes ROP leading o in-chain hioes e unc ion [10].
Unlike MDO, DOT is assumed o p esen a o able eac i i y a ios wi h
s y ene o ac yla es, and do unde go comple e ing opening (no ing
e en ion). Low con en s o DOT be ween 2–5 mol % we e su icien o
ob ain deg adable copolyme s. Deg ada ion h ough isop opylamine
and 1,5,7- iazobicyclo[4.4.0]dec-5-ene (TBD) was demons a ed.
Due o he g owing in e es in indus y o p oduce mo e sus ainable
polyme la exes, he syn hesis o wa e bo ne deg adable copolyme s is a
ho opic. The e o e, he esea ch on he syn hesis o new monome s
able o polyme ize by emulsion polyme iza ion, and ha will eadily
copolyme ize wi h common oil-based o no el bio-based monome s
oge he wi h he unde s anding and p ocess op imiza ion o al eady
desc ibed monome s is o pa amoun impo ance in he ield [24]. In
his con ex , his wo k assesses he copolyme iza ion o MDO in emul-
sion polyme iza ion. F om he cu en unde s anding o he in e ac ion
o MDO and wa e , i is clea ha o achie e wa e bo ne polyme pa -
icles wi h a deg adable backbone by emulsion copolyme iza ion o
MDO wi h o he monome s, he a e o consump ion o MDO by poly-
me iza ion (a unc ion o he adical concen a ion in he polyme iza ion
loci and o he comonome used) mus be as e han he a e o i s hy-
d olysis (which is a unc ion o he empe a u e and pH o he p esence
o p o ic eagen s) [5,20]. In his wo k, he kine ics o he hyd olysis o
MDO in aqueous media unde di e en condi ions ha e been e alua ed
and compa ed wi h he esul s al eady published in he ecen li e a u e.
Then, hese esul s a e used o guide in he selec ion o he ope a ion
condi ions o a o he inco po a ion o MDO in emulsion
copolyme iza ion.
2. Expe imen al sec ion
The expe imen s o he hyd olysis o MDO and he copolyme iza ion
o MDO wi h o he comonome s in wa e bo ne sys ems a e desc ibed.
Scheme 1. MDO is inco po a ed o a g owing polyme chain ei he by adical
Ring Opening Polyme iza ion ( ROP) (a) o by ing e en ion adical poly-
me iza ion (b).
F. Wenzel e al.
Polyme 307 (2024) 127285
3
2.1. Ma e ials
E hylenediamine e aace ic acid (EDTA, Sigma Ald ich), ammonium
hyd oxide solu ion (Sigma Ald ich), ammonium pe oxodisul a e (APS,
Sigma Ald ich), po assium hyd oxide (KOH, Sigma Ald ich), B üggoli
FF6 (B üggemann Chemical), i on(II)sul a e (Sigma Ald ich), n-bu yl
ac yla e (n-BA, Sigma Ald ich), 2-oc yl ac yla e (2-OA, BASF),
me hylene-1,3-dioxepane (MDO, Wacke ), Dow ax 2A1 (Dow Chemi-
cal), Disponil AFX 1080 (BASF) we e used as supplied. d-Chlo o o m
(Sigma Ald ich) and deu e a ed wa e (Sigma Ald ich) we e used as
deu e a ed sol en s in he NMR analysis. A comme cial ac ylic seed wi h
a pa icle size o 65 nm was used.
2.2. Cha ac e iza ion echniques
The cha ac e iza ion o he copolyme samples wi hd awn om he
eac o was ca ied ou by
1
H and
13
C NMR spec oscopy using he
B uke spec ome e s AVIII 300 MHz and AVII+500 MHz wi h he
sample heads o 10 mm BBO and 5 mm BFO, espec i ely. Deu e a ed
chlo o o m was used as sol en . Pa icle sizes we e analyzed by disc
cen i uge (Lumisize ) a 10 ◦C a a wa eleng h o 470 nm. pH alues
we e de e mined wi h a pH-me e (F20, Me le Toledo) and he solids
con en measu emen was ca ied ou by a he mo-balance HB43–S
(Me le Toledo) o he calcula ion o con e sions.
2.3. Hyd olysis s udies o MDO
The hyd olysis s udies o MDO we e done adding 100 mg o D
2
O and
600 mg o an aqueous KOH solu ion adjus ed o pH =10 o pH =8 in o a
Wilmad® NMR ube wi h a leng h o 18 cm, and a diame e o 5 mm
(wall hickness o 0.43 mm). The ube was hen hea ed o he desi ed
empe a u e (30, 40 o 50 ◦C), and when he empe a u e was s able, 50
μ
L o MDO we e added o he NMR ube wi h an Eppendo pipe e. The
liquid
1
H NMR spec a we e acqui ed ia NMR measu emen s wi h a
500 MHz B uke A ance NMR ins umen equipped wi h a Z g adien
b oadband obse e (BBO) p obe. Scans we e pe o med e e y 5 min
a e 2 min o s abiliza ion o he eac ion mix u e. The numbe o scans
was one o each o he measu emen s wi h a elaxa ion delay o 10 s, a
pulse wid h o 14
μ
s and an acquisi ion ime o 2.23 s.
2.4. Seeded semiba ch emulsion copolyme iza ion o MDO
Seeded semiba ch emulsion copolyme iza ion o MDO wi h he co-
monome s nBA and 2OA was ca ied ou in a 0.5 L glass eac o wi h
an ancho ype s i e (200 pm) and unde ni ogen a mosphe e. The
empe a u e o he eac o was con olled by a Hube Unis a Pe i e
Fleu he mos a uni and a P 100 senso in he eac o .
A comme cial ac ylic seed wi h a pa icle size o 65 nm was used as
he ini ial cha ge oge he wi h dis illed wa e , ammonia o adjus he
pH and EDTA as one pa o he ca alys o he edox ini ia o sys em.
The edox ini ia o sys em consis ed o FF6, APS, EDTA and I on(II)
sul a e (FeSO
4
) in a ios ha we e al eady desc ibed by Kohu -S elko
e al. [25]. When he desi ed eac ion empe a u e was eached APS,
I on(II)sul a e and FF6 we e added as sho s, each o hem dissol ed in
dis illed wa e . Subsequen ly, wo eeding s eams we e s a ed. One
con aining nea monome (which was nBA o 2-OA) and he o he one,
an aqueous solu ion consis ed o su ac an s Dow ax 2A1 and Disponil
AFX1080, wi h u he FF6 and dis illed wa e . The eeding imes we e
a ied in he ange 60–180 min. The pH alue was adjus ed by he
addi ion o ammonia du ing he eac ion (a pa o i was added ini ially
and ano he pa was ed in he aqueous solu ion) and he e olu ion o
he pH alue o e he eac ion ime was measu ed by a pH-me e .
A e wa ds, he eac ion empe a u e was kep o u he 30 min.
Then, he eac ion empe a u e was aised o 80 ◦C o u he 30 min.
Finally, he eac o was cooled down o 25 ◦C. The de ailed o mula ion
o he seeded semiba ch emulsion copolyme iza ions is shown in
Table 1.
3. Resul s and discussion
3.1. Kine ics o he hyd olysis o MDO
A i s , he hyd olysis o MDO o 4-hyd oxybu yl ace a e (4-HBA)
(Scheme 2) unde di e en condi ions was s udied o ind he bes pa-
ame e s o i s p e en ion and he e o e, o he success ul inco po a-
ion o MDO by emulsion copolyme iza ion.
Hyd olysis expe imen s we e ca ied ou by in si u
1
H NMR o ack
he disappea ance o he MDO p o ons and he appea ance o he p o-
ons o he hyd olysis p oduc 4-HBA. Fig. 1 p esen s he spec a o he
e olu ion o he hyd olysis eac ion (ca ied ou a 30 ◦C and pH =8)
moni o ed online wi h he assignmen o he main peaks co esponding
o MDO and 4-HBA p o ons. Recen ly, Ko des e al. [5] ha e ex ensi ely
analyzed he hyd olysis eac ion o MDO in homogeneous and he e o-
geneous condi ions. They no e ha due o he low wa e solubili y o
MDO, moni o ing he p og ess o he hyd olysis can lead o la ge inac-
cu acies due o phase sepa a ion. The e o e, in o de o ge homogenous
condi ions, hey used e hylene ca bona e as sol en , no only because i
gua an ees homogenei y, bu also because i does no eac wi h MDO,
unlike o he sol en s. They ound ha in he ange o empe a u es and
pH used (25–40 ◦C and 7–9, espec i ely), inc easing empe a u e hy-
d olysis accele a es and inc easing pH slows down he hyd olysis e-
ac ions. Ano he in e es ing ema k om his wo k is ha he hyd olysis
eac ion is mo e complex han he one depic ed in Scheme 2; namely,
ha al hough he main p oduc o he hyd olysis is 4-HBA, hey also
de ec ed (no in he
1
H NMR analysis, bu in
13
C NMR and gas ch o-
ma og aphy measu emen s) he o ma ion o ace ic acid, 1,4-diace oxy-
bu ane and 1,4-bu anediol. Al hough, hey p oposed a plausible eac ion
mechanism o he o ma ion o hese compounds due o he e y low
amoun s o hei comple e absence in ce ain condi ions, he hyd olysis
o MDO was moni o ed by acking he e olu ion o he 4-HBA peaks (1,
62-1,74 ppm) and MDO (3,0–3,1 ppm). The peak shi s o Fig. 1 co e-
sponding o he hyd olysis o MDO in a mix u e o D
2
O/H
2
O ca ied ou
in his wo k a e in easonable ag eemen wi h he peaks epo ed by
Table 1
Fo mula ion o he seeded semiba ch emulsion copolyme iza ions o MDO and
nBA and 2-OA ac yla e monome s.
Componen Amoun [g]
Ini ial cha ge Seed Dispe sion 20
EDTA 0.025
Ammonia 0.5
Wa e 110
Sho a eac ion empe a u e APS 0.84
FF6 0.21
FeSO
4
0.01
Wa e 20
Monome eed MDO 7/14
Co-monome 133/126
Aqueous solu ion Dow ax 2A1 3.11
Disponil AFX1080 0.44
FF6 0.63
Ammonia 0.65
Wa e 70
Scheme 2. Hyd olysis o MDO o 4-HBA.
F. Wenzel e al.
Polyme 307 (2024) 127285
4
Ko des e al. [5], bu sligh ly shi ed o highe ppms, which can be due o
he absence o e hyl ca bona e sol en in ou expe imen s. The e o e,
he e olu ion o he con e sion was calcula ed by ei he he peaks o
MDO ha dec eased o by he new peaks ha appea ed ha co espond
o 4-HBA. Fu he de ails o he calcula ion o he hyd olysis ex en om
he
1
H NMR spec a is p o ided in he suppo ing in o ma ion (SI, sec-
ion 1).
Fig. 2 displays he ex en o hyd olysis a he di e en condi ions
in es iga ed ( o ins ance, he empe a u e was a ied be ween 30 and
40 ◦C and he pH be ween 8 and 10). I can be seen ha a e 1 h, a pH
=8 and 30 ◦C, all he MDO was con e ed o 4-HBA, o in o he wo ds,
all he MDO was hyd olyzed. On he o he hand, o he cases in which
pH =8 and 40 ◦C and pH =10 and 30 ◦C, he appea ance o 4-HBA was
much as e , o al hyd olysis was achie ed in 40 min.
Al hough a he condi ions o he hyd olysis eac ion ca ied ou in
his wo k, he concen a ion o MDO (7.1 w % in his wo k and 2.5 w %
in e e ence Ko des e al. [5]) exceeded i s solubili y in wa e , he ki-
ne ics o hyd olysis a e in easonable ag eemen . Fo ins ance, in he
wo k o Ko des e al., a pH =8 and a 40 ◦C he MDO was comple ely
hyd olyzed in 50 min while in his wo k, comple e hyd olysis occu s a
40 min. As men ioned by Ko des e al. his is in con as wi h he sub-
s an ially slowe hyd olysis a es epo ed by Ca e e al. [15]. I needs
o be men ioned ha he condi ions o he hyd olysis expe imen o
MDO by Ca e e al. we e di e en . They dissol ed MDO i s in
DMSO‑d
6
and did he expe imen s changing he a ios o DMSO‑d
6
/D
2
O
solu ions be ween 10/1, 100/1 and 1000/1. They ound ou ha he a e
o hyd olysis o MDO was inc easing wi h he ac ion o deu e a ed
wa e in he solu ion.
Mo he e al. [6] ha e also comp ehensi ely in es iga ed he eac ion
mechanism and eac ion kine ics o he hyd olysis o CKAs, co e ing
5-membe ed o 8-membe ed ings. They ound ha hyd olysis occu ed
a acid, neu al and basic condi ions bu he a e was lowe a basic
condi ions. Fo MDO in pu e wa e hey ound ha a pH =10 and 2 h
comple e hyd olysis equi ed a leas 40 ◦C, whe eas a 30 ◦C only 55 %
was hyd olyzed, which do no ag ee wi h ou and Ko des e al. [5] ob-
se a ions e en hough he concen a ion used was 5 w %, which is
be ween he one used in his s udy and he one o Ko des and
co-wo ke s.
3.2. Seeded semiba ch emulsion polyme iza ion o MDO and ac yla e
monome s
Acco ding o he in o ma ion ga he ed in his wo k and epo ed in
he li e a u e on he e ec o pH and empe a u e in he hyd olysis ki-
ne ics o MDO in wa e , i can be concluded ha i is possible o slow
down he hyd olysis o MDO in wa e by adjus ing he pH o a sligh ly
basic alue (pH ≥8) and wo king a low empe a u es (e.g., 30 ◦C). In
he case o he emulsion (co)polyme iza ion o MDO, he consump ion o
MDO is a compe i ion be ween i s hyd olysis (once in con ac wi h
wa e ) and i s consump ion h ough copolyme iza ion eac ions ( ha
occu s in he polyme pa icles) as desc ibed in Scheme 3.
Pa hway (a) in Scheme 3 shows he hyd olysis o MDO o 4-HBA. In
all he o he cases, a adical is added o he MDO monome a i s ,
gene a ing a MDO adical. The adical hen has he possibili y o
Fig. 1.
1
H NMR spec a o one o he in si u hyd olysis expe imen s o MDO (pH =8 and 30 ◦C). Wi h assignmen o he p o ons o MDO and 4-HBA o he signals
( u he de ails can be ound in he suppo ing in o ma ion, sec ion 1).
Fig. 2. E olu ion o he mola ac ion o 4-HBA de e mined by
1
H NMR
spec a du ing he hyd olysis expe imen o MDO a di e en condi ions (de-
ails on he calcula ion o he 4-HBA ac ion p o ided in he suppo ing in-
o ma ion, sec ion 1).
F. Wenzel e al.
Polyme 307 (2024) 127285
5
unde go ing opening o o m an es e g oup in he main chain o he
ac i e adical (b). In he o he wo possibili ies, he MDO adical canno
open be o e ano he inyl g oup is added o i , ei he om ano he MDO
molecule (c) o om a co-monome molecule (nBA) (d). The polyme ic
backbone o med in cases (c) and (d) is he one called ing e en ion.
The e o e, in o de o a o pa h (b) (in Scheme 3), i was ied o
minimize he hyd olysis a e o o inc ease he polyme iza ion a e o
MDO. No e ha inc easing he la e migh also a o pa h (c) and (d),
which a e no desi ed. Acco ding o equa ion (1), he polyme iza ion
a e o MDO in an emulsion copolyme iza ion is p opo ional o he
p opaga ion a e coe icien s (kpi j), he MDO concen a ion in he
polyme pa icles ([MDO]P), he a e age numbe o adicals pe pa icle
(n), and he o al numbe o pa icles (NP).
RpMDO =(kpMDO MDOPp
MDO +kpi MDOPp
i)[MDO]P
n
NA
NP(1)
Whe e, Pp
i is he p obabili y o he adical o be e mina ed in a monome
uni o ype i, which is a unc ion o he eac i i y a ios o he co-
monome s, and N
A
is A ogad os’ cons an . Thus, he highe he num-
be o pa icles, he highe he polyme iza ion a e. One app oach o
ensu e a high numbe o polyme pa icles in a ep oducible way in
emulsion polyme iza ion is o use a p e o med seed. The smalle he
pa icle size, he highe he numbe o pa icles o he same solids
con en . Ca e e al. [17] used a simila s a egy bu in-si u gene a ing
he polyme pa icles a he onse o he semiba ch eac ion, including
all he edox ini ia o pai in he ini ial eac o load.
On he o he hand, he a e o hyd olysis o MDO is go e ned by he
hyd olysis a e coe icien , khyd o, ha is empe a u e and pH dependen
and he concen a ion o MDO in he aqueous phase,
Rhyd o,MDO =khyd o[MDO]w(2)
Thus, seeded semiba ch emulsion copolyme iza ion expe imen s o
MDO and ac yla e monome s we e ca ied ou a ying he low a es o
he co-monome s, he ype o co-monome , and he empe a u e while
main aining cons an he numbe o polyme pa icles and he pH in he
expe imen s. Table 2 p esen s a summa y o he expe imen s ca ied ou
wi h ac yla e co-monome s (nBA and 2-OA) and he mos ele an in-
o ma ion o he eac ion and inal la ices syn hesized.
Fig. 3 shows he ime-e olu ion o he ins an aneous monome
con e sion and pH e olu ion o h ee ep esen a i e expe imen s. The
ins an aneous con e sions a e highe , he highe is he empe a u e o
he eac ion ( o eeding ime o 60 min eac ions), and he highe is he
eeding ime ( o he 30 ◦C eac ions). Final con e sions a e abo e 95 %
in all he cases, indica ing he good adical gene a ion e iciency o he
edox pai a he low eac ion empe a u es used. Fu he mo e, he pH o
he eac ions was main ained a ound 8 o he whole eac ion as dis-
played in Fig. 3b.
13
C NMR measu emen s we e used o in es iga e i he MDO was
inco po a ed in o he copolyme (pa h b-d in Scheme 3) and i he
inco po a ion occu ed in he ing open o closed o ms (pa h b s c-d).
Rep esen a i e
13
C NMR spec a o h ee expe imen s (one o he
homopolyme iza on o nBA and wo o he copolyme iza ions wi h MDO
a he 95/5 a io ca ied ou a 30 ◦C and eeding imes o 60 and 180
min) a e shown in Fig. 4.
Peaks 1–6 indica e he gene a ion o he hyd olysis p oduc 4-HBA
and peaks a- belong o he nBA uni s o he polyme (see suppo ing
in o ma ion sec ion 2 o a de ailed assignmen o he peaks). Addi-
ionally, he ac ha he a io o he in ensi ies be ween peaks 1,4 and 5
is 1:1:1, indica es ha he e a e no ing-opened MDO uni s p esen in he
copolyme . Peak 1 exis s only in he hyd olysis p oduc , whe eas, peak 4
and 5 would also co espond o he ing-opened es e uni s wi hin he
copolyme . The appea ance o peaks x and y in he wo spec a o he
expe imen s in which MDO was used, indica es he inco po a ion o
MDO in o he copolyme in a ing e ained o m (see Schemes 1 and 3).
Table 2 summa izes he in o ma ion o he pe cen age o inco po-
a ion o MDO o all expe imen al condi ions es ed in his wo k o he
nBA/MDO comonome sys em. No e ha none o he
13
C NMR spec a
o he nBA/MDO copolyme iza ions, show any indica ion o he
inco po a ion o MDO in he open o med. Hence, he epo ed alues in
Table 2 co espond o he amoun o MDO inco po a ed in he closed
o med.
Table 2 shows ha o he same eac ion empe a u e (30 ◦C)
dec easing he eeding ime (o inc easing he low a e) he inco po-
a ion o MDO inc eased om 26 % o 76 %; namely, he hyd olysis was
educed by inc easing he polyme iza ion a e ha inc eased wi h
highe monome concen a ions in he polyme pa icles du ing he e-
ac ion (in ag eemen wi h eq. (1)). Fu he mo e, he inco po a ion
inc eased o 86 % o he same eeding ime when he eac ion em-
pe a u e was educed o 20 ◦C. This means ha he educ ion o he
empe a u e in his ange s ongly a ec ed he hyd olysis a e and only
mildly o he polyme iza ion a e, and hence he MDO inco po a ion was
a o ed o e i s hyd olysis. This is also illus a ed in he se ies o ex-
pe imen s ca ied ou wi h a eeding ime o 60 min and empe a u es in
he ange 20–50 ◦C. Inc easing he empe a u e, al hough inc eases he
polyme iza ion a e, also inc eases hyd olysis a e in an ex en ha ex-
ceeds he o me and he e o e, he inco po a ion o he MDO dec eases
d as ically o alues ci ca 8 % a 50 ◦C. Table 2 also p esen s an
expe imen a highe MDO a io in he copolyme iza ion (nBA/MDO =
90/10) ca ied ou a 30 ◦C and 60 min eeding ime. In e es ingly, he
Scheme 3. Possible pa hways which MDO can unde go in he emulsion
copolyme iza ion wi h nBA.
Table 2
Reac ion empe a u e, eeding ime, inal con e sion, a e age pa icle size, pH
and MDO inco po a ed as ace al uni s in o he copolyme (wi h espec o he
o al amoun o MDO used as monome ) o he seeded semiba ch emulsion
copolyme iza ion eac ions be ween ac yla e monome s and MDO.
Co-monome
a io
T
(◦C)
Feeding ime
(min)
Con .
(%)
d
p
(nm)
pH Ace al
uni s (%)
a
BA/MDO 95/
5
30 180 97 123 8 26
BA/MDO 95/
5
30 60 97 121 8 76
BA/MDO 95/
5
20 60 96 132 8 86
BA/MDO 95/
5
40 60 98 126 8 16
BA/MDO 95/
5
50 60 98 134 8 8
BA/MDO 90/
10
30 60 95 116 8 56
2-OA/MDO
95/5
40 180 94 160 8 0
a
See suppo ing in o ma ion sec ion 2 o de ails o he calcula ion.
F. Wenzel e al.
Polyme 307 (2024) 127285
6
inco po a ion o MDO is lowe (i dec eases om 76 % o 56 %) likely
because he inc ease on he MDO polyme iza ion a e does no
compensa e he inc ease amoun o MDO ha hyd olyzes (no e ha
inc easing he mola ac ion o MDO om 5 o 10 mol% implies an
inc ease o 45 % o he polyme iza ion a e o MDO conside ing he
epo ed eac i i y a ios o nBA and MDO [8] and a bi a y p opaga-
ion a e coe icien s o nBA and MDO o 10000 and 1000 L/mol⋅s,
espec i ely).
An addi ional expe imen was ca ied ou wi h a di e en ac yla e
monome (2-OA, ha has a longe es e chain han nBA) a 40 ◦C and
eeding he monome du ing 180 min. This expe imen esul ed in 100
% hyd olysis o MDO (0 % inco po a ion in Table 2) con i ming wha
was obse ed o nBA; namely, highe empe a u es and long eeding
imes a o ed hyd olysis o e polyme iza ion (low low a es and hence,
lowe concen a ion o MDO in he polyme pa icles).
Summing-up he in o ma ion ga he ed in Table 2, i can be
concluded ha in he seeded semiba ch emulsion copolyme iza ion o
nBA and MDO i is possible o inco po a e MDO in o he copolyme
chains in la ge ex en (abo e 85 %) by educing he empe a u e o 20 ◦C
and eeding he monome a high low a es. Howe e and un o u-
na ely, he MDO is p esen in he nBA/MDO copolyme as ace al uni s
and no as es e uni s, which hinde s he deg adabili y o he
copolyme s. The condi ions ound o minimize hyd olysis when
copolyme izing MDO in semiba ch emulsion polyme iza ion a e up o
ce ain poin compa able o he op imal condi ions ound by Ca e e al.
[15,17]. In bo h cases, well con olled low empe a u es (20–40 ◦C) and
basic pH’s (a ound 8), and high ins an aneous con e sions a e neces-
sa y. Fo achie ing he la e , a high adical lux (which in Ca e ’s
app oach also se ed o nuclea e a la ge numbe o pa icles) is p o-
posed. Unde hese condi ions, he copolyme iza ion o VAc/MDO yields
es e uni s in he backbone, whe eas he copolyme iza ion o BA/MDO
yields ace als. Appa en ly, he lowe eac i i y a ios o ac yla es and in
pa icula n-BA wi h MDO [8,26] a e he main eason o he di e en
inco po a ion o MDO in bo h copolyme iza ion sys ems.
Al hough a ma hema ical model o he emulsion copolyme iza ion
p ocess (including he hyd olysis eac ion o MDO) would allow o
op imize he p ocess o maximize he inco po a ion o MDO in o he
copolyme , o his pa icula ac yla e/MDO copolyme , op imized
polyme iza ion s a egies will no lead o deg adable copolyme s
because he MDO will be inco po a ed in a ing e en ion mode.
Pesen i and Nicolas [24] ha e e iewed he adical ing-opening
polyme iza ion and pa icula ly he copolyme iza ion beha io o
CKAs. They epo ed subs an ial di e ences in he copolyme iza ion
beha io ( om andom o al e na ing copolyme s), bu also in he mode
Fig. 3. E olu ion o ins an aneous con e sions (a) and pH alue (b) o he seeded semiba ch emulsion copolyme iza ions o MDO and nBA wi h eeding imes o 60
min and 180 min and a eac ion empe a u es 20 and 30
◦C.
Fig. 4.
13
C NMR spec a o he d ied polyme s om he seeded semiba ch emulsion copolyme iza ion o MDO and nBA. The polyme iza ion o 100 % nBA a 30 ◦C
wi h a eeding ime o 180 min (black spec um), he polyme iza ion o 95 w % nBA and 5 w % MDO a 30 ◦C wi h a eeding ime o 180 min (blue spec um) and
polyme iza ion o 95 w % nBA and 5 w % MDO a 20 ◦C wi h a eeding ime o 60 min ( ed spec um). (Fo in e p e a ion o he e e ences o colou in his igu e
legend, he eade is e e ed o he Web e sion o his a icle.)
F. Wenzel e al.
Polyme 307 (2024) 127285
7
o inco po a ion o he CKAs depending on he comonome used.
The e o e, u u e esea ch o p oduce wa e bo ne deg adable co-
polyme s con aining MDO o o he CKA’s should explo e ope a ion
condi ions whe e he hyd olysis is minimized and he inco po a ion o
he CKA’s is high in he ing opened o med. These can be done by
explo ing comonome s ha unlike he ac yla es, do lead o open mode o
inco po a ion o he MDO in copolyme iza ion, as he e y ecen ly
shown es e c o ona es [27] and/o using condi ions as ecen ly dis-
closed by Mo he e al. [20] ha we e able wo king a mode a e em-
pe a u es (a ound 70 ◦C) o educe hyd olysis in he ba ch emulsion
copolyme iza ion o MMA and MDO using neu al su ac an s and cos-
abilizing monome s.
4. Conclusions
The semiba ch emulsion copolyme iza ion o MDO and ac yla e
monome s (pa icula ly, nBA and 2-OA) ha e been explo ed wi h he
aim o maximize he inco po a ion o MDO in o he wa e bo ne copol-
yme o mula ions. The inco po a ion o MDO is elusi e because o i s
high sensi i i y o wa e ha makes he a e o hyd olysis highe han
he a e o copolyme iza ion. The e o e, in his wo k he polyme iza ion
condi ions aiming o a o copolyme iza ion e sus hyd olysis we e
explo ed. Thus, i s he e ec o he empe a u e and pH on he hy-
d olysis a e o MDO in a mix u e o wa e and deu e a ed wa e o ind
he bes condi ions o delay he hyd olysis eac ion we e analyzed. The
hyd olysis esul s ob ained in his wo k a e in ag eemen wi h he mos
ecen and ex ensi e analysis o he hyd olysis o MDO epo ed in he
li e a u e [5,6]. Acco ding o hese analysis, he hyd olysis eac ion can
be delayed by wo king a pH >8 and educing he empe a u e below
40 ◦C. The e o e, seeded semiba ch emulsion copolyme iza ion o MDO
and nBA we e ca ied ou a pH =8 and he e ec o he eac ion
empe a u e (in he ange 20–50 ◦C), he eeding a e o he co-
monome s, and he composi ion o he comonome (nBA/MDO =95/5
o 90/10) we e analyzed in e ms o he pe cen age o inco po a ion o
he MDO in he copolyme and he way in which he MDO was inco -
po a ed (open o closed o ms). I was ound, ha he lowe he em-
pe a u e (20 ◦C) and he lowe he eeding ime (i.e., he highe he low
a e o monome addi ion) he highe he inco po a ion o MDO in he
copolyme (a 20 ◦C and 60 min o monome eeding ime 86 % o he
MDO in he composi ion was inco po a ed). Howe e , when he mode in
which MDO was inco po a ed was analyzed by
13
C NMR, i was ound
ha he inco po a ion was as an ace al uni a he han in he desi ed
es e o med, and hence he copolyme s we e no deg adable.
No wi hs anding, he in o ma ion ob ained in his wo k can be e y
aluable because i is known ha he comonome a ec s he way he
MDO is inco po a ed in he polyme [24]. The e o e, he expe imen al
condi ions op imized in his wo k, and o he condi ions ecen ly e-
po ed in he li e a u e by o he esea ch g oups (e.g., educing he
cha ge densi y o he la ex pa icles [20]) would help in op imizing he
syn he ic p ocedu es owa ds he p oduc ion o copolyme s wi h
deg adable moie ies in he backbone.
CRediT au ho ship con ibu ion s a emen
Fabian Wenzel: W i ing – o iginal d a , Valida ion, In es iga ion,
Fo mal analysis, Da a cu a ion. Mi en Agui e: W i ing – e iew &
edi ing, Supe ision, Me hodology, In es iga ion. Jose R. Leiza:
W i ing – e iew & edi ing, Valida ion, Supe ision, Resou ces, P ojec
adminis a ion, In es iga ion, Funding acquisi ion, Fo mal analysis,
Concep ualiza ion.
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:
Jose Ramon Leiza epo s inancial suppo was p o ided by Basque
Go e nmen . Jose Ramon Leiza epo s inancial suppo was p o ided
by Spain Minis y o Science and Inno a ion. I he e a e o he au ho s,
hey decla e ha hey ha e no known compe ing inancial in e es s o
pe sonal ela ionships ha could ha e appea ed o in luence he wo k
epo ed in his pape .
Da a a ailabili y
Da a will be made a ailable on eques .
Acknowledgmen s
The inancial suppo om he Minis e io de Ciencia e Inno aci´
on
(PID2021-123146OB-I00) and he Basque Go e nmen (IT-1525-22) a e
g a e ully acknowledged.
Appendix A. Supplemen a y da a
Supplemen a y da a o his a icle can be ound online a h ps://doi.
o g/10.1016/j.polyme .2024.127285.
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