Poly(THF-co-cyano ethylene oxide): Cyano Ethylene Oxide (CEO) Copolymerization with THF Leading to Multifunctional and Water-Soluble PolyTHF Polyelectrolytes

Article

pubs.acs.org/Macromolecules

Poly(THF-co-cyano ethylene oxide): Cyano Ethylene Oxide (CEO)

Copolymerization with THF Leading to Multifunctional and Water-

Soluble PolyTHF Polyelectrolytes

Eva-Maria Christ,^†,‡Jana Herzberger,^†,‡Mirko Montigny,^§Wolfgang Tremel,^§and Holger Frey*^,†

^†Institute of Organic Chemistry, Johannes Gutenberg-University Mainz, Duesbergweg 10-14, D-55128 Mainz, Germany

^‡Graduate School Materials Science in Mainz (MAINZ), Staudingerweg 9, D-55128 Mainz, Germany

^§Institute of Inorganic Chemistry and Analytic Chemistry, Johannes Gutenberg-University, Duesbergweg 10-14, 55128 Mainz,

Germany

S

* Supporting Information

ABSTRACT: Cyano-functional polyether copolymers based

on THF were prepared via cationic ring-opening copoly-

merization of THF with cyano ethylene oxide (CEO). The

CEO content of poly(tetrahydrofuran) (polyTHF) based

copolymers varied from 3.3 to 29.3%, and molecular weights

ranged from 5100 to 31900 g·mol⁻¹with M_w/M_nin the range

of 1.31 to 1.74 (SEC in THF, PS standards). The

polymerization was conducted with methyl triﬂuoromethane-

sulfonate (MeOTf) as an initiator. Kinetic studies concerning

incorporation of both monomers were performed via NMR

spectroscopy. The cyano groups at the poly(THF-co-CEO)

copolymers enable direct access to amino (polyTHF−NH₂)

and carboxyl groups (polyTHF−COOH) in facile one-step procedures, respectively. The modiﬁed copolymers were

characterized via NMR, MALDI−ToF mass, and FT-IR spectroscopy. Thermal properties of the materials were studied via

diﬀerential scanning calorimetry (DSC), demonstrating a gradual decrease of the melting points with increasing amount of CEO

in the copolymers (from 30 °C for 3.3% CEO to 21 °C for 8.4% CEO). After postmodiﬁcation to carboxylic acid groups the

melting points decrease from 26 to 18 °C in the series of copolymers. Contact angles of water on thin ﬁlms of the polymers can

be tuned in a wide range from 72.7° to 17.8° by varying the CEO fraction as well as by postmodiﬁcation. Crystallization studies

of CaCO₃with water-soluble polyTHF−COOH revealed the composition-dependent inhibition of calcite growth, with crystallite

size in the mineralization process being controlled by the amount of carboxylic acid groups at the poly(THF) copolymers.

straightforward “end-of-life polymer”, since it can easily be

degraded to THF in a facile and inexpensive way.^6,7

INTRODUCTION

■

Poly(tetrahydrofuran) (polyTHF) is an extremely versatile

material that is characterized by its remarkably high chain

ﬂexibility and its apolar nature.¹PolyTHF possesses a low

melting point (28 °C), which contributes to its easy handling,

besides excellent solubility in a wide range of rather

hydrophobic solvents like chloroform or THF. This renders

the material interesting for manifold applications, e.g., as soft

component in the polyurethane production^2,3(e.g., for

Spandex), for the synthesis of ﬁbers, adhesives, and sealants,

and for coatings in the textile industry. Characteristic properties

like the high hydrolytic stability in contrast to other polyester

polyols, a high moisture vapor transmission, and high abrasion

resistance as well as microbial resistance play a key role for

these purposes. Furthermore, the resulting materials possess

good visible light transparency.^4,5Besides its applications in a

wide industrial ﬁeld, polyTHF is also favorable for manifold

biomedical applications, such as a key component in contact

lenses, due to its low solubility in water and its good

biocompatibility.⁴Last but not least, polyTHF represents a

The properties of polyTHF can be systematically expanded

and manipulated by modiﬁcation of the end-groups. Rowan et

al. reported the synthesis of nucleobase-terminated polyTHF,

which self-assembled to materials with ﬁlm and ﬁber-forming

capability.⁸By diversifying the initiator of the polymerization,

the starting group of polyTHF can be varied as well^9,10to

create telechelic and heterobifunctional polyTHF.¹¹The

introduction of functional groups, such as alkyl, −OH,

−NH₂, −COOH, and −COOR, is an attractive objective,

because these moieties can be used to tune the hydrophilic/

hydrophobic character, permeability, and mechanical proper-

ties, as demonstrated recently for polycarbonates.¹²Also for

related hydrophilic polyethers, multifunctionality is generally an

important target, as demonstrated in numerous publications in

Received: January 16, 2016

Revised: April 21, 2016

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recent years.¹³⁻¹⁹Amine-functional polyTHFs were presented

in two works; however, the amino groups were positioned only

as end-groups as well.^20,21As a further end-group functionalized

material, the group of Teixidor provided reversible, redox-active

polyTHF by combining polyTHF with metallacarboranes.²²

The direct copolymerization of THF with ethylene oxide has

been studied, e.g., by Bednarek and Kubisa²³and later by

(benzoylated) was used. For dialysis in protic solvents, regular

regenerated cellulose membranes were applied.

1

Instrumentation. H NMR (300 and 400 MHz) and ¹³C NMR

spectra (75 and 100.6 MHz) were recorded on Bruker AC300, Bruker

AC400, Avance III HD 300 (300 MHz, 5 mm BBFO-head with z-

gradient and ATM, B-ACS 60 sample changer) spectrometers with

Open-Access-Automation, Avance II 400 (400 MHz, 5 mm BBFO-

head with z-gradient and ATM, SampleXPress 60 sample changer)

with Open-Access-Automation or Avance III HD 400 (400 MHz, 5

mm BBFO-SmartProbe with z-gradient and ATM, SampleXPress 60

sample changer), respectively, and are referenced internally to residual

Hocker et al.,²⁴and was found to proceed in a random manner.

̈

The cationic copolymerization of THF with functional cyclic

monomers has been presented in a few intriguing works. In this

area, the group of Zhu reported the copolymerization of THF

with glycidol to create branched copolymers with numerous

hydroxyl groups²⁵and the group of Pomposo et al. combined

THF with glycidyl phenyl and glycidyl propargyl ether,²⁶based

on previous work of Du Prez and co-workers.²⁷THF was also

copolymerized with epichlorohydrin or bis(chloromethyl)-

oxetane to create high-energy binders after postmodiﬁcation,

resulting in materials with high nitrogen content.^28,29

1

proton signals of the deuterated solvents. H NMR experiments for

kinetic studies were acquired with a 5 mm BBFO z-gradient probe on

the 500 MHz Bruker AVANCE III system. For the respective ¹H

NMR spectra, 64 transients were used with a 10.6 μs long 90° pulse

and 10000 Hz spectral width together with a recycling delay of 10 s.

For the ¹³C NMR kinetic measurements, 32 scans were used with a

relaxation delay of 30 s (90° pulse, 13.2 μs, spectra width 30000 Hz).

The temperature was kept at 298.3 K and calibrated with a standard

¹H methanol NMR sample using the topspin 3.2 software (Bruker).

Control of the temperature was realized with a VTU (variable

temperature unit) and an accuracy of 0,1K.

In the current work we have studied the cationic random

(co)polymerization of THF with the novel functional monomer

cyano ethylene oxide (CEO) (Scheme 1).

For size exclusion chromatography (SEC) measurements in THF a

PU 1580 pump, an auto sampler AS1555, a UV-detector UV 1575

(detection at 254 nm) and a RI-detector RI 1530 from JASCO were

used. Columns (MZ-Gel SDplus 10²Å and MZ-Gel SDplus 10⁶Å)

were obtained from MZ-Analysentechnik. Calibration was carried out

with polystyrene (PS) standards purchased from Polymer Standard

Services (PSS). MALDI−ToF MS measurements were performed on a

Shimadzu Axima CFR MALDI-TOF mass spectrometer using

dithranol (1,8,9-trishydroxyanthracene) or CHCA (α-Cyano-4-

hydroxycinnamic acid) as a matrix. The samples were prepared from

pyridine and ionized by adding lithium chloride or potassium triﬂuoro

acetate.

Scheme 1. Copolymerization of CEO and THF, as Well as

Post-Modiﬁcation Reactions, Leading to PolyTHF

Copolymers with Carboxylic Acid and Amine Moieties

DSC measurements were carried out on a PerkinElmer DSC 8500

in the temperature range of −80 to 50 °C, using heating rates of 10 K

min⁻¹under nitrogen. Contact angle measurements were performed

on a Dataphysics Contact Angle System OCA using water as an

interface agent. SEM images were taken with a FEI Nova NanoSEM at

acceleration voltage of 5 kV and a vC detector or a FEI Phenom SEM

at 3 kV acceleration voltage, respectively.

TEM images were recorded using a FEI Technai T12 equipped with

a 4K CCD camera and a LaB₆cathode working on 120 kV acceleration

voltage. Samples for TEM were prepared by dropcasting 20 μL of the

sample dilution from crystallization beakers onto a carbon coated

copper grid (Plano GmbH, Wetzlar, Germany).

Raman-spectroscopy measurements for phase identiﬁcation were

carried out using a confocal HR800 μ-Raman by Horiba Scientiﬁc.

Raman stimulation was managed by exciting with λ = 633,318 nm He/

Ne laser without using any ﬁlters. To get best signal-to-noise possible a

pinhole with a 400 nm diameter has been used. The signal was

collected with a CCD detector with a 1024 × 256 pixels open

electrode chip.

We demonstrate that the combination of these two

monomers results in linear multifunctional polyTHF copoly-

mers with a large number of functional cyano groups (from 3.3

to 29.3%, analyzed via NMR). Comprehensive characterization

of all copolymers via MALDI−ToF mass spectrometry, NMR

spectroscopy, size exclusion chromatography (SEC), FT-IR

spectroscopy, and diﬀerential scanning calorimetry (DSC) has

been carried out. We also demonstrate that the cyano groups

can be postmodiﬁed to primary amine groups and carboxylic

acid groups, resulting in water-soluble polyTHF at elevated pH.

This material has been explored for the mineralization of

calcium carbonate, as will be discussed in the ﬁnal part of this

work.

Synthetic Procedures. Synthesis of Cyano Ethylene Oxide

(CEO). CEO was synthesized as described in the literature.³⁰Brieﬂy, in

the course of 3 h at 0 °C, 100 mL of sodium hypochlorite (13% active

chlorine) was added with a dropping funnel to cold acrylonitrile (100

mL, 1.53 mol). The mixture was stirred vigorously with a mechanical

stirrer at 0 °C for additional 21 h, leading to a yield of 39.5% (Lit.:

34.5%.³⁰). Subsequently, residual acrylonitrile was recovered by

distillation, and the product was puriﬁed by distillation in vacuo (60

°C, 10⁻²mbar). ¹H NMR (300 MHz, CDCl₃): δ (ppm) = 2.95-

EXPERIMENTAL SECTION

■

Materials. All reagents were purchased from Acros Organics or

Sigma-Aldrich and were used as received, unless otherwise stated.

Anhydrous DMSO and o-dichlorobenzene were stored over molecular

sieves prior to use. Column chromatography was performed on silica

gel (particle size 63−200 μm, Merck, Darmstadt, Germany).

Deuterated DMSO-d₆, pyridine-d₅, MeOD-d₃, CDCl₃, and HFIP-d₂

were purchased from Deutero GmbH. Tetrahydrofuran (THF) was

puriﬁed by standard methods and was distillated over sodium in the

presence of benzophenone. Dialysis membrane tubings were

purchased from Sigma-Aldrich or Orange Scientiﬁc, respectively. For

dialysis in chloroform, a membrane of regenerated cellulose

1

3.25(m, 2H, −CH₂−), 3.4−3.54 (m, 1H, −CH). H and ¹³C NMR

spectra of CEO are shown in the Supporting Information, Figure S1.

To avoid degradation to 3-cyanopropanal, the labile monomer CEO

was stored under argon at −18 °C.

Representative Procedure for the Synthesis of Poly(THF-co-CEO)

Copolymers. CEO (0.1 g, 1.45 mmol, 69.02 g mol⁻¹) and THF (1.05

g, 14.5 mmol, 72.06 g mol⁻¹) were mixed in a glass tube under argon

atmosphere at room temperature. Methyl triﬂuoromethanesulfonate

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Scheme 2. Hypothetic Reaction Mechanism of the (Co)polymerization of THF and CEO

(MeOTf) (1 μL) was added via syringe. After 24 h, the polymerization

was quenched with pyridine. The product was dissolved in 0.5 mL

pyridine and puriﬁed via dialysis in THF for 4 days. After every 24 h,

THF was renewed (yields: 53−84%). ¹H NMR (300 MHz, CDCl₃): δ

(ppm) = 3.5−3.85 (m, −CH₂−), 4.14−4.66 (m, −CH−), 3.31−3.52

(m, −CH₂−), 1.47−1.74 (m, −CH₂−).

the poly(THF-co-CEO)copolymer was dissolved in 2 mL of THF,

then 200 mg of Raney cobalt catalyst (Cr promoted, Grace 2724,

pretreated with hydroxide) in 2 mL of water was added and the

mixture was stirred at 40 °C and 100 atm H₂pressure, for 7 days. The

cooled reaction mixture was then ﬁltered and the solvents were

evaporated under reduced pressure. Puriﬁcation and further steps

follow the procedure of the carboxylic acid functionalized copolymers.

¹H NMR (300 MHz, CDCl-d₃): δ (ppm) = 4.26−4.21 (m, −CH−),

3.73−3.28 (m, −CH₂O−), 3.19 (m, −CH₃), 2.19 (m, CH₂NH₂),

1.75−1.55 (m, −CH₂CH₂−).

Mineralization of CaCO₃. Crystallization experiments were

carried out using the standard ammonia diﬀusion method reported

elsewhere³³⁻³⁵on well-deﬁned quarz-glass slides from Plano GmbH

with a diameter of 13 mm and a thickness of about 1 mm. The glass-

slides were placed on the bottom of 5 mL beakers ﬁlled with 2 mL of

an aqueous dilution of polyether polyacid polymer with as mentioned

concentration and a 5 M of calcium chloride. They were cleaned prior

crystallization by washing in acidic piranha solution for 2 h, washing

with ethanol and Millipore water until water reacted neutral. To make

sure that the atmosphere of the desiccator was oversaturated

permanently with ammonia and carbon dioxide, 7 g of ammonium

carbonate was used for a small sized desiccator. After 15 h of

crystallization, the glass slides were removed from solution, washed

Postpolymerization Modiﬁcation of Poly(THF-co-CEO) Copoly-

mers to Polyether Polyacids. The procedure used for postpolymeriza-

tion reaction of cyanide groups to carboxylic acid groups is comparable

to literature for other cyano-functional structures.³¹100 mg of the

poly(THF-co-CEO)copolymer was dissolved in 2 mL of THF, sodium

hydroxide (1 molar, 5 mL) was added and the reaction mixture was

stirred overnight at 55 °C. Subsequently, the polymer was puriﬁed and

the salts were removed via dialysis in THF/methanol (1:1) for 3 days.

THF/methanol was renewed every 24 h. The product was dried under

1

reduced pressure at 80 °C for 3 days (yield: 89%). H NMR (300

MHz, THF-d₈): δ (ppm) = 5.37 (m, CH−O−), 3.48−3.32 (m,

−CH₂O−), 3.28−3.25 (m, −CH₃), 2.53 (m, −OH), 1.56−1.54 (m,

−CH₂−).

Postpolymerization Modiﬁcation of Poly(THF-co-CEO) Copoly-

mers to Polyether Polyamines. The postpolymerization reaction of

cyanide groups to amine groups follows the description of Meijer et al.

developed for poly(propyleneimine) dendrimers.³²First, 100 mg of

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Table 1. Characterization Data for the Series of Poly(THF-co-CEO) Copolymers Prepared

a

b

composition

PTHF₅₈₆

[CEO]/%

CEO fraction /%

M_n/g mol⁻¹

M_w/M_n

0

5

0

42200

10900

21800

13400

9100

73000

18800

31900

9800

1.83

1.59

1.42

1.31

1.34

1.49

1.74

P(THF_146.2-co-CEO₅)

P(THF₂₈₉-co- CEO₁₄)

P(THF_174.8-co-CEO_11.7

3.3

4.6

6.3

6.9

8.4

29.3

5

)

6

P(THF_118.2-co-CEO_8.8

)

7

9700

P(THF_120.4-co-CEO_11.1

)

9

9400

8600

P(THF₅₃-co-CEO

)

22

25

5300

5100

a

b

1

Obtained from H NMR spectra. Determined by SEC measurements (THF, PS standards, RI signal).

occurs,⁴¹however this was observed only for other catalysts

and not for MeOTf.^{23,24,42−44}Finally, the polymerization of

ethylene oxide is known to follow the AM mechanism with

Broensted acids as a catalyst, in contrast to the polymerization

of THF.²⁹On the basis of this knowledge, we expected to

observe coexistence of both mechanisms in the copolymeriza-

tion of THF with CEO.

All copolymers prepared were characterized by SEC and

MALDI−ToF MS, as well as ¹H NMR and ¹³C NMR

spectroscopy. For SEC measurements, the samples had to be

dissolved in THF for 1 day to ensure complete solubility. The

resulting molecular weights and PDIs of all samples obtained by

SEC (measured in THF, PS standard) as well as the

comonomer fractions (vide infra) by NMR are listed in Table

1. Molecular weights range from 5100 to 31900 g·mol⁻¹with

low to moderate polydispersity (PDI) in comparison to

comparable literature.^9,46−48SEC elugrams with varied CEO

monomer ratio (from 3.3 to 29.3% of CEO incorporation in

the copolymer) are shown in Figure 1. With increasing CEO

carefully on both sides with saturated CaCO₃dilution and Millipore-

water to ensure resolving ammonium carbonate crystals without

inducing the resolving−recrystallization mechanism and to remove

excessive unbound polymer followed by drying under airﬂow.

RESULTS AND DISCUSSION

■

A. Monomer Synthesis and Copolymerization of CEO

with THF. Monomer Synthesis. Cyano ethylene oxide (CEO)

can be synthesized in a one step-procedure, following a

modiﬁed literature protocol.³⁰Dropping sodium hypochlorite

to acrylonitrile aﬀords the desired product. The excess of

acrylonitrile can be retrieved by distillation. In this way, the

moderate to low yield of the product CEO (39.5%) can be

enhanced by utilizing repetitive procedures. To avoid possible

degradation of the monomer CEO to 3-cyano propanal, it was

stored under argon at −18 °C. To date, CEO has not been

employed successfully as a monomer for polymerizations to the

best of our knowledge. First attempts to polymerize CEO were

described by Wei and Butler in the 1970s, however no polymer

could be obtained.³⁶

Copolymerization of THF and CEO. The copolymerization

of THF and CEO was carried out with methyl triﬂuorometha-

nesulfonate (MeOTf) as an initiator, following recently

reported results regarding cationic ROP of THF with MeOTf

as an initiator.³⁷We chose this initiator because of the high

reactivity of MeOTf for the initiation of the “living” THF

polymerization in a fast and quantitative way.³⁷The polymer-

ization mechanism of THF with this initiator is known to

follow the so-called “active chain end” (ACE) mechanism

(Scheme 2) regarding the polymerization of CEO, in

accordance to literature describing the polymerization of

THF.³⁸The commonly very powerful methylating agent

MeOTf³⁹methylates the ring system either of THF or CEO

to enable the following nucleophilic attack of the oxygen atom

at another cyclic monomer. This step can be repeated either

with CEO or THF monomers, leading to linear chains. The

(co)polymerization can be terminated either with a base, e.g.,

pyridine or with a protic compound, e.g., methanol or water.

Although the homopolymerization of THF is known to follow

the ACE mechanism, this is not necessarily the case for the

copolymerization of THF with other cyclic monomers.

As stated for the recently published copolymerization of

THF and glycidyl phenyl ether with B(C₆F₅)₃as a catalyst, the

(co)polymerization can be controlled by synthesis conditions,

such as reaction time, catalyst concentration, and monomer

concentration.⁴⁰However, a high THF content appears to be

necessary to avoid cyclic products.⁴⁰Furthermore, for the

(co)polymerization of THF with other cyclic monomers as,

e.g., ethylene oxide or the bisglycidyl ether of bisphenol A it

appears to depend on reaction conditions, whether the ACE

mechanism or the “Active Monomer” (AM) mechanism

Figure 1. SEC elugrams (in THF, PS standard) of several poly(THF-

co-CEO)copolymers with varied CEO incorporation ratio (from 3.3 to

29.3%).

fraction molecular weights clearly decrease, whereas the PDI

remains unchanged. We attribute this to the coexistence of the

ACE and AM mechanism. Hence, with increasing THF ratio

the ACE mechanism occurs, in accordance to literature,^24,37,38

and with increasing CEO fraction coexistence of ACE and AM

mechanism seems to take place, as expected.^24,40

1

Figure 2 depicts a series of H NMR spectra of copolymers

with diﬀerent monomer content, ranging from 3.3 to 29.3 mol

% CEO. With increasing amount of CEO in the copolymers,

the solubility of the materials in organic solvents decreased.

Thus, in this work we aimed at materials with a minority

D

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Figure 2. ¹H NMR spectra (CDCl₃, 300 MHz) of several poly(THF-co-CEO) copolymers with varied monomer ratio (from 3.3 to 29.3%). Bottom:

magniﬁcation of the relevant signals c and d.

Figure 3. Top: Inverse gated ¹³C NMR spectra (CDCl₃, 100.6 MHz). Bottom: ¹³C DEPT NMR spectra of P(THF-co-CEO) with a fraction of 6.9%

CEO (CDCl₃, 100.6 MHz) (C, CEO; T, THF).

1

fraction of CEO units. In the H NMR spectra, the signals of

the polyether backbone belonging to THF units appears at

1.47−1.74 ppm (Figure 2, a) and 3.31−3.52 ppm (Figure 2, b).

The signals of the polyether backbone that stem from the CEO

units are visible in the range of 4.14−4.66 ppm (Figure 2, CH)

and 3.5−3.85 ppm (Figure 2, CH₂). On the basis of these

assignments, the monomer incorporation rates of both THF

and CEO were calculated, as listed in Table 1.

(Figure 23, a) and 69.85−71.10 ppm (Figure S23, b). The

signals of CEO units are visible at 119.75−115.7 ppm (Figure

S23, CN, blue framed), 73.27−71.10 ppm (Figure S23, CH₂,

marked green) and 69.52−67.35 ppm (Figure S23, CH, marked

red).

A detailed assignment of the signals in the ¹³C NMR

spectrum is shown in Figure 3 for the spectrum of the

copolymer with 6.9% CEO incorporation. The assignments are

supported by the results of the ¹³C DEPT NMR (Figure 3) and

are in good agreement with literature values for THF

copolymers.^43,47

All relevant signals are found in the ¹³C NMR spectra as well

(Figure S23). Here, the signals of the polyether backbone

belonging to the THF units appears at 25.25−28.04 ppm

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Figure 4. Relevant section of inverse gated (IG) ¹³C NMR spectra (CDCl₃, 100.6 MHz) of several poly(THF-co-CEO) copolymers with varied

monomer ratio from 3.3 to 29.3% CEO incorporation (C, CEO; T, THF).

¹³C NMR Triad Analysis. To gain a deeper understanding of

the microstructure of the poly(THF-co-CEO)copolymers, ¹³C

NMR spectroscopy based triad analysis was carried out. The

analyzed triads (i.e., sequences of three subsequent monomer

units) were labeled as recently described for EO/EPICH

copolymers⁴⁸and as established for EO/PO copolymers,^50,51

EO/DEGA copolymers¹⁷or other amine-functional PEGs.¹⁸

Peak assignment was achieved by comparison with amine-

functional PEGs^13,18,17,52recently synthesized in our group, as

well as by comparison with THF/glycidol copolymers^23,53and

other comparable spectra.⁴⁹Figure 4 shows the relevant region

of the inverse gated ¹³C NMR spectra of several poly(THF-co-

CEO) copolymers with varied CEO ratio (from 3.3 to 29.3%

CEO incorporation).

With decreasing CEO content, the appropriate signals

belonging to CEO at 72.58, 71.94, 72.77, 71.43, 70.93, 70.82,

70.36, 70.17, and 68.73 ppm disappear, while the CH₂signal at

70.74−70.52 ppm, belonging to THF, is still visible, as

expected. It is conspicuous that the signal belonging to the

C−C−C triad does not increase with increasing CEO content,

as well as the signal for the C−C−T triad. Furthermore, the

triads T−C−C and T−C−T increase with increasing CEO

content. We attribute this to a random or very slight gradient

type microstructure, however, clearly not as a block-like

structure. Besides the triad analysis of CEO units, a triad

analysis of THF units was carried out as well, giving comparable

results, as shown in the Supporting Information (Figure S.21).

Kinetic Studies via NMR Spectroscopy. To support the

results of the triad analysis, kinetic studies have also been

carried out. Diﬀerent comonomer reactivity can lead to gradient

type or block-like polymer chain structures, which determine

the properties of the resulting materials. Hence, it is important

to investigate the functional group distribution within the

backbone. In the copolymerization of CEO and THF gradient

copolymer structures might be expected due to the higher

reactivity of oxiranes compared to oxolanes based on the

respective ring strain. ¹H NMR kinetic studies were carried out

by taking samples to compare the incorporation rates of THF

and CEO in the copolymers. The (co)polymerization was

conducted in bulk under argon atmosphere with MeOTf as an

initiator and at room temperature, following the procedure of

the synthesis of the materials listed in Table 1. Figure 5 shows

1

the H NMR spectrum of a mixture of CEO and THF (1:5)

before initiation and several ¹H NMR spectra after initiation in

a time frame of 1 min to 58 h. The kinetic studies were carried

out for 58 h due to the fact that the reaction mixture had still

not solidiﬁed. Compared to the synthesis of the copolymers

listed in Table 1 we expected solidiﬁcation of the reaction

mixture after 12 h. Hence, sampling of the reaction mixture

seemed to impede the (co)polymerization process. However,

the results show that the intensities of the signals of both

monomers, CEO (3.08−2.92 ppm, green, a) and THF (1.8−

1.68 ppm, blue, d), clearly decrease and signals belonging to the

polymer backbone increase with increasing time. The signals of

the CH₂−O− groups of the backbone overlay with a signal of

CEO (3.33−3.29 ppm, b) and are visible at 3.47−3.24 ppm.

Further signals belonging to the backbone are present at 1.61−

1.39 ppm for CH₂groups of THF units (blue framed, d′) and

at 4.69−4.11 ppm for the CH groups of CEO units (green

framed, b′).

To conﬁrm that the signals stem from the copolymers and

not from degradation products of the monomer, diﬀusion

ordered ¹H NMR spectroscopy (DOSY) of the puriﬁed

copolymer was carried out. The obtained spectrum is shown

in the Supporting Information (Figure S7) and exhibits signals

at 4.60 and 4.24 ppm, which are in agreement with the signals,

visible in Figure 2 and with the signals obtained from the

kinetic studies. However, the signals of the kinetic studies might

be more precise and separated due to the good solubility of the

growing oligomers. We attribute the presence of several signals

for the CH groups to the fact that there might be diﬀerent

chemical shifts depending on whether the protons belong to

terminal or linear units and whether CEO or THF is in the

neighboring monomer unit. Finally, the signal at 4.6 ppm is

visible via correlated spectroscopy (COSY) and correlates with

the CH₂signals of the CEO units at 3.69 ppm (please see

Supporting Information, Figure S8).

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Figure 5. Kinetic studies via ¹H NMR spectroscopy (300 MHz, CDCl₃), green: CEO and blue: THF in a time frame of 1 min to 58 h, (1:5, CEO:

THF), bottom: fraction of initial monomer concentration for both CEO and THF (M_x,t/M_x,0), normalized to 1(100%) for both monomers,

respectively, vs total monomer conversion.

The results show that THF is incorporated faster than CEO

(Figure 5, bottom). Thus, we expect a gradient type copolymer

structure. We attribute the slower incorporation of CEO to the

steric hindrance of the cyano group of the CEO comonomer,

however the ring strain of oxiranes is clearly higher than for

oxolanes (EO: 116 kJ mol⁻¹, THF: 23 kJ mol⁻¹).⁵⁴Figure S3 in

the Supporting Information shows a further plot of the

respective monomer conversion vs total monomer conversion.

In summary, the kinetic studies provide evidence for the

successful incorporation of both monomers, as well as a faster

incorporation of THF, leading to gradient type structures.

Additionally, we conducted in situ ¹H and ¹³C NMR kinetics in

bulk, however the lack of stirring during the measurements

impedes a detailed calculation of the reaction rates (Supporting

Information, Figures S4−S6).

the Supporting Information. Molecular weights up to 2200 g·

mol⁻¹were detected for the soluble fraction of the

homopolymers.

B. Postpolymerization Modiﬁcation of Poly(THF-co-

CEO) Copolymers to Water-Soluble Polyether Polyacids

and Polyetheramines. Linear polyacids with tunable number

of functional groups as well as molecular weights are promising

for various potential applications, e.g., as gelling agents,

lubricants, or ion exchange resins or for thickening in

pharmaceuticals, cosmetics, and paints. The most widely

applied example of polyacids is poly(acrylic acid) (PAA).⁵⁵

Especially the facile one-step postpolymerization procedure

renders the novel polyTHF copolymers interesting even for

potential industrial applications, due to the commercially

available chemicals like sodium hydroxide and THF, as well

as low temperatures (55 °C) and short reaction times. To date,

to the best of our knowledge no postpolymerization reaction of

functional polyTHF has been reported for the synthesis of

linear polyacids. In order to develop water-soluble polyTHF-

based polyelectrolytes, ﬁve poly(THF-co-CEO) copolymer

Homopolymerization of CEO was also carried out. However,

as shown in the Supporting Information, the homopolymer

PCEO shows very limited solubility in all solvents employed.

Nevertheless, some results regarding the soluble fraction of the

homopolymers are summarized in Table S3 and Figure S22 of

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samples used for the generation of poly(THF-co-carboxylic acid

ethylene oxide) (P(THF-co-CAEO)) have been prepared and

extensively characterized by NMR, MALDI−ToF MS, and FT-

IR spectroscopy.

concerning related molecular weights before and after

postpolymerization. Some deviations occur (e.g., sample 1 in

Table 2), which may be explained by utilizing diﬀerent solvents

for the ¹H NMR measurements (CDCl₃for P(THF_x-co-

CEO_1−x) and THF-d₈for P(THF_x-co-CAEO_1−x)). This was

necessary to ensure well dissolved materials, given that the

polyether polyacids were not completely soluble in CDCl₃,

which was the preferred solvent for the poly(THF-co-CEO)

copolymers. Most notably, results show, that the average

molecular weights do not decrease, which excludes degradation

of the polymer backbone during the reaction step with sodium

hydroxide. We suggest a possible steric hindrance of the

functional nitrile groups belonging to the CEO units, which are

closer to the polyether backbone in contrast to the alkaline

labile PEG-co-PEPICH copolymers.⁴⁸

Postpolymerization modiﬁcation was carried out following

the procedure of Peng et al.³¹The poly(THF-co-CEO)

copolymer was dissolved in THF, sodium hydroxide (1

molar) was added, and the reaction mixture was stirred

overnight at 55 °C. Subsequently, the polymer was puriﬁed and

the salts were removed via dialysis in THF/methanol (1:1) for

3 days. The THF/methanol mixture was renewed every 24 h.

This reaction step is described in Scheme 1. All resulting

polyether polyacids were soluble in water up to a concentration

of 1 mg mL⁻¹and at a pH value of 10. However, polyether

polyacids with a low CAEO fraction of 3.3 and 4.6% still yield

slightly cloudy solutions, which did not become clear even at

higher pH values. On the other hand, regarding the insoluble

polyTHF backbone of the materials it is striking that even low

amounts of hydrolyzed CEO units in the copolymers lead to a

certain solubility of the polyTHF copolymers in water.

Because of the known interaction of carboxylic acids with the

column material, no SEC measurements were carried out for

the acid functional copolymers. However, molecular weights

before and after modiﬁcation were comparable according to ¹H

NMR. Results are listed in Table 2 and show a trend

¹H and ¹³C NMR Spectroscopy. Figure S14 depicts a series

1

of H NMR spectra of polyether polyacids with varied CEO

ratio (from 3.3 to 8.4%) and a spectrum of a poly(THF-co-

CEO) copolymer with a fraction of 3.3% CEO for comparison.

At the top of Figure S14, a zoom-in of the respective spectra is

shown. At 3.48−3.32 ppm and 1.56−1.54 ppm the backbone of

the THF units of the copolymer is visible, which overlap with

the signals of the backbone of the functionalized CEO units.

The signal belonging to the CH groups of CEO units at 4.42

ppm disappears and a signal for the CH groups of the

carboxylic acids after transformation appears at 5.37 ppm,

demonstrating the successful postpolymerization reaction.

The successful postpolymerization modiﬁcation can be

shown via ¹³C NMR spectroscopy as well and even for the

copolymer with a low fraction of 3.3% CEO (see Figure 6 and

Figure S15). Unfortunately, it was not possible to ﬁnd a solvent

suitable for both copolymers before and after modiﬁcation.

However, the change of the solubility can be taken as a ﬁrst

indication for a successful postpolymerization reaction. As

presented in the zoom-in in Figure 6, the signal concerning the

cyanide group at 119.68−116.24 ppm disappears after

conversion and a signal at 160.14 ppm appears, belonging to

the carbon atoms of the carboxylic acid groups.

1

Table 2. Characterization Data of H NMR Measurements

for the Series of Poly(THF-co-CEO) Copolymers and the

Post-Polymerization Modiﬁcation to P(THF_x-co-CAEO_1−x

)

a

M_n(NMR)

a

CEO content /%

P(THF_x-co-CEO_1‑x

)

P(THF_x-co-CAEO_1‑x)

8.4

6.9

6.3

4.6

3.3

9400

9100

12100

7100

13400

21800

10900

10600

25400

9500

a

Calculated via ¹H NMR spectra in CDCl₃(P(THF_x-co-CEO_1−x)) and

in THF-d₈(P(THF_x-co-CAEO_1−x)), 300 MHz.

MALDI−ToF Mass Spectroscopy. Besides NMR spectrosco-

py, MALDI−ToF mass spectroscopy (MS) was performed to

Figure 6. ¹³C NMR spectra of the CEO-THF copolymer (300 MHz, CDCl₃) with a fraction of 3.3% CEO (bottom) and the same copolymer after

postpolymerization reaction to carboxylic acid groups (300 MHz, MeOD-d₃,). Top: magniﬁcation of the relevant section.

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Figure 7. FT-IR spectra of several poly(THF-co-CAEO)copolymers with varied CEO content (3.3−8.4%) after transformation of the nitrile groups

to carboxylic acid groups.

gain information on the successful copolymerization of CEO

and THF, as well as to investigate the complete postpolyme-

rization reaction of the cyanide groups. Furthermore, MALDI−

ToF MS is a method to support molecular weights obtained via

SEC or NMR spectroscopy, and to investigate possible

degradation of the copolymers during the modiﬁcation step.

Figure S9 (top) depicts the spectra of two exemplary

poly(THF-co-CEO) copolymers with a fraction of 8.4 and 6.9%

CEO, together with the spectra after postmodiﬁcation to

carboxylic acids of the same (blue), as well as the magniﬁcation

of these spectra (bottom). A complete signal assignment is also

given in Figure S9. The results show that the copolymerization

of CEO and THF was successful, resulting in incorporation of

both monomers. Furthermore, the postpolymerization reaction

was complete, given that no residual signals of the poly(THF-

co-CEO) copolymers were found. The average molecular

weights did not vary signiﬁcantly before and after postpolyme-

rization modiﬁcation (Figure S10). Molecular weights

determined by MALDI−ToF were slightly smaller than

observed via SEC or NMR. We attribute this to the so-called

“mass discrimination eﬀect”, which underestimates higher

molecular weight fractions.⁵⁶⁻⁵⁸

combination of polyTHF with functional amine groups was

described in literature¹¹with the aim to construct dendrimer

containing hybrid networks.⁶³An additional strategy to

combine polyTHF with amine groups is the end-capping of

polyTHF to obtain “ditopic” macromonomers.⁸Possible

applications of these structures are envisaged especially in the

polyurethane (PU) production, since polyTHF is a widely used

material for the soft segments in PUs and since amines are

typically added to catalyze urethane formation.

Postpolymerization modiﬁcation to P(THF_x-co-CAmEO_1−x

)

was carried out following the hydrogenation procedure

developed by Meijer et al. for polyamine dendrimers³²and

recently published routes of our group.⁴⁸The poly(THF-co-

CEO)copolymer was dissolved in THF, the Raney cobalt

catalyst, dissolved in water, was added and the mixture was

stirred under H₂pressure for 7 days. A detailed description is

given in the experimental section and the transformation is

shown in Scheme 1. Molecular weight before and after the

1

transformation determined via H NMR is comparable as well.

The results are listed in Table 3 and show similar molecular

1

Table 3. Characterization Data from H NMR

FT-IR Spectroscopy. As an additional method to investigate

the successful copolymerization of CEO and THF, and to

gather evidence for complete conversion to polyether polyacids,

FT-IR spectroscopy was carried out. The normalized spectra of

the ﬁve postpolymerized copolymers are depicted in Figure 7.

With increasing CEO fraction, the bands at 1600−1700 cm⁻¹

increase as well, which can be assigned to carboxylic salts, in

accordance to literature for carboxylic acids.³¹

C. Postpolymerization Modiﬁcation of Poly(THF-co-

CEO) Copolymers: Polyetheramines. Amino-functional

polyethers attract industrial as well as academic interest due

to their pH-responsive behavior.^{17,18,45,48,59−61}However, not

only the well-established and water-soluble poly(ethylene

glycol) has been applied for this purpose. The group of

Tsvetanov introduced an even more hydrophobic glycidylamine

derivative, glycidyl didodecylamine to provide high solubilizing

power toward extremely hydrophobic drugs.⁶²

Measurements for the Series of Poly(THF-co-CEO)

Copolymers and the Modiﬁcation to P(THF_x-co-

CAmEO_1−x

)

a

M_n(NMR/g·mol⁻¹

)

a

CEO content /%

P(THF_x-co-CEO_1‑x

)

P(THF_x-co-CAmEO_1‑x)

8.4

6.9

6.3

4.6

9400

9100

9000

7700

8700

9600

10400

13400

21800

10900

3.3

a

1

Calculated via H NMR spectra in CDCl₃, 300 MHz.

weights before and after modiﬁcation, with the exception of the

sample with 4.6% CEO fraction. Here, the molecular weight

after postmodiﬁcation is lower after hydrogenation, which

attribute this to solubilizing eﬀects of the amine groups in the

solvent.

The postpolymerization of poly(THF-co-CEO) copolymers

to polyether polyamines permits access to amine-functionalized

materials with moderate to high molecular weights. A

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1

Figure 8. H NMR (300 MHz, CDCl₃) of P(THF_0.95-co-CAmEO_0.05) (top) and the poly(THF-co-CEO) copolymer with a fraction of 4.6% CEO

(bottom) and the magniﬁcation of the relevant signals, respectively.

¹H NMR Spectroscopy. Figure 8 shows the ¹H NMR spectra

of the amine-functional polyTHF copolymers, together with a

magniﬁcation of the relevant sections, of P(THF_0.95-co-

CAmEO_0.05) (top) and of the poly(THF-co-CEO)copolymer

with a fraction of 4.6% CEO (bottom), respectively. A detailed

assignment of the signals stemming from the polymer backbone

of poly(THF-co-CEO)copolymers was given in the context of

the kinetic studies (Figure 5) and is comparable to the signal of

the backbone of the postmodiﬁed copolymers. A clear

transformation of the signals before and after postmodiﬁcation

is visible and depicted in the magniﬁcations. The signal

assigned to the CH groups at 4.54 ppm disappears completely

and a new signal occurs at 4.26−4.21 ppm (Figure 8, top, on

the left, a). Furthermore, a signal at 2.19 ppm appears, which

can be assigned to the CH₂groups next to the nitrogen atom.

The chemical shift of this signal is in analogy to comparable

structures in literature.^45,48

1519.3 cm⁻¹appear, which can be assigned to primary

amines.⁶⁴At 1003.91 cm⁻¹the C−N stretch is visible, followed

by the “out-of-plane NH bend” at 858.65 cm⁻¹.^64,65The results

conﬁrm the successful transformation of the cyanide groups to

carboxylic acid and amine groups, respectively.

D. Properties of the Polyether Copolymers. Diﬀerential

scanning calorimetry (DSC) has been used to quantify the

thermal properties of the materials. Table S2 lists the resulting

melting points (T_m) of the poly(THF-co-CEO) copolymers

with CEO fractions from 3.3 to 8.4%, as well as of the

copolymers after postmodiﬁcation to carboxylic acid and amine

groups, respectively. With increasing amount of CEO in the

copolymers the melting points decreased slightly from 30 (3.3%

CEO) to 21 °C (8.4% CEO). The same trend can be seen for

the carboxylic acid containing polymers, where the melting

point decreased from 26 to 18 °C and for the amine containing

polymers, where the melting point decreases from 28 to 23 °C

(3.3 to 6.9% CEO). The melting points of the copolymers with

carboxylic acid groups are slightly lower than before post-

modiﬁcation and lower than the melting points of the amine

functionalized analogues (see Figure S18). This is in

accordance with literature on related systems.⁴⁸In one case

no melting point of the amine functionalized copolymers could

be obtained. This might be attributed to the functional amine

groups, which seem to impede crystallization of the material.

For the polyTHF homopolymer T_gvalues can be found in

some publications and vary between −65⁴⁶and −84 °C.⁶⁶

Contact Angle Measurements. Besides the investigation of

the thermal behavior, contact angle measurements of water on

P(THF-co-CEO)-ﬁlms have been carried out to assess surface

properties of the materials. Furthermore, contact angles on

ﬁlms of P(THF-co-CEAO) as well as P(THF-co-CEAmO) were

measured to investigate the diﬀerent surface tensions of these

materials, before and after postmodiﬁcation. As expected, with

decreasing CEO content in the copolymers, the materials

showed increasing solubility in hydrophobic solvents. After

postmodiﬁcation, the carboxylic acid groups in the copolymer

should contribute to lowered contact angles. Figure 9 shows the

measured contact angles for the copolymers (Figure 9, black:

P(THF-co-CEO), green: P(CEAmO-co-THF), red: P(CEAO-

co-THF)). Silicon wafers were coated using copolymer

It is interesting to note that above a concentration of 7 mg

mL⁻¹of the amine-functionalized copolymers in suitable

solvents gelation is observed. Suitable solvents for the

formation of organogels are all solvents that dissolve the

THF units in the backbone, as listed in the Supporting

Information (Table SI 1). The copolymers can be redissolved

after drying of the gels and used for the generation of

organogels again reversibly. Further work on the nature of

gelation in these materials is in progress. Unfortunately, this

eﬀect impedes ¹³C NMR measurements, due to a higher

1

attended amount of the material in comparison to H NMR

measurements. However, the successful postmodiﬁcation of the

CEO-THF copolymers to amine groups was conﬁrmed via

MALDI−ToF MS as well as with FT-IR spectroscopy.

Via MALDI−ToF MS the transformation of the cyanide

groups to amine groups was investigated. Figure S12 in the

Supporting Information presents the spectrum of the exemplary

poly(THF-co-CEO) copolymer, modiﬁed to amine groups,

with a fraction of 8.4% CEO. No residual signals for

unmodiﬁed polymer chains were founded, as can be seen

after overlaying both spectra (see Figure S13). Besides

MALDI−ToF MS, FT-IR spectroscopy was carried out to

investigate the formation of amine groups (Figures S17).

Typical for amine groups two bands at 1603.41 and

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Figure 9. Contact angles of water at P(CEO_x-co-THF_1−x)-ﬁlms at

diﬀerent CEO/THF ratios (black), as well as contact angles of water

on postmodiﬁed copolymer-ﬁlms to carboxylic acids (red) and amines

(green).

solutions in chloroform or THF. Subsequently, the solvent was

evaporated under reduced pressure at 90 °C for 24 h. With

increasing amount of CEO the contact angle decreased from

60.7° for 3.3% CEO units down to 48.0° for 8.4% CEO units.

For the apolar polyTHF, we obtained a contact angle of 72.7°.

The results mirror the content of CEO, as expected. After

postmodiﬁcation, contact angles decrease slightly for the

carboxylic acids as well as for the amines, however the eﬀect

is more pronounced for the carboxylic acids. For instance, for

the copolymer with 8.4% carboxylic acid groups the contact

angle decreases to 17.8°, reﬂecting a highly polar ﬁlm surface.

With regard to the high contact angle of polyTHF (72.7°),

even the low content of 8.4% carboxylic acid groups in the

materials shows a strong eﬀect on the contact angles.

E. Mineralization of Calcium Carbonate. To the best of

our knowledge, polyethers with carboxylic acids have not been

employed for mineralization experiments, mainly due to their

very limited availability. In the case of the carboxylic acid

functional polyTHF copolymers, the unusual combination of an

apolar backbone with a controlled number of hydrophilic

carboxylic acid groups is an intriguing precondition for such

studies. CaCO₃is a well-established inorganic model system for

studying the eﬀect of additives on the crystallization

behavior.^33−35,67Besides its industrial importance as a major

source of water hardness,⁶⁸as a mineral ﬁller^69,70or raw

material for construction chemicals^71,72CaCO₃also represents

the most common biomineral with complex morphologies and

crystals exhibiting deﬁned crystallographic orientations in

shells⁷³and exoskeletons.^74,75A key feature of many

biominerals is that they are composed of smaller crystals of

similar size and shape, which are arranged in a regular periodic

Figure 10. SEM images (A, B) calcite reference; (C−F) calcite crystals

precipitated in the presence of 0.04 mmol·L⁻¹of postmodiﬁed

copolymer with a fraction of 8.4% CEO (sample 1, listed in Table 2)

to polyacids.

most stable and apolar surfaces). The most pronounced eﬀect

on crystal growth is observed on facets with highest polarity.

These are the [010] and [012] facets, which are oriented

parallel to the spatial (c axis) of the rhombohedra.⁷⁹In the

presence of polar additives polar steps are formed because of a

stabilization of the polar edges.⁷⁹If this occurs extensively, the

crystals will be elongated along the c axis,⁸⁰as shown in the

SEM images in Figure 10D−F. In addition, the decrease of the

crystal size from approximately 10−20 μm to 3−5 μm through

the polyether-polyacid additive (Figure 10C) indicates either

(i) an increase of the nucleation density or (ii) an inhibition of

the crystal growth. The model of growth inhibition is supported

by a statistical evaluation of the sizes of 100 mesocrystals

(Figures S19 and S20, Supporting Information) formed after

adding modiﬁed copolymers with increasing amounts of CEO.

A plot of the number of carboxylate groups of the polymer

versus the maxima of the Gaussian trend lines (Figure S19)

clearly shows a linear decrease of the CaCO₃crystal size with

the content of carboxylate groups in the PTHF copolymers.

This indicates that strong surface binding of the polymer to the

crystal steps through Ca²⁺surface complexation and a

concomitant increase of the number of steps (Figure S21

C,D for 3.3% of CEO and Figure 10 for 8.4% of CEO). The

polar steps are stabilized to a diﬀerent extent by CEO groups,

pattern. Colfen and co-workers coined the term mesocrystal⁶⁷

̈

to describe this oriented aggregation, where the smaller crystals

have parallel crystallographic alignment.^76,77Especially for

potential use as antiscalant or as soft component in a CaCO₃

hybrid material the inﬂuence of polyether polyacids on the

precipitation of CaCO₃has to be understood.⁷⁸In this context,

the postmodiﬁed carboxylic acid functional poly(THF-co-CEO)

copolymers have been used as additives to crystallize CaCO₃on

quartz glass slides.

As shown in Figure 10, without any additive CaCO₃

crystallizes in its thermodynamically most stable polymorph

calcite with rhombohedral crystal morphology and crystal sizes

between 10 and 20 μm and terminated by the [104] facets (the

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as illustrated in Scheme S1 (Supporting Information). We

assume that for copolymers with a smaller amount of

statistically distributed acidic groups a more ﬂexible polymer

chain is adsorbed on the polar facets. The loosely bound

polymer does not provide full surface coverage, and CaCO₃

continues to precipitate, whereas an even higher amount of

CEO groups forces stronger, less loopy and thus tighter binding

of the polymer. This prevents ions from adsorbing on the

edges, and new edges start to form. Surprisingly, the

hydrophobic backbone appears to exert a stronger stabilizing

eﬀect than the acidic binding groups due to steric shielding.

The growth of calcite rhombohedra can be understood from

Figure 10F showing a calcite mesocrystal with the characteristic

calcite morphology composed of nanoscopic surface-function-

alized building blocks. This is in agreement with the outcome of

previous studies, where a polymer-induced liquid precursor

phase (PILP)^80,81stabilized by PAA^{35,76,82−88}or Ca-binding

proteins^75,89,90played a leading role for the formation of

mesocrystals.⁶⁷

wavenumbers (279 cm⁻¹). The broadening of all other signals

indicates the presence of noncrystalline domains.^91,92In

essence, the strong surface binding properties make polyTHF

polyacids an eﬃcient crystallization inhibitor for the precip-

itation of CaCO₃(in analogy to the more polar PAA).⁸³The

strong stabilization in spite of a smaller number of acidic groups

is due to steric shielding of the polar edges by the more

hydrophobic backbone of polyTHF.

CONCLUSIONS

■

PolyTHF is generally known as an apolar, ﬂexible polymer. In

this work, we demonstrate that copolymerization of minor

amounts of a novel functional epoxide can be exploited to

generate new polyTHF copolymers that are water-soluble at

elevated pH and can even be used for mineralization studies in

aqueous solution, despite the mainly apolar polyTHF backbone

structure. To date copolymers consisting of THF and

functional monomer units have hardly been investigated.⁸⁻¹¹

Here the random cationic ring-opening copolymerization of

THF and cyano ethylene oxide (CEO) has been studied, using

varied CEO fractions from 3.3 to 29.3% and molecular weights

in the range of 5100 and 31900 g·mol⁻¹(molecular weight

distributions: 1.31−1.74, SEC in THF, PS standards, RI

detector). The polymerization was conducted with methyl

triﬂuoromethanesulfonate (MeOTf), and kinetic studies

concerning the reactivity of both monomers have been

performed via NMR spectroscopy. Furthermore, we present

postmodiﬁcation reactions of the cyano groups to carboxylic

acid groups as well as to amine groups in a one-step procedure.

The copolymerization of CEO and THF and the post-

modiﬁcation reactions have been characterized via NMR,

MALDI−ToF mass and FT-IR spectroscopy. The thermal

properties of the materials have been examined via DSC. To

investigate surface properties, contact angles have been

measured, which can be tuned in the range of 72.7° to 17.8°

by varying the CEO fraction as well as by postmodiﬁcation.

The eﬀect of polyether polyacids with diﬀerent amounts of

carboxylic groups on the crystallization of CaCO₃is not only

dominated by the number of carboxylate groups but also by the

steric shielding of the hydrophobic polyTHF backbone. The

polyether polyols seem to play multiple roles during

crystallization by (i) acting as nucleation sites, (ii) stabilizing

liquid droplets of amorphous CaCO₃(PILP) and (iii)

inhibiting the growth of calcite by surface binding. Further

studies on the materials properties of these unusual functional

polyethers are under way.

This hypothesis is also supported by TEM images (Figure

11) showing the formation of an amorphous (PILP) polymer-

Figure 11. TEM images of polymer micelles before crystallization (A),

polymer micelles and PILP after 1 h (B), agglomerated ACC from

PILP after 2 h (C), microstructure of CaCO₃particles agglomerated

on calcite rhombohedra after 4 h of reaction time (D). All samples

were prepared in the presence of 0.04 mmol/L of postmodiﬁed

copolymer with 8.4% CEO fraction.

ASSOCIATED CONTENT

■

S

* Supporting Information

The Supporting Information is available free of charge on the

ACS Publications website at DOI: 10.1021/acs.macro-

mol.6b00113.

stabilized liquid-like phase. The solidiﬁcation of the liquid

droplets (Figure 11A) starts 1 h after initiating the ammonia

diﬀusion in a desiccator (Figure 11B). Further increase of the

CO₂concentration leads to the formation of amorphous

calcium carbonate (ACC) agglomerates from the PILP (Figure

11C) and CaCO₃particles agglomerated on the surfaces of

calcite rhombohedra.

The eﬀect of the polymer is also visible in the Raman spectra

(Figure S22, Supporting Information), where besides the calcite

bands a background ﬂuorescence signal of the polymer was

observed. The lattice mode at 283 cm⁻¹is shifted to lower

Additional ¹H, ¹³C, DOSY, NMR kinetics, MALDI−ToF

and IR spectra and other characterization data (PDF)

AUTHOR INFORMATION

■

Corresponding Author

*(H.F.) E-mail: hfrey@uni-mainz.de.

Notes

The authors declare no competing ﬁnancial interest.

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(18) Herzberger, J.; Kurzbach, D.; Werre, M.; Fischer, K.;

Hinderberger, D.; Frey, H. Stimuli-Responsive Tertiary Amine

Functional PEGs Based on N,N -Dialkylglycidylamines. Macro-

molecules 2014, 47, 7679−7690.

ACKNOWLEDGMENTS

■

E.-M.C. and J.H. thank the Graduate School of Excellence

Material Science in Mainz “MAINZ” for ﬁnancial support and

acknowledges technical assistance from Michael Blaser. J.H. is

grateful to the Fonds der Chemischen Industrie for a

scholarship. M.M. thanks the Max Planck Graduate Center

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