One-step synthesis of triarm block copolymers by simultaneous atom transfer radical and ring-opening polymerization

O R I G I N A L P A P E R

One-step synthesis of triarm block copolymers

by simultaneous atom transfer radical and ring-opening

polymerization

Temel O

¨ ztu¨rk

_{Mahmut Yavuz}

_{Melahat Go¨ktas¸}

Baki Hazer

Received: 15 April 2015 / Revised: 8 September 2015 / Accepted: 11 November 2015 / Published online: 20 November 2015

Ó Springer-Verlag Berlin Heidelberg 2015

Abstract

One-step synthesis of poly(MMA-b-CL) triarm block copolymers was

carried out by atom transfer radical polymerization of methyl methacrylate (MMA)

and ring-opening polymerization of e-caprolactone (CL) using

3-chloro-1,2-propanediol trifunctional initiator. The triarm block copolymers comprising one

MMA arm and two CL arms were synthesized by changing some

poly-merization conditions such as monomer/initiator concentration, polypoly-merization

time. The effect of the reactions conditions on the polydispersity and molecular

weights was also investigated. The block lengths of the block copolymers were

calculated by using

H-nuclear magnetic resonance (

H-NMR) spectrum. It was

observed that the block length could be altered by varying the monomer and

ini-tiator concentrations. The characterization of the products was achieved by using

1

_{H-NMR, Fourier-transform infrared spectroscopy, gel-permeation}

chromatogra-phy, differential scanning calorimetry, thermogravimetric analysis and fractional

precipitation techniques.

Keywords

Atom transfer radical polymerization

 Ring-opening polymerization 

One-step polymerization

 Triarm block copolymer  Block length

& Temel O¨ztu¨rk temelozturk@msn.com

1

Department of Chemistry, Giresun University, 28100 Giresun, Turkey

2 _{Department of Chemistry, Kafkas University, 36100 Kars, Turkey} 3

Department of Science Education, Yu¨zu¨ncu¨ Yıl University, 65100 Van, Turkey

4

Department of Chemistry, Bu¨lent Ecevit University, 67100 Zonguldak, Turkey DOI 10.1007/s00289-015-1558-2

Introduction

Macromolecules of a desired structure and molecular weight can be synthesized by

controlled/‘‘living’’ radical polymerization (CRP) techniques, such as atom transfer

radical polymerization (ATRP) [

1

–

5

], nitroxide-mediated polymerization [

6

,

7

], and

reversible addition fragmentation chain transfer (RAFT) polymerization [

8

–

19

].

ATRP has a great number of advantages as compared with other CRPs. It includes a

lot of monomers, and offers a general and efficient way to synthesize various

(co)polymers [

20

], and does not require difficult conditions and has tolerance for

functional groups and impurities [

21

,

22

].

Block copolymers that have excellent physical properties are one of the most

important polymeric materials used in technological applications and theoretical

research because of their exceptional properties based on micro-phase separation

[

23

–

31

]. The viscosity of a star block copolymer is higher than that of linear

copolymer having the same molecular weight. Hence, star block copolymer is

mostly used as a resistant material. There are a great number of excellent articles

published on this subject [

32

–

43

].

In recent years, the one-step process has been successfully used for the synthesis

of block and graft copolymers using different techniques. The process has more

advantages than other popular methods. Due to the applicability of at least two

transformation steps simultaneously, side reactions which lead to homopolymer

formation are minimized [

44

–

58

]. Farah et al. carried out the synthesis of

poly(e-caprolactone-b-styrene) block copolymers through the combination of ATRP and

ROP in the presence of 2-bromoisobutyryl bromide and bipyridine using

N-methylpyrrolidione as the solvent [

59

]. Furthermore, various copolymers containing

styrene [

59

–

61

], n-butyl acrylate [

60

], methyl methacrylate [

61

], tert-butyl acrylate

[

62

], benzyl acrylate [

62

], e-caprolactone [

59

,

60

],

-lactide [

61

,

62

] monomers

were synthesized by a combination of the ATRP and ROP methods.

The present work is an extension of our recent studies involving the one-step

synthesis of copolymers through simultaneous RAFT polymerization and ROP

processes [

17

,

18

,

63

]. In this study, we synthesized poly (MMA-b-CL) triarm block

copolymers using 3-cholor-1,2-propiondiol (ATRP-ROP initiator) by the

simulta-neous ATRP and ROP of the reactants in one-step. Star block copolymers

synthesized could be used to prepare with the desired segment ratio by changing the

polymerization conditions. The effect of the reactions conditions on the parameters

was also investigated.

Experimental

Materials

3-Chloro-1,2-propanediol and copper(I) bromide (CuBr) were received from

Aldrich and used as received. Dibutyltindilaurate (DBTDL) and petroleum ether

were supplied by Merck and used as received. Benzene, chloroform, and

tetrahydrofuran (THF) were received from Sigma-Aldrich and used as received.

N,N,N

,N

,N

-Pentamethyldiethylenetriamine (PMDETA) was supplied by Fluka

and used as received. Methanol and ethanol were received from Birpa and used as

received. e-Caprolactone (CL) was supplied by Alfa Aesar and used as received.

MMA was received from Merck, which was purified as follows: it was washed with

a 10 wt% aqueous NaOH solution, dried over anhydrous CaCl

overnight, and

distilled over CaH

under reduced pressure before use. All other chemicals were

reagent grade and used as received.

Instrumentation

The molecular weights and molecular weight distributions were measured with

Malvern Viscotek RI-UV-GPC max gel-permeation chromatography (GPC) with

THF as the solvent. A calibration curve was generated with four polystyrene

standards: 2960, 50,400, and 696,500 Da, of low polydispersity. Fourier-transform

infrared (FTIR) spectra were recorded using an Alpha-p Bruker model FTIR

spectrometer.

H-nuclear magnetic resonance (

H-NMR) spectra of the samples in

CDCl

as the solvent, with tetra methylsilane as the internal standard, were recorded

using a Bruker Ultra Shield Plus, ultra-long hold time 400 MHz NMR spectrometer.

Thermogravimetric analysis (TGA) measurements of the polymers were carried out

under nitrogen using a Perkin Elmer Pyris 1 TGA and Spectrum thermal analyzer to

determine thermal degradation. Differential scanning calorimetry (DSC)

measure-ments were carried out by using a Perkin Elmer Diamond DSC series thermal

analysis system. Dried sample was heated at a rate of 10

°C/min under nitrogen

atmosphere.

One-step polymerization

Poly(MMA-b-CL) triarm block copolymers were synthesized using two different

monomers in one-step process. Specified amounts of ATRP-ROP initiator, MMA,

CL, DBTDL (catalyst for ROP of CL), PMDETA, CuBr, and benzene (as solvent)

were charged separately into a Pyrex tube, and subsequently argon was purged into

the tube through a needle. The tube was tightly capped with a rubber septum and

was dropped into an oil bath thermostated at 110

°C for fixed time. After the

polymerization, the reaction mixture was poured into an excess of methanol to

separate the block copolymers. The copolymers were dried at 40

°C under vacuum

for 3 days. The yield of the polymer was determined gravimetrically.

Fractional precipitations of the polymers

Fractional precipitations (c) of the polymers were carried out according to the

procedure reported in the literature [

63

–

65

]. Vacuum-dried polymer sample

(approximately 0.5 g) was dissolved in 5 mL of THF. Petroleum ether was added

as drop wise to the solution with stirring until turbidity occurs. At this point,

1–2 mL of petroleum ether was added to complete the precipitation. The precipitate

was removed by filtration. The solvent was THF and the nonsolvent was petroleum

ether. In this solvent–nonsolvent system, the c values were calculated as the ratios

of the total volume of nonsolvent used for the first fraction to the volume of solvent

used.

c value

¼

Volume of nonsolvent; mL

ðpetroleum etherÞ

Volume of solvent, mL

ðTHFÞ

The nonsolvent addition into the filtrate solution was continued according to the

same procedure mentioned above to determine the c value for the second fraction if

there is.

Results and discussion

One-step polymerization for poly(MMA-b-CL) triarm block copolymers

The one-step polymerization of a vinyl monomer and a lactone initiated by

ATRP-ROP initiator is shown in Scheme

1

. This process creates two new active sites—a

site on an equal number of hydroxyl group for ROP reaction and a chloride group

for ATRP. During this one-pot synthesis, ATRP of MMA is carried out

simultaneously as ROP of CL proceeds, to yield the block copolymer. The effects

Tabl e 1 The effec t o f the polyme rization time on one-st ep bloc k copolym erization for poly(MM A-b -CL) triarm blo ck copolym ers Code ATRP-R OP initiato r (g) MMA (g) CL (g) CuBr (g) PMDETA (g) Time (min) Yield (g) Conv. (wt%) c * Mn.GPC Mw /M n Poly-M MA/ poly-CL segm ent (mol/mo l) BA-2 0.12 6 3.05 8 2.396 0.132 0.162 80 1.283 22.98 0.60 96,6 72 3.04 1.000\0 .091 BA-3 0.13 5 3.00 7 2.003 0.132 0.190 120 1.407 27.35 0.68 – – 1.000\0 .085 BA-4 0.10 1 3.01 7 2.012 0.133 0.166 180 1.674 32.26 0.54 131, 325 2.39 – BA-5 0.12 2 3.02 6 2.005 0.132 0.192 240 1.852 35.94 0.64 89,8 24 2.55 1.000\0 .090 BA-6 0.11 2 3.26 3 2.084 0.134 0.171 270 2.606 47.73 0.50 81,1 23 3.23 – DBT DL = 6.32 9 10 -4g (1.00 9 10 -6mo l); pol ym. temp. = 110 °C; * nons olvent (petrol eum ether, mL)/so lvent (TH F, mL ); benzene = 1m L

Tabl e 2 The effec t o f the amount of ATR P-ROP initia tor on one-step block copol ymeriza tion for pol y(MM A-b-CL ) triarm block copol ymers Code ATR P-ROP initiato r (g) MMA (g) CL (g) CuBr (g) PMDETA (g) Y ield (g ) Co nv. (wt% ) c * M n.GP C M w /M n Poly-MMA/po ly-CL segm ent (mol/mo l) BC -2 0.09 7 3.145 2.072 0.125 0.133 0.76 5 14.4 0 0.52 209,729 2.16 1.00 0\0.094 BC -3 0.15 7 3.113 2.264 0.196 0.244 0.77 4 13.9 8 0.44 144,062 2.31 1.00 0\0.094 BC -4 0.30 5 3.063 2.262 0.403 0.481 0.77 9 13.8 4 0.54 85,820 1.98 1.00 0\0.084 BC -5 0.42 0 3.041 2.178 0.525 0.634 0.92 7 16.4 2 0.56 74,643 2.45 1.00 0\0.096 Polym. time = 120 min; DBTD L = 6.32 9 10 -4 g (1.00 9 10 -6 mo l); polym . temp. = 110 °C; * nons olvent (petrole um ether, mL) /solven t (THF, mL) ; benzene = 1m L

Tabl e 3 The effec t o f the amount of the monom er on one-st ep blo ck copolym erization fo r poly( MMA-b -CL) triarm blo ck copol ymers Code ATR P-ROP initiato r (g) MMA (g) CL (g) CuBr (g) PMDETA (g) Y ield (g ) Co nv. (wt% ) c * M n.GP C M w /M n Poly-MMA/po ly-CL segm ent (mol/mo l) BB -1 0.11 7 1.511 2.002 0.134 0.165 0.48 7 13.4 2 0.62 74,259 2.89 1,000\0 ,094 BB -2 0.15 6 2.012 2.020 0.131 0.170 0.67 2 16.0 4 0.54 82,535 2.94 1,000\0 ,097 BB -3 0.10 1 2.523 2.019 0.133 0.168 0.72 8 15.6 7 0.50 104,117 3.10 1,000\0 ,094 BB -4 0.11 6 3.250 2.043 0.132 0.178 1.70 7 30.4 3 0.44 100,723 2.88 1,000\0 ,096 BB -5 0.11 5 3.540 2.067 0.135 0.170 1.98 1 34.6 1 0.50 94,526 2.49 1,000\0 ,094 BB -6 0.11 9 3.771 2.022 0.144 0.181 2.20 7 37.3 2 0.52 – – 1,000\0 ,088 BB -7 0.11 4 4.130 2.086 0.136 0.165 2.31 6 36.3 8 0.48 121,715 2.73 1,000\0 ,093 BB -8 0.11 8 4.363 2.781 0.142 0.173 2.37 9 32.5 7 0.42 182,834 2.44 1,000\0 ,096 Polym. time: 150 min; DBT DL = 6.32 9 10 -4g (1.00 9 10 -6 mo l); polym . temp. = 110 °C; * nonsolv ent (petrole um ether, mL )/solvent (THF, mL); benzene = 1m L

of polymerization time, initiator concentration, and monomer concentration on the

copolymerization in the presence of ATRP-ROP initiator by the application of

simultaneous ATRP and ROP processes have been studied. The results of the

one-step polymerization of MMA and CL are shown in Tables

1

,

2

,

3

. The monomer

conversion was calculated from the weight of recovered polymer. The conversion of

monomer was between 13.42 and 47.73 wt%. Increases in the molecular weights of

the copolymers as compared with that of the initiator can confirm block copolymer

formation.

The FTIR spectrum of 3-chloro-1,2-propanediol in Fig.

1

a shows 3321 cm

for

–OH groups, 2884–2953 cm

for aliphatic –CH

and –CH groups, 1031 cm

for

–C–O groups, 704 cm

for –Cl groups. The FTIR spectrum of the triblock

copolymer is shown in Fig.

1

b. The signals at 2949–2993 cm

for aliphatic –CH

and –CH

, 1722 cm

-1

for –C=O, 1140 cm

for –C–O of the copolymer appear in

the FTIR spectra. The –OH signal diminishes at the FTIR spectrum of the

copolymer (Fig.

1

b) according to the –OH signal of the initiator (Fig.

1

a). The

H-NMR spectrum of 3-chloro-1,2-propanediol in Fig.

2

a shows the 3.6 ppm for –OH

protons, 3.9 and 4.0 ppm for –CH

and –CH protons, 4.0 and 5.0 ppm for –OCH

protons. Typical

H-NMR spectra of the copolymer in Fig.

2

b show 0.7 ppm for

–CH

protons of poly-MMA segment, 0.9 ppm for –CH

protons of poly-MMA

segment, 1.1 ppm for –OH protons of poly-CL segment, 1.3 ppm for –CH and

Fig. 1 FTIR spectrum of 3-chloro-1,2-propanediol trifunctional initiator (a), and poly(MMA-b-CL) triarm block copolymer (b)

–CH

protons of 3-chloro-1,2-propanediol, 1.8 ppm for –OCH

protons of poly-CL

segment, 3.5 ppm for –OCH

protons of poly-MMA segment.

The effect of the polymerization time on the one-step block copolymerization is

presented in Table

1

. Polymerization time dependence of M

on the one-step

copolymerization is shown in Fig.

3

. First, longer polymerization times cause higher

polymer molecular weights. Second, the polymers with lower molecular weights are

obtained for polymerizations of longer durations. Longer polymerization times

cause higher polymer yields. Higher amounts of ATRP-ROP initiator cause a higher

polymer yield (Table

2

). Interestingly, the value of M

can only decrease if new

chains are generated. However, that is not in accordance with a controlled

polymerization. Increased amounts of initiator in the reaction mixture lead to the

formation of a higher number of active centers. Consequently, increased numbers of

growing radicals are formed in the system. Hence, it may be expected that they have

shorter poly-MMA and poly-CL segments, which is confirmed by a decrease in the

molecular weights of the block copolymers, as shown in Table

2

. The same

situation was also observed in our previous articles [

16

,

17

,

63

]. Dependence of

ATRP-ROP initiator concentration on M

for the one-step copolymerization is

shown in Fig.

4

. Increasing the amount of monomers also causes an increase in both

the yield and the molecular weights of the copolymers as expected (Table

3

).

Dependence of MMA concentration on M

for the copolymerization is shown in

Fig. 3 Dependence of polymerization time on Mnfor poly(MMA-b-CL) triarm copolymers

Fig.

5

. The Mw/Mn

values of the triarm block copolymers are between 1.98 and 3.23

(Tables

1

,

2

,

3

). Because more than one propagating center initiates the

polymerization, the M

/M

values of the block copolymers are relatively higher

than expected. Because DBTDL, ROP catalyst of CL, can interfere with the radical

polymerization of MMA, the block copolymers with very broad molecular weight

distributions can be formed. All GPC chromatograms were unimodal and indicated

more the molecular weight values of block copolymers than that of ATRP-ROP

initiator. For example, Fig.

6

shows the unimodal GPC curves of the block

copolymers (MB-3, MB-4, MB-5, and MB-6 in Table

3

). The polymer composition

of the copolymers was calculated using the integral ratios of the signals

corresponding to the –OCH

groups of poly-MMA (d = 3.5 ppm), –OCH

groups

of poly-CL (d = 1.8 ppm). The poly-MMA content of copolymers was more than

the poly-CL content. Generally, the values of polymer composition of the

copolymers did not change as shown Tables

1

,

2

,

3

.

Thermal analysis of poly(MMA-b-CL) triarm block copolymers

Thermal analysis of the samples was carried out by taking DSC, and TGA curves.

All samples exhibited glass transition temperatures (T

). The reported T

values

were obtained from the second heating curves. T

value of the block copolymer

(BA-6) was 5

°C (Fig.

7

). T

values were reported in the literature for homo

poly-CL, and homo poly-MMA as -72

°C [

66

,

67

], and 105

°C [

68

], respectively. The

T

value observed by DSC appears between T

of the poly-MMA homopolymer and

T

of the poly-CL homopolymer. The only one T

value for the sample shows the

miscible nature of the related homopolymers. The same situation (the observation of

only one glass transition) can also be seen in our previous articles [

18

,

63

].

Similarly, TGA showed that in the block copolymers, poly-MMA, and poly-CL

blocks did not have individual decomposition temperatures (T

) (Fig.

8

). TGA

showed interesting properties of the block copolymer indicating continuous weight

loss starting from 13

°C to nearly 430 °C with a derivative at 375 °C. The first

decomposition observed at about 200

°C may have been caused by the solvent

traces. One main individual T

of the block copolymers can be attributed to the high

miscibility of the polymerizable methacrylate groups of poly-MMA with poly-CL

moieties of the copolymers.

Fig. 6 GPC curves of the triarm block copolymers

Fig. 7 DSC curve of the triarm block copolymer

Fractional precipitation

The fractional precipitation (c) values of poly(MMA-b-CL) block copolymers were

between 0.42 and 0.68. In the solvent–nonsolvent system, c values were found to be

0.50–0.55 for homo poly-MMA [

16

], 1.02–1.20 for homo poly-CL [

18

]. The c

values of the block copolymers were generally between that of homo poly-MMA

and that of homo poly-CL. Fractional precipitation behavior can give an evidence

for the formation of block copolymer.

Conclusions

One-step synthesis of block copolymer was carried out ATRP of MMA and ROP of

CL using 3-cholor-1,2-propiondiol initiator. The initiator has demonstrated the

characteristic initiator behavior in the copolymerization of MMA and CL. A set of

one-step synthesis, and ATRP and ROP conditions of triarm block copolymers,

poly(MMA-b-CL), were evaluated. The block copolymers were relatively obtained

in high yield and molar weight. The proposed procedure for the preparation of block

copolymers is simple and efficient. Basically, controlling the polymerization

parameters such as ATRP-ROP initiator concentration, monomer concentration, and

polymerization time, ATRP-ROP initiator can be promising materials in order to

obtain block copolymers.

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