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Pure and Applied Chemistry
ISSN: 1060-1325 (Print) 1520-5738 (Online) Journal homepage: https://www.tandfonline.com/loi/lmsa20
One-Step Synthesis of Triblock Copolymers via
Simultaneous Reversible-Addition Fragmentation
Chain Transfer (RAFT) and Ring-Opening
Polymerization Using a Novel Difunctional
Macro-RAFT Agent Based on Polyethylene Glycol
Melahat Göktaş, Temel Öztürk, Mehmet Nuri Atalar, Ahmet T. Tekeş & Baki
Hazer
To cite this article: Melahat Göktaş, Temel Öztürk, Mehmet Nuri Atalar, Ahmet T. Tekeş & Baki Hazer (2014) One-Step Synthesis of Triblock Copolymers via Simultaneous Reversible-Addition Fragmentation Chain Transfer (RAFT) and Ring-Opening Polymerization Using a Novel Difunctional Macro-RAFT Agent Based on Polyethylene Glycol, Journal of Macromolecular Science, Part A, 51:11, 854-863, DOI: 10.1080/10601325.2014.953366
To link to this article: https://doi.org/10.1080/10601325.2014.953366
Published online: 17 Oct 2014. Submit your article to this journal
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One-Step Synthesis of Triblock Copolymers via Simultaneous
Reversible-Addition Fragmentation Chain Transfer (RAFT)
and Ring-Opening Polymerization Using a Novel Difunctional
Macro-RAFT Agent Based on Polyethylene Glycol
MELAHAT G €OKTA¸S1, TEMEL €OZT €URK*,2, MEHMET NURI ATALAR1, AHMET T. TEKE¸S1, and BAKI HAZER3
1Kafkas University, Department of Chemistry, 36100 Kars, Turkey 2Giresun University, Department of Chemistry, 28100 Giresun, Turkey
3B€ulent Ecevit University, Department of Chemistry, 67100 Zonguldak, Turkey Received and Accepted May 2014
One-step synthesis of the triblock copolymers was carried out by reversible addition–fragmentation chain transfer (RAFT) polymerization of methyl methacrylate (MMA) and ring-opening polymerization (ROP) of b-butyrolactone (BL) ore-caprolactone (CL) using a novel difunctional macro-RAFT agent. For this purpose, primarily PEG-Br (polyethylene glycol bromine) was obtained by using 3-bromopropanoyl chloride and PEGs (polyethylene glycols) with different molecular weights. Then, macro-RAFT agent was synthesized by the reaction of potassium ethyl xanthogenate and PEG-Br. By using macro-macro-RAFT agent, poly (MMA-b-EG-b-BL), and poly(MMA-b-EG-b-CL) triblock copolymers were synthesized by changing some polymerization conditions such as monomer/initiator concentration, polymerization time. The effect of the reaction conditions on the polydispersity and molecular weights were also investigated. The block lengths of the triblock copolymers were calculated by using 1H-nuclear magnetic resonance (1H-NMR) spectra. It was observed that the block length could be altered by varying the monomer and initiator concentrations. The characterization of the products were achieved using 1H-NMR, Fourier-transform infrared spectroscopy (FTIR), gel-permeation chromatography (GPC), thermogravimetric analysis (TGA), and fractional precipitation (g) techniques. Keywords: Reversible-addition fragmentation chain transfer polymerization, ring opening polymerization, one-step polymerization;
difunctional macro-RAFT agent, triblock copolymer
1 Introduction
The block copolymers with various architectures such as linear diblock (AB), triblock (ABA or ABC), pentablock (ABABA), multi-block or segmented copolymers have been proposed (1–22). The synthesis of block copolymer, with a controlled molecular weight, and a better-designed macromolecular structure and composition, is one of the most meaningful and challenging works in thefield of poly-mer chemistry (12). The synthesis of block copolypoly-mers usu-ally requires efficient controlled/‘living’ polymerization
(23). Reversible addition–fragmentation chain transfer (RAFT) polymerization represents the most recently devel-oped controlled radical-polymerization method and is a powerful technique for the macromolecular synthesis of a broad range of well-defined polymers. The versatility of the method is proved by its compatibility with a very wide range of monomers and reaction conditions. Reversible chain transfer involves homolytic substitution or addition fragmentation, or some other transfer mechanisms (23–35). Carothers et al.first carried out ring opening polymeriza-tion (ROP) technique for lactones, cyclic anhydrides and carbonates (36, 37). The method has been applied to many monomers with a lot of initiator and catalyst systems (37).
Macrointermediates such as macroinitiators, macromo-nomers and macrocrosslinkers have been widely used for preparing various block/graft copolymers and their net-works via a radical initiated process (38–47). Polyethylene glycol (PEG) macromonomers are soluble in a large
*Address correspondence to: Temel €Ozt€urk, Giresun University, Department of Chemistry, 28100 Giresun, Turkey. E-mail: temelozturk@msn.com
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Journal of Macromolecular Science, Part A: Pure and Applied Chemistry (2014) 51, 854–863 Copyright © Taylor & Francis Group, LLC
ISSN: 1060-1325 print / 1520-5738 online DOI: 10.1080/10601325.2014.953366
variety of solvents including water and benzene (48). Block/graft copolymers having PEG units are very attrac-tive materials for chemicals, industrial and biomedical applications, because PEG has unique properties such high hydrophilicity,flexibility and ion absorbability, and a high degree of biocompatibility (49–55). The preparation of (co)polymers using PEG units was carried out using the RAFT process (56–63).
In recent years, the one-step process has been success-fully used for the synthesis of block/graft copolymers using different techniques, which thus has several advan-tages over other popular methods. Because of the applica-bility of at least two transformation steps simultaneously, side reactions that lead to homopolymer formation are minimized (64–80). Barner-Kowollik and coworkers (64) carried out the synthesis of poly(2-hydroxyethyl methacry-late-g-e-caprolactone) graft copolymers through the one-step combination of ROP and RAFT polymerization in the presence of cyanoisopropyl dithiobenzoate and tin(II) 2-ethylhexanoate using toluene as the solvent. Further-more, various copolymers containing styrene (65–74), chloromethyl styrene (73), butadiene (67), N-isopropyla-crylamide (75, 76), lactide (69, 74, 75, 77),e-caprolactone (CL) (70, 71, 76), 10-methylene-9,10-dihydroanthryl-9-spi-rophenylcyclopropane (68), ethylene oxide (69, 70), hydroxyethyl methacrylate (70, 71), methyl acrylate (77), hydroxyethyl acrylate (77), 1,3-dioxepane (72, 80), tetra-hydrofuran (THF) (73), 1,5-cyclooctadiene (67), and methyl methacrylate (80) monomers were synthesized by a combination of the RAFT and ROP methods.
In an earlier study, we prepared a PEO-macro-RAFT agent with a vinyl end-group. This PEO-macro-RAFT agent leads to crosslinked polymers rather than highly branching block/graft copolymers (47). We evaluated kinetic parameters of self-condensing polymerization and copolymerization with MMA by RAFT method in view of the effect of some different polymerization conditions. In the other study, we had reported the synthesis of a novel dual macromonomer initiator obtained from potassium salt of the ethyl xanthegonate and the terminally bromi-nated PEG for RAFT polymerization which is a method of controlled/‘living’ polymerization (81). The present work is an extension of the recent studies carried out by the authors of this article involving the one-step synthesis of copolymers through simultaneous free-radical polymer-ization or RAFT and ROP processes (5, 38, 82, 83). In this study, the synthesis of a novel difunctional macro-RAFT agent obtained by the reaction of potassium ethyl xan-thogenate with PEG-Br (polyethylene glycol bromine) is reported. PEG-Br was obtained by using 3-bromopropa-noyl chloride and PEGs with different molecular weights. Poly(MMA-b-EG-b-BL), and poly(MMA-b-EG-b-CL) triblock copolymers were synthesized using macro-RAFT agent by the simultaneous ROP and RAFT polymeriza-tion of two different monomers in one-step. By changing the polymerization conditions, block copolymers synthesis
could be used to prepare the desired segment ratio. Kinetic studies were carried out to investigate the one-step ROP and RAFT polymerization.
2 Experimental
2.1 Materials
The potassium salt of ethyl xanthogenate, dibutyltin dilau-rate (DBTDL), THF, PEG, triethylamine, ethanol, and methanol were supplied by Merck and used as received.
3-bromopropionyl chloride, 2,20-azobisisobutyronitrile (AIBN), petroleum ether, and diethyl ether were bought from Aldrich and used as received. N,N-dimethylforma-mide (DMF), chloroform, and dichloromethane were received from Sigma-Aldrich.
b-butyrolactone (BL) ande-caprolactone (CL) were sup-plied by Aldrich and Alfa Aesar, respectively, and dried with anhydrous CaSO4,then fractionally distilled. MMA
was supplied by Aldrich, which was purified as follows: it was washed with a 10 wt% aqueous NaOH solution, dried over anhydrous CaCl2overnight, and distilled over CaH2
under reduced pressure before use. All other chemicals were reagent grade and used as received.
2.2 Instrumentation
The molecular weights and molecular-weight distributions were measured with Polymer Labs PL-GPC 220 and Mal-vern Viscotek RI-UV-GPC max gel-permeation chroma-tography (GPC) with THF as the solvent. A calibration curve was generated with three polystyrene standards: 2,960, 50,400, and 696,500 Da, of low polydispersity. Fourier-transform infrared spectroscopy (FTIR) spectra were recorded using a Perkin Elmer Pyris 1 model FTIR Spectrometer.1H-nuclear magnetic resonance (1H-NMR) spectra of the samples in CDCl3as 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. Thermal analysis measurements of the polymers were carried out under nitrogen using a Perkin Elmer Pyris 1 TGA and Spectrum thermal analyzer to determine thermal degradation.
2.3 Synthesis of the Mono Terminally Brominated PEG (PEG-Br)
PEG-Br was obtained from the reaction of PEG-3000 (MnD 3000 Dalton) or PEG-1500 (MnD 1500 Dalton) with
3-bromopropanoyl chloride. Typically, a 40.00 g (13.33 mmol) of PEG-3000 in 30 mL of dry dichlorome-thane was mixed with 1.35 g (13.33 mmol) of triethylamine. The solution was transferred into a 250 mL Schlenkflask with a magnet and an argon gas inlet. The reactionflask was cooled down to 0C and then argon gas was purged into the
flask. 2.28 g (13.33 mmol) of 3-bromopropionyl chloride in 30 mL of dry dichloromethane was added to the solution at half an hour time. The reaction mixture was stirred for 1 hour at 0C. After that, the solution was slowly warmed to room temperature for a day. The solution wasfiltered. Sol-vent was partially evaporated and precipitated in cold diethyl ether:petroleum ether (1:1) solution. The product was dissolved in absolute ethanol and kept in a refrigerator overnight. Then, the precipitated triethylamine hydrochlo-ride crystals were removed. The solvent was evaporated; then the product was washed with cold diethyl ether, and dried under vacuum at room temperature. The same synthe-sis procedure was carried out by using PEG-1500.
2.4 Synthesis of a Novel Difunctional Macro-RAFT Initiator
Afixed quantity (32.00 g or 10.21 mmol) of PEG-Br (syn-thesized by using PEG-3000) was reacted with 16.34 g (102.12 mmol) of the potassium salt of ethyl xanthogenate in THF at 40C for 48 h ([Cl]/[K]D 1/10, mol/mol). The solution was filtered to remove the unreacted xanthate, and the solvent was removed by a rotary evaporator. Macro-RAFT agent was precipitated in cold diethyl ether: petroleum ether (1:1) solution and dried under vacuum at room temperature for four days. The same synthesis proce-dure was carried out for PEG-Br synthesized by using PEG-1500.
2.5 One-Step Polymerization
Poly(MMA-b-EG-b-BL) and poly(MMA-b-EG-b-CL) tri-block copolymers were synthesized using two different monomers in one-step process. Specified amounts of macro-RAFT agent, MMA, BL (or CL), AIBN, DBTDL (catalyst for ROP of BL and CL), and DMF (as solvent) were charged separately into a Pyrex tube, and subse-quently 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 90C for a fixed time. After the polymerization, the reaction mixture was poured into an excess of methanol to separate the copolymers. The polymers were dried at 40C under vac-uum for four days. The yield of the polymer was deter-mined gravimetrically.
2.6 Fractional Precipitations of the Polymers
Fractional precipitations of the polymers were carried out according to the procedure reported in the literature (84, 85). Vacuum-dried polymer sample (approximately 0.5 g) was dissolved in 5 mL of THF. Petroleum ether was added dropwise 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 byfiltration. The solvent was THF and the non-solvent was petroleum ether. In this non-solvent–nonsolvent system, the g values were calculated as the ratios of the total volume of nonsolvent used for thefirst fraction to the volume of solvent used.
g valueD Volumeof Nonsolvent; mL .petroleum ether/ volume of Solvent; mL.THF/
The nonsolvent addition into the filtrate solution was continued according to the same procedure mentioned above to determine the g value for the possible second fraction.
3 Results and Discussion
3.1 Synthesis of PEG-Br
PEGs with molecular weights 1500 and 3000 were used in the synthesis of terminally brominated PEGs. The yield of the products was over 90 wt%. The basic outline for the synthesis is shown at first line of Scheme 1. The FTIR spectrum of PEG-Br in Figure 1(a) shows 3434 cm¡1 for –OH groups, 2890 cm¡1 for aliphatic –CH
2 groups,
1728 cm¡1 for –CHO groups, 1060 cm¡1 for –OC groups, and 842 cm¡1for–Br groups. The1H-NMR spec-trum of PEG-Br in Figure 2(a) shows the 2.8 ppm for –CH2(CHO) protons of propanoyl group, 3.4 ppm for
–BrCH2protons of propanoyl group, 3.6 ppm for–OCH2
protons of PEG group, and 4.2 ppm for–OH protons for PEG group.
3.2 Synthesis of Macro-RAFT Agent
The novel dual initiator, macro-RAFT agent with an ethyl xanthogenate and a hydroxyl group, was prepared by the reaction of PEG-Br and the potassium salt of ethyl xan-thogenate. The yield of the products was greater than 60 wt%. Each of the data points in thefigures for percent conversion was obtained by a separate experiment. The basic outline for the synthesis of macro-RAFT agent is shown at the second line of Scheme 1. The FTIR spectrum of macro-RAFT agent in Figure 1(b) shows 3435 cm¡1 for–OH groups, 2881 cm¡1for aliphatic–CH2and–CH3
groups, 1730 cm¡1 for –C D O groups, 1633 cm¡1 for –CHS groups, and 1111 cm¡1for–OC groups. The
sig-nal of–CHS (1633 cm¡1) at the spectrum of macro-RAFT agent (Fig. 1(b)) are not observed at the spectrum of PEG-Br (Fig. 1(a)). The 1H-NMR spectrum of macro-RAFT agent in Figure 2(b) shows the 1.3 ppm for–CH3protons
of ethyl xanthogenate group, 2.7 ppm for –CH2(CHO)
protons of propanoyl group, 3.1 ppm for–SCH2 protons
of propanoyl group, 3.5 ppm for–OCH2protons of PEG
group and ethyl xanthogenate group, and 5.0 ppm for –OH protons for PEG group.
3.3 One-Step Polymerization for Poly(MMA-b-EG-b-CL) and Poly(MMA-b-EG-b-BL) Triblock Copolymers The one-step polymerization of a vinyl monomer and a lac-tone with initiated by macro-RAFT agent is shown in Scheme 1. This process creates two new active sites—a site on an equal number of hydroxyl group for the ROP reac-tion and one on the thiocarbonate group for RAFT poly-merization. However, it is more likely that there will be a population of three types of PEO, those with zero, one or two RAFT endgroups after the synthesis in Scheme 1. This would result in a mixture of polymers in the polymerization (the ABA, CBC, and ABC triblock copolymers). These problems resulted in broad molecular weight distributions of the block copolymers. We used [3-bromopropanoyl chlo-ride]/[PEO]D 1/1, mol/mol in the reaction. We think that there could be zero and two RAFT endgroups at a very small amount. To the best of our knowledge, at the large quantity macro-RAFT agent has been obtained with a hydroxyl group in the chain end because we are used 1/1
(mol/mol) ratio to synthesize the RAFT-ROP initiator. The other macro-RAFT agent possessed two hydroxyl functions and zero hydroxyl function could be obtained at the small quantities in the chain end. We are taking into account macro-RAFT agent possessed a hydroxyl function and xanthate function. During this one-pot synthesis, RAFT polymerization of MMA is carried out simulta-neously as the ROP of BL or CL proceeds, to yield the block copolymer. PBL is also known as poly(3-hydroxy butyrate) and is synthesized naturally by bacteria as an energy-reserve material (86–89). The effects of polymeriza-tion time, initiator concentrapolymeriza-tion, and monomer concentra-tion on the copolymerizaconcentra-tion in the presence of macro-RAFT agent by the application of simultaneous macro-RAFT and ROP processes have been studied. The results of the one-step polymerization of MMA and BL (or CL) are shown in Tables 1–3. The monomer conversion was calcu-lated from the weight of recovered polymer. The conversion of monomer was between 8.35 wt% and 33.36 wt%. Increases in the molecular weights of the copolymers as compared with that of macro-RAFT agent confirm block copolymer formation. Because of the plots are not strongly linear, we could not get the smooth rate constants. The FTIR spectrum of poly(MMA-b-EG-b-BL) triblock
copolymer is given in Figure 1(c). The signals at 3440 cm¡1 corresponding to –OH, 1730 cm¡1 corresponding to –CHO and 1633 cm¡1 corresponding to –CHS of the
copolymer appear in the FTIR spectra. This –CHS signal diminishes at the FTIR spectrum of the triblock copolymer according to the–CHS signal of macro-RAFT agent. Typi-cal 1H-NMR spectra of poly(MMA-b-EG-b-BL) triblock copolymer in Figure 2(c) shows the 0.8 ppm for–CH3
pro-tons of ethyl xanthogenate group, BL, and poly-MMA, 1.0 ppm for–CH2protons of poly-MMA, 1.3 ppm
for –CH2protons of propanoyl group, 1.8 ppm for–CH2
protons of poly-BL, 3.0 ppm for–OCH3protons of
poly-MMA, 3.5 ppm for –OCH2 protons of PEG group and
ethyl xanthogenate group, 5.2 ppm for –OCH protons of poly-BL, and 8.0 ppm for–OH protons for poly-BL.
The effect of the polymerization time on the one-step block copolymerization is presented in Table 1. Polymeri-zation time dependence of Mnon the one-step
copolymeri-zation is shown in Figures 3 and 4. It has been observed that higher molecular weights are obtained in the copoly-merization with longer durations. Longer polycopoly-merization time cause to higher polymer yields; these results being are
in good agreement with those stated by Heidenreich and Puskas (90) for the RAFT polymerization. Interestingly, the value of Mncan only decrease if new chains are
gener-ated. However, that is not in accordance with a controlled polymerization. Increased amounts of initiator in the reac-tion mixture lead to the formareac-tion of a higher number of active centers. Consequently, increased numbers of grow-ing macroradicals are formed in the system. Hence, it may be expected that they have shorter MMA and poly-BL (or 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
Fig. 1. FTIR spectrum of PEG-Br (a), macro-RAFT agent (b), and poly(MMA-b-EG-b-BL) triblock copolymer (c).
Fig. 2.1H-NMR spectra of PEG-Br (a), macro-RAFT agent (b), and poly(MMA-b-EG-b-BL) triblock copolymer (c).
in our previous articles (81, 82). Dependence of macro-RAFT agent concentration on Mnfor the one-step
copoly-merization is shown in Figure 5 and Figure 6. 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 Mnfor the copolymerization is shown in Figures 7 and
8. The Mw/Mn values of the triblock copolymers are
between 1.75 and 2.90 (Table 1-3). Because of more than one propagating center initiates the polymerization and macro-RAFT agent including PEG, the Mw/Mnvalues of
the block copolymers are relatively higher than expected. Because DBTDL, the ROP catalyst of BL and CL, can interfere with the radical polymerization of MMA, very broad molecular weight distributions of the block copoly-mers can be formed. Interestingly, molar masses of poly (MMA-b-EG-b-CL) triblock copolymer were higher than that of poly(MMA-b-EG-b-BL) triblock copolymer
(Table 1-3). All GPC chromatograms were unimodal and indicated more the molecular weight values of block copolymers than that of macro-RAFT agent. For exam-ple, Figure 9 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 calcu-lated using the integral ratios of the signals corresponding to the –OCH3 groups of poly-MMA (d D 2.9 ppm),
–OCH2groups of PEG (d D 3.6 ppm), ¡OCH groups of
poly-BL (dD 3.0 ppm), and –CH2groups of poly-CL (dD
2.0 ppm). Generally, the poly-BL and poly-MMA con-tents have increased with increasing of the polymerization time for the copolymers (Table 1). Interestingly, the values of polymer composition of the copolymers segments gener-ally do not change in Table 2. In general, the poly-BL, poly-MMA, and PEG contents are not affected by the amount of RAFT-ROP initiator. These results indicate that the one-pot reaction can be used to prepare block
Table 1. The effect of the polymerization time on one-step block copolymerization for poly(MMA-b-EG-b-BL) (KA series) and poly (MMA-b-EG-b-CL) (MA series) triblock copolymers
Code BL (g) CL (g) Time (min.) Yield (g) Mn,GPC Mw/Mn
Decomp. temp. (C) Poly-MMA/poly-BL/ PEG segment (mol/mol/mol) Poly-MMA/poly-CL/ PEG segment (mol/mol/mol) Td1 Td2 Td3 KA-2 1.550 – 45 0.700 41,931 1.83 317 416 431 1.00 / 0.24 / 0.05 – KA-3 1.509 – 60 0.814 44,998 1.75 215 400 509 1.00 / 0.18 / 0.04 – KA-6 1.524 – 180 1.055 48,959 1.89 220 305 410 1.00 / 0.27 / 0.06 – KA-7 1.517 – 240 1.015 59,215 1.96 201 327 403 1.00 / 0.36 / 0.09 – MA-1 – 1.510 30 0.264 59,906 2.05 252 402 499 – 1.00 / 0.27 / 0.38 MA-3 – 1.526 60 0.713 58,850 2.14 253 394 486 – 1.00 / 0.33 / 0.35 MA-4 – 1.527 90 0.730 61,901 2.23 255 396 502 – 1.00 / 0.48 / 0.31 MA-5 – 1.514 125 0.827 73,966 2.35 354 417 551 – 1.00 / 0.30 / 0.32 MA-6 – 1.507 190 0.725 76,023 2.38 392 487 592 – 1.00 / 0.30 / 0.35 MMAD 1.5 g; macro-RAFT agent D 0.1 g; AIBN D 1.5 £ 10¡3g; DBTDLD 6.32 £ 10¡4g (1.00£ 10¡6mol); polym. temp.D 90C; DMFD 3 mL.
Table 2. The effect of the amount of macro-RAFT agent on one-step block copolymerization for poly(MMA-b-EG-b-BL) (KC series) and poly(MMA-b-EG-b-BL) (MC series) triblock copolymers
Code Macro-RAFT agent (g) BL (g) CL (g) Yield (g) Mn,GPC Mw/Mn
Decomp. temp. (C) Poly-MMA/poly-BL/ PEG segment (mol/ mol/mol)
Poly-MMA/poly-CL/ PEG segment (mol/ mol/mol) Td1 Td2 Td3 KC-2 0.075 1.516 – 0.747 49,287 2.02 382 472 560 1.00 / 0.36 / 0.09 – KC-4 0.150 1.516 – 0.983 26,394 2.04 313 402 504 1.00 / 0.36 / 0.09 – KC-5 0.200 1.524 – 0.958 18,760 2.56 247 408 – 1.00 / 0.36 / 0.08 – KC-6 0.250 1.520 – 0.938 16,187 2.90 230 402 464 1.00 / 0.36 / 0.10 – MC-1 0.054 – 1.524 0.352 92,030 2.44 332 400 476 – 1.00 / 0.39 / 0.31 MC-2 0.076 – 1.520 0.807 64,575 2.13 254 402 492 – 1.00 / 0.57 / 0.31 MC-3 0.126 – 1.525 0.678 54,391 2.10 398 499 – – 1.00 / 0.48 / 0.20 MC-5 0.208 – 1.530 0.657 49,255 2.09 263 391 493 – 1.00 / 0.36 / 0.24 MC-6 0.254 – 1.508 0.713 44,293 1.99 499 549 576 – 1.00 / 0.33 / 0.34 MMAD 1.5 g; polym. time D 60 min; AIBN : between 1.1 £ 10¡3g and 4.6£ 10¡3g; DBTDLD 6.32 £ 10¡4g (1.00£ 10¡6mol); polym. temp.D 90C; DMFD 3 mL.
Table 3. The effect of the amount of the monomer on one-step block copolymerization for poly(MMA-b-EG-b-BL) (KB series) and poly(MMA- b-EG-b-CL) (MB series) triblock copolymers
Code BL (g) CL (g) MMA (g) Yield (g) Mn,GPC Mw/Mn
Decomp. temp. (C) Poly-MMA/poly-BL/ PEG segment (mol/ mol/mol)
Poly-MMA/poly-CL /PEG segment (mol/ mol/mol) Td1 Td2 Td3 KB-1 1.515 – 0.756 0.304 17,578 2.68 – – – 1.00 / 0.42 / 0.10 – KB-2 1.510 – 1.290 0.502 30,686 2.08 – – – 1.00 / 0.48 / 0.12 – KB-3 1.508 – 1.800 0.645 42,072 1.92 – – – 1.00 / 0.42 / 0.12 – KB-4 1.502 – 1.900 0.730 60,607 2.09 – – – 1.00 / 0.51 / 0.13 – KB-5 1.520 – 2.120 0.943 59,942 2.08 – – – 1.00 / 0.57 / 0.12 – KB-6 1.511 – 2.900 1.031 63,428 1.98 250 310 400 1.00 / 0.56 / 0.10 – MB-1 – 1.568 0.760 0.314 32,560 1.78 261 398 487 – 1.00 / 0.42 / 0.34 MB-2 – 1.505 1.010 0.466 50,330 2.22 275 403 493 – 1.00 / 0.81 / 0.26 MB-3 – 1.541 1.261 0.479 54,988 2.11 255 416 497 – 1.00 / 0.48 / 0.26 MB-4 – 1.530 1.768 0.909 61,948 2.27 254 394 431 – 1.00 / 0.39 / 0.34 MB-5 – 1.570 2.003 1.049 69,118 2.33 249 398 501 – 1.00 / 0.45 / 0.47 MB-6 – 1.540 2.264 1.122 91,610 2.22 220 305 410 – 1.00 / 0.45 / 0.26 Macro-RAFT agentD 0.1 g; polym. time: 60 min; AIBN D 1.0£10¡3g; DBTDLD 6.32 £ 10¡4g (1.00£10¡6mol); polym. temp.D 90C; DMF
D 3 mL.
Fig. 3. Dependence of polymerization time on Mn for poly (MMA-b-EG-b-BL) triblock copolymers.
Fig. 4. Dependence of polymerization time on Mn for poly (MMA-b-EG-b-CL) triblock copolymers.
Fig. 5. Dependence of macro-RAFT agent on Mn for poly (MMA-b-EG-b-BL) triblock copolymers.
Fig. 6. Dependence of macro-RAFT agent on Mn for poly (MMA-b-EG-b-CL) triblock copolymers.
copolymers containing the desired segment ratio by chang-ing the polymerization conditions.
Thermal analysis of the samples was carried out by tak-ing DSC curves. All samples exhibited glass transition temperatures (Tg). The reported Tg values were obtained
from the second heating curves. Tg value of the block
copolymer (KB-6) was 103C. The only one glass transi-tion was observed. The same situatransi-tion (the observatransi-tion of
Fig. 8. Dependence of MMA on Mnfor for poly(MMA-b-EG-b-CL) triblock copolymers.
Fig. 9. GPC chromatograms of the block copolymers (MB-3, MB-4, MB-5, and MB-6 in Table 1).
Fig. 10. TGA curves of the block copolymers: (a) TGA curve of KB-6 in Table 3, (b) TGA curve of MB-6 in Table 3.
Fig. 7. Dependence of MMA on Mnfor poly(MMA-b-EG-b-BL) triblock copolymers.
only one glass transition) can also be seen in our previous articles (14, 39, 83). Tgvalues were reported in the
litera-ture for homo poly-CL, and homo poly-MMA as ¡72C (91–92), and 105C (93), respectively. The Tgobserved by
DSC appears to be almost that of the poly-MMA homopolymer.
Decomposition temperatures (Td) of the triblock
copolymers are shown in Table 1–3. Thermo gravimetric analysis has showed interesting properties of the copoly-mers indicating continuous weight loss starting from 100C to nearly 450C with a derivative at 400C (Fig. 10(a)). In the case of poly(MMA-b-EG-b-CL) tri-block copolymer, PEG, poly-CL and poly-MMA tri-blocks have the individual decomposition temperatures as shown in Figure 10(b) [ca. 220C, 305C, and 410C, respec-tively]. The first decomposition observed at 120C may have been caused by the solvent traces.
3.4 Fractional Precipitation
The fractional precipitation values (g) of poly(MMA-b-EG-b-BL) block copolymers were between 0.84 and 1.10, and that of poly(MMA-b-EG-b-CL) block copolymers were between 0.56 and 0.68. In the solvent–nonsolvent system, the g-values were found to be 0.50–0.55 for homo poly-MMA (84), 1.33 for homo poly-BL (82), 1.02–1.20 for homo poly-CL (83), 0.94–1.00 for homo PEG-1500, and 0.92–1.00 for homo PEG-3000. The g values of the block copolymers were different from that of homo poly-MMA, homo poly-BL, homo PEG, and homo poly-CL.
4 Conclusions
Macro-RAFT agent containing PEG has demonstrated the characteristic initiator behavior in the copolymeri-zation of MMA and BL or CL. A set of one-pot syn-thesis, and ROP and RAFT polymerization conditions of triblock copolymers, poly(MMA-b-EG-b-BL) and poly(MMA-b-EG-b-CL), were evaluated. Triblock copolymers were relatively obtained in high yield and molar weight. The proposed procedure for the prepara-tion of block copolymers is simple and efficient. The block length can be adjusted by varying the monomer and initiator concentrations. Basically, controlling the polymerization parameters such as macro-RAFT agent concentration and polymerization time, RAFT-ROP initiators can be promising materials in order to obtain block copolymers.
Funding
This work was supported by the Scientific and Technologi-cal Research Council of Turkey (TUB_ITAK-Ankara)
(Grants#110T541) and partially supported by TUB_ITAK-Ankara (Grants#211T016).
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