Bearing Bromomethyl Functional Groups: Synthesis of the Block and
Graft Copolymers
TEMEL OZTURK,1SEVIL SAVASKAN YILMAZ,1BAKI HAZER,2YUSUF Z. MENCELOGLU3 1Department of Chemistry, Karadeniz Technical University, Trabzon, Turkey
2Department of Chemistry, Zonguldak Karaelmas University, Zonguldak, Turkey 3Faculty of Engineering and Natural Sciences, Sabancı University, Istanbul, Turkey
Received 11 November 2009; accepted 17 December 2009 DOI: 10.1002/pola.23898
Published online in Wiley InterScience (www.interscience.wiley.com).
ABSTRACT:This article reports the synthesis of the block and graft copolymers using peroxygen-containing poly(methyl meth-acrylate) (poly-MMA) as a macroinitiator that was prepared from the atom transfer radical polymerization (ATRP) of methyl meth-acrylate (MMA) in the presence of bis(4,40-bromomethyl benzoyl peroxide) (BBP). The effects of reaction temperatures on the ATRP system were studied in detail. Kinetic studies were carried out to investigate controlled ATRP for BBP/CuBr/bpy initiating system with MMA at 40 C and free radical polymerization of styrene (S) at 80C. The plots of ln ([Mo]/[Mt]) versus reaction time are linear, corresponding to first-order kinetics. Poly-MMA initiators were used in the bulk polymerization of S to obtain poly (MMA-b-S) block copolymers. Poly-MMA initiators contain-ing undecomposed peroygen groups were used for the graft copolymerization of polybutadiene (PBd) and natural rubber
(RSS-3) to obtain crosslinked poly (MMA-g-PBd) and poly(MMA-g-RSS-3) graft copolymers. Swelling ratio values (qv) of the graft copolymers in CHCl3 were calculated. The characterizations of the polymers were achieved by Fourier-transform infrared spec-troscopy (FTIR),1H-nuclear magnetic resonance (1H NMR), gel-permeation chromatography (GPC), differential scanning calori-metry (DSC), thermogravimetric analysis, scanning electron mi-croscopy (SEM), transmission electron microscopy (TEM), atomic force microscopy (AFM), and the fractional precipitation (c) techniques.VC 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 1364–1373, 2010
KEYWORDS:atom transfer radical polymerization (ATRP); atom transfer radical polymerization kinetics; block copolymers; graft copolymers; macroperoxy initiators; swelling ratio
INTRODUCTION Atom transfer radical polymerization (ATRP) has a lot of advantages when compared with other living radical polymerization. Since Wang and Matyjaszew-ski1put forward the concept of ATRP in 1995, the polymers with low polydispersity index, including poly (methyl) acryl-ates, styrene, acrylonitrile, and so forth2–20 have been syn-thesized, especially when using the Cu-based catalytic system.
Macrointermediates such as macroinitiators, macromono-mers, macrocrosslinkers are important in polymer modifica-tion leading to block and graft copolymers.21–30
Macroinitia-tors can be divided into two classes, according to the free radical initiator group: (1) macroazo initiators and (2) mac-roperoxy initiators.20 The polymeric peroxide initiators have been found to significantly influence both the molecular weight and the polydispersity index of the resulting poly-mers.31 In addition, they can produce interpenetrating poly-mer networks, block and graft copolypoly-mers, and so forth.31–34 Polymers containing labile azo, peroxide, and sulfur groups can initiate vinyl polymerization to obtain block
copoly-mers.35–39 Block copolymers have got substantial interest
due to their mechanical properties and practical applications. By using functional polymers containing appropriate alkyl halide and ether groups along the backbone as a macroinitia-tor, it is possible to obtain graft copolymers with a well-con-trolled structure. Grafting to the natural polypropylene (PP), natural rubber (RSS-3), polybutadiene (PBd), and biodegrad-able natural polyesters have become commercially important because of their excellent mechanical properties.32
In earlier study, we carried out ATRP of methyl methacrylate (MMA) with t-butyl peroxy ester and copolymerization with conventional vinyl monomers.20In this study, we present the synthesis of poly(methyl methacrylate) (poly-MMA) macro-peroxy initiators obtained by the ATRP of MMA with bis(4,40-bromomethyl benzoyl)peroxide (BBP) as an initiator. Kinetic studies were carried out to investigate controlled ATRP for BBP/CuBr/bpy initiating system with MMA at 40
C. The peroxygen groups do not decompose during the
ATRP reaction, because low reaction temperatures used for the ATRP are not enough to decompose them. Hence, these
Correspondence to: S. Savaskan Yilmaz (E-mail: sevily@ktu.edu.tr)
peroxygen groups can lead to react with a monomer by using appropriate reaction conditions to obtain the block and graft copolymers. For this purpose, poly-MMA initiators were used to synthesize poly (MMA-b-S) block copolymers. Furthermore, we synthesized poly (MMA-g-PBd) and poly (MMA-g-RSS-3) graft copolymers by the copolymerization of poly-MMA initiators with PBd or RSS-3.
EXPERIMENTAL
Materials
4-Methyl benzoyl chloride, CuBr, CuCl, bpy, AIBN, and Na2O2
were supplied from Merck and used as received. N-Bromosuc-cinimide (NBS) and PBd were supplied from Aldrich and used as received. 4-Bromomethyl benzoyl chloride was synthesized from 4-methyl benzoyl chloride reacted with NBS.24 S and
MMA were supplied from Merck and washed with a 10% aqueous NaOH, water dried over CaCl2, respectively, and was
then distilled on CaH2under reduced pressure before use. All
other chemicals were reagent grade and used as received. Polymer Characterization
Molecular weights and molecular weight distributions were measured with a Knauer gel-permeation chromatography (GPC) using ChromGate software, a WellChrom Interface Box, RI Detector K-2301, and WellChrom HPLC pump K-501. CHCl3 was used as an eluent at a flow rate of 1 mL/min. A
calibration curve was generated with six poly-S standards: 2500, 2950, 5050, 20,000, 52,000, and 96,400 Da, of low dis-persity purchased from Polyscience. Differential scanning cal-orimetry (DSC) measurement was carried out under nitrogen by using a Setaram DSC-141 series thermal analysis system. Dried sample was heated at a rate of 10 C/min from 50 to 120C under N2atmosphere. Thermogravimetric analyses
(TGA) of the polymers were performed on a PL TGA 1500 instrument to determine thermal degradation. Fourier-trans-form infrared spectroscopy (FTIR) spectra were recorded using a Perkin–Elmer 1600 Series FTIR Spectrometer. 1 H-nuclear magnetic resonance (1H NMR) of the products was recorded using a Varian/Mercury-200 NMR Spectrometer, in CDCl3solvent and tetra methyl silane as the internal
stand-ard. Scanning electron microscopy (SEM) was taken on a Jeol JXA-840A electron microscope. The specimens were frozen under liquid nitrogen, then fractured, mounted, and coated with gold (300 Angstrom) on an Edwards S 150 B sputter coater. SEM measurements were operated at 10 kV. The elec-tron images were recorded directly from the cathode ray tube onto a Polaroid film. The topography (height) and phase images of four polymer samples [1-PMMA, 2-PMMA, 3-poly (MMA-S)] were taken by Veeco (Digital Instruments) Multimode Scanning Probe Microscope. Polymers were dis-solved in dichloromethane at 5 wt % and casted on a freshly cleaved mica surface. After evaporation of the solvent the surface of the thin films adjacent to the mica were put to an-alyze in atomic force microscopy (AFM) Tapping Mode. To be sure of the images that they represent the whole polymer film surface, the measurements were taken at least three times with sizes decreasing from 5 5 lm2 to 500 500 nm2 length scales. In the height images of samples 1, 2, 3
were, in general, having very smooth surface in the range of 1–2 nm and in the phase images there were not any detecta-ble change (only 1–3 modulation that is due to features of the surface) that can be sign of a phase separation. However, in the sample 4 there was an obvious phase separation with 10 degrees of difference from maximum to minimum. The fea-tures of this phase separation have around 30–50 nm sizes. Synthesis of Bromomethyl Functional Peroxide
Initiator (BBP)
BBP was synthesized according to the procedure describe else where.40For example, to prepare BBP, 10 g of 4-bromo-methyl benzoyl chloride, 6.68 g of sodium peroxide, 5 g ice, and 50 mL of diethyl ether were stirred at 0C for 1 h, then at room temperature for 2 h. White BBP crystals were pre-cipitated with petroleum ether. The yield of the products was greater than 70 wt % peroxygen analysis was done using potassium iodide and isopropyl alcohol reflux and the sodium thiosulfate titration method.34 The peroxygen con-tent was found to be 7.39%, in agreement with the calcu-lated value (7.54%).
ATRP Reactions of MMA with BBP
Initiator (BBP), ligand (bpy), and monomer (MMA) were added to the flask in Schlank system. Then the flask was immersed in an oil bath at the required temperature. One hour of vacuum nitrogen was applied to remove oxygen, and then catalyst (CuBr or CuCl) was added to the solution. After a specific time, the flask was opened and the sample was poured into excess methanol to precipitate the polymer. The obtained polymer was dissolved into chloroform. The insolu-ble part of the polymer was separated. Poly-MMA macroper-oxy initiator was purified by precipitation from diethyl ether/petroleum ether (1/1) solution at room temperature and dried under vacuum to a constant weight. The dried polymer was dissolved in THF and passed through a small neutral alumina column to remove the remaining copper cat-alyst. The purified macroperoxy initiator was dried at 20 C under vacuum for 3 days.
Kinetic studies were accomplished to investigate controlled ATRP for BBP/CuBr/bpy initiating system with MMA at
FIGURE 1ATRP of MMA with the initiating system BBP and CuBr (run no 5, 6, 7 in Table 1).
40 C. Figure 1 shows the semi-logarithmic kinetic plots for the polymerization of initiating systems. Mwand MWD (Mw/
Mn) results versus conversion (%) are shown in Figure 2 for
BBP/ligand (bpy) initiating systems. Copolymerization of S with Poly-MMA Macroperoxy Initiators
The copolymerization of S was carried out in bulk system. S and the poly-MMA macroperoxy initiator were charged sepa-rately into a Pyrex tube, and then nitrogen was purged into the tube through a needle. The tube tightly capped with a rub-ber septum was put into an oil bath. After the required period of polymerization, reaction mixture was poured into excess methanol to separate the poly (MMA-b-S) block copolymer. Soluble and insoluble fractions of the block copolymers were separated by extracting with chloroform for purification. The yield of the polymer was determined gravimetrically. Scheme 1 contains the reaction pathway.
FIGURE 2Variation of the molecular weight with the conver-sion of MMA (run no 1, 2, 3, 4 in Table 1) [n: Mw,~: Mw/Mn].
Synthesis of Poly (MMA-g-PBd) and Poly (MMA-g-RSS-3) Graft Copolymers
As a typical procedure: 0.1 g of poly-MMA initiator, 0.1 g of PBd, and 30 mL of CHCl3as solvent were stirred for 24 h at
room temperature. This solution was spread on a glass plate and dried in the air at room temperature for 2 days to obtain a polymer film. After drying, the polymer film was put into a Pyrex tube. Then, the polymerization was carried out in an oil bath at 90 C under N2. The graft copolymer
mixture was extracted with CHCl3for 24 h, so swollen graft
copolymer was obtained. The swollen gels were filtered off and mixed with methanol. Then, the poly (MMA-g-PBd) graft copolymer was dried under vacuum at 50C for a week. The same grafting procedure was carried out with RSS-3 to obtain poly (MMA-g-RSS-3) graft copolymer.
Swelling Ratios of the Crosslinked Graft Copolymers The swelling ratios (qv) of the crosslinked graft copolymers
were carried out by storing 0.2 g of the samples in 50 mL of CHCl3 for 24 h at 20 C. The qv of the crosslinked graft
copolymers were calculated by the following equation:
qv¼Vdry polymerV þ Vsolvent dry polymer
¼Vswollen polymer
Vdry polymer
(1)
where Vdry polymer and Vsolvent are the volumes of dry
poly-mer and solvent, respectively.
RESULTS AND DISCUSSION
ATRP of MMA
MMA polymerization was carried out using a catalyst mix-ture composed of the bromomethyl derivative of benzoyl peroxide, CuX, and bpy at 0, 20, 30, and 40 C. BBP leads to the linear poly-MMA by ATRP. Poly-MMA macroperoxy initia-tor was soluble in common solvents when compared with BBP obtained from 4-bromomethyl benzoyl chloride. As a result of the ATRP of BBP with MMA, two-armed poly-MMA initiators were synthesized. The monomer conversion was calculated from the weight of recovered polymer. Generally
the conversion was high. The results and conditions of MMA polymerization are listed in Table 1. Kinetic studies were carried out to investigate ATRP of BBP/CuBr/bpy initiating systems with MMA. The plots of ln ([Mo]/[Mt]) versus
reac-tion time are not linear, corresponding to first-order kinetics. Nevertheless, the intercept for the kinetic plot is not zero, which is characteristic of the fast monomer polymerization as mentioned by Gnanou and coworkers.41 The linearity observed in the plots of the logarithmic change of the mono-mer concentration with time (Fig. 1) indicates not only a first order with the respect to the monomer but also that the growing radical concentration remained constant which was ratified by the linear dependence of Mwwith conversion
(Fig. 2). Mwand Mw/Mnversus conversion (%) plots
demon-strate the good control of molecular weight as a function of conversion for BBP/ligand (bpy) initiating system (Fig. 2). Based on the assumption that one molecule of BBP initiator generated one polymer chain, the theoretical molecular weight (Mn,th) for ATRP was calculated according to eq 2,
42
where [M]o and [BBP]o represent the initial concentrations
of the monomer and BBP initiator, (MW)o is the molecular
weight of the monomer and 424 is the molecular weight of BBP.
Mn;th¼ 428 þ fð½Mo=ð½BBPoÞg ðMWÞo conversion (2)
Synthesis of Poly (MMA-b-S) Block Copolymers
The poly-MMA macroperoxy initiators demonstrated the characteristic macroinitiator behavior in the copolymeriza-tion of S.27,38,39 Active block copolymers were obtained in high yield and with long polymerization times. Table 2 shows the conditions and the results of the polymerization of S with poly-MMA macroperoxy initiator. Molar masses of poly (MMA-b-S) block copolymers were higher than that of the corresponding poly-MMA macroperoxy initiator. Increases in the molecular weights of the products when compared with the macroperoxy initiators confirm block co-polymer formation. During the coco-polymerization of S with
TABLE 1ATRP Reactions of MMA with BBP/CuX/bpy Initiating System
Run No Temp. (C) Time (h) Yield (g) Conv. (wt %) Mn,th Mn,GPC Mw/Mn
f (Initiator Efficiency) Mn,th/Mn,GPC 1a 0 24 15.870 67.87 4,966 42,240 1.41 0.12 2a 20 72 17.004 72.67 5,287 74,893 1.18 0.07 3a 30 72 20.516 87.66 6,289 73,537 1.27 0.09 4a 40 72 22.304 95.32 6,801 67,968 1.61 0.10 5a 40 3 4.412 18.86 1,689 21,184 1.30 0.08 6a 40 4.5 4.465 19.89 1,758 21,760 1.54 0.08 7a 40 12 17.629 75.34 5,465 24,935 1.45 0.22 8b 0 5 4.283 18.30 1,652 10,330 1.15 0.16 9b 20 96 5.824 24.89 2,092 158,619 1.37 0.01 10b 40 4.5 22.006 94.04 6,716 203,145 1.58 0.03 CuBr¼ 7.0 103 mol, CuCl¼ 7.0 103 mol, BBP¼ 3.5 103 mol, bpy¼ 21.0 103mol, MMA¼ 2.34 101mol.
a
For CuBr/bpy initiating system.
b
poly-MMA macroperoxy initiator, not only the peroxide group but also the terminal-CH2Br may produce free radicals
to polymerize S monomers forming poly (S-b-MMA-b-S) tri-block copolymer instead of poly (MMA-b-S) ditri-block copoly-mer. Figure 3 shows an almost linear relationship between ln ([Mo]/[Mt]) and polymerization time.
Synthesis of the Graft Copolymers
As the macromonomeric poly-MMA initiators contain decom-posed peroxygen groups, the graft polymerization of poly-MMA initiators with PBd or RSS-3 were carried out at 90C. Here, poly-MMA macroperoxy initiators were used as radical generators in grafting polymerization. The conditions and results of the polymerization are listed in Tables 3 and 4. Crosslinked and soluble graft copolymer fractions were iso-lated by means of chloroform extraction for 24 h. After extraction with a suitable solvent, crosslinked copolymer films did not give a considerable soluble part which could be the homopolymer. The qv of the graft copolymers decreased,
with their increased conversion. Also, the qvdecrease as the
polymerization time increases. In case of grafting reactions with active poly-MMA, the total polymer conversion (wt %) of crosslinked poly (MMA-g-PBd) and poly (MMA-g-PBd) graft polymers varied from 48.79 to 71.78 and 50.24 to 73.40, respectively. The qv values of the graft copolymers in
CHCl3 varied from 1.91 to 7.21, which can be attributed to
large network structure.
Characterization of the Polymers
The FTIR spectrum of poly MMA initiator in Figure 4(a) shows 704 cm1 for Br, 766 cm1for 1,4 disubstitution of benzoyl peroxide, 1289 and 1314 cm1 for ACAO groups of MMA and benzoyl peroxide, 1681 cm1forAC¼¼O groups of MMA and benzoyl peroxide, 2858 and 2927 cm1 for ACH3andACH2groups of MMA and benzoyl peroxide, 3066
cm1 for aromatic ACH group of benzoyl peroxide. The 1H NMR spectrum of the initiator in Figure 5(a) shows the 1.0 ppm for ACH3protons of MMA, 1.8 ppm for ACH2protons
attached benzoyl group, 3.0 ppm for AOCH3 protons of
MMA, 3.6 ppm for ACH2protons of MMA, 6.6 and 7.0 ppm
for aromatic ring protons of benzoyl group.
The FTIR spectrum of poly (MMA-b-S) block copolymer in Figure 4(b) shows 668 and 699 cm1for monosubstitution of S, 754 cm1 for 1,4 disubstitution of benzoyl peroxide, 1150 and 1193 cm1forACAO groups of MMA and benzoyl peroxide, 1732 cm1forAC¼¼O groups of MMA and benzoyl peroxide, 2850, 2922, and 2951 cm1for ACH3 and ACH2
groups of S, MMA and benzoyl peroxide, 3026 cm1forACH groups of S and benzoyl peroxide. The1H NMR spectrum of the block copolymer in Figure 5(b) shows 1.3 ppm forACH3
protons of MMA, 2.1 ppm for ACH2 protons attached
ben-zoyl group, 3.5 ppm AOCH3 protons of MMA, 3.7 ppm for
ACH2 protons of MMA, 4.2 ppm forACH2protons of S, 4.4
ppm for ACH protons of S, 7.4 and 8.0 ppm for aromatic proton of S and the initiator.
The FTIR spectrum of poly (MMA-g-PBd) graft copolymer in Figure 4(c) shows 750 cm1for 1,4 disubstitution of benzoyl peroxide, 1149 and 1192 cm1 for ACAO groups of MMA and benzoyl peroxide, 1732 cm1forAC¼¼O groups of MMA and benzoyl peroxide, 2851 and 2949 cm1 for ACH2 and
ACH groups of MMA, benzoyl peroxide, and PBd, 3025 cm1
forACH group of S and benzoyl peroxide.
Molar masses of the poly-MMA samples measured GPC ther-mogram. MWD values of the initiators were between 1.15 and 1.61. The higher temperature and longer polymerization time gave the higher yields and higher molecular weight, as expected in ATRP. High conversion of MMA for BBP was observed because bromomethyl initiators are fast initiators in ATRP. Block copolymers purified by fractional precipita-tion indicated very narrow MWD between 1.38 and 1.58. Block copolymers were purified by using the fractional pre-cipitation technique. There was no considerable amount of homopolymer determined by the fractional precipitation. When the solvent is THF and the nonsolvent is petroleum ether, the gamma values (c) of the block copolymers were between 1.40 to 1.64 while the c for homo poly-MMA was
FIGURE 3Time dependence of ln (Mo/Mt) for free radical poly-merization of S at 80C.
TABLE 2Free Radical Polymerization of S Using Poly-MMA Macroperoxy Initiator (run no 7 in Table 1) at 808C
Run No Time (h) Poly-MMA Initiator (g) S (g) Yield (g) Conv. (wt %) ln[Mo]/[Mt] c Mn Mw/Mn
11 5 0.301 0.904 0.358 29.71 0.35 1.48 37,998 1.38 12 6 0.303 0.902 0.401 33.28 0.40 1.50 35,114 1.45 13 7 0.300 0.902 0.483 40.18 0.51 1.54 37,796 1.55 14 8 0.302 0.909 0.516 42.61 0.56 1.50 36,370 1.52 15 10 0.300 0.904 0.575 47.76 0.65 1.40 34,220 1.58 16 12 0.300 0.905 0.585 48.55 0.66 1.64 42,587 1.46
0.50–0.5531and for homo poly-S was 2.5–3.2.31 Thec of the block copolymers were between that of homo poly-MMA and that of homo poly(styrene) (PS). The c of the block copoly-mers were higher value than that of homo poly-MMA because of poly-S segments. Fractional precipitation behavior gives an evidence for the formation of block copolymer. Thermal analysis of the samples was carried out by taking DSC curves. All samples exhibited glass transition temperatures (Tg). The reported Tgvalues were obtained from the second
heating curves. Tg value of poly-MMA initiator was 76.10C
[Fig. 6(a)] and that of poly (MMA-b-S) block copolymer was 50.51C [Fig. 6(b)]. Tgvalue of poly (MMA-g-PBd) graft
copol-ymer was 43.14C [Fig. 6(c)]. Tgvalue reported in the
litera-ture for homo poly-MMA, for homo poly-S, for homo PBd as 105, 100,102C, respectively.43Tgvalues of the block and
graft copolymers changed to the value which was less than the value of poly-MMA initiator because of poly-S and PBd seg-ments, respectively. The only one glass transition temperature value for the samples shows the miscible nature of the related polymers. While the mass loss in TGA of poly-MMA initiator
96.2% at 300C that of poly (MMA-b-S) is 76.8% (Fig. 7). TGA showed interesting properties of the poly-MMA initiator indi-cating continuous weight loss starting from 250C to nearly 320C with a derivative at 285C [Fig. 7(a)]. Whereas, in case of the poly(MMA-b-S) block copolymers, PS and PMMA blocks had the individual decomposition temperatures as shown Fig-ure 7(b) (395 and 471C, respectively). Thermal properties
of the polymers were listed in Table 5.
SEM micrographs of the polymers were taken for the surface morphology characterization of the polymers. The polymers were coated with a thin layer of gold on their surfaces to provide electrical conductivity. The micrographs were photo-graphed from different views. Poly-MMA initiator has a con-tinuous PMMA matrix [Fig. 8(a)]. The SEM micrograph of poly (MMA-b-S) block copolymer shows a smooth surface and has got good homogenization [Fig. 8(b)]. All graft copolymers samples were characterized by a morphology consisting of gel sheets or platelets with irregular pores [Fig. 8(c,d)]. The TEM images of graft copolymers show a typical domain structure, that is, bright and dark regions [Fig.
TABLE 3Graft Copolymers of PBd with Poly-MMA Macroperoxy Initiator at 908C
Run No. Time (h) Poly-MMA initiator (g) PBd (g) Yield (g)
Yield of
Crosslinked Graft Polymer (g)
Con. (wt %) qv(in CH3Cl)
17 4 0.101 (run no. 7 in Table 1) 0.104 0.154 0.110 53.66 6.30
18 6 0.102 (run no. 7 in Table 1) 0.102 0.161 0.122 59.80 4.37
19 8 0.101 (run no. 7 in Table 1) 0.103 0.170 0.140 68.63 3.19
20 10 0.101 (run no. 7 in Table 1) 0.103 0.176 0.138 67.65 2.98
21 12 0.101 (run no. 7 in Table 1) 0.101 0.171 0.145 71.78 2.61
22 4 0.106 (run no. 10 in Table 1) 0.101 0.141 0.101 48.79 6.47
23 6 0.104 (run no. 10 in Table 1) 0.100 0.152 0.115 56.10 4.78
24 8 0.100 (run no. 10 in Table 1) 0.101 0.159 0.117 58.21 5.21
25 10 0.101 (run no. 10 in Table 1) 0.101 0.169 0.123 60.89 4.01
26 12 0.105 (run no. 10 in Table 1) 0.102 0.171 0.124 59.90 3.03
TABLE 4Graft Copolymers of RSS-3 with Poly-MMA Macroperoxy Initiator at 908C
Run No. Time (h) Poly-MMA initiator (g) RSS-3 (g) Yield (g)
Yield of Crosslinked Graft Polymer
(g) Con. (wt %) qv(in CH3Cl)
27 4 0.105 (run no. 7 in Table 1) 0.102 0.140 6.72 50.24 6.72
28 6 0.103 (run no. 7 in Table 1) 0.101 0.156 5.97 54.41 5.97
29 8 0.105 (run no. 7 in Table 1) 0.101 0.163 4.68 58.25 4.68
30 10 0.103 (run no. 7 in Table 1) 0.100 0.179 2.39 68.97 2.39
31 12 0.102 (run no. 7 in Table 1) 0.101 0.180 1.91 73.40 1.91
32 4 0.101 (run no. 10 in Table 1) 0.101 0.147 0.104 51.49 7.21
33 6 0.101 (run no. 10 in Table 1) 0.101 0.144 0.105 51.98 5.95
34 8 0.101 (run no. 10 in Table 1) 0.101 0.151 0.110 54.46 3.09
35 10 0.100 (run no. 10 in Table 1) 0.101 0.155 0.118 58.71 2.76
8(e,f)]. These regions dispersed in the polymer matrix. The gel consists of a dense packing of rather large pores, sepa-rated by porous walls with channels.
The study of surface morphology of the polymers was car-ried out by atomic force microscopy (AFM) on thin films obtained by spin-coating [Fig. 9(a–e)]. The study of surface morphology of the copolymers was carried out by AFM on thin films obtained by spin-coating. Figure 9(a) shows the AFM image of PMMA macroperoxy inititor (run no 3 in Table 1). Scans (1.992lM) show that the surface of PMMA macro-peroxy inititor is flat. PMMA macromacro-peroxy inititor decoration is uniform. Also, scans (5 lM) show that the surface of PMMA macroperoxy inititor (run no 9 in Table 1) is flat. PMMA macroperoxy inititor decoration is uniform [Fig. 9(b)]. AFM images of the PMMA-b-PS block copolymers (run no 11 in Table 2) is in Figure 9(c), we can observe the top surface organization of the diblock copolymer with the formation of PMMA nodules in PS continuous matrix. Because of the monomer composition, the S is the majority monomer that forms the continuous phase of these materials. These images provide additional evidence of a change in film morphology from smooth and uniform to a more complex,
bicontinuous-FIGURE 4FTIR spectrum of the polymers; (a) poly-MMA initia-tor; (b) poly (MMA-b-S) block; (c) poly)MMA-g-PBd) graft copolymers.
FIGURE 51H NMR spectrum of the polymers; (a) poly-MMA initiator; (b) poly(MMA-b-S) block copolymer.
FIGURE 6DSC curves of the polymers (a) poly-MMA initiator; (b) poly(MMA-b-S) block; (c) poly(MMA-g-PBd) graft copolymers.
FIGURE 7TGA curves of (a) poly-MMA initiator; (b) poly(MMA-b-S) block copolymer.
type morphology. An AFM profile of PMMA-b-PS block copolymer (run no 15 in Table 2) is shown in Figure 9(d). The different spots on one PMMA-b-PS block copolymer indi-cated by yellow and brown arrows in Figure 9(d). When the proportion of MMA decreases in macromolecular chain com-position, the coagulation of nodule can be observed with the formation of ‘‘peanuts’’ nodules on the extreme surface. This behavior could be associated to the presence of two distinct phase transitions by rheology. The macromolecular chain increasing the miscibility between the two chains ends rich in
TABLE 5Thermal Properties of the Polymers
Polymer Decomp. Temp. (C) Td1 Td2 PMMA-initiator 285 – Poly(MMA-b-S) 395 471 Poly(MMA-g-PBd) 314 384 Poly(MMA-g-RSS-3) 222 290
FIGURE 8SEM and TEM micrographs of the polymers (a) SEM image of poly-MMA initiator (5000); (b) SEM image of poly (MMA-b-S) block (2500); (c) SEM image of poly (MMA-g-PBd) graft (1000); (d) SEM image of poly (MMA-g-RSS-3) graft copoly-mers (750); (e) TEM image of poly (MMA-g-PBd) graft; (f) TEM image of poly (MMA-g-RSS-3) graft copolycopoly-mers.
PMMA and PS. No gradient can be observed between the nod-ule centers and the matrix because the strong composition variations in the macromolecular chains close to a block copolymer segregation [see Fig. 9(d)]. Moreover, these nodules
are characteristic of the presence of a strong phase separation, as previously observed with rheological properties, observed by AFM technique. This study presents here for the first time, a submicron phase separation in block and graft copolymers.
FIGURE 9(a) AFM images of poly-MMA initiator (run no 3 in Table 1). (b) AFM images of PMMA macroperoxy inititor (run no 9 in Table 1). (c) AFM images of PMMA-b-PS block copolymer (run no 11 in Table 2). (d) AFM images of PMMA-b-PS block copolymer (run no 15 in Table 2). (e) AFM images of poly (MMA-g-PBd) copolymers (run no 17 in Table 3).
As shown in Figure 9(e), crystalline and amorph domains can be easily seen in AFM image of poly (MMA-g-PBd) copolymers (run no 17 in Table 3), and the surface of film is relatively rough. The vicinal holes coalesced, forming a net-work-like structure with large droplets formed at the junction of the network. Thin film of the graft copolymer has a much smoother surface due to the dramatic decrease in crystallinity on grafting (as revealed from DSC measurements). The AFM image of the graft copolymer [Fig. 9(e)] provides further evi-dence of the successful graft copolymerization, because mac-roscopic phase separation would have been observed if the re-sultant polymer is a mixture of poly (MMA-g-PBd) and PBd homopolymer due to the known incompatibility between poly-MMA macroperoxy inimers and PBd. These graft copoly-mers could be of interest for modifying the compatibility between PMMA macroperoxy initiator and PBd by blending.
CONCLUSIONS
Mostly ATRP are carried out at high temperatures. Earlier, we reported that ATRP is particularly effective under low tempera-tures in the bulk system.20In this article indeed, poly-MMA mac-roperoxy initiators have been synthesized at low temperatures by using ATRP. According to this synthesis, the poly-MMA initia-tors did not loose their peroxygen groups after the ATRP at low temperatures. It was revealed that the reactivity of poly-MMA macroperoxy initiators was comparable with other common per-oxide initiators. Also poly (MMA-b-S) block and crosslinked poly (MMA-g-PBd) and poly (MMA-g-RSS-3) graft copolymers have been prepared by using these macroperoxy initiators.
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