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Original article
7 (
2
); 209-218
doi:
10.1016/j.arabjc.2010.10.026

Synthesis and characterization of alkoxy derivatives with double-headed initiators for the preparation of poly(ε-caprolactone)-β-polyacrylonitrile (PCL-β-PAN) and poly(l-lactide)-β-polyacrylonitrile (PLLA-β-PAN) copolymers

,
 Organic-III, Indian Institute of Chemical Technology, Tarnaka, Hyderabad 500 007, A.P., India

*Corresponding author. Tel.: +91 40 27173026 taimurathar2001@gmail.com (Taimur Athar) taimur1957@yahoo.co.in (Taimur Athar)

Received: , Accepted: ,
© The Author(s) 2011
Disclaimer:
This article was originally published by Elsevier and was migrated to Scientific Scholar after the change of Publisher.

Peer review under responsibility of King Saud University.

Available online 3 November 2010

Abstract

The synthesis of simple single source molecular precursor based on metal alkoxides of the type,[(MMPEP)Al(μ-OBnCH2Cl)]2 (1),[(MMPEP-H)Li·(BnOH)]2 (2) and[(MMPEP-H)Li·(HOB-nCH2Cl)]2 (3) has been reported herein. Complex 1 was prepared by the reaction of[(MMPEP)Al(CH3)(Et2O)] with p-(chloromethyl)benzyl alcohol. The reaction of 2,2′-methylene-bis(4,6-di(1-methyl-1-phenylethyl)phenol) (MMPEP-H2) with nBuLi, BnOH or p-(chloromethyl)benzyl alcohol was added to give complexes 2 and 3, respectively. Among them, only complex 1 shows excellent catalytic properties towards ring-opening polymerization (ROP) of ε-caprolactone. However, complexes 2 and 3 are active for ROP of l-lactide only. Block copolymers of poly(ε-caprolactone)-β-polyacrylonitrile and poly(l-lactide)-β-polyacrylonitrile were synthesized by using a technique known as atom transfer radical polymerization (ATRP) and the ring opening polymerization (ROP). TEM micrograph of PCL-β-PAN shows the microphase property with the help of self-assembly.

Keywords

Alkoxy based initiator
ε-Caprolactone
l-Lactide
Polymerization
1

1 Introduction

For last one decade, demands for developing new materials have dramatically increased due to their high performance-versus-price ratio (Burchell, 1999). Polyacrylonitrile (PAN) is one of the many reagents used for manufacturing activated carbon materials (Yang and Yu, 1998). The formation of well-oriented nanotube with regular textured is considered to be most expensive, tricky and complicated, it is prepared either by vapor deposition process (Fan et al., 1999). It is a great challenge to the synthetic chemist to explore an easy and cheap eco-friendly method by using a mild reaction conditions. Many nanotemplates has been used as a building blocks for their potential applications in polymerization (Rzayev and Hillmyer, 2005; Ha et al., 2004; Zalusky et al., 2002; Bates and Fredrickson, 1999).

A novel, synthetic route, based on block copolymer has been designed to generate nanostructured materials with well-defined properties (Kowalewski et al., 2002, 2003; Tang et al., 2004). Copolymer of poly(ε-caprolactone) and polyacrylonitrile has been reported by blending method (Runt and Rim, 1982; Keroack et al., 1998; Tsarevsky et al., 2002). The preparation of homo- and copolymer polyacrylonitrile was carried out via free radical and anionic polymerization method without having control in the molecular weight and its polydispersites (Nuyken et al., 1992). Matyjaszewski and co-workers reported the synthesis of polyacrylonitrile by using atom transfer radical polymerization (ATRP) technique (Matyjaszewski et al., 1999; Trofimoff et al., 1987; Duda et al., 1990, 2000; Chisholm et al., 2000, 2001, 2005; Chisholm and Delbridge, 2003a,b; Jhurry et al., 2001; Ma et al., 2003, 2005; Taden et al., 2000; Hormnirun et al., 2004; Ishii et al., 2004; Nomura et al., 2002; Zhong et al., 2002; Sawhney et al., 1993; Zhang et al., 1994; Kricheldorf et al., 2000; Aubrecht et al., 2002; Dove et al., 2001; Majerska et al., 2000; Chamberlain et al., 2001; Simic et al., 1997; Spassky et al., 2000; Dittrich and Schulz, 1971; Williams et al., 2002, 2003; Rieth et al., 2002; Webster, 1991; Aida and Inoue, 1996; Meyer et al., 2002). Herein the clean synthesis of complexes has been reported via soft chemical approach for the preparation of block copolymers with well defined catalytic properties (Hawker et al., 1998).

2

2 Experimental

2.1

2.1 General

All manipulations were carried out in a dry nitrogen atmosphere. Solvents used for the synthesis of initiators of PCL and PLLA were dried by refluxing for at least 24 h over sodium/benzophenone (toluene, n-hexane and diethyl ether), phosphorus pentaoxide (CH2Cl2), or magnesium sulfate (benzyl alcohol). Deuterated solvents were dried over 4 Å molecular sieves.[(MMPEP)Al(CH3)(Et2O)] and p-(chloromethyl)benzyl alcohol (Pierce et al., 1996) were prepared as reported in the literature. Copper(I) bromide was purified by washing with acetic acid. Acrylonitrile, 2,2′-bipyridine, ethylene carbonate, NaOH, EDTA, MeOH and aluminum oxide (standard grade, ∼150 mesh, 58 Å) were purchased and used as such without further purification. 1H and 13C NMR spectra were recorded on a Varian Mercury-400 (400 MHz) or a Varian Unity Inova 600 MHz (the 13C NMR spectra of complex 3) spectrometer by reporting a chemical shifts given in ppm by using the internal standard TMS. Microanalysis was performed by using a Heraeus CHN-O-RAPID instrument. An infrared spectrum was recorded from a Bruker Equinox 55 spectrometer. The GPC measurements were performed on a Hitachi L-7100 system equipped with a differential Bischoff 8120 RI detector using THF (HPLC grade) as an eluent (for PCL and PLLA) or a Postnova PN1122. Solvent Delivery system equipped with a RI Detector PN3110 using DMF (HPLC grade) as an eluent (for PCL-β-PAN). Molecular weight and its distributions were calculated by using polystyrene as standard.

2.2

2.2 [(MMPEP)Al(μ-OBnCH2Cl)]2 (1)

At 0 °C[(MMPEP)Al(CH3)(Et2O)] (1.56 g, 2 mmol) was added into the solution of p-(chloromethyl)benzyl alcohol (0.32 g, 2 mmol) in toluene, the reaction mixture was stirred at room temperature for 3 h. After removal of volatile materials under vacuum and the residue was redissolved in toluene and then concentrated. It was heated till the solution become clear. The solution was allowed to cool at room temperature, colorless crystalline solids were obtained after 24 h. Yield: 1.13 g (66%). 1H NMR (CDCl3, ppm): δ 6.69–7.28 (m, Ph), 4.27 (s, CH2Cl), 3.19 (s, OCH2), 2.37 (d, PhCH2Ph, JH–H = 14.8 Hz), 2.04 (d, PhCH2Ph, JH–H = 14.8 Hz), 1.82, 1.58, 1.57, 1.44 (s, CH3). 13C NMR (CDCl3, ppm): δ 151.50, 151.13, 150.70, 140.48, 137.33, 136.47, 135.74, 129.24, 128.55, 128.22, 128.00, 127.82, 126.61, 126.51, 125.82, 125.64, 125.35, 125.30, 124.74 (Ph), 66.09 (OCH2), 45.60 (CH2Cl), 43.00, 42.25 (PhC(CH3)2Ph), 33.73, 31.04, 31.02, 30.73(C(CH3)2), 27.98 (PhCH2Ph). IR (KBr, cm−1): 3025 (m), 2965 (s), 2873 (m), 1597 (m), 1478 (s), 1373 (m), 1276 (s), 1203 (m), 1149 (m), 1093 (m), 1027 (m), 923 (m), 834 (m). Anal. Calcd for C114H116Al2O6Cl2: C, 80.21; H, 6.85. Found: C, 79.64; H, 6.22%. Mp = 184–186 °C.

2.3

2.3 [(MMPEP-H)Li·(BnOH)]2 (2)

At 0 °C 2,2-methylene-bis(4,6-di(1-methyl-1-phenylethyl)phenol) (MMPEP-H2) (2.71 g, 4.0 mmol) was taken in diethyl ether, and benzyl alcohol (0.42 mL, 4 mmol) mixture followed by the addition of BuLi (2 mL, 5 mmol in n-hexane). The resulting mixture was stirred for 3 h. Removal of volatile materials was undertaken in vacuum and the residue was extracted in toluene. The extract was concentrated, followed by the addition of n-hexane. Keeping for 24 h. at room temperature the white solid was obtained. Yield: 2.04 g (65%).

2.4

2.4 [(MMPEP-H)Li·(HOBnCH2Cl)]2 (3)

At 0 °C 2,2-methylene-bis(4,6-di(1-methyl-1-phenylethyl)phenol) (MMPEP-H2) (2.71 g, 4.0 mmol) and p-(chloromethyl)benzyl alcohol (0.63 g, 4 mmol) were added slowly into nBuLi (2 mL, 5 mmol in n-hexane) in ethyl ether and then the reaction mixture was stirred for 3 h. The volatile materials were removed under vacuum and the residue was redissolved in toluene and then concentrated. On keeping for 24 h a white solid was obtained. Yield: 2.40 g (72%).

2.5

2.5 Synthesis of p-(chloromethyl)benzyl end-functionalized PCL

The synthesis of PCL-50 (the number 50 indicates the designed[M]0/[I]0) was carried out. To a stirring solution of[(MMPEP)Al(μ-OBnCH2Cl)]2 (0.09 g, 0.05 mmol) was added ε-CL (0.53 mL, 5.0 mmol) in toluene. The reaction mixture was stirred for 1 h at 50 °C. The reaction was quenched with H2O; the polymer was precipitated out in n-hexane. White precipitate was redissolved in dichloromethane and then precipitated into n-hexane and then dried under vacuum to give a white solid. The peaks at 5.12 (–OCH2Ph–), 4.58 (–OCH2Cl), 4.05 (–CH2OC(⚌O)–) and at 3.65 (–CH2OH) ppm in CDCl3.

2.6

2.6 Preparation of PLLA

A[(MMPEP-H)Li·(BnOH)]2 (0.08 g, 0.05 mmol) was added l-LA (0.22 g, 1.5 mmol) in CH2Cl2. The reaction mixture was stirred at 0 °C for 5 h. After the removal of volatile materials the residue was redissolved in toluene and then quenched with H2O. The polymer was precipitated out in n-hexane and then redissolved in dichloromethane and then precipitated as a white solid. The peaks at 7.27–7.37 (–CH2Ph) 5.18 (–OCHMeC(O)–), and 4.36 (–CHMeOH) ppm in CDCl3.

2.7

2.7 Synthesis of p-(chloromethyl)benzyl ester end-functionalized PLLA

A[(MMPEP-H)Li·(HOBnCH2Cl)]2 (0.09 g, 0.05 mmol) was added with l-LA (0.36 g, 2.5 mmol) in CH2Cl2. The reaction mixture was stirred at 0 °C for 5.5 h. After the removal of volatile materials the residue was redissolved in toluene followed by quenching with H2O. The white polymer was precipitated out in n-hexane and then redissolved in dichloromethane and again precipitated out as white solid in n-hexane. The peaks at 7.27–7.37 (–CH2Ph–), 5.18 (–OCHMeC(O)–), 4.58 (–OCH2Cl) and 4.36 (–CHMeOH) ppm in CDCl3.

2.8

2.8 Synthesis of poly(ε-caprolactone)-β-polyacrylonitrile copolymer

A 0.33 g (2.25 mmol) CuBr, 0.71 g (4.5 mmol) 2,2-bipyridine and 25 g ethylene carbonate were taken together in a flask and then dried for 1 h. The color of the reaction mixture changes to dark-brown followed by the addition of ethylene carbonate and then heated at 70 °C. By cooling with an addition of p-(chloromethyl)benzyl ester end-functionalized PCL (PCL-2350, 3.53 g, 1.5 mmol) in 14.31 g (270 mmol) acrylonitrile and stirred at 70 °C for 24 h. The reaction was quenched with MeOH followed by overnight stirring. The dark yellow powder was obtained after filtration. The powder was dissolved in DMF and then followed by addition of 1 mM EDTA/alkali solution to give light yellow powder. The powder was redissolved in DMF and then filtered through a mixture of MeOH–H2O (1:1) of Al2O3 and the grey solid was obtained. The solid was washed with hot MeOH many times and then finally dried under vacuum to obtain a copolymer. The peaks at 7.23–7.29 (–CH2Ph–), 5.03 (–CH2Ph–), 3.97 (–CH2OC(⚌O)–) and 3.12 (–CH(CN)–) ppm in DMSO-d6.

2.9

2.9 Synthesis of polylactide-β-polyacrylonitrile copolymer

Add 0.22 g (1.5 mmol) CuBr, 0.47 g (3.0 mmol) 2,2′-bipyridine and 20 g ethylene carbonate was taken and then heated to 70 °C in nitrogen atmosphere then cooled to room temperature. Followed by the addition of p-(chloromethyl)benzyl ester end-functionalized PLLA in acrylonitrile. The reaction mixture was stirred at 70 °C for 24 h. after quenching the reaction with MeOH a dark-white powder was obtained in good yield.

3

3 Results and discussion

3.1

3.1 Synthesis and characterization

[(MMPEP)Al(μ-OBnCH2Cl)]2 (1) was obtained by the reaction of[(MMPEP)Al(CH3)(OEt2)] with an equivalent amount of p-(chloromethyl)benzyl alcohol (Pierce et al., 1996) in toluene. 1H NMR studies of 1 reveal two singlet at 4.27 (CH2Cl) and 3.19 (OCH2) consistent with the expected structure.

Alkoxy derivatives of lithium were synthesized[(MMPEP-H)Li·(BnOH)]2 (2) and[(MMPEP-H)Li·(HOBnCH2Cl)]2 (3). Complex 2 was obtained by the reaction of nBuLi to the mixture of 2,2′-methylene-bis(4,6-di(1-methyl-1-phenylethyl)phenol) (MMPEP-H2) with an equal equivalent of BnOH in diethyl ether. 1H NMR (CDCl3, ppm): δ 6.78–7.37 (m, Ph), 5.10 (br, PhOH), 4.63 (s, BnOH), 3.59 (s, PhCH2Ph), 1.63, 1.54 (s, CH3). 13C NMR (CDCl3, ppm): δ 151.67, 140.57, 139.37, 134.91, 129.50, 128.66, 128.39, 127.76, 127.51, 127.10, 127.00, 126.73, 126.43, 125.68, 125.23, 123.16 (Ph), 66.03 (OCH2), 42.38, 42.10 (PhC(CH3)2Ph), 32.73, 31.07(C(CH3)2), 29.83 (PhCH2Ph). IR (KBr, cm−1): 3500 (br), 2868 (m), 1599 (m), 1492 (s), 1462 (s), 1441 (s), 1381 (m), 1361 (m), 1319 (m), 1202 (m), 1030 (m). Anal. Calcd for C112H118Li2O6: C, 85.46; H, 7.56. Found: C, 85.59; H, 7.55%. Mp = 143–145 °C.

Complex 3 was synthesized by similar method that was used for the preparation of 2 (Scheme 1). 1H NMR (CDCl3, ppm): δ 6.64–7.38 (m, Ph), 5.13 (br, PhOH), 4.66 (s, BnOH), 4.60 (s, PhCH2Cl), 3.58 (br, PhCH2Ph), 1.64, 1.49 (s, CH3). 13C NMR (CDCl3, ppm): δ 152.11, 151.53, 136.67, 134.92, 128.75, 127.93, 127.81, 127.56, 127.19, 126.72, 126.35, 125.94, 125.17, 124.54, 123.75, 123.08 (Ph), 64.87 (OCH2), 46.04 (CH2Cl), 42.40, 42.03 (PhC(CH3)2Ph), 31.04 (C(CH3)2), 29.75 (PhCH2Ph). IR (KBr, cm−1): 3527 (s), 3482 (s), 2961 (s), 2866 (m), 1599 (s), 1492 (m), 1459 (s), 1440 (s), 1382 (m), 1319 (s), 1264 (m), 1218 (m), 1028 (m), 987 (m). Anal. Calcd for C114H120O6Li2Cl2: C, 81.94; H, 7.24. Found: C, 81.58; H, 6.95%. Mp = 148–149 °C.

Scheme 1

3.2

3.2 Ring-opening polymerization ε-caprolactone initiated by 1

The catalytic behavior of 1 towards ROP of ε-caprolactone (ε-CL) has been systematically examined and it was observed that the polymerization of ε-CL proceed smoothly. GPC analyses reveal that poly(ε-caprolactone) formation takes place with the help of initiator 1 having PDI value ranging from 1.07 to 1.18, with controlled polymer properties. The linear relationship between the number-average molecular weight (Mn) and the monomer-to-initiator ratio ([M]0/[I]0) has been shown in Fig. 1. These reactions are useful for designing of biomedical material due to the presence of limited amount of metal content. It was found that when the reaction was performed in the higher[p-(chloromethyl)benzyl alcohol/initiator] ratio, the conversion rate is much faster. 1H NMR spectrum of PCL-50 gives an intensity ratio close to 1 between He (CH2 from ε-CL at the benzyloxide chain end) and Ha (CH2 from ε-CL at the hydroxy end) (Fig. 2). These result support that the initiation occurs through insertion of a p-(chloromethyl)benzyl alkoxy group from compound 1 to ε-caprolactone, giving an alkoxide as an intermediate product (see Table 1).

Polymerization of ε-CL initiated by 1 in toluene at 50 °C. The relationship between Mn (GPC) (□) (PDI (●)) of the polymer and the initial ratio[M]0/[I]0 is shown.
Figure 1
Polymerization of ε-CL initiated by 1 in toluene at 50 °C. The relationship between Mn (GPC) (□) (PDI (●)) of the polymer and the initial ratio[M]0/[I]0 is shown.
The 1H NMR spectrum of PCL-50 in CDCl3.
Figure 2
The 1H NMR spectrum of PCL-50 in CDCl3.
Table 1 Ring-opening polymerization of ε-CL initiated by 1.a
Entry [M]0:[I]0:[ROH]b Time (h) Mn (Calcd)c Mn (NMR)d Mn (GPC)e PDIe Conv (%)d
1 100:2:0 1 5800 6700 13,900 1.08 99
2 200:2:0 1 10,400 10,600 19,600 1.07 90
3 300:2:0 3 15,700 16,100 29,400 1.08 91
4 400:2:0 5 22,700 23,200 42,100 1.18 99
5 100(100):2:0 1(1) 11,200 11,100 19,200 1.07 99(95)
6 800:2:14 2 5700 6550 11,100 1.05 97
7 800:2:78 1 1300 1350 1950 1.15 93
a The reaction condition is in 15 mL toluene at 50 °C and 1 was used 0.05 mmol in each entry.
b ROH is p-(chloromethyl)benzyl alcohol.
c Calculated from the molecular weight of ε-CL times[M]0/[I]0 times conversion yield.
d Obtained from 1H NMR analysis.
e Obtained from GPC analysis.

3.3

3.3 Ring-opening polymerization of benzyl and p-(chloromethyl)benzyl l-lactide Initiated by 2 and 3

Due to excellent chemico-mechanical properties of PLA are considered to be a good substitute for nonbioresorbable polymers (Vert et al., 1995). Ring-opening polymerization of l-lactide (l-LA) by complexes 2 and 3 was examined (Table 2). Experimental results indicate that both complexes 2 and 3 are used as efficient initiators for the ROP of l-lactide. Polymerization goes to completion within 8 h at 0 °C with polydispersity indexes (PDIs) range from 1.06 to 1.16 with controlled properties in PLLA. The low PDIs value support a linear relationship between the number-average molecular weight (Mn) and the monomer-to-initiator ratio ([M]0/[I]0) (Fig. 3), suggesting the absence of back-biting reactions. These reactions were further verified with the help of 1H NMR studies. 1H NMR spectrum of PLLA-15,50 (the number of 15,50 indicates the designed[M]0/[I]0 ratio) (Fig. 4) indicates that the polymer chain is capped with benzyl alcohol in one end, p-(chloromethyl)benzyl ester and other end with hydroxyl end, respectively (see Fig. 5).

Table 2 Ring-opening polymerization of l-LA initiated by 2 and 3.a
Entry Initiator [M]0:[I]0b Time (h) Mn (Calcd)c Mn (NMR)d Mn (GPC)e PDIe Conv (%)d
1 2 30:2 5 2150 2050 3150 1.14 95
2 2 50:2 5.5 3450 2900 4650 1.16 93
3 2 100:2 7 6450 5250 7600 1.07 88
4 2 150:2 8 8750 6900 8600 1.06 80
5 3 50:2 5.5 3600 2850 4900 1.16 96
6 3 100:2 6.5 6700 5500 7100 1.10 91
7 3 150:2 7.5 10,200 8750 11,300 1.06 93
8 3 200:2 8.5 13,400 11,700 15,400 1.07 92
a The condition of the polymerization is in 10 mL CH2Cl2 at 0 °C, 2and 3 was used 0.05 mmol in each entry.
b Calculated from the molecular weight of l-lactide times[M]0/[I]0 times conversion yield plus the molecular weight of benzyl alcohol/p-(chloromethyl)benzyl alcohol.
c Obtained by 1H NMR.
d Obtained by GPC.
e Obtained from GPC analysis.
Polymerization of l-LA initiated by 3 in toluene at 0 °C. The relationship between Mn (GPC) (□) (PDI (●)) of the polymer and the initial ratio[M]0/[I]0 is shown.
Figure 3
Polymerization of l-LA initiated by 3 in toluene at 0 °C. The relationship between Mn (GPC) (□) (PDI (●)) of the polymer and the initial ratio[M]0/[I]0 is shown.
The 1H NMR spectrum of PLLA-15 in CDCl3.
Figure 4
The 1H NMR spectrum of PLLA-15 in CDCl3.
The 1H NMR spectrum of PLLA-50 in CDCl3.
Figure 5
The 1H NMR spectrum of PLLA-50 in CDCl3.

3.4

3.4 Preparation of PCL-β-PAN

PCL-β-PAN was prepared by the polymerization of acrylonitrile with atom transfer radical polymerization (ATRP) technique by using CuBr/2,2-bipyridine as a catalyst which leads to the formation of poly(ε-caprolactone) with an average molecular weight (Mn) 2350 (PDI = 1.10) by using ethylene carbonate as a macroinitiator at 70 °C (Matyjaszewski et al., 1999) (see Table 3). 1H NMR spectrum of PCL-β-PAN was determined by 1H NMR (Fig. 6) shows that acrylonitrile has been polymerized and the GPC studies support the formation of block copolymer (PDI = 1.24) (see Scheme 2).

Table 3 Polymerization of acrylonitrile and PCL by ATRP.a
Entry Temp. (°C)/time (h) PCL [PCL]/[AN] PCL-PAN PAN VPAN:VPCLd
Mn (NMR)b PDIc Mn (GPC)c PDIc Mn (NMR)b
1 70/24 2350 1.10 1/270 58,200 1.24 9600 78:22
2 70/24 1350 1.20 1/29 18,000 1.24 2000 57:43
3 70/24 1350 1.20 1/58 24,100 1.31 4450 74:26
4 70/24 1350 1.20 1/145 44,620 1.34 8150 84:16
a The reaction was in 25 g, (entry 1) 10 g (entry 2) and 20 g (entry 3 and 4) ethylene carbonate.
b Obtained by 1H NMR.
c Obtained by GPC.
d PCL amorphous density = 1.08 g/cm3, PAN density = 1.23 g/cm3.
The 1H NMR spectrum of PCL-β-PAL in CDCl3.
Figure 6
The 1H NMR spectrum of PCL-β-PAL in CDCl3.
Scheme 2

3.5

3.5 Preparation of PLLA-β-PAN

The synthesis of PLLA-β-PAN was carried out in a similar fashion as used for the preparation of PCL-β-PAN. PLLA-50 was obtained by ring-opening polymerization of l-lactide by using 3 as an initiator (PDI = 1.26). The PDI value of PLLA-β-PAN was compared with PCL-β-PAN. The 1H NMR (Fig. 7) shows the peak at 4.47 ppm which corresponds to ethylene carbonate and the peaks at 3.33 and 2.59 ppm are due to the presence of DMSO-d6. Depending on the concentration of precursor, temperature and reaction time, the synthesis of polyacrylonitrile is underway with good stereo-chemical yield (see Scheme 3).

The 1H NMR Spectrum of PLLA-β-PAN in d-DMSO.
Figure 7
The 1H NMR Spectrum of PLLA-β-PAN in d-DMSO.
Scheme 3

3.6

3.6 The morphological study for PCL-β-PAN

Fig. 8 shows the TEM micrograph of PCL-β-PAN ( f PAN V = 78 % ) . Bulk samples of the block copolymers were prepared by solution casting. The PAN-β-PCL was taken in DMF with 100 mg/mL, for 3 days. After solvent removal the samples was annealed in vacuum oven at 160 °C for 12 h. The carbonization procedure was carried out for 2 h at 260 °C in an Ar atmosphere. The specimens for TEM are embedded in epoxy and subsequently sectioned by ultramicrotome with specimen were stained by RuO4. The stained PAN microdomains appear dark while the PCL microdomains appear light. TEM image exhibits a typical microphase-separated by lamellar morphology with d-spacing around 19 nm in the microphase.

TEM micrograph of PCL-β-PAN samples.
Figure 8
TEM micrograph of PCL-β-PAN samples.

4

4 Conclusion

The synthesis of metal alkoxy derivative 1–3 has demonstrated their use as efficient catalytic initiators for the ROP of ε-caprolactone/l-lactide. 1H NMR studies supports that the initiation occurs with the help of insertion of the p-(chloromethyl)benzyl alkoxy group to ε-caprolactone/l-lactide. The catalytic properties help to synthesize polymer-chains with low PDI with good stereochemical properties. Novel block copolymers have been prepared and well characterized. TEM studies support the formation of block copolymer of PCL-β-PAN with good morphological properties having good compatibility and phase distribution.

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