Indian Journal of Science · Indian Journal of Science, 2013, 5(13), 41-48 (PECH) wit hydrophobic...

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Indian Journal of Science • Analysis Sribala et al. Synthesis and Characterizations of Poly (ε-caprolactone) based hydrophobic Copolymers, Indian Journal of Science, 2013, 5(13), 41-48, www.discovery.org.in http://www.discovery.org.in/ijs.htm © 2013 Discovery Publication. All Rights Reserved Page41 Sribala MG 1 , Hung-Hsia Chen 2 , Ping-Hei Chen 2 , Meenarathi B 1 , Kannammal L 1 , Siva P 1 , Anbarasan R 11. Centre for Research, Department of Polymer Technology, Kamaraj College of Engineering and Technology, Virudhunagar – 626 001, Tamil Nadu, India 2. Department of Mechanical Engineering, MEMS Thermal Control Lab, National Taiwan University, Taipei – 10617, Taiwan, ROC Corresponding Author: Professor, Centre for Research, Department of Polymer Technology, Kamaraj College of Engineering and Technology, Virudhunagar – 626 001, Tamil Nadu, India. E-Mail: [email protected] Received 22 July; accepted 29 September; published online 08 October; printed 28 October 2013 ABSTRACT A novel copolymer was synthesized towards the attainment of hydrophobicity and the results were compared with the conventional copolymer. The copolymers were characterized by various analytical techniques like FTIR, NMR, UV-visible, Fluorescence, XPS, SEM, FESEM, TEM, DSC, TGA and GPC. Finally, the water contact angles of the copolymers were tested. The results indicated that the thermal, fluorescence, molecular weight and water contact angle properties of the copolymer depended on the structure and nature of the copolymers. The analytical results also declared that the interface between hydrophobic and hydrophilic region had the nano structure, due to the reduction in the size. On heating under air atmosphere the hydrophilic segments degraded first followed by the hydrophobic segments. Keywords: Copolymer; Characterizations; TEM; FESEM; XPS; Contact angle To Cite This Article Sribala MG, Hung-Hsia Chen, Ping-Hei Chen, Meenarathi B, Kannammal L, Siva P, Anbarasan R. Synthesis and Characterizations of Poly (ε- caprolactone) based hydrophobic Copolymers. Indian Journal of Science, 2013, 5(13), 41-48 1. INTRODUCTION Copolymerization is a technique used to improve the physical, chemical, optical, thermal, hydrophilic, hydrophobic and mechanical property of a polymer. Synthesis of such a novel material in a block copolymer form is a fascinating field of research. Even then, some restrictions are there due to phase separation. This can be outwitted by selecting a polymer with reactive end groups which can act as an initiator for some other monomer without adding any surfactant. In such a way one can produce a surfactant free polymeric nano particles. This key idea is applicable in the case of poly (epichlorohydrin) (PECH) with active OH end group. Syntheses of PECH with different methodologies are reviewed here. By using an atom transfer radical polymerization (ATRP) method, PECH was grafted onto poly (methyl methacrylate) (PMMA) (Lee et al. 2009). Block graft copolymers of PECH and PMMA was synthesized by NMP and ATRP coupled methods (Tasdelen et al. 2007). Thermo analytical life time testing of PECH and its derivatives with poly (glycidyl azide) were reported (Eroglu et al. 1998). Controlled synthesis of PECH with pendent cyclic carbonate was characterized by IR, NMR, and GPC techniques (Brocas et al. 2011). A novel copolymer was synthesized by using epichlorohydrin (ECH) and thio ether units (Changhai et al. 2010). PECH with multiple melting behaviors was reported by Singhfield and co-workers (Singhfield et al. 1999). ECH and allylglycidyl ether copolymer was synthesized by conventional anionic ring opening polymerization method (Erberich et al. 2007 and Lukaszczyk et al. 2002). Acetate functionalized ECH copolymer was synthesized by using PECH as a base polymer (Sarbu et al. 2000). ECH cross-linked starch was prepared in the presence of ammonium hydroxide for ion- exchange purpose (Simkovic et al. 1996). Super hydrophobic character of a material is generally obtained by the combination of surface roughness and low surface energy with flower like morphology. Currently Victor and co-workers (Victor et al. 2012) reported about a low cost method for the generation of super hydrophobic polymer surfaces. In 2008, poly (styrene) (PS) was tried as a super hydrophobic material at ambient conditions (Tan et al. 2008). A copolymer between butyl methacrylate and ethylene dimethacrylate exhibited a water contact angle of >170 0 (Levkin et al. 2009). Cunha et al. (2010) reviewed the turning of polysaccharides into hydrophobic materials. The super hydrophobic surface with double scale roughness was obtained after spin coating with Teflon (Wu et al. 2010). By thorough literature survey we could not find any report based on the synthesis of hydrophobic poly (Caprolactone) (PCL) by using hydrophilic PECH and poly (MMA-silane) as a prepolymer with OH functional group. The novelty of the present investigation is the PECH with OH group is act as an initiator for the preparation of PCL by bulk polymerization method. 2. MATERIALS AND METHODS RESEARCH • POLYMER TECHNOLOGY Indian Journal of Science, Volume 5, Number 13, October 2013 Synthesis and Characterizations of Poly (ε-caprolactone) based hydrophobic Copolymers Science Indian Journal of ISSN 2319 – 7730 EISSN 2319 – 7749

Transcript of Indian Journal of Science · Indian Journal of Science, 2013, 5(13), 41-48 (PECH) wit hydrophobic...

Page 1: Indian Journal of Science · Indian Journal of Science, 2013, 5(13), 41-48 (PECH) wit hydrophobic materials. The super hydrophobic surface with double scale roughness was obtained

Indian Journal of Science • Analysis

Sribala et al. Synthesis and Characterizations of Poly (ε-caprolactone) based hydrophobic Copolymers, Indian Journal of Science, 2013, 5(13), 41-48, www.discovery.org.in http://www.discovery.org.in/ijs.htm © 2013 Discovery Publication. All Rights Reserved

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Sribala MG1, Hung-Hsia Chen2, Ping-Hei Chen2, Meenarathi B1, Kannammal L1, Siva P1, Anbarasan R1☼

1. Centre for Research, Department of Polymer Technology, Kamaraj College of Engineering and Technology, Virudhunagar – 626 001, Tamil Nadu, India 2. Department of Mechanical Engineering, MEMS Thermal Control Lab, National Taiwan University, Taipei – 10617, Taiwan, ROC ☼Corresponding Author: Professor, Centre for Research, Department of Polymer Technology, Kamaraj College of Engineering and Technology, Virudhunagar – 626 001, Tamil Nadu, India. E-Mail: [email protected] Received 22 July; accepted 29 September; published online 08 October; printed 28 October 2013

ABSTRACT A novel copolymer was synthesized towards the attainment of hydrophobicity and the results were compared with the conventional copolymer. The copolymers were characterized by various analytical techniques like FTIR, NMR, UV-visible, Fluorescence, XPS, SEM, FESEM, TEM, DSC, TGA and GPC. Finally, the water contact angles of the copolymers were tested. The results indicated that the thermal, fluorescence, molecular weight and water contact angle properties of the copolymer depended on the structure and nature of the copolymers. The analytical results also declared that the interface between hydrophobic and hydrophilic region had the nano structure, due to the reduction in the size. On heating under air atmosphere the hydrophilic segments degraded first followed by the hydrophobic segments. Keywords: Copolymer; Characterizations; TEM; FESEM; XPS; Contact angle To Cite This Article Sribala MG, Hung-Hsia Chen, Ping-Hei Chen, Meenarathi B, Kannammal L, Siva P, Anbarasan R. Synthesis and Characterizations of Poly (ε-caprolactone) based hydrophobic Copolymers. Indian Journal of Science, 2013, 5(13), 41-48

1. INTRODUCTION Copolymerization is a technique used to improve the physical, chemical, optical, thermal, hydrophilic, hydrophobic and mechanical property of a polymer. Synthesis of such a novel material in a block copolymer form is a fascinating field of research. Even then, some restrictions are there due to phase separation. This can be outwitted by selecting a polymer with reactive end groups which can act as an initiator for some other monomer without adding any surfactant. In such a way one can produce a surfactant free polymeric nano particles. This key idea is applicable in the case of poly (epichlorohydrin) (PECH) with active OH end group. Syntheses of PECH with different methodologies are reviewed here.

By using an atom transfer radical polymerization (ATRP) method, PECH was grafted onto poly (methyl methacrylate) (PMMA) (Lee et al. 2009). Block graft copolymers of PECH and PMMA was synthesized by NMP and ATRP coupled methods (Tasdelen et al. 2007). Thermo analytical life time testing of PECH and its derivatives with poly (glycidyl azide) were reported (Eroglu et al. 1998). Controlled synthesis of PECH with pendent cyclic carbonate was characterized by IR, NMR, and GPC techniques (Brocas et al. 2011). A novel copolymer was synthesized by using epichlorohydrin (ECH) and thio ether units (Changhai et al. 2010). PECH with multiple melting behaviors was reported by Singhfield and co-workers (Singhfield et al. 1999). ECH and allylglycidyl ether copolymer was synthesized by conventional anionic ring opening polymerization method (Erberich et al. 2007 and Lukaszczyk et al. 2002). Acetate functionalized ECH copolymer was synthesized by using PECH as a base polymer (Sarbu et al. 2000). ECH cross-linked starch was prepared in the presence of ammonium hydroxide for ion-exchange purpose (Simkovic et al. 1996).

Super hydrophobic character of a material is generally obtained by the combination of surface roughness and low surface energy with flower like morphology. Currently Victor and co-workers (Victor et al. 2012) reported about a low cost method for the generation of super hydrophobic polymer surfaces. In 2008, poly (styrene) (PS) was tried as a super hydrophobic material at ambient conditions (Tan et al. 2008). A copolymer between butyl methacrylate and ethylene dimethacrylate exhibited a water contact angle of >1700 (Levkin et al. 2009). Cunha et al. (2010) reviewed the turning of polysaccharides into hydrophobic materials. The super hydrophobic surface with double scale roughness was obtained after spin coating with Teflon (Wu et al. 2010). By thorough literature survey we could not find any report based on the synthesis of hydrophobic poly (Caprolactone) (PCL) by using hydrophilic PECH and poly (MMA-silane) as a prepolymer with OH functional group. The novelty of the present investigation is the PECH with OH group is act as an initiator for the preparation of PCL by bulk polymerization method.

2. MATERIALS AND METHODS

RESEARCH • POLYMER TECHNOLOGY Indian Journal of Science, Volume 5, Number 13, October 2013

Synthesis and Characterizations of Poly (ε-caprolactone) based hydrophobic Copolymers

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Indian Journal of Science • Research • Polymer Technology

Sribala et al. Synthesis and Characterizations of Poly (ε-caprolactone) based hydrophobic Copolymers, Indian Journal of Science, 2013, 5(13), 41-48, www.discovery.org.in http://www.discovery.org.in/ijs.htm © 2013 Discovery Publication. All Rights Reserved

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Epichlorohydrin (ECH, Sigma Aldrich, Germany), ɛ - caprolactone – (CL, Alfa Aesar, England), methacrylic acid (MA, Spectrum reagent and chemicals, India), stannous octoate (S.O, Sigma Aldrich), chloroform (CHCl3), methylmethacrylate (MMA), diethylether, sodiumlauryl sulphate (SLS) and tetrahydrofuran (THF) were purchased from Spectrum reagent and chemicals. Double distilled (DD) water was used for solution preparation purpose. Vinyl hexamethylene trimethoxy silane (TMOS) was purchased from Sigma Aldrich and used without any further purification. Potassium proxydisulphate (PDS) initiator was purchased from Spectrum reagent and chemicals.

2.1. Synthesis of P1 Synthesis of PCL grafted Poly (MMA-co-THS) includes three steps. The first step indicates the synthesis of copolymer; the second step shows the hydrolysis of as synthesized copolymer. The last step reports the chemical grafting of PCL onto the copolymer structure. The synthesis procedure is briefly mentioned here. The reactants were measured in weight basis. 2.0 g of MMA and 2.0 g of TMOS were taken in a 25 mL two way necked round bottom flask (RBF). The contents were deoxygenated by purging N2 gas for 30 min. The surfactant (SLS) (1.0 g) was slowly added to the RBF followed by the addition of PDS (initiator) (0.05 g) under vigorous stirring condition. The reaction temperature was raised to 650C and the stirring was continued for another 4 hours. Thus obtained precipitate was the copolymer and washed with water for 3 times to remove the unreacted SLS and PDS. Now the copolymer sample was freeze dried, weighed and zipper logged. Thus obtained copolymer has trimethoxy silane group and further which can be activated by hydrolysis reaction. 0.50 g of copolymer was dissolved in 10 mL of 1 M HCl at room temperature for 4 hours under N2 atmosphere. The trimethoxy group of silane was readily hydrolyzed by HCl to trihydroxy silanol. Again the product was purified by freeze drying method.

In the last step, 0.10 g of hydrolyzed copolymer was taken in a 25 mL two way necked RBF. With this, 1.0 g of CL and 0.001 g of SO (catalyst) ([M/C]=1000) were taken and the contents were heated to 1400C under N2 atmosphere for 2 hours. During the bulk polymerization reaction, the CL units undergone to ROP and formed the PCL. In the present investigation hydroxyl groups from silane units involved in the ROP of reaction of CL. After 2 hours of ROP, the reaction medium becomes highly viscous and dissolved in CHCl3 and further precipitated by adding 250 mL of diethylether. After air drying, a white crystalline powder was obtained which can be further purified by freeze drying method. Thus obtained polymer is designated as P1 and the reactions are mentioned in Scheme 1.

2.2. Synthesis of P2 A new block copolymer, P2, was prepared by a two step synthesis. MA was used as an initiator for the ring opening polymerization of ECH. 10 mL of ECH was weighed into a dry flask and 10 mL of MA and DD water were subsequently added. In order to activate the ring opening polymerization of ECH, equimolar mixture of monomer and initiator was taken. The reaction mixture was stirred for 6 hours at 45 0C under nitrogen atmosphere. The resulting viscous resin was heated to 130 0C to remove the unreacted ECH, MA monomers and water molecules. Copolymerization was carried out by adding 0.10 g viscous PECH resin (initiator) with 1.0 g of CL (M/I=10) into a dry flask. The reaction mixture was stirred at 1600C under N2 atmosphere in a preheated oil bath in the presence of 0.001 g of SO. The resulted copolymer was dissolved in 20 mL of chloroform and re-precipitated into 250 mL of diethylether. Then the copolymer was dried in fuming cupboard to remove solvent and remaining unreacted monomer. The synthesis reaction is shown in Scheme 2.

Reaction Scheme 1

Reaction Scheme 2

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Indian Journal of Science • Research • Polymer Technology

Sribala et al. Synthesis and Characterizations of Poly (ε-caprolactone) based hydrophobic Copolymers, Indian Journal of Science, 2013, 5(13), 41-48, www.discovery.org.in http://www.discovery.org.in/ijs.htm © 2013 Discovery Publication. All Rights Reserved

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2.3. Characterizations The copolymers were characterized by FTIR Spectroscopy. FTIR spectra were recorded with the help of Shimazdu 8400 S, Japan model instrument by KBr pelletization method from 400 – 4000 cm-1. 3 mg of copolymer was grinded with 200 mg of spectral grade KBr and made into disc under the pressure of 7 tons. 1H and 13C- NMR spectra of the block copolymers were recorded by using Bruker Biospin High Resolution Digital 300 MHz NMR Spectrometer, USA. Dueterated chloroform (CDCl3) was used as the solvent, and tetramethyl silane (TMS) served as the internal standard. Absorption spectroscopy was done by a UV-visible NIR spectrophotometer, Jasco V-570 instrument, USA. Absorption scans were performed in the range of 260 – 800 nm, with a 3 nm slit size. Samples were prepared by dispersing the copolymers in THF solution. Surface morphology of the sample was measured by JSM 6300, Jeol product, SEM instrument. The size of the material was determined by TEM 3010, a product of Jeol. The binding energy was determined by XPS, (XPS, Thermo Scientific, Theta Probe, and UK). The water contact angle of the sample was determined by VCA 2500, Taiwan instrument. A Waters 2690 GPC instrument was used to determine the Mw of the polymer samples using THF as an eluent at room temperature at the flow rate of 1mL min−1 against polystyrene (PS) standards. The melting temperature (Tm) of the polymer samples were determined by using

Dupont Thermal Analyst 2000 Differential Scanning Calorimeter 910S, USA model instrument. All the measurements were done under N2

atmosphere in a temperature range of RT to 1000C with 100C/min heating rate. Thermal stability of block

copolymer was measured by Dupont 951 thermogravimetric analyzer, USA. Thermograms were recorded under air atmosphere in a temperature range of 30 to 800 0C at the heating rate of 10 0C/min. Field emission scanning electron microscopy (FESEM) was used to examine morphological behaviour of copolymer with the help of FESEM – Hitachi S4800 Japan, instrument.

Figure 1 FTIR spectrum of (a) P1, (b) P2

Figure 2 1H-NMR spectrum of (a) P1, (b) P2

Figure 3 13C-NMR spectrum of (a) P1, (b) P2

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Indian Journal of Science • Research • Polymer Technology

Sribala et al. Synthesis and Characterizations of Poly (ε-caprolactone) based hydrophobic Copolymers, Indian Journal of Science, 2013, 5(13), 41-48, www.discovery.org.in http://www.discovery.org.in/ijs.htm © 2013 Discovery Publication. All Rights Reserved

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3. RESULTS AND DISCUSSION 3.1. FTIR study The functional groups present in the copolymers can be confirmed by FTIR spectral data. Figure 1(a) indicates the FTIR spectrum of P1. The important functionalities are characterized below: A small hump at 524 cm-1 explains the Si-O stretch. The O-H stretch is observed around 3500 cm-1. The intensity of the O-H peak confirmed that all the three hydroxyl groups of silane were involved in the ROP of CL. The intermolecular hydrogen bonding can be explained by observing a peak at 3747 cm-1. The spectrum also declared that the carboxyl group present in the P1 also involved in the ROP of CL. The C-H symmetric and anti-symmetric stretching is observed at 2872 and 2946 cm-1 respectively. A sharp peak at 1730 cm-1 is ascribed to the C=O stretching of CL units. A broad peak at 1202 cm-1 accounts for the ester (C-O-C) group of PCL. The C-H out of plane bending vibration can be seen at 727 cm-1. The peak assignments are in accordance with our earlier communication (Chen et al. 2011). The FTIR spectrum of MA initiated block copolymer of P2 is shown in Figure 1(b). Here also the above said peaks corresponding to the PCL are observed. Apart from those, some new peaks are observed due to the ECH units present in the copolymer. A hump at 1642 cm-1 depicts the C=C stretching of MA. A stretching due to chlorine from ECH unit is observed at 589 cm-1. The C-H bending vibration is noted at 1647 cm-1. Thus the FTIR spectrum confirmed the functional groups present in the copolymer structures.

3.2. NMR characterization Further, the structure of block copolymer can be confirmed by NMR spectrum. Figure 2(a) represents the 1H-NMR spectrum of block copolymer P1. Peaks corresponding to PCL protons are observed here as mentioned in the figure. Unfortunately, the signals due to MMA and silanols are not observed due to poor salvation effect of d-DMSO and also due to the minimum quantity (Chen et al. 2011). Figure 2(b) indicates the 1H-NMR spectrum of P2. The methylene and methyne protons of ECH units are appeared around 3.6 ppm. The oxy – methylene protons of PCL is appeared at 4.04 ppm. The methylene proton nearer to ester group of PCL is observed at 2.3 ppm. The remaining protons of PCL can be seen at 1.3 and 1.6 ppm. Apart from these, two more important peaks are present. A methylene proton at 1.25 ppm is due to the methylene group of MA. A small peak at 1.94 ppm accounts for the presence of methylene group associated with the double bond. The end O-H proton can be seen at 4.16 ppm.

The 13C-NMR spectrum of P1 is shown in Figure 3(a) by using d-DMSO as a solvent. Due to the poor salvation effect peaks corresponding to MMA units and silanol units are not observed. At the same time peaks due to PCL units are clearly observed, as mentioned in the figure. Figure 3(b) shows the 13C-NMR spectrum of P2. A peak at 173.49 ppm is due to the

Figure 4 UV-visible spectrum of (a) P1, (b) P2

Figure 5 Fluorescence spectrum of (a) P1, (b) P2

Figure 6 DSC of (a) P1, (b) P2

Figure 7 TGA of (a) P1, (b) P2

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Sribala et al. Synthesis and Characterizations of Poly (ε-caprolactone) based hydrophobic Copolymers, Indian Journal of Science, 2013, 5(13), 41-48, www.discovery.org.in http://www.discovery.org.in/ijs.htm © 2013 Discovery Publication. All Rights Reserved

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carbon of carbonyl group. A triplet peak at 76 ppm is associated with the solvent (CDCl3). In 2011, (Anbarasan et al. 2011) explained the 13C-NMR spectrum of fluorescent PCL. The carbon atoms of ECH are appeared at 62.52, 32.23 and 24.29 ppm as mentioned in the spectrum. The remaining peaks are corresponding to carbon atoms of CL units. In the case of 13C-NMR spectrum peaks due to the MA units are not observed due to the poor content of MA in the copolymer structure.

3.3. UV-visible study The UV-visible spectrum of P1 is shown in Figure 4(a). A peak at 362.5 nm is associated with the n∏* transition of Si-O. The ∏∏* transition of C=O group occurs at 274 nm. Figure 4b reveals the UV-visible spectrum of P2. A broad peak at 308 nm confirms the presence of possible ∏∏* transition (of ECH units) in the copolymer structure. (i.e.) the C=C present in the MA/ECH is observed here. The C=C double bond is formed from ECH units during the ROP of CL itself 17. The n∏* transition of ester carbonyl is absent. The presence of C=C present in the P2 was confirmed by FTIR and NMR spectra and further supported by the UV-visible spectrum. In the present investigation the C=C formation might be activated by the high reaction temperature (160 0C).

3.4. Fluorescence study The fluorescence emission peak of P1 is indicated in Figure 5(a). Due to the presence of Si, P1 produced the fluorescence emission with less fluorescence emission intensity (8.9 cps) at 335 nm. Figure 5b indicates the fluorescence emission peak of MA initiated copolymer P2. The emission spectrum shows one sharp peak at 312.4 nm. The emission intensity value is noted as 426.3 cps. The important point noted here is the homopolymers of either CL or ECH never show any fluorescence behavior. In the present investigation, the fluorescence emission is associated with the formation of polymer nano particles or C=C conjugation in the ECH units. The hydrophobic (PCL) and hydrophilic (PECH) units are covalently attached with each other. The interface region between PCL and PECH units are having some special properties like fluorescence due to the formation of nano sized polymer and C=C conjugation (Perez et al. 2001).

3.5. DSC analysis The DSC thermogram of P1 is indicted in Figure 6(a). Figure 6a exhibits one broad peak at 73.40C due to the melting of CL units. The Tm of PMMA or silanol units are not observed. Again this confirmed that all the –OH groups of P1 were actively involved in the ROP of CL. This supported the FTIR results. The DSC melting temperature of P2 is shown in Figure 6(b). The thermogram exhibits one sharp peak at 55.1°C due to the melting of PCL units (Chen et al. 2011). The melting endothermic peak due to PECH is not observed due to resinous nature of PECH. The melting temperature again confirmed the presence of CL units in the copolymer structure.

3.6. TGA profile The thermal stability of block copolymer was analyzed through TGA method and it is represented in Figure 7. The TGA thermogram of P1 is exhibited in Figure 7(a) with a three step degradation process. The first minor weight loss up to 2000C is due to the loss of moisture. The second major degradation step is ascribed to the degradation of P1 backbone. The third minor weight loss step is associated with the degradation of PCL backbone. Above 4500C it exhibited around 93% weight residue remained. The TGA of P2 is mentioned in Figure 7(b) with a two-step degradation process. The first minor weight loss step from 200-3000C with a loss of 18%

Figure 8 GPC of (a) P1, (b) P2

Figure 9 XPS of (a) P1, (b) P2

Figure 10 SEM of (a) P1, (b) P2

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Sribala et al. Synthesis and Characterizations of Poly (ε-caprolactone) based hydrophobic Copolymers, Indian Journal of Science, 2013, 5(13), 41-48, www.discovery.org.in http://www.discovery.org.in/ijs.htm © 2013 Discovery Publication. All Rights Reserved

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weight is due to the degradation of PECH segments, the remaining 82% weight loss around 3350C is corresponding to the degradation of PCL structure. In the present investigation the degradation due to the CL structure is considered as a major one, it means in the block copolymer structure few number of ECH segments with more number of CL segments are presented. Around 450 0C, the thermogram exhibits approximately 2 % weight residue remained. The TGA results of PCL are in accordance with our earlier publications (Chen et al. 2011 and Gotelli et al. 2011). The TGA thermogram insists one more point that the hydrophilic segments are degraded earlier than the hydrophobic segments. As a result, PECH segments degraded first followed by the degradation of PCL units. In comparison, P2 exhibited higher degradation temperature whereas P1 exhibited higher % weight residue remained at 450 0C.

3.7. GPC report The efficiency of macro initiator was confirmed by GPC measurement (Figure 8). P1 yielded the Mw of 17,727 g/mol [Figure 8(a)] whereas P2 produced the same with 28,367 g/mol [Figure 8(b)]. The GPC results confirmed the high molecular weight for P2 and this supported the higher thermal stability [Figure 7(b)]. At the same time P2 produced different molecular weight due to the increase in the viscosity of the medium during the copolymer formation. The poly dispersity value was determined as 1.3 and 1.7 for P1 and P2 respectively. Moreover, the nature and number of initiating groups are varied. As a result of change in initiating species, their initiating efficiency is also varied. The ROP of CL can be done by various initiating species like –OH 16,18, -SH, -CO2H (Gotelli et al. 2011), -NH2, -SO3H etc., In the present investigation the –OH group with different environment was involved in the ROP of CL through co-ordination insertion reaction. The capability of forming co-ordination linkage with -OH group was changed and resulted with the change in the molecular weight of polymer.

3.8. XPS history The XPS of P1 is shown in Figure 9(a). It shows Si2p (106.8eV), Si2s(158.4eV), C1s(288.5eV) and O1s(535.44eV) peaks. The appearance of Si2s and Si2p confirmed the presence of Si in the copolymer structure. Figure 9b indicates the XPS of P2. The spectrum exhibits three important peaks corresponding to chlorine, carbon and oxygen and the corresponding binding energies are 193.8eV, 289.2eV and 534.8eV respectively. The binding energy of C, O, Si and halogen are in accordance with our earlier reports (Anbarasan et al. 2001, Chen et al. 2011, Anbarasan et al. 2011). 3.9. SEM morphology Figure 10 represents the SEM of P1. Figure 10(a) shows the SEM morphology of P1 with the size of ~1 µM. Figure 10b indicates the typical morphology of PCL with the micro voids (Anbarasan et al. 2001 and Chen et al. 2011) which recommends for the bio-medical application such as for drug delivery. And also one can see the dispersion of nano particles on the PCL backbone. The morphology study clearly indicates the nano particles formation in the interface between the silane and PCL. Recently, Kohila and research team (Kohila et al.) studied about the nano particle formation in the interface between the silk fibre and the poly (Congo red) dye. The result from the present investigation is in accordance with Kohila’s report.

3.10. FESEM report Figure 11 indicates the FESEM image of the MA initiated block copolymer P2. Figure 11(a) explains the surface morphology of PECH-b-PCL. Figure 11(b) clearly indicates the uniform dispersion of nano sized polymer in

the inter face. The size of the particle was determined between 50 and 200 nm. The appearance of nano sized materials in the copolymer structure is purely due to the presence of nano sized polymer. Figure 11(c) shows a dried sky like morphology

Figure 11 FESEM of (a) P1, (b) P2

Figure 12 TEM of (a) P1, (b) P2

Figure 13 Water contact angle of (a) P1, (b) P2

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Sribala et al. Synthesis and Characterizations of Poly (ε-caprolactone) based hydrophobic Copolymers, Indian Journal of Science, 2013, 5(13), 41-48, www.discovery.org.in http://www.discovery.org.in/ijs.htm © 2013 Discovery Publication. All Rights Reserved

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due to the PCL backbone. Figure 11(d) represents the distribution of nano particles on the PCL backbone. Again the formation of nano polymer structure can be explained on the basis of interaction between both hydrophilic and hydrophobic segments. The above FESEM study revealed that the conjugation of both hydrophilic and hydrophobic segments of block copolymer lead to the formation of polymer with nano structure. The nano structure formation is very much important in the drug delivery application of bio-medical polymer like PCL.

3.11. TEM morphology The nano particle formation in P1 can be confirmed by recording TEM and is shown in Figure 12(a). The rod like structure with the size of ~5 nm describes the various crystal planes of silane copolymer. Here the crystal growth occurs in a multi direction. Figure 12(b) reveals the TEM of P1. A nano sphere of 3 to 10 nm size can be seen here. The TEM report supported that during the copolymer formation between hydrophobic and hydrophilic segments, the inter face segments were compressed to nano size. The present investigation is attempting to synthesize a copolymer with a hydrophobic character. In order to attain the hydrophobic character the hydrophilic prepolymer was functionalized by a hydrophobic PCL segments. P1 and P2 exhibited the water contact angles of 127 [Figure 13(a)] and 1040 [Figure 13(b)] respectively. These results confirmed that P1 has a hydrophobic character with the nano structure. P1 is a suitable candidate for opto electronic applications and in self cleaning of car windows. Cunha et al. (2010) explained the water contact angle of a copolymer with >1700, but due to the change in the structure and surface morphology, the present investigation exhibited lower water contact angle. Currently our research team is working hard towards the attainment of higher water contact angle through the grafting of hydrophobic polymer onto the backbone of another one hydrophobic copolymer.

4. CONCLUSIONS From the present investigation, the following important points are presented here as conclusions. Both FTIR and NMR spectra confirmed the structure of copolymers. The UV-visible spectrum confirmed the presence of C=C in P2 system. P2 exhibited the fluorescence activity due to the presence of polymer nano particle and C=C conjugation. P1 showed higher Tm (73.40C) whereas P2 exhibited higher thermal degradation temperature. The Mw of P2 was greater than that of P1 due to the change in functional groups and structure. The XPS confirmed the presence of Cl in P2 at 193.8eV. The surface morphology and topography results declared the presence of polymer nano particles in the interface of the copolymer. P2 showed higher water contact angle (1270) than P1 due to the structure of P2.

FUTURE ISSUES Our main aim is to synthesise a polymer based superhydrophobic material. ACKNOWLEDGMENTS We express our sincere thanks to our colleagues. REFERENCE

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Indian Journal of Science • Research • Polymer Technology

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1. Chen HH, Anbarasan R, Kuo LS, Chen PH. Synthesis and characterizations of novel acid functionalized and fluorescent poly(ε-caprolactone). J. Mater. Sci. 2011, 46, 1796

2. Chen HH, Anbarasan R, Chen PH. Application of Eosin Y functionalized MWCNT as an initiator for the ring opening polymerization of ε-caprolactone. Mater. Chem. Phys. 2011, 126, 584