Chapter Graft copolymers of polythiophene and polystyrene based on 3-{ -[1-(p-vinylphenyl)]hexyl}thiophene 1. Introduction: For over two decades, conducting polymers have been hailed as futuristic materials. However, the insolubility and infusibility of classical conducting polymers (polyacetylene, polyaniline, polythiophene, and polypyrrole) make them difficult to be processed, thus limiting their applications. Combining the classical conducting polymers with processable insulating compounds has been demonstrated to be an effective way to improve the processability of polymers [1a-d]. Graft co-polymerisation of conducting polymers with commodity polymers like poly(methyl methacrylate) (PMMA) and polystyrene (PS) as an alternative route to improve the physical properties of conducting polymers is attracting much attention lately. The advantage of this method over the physical blending of conducting polymers and commodity polymers is that long-term stability problems are avoided due to the strong chemical bonds formed between the two different types of polymers [2]. There has been a report on electrochemically grafting polypyrrole on a polystyrene backbone [3], as well as grafting polyaniline on poly(p-aminostyrene) [4]. Polypyrrole copolymer films can also be prepared electrochemically [5]. Block or graft copolymers of polystyrene and polythiophene or its derivatives have also been described [6-8]. These materials were formed by direct linkages between styrene and thiophene moieties. 79 As discussed in the previous chapter, introducing p-vinylphenyl functional groups to replace reaction -bromo moiety on poly(3- -bromoalkyl)thiophene through Grignard was difficult. In a different approach, novel 3-{ -[1-(p- vinylphenyl)]hexyl}thiophene was synthesised. This monomer was polymerised through a two-step process to yield a graft copolymer. It was also copolymerised with styrene in different ratios to form a precursor copolymer, which was then subjected to an oxidative polymerisation step to form a graft copolymer with polythiophene backbone. Similar precursor copolymers were either further copolymerised with thiophene to form new graft copolymers, or copolymerised with a mixture of 3-alkylthiophene and 3-( -bromoalkyl)thiophene to give different thiophene co styrene graft copolymers. Their structures and properties were then studied. Some of the properties were compared to the blended poly(3octylthiophene) and polystyrene. 80 2. Experiment: 2.1 Monomer Synthesis: The key monomer for this series of graft copolymer, 3-{ -[1-(p- vinylphenyl)]alkyl}thiophene (3), can be synthesised by either Grignard coupling of 4-bromostyrene with 3-( -bromohexyl)thiophene or Grignard coupling of 1chloromethyl-4-vinyl-benzene with 3-( -bromohexyl)thiophene. These two reaction routes were attempted. It was found, however, that the yield of the product obtained from the Grignard coupling using 1-chloromethyl-4-vinylbenzene was very low. There are two possible reasons. Firstly brominated compounds are generally more suitable for Grignard reactions, and secondly the catalyst used for these reactions affects the yield. Ni(dppp)2Cl2 is known to be more effective when the coupling agents contained brominated aromatic ring structure. Therefore, the monomers used in this part of the project were all afforded through 4-bromostyrene coupling reaction. The novel monomer 3-{ -[1-(p-vinylphenyl)]hexyl}thiophene (3) was formed through a Grignard reaction (see scheme 3.1) between 4-bromostyrene (2) and 3( -bromohexyl)thiophene (1). Sufficient amounts of 3-( -bromohexyl)thiophene (1) was prepared following the procedure reported by Bäuerle et al. [9] as described in the previous chapter. 81 C6H12Ph C6H12Br 1. Mg/THF + S Scheme 3.1 2. Ni(dppp)2Cl2 Br S Synthesis of the monomer 3-{ -[1-(p-vinylphenyl)]hexyl}thiophene 82 2.2 Copolymers syntheses: Through a straightforward two-step polymerisation reaction, monomer can be converted into a graft copolymer of polystyrene and poly(3-hexylthiophene). In the first step, AIBN was used as initiator to yield the precursor polymer 3a. This polymer was further polymerised by FeCl3 following the method reported by Casa et al. [10] to afford a graft co-polymer with two backbones. Since this copolymer was made of 100% monomer 3, it was named Graft 100 (see scheme 3.2). n n C6H12Ph C6H12Ph C6H12Ph AIBN FeCl3 S S S 3a Graft 100 Scheme 3.2 m Direct two-step polymerisation to afford copolymer Graft 100 It was found that the graft copolymer formed in the way described in Scheme 3.2 was not soluble at all. This is despite its precursor copolymer 3a being soluble. It is therefore worthy of investigation to find out if lowering the content of polythiophene in the system will help produce a more processible copolymer since polythiophene is known to have lower solubility. One way to achieve this is to introduce styrene into the copolymer system (Scheme 3.3). When monomer was polymerised together with styrene using AIBN as initiator, monomer and styrene will fuse via a radical reaction. This reaction produces a copolymer that contained more phenyl rings than thiophene rings. Further oxidative 83 polymerisation of this copolymer resulted in a copolymer with a longer polystyrene backbone compared to that of the polythiophene backbone. The experiments are illustrated in Scheme 3.3. n C6H12Ph C6H12Ph AIBN 1xStyrene S n Ph C6H12Ph Ph FeCl3/CH3NO2 S S m Graft 21(m:n=1:1) 3b n AIBN 4xStyrene C6H12Ph n Ph C6H12Ph Ph FeCl3/CH3NO2 S 3c Scheme 3.3 S m Graft 51(m:n=1:4) Polymerisation of styrene and monomer in the ratio of 1:1 and 4:1 afforded 3b and 3c respectively, which can be further polymerised to give copolymers Graft 21 and Graft 51 A series of precursor copolymers, 3b, 3c and 3d (not shown in scheme), were prepared first by co-polymerising monomer with styrene in different ratios using AIBN as initiator. In this step, co-polymer 3b was obtained when the feed ratio of monomer to styrene is 1:1. While the feed ratio was 1:4 and 1:10 respectively, 3c and 3d was produced. In the next step, when oxidative polymerisation was carried out using copolymer 3b, a graft copolymer with a structure that is similar to that of 3a was obtained. Based on the monomer and styrene feed ratio for 3b, the theoretical ratio of phenyl rings to thiophene rings in such a copolymer should 84 be 2:1. This copolymer was therefore named Graft 21. The same rationale is applied to 3c. Since 3c had a monomer to styrene feed ratio of 1:4, the resultant copolymer should theoretically contain times more phenyl rings than thiophene rings. This copolymer was therefore named Graft 51. The actual ratios of phenyl rings to thiophene rings in the copolymers Graft 21 and Graft 51 will be slightly different from that of the expected theoretical values. The difference can be attributed to the first polymerisation process where not all styrene can be incorporated into the copolymer system. These ‘impurities’ will be in the form of styrene oligomers or polymers that monomer was not incorporated in. They are carried over to the next step. These compounds should not affect the second oxidative polymerisation process and will be discarded when the crude grafted copolymers, Graft 21 or Graft 51, are subjected to soxhlet extraction using methanol and acetone in turn. Despite the lowered percentage molecular weight of the thiophene unit in the two graft copolymers Graft 21 and Graft 51, these two polymers were still found to be insoluble. One possible reason for this could be the possible presence of rigid cross-linked structures of the three grafted copolymers: Graft 100, Graft 21 and Graft 51. This will be discussed in further detail in the later parts of this chapter. In order to obtain a more processible polymer, 3-alkylthiophene or its derivatives will be introduced into the copolymer system to impart a less rigid structure and to promote solvent-polymer interaction. The graft copolymer formed in such a 85 way will have two polymer backbones: the polystyrene backbone and the polythiophene backbone. Unlike Graft 100, Graft 21 or Graft 51, not all thiophene rings are linked to the polystyrene backbones in the newly formed graft copolymers. This will give the polythiophene backbones more freedom of movement and hence introduce different physical & chemical properties to these copolymers. As such, experiments were carried out to form graft copolymers consisting two backbones but linked only at certain points. The idea is illustrated below: PS PS PS PS PS PS PS PS PS PS PS PS TH TH TH TH TH TH TH TH TH TH TH TH These copolymers should have about equal amounts of thiophene and styrene in order for a comparison to be carried out with Graft 100. In the first step of a twostep synthesis (see Scheme 3.4), the monomer to styrene ratio was fixed at 1:10 to form copolymer 3d. In the second step, copolymer 3d will be mixed with 3alkylthiophene or its derivatives in a 1:10 mole ratio. The resultant graft copolymer would therefore, have about equal amounts of styrene and percentage molecular weight of the thiophene unit. The ratio of 1:10 was used in the hope of giving the polymer backbone enough space for movement (especially for polythiophene backbones). Ideally, on the polythiophene backbone in the graft copolymer, there should be about ten thiophene rings that are not linked with the 86 polystyrene backbone alternating between two thiophene rings that are linked with the polystyrene backbone via alkyl chain linkages to facilitate movement. In the experiment, copolymer 3d was mixed in a 1:5 mole ratio with 3-( bromohexyl)thiophene and in a 1:5 mole ratio with 3-octylthiophene before oxidative copolymerisation was carried out for the mixture. The resultant graft copolymer 4, therefore, should theoretically have about equal numbers of phenyl rings and thiophene rings. 3-( -bromohexyl)thiophene was introduced to show if radical polymerisation step using AIBN as initiator affected the thiophene group. The results will be discussed later in this chapter. Graft co-polymer was produced based on precursor co-polymer 3d. Polymerisation of a mixture of 3d and thiophene in 1:10 mole ratio using Casa’s method [10] produced (see scheme 3.4). As comparison, a polymer blend of polystyrene and poly(3-octylthiophene) was also prepared. Polystyrene was formed by polymerising styrene in a 1:1 styrene and 3-octylthiophene mixture using AIBN as initiator. Subsequently, CH3NO2 solution of FeCl3 was added in situ to polymerise 3-octylthiophene. 87 Copolymer has a unique three-step thermal degradation pattern in this series of copolymers, as shown below. Copolymer is also the only copolymer of the series that possesses free alkyl pendant groups. Its unique thermal degradation profile may be justifiable by its unique structure. The thermal degradation of copolymer started at about 245oC, which is slightly lower than copolymer Graft 100. On the Derivative Weight (%/oC) plot, a shoulder peak is observed at the second decomposition stage. The decomposition process was complete at a temperature slightly above 600oC with less than 2% residue. n C6H12Ph Ph (CH2)6 Br S S m S x C8H17 Fig. 3.19 TGA plot for copolymer in air 115 Copolymer was the least thermally stable in air amongst this series of polymers. It started to decompose at about 220oC. Its decomposition pattern resembles the two-step degradation pattern of copolymers Graft 21, Graft 51 and Graft 100. The Differential Scanning Calorimetry (DSC) plots of copolymers Graft 100, and are shown below. The glass transition points (Tg) of the copolymers are reported above in Table 3.5. Fig. 3.20 Overlaid DSC plots for copolymers (from top to bottom) 4(1), Graft 100(2) and 5(3). 116 All samples were heated up to 200oC and rapid cooling down to -10oC to -20oC [22]. In this series of copolymers, Graft 100 has the highest Tg of 149oC. Since Tg can be viewed as a measure of rotational freedom in the polymer molecules, copolymer Graft 100 should be deemed as the most rigid. In the molecules of copolymer Graft 100, every phenyl group in the polystyrene backbone is linked with a thiophene group in the polythiophene backbone. This is on top of the fact the there is possible cross-linking in the polymer structure. The combined effects of these likely factors are a very rigid molecular structure of the copolymer. In copolymers Graft 21 and Graft 51, phenyl groups that are not linked with the thiophene groups were introduced into the polystyrene backbone. This should have given their structure more rotational freedom compared to copolymer Graft 100 possibly resulting in their lowered observed Tg. The Tg of copolymer was found to be much higher than the Tg of copolymer 5. This is in spite of the fact that the only structural difference between copolymers and is the polythiophene backbone in copolymer compared to the poly(alkylthiophene) backbone in copolymer 4. Apparently, the bulkier side chain of copolymer does affect the rotational freedom in its molecules to a greater extent than expected causing its Tg to be much higher than that of copolymer [23]. 117 3.2.8 GPC and conductivity study Gel permeation chromatography (GPC) results and conductivity measurements are listed in the table below. Table3.6 GPC analyses, conductivity measurements and UV-Vis results for copolymers formed GPC results Polymer Graft51 Graft21 Graft100 BlendTHPS Mw Mn ---35,900 34,400 12,200 ---15,600 13,300 8,330 PDI ---2.31 2.58 1.46 Conductivity I2 doped(Scm-1) UV-Vis max (nm) 1.8x10-7 1.8x10-6 3.5x10-5 0.02 -- ---440 424 422 The molecular weight of copolymers Graft 21, Graft 51 and Graft 100 were not measured using GPC due to their poor solubility. Copolymers and have a higher average molecular weight (Mn) and higher polydispersity index (PDI) compared to that of the blended copolymer formed under similar conditions. Between copolymers and 5, copolymer has a higher average molecular weight. If we also take into consideration that copolymer has higher percentage molecular weight of the thiophene unit (Table 3.1), we can then expect copolymer to have a longer polythiophene backbone. This argument seems to be supported by the UV-Vis spectrum. Copolymer showed a higher max absorption compared to copolymer 4, which suggests higher conjugation length of the polythiophene backbone in the former. It is important to note that all these comparisons are made 118 based on the data collected from the soluble portions of copolymers and 5. Since a major portion of both copolymers are not soluble, the situation on the whole may be very different. This could especially be true for copolymer because only ~10% of it was found to be soluble. Conductivities of copolymers Graft 51, Graft 21 and Graft 100 can generally be correlated to their percentage molecular weight of the thiophene unit. Copolymer Graft 51 with the lowest percentage molecular weight of the thiophene unit of 14.16% is an insulator, possibly because its polythiophene backbone is below the critical length for conducting. Copolymer Graft 100’s conductivity is about one order higher than that of copolymer Graft 21, likely to be the result of increased percentage molecular weight of the thiophene unit. However that is still a few orders lower than that of copolymer 4, which attained the highest conductivity amongst this series of copolymers. This is despite the fact that copolymer had the lowest percentage molecular weight of the thiophene unit amongst these copolymers. Their large differences in conductivity, therefore, are mostly likely due to their structural differences. A plausible explanation is as follows: As shown in the Fig 3.21 below, if the thiophene rings that are next to each other and on the same precursor copolymer were to be joined, the phenyl rings will be forced to adopt a state of higher energy that is similar to that of a ‘cis’ conformation. To avoid this, thiophene rings from different precursor copolymer chains are likely to be joined, which will result in a cross-linked configuration. 119 The consequences of cross-linking would be poor polymer solubility and could possibly account for the low polymer conductivity as well. In copolymer 4, the introduction of styrene and 3-alkylthiophene derivatives into the co-polymer system gives the copolymer more ‘flexibility’ in its structure. A more rotatable and lower energy confirmation can be adopted. Chances for crosslinking are thus reduced. It is much easier for the polythiophene backbone to take on the ‘head to tail’ configuration. All these factors contribute to a more soluble, more conducting and possibly less cross-linked co-polymer. S S S S Fig. 3.21 S S S S Illustration of possible structures of copolymers Graft 100 and The percentage molecular weight of the thiophene unit of copolymer is comparable to that of copolymer Graft 100. The highest conductivity it can achieve is one order higher than that of copolymer Graft 100. However, the value is still much lower than copolymer 4. As mentioned above, graft copolymers and have similar structures save for the fact that the thiophene backbone of 120 contains mainly thiophene rings while 3-alkylthiophene derivatives made up most of the thiophene backbone in copolymer 4. Therefore, the difference in properties between these two copolymers may be related to the differences in properties between polythiophene and poly-3-alkylthiophene [24]. Polythiophene is generally less soluble compared to poly-3-alkylthiophene. The steric factor inserted by the long alkyl chains will improve regioregularity of the polythiophene backbone and, hence, solubility and conductivity of the co-polymer formed for copolymer [15]. XRD studies also indicated that the structure of copolymer has a higher degree of crystallinity than that of copolymer 5. The combined effect of the above will result in a co-polymer that is more soluble and more conductive, as we have observed in copolymer 4. In short, the properties of Graft 21, 51, and 100 give strong indication that they contained only short thiophene oligomers, cross linking the polystyrene chains. This is most likely a result of the two-step polymerisation method. This point will be discussed in further detail in chapter of this thesis. The notation that these polymers contain a polythiophene backbone, therefore, should be viewed as the original experimental design that may not be realised in practise. Cross linkages most likely exist in copolymers and as well. However, their conductivities showed that extended conjugation must exist in their structures. Hence these two copolymers should possess polythiophene backbones. 121 4. Conclusion: A novel monomer, 3-{ -[1-(p-vinylphenyl)]hexyl}thiophene, was synthesised by a relatively straightforward route. Based on which, five new graft copolymers were synthesised. It was found that a direct two-step polymerisation of the monomer only yielded a graft copolymer (copolymer Graft 100) that was insoluble and with relatively low conductivity. Reducing the amount of thiophene by introducing more styrene into the copolymer structure (copolymer Graft 21, Graft 51) did not improve the solubility. Instead, a decline in the conductivity was noted. However by introducing more thiophene rings (copolymer 5) or 3alkylthiophene derivatives into the structure (copolymer 4), both solubility and conductivity were improved. Hence, by modifying the structure one can expect better processibility and electronic properties from such graft copolymers. 122 5. Experimental General: Electrical conductivity measurements were effected on a four-point probe connected to a Keithley constant-current source system under atmospheric conditions at room temperature. Elemental analyses were performed on a Perkin Elmer 240C elemental analyser for C, H and S determinations. Halogen determinations were done either by ion chromatography or the oxygen flask method. FT-IR spectra of monomers and polymers dispersed in KBr disks were recorded on Bio-Rad TFS165 spectrometer. 1H NMR spectra of polymers were recorded on a Bruker AM300 spectrometer. UV-Vis spectra were obtained on a Perkin-Elmer Lamda 900 spectrophotometer. Thermogravimetric analyses (TGA) of polymer powders were conducted on a Du Pont Thermal Analyst 2100 system with a TGA 2960 thermogravimetric analyzer. A heating rate of 20 C min-1 with airflow of 75 ml min-1 was used. The runs were conducted from room temperature to 600 C. Gel permeation chromatography (GPC) analyses were carried out using a Waters 600E system controller and Waters 410 differential reflectometer together with PhenogelTM MXL and MXM columns (300 mm 4.6 mm ID) calibrated using polystyrene standards and THF as eluant. The synthesis of the monomer is shown in Scheme 1. The procedure described by Bäuerle et al. [9] was used to prepare 3-(6-bromohexyl)thiophene, as shown in chapter 2. 3-{ -[1-(p-vinylphenyl)]hexyl}thiophene: Compound 3-( - bromohexyl)thiophene (0.125 mol) in 40 ml of anhydrous ether was added under 123 inert atmosphere to magnesium turnings (0.15 mol) in 15 ml of ether, the reaction mixture was then refluxed for 5-6 hr. The Grignard solution of (see Scheme 1) was subsequently transferred dropwise via cannula to a second apparatus containing Ni(dppp)Cl2 (1 mol%) and ether solution of (0.106 mol) at C over hr. The reaction mixture was refluxed for 12-15 hr before being hydrolysed by 40 ml of saturated NH4Cl solution and 150 ml of ice water. This is followed by extraction of the organic layer with several portions of ether. Washing to neutrality then drying of the combined organic phases and removal of the solvent in vacuum afforded a yellowish-white liquid, which was purified by silica gel chromatographic method with hexane and ethyl acetate as solvent to afford analytically pure compound as a colorless oil. 1H-NMR (CDCl3, TMS as standard) [ppm]: 1.30-1.65(m, 8H); 2.65(q, 4H, J=8Hz); 2.9(s, 1H); 5.22(d, 1H, J=11Hz); 5.73(d, 1H, J=11Hz); 6.73(dd, 1H, J=11Hz, J=6Hz); 6.93-7.37(m, 7H). 13 C-NMR (CDCl3, ppm): 143.0; 142.5; 136.7; 136.6; 135.0; 131.3; 130.2; 128.2; 126.2; 125.0; 119.7; 113.1; 112.7; 37.3; 37.1; 35.6; 31.2; 29.0. Elemental analysis (experiment): C 79.63%, H 8.35%, H 11.83%. Expected: C 79.94%, H 8.20%, S 11.86%. 3a, 3b, 3c, 3d (see scheme 2, 3, 4): THF solution of and an applicable amount of styrene (0, 100, 400, 1000 mole % for 3a, b, c, d accordingly) were stirred under N2 atmosphere before mole % of AIBN was added. The reaction mixture was then heated to 60 C and stirred at that temperature for hr. It was then cooled 124 down to r.t. before being poured into methanol. The white ppt obtained was filtered before being soxhlet-extracted with methanol and hexane in turn. The method reported by Casa et al. [10] was used to form copolymers Graft 100, Graft 21, Graft 51, and 4. The polymerisation processes were carried out in anhydrous solvents at room temperature, under vigorous stirring. A dry nitrogen atmosphere was maintained throughout the reaction. Graft 100, Graft 21 and Graft 51 (see scheme 2, 3): A solution of anhydrous FeCl3 in MeNO2 was added dropwise in a 20 period to a CCl4 solution of 3a, 3b, 3c. After stirring the reaction mixture for 40 min, the reaction mixture was then poured into MeOH. The black solid was filtered and soxhlet-extracted with MeOH and acetone in turn. The polymer obtained was dedoped by washing with 40% hydrazine solution for 24 hr before it was vacuum dried. and (see scheme 4): A solution of anhydrous FeCl3 in MeNO2 was added dropwise over a 20 duration to a CCl4 solution of 3d and 100 mole % of thiophene (for copolymer 5) or 50 mol% of 3-octylthiophene and 50 mol% of 3( -bromohexyl)thiophene (for copolymer 4). The reaction mixture was stirred for 40 before being poured into MeOH. The black solid was filtered and soxhletextracted with MeOH and acetone in turn. The polymer obtained was dedoped by washing with 40% hydrazine solution for 24 hr before it was vacuum dried. 125 Copolymer Graft100 Found (%): (C: 78.15, H: 7.29, S: 11.83) Expected (%): (C: 79.9, H: 8.20, S: 11.86) Copolymer Graft21 Found (%): (C: 81.43, H: 7.79, S: 9.76) Expected (%): (C: 82.7, H: 7.69, S: 8.5) Copolymer Graft51 Found (%): (C: 84.16, H: 7.59, S: 5.28) Expected (%): (C: 87.7, H: 7.69, S: 4.04) Copolymer Found (%): (C: 76.67, H: 6.53, S: 11.40) Expected (%): (C: 77.8, H: 5.64, S: 16.5) Copolymer Found (%): (C: 71.88, H: 8.48, Br: 10.49, S: 9.15) Expected (%): (C, 70.37; H, 7.37; Br, 11.82; S, 10.44) Blend co-polymer of polystyrene and poly(3-octylthiophene): A THF solution of 1:1 mole ratio of styrene and 3-octylthiophene was stirred under N2 atmosphere before mole % of AIBN was added. The reaction mixture was then heated to 60 C and was stirred at that temperature for hr. 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Styrene S S 3 3d 3- octylthiophene/ 3- (w-bromohexyl)thiophene thiophene FeCl3 FeCl3 n n C6H12Ph Ph C6H12Ph (CH2)6 Br S S S Ph m S x C8H17 4 m S 5 Scheme 3. 4 Polymerisation of styrene and monomer 3 in the ratio of 10:1 produced 3d, which can be further co- polymerised with 3octylthiophene and thiophene 88 3 Results and Discussion: 3. 1 Monomer synthesis and characterisation of The novel monomer 3 was characterised... similar environments to that of copolymer 5 C 1s core level deconvolution of copolymer Graft 100 is show in Fig 3. 13 107 n C6H12Ph S m Graft 100 Fig 3. 13 C 1s core level of XPS spectrum of copolymer Graft 100 The S 2p envelope of all three copolymers turned out to have very similar environments The deconvoluted S2p core level of copolymer 4 is shown in Fig 3. 14 The binding energies (BE) at 164.1 and 165.1... by proton atom that is adjacent to the benzene ring Apart from coupling with the other allylic proton, the cis and trans proton atoms also have strong geminal coupling, giving rise to doublets at 5.22 and 5. 73 ppm Fig 3. 2 shows the 13C NMR spectrum of the monomer 89 C6H12Ph S 3 Fig 3. 1 1H NMR spectrum of monomer 3 C6H12Ph S 3 Fig 3. 2 13 C NMR spectrum of monomer 3 90 The peaks at 136 .7 ppm and 136 .6... broad peak at ~3. 5 ppm on 4, which was caused by –CH2Br It has to be noted that the NMR spectra of grafted copolymers may give qualitative structural information of the polymer, e.g., type of bonding and functional groups The integration of the peaks, on the other hand, might not have provided the correct information on the chemical composition of each functional group in the bulk of the copolymer This... environment and give a single broad peak at 2.6 ppm The low intensity of the band is due to the fact that the alkyl side chain content is relatively low in this copolymer a n b Ph CH2Ph (CH2)4 c CH2 S m S 5 Fig 3. 8 1 H NMR spectrum of grafted copolymer of PS and polythiophene (5) 100 3. 2 .3 FT-IR Fig 3. 9 is the IR spectra of graft copolymers 4, 5 and the blended copolymer Fig 3. 9 IR spectra of copolymers... the intermediate co -polymers, 3a, 3b, 3c and 3d, were white powders that were soluble in common polar solvents such as chloroform and THF, similar to polystyrene However, upon the second polymerisation process, the morphology of the grafted co- polymer changed drastically Copolymer Graft 51 was a yellow powder Copolymers Graft 21 and Graft 100 were orange-coloured powders These three co -polymers were found... (mole%) unit (mole%) 14.16 12.26 26. 13 22.49 31 .40 31 .40 31 .72 43. 05 23. 92 27 .38 Graft51 C50H54S C43H46S Graft21 C26H30S C22H26S Graft100 C18H20S C18H20S C 138 H142S11 C197H201S11 5 C196H247Br5S11 C229H 330 Br5.5S11 4 a Calculated based on monomer(s) feed ratio b Calculated based on the elemental analyses results of the co polymers 104 3. 2.5 XPS The XPS spectrum of copolymer 4 is shown below as an example:... and 3d showed similar features except that the peaks caused by the polystyrene backbone are stronger due to co- polymerisation with styrene An example spectrum of 3c is shown in Fig 3. 4 n C6H12Ph S Fig 3. 4 Ph 3c NMR spectrum of precursor copolymer 3c While studying the NMR spectra of these precursor copolymers, one of the complications encountered is that if some of the thiophene moiety in the monomer... air Deconvolution of C1s and S2p core levels showed that these three graft copolymers have similar carbon environment Apparently the differences in their structures are negligible when it comes to deconvoluting the core level chemical environment in XPS n C6H12Ph Ph (CH2)6 Br S S m S x C8H17 4 Fig 3. 14 S 2p core level XPS spectrum of copolymer 4 109 3. 2.6 XRD The XRD for copolymers Graft100, 4, and 5... surface of poly [3- ( -bromoalkyl)thiophene] has been discussed based on the XPS data Deconvolution of the C1s envelopes of these copolymers showed similar chemical environments due to their similar structures The binding energy of the C 1s core level of 5 is tabulated in Table 3. 3 Upon compensating for the charging effect and the Fermi level shift, three environments can be resolved 106 The main environments . 5.22 and 5. 73 ppm. Fig 3. 2 shows the 13 C NMR spectrum of the monomer. 90 Fig 3. 1 1 H NMR spectrum of monomer 3 Fig 3. 2 13 C NMR spectrum of monomer 3 S C 6 H 12 Ph 3 S C 6 H 12 Ph 3 . that of the polythiophene backbone. The experiments are illustrated in Scheme 3. 3. Scheme 3. 3 Polymerisation of styrene and monomer in the ratio of 1:1 and 4 :1 afforded 3b and 3c respectively,. classical conducting polymers with processable insulating compounds has been demonstrated to be an effective way to improve the processability of polymers [1 a-d]. Graft co- polymerisation of conducting