REGULAR ARTICLE
Synthesis and characterization of poly(linoleic-g- e -caprolactone) graft copolymers via ‘‘click’’ reaction and ring-opening
polymerization
SEMA ALLI
Department of Chemistry, Du¨zce University, 81620 Du¨zce, Turkey E-mail: semaalli@duzce.edu.tr
MS received 19 February 2021; revised 1 April 2021; accepted 9 April 2021
Abstract. Linoleic acid modified with auto-oxidation, hydroxylation, bromination and azidation was used to synthesis graft copolymers usingx-alkyne-terminated poly(e-caprolactone) (alk-PCLs)via‘‘click’’ reac- tion. In the first step, the polymeric linoleic acid (PLina) as macroinitiator was obtained by the autoxidation of linoleic acid. Hydroxylation of the PLina was then carried out using diethanolamine to produce hydroxylated polymeric linoleic acid (PLina-OH). The PLina-OH was chemically modified with 2-bromopropionyl bro- mide to obtain bromo-functionalized polymeric linoleic acid (PLina-Br). This macroinitiator was then modified with sodium azide, resulting in azide polymeric linoleic acid (PLina-N3). In a parallel process, x- alkyne-terminated poly(e-caprolactone) (alk-PCLs) were preparedviaROP of thee-caprolactone monomer in the presence of propiolic acid, 3-butyn-1-ol, 5-hexynoic acid, and propargyl alcohol as the precursors and tin(II) 2-ethyl hexanoate (Sn(Oct)2) as the catalyst. These preliminary steps involved the synthesis of azide and alkyne compounds capable of being linked togetherviathe alkyne-azide cycloaddition reaction catalyzed by copper (Cu(I)), which led to poly(linoleic acid)-g-poly(e-caprolactone) (PLina-g-PCL). The obtained polymers were characterized by proton nuclear magnetic resonance (1H NMR), Fourier-transform infrared (FTIR), differential scanning calorimetry (DSC), thermal gravimetric analysis (TGA) and elemental analysis.
Keywords. Auto-oxidation; Hydroxylation; Ring-opening polymerization; ‘‘click’’ reaction; Graft copolymer.
1. Introduction
Ever-increasing environmental concerns, as well as the decrease in crude oil reserves and the rising cost of commodity chemicals derived from petroleum have led to a growing interest in renewable polymeric materials.1,2 Vegetable oils are considered one of the most prestigious groups of renewable resources for the chemical industry in the synthesis of fine chemicals, monomers, and polymers.3–7A number of researchers from around the world have carried out studies on polymer chemistry using vegetable oils and on their current applications in various fields.8–10Autoxidation is a practical method involving the reaction of unsat- urated oil acids with oxygen. In nature, with the impact of light and air, the oxidation of unsaturated oil acids and triacylglycerols persists as autoxidation, which contributes to the off-flavor of compounds and decreases the quality of the oil.11,12 The presence of
free radical intermediates caused by air oxidation leads to isolation of allylic hydrogen and subsequent delo- calized free radical formation. These free radicals react with atmospheric oxygen to produce peroxy radicals which, through H abstraction, are converted into peroxide or hydroperoxide. The ultimate goal of the research involved achieving the autoxidation of unsaturated vegetable oils and oil acids in an envi- ronmentally friendly manner at room temperature under daylight and ambient conditions without the use of a catalyst. Thus, in this way, the initiators of macro peroxide could be obtained from many oils and oil acids.13–15 Poly(linoleic acid-g-styrene-g-e-caprolac- tone) graft copolymers were synthesized in the pres- ence of styrene and e-caprolactone monomers using macro peroxide linoleic acid as the initiatorvia ring- opening polymerization (ROP) and free radical poly- merization.16The enzymatic degradation properties of these copolymers in the presence of pseudomonas lipase were studied.17Moreover, the use of this macro
*For correspondence
https://doi.org/10.1007/s12039-021-01923-4Sadhana(0123456789().,-volV)FT3](0123456789().,-volV)
peroxide linoleic acid as the initiator was investigated in the presence of tetramethyl piperidinyl-1-oxy (TEMPO) via the nitroxide-mediated radical poly- merization (NMRP) method.18 In our recent article, poly(linoleic acid-g-methyl methacrylate-g-lactide) graft copolymers were synthesized using macro per- oxide linoleic acid as the initiator via ROP and free- radical polymerization in one pot. Furthermore, these graft copolymers were investigated as gate dielectric material for organic field-effect transistor (OFET) application.19 In another study, hydroxylated soybean oil was prepared as a fully water-soluble soybean oil polymer from oxidized soya oil polymer and dietha- nolamine.20 Biswas et al. reported that they had developed a new eco-friendly synthetic pathway for preparing azide derivatives of soybean oil and oil esters.21
Many studies have been carried out lately on azides.
In organic synthesis, the azide functionality is bene- ficial as an intermediate. It is a good synthon for click chemistry as well. Click chemistry was recently introduced by Sharpless et al. as a new way to cate- gorize highly successful, moderate, and selective organic reactions that are modular in nature and involve only basic reactions and working processes.22 The many applications of click chemistry have since been investigated.23–34 The method’s flexibility is evidenced by its suitability under a wide range of reaction conditions. In click chemistry, many reactions under the condition of tolerance limits (temperature, solvent, catalyst) take place in water and oxygen environments. The click chemistry method can be used to synthesize block, brush, linear, and block/graft copolymers, cyclic and star polymers, dendrimers, and network and graft copolymers. Moreover, the reactions take place in the 4-11 pH range without addition of any special buffers, acids or bases. Many scientists have reported that they are conducting studies using the azide-alkyne cycloaddition copper-catalyzed (CuAAC) reaction.35–39A variety of monomers with a great number of initiators and catalyst systems have been applied via ROP.37,40–44 Chen et al. (2016) reported the UV curing of castor-based multifunc- tional polyurethane acrylate via the photo-click chemistry method.
The use of both the click reaction and ROP to synthesize a well-defined azide-functionalized PLina macroinitiator was reported for the first time in this study. As the first step in this method, the azide- functionalized PLina macroinitiator was prepared. The alkyne-functionalized poly(e-caprolactone) (alk-PCL) were then synthesized by ROP ofe-caprolactone with stannous 2-ethyl hexanoate as the catalyst and
propiolic acid, propargyl alcohol, 3-butyn 1-ol, and 5-hexynoic acid as initiators. Finally, the poly(linoleic acid)-g-poly(e-caprolactone) (PLina-g-PCL) graft copolymers were synthesized using the click reaction between the azide-functionalized PLina macroinitiator and the alkyne-functionalized PCLs.
2. Experimental 2.1 Chemicals
Linoleic acid (octadeca-9,12-dienoic acid) technical, 58-74% (GC) was supplied by Sigma-Aldrich and used as obtained. The e-caprolactone (CL), also from from Sigma-Aldrich, was fractionally distilled with dried anhydrous CaSO4. All other chemical substances and solvents were used as supplied. Propiolic acid, 3-butyn-1-ol, 5-hexynoic acid, propargyl alcohol, tin 2-ethyl hexanoate (Sn(Oct)2, sodium azide (NaN3) triethylamine (TEA), pentamethyldiethylenetriamine (PMDETA), CuCl, 2-bromopropionyl bromide, and diethanolamine were procured from Sigma-Aldrich.
CuCl (98%) was purified by stirring overnight in acetic acid. Chloroform, tetrahydrofuran (THF), dichloromethane (DCM), N-dimethylformamide (DMF), diethyl ether, petroleum ether, and methanol were purchased from Merck.
2.2 Instrumentation
Proton nuclear magnetic resonance (1H-NMR) mea- surements were recorded using a Bruker 400 MHz NMR spectrometer with chloroform-d as the solvent.
Fourier-transform infrared (FTIR) spectra were col- lected using the IR Prestige 21 model FTIR and Shi- madzu FTIR Spectrometer 100. The FTIR spectra were measured as KBr samples of the graft copoly- mers. The EcoSEC HLC-8320 SEC system fitted with a UV (254 nm) and refractive index (RI) detector was used to carry out molecular sieve (size-exclusion) chromatography (SEC) measurements. Calibration was performed by Polymer Laboratories using poly (styrene) standards (1260 Da, 4920 Da, 9920 Da, 30.300 Da, 60.450 Da, 170.800 Da, and 299.400 Da).
Tetrahydrofuran (THF) was used at at 40 °C and a flow rate of 0.6 mL/min as an eluent. For the thermal analysis of the sample, the Shimadzu (DSC 60 series) differential scanning calorimetry (DSC) system was used under nitrogen. The polymer sample was first dried in a 40 °C vacuum oven for 24 h, and then, 10 mg of the sample was sealed in an aluminum DSC
pan and heated under N2 atmosphere from 20 to 600 °C at a rate of 10 °C / min. A Shimadzu-DTG 60H thermo-gravimetric analyzer was used to prevent thermal decomposition of the sample. For thermal gravimetric analysis (TGA), 10 mg of the sample was sealed in an aluminum TGA pan and heated under N2 atmosphere from a temperature of 20 to 1200 °C at a rate of 10 °C / min.
2.3 Autoxidation of linoleic acid (PLina)
Autoxidation of the linoleic acid was performed according to the procedure reported in the litera- ture.13,16,18For this, 30 g of linoleic acid was spread in a Petri dish (U = 10 cm at an oil layer thickness of
*1.5 mm). The oil was subsequently exposed to daylight for 90 days at room temperature under atmospheric conditions. During this time, the linolei- c acid was oxidized by uptaking oxygen from the air, thus forming polymeric linoleic acid (PLina).
2.4 Hydroxylation of polymeric linoleic acid (PLina-OH)
Hydroxylation of the PLina was carried out by using diethanolamine.20 The peroxide, epoxide, and hydroperoxide groups of the PLina were converted to hydroxyl groups. Similarly, 10.0 g of PLina and 10.0 mL of diethanolamine were maintained in a round middle-neck flask (250 mL) for one day in a silicone oil bath at 90 °C. The crude product was dissolved in 20 mL of acetone. This solution was then precipitated in 200 mL of petroleum ether. The hydroxylated polymeric linoleic acid (PLina-OH) was dried under vacuum for a day at room temperature.
2.5 Bromination of polymeric linoleic acid (PLina-Br)
The PLina-OH (4.50 g, 0.007 mmol), dichloromethane (50 mL), and TEA (0.77 mL, 5.30 mmol) were charged into a 50-mL flask equipped with a magnetic stirring bar and the resulting solution was cooled to -10 °C using a salt-ice bath. A solution of 2-bromo- propionyl bromide (1.13 g, 5.25 mmol) in 30 mL dichloromethane was then added dropwise, and the resulting homogeneous solution was stirred for 24 h at room temperature. Next, the solvent was separated by a rotary evaporator and the bromo-functionalized polymeric linoleic acid (PLina-Br) was formed as a precipitate in cold diethyl ether. The substance was
dissolved in 95% ethanol and placed in a refrigerator for full precipitation of the hydrochloride triethyl amine crystals overnight. Finally, the PLina-Br was filtered to remove the triethylamine hydrochloride crystals, washed with cold diethyl ether, and dried under vacuum for 24 h.
2.6 Azidation of polymeric linoleic acid (PLina- N3)
In a round-bottom flask, 0.50 g of the previously obtained PLina-Br (1.02 mmol) was dissolved in 20 mL of DMF and 0.18 g of NaN3(2.80 mmol) was then added to the solution. The mixture was homog- enized under a nitrogen atmosphere and vigorous stirring for 24 h at 90 °C. After this mixture was cooled to room temperature, it was transferred into water (200 mL) and extracted using diethyl ether (29 75 mL). The organic phases were collected and dried with MgS04. The solvent was then removed via a rotary evaporator and the final product (PLina-N3) was dried under vacuum for 24 h.
2.7 Synthesis of PCLs with alkynes
The synthesis procedure of the alkyne end-func- tionalized PCL was carried out according to previ- ous works in the literature.45,46 Alkyne end- functionalized PCLs were prepared of e-CL (10.0 mL, 90 mmol)viaROP in bulk using stannous 2-ethyl hexanoate (0.022 mmol) as the catalyst and propiolic acid (0.27 mL, 4.42 mmol), 3-butyn-1-ol (0.33 mL, 4.42 mmol), 5-hexynoic acid (0.49 mL, 4.46 mmol), and propargyl alcohol (0.26 mL, 4.64 mmol) as the initiators. In the order described above, the monomer, catalyst, and initiators were added to a previously flamed Schlenk tube fitted with a magnetic stirring bar. After argon gas was passed through the tube for 2 min, it was placed in an oil bath at 110 °C for 24 h. Following the poly- merization, the mixture was diluted with THF and precipitated into an excess amount of methanol. It was then filtered and dried under vacuum overnight at room temperature. The percent yields of Alk- PCL-1, Alk-PCL-2, Alk-PCL-3, and Alk-PCL-4 were 95%, 95%, 95%, and 93%, respectively.
2.8 Click polymerization procedure
The click reactions between PLina-N3 (500 mg, 0.641 mmol) and propargyl-PCL-1 (2410 mg,
0.322 mmol) were carried out in a 25 mL-flask with 4 mL DMF as the solvent and CuCl/PMDETA (63.4 mg, 0.641 mmol/0.134 mL, 0.641 mmol) as the catalyst.35 After the polymerization mixture was purified for 3 min with argon, it was subjected to vigorous mixing at 40 °C for one day. The product obtained was diluted with THF, purified by passing it through a neutral alumina column to remove the copper complex, and precipitated in cold petroleum ether. It was then dried under reduced vacuum for 24 h (molar ratio of [PLina-N3]:[Alk-PCL-1]:[CuCl]:[PM- DETA] = [1]:[0.50]:[1]:[1]).
3. Results and Discussion
3.1 Macroperoxy initiator from linoleic acid (PLina)
It has been known for a century that after exposure to air under sunlight at ambient temperature, polyunsat- urated oil/oil acids will polymerize through the oxygen in the air, resulting in polymeric oil/oil acid perox- ides.47–49 In this work, polymeric linoleic acid per- oxide (PLina) was obtained through autoxidation of linoleic acid as previously reported.50,51 The PLina was autoxidized for 90 days and a molar mass of 1060 Da (PDI = 2.27) was obtained in quantitative yields.
The peroxygen content of the soluble part of the PLina was found to be 1.10 wt%. The 1H NMR and FTIR analyses characterized the structure of the PLina. In the 1H NMR spectrum, PLina was indicated in the characteristic peaks of the relevant groups (Figure 2a) as (d, ppm): 5.30–5.27 ppm (the olefinic protons –CH=CH– of the oil acid macro peroxides) and 2.29–2.26 ppm (–CH2–COOH of the oil acid macro peroxide). The FTIR spectrum (Figure 3a) revealed additional bands of PLina at 3400 cm-1(hydroperoxide groups) and at 1705 cm-1 (carboxyl groups).
3.2 Hydroxylated polymeric linoleic acid (PLina- OH)
Keles¸ and Hazer (2009) transformed oxidized soya polymer to hydroxylated soya polymer by using an iron (III) catalyst that was swellable in water. How- ever, this soybean oil polymer was not water-soluble.
In another study, cold-water-soluble soybean oil polymers were synthesized using diethanolamine.20In this study, hydroxylated and water-soluble polymeric linoleic acid was obtained and subsequently, epoxide, peroxide and hydroperoxide groups of autoxidized PLina polymer were simply converted to hydroxyl
groups by using diethanolamine. The result of the hydroxylation reaction is represented in Table 1.
Scheme1shows the representative chemical structure of linoleic acid and the reactions of autoxidation, hydroxylation, bromination, and azidation of poly- meric linoleic acid. Results of the elemental analysis of the PLina-OH also confirmed that diethanolamine had been introduced into the polymeric linoleic acid.
Table1 presents the percentage of C, H, N, and O in the PLina-OH.
Figure1shows the SEC analysis of the water-soluble polymer sample of PLina-OH. The number-average molecular weight (Mn) of the PLina decreased from 1060 to 810 Da after hydroxylation (as PLina-OH). A previously published study also reported similar behavior and concluded that the hydroxylation reaction had caused partial degradation of the oxidized soybean oil polymer.20The hydroxylation reaction of the poly- meric linoleic acid showed results consistent with the literature and corroborated by the unimodal SEC profile that supports a smooth, single-mode SEC curve, resulting in lower molecular weight. Results of the elemental analysis of the PLina-OH also confirmed that the diethanolamine had been incorporated into the polymeric linoleic acid. Spectrometric characterization carried out by 1H NMR and FTIR was also used to evaluate the chemical structure of the PLina-OH. In the1H-NMR spectrum of the PLina-OH obtained using diethanolamine (Figure 2b), new bands.52–54 appeared at 3.80 ppm (–N–CH2–CH2–OH), 4.34 ppm (–C–O–, –C–OH induced), and 2.96 ppm (–N–CH2–CH2–OH) which again confirmed the amidation reactions that had occurred during the hydroxylation reactions induced by the diethanolamine. The FTIR spectrum (Figure3b) of the diethanolamine-induced PLina-OH contained new bands at 3300 cm-1 (diethanol amine contains alcohol groups), at 1557 cm-1(amide carbonyl group), and at 1053 cm-1 (C–O bands), while the carboxylic acid ester carbonyl band at 1705 cm-1and the original C–O bands at 1177 cm-1had disappeared.
3.3 Brominated polymeric linoleic acid (PLina- Br)
The use of 2-bromopropionyl bromide has been reported in the modification of many products con- taining hydroxyl groups such as monomer and mac- romonomer microbeads, formaldehyde resin, agarose palmitate, and polysaccharides.55–60 Therefore, 2-bromopropionyl bromide was used for brominating the PLina in this study. The preparation of bromo- functionalized polymeric linoleic acid (PLina-Br) was
carried out by esterification of the hydroxyl function of the PLina with 2-bromopropionyl bromide in the presence of Et3N to give this unit a bromide function (Scheme 1). In Figure 1, the SEC analysis of the PLina-Br shows a modest change of the average molecular weights with a measured Mn of 920 Da (Table 1).
Spectrometric characterization performed by 1H NMR and FTIR was also used to evaluate the chem- ical structure of the PLina-Br. The1H NMR spectrum of the PLina-Br showed the resonance signals of protons at 4.35–4.40 ppm (–CH–Br ) and 1.40–1.45 ppm CO–CH(CH3)–Br (Figure 2c). The FTIR
spectrum of the 2-bromopropionyl bromide-induced PLina-Br contains new bands at 1620 cm-1 (ester carbonyl group, Figure3c).
3.4 Azidation of polymeric linoleic acid (PLina- N3)
The PLina-Br was used as the precursor material for the click modification by converting it to an azide- functional via nucleophilic substitution. The bromine was transformed into azide groups through the nucle- ophilic substitution reaction with NaN3 in DMF Table 1. The results of PLina, PLina-OH, PLina-Br and PLina-N3 molecular weights and
elemental analysis.
Code Conversion (wt%)
Mn,SECMw,SEC
Mw/Mn
Elm. Analysis, (wt%)
(kDa) (kDa) C H N O
PLina 99 1.06 2.41 2.27 37.12 7.04 – 55.84
PLina-OH 80 0.81 0.89 1.10 55.20 9.70 6.10 29.00
PLina-Br 88 0.92 1.22 1.33 47.30 8.00 5.20 39.50
PLina-N3 97 0.78 1.32 1.70 53.20 8.10 10.80 27.90
Scheme 1. Representative chemical structure of PLina-N3.
(Scheme 1). Figure 1 shows the SEC analysis of the azide-functionalized PLina macroinitiator (PLina-N3).
The SEC analysis showed a modest change in the average molecular weights with a measured Mn of 780 Da (Table1). The structure of the new PLina-N3was confirmed by elemental analysis as well as via spec- troscopic investigations. Elemental analysis showed that the PLina-OH was found to be 6.10% nitrogen.
This ratio was determined as 10.80% for the PLina-N3. The elemental analysis determined that the increase in the amount of nitrogen in the structure was related to the azide content (Table1). The1H NMR spectrum of the PLina-N3showed the resonance signals of protons as –CH2–CO–N–CH2–CH2–CO–CH(CH3) –N3, at 1.99-1.97 ppm (–CH2–CO–N–), at 3.20-3.15 ppm (–CO–N–CH2-CH2–), 4.32 ppm (–CH2–CO–N–CH2– CH2–CO–CH–), at 2.31–2.25 ppm (–N–CH2–CH2– CO–CH(CH3)–N3 and 1.43–1.41 ppm (–N–CH2– CH2–CO–CH(CH3) –N3(Figure2b). Further evidence for the formation of PLina-N3 could be seen in the
FTIR spectrum in Figure 3d. The characteristic absorption bands of the ester carbonyl group, amide carbonyl group, and azide groups were observed at 1732, 1585, and 2104 cm-1, respectively.
3.5 Characterization of PCLs with alkynes
Alkyne-functionalized PCLs (Alk-PCLs) were pre- pared in bulk by ROP of e-CL using Sn(Oct)2 as the catalyst and propargyl alcohol, propiolic acid, 3-bu- tyn-1-ol, and 5-hexynoic acid as initiators. Molar ratios of 20/1 and 200/1 were used for [e-CL] / [propargyl alcohol, propiolic acid, 3-butyn-1-ol, 5-hexynoic] and [propargyl alcohol, propiolic acid, 3-butyn-1-ol, 5-hexynoic]/[Sn(Oct)2], respectively. By selecting these initiator systems, the PCLs function- alized with alkyne end groups were obtained, as shown in Scheme 2. The experimental conditions and results are summarized in Table2.
The successful formation of Alk-PCL-3 was also confirmed by FTIR analysis. In the FTIR spectrum, the characteristic alkyne stretching band (–C:C–) at 2106 cm-1 and the typical bands of PCL such as C=O stretching at 1720 cm-1, asymmetric C–O–C stretching at 1240 cm-1, and C–C stretching at 1044 cm-1 could be seen (Figure 4a). The 1H NMR spectrum of Alk- PCL-1 showed the resonance signals of protons for CH2-C CH at 4.66 ppm (b in Figure 5a) and at 2.47 ppm (ain Figure5a), and for the repeating PCL units’
protons at 2.35–2.27, 1.67–1.57, 1.40–1.38, and 4.00 ppm, and the –OH end group of PCL protons at 3.65 ppm, which indicated the completion of ROP.
3.6 Characterization of PLina-g-PCL graft copolymers
PLina-g-PCL graft copolymers were obtained at 40°C for 24 hviathe click reaction of alk-PCLs and PLina- N3 (Table 3). The reaction path for the graft copoly- mer is included in Scheme 3. The SEC measured the average molecular weights and molecular weight dis- tributions of the PLina-g-PCL graft polymers, and the related data are summarized in Table3. The polymers showed symmetrical and unimodal elution peaks and significantly narrow polydispersities (PDIs) within the 1.11–1.25 range.
The FTIR spectrum of the PLina-g-PCL graft copolymer (PLinaPCL-3 in Table 3) as shown in Figure 4c displays characteristic signals belonging to the PLina and PCL units. Moreover, the absence of azide (2104 cm-1) and propargyl (2106 cm-1) bands in Figure 1. SEC profiles of PLina and functionalized PLina
[PLina series in (Table1)].
Figure 2. 1H NMR spectra of (a) PLina; (b) PLina-OH, (c) PLina-Br; (d) PLina-N3.
the spectrum and the presence of the aromatic triazole -N=N- (1626 cm-1) bands may be due to the click reaction between the homopolymers.
The 1H-NMR spectrum of the PLina-g-PCL graft copolymer (PLinaPCL-1) shown in Figure5b supports this idea. The 1H-NMR spectrum of PLina-g-PCL
graft copolymer (PLinaPCL-1 in Table 3) displayed peaks at 8.3 ppm for the aromatic triazole -CH, 0.9 ppm for –CH3 of the PLina unit, and protons of the PCL repeating unit at 2.35–2.27, 1.67–1.57, 1.40–1.38, and 4.00 ppm for aliphatic –CH2 (Fig- ure5b). In the chemical structures in question, all the Figure 3. FTIR spectra of PLina (a), PLina-OH (b), PLina-Br (c) and PLina-N3(d).
signals in the spectrum were aligned with the mag- netic-related protons. Signals at about 8.3 ppm in the spectrum are unquestionable evidence of the aromatic triazole proton.60–62 Figure6 shows the SEC analysis of the PLina-g-PCL graft copolymers in comparison with those of the corresponding PLina-N3 and Alk- PCLs precursors.
Differential scanning calorimetry (DSC) and ther- mal gravimetric analysis (TGA) were used for the thermal analysis of PLina-N3, Alkyne-functionalized PCLs and graft copolymers (Table 4). Reported as a representative for investigating the thermal properties of samples synthesized by the click reaction of alkyne-
functionalized PCLs with PLina-N3. As seen in the DSC curve of PLina-N3 the melting temperature was observed at 28°C for the PLina-N3sample. Also, it is a well-known phenomenon that melting temperatures o of polymeric linoleic acid are observed.15,16 The ROP of e-CL by using propargyl alcohol, propiolic acid, 3-butyn-1-ol, and 5-hexynoic acid as initiators the achieved Alk-PCL-1 Alk-PCL-2, Alk-PCL-3, and Alk-PCL-4 had the melting temperature at 63, 62, 54 and 60 °C, respectively. The melting temperature is related to an endothermic phase transition of a crys- talline structure. The melting point of polymers is affected by their crystallinity.63 In polymers, the Scheme 2. Reaction pathways in the syntheses of alkyne-functionalized poly (e-caprolactone).
Table 2. Synthesis of alkyne-functionalized poly(e-caprolactone) by ring-opening polymerization at 110°C for 24 h.
Code e-CL (g)
Propargyl alcohol, (g)
Propiolic acid, (g)
3-Butyn-1-ol (g)
5-Hexynoic acid, (g)
Conv.
(wt%)
Mn,SEC
(kDa) Mw/Mn
Alk-PCL-1 10.00 0.24 – – – 95 7.54 1.32
Alk-PCL-2 10.10 – 0.31 – – 95 17.90 1.38
Alk-PCL-3 10.03 – – 0.31 – 95 4.56 1.13
Alk-PCL-4 10.05 – – – 0.49 93 12.64 1.16
[e-CL] / [Propargyl alcohol, Propiolic acid; 3-Butyn-1-ol;5-Hexynoic acid] = [20] / [1]
[Sn(Oct)2] / [Propargyl alcohol; Propiolic acid; 3-Butyn-1-ol;5-Hexynoic acid] = [1] / [200]
interactions between the chains, entanglements and the different lengths of the chains are the factors affecting their melting temperature. The difference between the melting temperatures of PCLs of different molecular weights may be due to crystallinity and crystal size.
The click reaction of PLina-N3 by using Alkyne- functionalized PCLs, the achieved PLinaPCL-1, PLinaPCL-2, PLinaPCL-3, and PLinaPCL-4 graft
copolymers had the melting temperature at 58, 58, 51 and 57 °C, respectively. The reason for low values in melting temperatures compared with that of Alk-PCL is the plasticizing effect of the PLina backbone caused to increased polymer chain mobility.15,16
Figure 7 shows the DSC thermogram of PLina-N3, Alk-PCL-2, PLinaPCL-2. The DSC thermogram of Figure 4. FTIR spectra of Alk-PCL-3 (a), PLina-N3(b), and PLina-g-PCL-3 (c) graft copolymer.
PLinaPCL-2 showed three peaks at 58°C, 215°C, and 345°C, respectively. The peak is seen at around 58°C which is attributed to a phase change (melting of the PCL crystalline phase); the second peak is exothermic, which is seen at 217.8 °C and is attributed to a chemical reaction (decomposition of PLina). The third
peak is exothermic, which is seen at 345 °C and related to the degradation of PCL.
Figure 8 shows the TGA traces of the PLina-N3, Alk-PCL-2, PLinaPCL-2 samples. In TGA curves, the graft copolymers have three decomposition steps:
decomposition at 177–182 °C may come from the Figure 5. 1H NMR spectra of (a) alkyne-PCL-1; (b) PLina-g-PCL graft copolymer (PLinaPCL-1).
peroxide decomposition of the undecomposed peroxide groups of polymeric oil peroxides.
329–408 °C belongs to the decomposition of the PCL blocks and Td around 400 °C belongs to the
PCL and polymeric oil acid blocks. The decompo- sition temperatures (Tds) of the graft copolymers were observed to be similar to those of the PLina and PCL.
Table 3. Results and conditions of PLina-g-PCL graft copolymers by click reaction.
Code
PLina-N3 (g)
Alk-PCL (g)
PLina* (wt %)
PCL* (wt %)
Conversion (wt%)
Mn,SEC
(kDa) Mw/Mn
PLinaPCL-1 0.51 2.43 (a in Table2) 3.88 96.12 84 11.83 1.25
PLinaPCL-2 0.50 2.31 (b in Table2) 2.95 97.05 83 24.44 1.20
PLinaPCL-3 0.51 1.47 (c in Table2) 5.70 94.30 85 7.31 1.15
PLinaPCL-4 0.50 1.63 (d in Table2) 2.52 97.48 82 15.57 1.11
*calculated from1H NMR. [PLina-N3]:[Alk-PCLs]:[CuCl]:[PMDETA] = [1]:[0.5]:[1]:[1]
Scheme 3. Reaction design of PLina-g-PCL graft copolymer viaclick reaction.
Figure 6. SEC profiles of PLina-N3, Alk-PCLs polymers [Alk-PCL series in (Table 2)] and PLina-g-PCL graft copolymers [PLinaPCL series in (Table 3)].
Table 4. DSC and TGA data of PLina-N3, Alk-PCLs and PLina-g-PCL graft copolymers.
Code
DSC (0C) TGA (0C)
Tm Td1 Td2 Td3 Td1 Td2 Td3
PLina-N3 28 122 260 480 161 329 478
Alk-PCL-1 63 364 – – – 366 416
Alk-PCL-2 62 362 – – – 354 420
Alk-PCL-3 54 328 – – – 408 482
Alk-PCL-4 60 343 380 405 – 353 427
PLinaPCL-1 58 140 367 415 180 335 424
PLinaPCL-2 58 159 230 365 182 343 425
PLinaPCL-3 51 95 218 335 177 350 420
PLinaPCL-4 57 160 295 366 178 332 422
4. Conclusions
The click chemistry synthesis of PLina-g-PCL graft copolymers was carried out between azide-function- alized PLina (PLina-N3) and alkyne-functionalized
PCLs. The PLina-g-PCL graft copolymers were gen- erated in great yields and at high molecular weights.
This method for the synthesis of the graft copolymer is efficient and straightforward. Characterization of the polymers was accomplished and the synthesis of the graft copolymer confirmed using a variety of instru- ments. This approach is particularly advantageous in preparing PLina with functional groups. Thus, PLina- N3can be used as a starting material and coupled with click chemistry to synthesize many new materials.
Considering the biocompatibility of PLina and the biodegradability of PCL, these findings may be used to expand the application of PLina-g-PCL graft copoly- mers in the biomedical field.
Acknowledgements
This study was funded by the Du¨zce University Research Fund (Grant Number: 2016.07.06.487, 2019.07.06.1021).
References
1. Meier M A R, Metzger J O and Schubert U S 2007 Plant oil renewable resources as green malternatives in polymer science Chem. Soc. Rev.361788
2. Gandini A 2008 Polymers from renewable resources: A challenge for the future of macromolecular materials Macromolecules419491
3. Lligadas G, Ronda J C, Galia´ M and Ca´diz V 2010 Plant oils as platform chemicals for polyurethane synthesis:
current state-of-the-artBiomacromolecules112825 4. Biermann U, Bornscheuer U, Meier M A R, Metzger J
O and Scha¨fer H J 2011 Oils and fats as renewable raw materials in chemistryAngew. Chemie. Int. Ed.503854 5. Gandomkar S, Dennig A, Dordic A, Hammerer L, Pickl M, Haas T, et al. 2018 Biocatalytic oxidative cascade for the conversion of fatty acids into a-ketoacids via internal H2O2recyclingAngew. Chemie. Int. Ed.57427 6. Metzger J O 2009 Fats and oils as renewable feedstock
for chemistryEur. J. Lipid. Sci. Technol.111 865 7. Fraile J M, Garcı´a J I, Herrerı´as C I and Pires E 2017
Synthetic transformations for the valorization of fatty acid derivativesSynth.491444
8. Keles¸ E and Hazer B 2009 Synthesis of segmented polyurethane based on polymeric soybean oil polyol and poly (ethylene glycol)J. Polym. Environ.17153 9. Xia Y and Larock R C 2010 Vegetable oil-based
polymeric materials:Synthesis, properties, and applica- tionsGreen Chem. 121893
10. Tremblay-Parrado K K and Ave´rous L 2020 Renewable responsive systems based on original click and poly- urethane cross-linked architectures with advanced prop- erties ChemSusChem.13238
11. Chen B, Han A, McClements D J and Decker E A 2010 Physical structures in soybean oil and their impact on lipid oxidation J. Agric. Food Chem.58211993 12. McClements D J and Decker E A 2000 Lipid oxidation
in oil-in-water emulsions: Impact of molecular Figure 7. DSC traces of (a) PLina-N3; (b) Alk-PCL-2;
(c) PLinaPCL-2.
Figure 8. TGA traces of PLina-N3, Alk-PCL-2, PLi- naPCL-2.
environment on chemical reactions in heterogeneous food systemsJ. Food Sci. 651270
13. Alli A and Hazer B 2011 Synthesis and characterization of poly(N-isopropyl acrylamide)-g-poly(Linoleic acid)/
poly(linolenic acid) graft copolymersJ. Am. Oil Chem.
Soc.88255
14. Hazer B and Eren M 2019 Ecofriendly autoxidation of castor oil/ricinoleic acid multifunctional macroperoxide initiators for multi block/graft copolymers J. Am. Oil Chem. Soc.96421
15. AllıA, ArıY and Go¨kc¸en M 2016 Novel poly(linolenic acid) graft copolymers: synthesis, characterization and electrical propertiesJ. Am. Oil Chem. Soc.93895 16. Alli A, Alli S, Becer C R and Hazer B 2014 One-pot
synthesis of poly(linoleic acid)-g poly(styrene)-g-poly (e- caprolactone) graft copolymersJ. Am. Oil Chem. Soc.
91849
17. Alli S, Tigli Aydin R S, Alli A and Hazer B 2015 Biodegradable poly(e-caprolactone) based graft copoly- mers via poly(linoleic acid): In vitro enzymatic evalu- ationJ. Am. Oil Chem. Soc.92449
18. Alli A, Alli S, Becer C R and Hazer B 2016 Nitroxide- mediated copolymerization of styrene and pentafluo- rostyrene initiated by polymeric linoleic acid Eur.
J. Lipid. Sci. Technol.118279
19. Demir A, Alli S, AllıA and Ko¨semen A 2019 Organic field effect transistor with a novel poly(linoleic acid)- g-poly(methyl methacrylate)-g-poly(D, L-lactide) graft copolymer insulator using a PEDOT:PSS com- posite electrode J. Mater. Sci. Mater. Electron. 30 11034
20. Acar M, C¸ oban S and Hazer B 2013 Novel water soluble Soya oil polymer from oxidized Soya oil polymer and diethanol amineJ. Macromol. Sci. Part A Pure Appl. Chem.
50287
21. Biswas A, Sharma B K, Willett J L, Advaryu A, Erhan S Z and Cheng H N 2008 Azide derivatives of soybean oil and fatty estersJ. Agric. Food Chem.565611
22. Kolb H C, Finn M G and Sharpless K B 2001 Click chemistry: diverse chemical function from a few good reactionsAngew. Chemie. Int. Ed.402004
23. Moses J E and Moorhouse A D 2007 The growing applications of click chemistry Chem. Soc. Rev. 36 1249
24. He M, Jiang S, Xu R, Yang J, Zeng Z and Chen G 2014 Facile functionalization of soybean oil by thiol-ene photo-click reaction for the synthesis of polyfunctional acrylateProg. Org. Coat. 77868
25. Chen J, Xiang J, Cai Z, Yong H, Wang H, Zhang L, et al. 2010 Synthesis of hydrophobic polymer brushes on silica nanoparticles via the combination of surface- initiated ATRP, ROP and click chemistryJ. Macromol.
Sci. Part A Pure Appl. Chem.47655
26. Xu J, Ye J and Liu S 2007 Synthesis of well-defined cyclic poly(N-isopropylacrylamide) via click chemistry and its unique thermal phase transition behavior Macromolecules409103
27. Wang Y, Chen H, Xu Y, Sun J, Bai L, Qu R, Wang D and Yu L 2015 Synthesis of Polyvinyltetrazole Resin by Combination of RAFT Polymerization and Click Chemistry for Adsorption of Hg(II)J. Macromol. Sci.
Part A Pure Appl. Chem.52707
28. Tunca U 2013 Triple click reaction strategy for macromolecular diversity Macromol. Rapid. Commun.
3438
29. Altintas O and Tunca U 2011 Synthesis of terpolymers by click reactions Chem. Asian J.62584
30. Kempe K, Krieg A, Becer C R and Schubert U S 2012
‘‘Clicking’’ on/with polymers: A rapidly expanding field for the straightforward preparation of novel macro- molecular architecturesChem. Soc. Rev. 41176 31. Slavin S, Burns J, Haddleton D M and Becer C R 2011
Synthesis of glycopolymers via click reactions Eur.
Polym. J.47435
32. Becer C R, Kokado K, Weber C, Can A, Chujo Y and Schubert U S 2010 Metal-free synthesis of responsive polymers: Cloud point tuning by controlled ‘‘click’’
reaction J. Polym. Sci. Part A Polym. Chem.481278 33. Acik G 2020 Bio-based poly(e-caprolactone) from
soybean-oil derived polyol via ring-opening polymer- ization.J. Polym. Environ.28668
34. Binder W H and Sachsenhofer R 2007 ‘‘Click’’
chemistry in polymer and materials scienceMacromol.
Rapid Commun.2815
35. Gao H and Matyjaszewski K 2006 Synthesis of star polymers by a combination of ATRP and the ‘‘click’’
coupling method Macromolecules394960
36. Altinkok C, Karabulut H R F, Tasdelen M A, Acik G 2020 Bile acid bearing poly (vinyl chloride) nanofibers by combination of CuAAC click chemistry and elec- trospinning processMater. Today Commun. 25101425 37. Wang C W, Liu C, Zhu X W, Yang Z Y and Sun H F 2016 Synthesis of well-defined star shaped poly(e- caprolactone)/poly(ethylbene glycol) amphiphilic conetworks by combination of ring opening polymer- ization and ‘‘click’’ chemistry J. Polym. Sci. Part A Polym. Chem.54407
38. Hong J, Luo Q and Shah B K 2010 Catalyst- and solvent-free ‘‘click’’ chemistry: A facile approach to obtain cross-linked biopolymers from soybean oil Biomacromolecules112960
39. Arseneault M, Wafer C and Morin J F 2015 Recent advances in click chemistry applied to dendrimer synthesisMolecules209263
40. Go¨ktas M, O¨ ztu¨rk T, Atalar M N, Tekes A T and Hazer B 2014 One-step synthesis of triblock copolymers via simultaneous reversible-addition fragmentation chain transfer (RAFT) and ring-opening polymerization using a novel difunctional macro-RAFT agent based on polyethylene glycol J. Macromol. Sci. Part A Pure Appl. Chem.51854
41. Coulembier O, Dege´e P, Hedrick JL and Dubois P 2006 From controlled ring-opening polymerization to biodegradable aliphatic polyester: Especially poly(b- malic acid) derivatives Prog. Polym. Sci.31723 42. Uyar Z, Genli N, Cay B, Arslan U, Durgun M and
Degirmenci M 2019 Synthesis and characterization of an A2B2-type miktoarm star copolymer based on poly(e- caprolactone) and poly(cyclohexene oxide)Polym. Bull.
76553
43. Degirmenci M, Sarac M A and Genli N 2014 Synthesis and characterization of mid-chain macrophotoinitiator of poly(e-caprolactone) by combination of ROP and click chemistryPolym. Bull.711743
44. Deanin R D 1992 New useful polymers by ring-opening polymerizationPolym. Plast. Technol. Eng.31229 45. Amici J, Kahveci M U, Allia P, Tiberto P and Yagci Y
2012 Sangermano M. Polymer grafting onto magnetite nanoparticles by ‘‘click’’ reactionJ. Mater. Sci.47412 46. Tasdelen M A 2011 Poly(epsilon-caprolactone) / clay nanocomposites via ‘‘click’’ chemistryEur. Polym. J. 47 937
47. Powers P O 1949 Mechanism of the oxidation of drying oilsInd. Eng. Chem. 41304
48. Cowan J C 1949 lsomerization reactions of drying oils Ind. Eng. Chem.41294
49. Taylor W L 1950 Blowing drying oilsJ. Am. Oil Chem.
Soc.27472
50. Hazer B, Hazer D B and Coban B 2010 Synthesis of microbial elastomers based on soybean oil Autoxidation kinetics, thermal and mechanical properties J. Polym.
Res.17567
51. Cakmakli B, Hazer B, Tekin I O, Kizgut S, Koksal M and Menceloglu Y 2004 Synthesis and characterization of polymeric linseed oil grafted methyl methacrylate or styreneMacromol. Biosci.4 649
52. Andrade D F, Mazzei J L, Kaiser C R and D’Avila L A 2012 Assessment of different measurement methods using 1H-NMR data for the analysis of the transester- ification of vegetable oilsJ. Am. Oil Chem. Soc.89619 53. Kuo P L, Hou S S, Teng C K and Liang W J 2001 Function and performance of silicone copolymer (VI) Synthesis and novel solution behavior of water-soluble polysiloxanes with different hydrophilesColloid. Polym. Sci.279286 54. KenJie L M S F and Lam C C 1995 1H-Nuclear magnetic
resonance spectroscopic studies of saturated, acetylenic and ethylenic triacylglycerolsChem. Phys. Lipid.77155 55. Berthier D L, Herrmann A and Ouali L 2011 Synthesis of hydroxypropyl cellulose derivatives modified with amphiphilic diblock copolymer side-chains for the slow release of volatile moleculesPolym. Chem.222093 56. Das D, Mukherjee S, Pal A, Das R, Sahu S G and Pal S
2016 Synthesis and characterization of biodegradable
copolymer derived from dextrin and poly(vinyl acetate) via atom transfer radical polymerization RSC Adv. 6 9352
57. Seidi F and Zarei A 2016 ATRP grafting of poly(N, N-dimethylamino-2-ethyl methacrylate) onto the fatty- acid-modified agarose backbone via the ‘‘grafting- from’’ techniqueStarch/Staerke 68644
58. Zhai S, Shang J, Yang D, Wang S, Hu J, Lu G and Huang X 2012 Successive SET-LRP and ATRP synthesis of ferrocene-based PPEGMEA-g-PAEFC well-defined amphiphilic graft copolymer J. Polym.
Sci. Part A Polym. Chem.50811
59. Cakmak S, Cakmak A S and Gu¨mu¨s¸dereliogˇlu M 2013 PNIPAAm-grafted thermoresponsive microcarriers:
Surface-initiated ATRP synthesis and characterization Mater. Sci. Eng. C 333033
60. Carvalho L T, Moraes R M, Alves G M, Lacerda T M, Santos J C, Santos A M and Medeiros S F 2020 Synthesis of amphiphilic pullulan-graft-poly(e-capro- lactone) via click chemistryInt. J. Biol. Macromol.145 61. Catıker E, Meyvacı701 E, Atakay M, Salih B and O¨ ztu¨rk T 2019 Synthesis and characterization of amphiphilic triblock copolymers including b-alanine/a-methyl-b- alanine and ethylene glycol by ‘‘click’’ chemistry Polym. Bull.762113
62. Mansour Lakouraj M, Hasantabar V and Bagheri N 2013 Synthesis of polyethers containing triazole units in the backbone by click chemistry in a tricomponent reaction J. Polym.20131
63. Rukmanikrishnan B and Muthusamy S 2018 Prepa- ration and properties of polyimides containing 1,2,3 triazole moieties Adv. Polym. Technol. 37 50 64. Babaie A, Rezaei M and Sofia R L M 2019 Investiga-
tion of the effects of polycaprolactone molecular weight and graphene content on crystallinity, mechanical properties and shape memory behavior of polyuretha- ne/graphene nanocomposites J. Mech. Behav. Biomed.
Mater. 9653
