Materials Letters 102–103 (2013) 68–71

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Materials Letters

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n CorrE-m

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Synthesis and characterization of a novel bornadiene/carbon monoxidepolyketone based on a renewable α-pinene derivative

Xiao-Qin Yang a,b, Hui Pan b, Li-Juan Du a, Tao Zeng a,n

a Jiangsu Key Lab of Biomass-based Green Fuels and Chemicals, Department of Chemical Engineering, Nanjing Forestry University, Nanjing 210037, PR Chinab Calhoun Research Station, Louisiana State University Agricultural Center, Calhoun, LA 71225, USA

a r t i c l e i n f o

Article history:Received 26 September 2012Accepted 25 March 2013Available online 1 April 2013

Keywords:α-PineneBornadieneCarbon monoxidePolyketoneRenewable

7X/$ - see front matter & 2013 Elsevier B.V. Ax.doi.org/10.1016/j.matlet.2013.03.113

esponding author. Tel.: +86 13951634620.ail address: zengtao@njfu.com.cn (T. Zeng).

a b s t r a c t

Bornadiene (BD), synthesized from renewable α-pinene, was copolymerized with carbon monoxide (CO)to produce a novel polyketone with carbonyl groups and strained ring structures. The bornadiene/carbonmonoxide (BD/CO) polyketone is a white solid with molecular weight (Mw) of 19,400 g mol−1 and showsgood solubility in less polar organic solvents. FT-IR, 1H NMR, 13C NMR, and elemental analysis confirmedthat the BD/CO polyketone contained carbonyl groups and strained ring structures. The thermal analysesshowed that the resulting polyketone has excellent thermal stability.

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1. Introduction

Polyketones, which are synthesized from the copolymerizationof olefins with carbon monoxide (CO), are a class of new polymerswith outstanding chemical and physical properties including highheat and corrosion resistance, excellent mechanical properties,high machinability, the ability to undergo photodegradation andbiodegradation, and ease of functionalization [1]. Currently, theindustrial applications of polyketones include fibers, film coatings,adhesives, membranes, photoresistance, and packaging materials.The continuous discovery of new structures suggests that newpotential applications, especially in optoelectronic and electronicdevices, will emerge [2].

Properties of the polyketone can be finely tailored via theselection of appropriate olefin monomers and catalysts [3–5].Strained olefins, in particular, are attractive substrates for thecopolymerization reaction with CO, due to the unique structuresand chemical properties of the resulting copolymers and co-oligomers [6]. 2,5-Norbornadiene, norbornene, and their deriva-tives have been extensively studied as strained comonomers forcopolymerization with CO [7–10]; however, all of these productsare derived from petroleum. Because of the sharp decrease in theavailability of non-renewable petroleum resources and the aim ofachieving sustainable development, the search for renewablealternatives has become especially attractive to both researchersand manufacturers [11]. Bornadiene (BD) has similar structures to

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2,5-norbornadiene and can be a promising substitute. In addition,BD can be synthesized from α-pinene, a renewable feedstock.α-Pinene exists widely in nature as a typical renewable biomassresource and has the potential to provide a functionally equivalent,and environmentally friendly replacements for fossil-based rawmaterials [12].

In the present work, we report the synthesis and characteriza-tion of a novel polyketone with carbonyl groups and strained ringstructures using α-pinene as one of the raw materials. This processmay provide future opportunities for the synthesis of new func-tional materials from renewable biomass resources. We are alsoworking on the chemical modification of the resulting BD/COpolyketone to obtain excellent starting materials for the synthesisof new functional polymers, and the results will be reported inmore detail in the future.

2. Experimental

Materials: α-Pinene (≥96%) was supplied by Glorychem Com-pany (Guangdong, China). Carbon monoxide (CO) (≥99.9%) waspurchased from Nanjing Specialty Gases Factory (Jiangsu, China).Palladium (II) acetate [Pd(OAc)2], nitrobenzene, 2,2′-bipyridine,1,10-phenanthroline and copper (II) trifluoromethanesulfonate [Cu(OTf)2] were purchased from Sinopharm Chemical Reagent Com-pany (Jiangsu, China). Other chemicals and solvents were pur-chased from Nanjing Chemical Reagent Company (Jiangsu, China).All reagents were of analytical or HPLC grade and were useddirectly without purification.

Fig. 1. Synthesis of BD and BD/CO polyketone.

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(b) BD/CO polyketone

T/%

Wavenumber/cm-1

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1745cm-1

3060cm-1

950-1050 cm-1

Fig. 2. FT-IR spectrum of the BD (a) and the BD/CO polyketone (b).

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Synthesis of polyketone—Preparation of BD monomer:Bornadiene (1,7,7-trimethyl-bicyclo [2.2.1] hepta-2,5-diene) wasprepared from α-pinene (Fig. 1), based on literature methods[13,14].

A white solid was obtained with an yield of 75% and purity (GC)of 99.9%. 1H NMR (300 MHz, CDCl3, δ, ppm) spectra revealed 0.98(s, 6H), 1.16 (s, 3H), 3.05 (s, 1H), 6.35 (d, 2H), and 6.62 (t, 2H). IR(cm−1) absorption was 3050 and 1530, characteristic of C¼C.Calculation for C10H14, C, 89.55% and H, 10.45%. Element analysisfound: C, 88.96% and H, 11.56%.

Copolymerization of BD and carbon monoxide: The copolymer-ization reactions were performed using a 250 ml stainless-steelautoclave equipped with a magnetic stirrer. In a typical experi-ment, BD (15 mmol) was placed into the autoclave. A homoge-neous catalyst containing Pd(OAc)2 (0.15 mmol), 2,2′-bipyridine(0.09 mmol), Cu(OTf)2 (0.03 mmol), and nitrobenzene (0.1 mmol)was dissolved in a solvent mixture (15 ml) composed of toluene/methanol (2:1, v/v). The solution was charged, and the autoclavewas subsequently pressurized to 3.5 MPa with CO. The mixturereacted at 60 1C for 2 h under stirring. The autoclave was thenallowed to cool to room temperature, and the unreacted CO wasreleased. Resulting polyketone was precipitated with methanol,washed three times, and air-dried.

Characterization of polyketone: Qualitative solubility of theBD/CO polyketone was determined by dissolving 20 mg of poly-ketone in 3.5 ml different organic solvents at 25 1C. Gas chroma-tography (GC) analysis of BD was performed on a GC-14B gaschromatograph (Shimadzu, Japan). 1H NMR and 13C NMR spectrawere recorded on a Bruker AV-500 spectrometer (Bruker,Germany) using deuterate chloroform (CDCl3) as solvent andtetramethylsilane (TMS) as internal standard. Elemental analysiswas conducted using an Elementar Vario EL III instrument (Ele-mentar, Germany). FT-IR spectra were recorded on a Nicolet iS10spectrometer (Thermo, USA), no sample preparation was required.GPC analysis was performed using a PL-GPC 600 instrument(Tianpu, China). DSC analysis was performed on a PerkinElmer DSC-7 (Thermo, USA) with a heating rate of 20 1C/min from40 1C to 500 1C under a nitrogen atmosphere. TG analysis wasperformed using a DTG-60AH analyzer (Shimadzu, Japan) with aheating rate of 20 1C/min from 40 1C to 800 1C under a nitrogenatmosphere.

3. Results and discussion

Solubility of the BD/CO polyketone: The BD/CO polyketone was awhite solid with molecular weight (Mw) of 19,400 g mol−1. It wasreadily soluble in less-polar solvents such as hexane, benzene,toluene, tetrahydrofuran, and chloroform, but showed poor solu-bility in polar solvents (SI Table 1), which probably due to the BD/CO polyketone is less polar polymer and partially crystalline. Theresult of X-ray diffractogram confirmed that the BD/CO polyketonehad a degree of crystallinity which showed a sharp peak at2θ¼15.51 (SI Fig. 1).

Structural analyses of the BD/CO polyketone: The structure of theresulting polyketone polymer was characterized by FT-IR, NMR,and elemental analysis. As shown in Fig. 2, the infrared spectrumof the BD/CO polyketone showed bands of methyl and methylenegroups at 2960 cm−1, 2870 cm−1 (C–H stretching vibration) and1450 cm−1, 1370 cm−1 (C–H deformation vibration). By compar-ison with the spectrum of BD, these absorption peaks were widerand stronger in the polyketone due to many newly formed methyland methylene groups in the structure of BD/CO polyketone. A

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Fig. 3. TG (a) and DSC (b) curves of the BD/CO polyketone.

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strong band at 1745 cm−1 can be attributed to carbonyl groups(C¼O stretching vibration) in the polyketone structure. This resultwas also confirmed by 13C NMR spectra [SI Fig. 2(b)], in whichthe carbonyl group was displayed as a signal at 201.9 ppm. Theabsorption bands at 3060 cm−1 (¼C–H stretching vibration) and950–1050 cm−1 (¼C–H wagging vibration) in FT-IR spectra areassociated with the unsaturated bonds in BD units. Similarly, thepresence of unsaturated vinyl hydrogen and carbon were corre-sponded to signals at 6.37 ppm and 6.46 ppm in the 1H NMRspectra [SI Fig. 2(a)] and 129.24 ppm in the 13C NMR, respectively.However, the 1H NMR spectra reveal that the ratio of vinylicprotons was significantly lower than that predicted on the basis ofstructure A. This indicates that there is carbonylation of some ofthe second C¼C bonds of the BD units, which would lead to acarbon monoxide to BD ratio of more than 1 [15]. C and H elementanalysis of the BD/CO copolymer revealed a BD:CO ratio of 1:1.2.Calculation for (C10H14) � (CO)1.2; C, 80.19%; and H, 8.35%. Analyticfound: C, 80.36%, and H, 8.70%. Fig. 1 shows the overall reactionand the BD/CO polyketone structure was proposed.

Moreover, because of the repeating carbonyl units and theunsaturated double bonds of the BD/CO polyketone which lendthemselves to further chemical modifications, the polyketone haspotential photo- and biodegradable properties [16].

Thermal properties of the BD/CO polyketone: The thermal proper-ties of the BD/CO polyketone were investigated by TG and DSCanalysis.

In Fig. 3(a), the TG result showed that BD/CO polyketone wasvery stable to 290 1C (4% weight loss). This small weight may beattributed to the volatilization of residue solvent and small organicmolecule. A weight loss of less than 5% is important becausepolyketones with higher weight-loss levels should not be usedbecause of substantial deterioration in their mechanical properties.When the temperature passed 290 1C, the BD/CO polyketone beganto degrade quickly. It can be seen from the TG plot that the sampledegraded in two stages. The first stage occurred between 290 1Cand 521 1C with a weight loss of 53% which would be ascribed tothe decomposition of short chain and/or amorphous polyketones.The second stage of the degradation occurred at approximately522 1C and continued until 775 1C with a total weight loss of 94%indicating the further decomposition of long chain and crystallinepolyketone. Around 6% residue was remained as char.

The DSC curve [Fig. 3(b)] of the BD/CO polyketone showed aweak glass transitions at 145 1C (Tg), The melting and decomposi-tion state showed the same endothermic peak from 300 to 360 1Cbecause of the approximation of the melting point (Tm) anddecomposition temperature, as evident in the TG curve, thedecomposition of polyketone started at 290 1C, and the weightloss between 300 1C and 360 1C was 12%. Lommerts et al. [17] haveindicated that the high Tm is due to a high enthalpy of fusion,which results from the strong interactions between the polymerchains. In addition, because of the initial chemical bond breakingneed to absorb heat which gave rise to the appearance of theendothermic peak, and subsequent severe decomposition processwill give off a huge amount of heat which led to the appearance ofexothermic peak in the DSC curve from 360 to 420 1C.

4. Conclusions

In this study, a novel polyketone was prepared using renewableα-pinene as one of the starting materials. The resulting polyketonefeatures a strained ring structure with carbonyl groups andunsaturated double bonds. The thermal analysis also indicatedthat the BD/CO polyketone has excellent thermal stability. Giventhe above properties, this bio-based BD/CO polyketone has greatpotential for synthesis of new functional materials.

Acknowledgment

We would like to thank the Doctorate Fellowship Foundation ofNanjing Forestry University (2011YB016), the Innovation Project forGraduate Education of Jiangsu Province (CXZZ11_0528), the NationalNatural Science Foundation of China (30771686), and the PriorityAcademic Program Development of Jiangsu Higher Education Institu-tions (PAPD, 164020639) for providing the financial support.

Appendix A. Supporting information

Supplementary data associated with this article can be found in theonline version at http://dx.doi.org/10.1016/j.matlet.2013.03.113.

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