Synthesis of a Bio-Based Methacrylic Polymer Using Camphor Terpene as a Renewable Resource ^†

Abstract

Sustainable polymers derived from biomass have the potential to reduce environmental impacts while offering significant performance and cost advantages over petrochemical-derived macromolecules. We present here a facile and efficient approach to the synthesis of a biomethacrylic monomer, isobornyl/bornyl methacrylate (IBOMA/BOMA), using the naturally available camphor terpene in the essential oil of the Algerian plant Artemisia arborescens (Absinthe) as a key intermediate. The essential oil of the aerial part of the Artemisia arborescens plant naturally distributed in northwest Algeria was isolated by hydrodistillation and analyzed using gas chromatography–mass spectrometry (GC/MS) techniques. Nine components were identified, representing 90.7% of the total content. The main constituent of Artemisia arborescens essential oil is camphor (71.8%). Camphor was purified and modified to produce an 80% renewable-carbon-based methacrylic monomer. This terpene-derived methacrylic monomer was free radically polymerized to create a biosourced methacrylic polymer. Nuclear magnetic resonance (NMR) was used to characterize the structure of camphor terpene, isobornyl/bornyl methacrylate, and poly (isobornyl/bornyl methacrylate) (PIBOMA)/(PBOMA).

1. Introduction

In the contemporary landscape, a substantial portion of essential materials is currently derived from fossil fuels, yet the consensus among various researchers suggests a bleak prognosis: the depletion of all fossil resources within the next century. Consequently, an urgent call to action revolves around the transformation of chemical synthesis by adopting renewable resources, an ambitious quest vital for advancing sustainable development and, more specifically, the production of monomers [1,2,3,4,5,6,7,8,9].

The realm of renewable polymers has witnessed a transformative influence from the advent of natural molecular biomass. This biomass, akin to its petroleum-derived monomer counterparts, exhibits the versatility to serve as a direct source, whether in the form of terpenes or carbohydrates, or to undergo derivatization, ultimately evolving into a monomer suitable for uncontrolled or controlled polymerization processes [8]. Biomass-derived monomers can be broadly categorized into four principal classes, contingent upon the origin of their natural resources: oxygen-rich monomers, including carboxylic acids (lactic, succinic, itaconic, and levulinic acids) and furans; hydrocarbon-rich monomers, encompassing vegetable oils, terpenes, terpenoids, fatty acids, and bietic acids; bio-olefins, representing yet another group of hydrocarbon monomers; and carbon dioxide, a non-hydrocarbon monomer. The development of novel bio-based methacrylic monomers and polymers from terpenes has garnered significant attention in recent years [10]. Terpenes, a family of naturally occurring, hydrocarbon-rich molecules prevalent in essential oils [11,12], exhibit a diverse array of structures. Terpenes featuring an isoprene moiety can be facilely polymerized through radical polymerization reactions [8,13]. Additionally, cyclic terpenes boasting alcohol or ketone functionalities can be strategically tailored for the pursuit of bio-sourced polymers [14,15].

This study is a focal point for the synthesis of a bio-based methacrylic monomer, with the terpene camphor serving as a pivotal intermediate. The process involves the extraction of camphor from the Artemisia arborescens plant, followed by purification and modification to generate the bio-sourced methacrylic monomer. Subsequently, this monomer is subjected to free radical polymerization, culminating in the creation of a bio-sourced thermoplastic methacrylic polymer, as exemplified in Scheme 1.

2. Experimental

2.1. Artemisia Arborescens Oil Extraction

The aerial part of the A. arborescens plant was collected in Tlemcen, western Algeria. The station’s relative GPS coordinates are 1°44′52″ W longitude and 35°00′48″ N latitude and it is 355 m above sea level. The essential oil of the aerial part of Artemisia arborescens was obtained by hydro distillation for 3h employing Clevenger-type apparatus.

2.2. Reduction of Camphor

Camphor was reduced to isoborneol/borneol in the presence of NaBH₄ in MeOH (Figure 1). Camphor (0.01 mol) and methanol (3 mol) were introduced into a flask and stirred until a homogeneous solution was obtained. Next, 0.2 g of sodium tetrahydridoborate (NaBH₄) was added. The mixture was heated to 60 °C for 1 h. The mixture was then removed and cooled. Finally, 20 mL of ice-cold water was added to the mixture, and the mixture was filtered.

2.3. Esterification of Isoborneol

Into a 50 mL flask, 25 mL of dichloromethane was introduced. An amount of 1.5 g of isoborneol/borneol was added, followed by 0.7 mL of triethylamine. The mixture was stirred in an ice bath. Next, 0.9 mL of methacryloyl chloride was added dropwise. After complete addition, the mixture was brought to room temperature and stirred for 24 h. The product was washed with water (3 × 70 mL) and dried over anhydrous MgSO₄. Product purification was carried out in a silica gel chromatography column using a mixture of heptane and ether (90/10). For 1g of product, 30 g of silica gel was used (Figure 1).

2.4. Polymerization of Isobornyl Methacrylate

We decided to work with the mixture (isobornyl/bornyl methacrylate) without separating it. In a 25 mL flask, 0.01 mol of monomer (isobornyl/bornyl methacrylate) was introduced, then 9 × 10⁻⁴ g of AIBN was added. The mixture was bubbled with nitrogen for 15 min, then stirred at 80 °C for 6 h. The resulting polymer was purified by precipitation in methanol, filtered, and dried in an oven at 60 °C (Figure 1).

3. Results and Discussion

GC/MS analysis of A. arborescens essential oil shows that the oil is dominated by camphor (71.8%) (

Table 1. Chemical composition of essential oil of A. arborescens determined by GC/MS analysis.

No.	Compounds a	RIa b	RIa c	%
1	α-Thujene	913	914	3.6
2	Camphene	946	944	2.1
3	Artemisiatriene	922	924	2.5
4	α-Terpineol	1185	1183	1.0
5	β-Pinene	979	978	2.2
6	Terpinen-4-ol	1171	1169	1.7
7	Camphor	1143	1048	71.8
8	Sabinene	952	954	0.8
9	Chamazulene	1735	1734	4.8

^a The order of elution is given in the non-polar column (HP-5MS). ^b Retention indices (RIa) in the non-polar column are reported from the literature. ^c Retention indices with respect to C8–C29 n-alkanes calculated onnon-polar (HP-5MS) capillary column. RI: retention index. MS: mass spectrometry in electronic impact mode.

).

The structure of each synthesized compound was analyzed via NMR, and the polymer was analyzed via NMR and Raman spectroscopy. The band at 625 cm⁻¹ was attributed to C-C-C in planar bending (ring), 875 cm⁻¹ to CH₂ rocking, 1470cm⁻¹ to CH deformation, and 1720 cm⁻¹ and 2950 cm⁻¹ to C=O and CH₂ stretching, respectively [16] (Figure 2).

4. Conclusions

In conclusion, this work elucidates the synthesis of poly(isobornyl/bornyl methacrylate) by leveraging the terpene camphor, naturally occurring in the essential oil extracted from Artemisia arborescens, as a fundamental intermediate. The essential oil analysis conducted via gas chromatography/mass spectrometry (GC/MS) demonstrated a significantly high concentration of camphor terpene in the Artemisia arborescens plant extract. This finding underscores the potential of utilizing this natural resource as a crucial building block for synthesizing advanced materials.

The chemical modification of the camphor terpene offers a promising pathway for the development of a biopolymer characterized by an impressive 80 percent bio-based carbon content. This innovative approach capitalizes on the renewable nature of terpenes, paving the way for the sustainable production of high-performance materials.

Throughout this study, each step involved in the separation of camphor and subsequent modifications leading to the formation of the biopolymer was meticulously executed, resulting in successful outcomes. This accomplishment signifies a significant advancement in the realm of biopolymer synthesis, showcasing the feasibility and efficacy of utilizing natural terpenes as precursors for eco-friendly material production.

The utilization of natural compounds, such as camphor terpene from Artemisia arborescens, not only presents an opportunity for reducing reliance on non-renewable resources but also contributes to the development of environmentally friendly materials. The successful completion of this synthesis process highlights the potential of bio-based polymers derived from natural sources, emphasizing the importance of sustainable methodologies in material science and engineering.