Novel photocrosslinkable and biodegradable polyester from bio-renewable resource
Introduction
The use of non-renewable traditional commercial polymers, derived from fossil feedstocks such as petroleum and natural gas, has led to many environmental problems related to their disposal. The researchers around the world are searching for alternative thermoplastics that mimic the properties and functions of the packaging materials [1], [2]. Ideally, they will derive from bio-renewable feedstocks and degrade in a reasonable timeframe, harmlessly, back into the environment [3].
Some commercial biodegradable polymers from renewable resources, poly(lactic acid) (PLA) and poly(hydroxybutyrate) (PHB), etc. have been developed for many years and successfully applied in many areas [2]. Recently, another series of biodegradable polymers are synthesized on basis of various bio-based monomers. Miller has taken the challenge of developing thermoplastic materials that are derived from lignin by preparing polyalkylene 4-hydroxybenzoates, polyalkylene vanillates, and polyalkylene syringates with good thermal properties [3]. Mecking’ team has obtained the fully renewable polyester by polycondensation of long-chain linear C19 C23 monomers, which are produced from isomerizing alkoxycarbonylation of fatty acids [4]. Barrett has prepared several photocurable polyesters based on different polyols and itaconic acid that is a photoactive renewable monomer [5]. l-Tartaric acid, a widely available and relatively inexpensive natural resource from a large variety of fruits, has been used for synthesis of polyamides [6], poly(ester amide)s [7], polycarbonates [8] and polyesters [9], [10].
Cinnamoyl polymers are known as one of biodegradable polymers, and they are recently paid attention after firstly reported by M. Akashi et al [11], [12], [13]. It has been reported that a series of biodegradable polymers using bio-based monomers, coumaric acid derivative, demonstrate many interesting properties including liquid crystalline behavior, high mechanical and thermal properties, photoreactivity and cell compatibility. Known coumaric acid derivatives are 4-hydroxycinnamic acid (4HCA), 3-hydroxycinnamic acid (3HCA), 3-methoxy-4-hydroxycinnamic acid (MHCA) and 3,4-dihydroxycinnamic acid (DHCA, coffeic acid). These molecules are found in the biosynthetic pathway of plants that synthesize lignin [14] and in several photosynthetic bacteria as one of the protein components [15]. The aforementioned monomers contain cinnamoyl groups, which are photoreactive and can undergo at least two photoreactions, a [2+2] cycloaddition and trans/cis isomerization [16].
Among the cinnamoyl polymers, homopolymer of DHCA (PDHCA) is too brittle and hard to be molded [11], [17]. An effective method for enhancing the mechanical properties is its copolymerization with other monomers. A new type of polyester prepared by copolymerization of DHCA and l-lactide (LLA) shows high thermal stabilities [18], [19]. Another polyester composed of DHCA and 4HCA exhibits high tensile strength and Young’s modulus, and their mechanical properties are further improved and the rate of hydrolysis accelerates after photo-crosslinking [11]. However, the above mentioned findings are not involved in the ductility of copolymers. The application of polyesters will be limited due to its brittleness. It is necessary to fabricate the ductile polyesters form DHCA and second monomers.
10-hydroxycapric acid (HDA) is a kind of bio-monomer from castor oil with flexible long linear chain [20]. To the best of our knowledge, the ductility of bio-based polyester would be increased by the introducing flexible monomer, HDA. In this paper, the synthesis and characterization of bio-renewable copolymers of DHCA and HDA are described, and the ductile polyesters are desired to be achieved by copolymerization of DHCA and HDA.
Section snippets
Materials
3,4-dihydroxycinnamic acid (DHCA) as monomer was purchased from Huzhou biological material Co. Ltd. and recrystallized from DMF/H2O (1/50, v/v) before use. 10-hydroxycapric acid (HDA) was produced by Yingkou Tianyuan fine chemical Co. Ltd. Anhydride acetic acid (Ac2O), sodium acetate (NaOAc), deuterated trifluoroacetic acid used as NMR solvent and other solvents supplied by Shanghai chemical reagent station were used without further purification.
Synthesis of poly(DHCA-co-HDA)
Poly(DHCA-co-HDA) copolymers were synthesized by
Characterization of poly(DHCA-co-HDA)
Table 1 shows that the synthetic conditions and copolymer composition of poly(DHCA-co-HDA)s. The composition ratios of DHCA and HDA in the polyesters calculated by 1H NMR is similar to these of starting monomers. The polyester is not an altering copolymer but a random one. According to Flory’s theory, polymerization of AB2-type multifunctional monomers such as DHCA with one functional group (A) of one type and two groups (B) of another type created a hyperbranched architecture without
Conclusion
Novel photocrosslinkable and biodegradable poly(DHCA-co-HDA) copolymers were successfully synthesized from bio-renewable monomers. The molecular weight and chemical structure of the polymers were characterized by GPC, 1H NMR and FTIR. The introduction of HDA into the main chain of polyester the glass transition temperature decreased. The photoreactivity of poly(DHCA-co-HDA) were dependent on their compositions. The higher content of HDA in poly(DHCA-co-HDA) copolymers, the higher
Acknowledgment
This work is supported by National Natural Science Foundation of China (51003042, 51173072) and the Fundamental Research Funds for the Central Universities (JUSRP10906, JUSRP11109, JUSRP31001, JUSRP211A08).
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