Please use this identifier to cite or link to this item: http://scholarbank.nus.edu.sg/handle/10635/18804
Title: Enzymatic preparation of microbial polyester-based novel block copolymers as thermoplastic biomaterials
Authors: DAI SHIYAO
Keywords: Enzyme, Microbial Polyester, block copolymers, Thermoplastic, Biomaterials
Issue Date: 13-Aug-2009
Citation: DAI SHIYAO (2009-08-13). Enzymatic preparation of microbial polyester-based novel block copolymers as thermoplastic biomaterials. ScholarBank@NUS Repository.
Abstract: Microbial poly[(R)-3-hydroxyalkanoates]s (PHA) are biodegradable and biocompatible materials with applications in several biomedical fields. However, their applications as thermoplastic biomaterials are limited due to the poor thermoplastic properties. This PhD thesis focuses on the enzymatic modification of microbial polyesters, poly[(R)-3-hydroxybutyrates] (PHB), to prepare novel block co-ploymers with improved thermoplastic properties for biomedical applications. It includes the following major research work: a), enzymatic modification of PHB by ring-opening polymerization (ROP) of e-caprolactone (CL) with low-molecular weight telechelic hydroxylated poly[(R)-3-hydroxybutyrate] (PHB-diol) as initiator and Novozym 435 (immobilized Candida antarctica Lipase B) as catalyst in anhydrous 1,4-dioxane or toluene. A good selectivity of polymerization on primary OH was demonstrated and the application of PHB-diol as a telechelic macro-initiator provides a new method for the preparation of PHB-based block copolymers as biomaterials with good thermoplastic properties and novel structures containing functional end groups. As a successful example, di-block poly[HB(28wt%)-co-CL(72wt%)] with Mn (NMR) of 7100 gave excellent thermal properties of Tg of -60°C, Tm of 147 and 50 °C. b) enzyme-catalyzed ring-opening polymerization of trimethylene carbonate with PHB-diol, PCL-diol, and di-block PHB-co-PCL-diol, respectively, to prepare corresponding di- or tri-block co-poly(ester-carbonate)s containing PHB as hard segment and poly(trimethylene carbonate) (PTMC) and/or PCL as soft segment. These copolymers with Mn (GPC) of 4400-9600 in 57-89 % yield showed improved thermal properties with Tg values for the soft domain ranged from -20 to -48oC. They were further polymerized with MDI to prepare poly(ester-urethane)s (PU), and the mechanical test of PU prepared from poly(HB-co-TMC) with HB:TMC weight ratio of 26:74 showed a Young¿s modulus of 23 MPa, the maximum stress of 6.37 MPa and elongation at break of 252%; PU prepared from poly(HB-co-CL-co-TMC) with HB:CL:TMC weight ratio of 14:25:51 had a Young¿s modulus of 18 MPa, the maximum stress of 8.30 MPa and elongation at break of 304%.; c) enzyme-catalyzed polycondensation of polyester-diols such as PHB-diol and poly[(R)-3-hydroxyalkanoate] (PHO)-diol with a divinyl ester to prepare block-copolyesters containing the two microbial polyesters as the hard and soft block, respectively. In each case, the enzymatic approach is novel, selective, and high-yielded. Block poly(HB-co-HO)s (Mn of 8800-14200, GPC) demonstrated Tm of 136 to 153 oC and Tg of -37 to -39 oC, being potentially useful thermoplastic biodegradable and biocompatible materials.
URI: http://scholarbank.nus.edu.sg/handle/10635/18804
Appears in Collections:Ph.D Theses (Open)

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