Design And Tailor-Making Of Biodegradable Polyester Macromonomers

Polyesters are one of very important polymeric materials and possess many applications in building, automobile, medicine, food, and packaging industries because of their superior properties. Since the monomers used for the production of polyesters are derived from non-renewable petrochemicals, which make them non-degradable and have a potential negative impact on the environment, it will be sustainable if renewable biomass feedstocks can be used as replacement. Oxygen rich monomers from biomass feedstocks are promising in the synthesis of biodegradable polyester materials. However, oxygen rich monomers are normally less reactive and lack of variety in functional groups. Design and tailor-making of reactive biodegradable polyester macromonomers derived from oxygen rich monomers is one of the most effective approaches to tackle the problems.L-lactide(L-LA) and ε-caprolactone(ε-CL) were used for ring opening copolymerization with stannous octoate (Sn(Oct)2) as catalyst and hydroxyethyl methylacrylate (HEMA) as initiator in this work. The effects of various monomer compositions and polymer chain lengths on the copolymerization kinetics were investigated. It was observed that trans-esterification side reactions were reduced and biodegradable polyester macromonomers having lower glass transition temperatures were synthesized via a semi-batch strategy with step-feeding equal amount of L-LA. A corresponding mathematical model was developed by considering reversible initiation, propagation, chain transfer, and trans-esterification reactions. The diffusion control associated with polymer chain length was also considered in the model. The model can successfully predict monomer conversions, number-average molecular weights, polydispersity index values, and cumulative copolymer compositions for ring opening copolymerizations of L-lactide with ε-caprolactone.In order to resolve metal residues in biodegradable macromonomers catalyzed by organic metal complexes, an organic catalyst, 1,1-Binaphthyl-2,2-Diyl Hydrogenphosphate (BNPH), has been developed for the L-LA/ε-CL ring opening copolymerization. Optimum copolymerization conditions were obtained with polymerizing at 140℃ and using 0.5mol% BNPH as catalyst. Effects of different feeding policies on the macromonomer formations were also investigated. High monomer conversions without scarifying molecular weight distribution were achieved through the semi-batch feeding policies. A direct evidence that trans-esterification side reactions could be negligible in the organo-catalyzed ring opening copolymerization was observed by 13C NMR measurements of copolymer chain structures. Block sequence structures in biodegradable polyester macromonomers were also minimized with the semi-batch feeding strategy.The innovations in this work comprise:1) In Sn(Oct)2 catalyzed L-LA/ε-CL ring opening copolymerizations, trans-esterification side reactions were controlled and biodegradable polyester macromonomers having lower glass transition temperatures were synthesized via a semi-batch strategy with step-feeding equal amount of L-LA.2) A kinetic model comprising chain length dependent diffusion control for the Sn(Oct)2-catalyzed ring opening copolymerization of L-LA and ε-CL has been established for simulating the monomer conversions, molecular weights and distributions, and copolymer compositions.3) An organic catalyst, BNPH, with high reactivity and good control on trans-esterification has been developed for ring opening copolymerization of L-LA and ε-CL, which is beneficial to tailor-make biodegradable polyester macromonomers.