Synthesis And Properties Of Polyurethane Materials Based On ?-butyrolactone

As one important member of polymer family,polyurethanes have been widely used in a variety of applications ranging from aerospace,automobile,biomedical technologies and daily commodity due to their high elasticity,good wear resistance,lubricity,durability and good biocompatibility and excellent mechanical properties.In recent years,due to the dual challenges of environment and resources,the degradable and recyclable bio-based polyurethanes with aliphatic polyesters as soft segments have attracted more and more attentions.In this thesis,the ring-opening polymerization(ROP)of bio-based?-butyrolactone(?-BL)to prepare a series of poly(?-butyrolactone)(P?BL)polyols with different molecular weights were successfully achieved using strong base/urea binary catalysts.A series of polyurethanes were then prepared by reacting the P?BL polyols with isocyanates.The thermal,mechanical and degradation properties of P?BL based polyurethanes are systematically investigated.The thesis mainly contains the following results:(1)The ROP of ?-butyrolactone(?-BL)was achieved using a strong base/urea binary catalyst to prepare telechelic hydroxyl terminated poly(?-butyrolactone)(P?BL)polyols,which were subsequently reacting with isocyanates(MDI or IPDI)to produce a series of polyurethanes.It was found that: a)The number-average molecular weights of polyurethanes firstly increased and then decreased with the increase of NCO/OH ratio;b)The number-average molecular weight of polyurethane increased firstly and then decreased with the increase of the molecular weight of P?BL polyols.c)Cross-linking occurred at a long reaction time since-NH-of the carbamate bond will further react with NCO to form allophanate.(2)The effects of polyurethane molecular weights,isocyanates and P?BL molecular weights on the thermal and mechanical properties of polyurethanes were systematically studied.The hydrolytic behaviors of P?BL based polyurethane in aqueous solutions with different p H values were investigated.The chemical recycling of P?BL based polyurethanes were also studied.It was found that: a)The thermal stability and the glass transition temperatures of P?BL based polyurethanes increased with their molecular weights.b)The properties of obtained polyurethanes are strongly dependent on the molar mass of used P?BL diol precursors.When P?BL diol with a low molar mass of 1.2 or 2.5k Da was used as precursors,the resultant polyurethanes were amorphous and exhibited elastomeric properties.The tensile strength and ultimate elongation increased as the increase of the molecular weights of P?BL based polyurethanes.When P?BL diol with a moderate molar mass of 3.6 or 6.5 k Da was used as precursors,the resultant polyurethanes were semi-crystalline and exhibited thermoplastic properties.The mechanical properties remained almost unchanged with the the molecular weights of P?BL based polyurethanes.c)The degradation rate of the P?BL based polyurethane in alkaline aqueous solution is fastest.The chemical recycling of P?BL based polyurethane to recover high-purity ?-BL was achieved by vacuum distillation using stannous octoate as a catalyst.