The Ring-opening Polymerazation Of Lactones Catalyzed By Bifunctional Organic Small Molecule Catalysts

Aliphatic polyester is an ideal environmental friendly material,which has attracted attention for the nature of biocompatible,biodegradable,recyclable,and excellent in mechanical properties.It has been widely used in biomedical applications,tissue materials,industrial and food packaging.Ring-Opening polymerization?ROP?of lactones is an important method for the synthesis of aliphatic polyesters.It has been proved that cheap and easily available metal compounds have excellent catalytic effect on ring-opening polymerizations of lactones.However,due to the presence of metal residues,cytotoxicity,and other problems in this type of catalyst,its widespread use has been limited.Therefore metal free organocatalytic has attracted more and more attention in the synthesis of aliphatic polyesters.Organocatalysts have been widely concerned due to mild polymerization conditions,controlled polymerization and no metal residua.At present,metal free organocatalytic ROPs of lactones has become an important research direction.In the organic non-metal catalyst system,bifunctional organic molecule catalyst is an effective and valuable catalyst,which has obvious superiority in the selectivity and the rate of the reaction.This thesis mainly studied the ring-opening polymerization of lactones catalyzed by bifunctional organic small molecule catalysts.The main contents are as follows:1)The ring-opening polymerization?ROP?of?-caprolactone??-CL?has been studied with 1,4-butanediol as the initiator and 1,5,7-triazabicyclo-[4.4.0]dec-5-ene?TBD?as the catalyst.Kinetic studies were conducted in toluene to better understand the reaction mechanism of TBD catalyzed?-caprolactone.It was found that the polymerizations showed a linear increase of molecular weight with conversion.The rate of propagation is first-order in monomer concentration,while k_p is independent of the concentration of TBD.Moreover,the reaction rate?k?was determined through kinetic studies in a series of temperatures.The relationship between k and the polymerization temperature was in good agreement with the Arrhenius equation.The value of activation energies?Ea?is 22.46 kJ?mol^-1.As a contrast,the ROP of CL initiated by n-butanol was carried out with an Ea of 39.49 kJ?mol^-1.It is proved that the activation energy of diatomic alcohol is lower than that of monobasic alcohol.2)The gold nanoparticles with uniform morphology and size were prepared by a crystal growth method,and 4-nonylphenol was added to modify surface of the gold nanorods.Then,TBD was used as the catalyst.The hydroxyl end groups of nonylphenol modified gold nanorods are used to initiate the ring-opening polymerization of caprolactone by the way of“grafting from”.Finally,polycaprolactone-modified gold nanorods were successfully prepared.Meanwhile,the behavior of PCL on the surface of AuNRs was investigated.It was found that PCL mainly forms two morphologies,one is spherical and the other is square,and the square structure is a new morphology of PCL that has not appeared in the literature.3)Eight?thio?urea/amine bifunctional organocatalysts were prepared and a series of experiments were conducted to study the structural changes of?thio?urea/amine organocatalysts and their effects on the common monomer ROP efficiency.It is concluded that the cyclohexyl bridged?thio?urea/amine catalyst has higher catalytic activity than the linear alkyl bridged?thio?urea/amine catalyst;And the higher the basicity of the amine functional group,the better the catalytic effect of the catalyst;Due to the different catalytic effects of different catalysts on different monomers,the catalytic activity of the urea/amine catalyst system in the ring-opening polymerization of caprolactone is higher than that of the thiourea/amine catalyst system,and the catalytic activity of thiourea/amine catalyst system in the ring-opening polymerization of valerolactone is higher than that of urea/amine catalyst system.On the other hand,the?thio?urea/amine bifunctional organic small molecule catalyst has a higher catalytic activity for valerolactone and no transesterification reaction during the reaction.