Study On Preparation And Properties Of Polyesters Composed Of Cinnamic Acid Derivatives

Researches and developments of functional biodegradable polymers which play a goodrole not only in the increasingly serious problems of resources and environment but also inthe development of new materials of the clinical medicine, biomedical and other fields havebecome a current research focus. In a variety of degradable polymers, Polymers based onpolycaprolactone (PCL) have been paid more attention owing to the characteristics ofexcellent biocompatibility, biodegradability, drug permeability and nontoxicity. Hydroycinnamic acid which derived from plants is a kind of photoreactive “plant monomer”. Thephotoreactive polyesters obtained from the two monomers by different forms of chemicalbond have the concentrated properties of both the two monomers, the weakness can beimproved and the advantages can be promoted. Regulation of such polyester performance canbe achieved through the control of their structure, composition. The regulation of theproperties of these kinds of polyesters can be achieved through the control of their structuresand compositions.In this paper, PCL homo-polymers with different molecular weight were synthesized bya ring-opening polymerization method, and then series of PCL-co-P4HCA copolymers werealso synthesized via a thermal polycondensation method using PCL and4HCA monomers.The structures of the copolymers have been confirmed by FTIR and1H NMR. The results ofGPC showed that the molecular weights of PCL-co-P4HCA were between8.7×104-10.1×104g/mol, and the molecular weight distribution would much wider when the molecularweight was higher. PCL-co-P4HCA copolymers were photoreactive, and the absorption ofthe cinnamoyl group at306nm decreased rapidly and then decreased gradually withincreasing time of302nm UV irradiation. Moreover, PCL-co-P4HCA copolymers withhigher4HCA compositions showed greater photoreactivity rates and the decline degree after50min. PCL-co-P4HCA copolymers have fluorescence properties, the maximum emissionpeak intensity at450nm of these polymers decreased linearly with a decrease in4HCAcontent and the increase time of UV irradiation. The results of DSC and WXRD showedPCL-co-P4HCA copolymers were crystalline of PCL and P4HCA homo-polymers, thecrystallinity would decrease with a decrease of PCL composition. PCL-co-P4HCAcopolymers have excellent thermal stabilities which decrease regularly when irradiated withUV rays. The water contact angles of the PCL-co-P4HCA sheets increased with a decrease in4HCA content and the increase time of UV irradiation. The hydrolysis rate of thePCL-co-P4HCA sheets increased with an increase in4HCA content, and the rates ofhydrolysis were significantly higher under alkaline conditions than under neutral conditions.The degradation rates of the copolymers after UV irradiation were slightly slower due to the higher surface hydrophobicity.Hyprebranched PCL-co-PDHCA copolymers were obtained by thermalmelt-polycondensation of PCL and AB2type DHCA monomer. The structures and thebranching degree were identified by1H NMR, and transesterification during thepolymerization might also occur from the results of FTIR and GPC. PCL-co-PDHCAcopolymers were photoreactive, and the crosslinking degree after75min UV irradiationwhich increased with an increase of DHCA composition might achieve about30%. Thefluorescence properties of PCL-co-PDHCA will be influenced by branching degree. Theemission intensity increased with increasing of the DHCA composition under the lowerbranching degree, a high branching degree will cause the fluorescent quenched and induce adecline of the emission intensity. The results of DSC and WXRD showed the crystallinity ofPCL-co-PDHCA copolymers reflected the PCL chain mainly, and the melt point andcrystallinity would decrease with an increase of DHCA composition. PCL-co-PDHCAcopolymers have excellent thermal stabilities which will influence by polymer component,branching degree and UV irradiation. The degradation rates of copolymers sheets would slowdown by increasing the PCL composition and UV irradiation.Linear P4HCA, PCL-co-P4HCA and hyperbranched PDHCA, PCL-co-PDHCApolymers were obtained using anhydrous sodium phosphate as a catalyst. The structures ofthe polymers have been confirmed by FTIR and1H NMR. The reactivity of AB2type DHCAis higher than4HCA. The photocrosslinking degrees of hyperbranched polymers are higherthan the one of linear polymers after55min UV irradiation. However, the linear architectureis more prone to carry out the cis-trans isomerization, and the linear polymers have strongerfluorescence intensity. Hyperbranched architectures cause the better thermal stability of thepolymers due to the stronger π-π stacking. The result of WXRD and accelerated degradationtest showed the stronger crystalline of PCL-co-P4HCA lead to the slower degradation rate.PECL-4ACA triblock copolymers were obtained from PECL synthesized byring-opening polymerization and4ACC. The results of DSC showed the copolymers werecrystalline, and the melting point increased with the increasing of the PCL chain composition.The thermal stability of the copolymers has been enhanced owing to the4ACA terminalgroups which restrain thermal decomposition of the aliphatic polyester PCL segment.PECL-4ACA copolymers display a reversible photosensitivity under302and254nm UVirradiation. PEG chains play a dominant role in the contact angle which express declinetendency as the introduction of4ACA terminal groups. The polymers which were muchhydrophilic had the faster degradation rate.