Preparation Of Biodegradable Shape Memory Polymers And Their Properties Based On Thiol-isocyanate Click Reaction

Currently,research on biodegradable shape memory polymers is focused on polycaprolactone and polylactic acid,while the findings of studies present promising avenues for application,the extant biodegradable shape memory polymers exhibit certain shortcomings,including inhomogeneous crosslinking networks within the synthesized polymers.This inhomogeneous results in wide trigger temperature intervals and uneven degradation,leading to rapid deterioration of the implants’ mechanical properties,even fragmentation.Consequently,the preparation of a biodegradable shape memory polymer with a uniform crosslinking network and consistent mechanical properties remains a pressing issue requiring resolution.In this study,polythiourethane(PTU)biodegradable shape-memory polymers were synthesized via click chemistry reactions involving thiol-isocyanate.The shape memory,thermal,and biodegradable attributes of PTU were examined in both thermosetting and photocuring processes,yielding the following observations:1.An analysis of the impact of isocyanate and thiol compound structures on the thermal curing reaction activity within the thiol-isocyanate system elucidated the nucleophilic addition nature of the thiol-isocyanate reaction.The reactivity of diisocyanates followed the order toluene diisocyanate>hexamethylene diisocyanate>isophorone diisocyanate,while thiol compounds exhibited reactivity in the sequence 3,6-dioxa-1,8-octanedithiol>ethylene glycol bis(3-mercaptopropionate)>trimethylolpropane tris(3-mercaptopropionate)within the thermal curing system.While at photo curing system,as initiator dosage and irradiation intensity increased,the induction period was considerably reduced or even eliminated,with curing processes completed in approximately 90 s at 1 wt%and 60 mW/cm2,or 180 s at 2 wt%and 30 mW/cm2.2.The crosslinked networks of products procured through thermal and photo curing were consistent and uniform,with tanδ half-peak widths not exceeding 15℃.Moreover,exceptional shape memory performance was demonstrated,with both Rf and Rr surpassing 90%.PTUs obtained via the two distinct curing methods exhibited favorable hydrophilicity,rendering them viable candidates for biomaterial applications.The degradation rate of thermal curing PTU in PBS solution was approximately 10%per month,making it suitable as a medium to long term biodegradable material.Conversely,the degradation rate of photocured PTU in PBS solution was about 18%per month,positioning it as a short to medium term biodegradable material.Additionally,thermally cured PTU can be recycled through grinding and thermopressing processes,albeit with marginally diminished modulus and shape memory properties after recycling.