The Study Of Crystallization Behaviours Of Cyclic Poly(?-caprolactone)s

The topology of polymer is of great importance that could significantly influence its physical properties.And cyclic polymers are the simplest model for studying the effects of topology.To explore the topological effect on crystallization behaviors,spherulitic morphology,spherulite growth rates,crystallinity and the formation of banded spherulites,we carried out a series of experiments on cyclic and linear poly(?-caprolactone)s.The results of POM showed that the spherulitic morphologies of linear and cyclic PCLs are similar that all presented Maltese-cross spherulites during isothermal crystallization.The density of spherulites and spherulite growth rates decrease with the increasement of isothermal crystallization temperature,while the radii of spherulites increased.The spherulite growth rates of cyclic PCLs are significantly lower than that of linear counterparts with similar molecular weight that is only about1/7 of the latter.The WAXS experimental results indicated that crystal forms of both cyclic and linear PCLs are identical and the degree of crystallinity of cyclic PCL is about 38%while the value of linear PCL is about 50%.The results of WAXS and DSC experiments manifested that the overall crystallization rates of cyclic PCLs are lower than that of linear PCL counterparts.The calculated zero growth temperature of both cyclic and linear PCL is identical with the value of 81?.The differences of crystallization rates between cyclic and linear PCLs may result from conformational transition differences due to different topological structures.In the presence of CHCl₃,the linear PCL sample with low molecular weight produced banded spherulites,and the banded spherulites became more regular with the rise of crystallization temperature.While for high molecular weight linear PCL and cyclic PCL,there is no banded spherulites presented.These special differences could be explained by the rhythmic growth model.