Study On Crystal Structure Formation Of Isotactic Polybutene-1

Isotactic polybutene-1(iPB-1)is a semi-crystalline polymer with several crystal forms.While melt processing,the metastable form II is usually preferred and then slowly transits into stable form I,which hinders the wide applications of iPB-1 in various fields.To focus on how to obtain the stable crystal forms of iPB-1 directly from the bulk melt while processing and to study on the crystallization mechanism are of theoretical and practical importance.In this thesis,the non-isothermal and isothermal crystallization processes of iPB-1 were investigated by the in-situ synchrotron radiation wide angle X-ray scattering(WAXS)and Fourier transformed infra-red spectroscopy(FTIR).The main conclusions are shown as follows:1.Synchrotron X-ray radiation can promote iPB-1 melt to crystallize into form I?.After this form I? was melted to a certain temperature,the obtained melt could show its memory effect to crystallize back into form I?.Since form I? has the same 3/1 helices as what is in form I and is also thermodynamically stable,the synchrotron X-ray radiation may first promote the formation of 3/1 helices and the related mesophase.Then the 3/1 helices and mesophase would finally develop into form I?.In addition,the 3/1 helices and the mesophase could survive while heated to certain high temperatures with form I? completely melted.Once cooled again,the melted form I? could recover to form again,showing melt memory effect.2.Under synchrotron X-ray radiation,iPB-1 melt could crystallize into form II prior to the appearance of form I? while cooling.A low cooling rate favours more form I?.If a certain amount of form I? in the iPB-1 sample was melted and the sample was cooled to crystallize again,the formation of form II was found to be inhibited.The results showed that formation of form I? and form II affected each other.The 3/1 helices and the related mesophase,which could crystallize into form I?,could not turn to crystallize into form II,and the neighbouring iPB-1 chain segments also inhibited to crystallize into form II.The results shed lights on understandings to the crystallization behaviours and the crystallization mechanism of iPB-1,which are of practical importance to control the crystal forms of iPB-1 and also of theoretical value to developments of polymer crystallization mechanism.