Mechanical Properties and Stress-Induced Phase Transformationsof Metallocene Isotactic Poly(1-butene): The Influence of Stereodefects.

A studyof the mechanical properties and of the crystallizationbehavior of samples of isotactic polybutene (iPB) of different stereoregularityprepared with metallocene catalysts is presented. Stereoregular sampleswith concentration of rrdefects lower than 2 mol% crystallize from the melt by compression-molding and fast coolingto room temperature in form II, whereas more stereoirregular samplescrystallize surprisingly mainly in form III. The stereodefective iPBsamples show interesting mechanical properties of high ductility andflexibility that increase with increasing concentration of rrstereodefects, with values of deformation at break higherthan 1000% for the most stereoirregular sample containing about 5mol % of stereodefects. The aging at room temperature produces transformationof form II into form I in more stereoregular samples, whereas no phasetransformation occurs in more stereoirregular samples crystallizedmainly in form III. A strong increase of Young’s modulus andof stress at yield is observed after transformation of form II intoform I. For more stereoirregular samples with concentration of rrdefects higher than 2 mol % crystallized in form III,the mechanical properties do not change significantly upon aging atroom temperature because no phase transformations occur during aging.Also for the aged samples, a remarkable increase of ductility andflexibility with increasing concentration of rrstereodefectsis observed. The mechanical deformation is associated with stressinduced transformations of form II and form III into form I. Theseresults indicate that mechanical properties of iPB can be modifiedby the controlled incorporation of stereodefects and improvement ofductility is easily obtained while maintaining high crystallinityby inclusion of small amounts of rrstereodefects. [ABSTRACT FROM AUTHOR]