Effects Of Molecular Structures And Tensile Field On Phase Transition In Butene-1 Copolymers

Phase transition from the kinetically favored tetragonal form II into the thermodynamically stable hexagonal form I is the general phenomenon and core issue in application of polybutene-1 based materials.It is known that the variation of molecular structure by copolymerizing counits and the imposition of external stretching both greatly affect phase transition.In present work,polybutene-1 homopolymer,butene-1/4-methyl-1-pentene(4M1P)random copolymers,and butene-1/4,4-dimethyl-1-pentene(44M1P)random copolymers were synthesized with dimethylpyridylamidohafnium/organoboron catalyst,where the 4M1P and 44M1P incorporated are the counit types of depressing ?-? phase transition.Mechanical tests were combined with in situ wide angle X-ray diffraction(WAXD)method,to study the competing effects of presence of 4M1P and 44M1P counits and stretching on ?-? phase transition.First of all,the quiescent experiments reveal that addition of 4M1P and 44M1P counits not only slows down transition kinetics,but also decreases ultimate form I fraction in transition plateau.When the counit concentration reaches a certain value,the ?-? phase transition is completely impeded even the aging time is as long as four months.Second,stretching-induced phase transition was explored with the combined structural and mechanical information from WAXD and mechanical characterizations,respectively.The influence of stretching stimuli in phase transition varies with counit concentration.For low counit concentration,stretching significantly accelerates transition kinetics and induces the complete transition of form II.For intermediate counit concentration,stretching effectively triggers occurrence of ?-? phase transition,which does not start under quiescent condition,but only induces partial transition until fracture.For high counit concentration,stretching just orientates the form II crystallites without starting any phase transition to form I.Third,as increase the concentration of counits,phase transition is accomplished with different orientations,which determines the microscopic stress applied to lamellae.Then,detailed kinetics of ?-? phase transition was correlated with the stretching stimuli of total true stress,component stresses parallel and perpendicular to c-axis in crystal lattice.It was interesting to find that transition kinetics is dominated by the component stress perpendicular to c-axis for the off-axis orientation pathway.For molecular mechanism of phase transition,this indicates that the activated chain lateral slip is the dominant process for nucleation of form I within original form II.Moreover,Avrami equation was applied to analysize kinetics of ?-? phase transition under quiescent condition,continuous stretching,and constant true stress.This thesis quantifies the correlation between the kinetics of quiescent phase transition and concentration of 4M1P and 44M1P counits,and identifies the critical counit concentration to completely suppress phase transition.For stretching-induced phase transition,counit-concentration dependence and the crucial role of segmental lateral movement were revealed.Moreover,the stabilized form II exhibits ultra-high fracture strain over 1000%.