Crystallization Behavior Of 1-Butene Copolymers Containing Cyclic Units

Isotactic poly(1-butene)is one kind of important and advanced polyolefin materials,which exhibits excellent mechanical properties,such as creeping resistance and environmental stress cracking resistance.However,isotactic poly(1-butene)often easily crystallizes into the kinetically favored tetragonal crystallites but subsequently transforms into the most thermodynamically stable trigonal phase.The complex crystallization polymorphism and the spontaneous phase transition make the control of crystallite aggregation structure to remain a great challenge.It was demonstrated recently that the synthesis of 1-butene copolymers is an effective way to control the crystallization polymorphism,but the current relationship between chain structure and crystalline structure is just revealed for the quiescent crystallization in several copolymers containing linear units.Aiming at controlling the crystallization polymorphism,a series of novel 1-butene copolymers containing cyclic units were designed and synthesized in this thesis,and their melt crystallization and solid phase transition were systematically studied for both quiescent and flow-induced conditions.The chain archirecture-flow-crystallization polymorphism relation was attempted to be established,which is expected to provide support for the preparation and application of1-butene copolymers.The main results are as follows:1.By using dimethylpyridylamidohafnium,1-butene/1,5-hexadiene copolymers and1-butene/cyclopentene copolymers were synthesized to contain five-membered cyclic units in the main chain,while 1-butene/1,6-heptadiene copolymers and 1-butene/cyclohexene copolymers were prepared to contain the six-membered cyclic units in the main chain,different from the obtained 1-butene/vinylcyclopentane copolymer and 1-butene/vinylcyclohexane copolymer containing cyclic units in the side chain.The crystallinity can be regulated by changing the degree of incorporation,where the low crystallinity below 38% could induce the appearance of memory effect above the equilibrium melting temperature.Among these copolymers,the 1-butene/1,5-hexadiene copolymer can directly crystallize into the thermodynamically stable trigonal phase from amorphous melt.For isotropic crystallites formed by quiescent crystallization,the five-membered cyclic units within the main chain promote phase transition,while the six-membered cyclic units suppress the phase transition.2.Employing in-situ synchrotron wide angle X-ray diffraction,flow-induced crystallization was studied for 1-butene/1,5-hexadiene copolymers,whose quiescent crystallization can generate the trigonal phase.Flow accelerates the crystallization kinetics of both trigonal and tetragonal phases,while because of the changed crystallization competition,the increase of strain facilitates the formation of the tetragonal phase.The critical strains to cause form II-favored crystallization and form II-dominant crystallization to both increase with the increase of incorporation.Therefore,the dynamic phase diagram of flow-induced crystallization was established with variables of strain and incorporation.3.For the flow-induced oriented tetragonal crystallites,the relationship of the solid phase transition with the chain structure was studied.The increase of strain always accelerates phase transition of poly(1-butene)homopolymer,whereas in 1-butene copolymers,influence of flow on phase transition depends on the incorporation.A critical incorporation of co-units was identified,above which flow suppresses the phase transition with respect to the quiescent case.Compared with the five-membered cyclic units,the larger six-membered cyclic units prepared interestingly show the larger critical incorporation,leading to the broadened incorporation range to allow the flow field to accelerate phase transition.