Regulation Of Polybutene-1 Crystallization Properties By Ionic Groups And Long Side Chains

As a typical polymorphic polymer,one of the significant features of polybutene-1 is that the form II crystal with kinetic advantage can spontaneously transform into the thermodynamically stable form I crystal.Reasonable regulation of the phase transition process of polybutene-1 is a difficult and key research.The molecular structure regulation of the polymer is a commonly used method for regulating the transformation of polybutene-1.In this work,novel polybutene-1materials with long side chains and ionic groups were designed and synthesized,and the crystallization properties and II-I phase transition behavior of this series of polymers were studied.Firstly,this work synthesized the 1-butene/11-iodo-1-undecene copolymer(PB-IUD)containing long side chains.Based on this,we synthesized polybutene-1ionomers with different ions(PF₆^-,BF₄^-,Tf₂N^-).This is the first time that the ionic groups have been introduced into a polybutene-1 system.The results show that the long-chain branch retards the II-I phase transition in copolymer PB-IUD.Unexpectedly,in ionomers,presence of ionic functional groups accelerates II-I phase transition with respect to aforementioned PB-IUD,although they have exactly the same density of branches.What is more interesting is that ionomer II-I phase transition can happen at the crystallization temperature,where there is actually no cooling step to provide the internal thermal stress.This indicates that in ionomers,some additional crystallization-associated internal stress is generated for form I nucleation.Furthermore,the temperature dependence of II-I phase transition was systematically explored for both transition and crystallization steps.For ionomers,the broad temperature window of II-I phase transition ranges from the glass transition temperature to high temperature close to melting region.Stepwise annealing protocol was utilized to reveal that this broad transition temperature window is due to persistent nucleation ability at elevated temperatures.As crystallization temperature was decreased,an increasing tendency of II-I transition rate was found for ionomers,which is opposite to that of polybutene-1 homopolymer.Based on this,the proposed continuous cooling protocol was capable of endowing the branched ionomers with the accelerated transition even faster than the linear homopolymer.Next,butene-1 copolymers grafted with polyethylene glycol(PEG)having different molecular weights(M_n=750,2000 and 4000 g/mol)were synthesized.For the first time,long-chain branches were introduced into the polybutene-1 backbone.With respect to the linear homopolymer,incorporation of trimethylsilyl group decreases the cooling crystallization temperature(T_c),whereas presence of the long PEG grafts unexpectedly elevates T_c.For isothermal crystallization,a critical temperature was found at 70°C,below which all PB-PEG copolymers have faster crystallization kinetics than PB.The subsequent melting process shows that these isothermally-crystallized melting temperatures are lower in PB-PEG than in PB.Moreover,II-I phase transition behavior of copolymers is also dependent on the length of PEG grafts.When the form II obtained from isothermal crystallization at60°C was annealed at 25°C,PB-PEG-750 with the shortest PEG grafts of M_n=750g/mol could have the faster transition rate than PB.However,PB-PEG-750 exhibits a negative correlation between transition rate and crystallization temperature.Differently,in PB-PEG copolymers with PEG grafts M_n=2000 and 4000 g/mol,transition rates rise with elevating crystallization temperature,which is similar with homopolymer PB.