Unusual II-I Phase Transition Behavior of Polybutene-1 lonomers in the Presence of Long-Chain Branch and Ionic Functional Groups

The mutual effects of long-chain branch and ionic functional groups on polybutene-1 (PB-1) phase transition from tetragonal form II into hexagonal form I of polybutene-1 were investigated using differential scanning calorimetry and various thermal protocols. The novel butene-1/11-iodo-1-undecene (PB-IUD) copolymer was synthesized to incorporate the long-chain branches, and its iodine groups were reacted as the active sites to introduce ionic functional groups with BF4-, Tf2N-, and PF6- counterions. To the best of our knowledge, this is the first work to introduce physical ionic bonding into polybutene-1 (PB-1) ionomers and explore the affected phase transition. The results show that compared with the linear homopolymer, the long-chain branch largely retards the II-I phase transition of the PB-IUD copolymer. Unexpectedly, after introducing the ionic functional groups, ionomers have significantly accelerated transition with respect to reference PB-IUD, although they have exactly the same branching densities, This II-I phase transition of the ionomer can even happen at the crystallization temperature, where there is actually no cooling step to provide internal thermal stress. This indicates that additional crystallization-associated internal stress may be generated in ionomers for triggering form I nucleation. Moreover, the correlations of transition kinetics with annealing and crystallization temperatures were explored in depth. Ionomer phase transition can happen in a broad temperature range, which covers from the glass-transition temperature to high temperatures close to the melting region. Utilizing a stepwise annealing protocol, it was found that this broad transition temperature window originates from the persistent nucleation ability at elevated temperatures. On the other hand, ionomer transition kinetics increases with decreasing crystallization temperature, which, however, is opposite to that of the homopolymer. Based on this, a continuous cooling protocol was proposed and verified capable of endowing the branched ionomers with transition faster than the homopolymer.

利用差示扫描量热法和各种热程序，研究了长链支链和离子官能团对聚丁烯 - 1（PB - 1）从四方晶型II向六方晶型I转变的相互影响。合成了新型的丁烯 - 1/11 - 碘 - 1 - 十一碳烯（PB - IUD）共聚物以引入长链支链，并将其碘基团作为活性位点与BF₄⁻、Tf₂N⁻和PF₆⁻反离子反应引入离子官能团。据我们所知，这是首次将物理离子键引入聚丁烯 - 1（PB - 1）离聚物并探索其受影响的相变的工作。结果表明，与线性均聚物相比，长链支链在很大程度上延缓了PB - IUD共聚物的II - I相变。出乎意料的是，在引入离子官能团后，尽管离聚物与参考的PB - IUD具有完全相同的支化密度，但离聚物相对于参考的PB - IUD相变显著加快。这种离聚物的II - I相变甚至可以在结晶温度下发生，而在该温度下实际上没有冷却步骤来提供内部热应力。这表明离聚物中可能会产生额外的与结晶相关的内部应力以触发I型晶核的形成。此外，还深入探讨了转变动力学与退火温度和结晶温度的相关性。离聚物相变可以在很宽的温度范围内发生，范围从玻璃化转变温度到接近熔融区域的高温。利用逐步退火程序，发现这种宽的转变温度窗口源于高温下持续的成核能力。另一方面，离聚物转变动力学随着结晶温度的降低而增加，然而这与均聚物的情况相反。基于此，提出并验证了一种连续冷却程序，该程序能够使支化离聚物比均聚物具有更快的转变。