Crystalline Structures and Transitions in Chemically Recyclable Poly(oligocyclobutane): Monomer Sequence and Tacticity*

Chain extension of telechelic (1,n′-divinyl)oligocyclobutane (DVOCB) oligomers using acyclic diene metathesis yields pDVOCB, a new class of semi-crystalline polyolefin. At temperatures below its melting point (Tm), pDVOCB exhibits a crystal-crystal transition (Tcc) in which pDVOCB chains become rotationally disordered around the chain axis. These transitions are examined in a series of pDVOCB polymers of varying oligomeric repeat unit, manifesting as a reduction in both Tm and Tcc with decreasing oligomer length. The influence of cis and trans content on pDVOCB phase behavior is investigated through saturation of the pDVOCB backbone to achieve HpDVOCB. Hydrogenation leads to improved stability of the HpDVOCB polymorphs, as reflected by a significant increase in both Tcc and Tm. These experimental results are complemented using simulations, providing insights into the effects of chain sequence and dispersity on pDVOCB crystalline behavior. Their crystallization behavior is key to their chemical solubility, which in turn determines the depolymerization efficacy. Thus, understanding these behaviors may guide polymer design and expand our control over the depolymerization potential of these chemically recyclable polyolefins.