Crystalline−Crystalline Diblock Copolymers of Linear Polyethylene and Hydrogenated Polynorbornene

Abstract

Double-crystalline diblock copolymers of linear polyethylene (LPE) and hydrogenated polynorbornene (hPN) are synthesized, and their crystallization is examined. LPE and hPN homopolymers are both highly crystalline, with similar melting points near 150 °C and χhPN/LPE = 0.02. For symmetric diblocks, even when moderately segregated, crystallization of hPN breaks out of the melt microdomains to create volume-filling spherulites. The LPE block subsequently crystallizes between the hPN crystallites, with the hPN and LPE crystal stems oriented orthogonally. At shallow undercoolings, crystallization proceeds in two distinct steps, but at deeper undercoolings, only a single process is observed, following the temperature dependence of hPN crystallization. At these deeper undercoolings, crystallization of hPN initiates LPE crystallization so that the two processes are nearly simultaneous. By changing the block ratio, the crystallization behavior can be broadly tuned: in hPN-rich diblocks, the two crystallization processes are well-separated at any temperature, while in LPE-rich diblocks, the LPE block crystallizes first.

Handspinning Enabled Highly Concentrated Carbon Nanotubes with Controlled Orientation in Nanofibers

“…Broad peaks were observed at 2θ = 13° from both the handspun and electrospun samples, typically indicating semi-crystalline regions attributable to the ordering of the polymer chains by hydrogen bonding3435. Although both ES and HS fibers had relatively low crystallinity due to the rapid fabrication process, it was noted that the handspun fiber exhibited lower intensity than the electrospun fiber, and this was attributed to the decrease of the overall crystallinity of the PVAc/CNT nanofibers36; in other words, the handspun sample had a greater amorphous portion. There could be two scenarios to explain the phenomena.…”

Effect of block asymmetry on the crystallization of double crystalline diblock copolymers

“…[21][22][23][24][25][26][27][28][29] During crystallization, high melting block crystallizes first creating spatial confinement for the crystallization of the low melting block resulting less crystallinity in the second block. [21][22][23][24][26][27][28][29][30][31][32][33][34] However, depending on the nature of the blocks in diblock copolymer, they may crystallize simultaneously (viz., coincident crystallization). 28,32,[35][36][37][38] Primarily, the interplay between crystallization and microphase separation plays a crucial role in dictating the final crystal morphology of the semi crystalline materials.…”

“…In hPN rich diblock copolymer, hPN crystallizes first whereas in LPE rich diblock copolymer, LPE crystallizes first followed by the hPN block. 33 Small angle X-ray scattering (SAXS) and wide angle X-ray scattering (WAXS) studies showed that the crystal orientation is equally influenced by the block length ratio. The first crystallizable block creates a structural template in which the crystallization of the second block is confined with perpendicular orientation.…”

Crystallization of Double Crystalline Diblock Copolymer by Dynamic Monte Carlo Simulation

“…Therefore, an intense study associated with the crystallization of double crystalline diblock copolymer is propitious as the system having competitive crystallization along with microphase separation which primarily determines the final crystal morphology. Usually the block with higher melting point crystallizes first followed by the other block having lower melting points resulting sequential crystallization in diblock copolymer . For example, the PCL‐ b ‐PE diblock copolymer exhibits sequential crystallization as the melting temperature of PE block (viz., 96 °C) is higher than the PCL block (viz., 56 °C).…”