Structure and Properties of Novel Homopolymers and Block Copolymers Synthesized by Ring-Opening Metathesis Polymerization or Chain Shuttling Polymerization

Abstract

In this thesis, the material properties of novel homopolymers and block copolymers, synthesized by either ring-opening metathesis polymerization (ROMP) or chain shuttling polymerization, are examined. For the homopolymers, their glass transition temperatures (Tg) are compared, to probe the impacts of monomer <italic>endo</italic>/<italic>exo</italic> ratio, ROMP initiator type, and backbone and sidegroup saturation. For the block copolymers, their melt and solid-state morphologies are investigated using various X-ray scattering techniques.

Novel polymers of 5-phenyl-2-norbornene (PhNb) are synthesized using ROMP. A comparison of the polymer Tg values reveals that varying the ROMP initiator type, polymerization-rate-regulating phosphine concentration, and monomer <italic>endo</italic>/<italic>exo</italic> ratio all result in negligible effects on polymer Tg. In contrast, saturation of the polymer backbone and/or sidegroup changes the polymer's Tg significantly: saturation of the backbone produces a 17 &degC decrease in Tg, while saturation of the sidegroups produces a 14 &degC increase in Tg.

Besides the synthesis of novel homopolymers, ROMP is also employed to synthesize double-crystalline block copolymers of linear polyethylene (LPE) and hydrogenated polynorbornene (hPN). The crystallization sequence in hPN/LPE diblocks is determined by time-resolved small-angle (SAXS) and wide-angle X-ray scattering (WAXS), and the structure-templating block is found to switch from hPN to LPE as the diblock molecular weight is reduced. The relative orientation of the LPE and hP crystals is examined either by 2D WAXS on fiber specimens (higher molecular weight diblocks) or by modeling the changes in SAXS primary peak intensity which occur through the hPN crystal-crystal transition (lower molecular weight diblocks). In both the high- and low-molecular-weight diblocks, a perpendicular stacking of hPN and LPE crystals is confirmed, regardless of the identity of the templating block.

Lastly, the melt and solid-state morphologies of polydisperse olefin diblock and multiblock copolymers, synthesized via chain shuttling polymerization, are examined using 2D synchrotron SAXS/WAXS on flow-aligned specimens. Both the olefin diblocks and multiblocks are found to have lamellar morphologies in the melt which are preserved after crystallization. When comparing the domain spacings of the polydisperse block copolymers to those of their near-monodisperse counterparts, significant domain swelling is observed in both the olefin diblocks (3x increase) and multiblocks (5x increase), attributed to interblock phase mixing resulting from the large polydispersity. The extensive mixing between the hard and soft blocks also results in the observation of "pass-through" crystallization, where short hard blocks dissolved in the soft-block-rich domains allow the hard block crystallization to proceed across the lamellar domain interfaces. Interestingly, despite the interblock phase mixing, the lamellar melt morphology is still well preserved in the solid-state, and the polyethylene crystals show preferred orientation (observed in multiblocks where hard block crystallinity is sufficiently high) similar to that observed in crystals confined between glassy lamellae.