Model crystallizable copolymers of norbornene and two 5-alkylnorbornenes were synthesized to investigate the extent and consequences of defect inclusion into hydrogenated polynorbornene (hPN) crystals. Living ring-opening metathesis polymerization yielded narrow-distribution polymers of targeted molecular weights, with modest down-chain compositional gradients controllable through the polymerization conversion; hydrogenation yielded semicrystalline copolymers. When the comonomer was 5-methylnorbornene (MeN), extensive inclusion of MeN units into the hPN crystal was observed; the copolymers showed substantial crystallinities even above 30 mol % MeN, and the dependence of the melting point Tm on crystal thickness followed that for hPN homopolymer. By contrast, when the comonomer was 5-hexylnorbornene, the more usual case of strong exclusion of the counits from the crystal was observed. hPN shows a transition between two crystal polymorphs below Tm, at a temperature Tcc; comonomer incorporation reduces Tcc more rapidly than it reduces Tm, expanding the region over which the high-temperature rotationally disordered polymorph is stable and providing insight into the dependence of the free energy for the two polymorphs on crystal thickness.
All Science Journal Classification (ASJC) codes
- Organic Chemistry
- Materials Chemistry
- Polymers and Plastics
- Inorganic Chemistry