Counit Inclusion in Hydrogenated Polynorbornene Copolymer Crystals

• Published in: Macromolecules 2013-12, Vol.46 (23), p.9288-9295
• Main Authors: Showak, Michael T, Burns, Adam B, Stella, Andrew J, Register, Richard A
• Format: Article
• Language: English
• ISSN: 0024-9297; 1520-5835
• DOI: 10.1021/ma401834t

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 T m 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 T m, at a temperature T cc; comonomer incorporation reduces T cc more rapidly than it reduces T m, 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.