Structure-property relationships for n-alkyl-isocyanate-containing polymers.

Poly(n-hexyl isocyanate) (PHIC), poly(n-butyl-isocyanate) (PBIC), poly(n-butyl-co-cyclohexyl isocyanate) (PBCHIC), poly(n-hexyl isocyanate-b-isoprene) (HI), poly(n-butyl isocyanate-b-isoprene) (BI) and poly(n-hexyl isocyanate-b-isoprene- b-styrene) (MS) were synthesized and characterized with respect to composition, molecular Weight and polydispersity. PHIC, HI and HIS were found to be lyotropic liquid crystalline whereas PBIC, PBCHIC and BI were found to be non-lyotropic. A lyotropic-nematic liquid crystalline phase diagram was determined for the PHIC/xylene system. A novel and reversible electric-field-induced biphasic-paranematic phase transition was found for the PHIC/xylene system from the dynamics of topological defects. The electric-field-induced phase diagram for PHIC/xylene agreed with the theoretically predicted field-induced phase diagram of Khokhlov and Semenov for semiflexible-persistent polymers. The dielectric characteristics, steady-state electrically induced birefringence and steady-state electroheological (ER) activity of PHIC, PBIC and PBCHIC solutions were compared as a function of polymer concentration. The role of lyotropic liquid crystalline ordering in the functional ER mechanism of poly( n-hexyl isocyanate) solutions is presented. PBCHIC was found to thermally decompose by a first-order rate process which became slower with increasing cyclohexyl isocyanate content from thermal gravimetric analysis. Competition between monomer dissociation and degradative trimerization as well as a non-alternating sequence distribution were determined for PBCHIC from direct pyrolysis/mass spectrometry. The Arrhenius activation energy, pre-exponential factor and entropy for diffusion and evaporation of xylene from PHIC, were found to be functions of initial polymer concentration whereas the intrinsic diffusion coefficient of the solvent was found to be independent of initial polymer concentration. The cross polarized/magic angle spinning solid state 13C-NMR spectra of PBCHIC revealed perturbations to the helical polymer backbone structure. The wide angle x-ray diffraction pattern for the n-hexyl isocyanate containing polymers was found to be a function of DC electric field strength applied during isothermal crystallization from solution. The PHIC, backbone was protonated on a small percentage of monomer units by reaction with BF3 and H2O with no detectable chain scission but a loss of lyotropic liquid crystallinity. Methyl-N-(1,1-dimetboxyperfluroro- n-heptyl)carbamate was isolated from the reaction of perfluoro- n-heptyl isocyanate with excess methanol. 2,5-Dioxahexyl isocyanate and 2,5,8-trioxanonyl isocyanate were synthesized.PhDApplied SciencesMaterials sciencePhysical chemistryPolymer chemistryPure SciencesUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/131596/2/9929778.pd