Compounds of palladium with many different chelated bisphosphine ligands were investigated for their catalysis of alternating copolymerization of propylene (P) with carbon monoxide (CO). The bisphosphine structure and chelate ring size influence strongly the activity, regio- and stereo-selectivity of the catalysts. Molecular mechanics calculations on $\pi$-olefin complex showed that the non-bonded interaction between propylene and the ligands on Pd is both regio- and stereo-selective. Electronic factor and presence of chiral center were crucial for the regio- and stereo-regularity control of the catalyst, respectively. Primary insertion is more probable than secondary insertion, and the enantioselective catalysts favor the meso enchainment of propylene. The crystalline copolymer has the hexagonal unit cell structure with a = b = 15.5 A, and c = 8.97 A. The single crystalline copolymer chain is a 3$\sb1$ fold helix. GC-MS of oligomers showed that most chains are initiated by Pd-H species; and $\beta$-hydrogen elimination is the dominant chain termination process. The anaerobic photodegradation behaviors of bulk alternating copolymers of P-CO and E-CO have been studied by irradiation with 2537 A light. Photolysis of the former resulted in weight loss, molecular weight depression, cross-linking, and the formation of hydroxyl and terminal vinyl groups. The room temperature quantum yields of chain scission and Norrish type II reactions were found to be 0.015 $\pm$ 0.002 and 0.011 $\pm$ 0.002. P-CO alternating copolymer was blended with poly(methyl methacrylate) (PMMA) by solution precipitation. Various aspects of blends behavior were studied by DSC, DMTA, DETA, FTIR, and CP-MAS solid state NMR. The blends exhibited single $T\rm\sb{g}$'s at all compositions, which is an indication of the miscible blends. $\beta$-relaxation of P-CO copolymer was detected by DETA at $-65\sp\circ$C for the first time. The measurement of rotating frame NMR relaxation time, $\rm T\sb{1\rho}\sp{H}$, showed that the average distance between P-CO and PMMA is less than 30 A.
| Identifer | oai:union.ndltd.org:UMASS/oai:scholarworks.umass.edu:dissertations-8928 |
| Date | 01 January 1994 |
| Creators | Xu, Frank Yi |
| Publisher | ScholarWorks@UMass Amherst |
| Source Sets | University of Massachusetts, Amherst |
| Language | English |
| Detected Language | English |
| Type | text |
| Source | Doctoral Dissertations Available from Proquest |
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