College of Computer, Mathematical & Natural Sciences
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Effective October 4, 2010, the University established the College of Computer, Mathematical, and Natural Sciences (CMNS) by integrating the former colleges of Chemical and Life Sciences (CLFS) and Computer Mathematical and Physical Sciences (CMPS).
The collections in this community comprise faculty research works, as well as graduate theses and dissertations.
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Browsing College of Computer, Mathematical & Natural Sciences by Subject "1, 6-Heptadiene"
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Item On the Cyclopolymerization of 1,6-Heptadienes, and their Role as Poly(methylenecycloalkane)s in Stereoengineering and Block Copolymers(2015) Crawford, Kaitlyn; Sita, Lawrence R; Chemistry; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The research presented herein, addresses key issues of homogeneous Group 4 single-site coordination polymerization (CP) catalysts for the production of polyolefins and polyolefin-like materials. Specifically, this research moves beyond the `one-catalyst one-material' paradigm to afford an array of amorphous polyolefin materials with high Tg from a single monomer. The multitude of microstructurally distinct materials available from a single starting olefin is attributed to stereoengineering: a technique, which reduces stereoblock length in a highly controlled fashion while retaining regioselectivity. The precatalysts employed in this work are previously reported Group 4 CS-symmetric or C1-symmetric pentamethylmonocyclopentadienyl amidinate complexes with the general formula {(η5-C5R5)M[N(R1)C(R2)N(R3)]-(Me2)} (M = Zr, Hf, R = alkyl, Me = methyl), which are activated by cocatalysts such as N,N-dimethylanilinium tetrakis(pentafluorophenyl)-borate ([PhNMe2H][B(C6F5)4]). Living CP of 1,6-heptadiene and stereoengineering of the subsequent poly(methylenecycloalkane)s with the above complexes reveal a variety of stereochemically controlled, yet amorphous, poly(methylene-1,3-cyclohexane) (PMCH) materials with Tg values as high as 101 °C. Similar polymerization techniques have been applied, for the first time with Sita group complexes, towards the CP of the heteroatom-olefins such as diallyldimethylsilane (DAS). The controlled CP and stereoengineering of DAS resulted in amorphous poly(3,5-methylene-1,1-dimethyl-1-silacyclohexane) materials with Tg values as high as 127 °C. The living character and tunable stereoblock lengths of PMCH provided the opportunity to explore the high Tg polyolefin as the `hard' domain (A segment) in pure polyolefin AB block copolymers, BCPs. Specifically, amorphous AB diblock copolymers were synthesized using poly(1-hexene) as the `soft' B block to afford a series of microphase-separated morphologies without the deleterious effects of crystallization. Microphase-separated morphologies for were also observed for ABA triblock copolymers using atactic polypropylene as the `soft' segment (B block) and primary component. The latter BCPs were found to exhibit thermoplastic elastomeric properties. The work described in this document provides a foundation for the further expansion of the currently-limited pool of monomers to include heteroatom-olefins for CP with the aforementioned Group 4 transition metal complexes. Moreover, the formation of well-defined pure polyolefin block copolymers serve as an important contribution to the development of new polyolefin architectures.