Abstract/Details

Synthesis and characterization of novel thermoplastic elastomers employing polyhedral oligomeric silsesquioxane physical crosslinks


2008 2008

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Abstract (summary)

Polyhedral oligomeric silsesquioxanes (POSS) are molecularly precise isotropic particles with average diameters of 1-2 nm. A typical T 8 POSS nanoparticle has an inorganic Si8O12 core surrounded by eight aliphatic or aromatic groups attached to the silicon vertices of the polyhedron promoting solubility in conventional solvents. Previously, efficient synthetic methods have been developed whereby one of the aliphatic groups on the periphery is substituted by a functional group capable of undergoing either homo- or copolymerization. In the current investigations, preparative methods for the chemical incorporation of POSS macromonomers in a series elastomers have been developed.

Analysis of the copolymers using WAXD reveals that pendant POSS groups off the polymer backbones aggregate, and can crystallize as nanocrystals. From both line-broadening of the diffraction maxima, and also the oriented diffraction in a drawn material, the individual POSS sub-units are crystallizing as anisotropically shaped crystallites. The formation of POSS particle aggregation is strongly dependent on the nature of the polymeric matrix and the POSS peripheral group. X-ray studies show aggregation of POSS in ethylene-propylene elastomers occurred only with a phenyl periphery, whereas POSS particles with isobutyl and ethyl peripheries disperse within the polymer matrix. By altering the polymer matrix to one containing chain repulsive fluorine units, aggregation is observed with both the phenyl and isobutyl peripheries. Altering the polymer chain to poly(dimethylcyclooctadiene), POSS aggregates with isobutyl, ethyl, cyclopentyl, and phenyl peripheries.

The formation of POSS nanocrystals increases the mechanical properties of these novel thermoplastic elastomers, including an increase in the tensile storage modulus and formation of a rubbery plateau region. Tensile tests of these elastomers show an increase in elastic modulus with increasing POSS loading. The elongation at break was as high as 720%. Cyclic tensile test show some hysteresis of the elastomers. However, the curves show Mullins effect behavior, commonly seen in elastomers. Elastomers with POSS dispersion, however, show poor mechanical properties. These results demonstrate the novel material property gains by the incorporation and aggregation of POSS in thermoplastic elastomers, as well as the influence of the POSS periphery.

Indexing (details)


Subject
Polymers;
Materials science
Classification
0495: Polymers
0794: Materials science
Identifier / keyword
Applied sciences; Pure sciences; Polyhedral oligomeric silsesquioxanes; Silsesquioxane; Thermoplastic elastomers
Title
Synthesis and characterization of novel thermoplastic elastomers employing polyhedral oligomeric silsesquioxane physical crosslinks
Author
Seurer, Bradley
Number of pages
150
Publication year
2008
Degree date
2008
School code
0118
Source
DAI-B 69/08, Dissertation Abstracts International
Place of publication
Ann Arbor
Country of publication
United States
ISBN
9780549663607
Advisor
Coughlin, E. Bryan
Committee member
Crosby, Alfred; Winter, Henning
University/institution
University of Massachusetts Amherst
Department
Polymer Science & Engineering
University location
United States -- Massachusetts
Degree
Ph.D.
Source type
Dissertations & Theses
Language
English
Document type
Dissertation/Thesis
Dissertation/thesis number
3315482
ProQuest document ID
230683091
Copyright
Database copyright ProQuest LLC; ProQuest does not claim copyright in the individual underlying works.
Document URL
http://search.proquest.com/docview/230683091
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