Thesis (MSc (Chemistry and Polymer Science))--University of Stellenbosch, 2006. / Polyurethanes (PUs) are finding increasing application and use in many industries due
to their advantageous properties, such as a wide range of flexibility combined with
toughness, high chemical resistance, excellent weatherability, and very low temperature
cure. PUs do however have some disadvantages, for instance, PU is considered an
expensive polymer, especially when considered for solvent based adhesives. A
motivation for this study was to consider a largely unstudied area of PU chemistry by
combining PUs with polyacrylates. Polyacrylates are well known adhesives and can
carry specific functionality, but have the disadvantage that their flexible backbones
impart limited thermal stability and mechanical strength. In this study PU was
incorporated into acrylates in an effort to obtain acrylate-g-urethanes with good
properties. The mode of incorporation chosen was urethane macromonomers (UMs), a
hardly mentioned substance in literature, yet one deserving investigation.
UMs having different urethane chain lengths (X) were synthesized by the polyaddition
polymerization of toluene diisocyanate (TDI) and ethylene glycol (EG) by the prepolymer
method, which was terminated by 2-hydroxy ethyl methacrylate (HEMA) and
isopropanol. The UMs were characterized by Fourier-transform infrared spectroscopy
(FTIR), proton NMR (1H NMR), carbon NMR (13C NMR), gel permeation chromatography
(GPC), thermogravimetric analysis (TGA) and dynamic mechanical analysis (DMA).
Various percentages of the respective UMs (0-40 wt % according to acrylate monomers)
were then incorporated into methyl methacrylate (MMA) and into normal butyl
methacrylate (n-BMA) backbones via solution free radical copolymerization. The
resulting methyl methacrylate-urethane graft copolymers (PMMA-g-urethane) and
normal butyl methacrylate-urethane graft copolymers (n-PBMA-g-urethane) were
characterized by GPC, 1H NMR and 13C NMR, FTIR, TGA, and DMA. Phase separation
between the urethane segment and acrylate segment in the yield of graft
copolymerization products was investigated by DMA and transmission electron
microscopy (TEM).
As the concentration of the UMs in the free radical copolymerization feed increased,
lower yields of both graft copolymers PMMA-g-urethane and n-PBMA-g-urethane were observed and more UM was incorporated into the PMMA and n-PBMA backbones. It
also was found that the thermal stability of the PMMA-g-urethane and n-PBMA-gurethane
copolymers increased with increasing UM concentration.
DMA results showed that in most graft copolymer products the two respective
component parts of PMMA-g-urethane or n-PBMA-g-urethane were completely
compatible as only one Tg was observed. Two glass transitions, at temperatures of 22.0
and 76.0 oC, corresponding to the n-PBMA and urethane moieties, were observed when
the chain length of the UMs was increased from X=4 to X=32 [the amount of this UM
used in the copolymerization feed was increased to 40%, and microphase separation
was indicated].
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:sun/oai:scholar.sun.ac.za:10019.1/1589 |
| Date | 12 1900 |
| Creators | Alshuiref, Abubaker |
| Contributors | Sanderson, R. D., Seboa, S., University of Stellenbosch. Faculty of Science. Dept. of Chemistry and Polymer Science. |
| Publisher | Stellenbosch : University of Stellenbosch |
| Source Sets | South African National ETD Portal |
| Language | English |
| Detected Language | English |
| Type | Thesis |
| Format | 2165971 bytes, application/pdf |
| Rights | University of Stellenbosch |
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