In this thesis, I describe experiments that provide a new and deeper understanding of factors that affect polymer diffusion in acrylic latex films. This is the step that leads to the growth of mechanical properties of these films. Polymer diffusion was studied by fluorescence resonance energy transfer (FRET) in films prepared from dye-labeled latex particles.
Poly(n-butyl acrylate-co-methyl methacrylate) [P(BA-MMA)] was chosen for the study of copolymer composition on the polymer diffusion rate. Four sets of P(BA-MMA) copolymers were prepared from various weight ratios of BA/MMA. Polymer diffusion was monitored as a function of annealing temperature, and apparent diffusion coefficients (Dapp) were calculated from the FRET data, using a simple diffusion model. The temperature dependence of polymer dynamics (G’, G”) obtained by linear rheology measurements is in good agreement with the temperature dependence of Dapp. Increasing the BA content of the copolymer led to an apparent increase in long-chain branching, which is reflected in both the time dependence of Dapp and in the dynamic moduli measurements.
To study the effect of branching on polymer diffusion rates, latex particles comprised of branched poly(n-butyl methacrylate) (PBMA) were prepared. The degree of branching was controlled by adding various amounts of bisphenol A dimethacrylate as a branching agent, plus 1-dodecanethiol as a chain transfer agent to prevent gel formation and to control the polymer molecular weight. The results of rheology (G’, G”) measurements are consistent with the absence of entanglement in these polymers. After correcting for the effects of Tg, by comparing results at a constant T- Tg, ET data show that the PBMA with the highest degree of branching had the highest diffusivity.
In a separate set of experiments I tested the effect of incorporating the highly branched PBMA (HB-PBMA) into P(BA-MMA) dispersions to examine its influence on polymer diffusion in the latex films. Three different approaches were taken to combine these different polymers: latex blends, using HB-PBMA seeds in the synthesis of P(BA-MMA) by semicontinuous emulsion polymerization, and dissolving HB-PBMA in the mixture of BA and MMA for latex particles prepared by miniemulsion polymerization. ET studies indicate that HB-PBMA significantly enhances polymer diffusion rate, comparable with TexanolTM, a volatile organic coalescing agent. Tensile tests show that the films containing HB-PBMA have significant higher mechanical properties than the films containing TexanolTM.
| Identifer | oai:union.ndltd.org:TORONTO/oai:tspace.library.utoronto.ca:1807/26468 |
| Date | 08 March 2011 |
| Creators | Liu, Yuanqin |
| Contributors | Winnik, Mitchell A. |
| Source Sets | University of Toronto |
| Language | en_ca |
| Detected Language | English |
| Type | Thesis |
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