Effect of Reaction Temperature on Tacticity in Polymerization of Methyl Methacrylate: A Study by Nuclear Magnetic Resonance Spectroscopy

Hypothesis: 

In the synthesis of vinyl polymers, one of the important parameters that play a significant role in the physical-mechanical properties is the tacticity of monomers within the polymer chain. Polymethyl methacrylate is considered one of the important industrial polymers. The method of its synthesis can have a major effect on this parameter and finally on the final properties. One of the parameters that has a significant effect on the stereoregularity of this polymer is the reaction temperature.

The poly methyl methacrylate was synthesized at three different temperatures of 50, 150, and 250 °C via bulk thermal polymerization method. The most important instrument that can be used to study tacticity order is nuclear magnetic resonance spectroscopy. The tacticity of the polymethyl methacrylate (PMMA) was investigated and studied through alpha-methyl protons splitting and alpha-methyl and carbonyl carbons splitting, respectively, by proton (1HNMR) and carbon (13CNMR) nuclear magnetic resonance spectroscopy in deuterated chloroform (CDCl3) and deuterated tetrahydrofuran (THF-d8). The assignment of all stereosequences at triad level for alpha-methyl proton and pentad level for alpha - methyl carbon and carbonyl carbon were carried out by liquid nuclear magnetic resonance spectroscopy in deuterated chloroform. Bernoullian and first-order Markov statistics models were calculated for the synthesized sample and compared with the experimental results.

The results indicated that probability of meso (Pm) was increased by increasing the methyl methacrylate polymerization temperature. The corresponding probability of meso values determined for synthesized polymethyl methacrylate at 50, 150, and 250°C were 0.203, 0.274, and 0.356, respectively. Finally, the effect of tacticity on glass transition temperature using differential scanning calorimetry (DSC) is discussed. The temperature glassy (Tg) values by DSC results were shown that the synthesized polymethyl methacrylate at 50, 150, and 250°C had 126.0, 125.1 and 102.9 oC, respectively.