Four potential new monomers were prepared, all of which were structural analogues of BisGMA (2,2-bis(4-(2-hydroxy-3-methacryloxyprop-1-oxy) phenyl)propane). The synthesis of these tetrafunctional dimethacrylate monomers was based on structural modifications of Bis-GMA in the core and the side chain and required a two-step reaction. The first step was propoxylation or ethoxylation of the bisphenols and the second step was the methacrylation of the resulting products. The core structures are designated by Bis-A for isopropylidene and 6F for hexafluoropropyl. The side chain structures were designated on the basis of the pendant side chains in the glycidyl moiety as -OH, -H, and -CH3 from the epichlorohydrin, ethyleneoxide, and propyleneoxide reaction products with the bisphenols, respectively. Bis-GMA was commercially obtained and used as a standard for comparison of the experimental monomers. All the monomers were prepared by the following general procedure of propoxylation or ethoxylation of the biphenols followed by methacrylation. They were characterized by NMR, FTIR, DSC and Cone and Plate Viscometry. All the experimental monomers exhibited lower viscosities and glass transition temperatures than the control, which was attributed to the elimination of the hydrogen bonding. The monomers were photopolymerized in a differential scanning calorimetry modified with an optics assembly (DPA 7; Double Beam Photocalorimetric Accessory) to study the photo-induced crosslinking reactions. The influence of monomer structure, temperature, light intensity, and initiator concentration on the photopolymerization kinetics of ethoxylated and propoxylated dimethacrylates was investigated by isothermal DSC. The DSC curves showed a rapid increase in rate due to the Trommsdorff effect, and then a decline due to the decrease of monomer concentration and the autodeceleration effect. The monomers with lower viscosities and glass transition temperatures exhibited higher conversions of the double bonds. The final extent of conversion increased with curing temperature, light intensity and initiator concentration. The radiation intensity exponent varied from 0.68 (BisGMA) to 0.74 for the ethoxylated 6F system. The initiator exponent were varied from 0.34 (for BisGMA) to 0.44 for the propoxylated BisA system. The ratio of the reaction rate constant (kt/kp) was calculated for PropBisAdm from both steady-state and non steady-state conditions. The effect of dilution on photopolymerization kinetics of BisGMA/triethyleneglycoldimethacrylate (TEGDMA) mixtures was also studied by isothermal photo-DSC. Dilution with TEGDMA significantly reduced the viscosity and glass transition temperatures of the mixtures due to the increase in the flexibility. The extent of polymerization increased with increasing TEGDMA and curing temperature. The calculation of ratio of rate constants (kt/kp) was also determined and the significance was discussed herein. / Master of Science

A distribuição de pesos moleculares (DPM) de um polímero afeta as propriedades mecânicas, térmicas e reológicas do material. Além disso, a análise em tempo real de uma reação de polimerização é uma tarefa complicada e, consequentemente, os procedimentos de controle devem ser baseados em valores gerados pelos modelos. Por isso, é extremamente importante ter dados confiáveis sobre distribuições de pesos moleculares, melhorar a eficiência dos métodos existentes e desenvolver novos métodos capazes de prever as heterogeneidades das reações de polimerização. Experimentalmente, a DPM pode ser obtida usando técnicas como a cromatografia de permeação em gel. Para predizer a DPM, vários métodos foram desenvolvidos nas ultimas décadas. Um dos principais é o dos momentos estatísticos, baseado em conceitos puramente estatísticos, que não conseguem descrever completamente a DPM. Além disso, as aproximações com método de Galerkin usam polinômios ortogonais - no caso especifico polinômios de Laguerre - cujos coeficientes são calculados empregando os momentos estatísticos e a distribuição é gerada resolvendo um número de equações definido pelo usuário, relacionado à precisão desejada. Enfim, o método das funções geradoras de probabilidades foi utilizado para prever as DPMs, porém necessitando uma inversão da transformada de Laplace, que introduz problemas numéricos nem sempre possíveis de serem resolvidos. No presente trabalho, o sistema rigoroso de equações diferenciais ordinárias foi resolvido, com objetivo de reduzir as imprecisões e as limitações introduzidas pelas aproximações. Obter diretamente a DPM completa requer a resolução de um sistema contendo cerca de 2Nmax até 3Nmax equações diferenciais ordinárias rígidas, tarefa que há alguns anos era inviável devido a limitações relacionadas à capacidade de cálculo. Foi modelada a DPM para uma reação de polimerização radicalar livre de estireno e de metacrilato de metila. Um interesse especial foi dado à taxa de terminação que é, no momento, um dos temas mais investigados em polimerização por radicais livres. Os resultados das simulações foram comparados com dados experimentais tirados de reatores convencionais e, subsequentemente, com dados experimentais provenientes de um millireactor não convencional. / It is well known that the molecular weight distribution (MWD) of a synthetic polymer affects its mechanical, thermal and rheological properties. Furthermore, the on-line analysis for polymerization reaction is a difficult task and, consequently, the control procedures must rely on values given by models. As such, it is extremely important to have reliable data on the MWD, improve the efficiency of existing methods and develop new ones to predict the heterogeneities of polymerization reactions. Experimentally, the MWD can be obtained using techniques such as Gel Permeation Chromatography (GPC). To predict the MWD, many methods have been developed over the last decades. One of the main methods is the statistical moment treatment, which is based on a pure statistical concept and do not describe the whole MWD. Moreover, Galerkin approximation uses orthogonal polynomials -in general Laguerre polynomials- whose coefficients are calculated exploiting the statistical moment definition and the distribution is generated by solving a user-defined number of equations based on the desired precision. Finally, probability-generating functions that have been used to predict MWDs require Laplace transforms inversions, introducing numerical issues that must be bypassed and are not always solvable. It has been decided to base the approach without adopting any of these methods but directly solving the rigorous ordinary differential equation (ODE) system in order to reduce the inaccuracies and the limitations introduced by approximations. The direct obtention of the MWD requires the resolution of a system containing approximately 2Nmax up to 3Nmax stiff ODE equations that, a few years ago, was unfeasible due computational time limitations. The MWDs for a free radical styrene polymerization system and a methyl methacrylate system have been modeled. A special focus was given to the termination rate constant, which is, at the present, one of the most investigated topics in free radical polymerization. The results of the simulations were compared to experimental data taken from conventional reactors and, subsequently, to experimental data coming from an unconventional millireactor.

A distribuição de pesos moleculares (DPM) de um polímero afeta as propriedades mecânicas, térmicas e reológicas do material. Além disso, a análise em tempo real de uma reação de polimerização é uma tarefa complicada e, consequentemente, os procedimentos de controle devem ser baseados em valores gerados pelos modelos. Por isso, é extremamente importante ter dados confiáveis sobre distribuições de pesos moleculares, melhorar a eficiência dos métodos existentes e desenvolver novos métodos capazes de prever as heterogeneidades das reações de polimerização. Experimentalmente, a DPM pode ser obtida usando técnicas como a cromatografia de permeação em gel. Para predizer a DPM, vários métodos foram desenvolvidos nas ultimas décadas. Um dos principais é o dos momentos estatísticos, baseado em conceitos puramente estatísticos, que não conseguem descrever completamente a DPM. Além disso, as aproximações com método de Galerkin usam polinômios ortogonais - no caso especifico polinômios de Laguerre - cujos coeficientes são calculados empregando os momentos estatísticos e a distribuição é gerada resolvendo um número de equações definido pelo usuário, relacionado à precisão desejada. Enfim, o método das funções geradoras de probabilidades foi utilizado para prever as DPMs, porém necessitando uma inversão da transformada de Laplace, que introduz problemas numéricos nem sempre possíveis de serem resolvidos. No presente trabalho, o sistema rigoroso de equações diferenciais ordinárias foi resolvido, com objetivo de reduzir as imprecisões e as limitações introduzidas pelas aproximações. Obter diretamente a DPM completa requer a resolução de um sistema contendo cerca de 2Nmax até 3Nmax equações diferenciais ordinárias rígidas, tarefa que há alguns anos era inviável devido a limitações relacionadas à capacidade de cálculo. Foi modelada a DPM para uma reação de polimerização radicalar livre de estireno e de metacrilato de metila. Um interesse especial foi dado à taxa de terminação que é, no momento, um dos temas mais investigados em polimerização por radicais livres. Os resultados das simulações foram comparados com dados experimentais tirados de reatores convencionais e, subsequentemente, com dados experimentais provenientes de um millireactor não convencional. / It is well known that the molecular weight distribution (MWD) of a synthetic polymer affects its mechanical, thermal and rheological properties. Furthermore, the on-line analysis for polymerization reaction is a difficult task and, consequently, the control procedures must rely on values given by models. As such, it is extremely important to have reliable data on the MWD, improve the efficiency of existing methods and develop new ones to predict the heterogeneities of polymerization reactions. Experimentally, the MWD can be obtained using techniques such as Gel Permeation Chromatography (GPC). To predict the MWD, many methods have been developed over the last decades. One of the main methods is the statistical moment treatment, which is based on a pure statistical concept and do not describe the whole MWD. Moreover, Galerkin approximation uses orthogonal polynomials -in general Laguerre polynomials- whose coefficients are calculated exploiting the statistical moment definition and the distribution is generated by solving a user-defined number of equations based on the desired precision. Finally, probability-generating functions that have been used to predict MWDs require Laplace transforms inversions, introducing numerical issues that must be bypassed and are not always solvable. It has been decided to base the approach without adopting any of these methods but directly solving the rigorous ordinary differential equation (ODE) system in order to reduce the inaccuracies and the limitations introduced by approximations. The direct obtention of the MWD requires the resolution of a system containing approximately 2Nmax up to 3Nmax stiff ODE equations that, a few years ago, was unfeasible due computational time limitations. The MWDs for a free radical styrene polymerization system and a methyl methacrylate system have been modeled. A special focus was given to the termination rate constant, which is, at the present, one of the most investigated topics in free radical polymerization. The results of the simulations were compared to experimental data taken from conventional reactors and, subsequently, to experimental data coming from an unconventional millireactor.