was carried out using a Two-Parameter (TP) scheme. The theoretical-experimental behaviour of A2 in a series of polysiloxanes was investigated considering the effects of the type of substituent on the main chain, molecular conformation, and molecular weight. The results obtained were strongly dependent on the flexibility of the side groups and the molecular weight of the polymer. Within the HW model and TP scheme, the A2 value for poly (dimethylsiloxane) (PDMS1 and PDMS2), poly(diethylsiloxane)and poly(methylhexylsiloxane) agrees with the experimental results obtained through the coupled system (Gel Permeation Chromatography/Light Scattering: GPC/LS). However, the A2 calculated for PDMS3, poly(methylhexadecylsiloxane) (PMHDS) and poly(methylphenylsiloxane) (PMPS) showed a significant difference from the experimental value. On the basis of the theory for the HW model, the deviation in PDMS3 may be due to the effect of the end chains. For PMHDS and PMPS, the model used is outside of the coil limit (validity of TP model). In PMHDS the determination of the (RMSradius)² value from the GPC/LS system is strongly influenced by the interaction between the bulky side group and the main chain, which affects the calculation of A2.]]>
fue llevada a cabo utilizando el esquema de los Dos Parámetros (TP). El comportamiento teórico-experimental del A2 para la serie de polisiloxanos fue investigado considerando los efectos del tipo de grupo lateral unido a la cadena principal de la conformación molecular y del peso molecular del polímero. Los resultados obtenidos muestran una fuerte influencia de la flexibilidad de los grupos laterales y del peso molecular del polímero. Dentro del modelo HW y el esquema TP, el valor del A2 para el poli(dimetilsiloxano) (PDMS1 y PDMS2), poli(dietilsiloxano) y poli(metilhexilsiloxano) se encuentra en buena aproximación con el obtenido a traves del sistema acoplado de Cromatografía de Permeación en Gel/Dispersión de Luz (GPC/LS). Sin embargo, el cálculo del A2 para el PDMS3, poli(metilhexadecilsiloxano) y poli(fenilmetilsiloxano) presenta una significativa diferencia con el valor obtenido experimentalmente. Con base en la teoría del modelo HW, la desviación en el PDMS3 puede provenir de los efectos de los grupos terminales de la cadena de siloxano. Para el PDMHDS y PMPS se utilizó un modelo que se encuentra fuera del límite de ovillo (validez del modelo TP). En PDMHDS, la determinación del tamaño molecular (RMSradius)² a través del sistema acoplado GPC/LS está fuertemente influenciada por la interaccion entre el grupo lateral alquilo más largo y la cadena principal, lo cual afecta el cálculo del A2.]]>
Investigación
Second virial coefficient of a series of polysiloxanes: the effect of side groups and molecular weight
Recibido el 6 de septiembre de 2005A aceptado el 28 de noviembre de 2006
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Abstract
This study reports the results of analyzing the second virial coefficient (A2) in a good solvent for a series of polysiloxane chains in which the pairs of substituents connected to the silicon are CH3, CH3;C2H5, C2H5; CH3, C6H13;CH3, C16H33; and CH3, C6H5. The effect of the side group and molecular weight on A2 was investigated using the Helical Wormlike (HW) chain model. A theoretical analysis of the interpenetration function was carried out using a Two-Parameter (TP) scheme. The theoretical-experimental behaviour of A2 in a series of polysiloxanes was investigated considering the effects of the type of substituent on the main chain, molecular conformation, and molecular weight. The results obtained were strongly dependent on the flexibility of the side groups and the molecular weight of the polymer. Within the HW model and TP scheme, the A2 value for poly (dimethylsiloxane) (PDMS1 and PDMS2), poly(diethylsiloxane)and poly(methylhexylsiloxane) agrees with the experimental results obtained through the coupled system (Gel Permeation Chromatography/Light Scattering: GPC/LS). However, the A2 calculated for PDMS3, poly(methylhexadecylsiloxane) (PMHDS) and poly(methylphenylsiloxane) (PMPS) showed a significant difference from the experimental value. On the basis of the theory for the HW model, the deviation in PDMS3 may be due to the effect of the end chains. For PMHDS and PMPS, the model used is outside of the coil limit (validity of TP model). In PMHDS the determination of the (RMSradius)2 value from the GPC/LS system is strongly influenced by the interaction between the bulky side group and the main chain, which affects the calculation of A2.
Este estudio reporta los resultados del análisis del segundo coeficiente del virial A2 para una serie de cadenas de polisiloxano en las cuales los pares de grupos laterales unidos al silicio son: CH3, CH3; C2H5, C2H5;CH3, C6H13; CH3,C16 H33;CH3 y C6H5. El efecto del grupo lateral y peso molecular en el valor del A2 es analizado a traves del modelo de cadena Helicoidal tipo Gusano (HW). El análisis teórico de la función de interpenetración fue llevada a cabo utilizando el esquema de los Dos Parámetros (TP). El comportamiento teórico-experimental del A2 para la serie de polisiloxanos fue investigado considerando los efectos del tipo de grupo lateral unido a la cadena principal de la conformación molecular y del peso molecular del polímero. Los resultados obtenidos muestran una fuerte influencia de la flexibilidad de los grupos laterales y del peso molecular del polímero. Dentro del modelo HW y el esquema TP, el valor del A2 para el poli(dimetilsiloxano) (PDMS1 y PDMS2), poli(dietilsiloxano) y poli(metilhexilsiloxano) se encuentra en buena aproximación con el obtenido a traves del sistema acoplado de Cromatografía de Permeación en Gel/Dispersión de Luz (GPC/LS). Sin embargo, el cálculo del A2 para el PDMS3, poli(metilhexadecilsiloxano) y poli(fenilmetilsiloxano) presenta una significativa diferencia con el valor obtenido experimentalmente. Con base en la teoría del modelo HW, la desviación en el PDMS3 puede provenir de los efectos de los grupos terminales de la cadena de siloxano. Para el PDMHDS y PMPS se utilizó un modelo que se encuentra fuera del límite de ovillo (validez del modelo TP). En PDMHDS, la determinación del tamaño molecular (RMSradius)2 a través del sistema acoplado GPC/LS está fuertemente influenciada por la interaccion entre el grupo lateral alquilo más largo y la cadena principal, lo cual afecta el cálculo del A2.
Descriptores: Polisiloxano; segundo coeficiente del virial; factor de expansión del radio de giro; función de interpenetración; conformación molecular.
This work was supported by the Universidad de Guanajuato and CONCYTEG (Consejo de Ciencia y Tecnología del Estado de Guanajuato: GTO-04-C02-116). The authors wish to thank Professor Emerita Petey Young of Southern Oregon University for the revision of manuscript.
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was carried out using a Two-Parameter (TP) scheme. The theoretical-experimental behaviour of A2 in a series of polysiloxanes was investigated considering the effects of the type of substituent on the main chain, molecular conformation, and molecular weight. The results obtained were strongly dependent on the flexibility of the side groups and the molecular weight of the polymer. Within the HW model and TP scheme, the A2 value for poly (dimethylsiloxane) (PDMS1 and PDMS2), poly(diethylsiloxane)and poly(methylhexylsiloxane) agrees with the experimental results obtained through the coupled system (Gel Permeation Chromatography/Light Scattering: GPC/LS). However, the A2 calculated for PDMS3, poly(methylhexadecylsiloxane) (PMHDS) and poly(methylphenylsiloxane) (PMPS) showed a significant difference from the experimental value. On the basis of the theory for the HW model, the deviation in PDMS3 may be due to the effect of the end chains. For PMHDS and PMPS, the model used is outside of the coil limit (validity of TP model). In PMHDS the determination of the (RMSradius)2 value from the GPC/LS system is strongly influenced by the interaction between the bulky side group and the main chain, which affects the calculation of A2.