Study of swollen crosslinked polymers by low-temperature adsorption of nitrogen using blocking siloxane agent

We have investigated pore systems in several crosslinked polymers in the presence of poly (methylphenyl dimethyl) siloxane. Structural modifications of the polymers during swelling were studied through the nitrogen adsorption. The commercial acrylic resins Amberlite XAD7 HP and styrene divinylbenzene Amberlite XAD4 were used as model porous polymers. Nitrogen adsorption experiment was applied to determine a free pore space at different stages of swelling and polymer network deformation. Distribution of a nonvolatile siloxane as an effective swelling agent within the pore structure of a crosslinked polymer was studied on the basis of pore size distributions estimated from the nitrogen adsorption/desorption isotherms. Application of nonvolatile blocking and swelling agent enables an unique possibility to follow changes in the pore system of polymers during swelling and provide information on penetration of the swelling agent into polymer network. The textural properties and morphology of polymers under study were additionally elucidated with the use of high resolution SEM. Siloxane oil phase used in the experiments allows for the first time, according to our knowledge, to observe some details concerning the mechanism of pore filling with use of the conventional nitrogen adsorption method. Changes of the pore volume in the swollen particles may be monitored thanks to the non-volatility of silicone oil, which is, however, a perfect swelling agent. Considering the relation of the pore volume changes in the real swelling samples and the model non-swelling case, it is possible to separate the initial “internal” swelling and the total swelling of the particle.