(447g) The Impact of Sol Molecular Weight on the Mechanical and Adhesive Properties of Polymer Gels

The addition of non-reactive soluble material (sol) to a polymer network can have a dramatic impact on the resulting physical properties. The degree of property change is dependent on the sol quality and loading. We are interested in determining the impact of the sol size on the mechanical and adhesive properties of the gel. To investigate the impact of the sol, a model silicone system with the ability to control the crosslink density was used. The incorporated sols have a molecular weight range from ~1,000 to ~ 400,000 g/mol. The initial results from a model network with a low crosslink density indicate a distinct change when the molecular weight of the sol is below and above the molecular weight of entanglement. The scaling factors for sol sizes below the molecular weight of entanglement approach the theoretical scaling factor of 2.3 determined for networks formed in the presence of a theta solvent. Sols with molecular weight higher then the molecular weight of entanglement exhibit a decreased scaling factor, indicating a reduced influence on the storage modulus, and a more pronounced frequency dependence. The decreased scaling factor is attributed to the higher molecular weight sols ability to entangle with the polymer network and contribute to the modulus. The frequency dependence is likely the result of the longer reptation times of the higher molecular weight sols resulting in a higher effective storage modulus at high frequencies. The study is currently being expanded to network gels that have crosslink densities at and below the molecular weight of entanglement. We anticipate that the results of this study will aid in the design of gel materials to determine the optimum sol loading and molecular weight at a given crosslink density to provide tailored adhesive and mechanical performance.