A family of reworkable polymer networks by the incorporation of sterically hindered urea linkages

Crosslinked polymer networks are excellent materials for multiple applications. However, while their crosslinked structure gives the networks many positive attributes, it also makes them essentially intractable after the covalent crosslinks are formed. Therefore, it is exceedingly difficult to reprocess polymer networks once crosslinked without exposure to extreme degradation conditions.; The first part of this work focuses in creating crosslinked networks that could show controlled disassembly upon stimulus. It was found that a controlled network disassembly process could be invoked by the incorporation of sterically hindered urea linkages into the polymer network. This network was shown to disassemble upon exposure to heat, whereas in the absence of heat, the network was found to maintain its crosslinked structure. The disassembly temperature could be varied by careful selection of the cleaving agent based on controllable considerations. This work focuses on showing controlled network disassembly of a crosslinked polymer matrix. Herein, we describe the factors that control the disassembly temperature and conclude with a possible mechanism for the disassembly process based on experimental data.; Once disassembly could be shown to occur using sterically hindered urea linkages, polymer molecules were incorporated directly into the reworkable network. The presence of the polymer was found to significantly effect the reworkable behavior and these effects were detailed and an explanation for the behavior was provided. The work then focused on the effects of sterics along the length of the reworkable crosslinker. It was found that sterics along the length of the chain did have an effect. Specifically, as the steric hindrance increased around the urea linkage the rework temperature was found to decrease.; Our focus then shifted to study the effects of changing the number of reworkable linkages per crosslinker. As the number per crosslinker changed from two to one the disassembly properties of the network changed significantly. This change was detailed and a model was built that considered the enthalpic and the entropic changes that occurred when the number of reworkable crosslinkers changed from one to two. The model showed how differences in the entropy and enthalpy explained the differences that are observed.; The work then shifted to another model to evoke reworkability. This second rework model required a material that had a glass transition temperature that was below the crosslinking temperature. Thereby, if the material needed to be reworked, the material could be heated and undergo glass transition and be reworked. If rework was not required then the material could be heated above its crosslinking temperature, initiating internal crosslinking rendering the material intractable.; We believe that the materials presented in this dissertation provide for a method for controlled network reworkability. The molecules presented allow for the positive attributes of crosslinked networks to be maintained while at the same time addressing the recycling issue.