Sequence and geometric control are essential to the development of highly functional and tunable materials for advanced applications. Materials used in applications that require high strength, solvent resistance and high temperature performance traditionally employ thermosetting plastics. Thermosets are made by cross-linking polyfunctional monomers or reactive polymer or macromer chains via permanent covalent bonds to give hard insoluble solid materials with high modulus, solvent resistance, high temperature stability, and low creep. In these networks, the cross-link density and distribution are the primary determinants of material properties. Cross-link density is dependent on the functionality and geometry of the monomer/crosslinker. Since most cross-linking reactions are kinetically controlled, network topology is determined by monomer geometry, composition, sterics, and sequence of the reactive functional groups. The dependence on geometry is greater in rigid aromatic monomers and macromers. The work in this thesis is driven by the hypothesis that topology and network connectivity in thermosets can be tuned by encoding different monomer geometries into the macromer chain prior to curing. We will investigate this hypothesis by exploiting a recently developed scalable sequence-defined polyurethane macromer (SD-PUM) platform. SD-PUMs are synthesized on the gram-scale via an iterative, support-free approach using vanillin isomers (an inexpensive, sustainable monomer sourced from lignin). This facilitates the assembly of oligomers with tunable backbone conformations and pendant groups. A series of SD-PUMs with different end-groups and conformations have been synthesized and cross-linked into thermoset networks via multivalent thiol crosslinkers. The optical, thermal and mechanical properties of these networks have been explored to provide insight into the effect of geometry and composition on network properties. The results show that the thermomechanical properties of the network can be tuned with changes to the free volume of the end-groups and the conformation of the backbone. Further results demonstrate that changes in monomer geometry resulted in more pronounced changes in material properties when a crosslinker with higher functionality was used. The work in this thesis showcases the robustness of the SD-PUM platform and its use of monomer geometry to tune and control material properties.