With the assistance of polymerisable maleate surfactant and costabilizer, core-shell emulsions with poly(butyl acrylate) core (PBA) and poly(butyl acrylate-styrene-methacryloxypropyl trimethoxysilane) shell (PSBM) were prepared through seeded emulsion polymerization. Effects of MPTS on rheological, mechanical, and thermal properties were investigated. Simultaneously, the emulsions were utilized as paper surface sizing agents, and corresponding properties were studied. It was found that the emulsion possessed viscoelastistic nature and changed from viscous to elastic with MPTS addition. At the same time, enhanced internal network strength among particles was detected, which was weakened when MPTS concentration was 8%. The tensile strength and thermal stability of copolymer films were therefore increased accordingly. However, decrease in tensile strength, elongation at break and thermal properties was observed with higher MPTS concentration due to weakened interaction among different shells. It was also found that glass transition temperature (T (g)) did not influence greatly by MPTS, and two phases corresponding to core and shell copolymer were observed with low degree of microphase separation. Furthermore, the interaction between polymer and fiber was improved, resulting in improved sizing degree, ring crush strength, surface strength, and folding strength. While the surface strength and folding endurance decreased due to the increase of brittleness with higher crosslinking degree.