This research revealed that in the synthesis process of methyl methacrylate-poly(dimethylsiloxane) copolymers, the difference in monomer reactivity ratio and monomer concentration resulted in a low content of PDMS in the macromolecules formed at the early stage of polymerization, while a high content at the end stage.

Abstract

Methyl methacrylate (MMA) was copolymerized with a methacryloxy- terminated poly(dimethylsiloxane) macromer (M-PDMS) in order to improve the mechanical properties. The results of dynamic mechanical analysis, differential scanning calorimetry, infrared spectroscopy, scanning electron microscopy, small-angle X-ray scattering and atomic force microscopy confirmed that the monomer concentrations and reactivity ratios affected the polymerization kinetics, resulting in the formation of two different macromolecules at the beginning and end of the polymerization. With the addition of M-PDMS, the phase separation of the MMA-PDMS copolymers (M-PDMS_X, X represents the mass fraction of M-PDMS in the copolymers) became more pronounced, but the difference in molecular structure between the continuous phase and the dispersed phase became smaller, which led to higher light transmittance, hydrophobicity and thermal stability. Tensile tests confirmed that the tensile strength and tensile modulus of M-PDMS_20 (33.10 MPa and 1.35 GPa) was 55 times and 229% those of PMMA (0.6 MPa and 0.59 GPa). An in vitro cytotoxicity test confirmed the MMA-PDMS copolymer was biocompatible. This research revealed the formation mechanism of the microstructure of the MMA-PDMS copolymer, and provided valuable guidance for the design and synthesis of this material.