(217k) Diffusion and Subsequent Polymerization of Monomer in Polymer Pellets——An Effective Approach to Prepare Polymer Nanoblends

Nanoblends, in which the dispersed-phase domains exhibit length scale of 100 nm or less, is of growing interest due to the potential for enhanced properties. It is hard to prepare nanoblends under traditional melt blending conditions. Some methods have been reported to prepare nanoblends, including solid grinding technology, high shear processing, reactive extrusion, supercritical fluid-assisted diffusion polymerization and so on. All the methods have limitations. Thus, developing simple processes to prepare polymer nanoblends is still interesting and challenging.

    A so called “diffusion and subsequent polymerization” process is investigated by our group, where monomer diffuses into the semi-crystalline polymer pellets dispersed in water medium, and then initiated for polymerization to form nano-scale dispersed phase. The size of the dispersed phase is restricted by the free volume of the matrix polymer. To demonstrate the feasibility of this approach, a series of isotactic polypropylene/polystyrene (iPP/PS) nanoblends with iPP matrix and PS nanoparticles as dispersed phase have been prepared by diffusion of styrene (St) into iPP pellets in hot water medium with polyvinyl alcohol (PVA) as a suspending agent and subsequent polymerization initiated by benzoyl peroxide (BPO). It is recognized that the diffusion behaviors above 60 °C have characteristics of Fickian diffusion processes. The average diffusion coefficient above 60 °C calculated using a typical model of Fickian diffusion increases as the temperature increases and show a remarkable increase at 90 °C, being 2.8 times of that at 80 °C, attributed to the α relaxation of iPP segments. Microscopic Fourier transform infrared spectra (Micro FTIR) show that PS exists at the center of the pellets prepared at 90°C but not at the center of the pellets prepared at lower temperatures such as 60°C. Field emission scanning electron microscope (FESEM) observation of the PS particles shows an average particle size of about 90 nm in the inner part of the iPP pellets.

    A series of common monomers such as butyl methacrylate (BMA), methyl methacrylate (MMA) and polyfunctional comonomer divinylbenzene (DVB), were successfully diffused into iPP pellets and polymerized inside the pellets. Other types of polymer pellets were also used as matrices. The diffusion ability of different monomers is different in terms of diffusion amount and coefficient. Micro FTIR spectra indicate that monomers can penetrate into the center of the pellets and FESEM photos show the domain size is not big, e.g. 140 nm for PBMA domains in iPP pellets.

    In conclusion, diffusion and subsequent polymerization is a simple and effective way to prepare nanoblends, suitable for a wide variety of polymer/monomer combinations. The pellets prepared through such low-carbon method can be directly used for injection molding, indicating promising prospect in industry.

    The authors gratefully acknowledge the financial support from the National Natural Science Foundation of China (No. 51173095).