Summary: In the present work, the synthesis and characterization of composite materials based on HDPE, and PMMA with nanometric hydroxyapatite, are studied. Composites preparation was carried out by dilutions of the commercial polymers, using decaline as solvent for the polyolefin and 2-butanone for PMMA. In the synthesis of Hydroxyapatite (HA), ammonium phosphate [(NH 4 ) 2 HPO 4 ] and calcium hydroxide [Ca(OH) 2 ] were used as precursors. Composites with 20, 30 and 40 wt% of HA were prepared. The polymer dilutions and the precursors of the HA were placed simultaneously in a reactor under ultrasonic radiation at 20 kHz, for periods of 15, 25 and 35 min. The products obtained were characterized by FTIR, TGA, TEM, XRD and biocompatibility studies were also carried out. The results showed the presence of nanometric HA and clear interactions between HA and PMMA polymers were observed by FTIR. These results were corroborated by TEM showing that nanometric HA particles are encapsulated into the polymeric PMMA matrix. For the composites of HDPE, these interactions were not observed.

Summary: The use of PMMA as dental and osseous cement and also in the fabrication of intraocular lenses has been widely reported. The combination of its excellent properties with those of hydroxyapatite (HA) to form a composite material, can result in very interesting properties as a biomaterial. The key is to obtain a good filler dispersion and interface bonding. Ultrasonic radiation seems to be a very versatile method for the synthesis of these materials, since the use of conventional initiators can be avoided, the filler dispersion improved and the interface interaction can be promoted. In the present work PMMA/HA composite materials were prepared by three different synthesis routes using ultrasonic radiation, in order to study the effect of the synthesis method on the final microstructure. Method I: in situ synthesis of PMMA and HA, under ultrasonic radiation by emulsion polymerization of MMA and HA precursors. Method II: in situ synthesis of HA, (from its precursors) by high frequency ultrasound in commercial PMMA solution Method III: in situ polymerization of MMA under high frequency ultrasonic radiation and adding HA to the solution and Method IV Mixing of hydroxyapatite nanocrystals, in different proportions, in a solution of commercial PMMA, by different periods from 10 min to 7 h, under low frequency (conventional) ultrasonic radiation, to compare the effect of high frequency and conventional ultrasound radiation. The different materials were characterized by FTIR, SEM, TEM, DRX, 1H NMR and TGA. The results showed that, all the composites prepared by in situ synthesis showed an interaction between HA and PMMA, manifested by a bonding of the phosphate groups with the polar groups of the polymer matrix observed by FTIR. On the other hand, when the synthesis was carried out simultaneously adding HA and PMMA precursors a inhibition of the polymerization reaction of MMA was observed.

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We have studied the influence of surfactant nature and concentration, and monomer concentration on the synthesis of poly(methyl methacrylate) (PMMA) using high-frequency ultrasound. Polymerization was carried out via free radicals from aqueous solutions with several concentrations of an anionic (sodium lauryl sulfate, SLS) or a cationic surfactant (cetyltrimethylammonium bromide, CTAB) and different concentrations of the insoluble monomer methyl methacrylate (MMA) as the dispersed phase. The polymer particles obtained were characterized by FTIR, differential scanning calorimetry (DSC) and scanning electron microscopy (SEM). The IR spectra show the presence of the characteristic absorption bands for PMMA when SLS was used. When CTAB was employed, for all surfactant concentrations and high monomer concentration (14% v/v), PMMA was obtained. However, bands of the surfactant were present for lower monomer concentrations. The glass transition temperature measured by DSC was in the range 106 - 126°C characteristic of PMMA. Maximum conversion was obtained when the anionic surfactant was employed. SEM studies show the formation of sub-micrometric PMMA latex spheres with average particle size from 65 to 100 nm when the anionic surfactant was used and 65 nm - 0.3 μm for the cationic surfactant.