“Anchor effect” in poly(styrene maleic anhydride)/TiO2 nanocomposites

Abstract

Multi-component composites or hybrid materials of inorganic matter and organic polymers have been reported recently [1–3]. It is well known that styrene and maleic anhydride usually copolymerize in an alternating way, resulting in a poly(styrene maleic anhydride) (PSMA) alternating copolymer with highly regular anhydride groups on backbone chains which may provide regular sites for combination with other substances. Nanocomposites of inorganic materials in organic matrices are of a particular interest, which combine typical properties of organic polymers (e.g., elasticity, transparency or specific absorption of light, dielectric properties) with the advantages of nanoparticles, particularly, the high specific surface and the high ratio of surface atoms to innersphere atoms. Among the nanostructured materials investigated, nanometer-sized TiO2 particles are technologically important in many applications, which greatly increases their activity as a catalyst and sensitivity as a sensor [4, 5]. However, a serious problem is its aggregation with varied ambient conditions. In this paper, we report the synthesis of PSMA/TiO2 nanocomposites via a multi-component solution. The PSMA can provide functional groups, which anchor TiO2 particles and prevent them from aggregating. The PSMA gives a 1 : 1 alternating structure consisting of styrene and maleic anhydride, as shown in Fig. 1 [6]. PSMA was dissolved in THF (tetrahydrofuran) with stirring at 40 ◦C for 12 h, then acacH (acetylacetone) and deionized water (mol ratio 1 : 25) were dropped into the polymer solution. The acacH was used to reduce the hydrolyzing rate of Ti(OBu-n)4 (tetrabutyl titanate). The pH value of the mixture was adjusted to about 1.7 with concentrated hydrochloric acid (37%). After stirring for 20 min, the precursor Ti(OBu-n)4 dissolved in THF was dropped into the mixture. After that, the reactant mixture was heated to 60 ◦C, and stirred at this temperature for 4 h. Finally, the homogeneous mixture was sealed in a baking oven and kept at room temperature for 4 days. Several punctures were made in the sealing adhesive tape with a pin to volatilize THF at 40 ◦C in flowing air, and thus orange-red and optically transparent samples of PSMA/TiO2 composites were obtained. The samples were dried under vacuum at 80 ◦C for 2 days. FT-IR spectra of the samples indicate the existence of absorbed water from air, which gave rise to an absorption band [7] at 1620 cm−1, and especially, the broad band around 3500 cm−1. The IR spectrum of PSMA (Fig. 2a) shows that the adsorption bands at 1858 and 1778 cm−1 which are characteristic bands of the copolymer of styrene maleic anhydride [8], which are attributed to asymmetrical and symmetrical νC=O (C=O stretching vibration) of the maleic anhydride moiety [9], respectively. The peaks at 1600, 1500 and 1450 cm−1 are the νC=C of the phenyl group on the backbone chain [9, 10]. The band at 1214 cm−1 is attributed to the νC–O–C of maleic anhydride units, for a five-numbered cyclo-anhydride shows a νC–O–C band at 1310∼1210 cm−1 wavenumber [7]. The band at 700 cm−1 is the δC=C (C=C bending vibration) of the phenyl group [10], which was used as an internal reference to offset differences in the thickness of IR samples. The spectrum of pure TiO2 (Fig. 2b) shows a strong and broad adsorption peak between 650 and 400 cm−1, which is accounted for by vibrations of Ti–O–Ti groups [11], and regarded as the characteristic peak for TiO2 [12]. The IR information of both