Macromolecular NanotechnologyInfluence of UV irradiation and two photon processing on the cinnamate monomers polymerization and formation of hybrid composites with nanosized ZnO
Graphical abstract
Highlights
► Cinnamate dimethacrylates synthesis and their photobehavior is described. ► Photopolymerization of cinnamates/silyl methacrylate give good conversions (57–81%). ► Using UV light and 2PP hybrid nanocomposites with ZnO nanoparticles were obtained. ► AFM/SEM confirmed creating microstructures by laser writing with femtosecond pulses. ► Fluorescence of these “ormocer” materials was evidenced by fluorescence microscopy.
Introduction
It is well known that the photoinitiated polymerization of some multifunctional monomers represents one of the most rapid and simple processes practically validated for producing the crosslinked materials starting from liquid precursors. Nowadays, photopolymerization has a growing relevance for a lot of industrial applications, such as coatings, adhesives, dental materials, steriolithography, and so forth [1], [2], [3], [4]. As compared with other conventional polymerizations, this technique allows for fast curing of acrylate monomers at room temperature and can provide a temporal and spatial control of two-/three-dimensional structures to form macro- and microstructures, of great interest in the field of optoelectronics, microelectronics, and microfabrication by photopolymerization [5]. In fact, the family of (meth)acrylates are considered the most versatile monomers (oligomers) that can be used in diversified fields of application [6], reason for that the development of novel mono- and diacrylates of moderately low viscosities, but with enhanced reactivity and superior polymer properties is still important issue to be approached. Investigation of the UV crosslinkable monomers through differential scanning calorimetry, dilatometry, dynamic mechanical testing, and real-time IR spectroscopy [7], [8] showed that the photopolymerization of the acrylic systems is often complicated due to some peculiar features such as auto-acceleration, autodeceleration, incomplete conversion, trapping of radicals and physical inhomogeneities in networks, different reactivity of the functional groups, and the diffusion-controlled termination reaction, all governing the end properties and performance of these materials [9], [10], [11]. Besides, the reactivity of acrylic monomers depends on their chemical structure including the type and number of functional groups, the distance and flexibility between functional groups, hydrogen bonding, viscosity, and others [12], [13], [14]. In these conditions, it is necessary to evaluate the effect of each monomer structure on the photoreactivity, because polymerization of some monomers/macromers only in illuminated areas enables the generation of high resolution images for the production of printing plates, optical discs and microcircuits [15]. More recently, applications for this technology have comprised three-dimensional stereolithography and holographic recordings [16]. In connection, femtosecond laser two-photon polymerization (2PP) based on ultra-local polymerization reaction initiated by non-linear absorption of focused laser beam has been employed as a modern tool for the creation of 3D (micro)nanostructures out of photopolymers [17], [18]. Obviously, the major advantages of in situ formation, fast reaction rates, and simple processing into variable geometries have been explored and exploited in preparing of biomaterials for applications in tissue regeneration [19], drug delivery carriers [20], and coatings for biosensors or artificial implants [21]. In particular, hybrid sol gel polymer ORMOSILS (organically modified silanes) or ORMOCERS (organically modified ceramics) were successfully utilized in dental materials [22] and the fabrication of micro/nanoobjects for optical devices [23].
In modern chemistry and materials science, nanotechnology has provided a promising field for creating novel polymer materials with interesting physicochemical properties that arise from the synergistic interaction between the components [24]. One of the attractive routes of producing hybrid nanocomposites is the uniform dispersion of nanometer-scale inorganic particles within the organic matrix followed by polymerization in situ [25]. For instance, the addition of silice [26], hydroxyapatite [27] or silver/gold nanoparticles [28], [29] to name just a few, in photo-polymerizable monomers led to biomaterials with applications in dentistry [30] and in the area of antibacterial systems [31], [32]. Similarly, the introduction of ZnO nanoparticles in acrylic monomers [33], [34], [35] or N-vinylcarbazole [36] had as relevant effect an improvement of the free radical polymerization/photopolymerization and the resulting materials properties (e.g. antibacterial activity, photoconduction).
The objective of this research is to synthesize a novel cinnamate dimethacrylate to be evaluated comparatively with a photoreactive poly(oligo(ethylene oxide)dimethacrylate, following the main factors that affect crosslinking them by UV irradiation and femtosecond laser beam-induced two photon polymerization in the presence of urea organosilan comonomer used in the formation of photosensitive materials of ormosil type. The possibility to obtain hybrid polymer structures incorporating a small quantity of ZnO nanoparticles with photoluminescent properties was also investigated.
Section snippets
Materials
Diethanolamine, cinnamoyl chloride, triethyl amine, poly(ethylene glycol) (PEG, MPEG = 400 g mol−1), isophorone diisocyanate (IPDI), 2-hydroxyethyl methacrylate (HEMA), 3-aminopropyl(diethoxy)methylsilane, 2-isocyanatoethyl methacrylate, and dibutyltin dilaurate were purchased from Sigma Aldrich Chemical Co. and used without further purification. The initiators used were Darocur TPO and Irgacure 651 from Ciba, and zinc acetate dehydrate and hexamethyl tetramine (HMT) were purchased from
Synthesis of N,N-bis(methacryloyloxyethyl carbamoyloxyethyl) cinnamamide
The new photosensitive dimethacrylate namely, N,N-bis(methacryloyloxyethyl carbamoyloxyethyl) cinnamamide (Cin-DMA) was synthesized by a classical addition reaction between N,N-bis(2-hydroxyethyl) cinnamamide prior obtained, and 2-isocyanatoethyl methacrylate under appropriate conditions. For comparison, we used in our study the difunctional macromer with spaced polymerizable end groups (OCin-DMA) obtained by addition reaction between poly(ethylene glycol) (PEG, Mw = 400 g/mol), isophorone
Conclusions
In summary, we have synthesized and evaluated a new cinnamate dimethacrylate for potential use in the production of hybrid photopolymers with and without ZnO nanoparticles into the organic matrix. We have demonstrated that photopolymerization of a monomer mixture based on cinnamate dimethacrylate of monomer (Cin-DMA) or oligomer (OCin-DMA) type and urea-silyl methacrylate (UH-MA) led to the formation of polymeric networks, in which the maximum rate of polymerization (Rpmax) and the maximum
Acknowledgment
This work was supported by CNCSIS-UEFISCDI, Project number PN-II-ID-PCE-2011-3-0164 (40/5.10.2011).
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