Elsevier

European Polymer Journal

Volume 48, Issue 12, December 2012, Pages 1976-1987
European Polymer Journal

Macromolecular Nanotechnology
Influence of UV irradiation and two photon processing on the cinnamate monomers polymerization and formation of hybrid composites with nanosized ZnO

https://doi.org/10.1016/j.eurpolymj.2012.09.012Get rights and content

Abstract

In a first part, N,N-bis(methacryloyloxyethyl carbamoyloxyethyl) cinnamamide (Cin-DMA) and its corresponding oligocinnamate were synthesized and used as organic matrix for preparing hybrid nanocomposites containing siloxane structure derived from urea-silyl monomer, PEG400 sequences and ZnO nanoparticles upon exposure to UV irradiation or femtosecond laser beam. 1H NMR, 13C NMR and FTIR spectroscopies sustain the expected structure, and the photopolymerization progress of Cin-DMA relating to a oligodimethacrylate alone and in combination with the hybrid monomer was investigated by photo-DSC, the time to reach the maximum polymerization heat (tmax), the degree of conversion (DC) and polymerization rate being determined. The photopolymerization results revealed that the investigated monomers exhibit a good photoreactivity (DC: 57–81%) during the formation of crosslinked polymers, and the degree of conversion depend especially on the chemical structure, photoinitiator nature (Darocur TPO, Irgacure 369) and its concentration. Incorporation of 0.5 or 1 wt.% spherical-shaped ZnO nanoparticles (average diameter: 50–100 nm; height: 50 nm) slightly decreased the polymerization rate from 0.08 to 0.068 s−1, respectively. Additionally, two-photon photopolymerization of cinnamate monomers alone and in monomer mixture in the presence or the absence of ZnO nanoparticles (0.5–2 wt.%) has been used in creating 2D and 3D polymeric microstructures via direct laser writing process by femtosecond laser pulse visible-light beams, whose morphology and fluorescence properties were explored to further exploit the new possibilities of micro/nanostructuring technology of the last fluorescent scaffolds.

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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