Laurence Lecamp

Photoinitiated polymerization of a dimethacrylate oligomer : 1. Influence of photoinitiator concentration, temperature and light intensity

Abstract The photoinitiated polymerization of dimethacrylate oligomer with 2,2-dimethyl-2-hydroxy acetophenone (Darocur 1173) as radical photoinitiator was studied by using isothermal photocalorimetry. The effect of temperature, light intensity and photoinitiator concentration on reaction was investigated. The maximum conversion was obtained at temperature near 90°C. This temperature is above the glass transition temperature of the resulting material and below the thermal polymerization temperature of the reacting system. Above 90°C, thermal polymerization interferes on photocalorimetric measures. Assuming that glass transition temperature of the final polymer and conversion are connected, we have estimated thermal conversion. A maximum conversion was obtained for a photoinitiator concentration of 1% (w/w) and for the highest light intensity studied (2.7 mW cm −2 ).

Photoinitiated cross-linking of a thiol-methacrylate system

Abstract The photoinitiated thiol–ene cross-linking of a dimethacrylate polyether of Bisphenol A and pentaerythritol tetrakis 2-mercaptopropionate was studied in the presence of 2,2-dimethyl-2-hydroxy acetophenone (Darocur 1173). Two complementary techniques were used: photocalorimetry and real-time infrared spectroscopy. In the first part, the kinetic reaction was characterized by a stoichiometric mixture in reactive functions. The influence of temperature, photoinitiator concentration and ultraviolet (UV) light intensity was investigated. The results mainly show that the methacrylate homopolymerization is faster than the thiol–ene addition so that the reaction is usually stopped because of the complete consumption of the methacrylate double bonds. A theoretical approach has allowed us to determine a transfer constant of 0.26. Moreover, an increase in the autoacceleration rate was observed in the presence of the thiol monomer. In the second part, the molar fraction of methacrylate double bonds and thiol functions was changed to determine the effect on the kinetic reaction and the glass transition temperature of the final material.

Photoinitiated polymerization of a dimethacrylate oligomer: 2. Kinetic studies

The kinetic of photoinitiated polymerization of a dimethacrylate oligomer was studied by using isothermal photocalorimetry. The reaction was realized with 2,2-dimethyl-2-hydroxyacetophenone (Darocur 1173) as radical photoinitiator. Two kinetic models were applied. First, it was shown that an autocatalytic model can describe this reaction in a satisfying way. The reaction temperature does not influence the m and n orders of the reaction which were found to be constant and respectively equal to 0.8 and 2. The phenomenological rate constant k varies with temperature according to the Arrhenius law up to 80°C. Above this temperature, this law can again be checked if the initial variation of double bond concentration due to thermal polymerization is taken into account. In addition, by means of a mechanistic model, the kp and kt rate constants were calculated. Their evolution with conversion was studied at 50°C and well illustrates the importance of the reactive diffusion mechanism.

Photoinitiated polymerization of a dimethacrylate oligomer: Part 3. Postpolymerization study

Abstract The effects of the presence of trapped radicals after UV irradiation were studied on a dimethacrylate oligomer. The postpolymerization reaction was characterized by differential scanning calorimetry and dynamic mechanical analysis. The photopolymerization was realized with 2,2-dimethyl-2-hydroxyacetophenone (Darocur 1173) as radical photoinitiator by using isothermal photocalorimetry. The postpolymerization was clearly shown in the isothermal mode and under N 2 atmosphere by following the variation of the glass transition temperature of the samples. The influence of crosslinking density, O 2 and thermal postcure were investigated.

Synthesis of a new phosphonated dimethacrylate : Photocuring kinetics in homo- and copolymerization, determination of thermal and flame-retardant properties

In this work, we describe the synthesis of a new dimethacrylate phosphonate monomer by condensation of methacryloyl chloride with a phosphonate diol resulting from a radical addition of allyldiethyl phosphonate with 3-mercapto propane-1,2-diol. The photochemical polymerization of this new monomer was first studied as a function of reaction temperature. The optimal conversion of the photopolymerization was 63% at 70°C. This new monomer is less reactive than the commercial dimethacrylate polyether of Bisphenol A, that we have used for copolymerization. The mechanical and thermal properties of the final material were studied as a function of dimethacrylate phosphonate monomer content. The ultimate conversion slightly decreases (from 72 to 55%) and the glass transition temperature drops from 44 to –26°C when the phosphorus content increases. The addition of phosphorus leads to an improvement of the thermal and flame-retardant properties, i. e. a significant decrease in the degradation rate (factor 4.5) and a high increase in the amount of residue that remained after combustion (15% for the 2.5% phosphorus copolymer). Moreover, the Limited Oxygen Index (LOI) is increased from 16.9 (0% P) to 21.5 (2.5% P).

Gradient structure materials from homogeneous system induced by UV photopolymerization

Abstract This work deals with the synthesis of a gradient structure material from a homogeneous system of monomers. This new synthesis involved hydroxyethylmethacrylate, a hydroxytelechelic polybutadiene, and 4,4′-methylene-bis(cyclohexylisocyanate). These materials were made in two steps. The first one consisted in creating a photopolymerization gradient in methacrylic double bonds under UV exposure thanks to the decay of UV light intensity through the sample thickness. The second one involved a thermal crosslinking reaction leading to the formation of a polyurethane network in order to set the obtained gradient. Using FTIR and UV spectroscopies, the required experimental conditions to obtain and keep the gradient were investigated. Thus, these parameters enabled us to obtain a 20% hydroxyethylmethacrylate double bonds conversion gradient in the ultimate 5 mm thick material. Further DMA analysis well revealed a difference of structures between the two sides of the material.

A solventless synthesis process of new UV-curable materials based on linseed oil

A new synthesis process of polymer materials based on vegetable oil has been developed. First, linseed oil was thermally polymerized in bulk at 300 °C under an inert atmosphere. Next, the obtained stand oil was functionalized in a two-step one-shot process without solvent in order to graft on some photopolymerizable groups. The first step consisted of a bulk reaction with maleic anhydride at 220 °C under an inert atmosphere. The grafted anhydride groups were then used in the second step as an anchor for grafting 2-hydroxyethylmethacrylate at room temperature. Finally, the materials were prepared by UV-curing of the modified linseed oil and then characterized. The obtained materials are flexible, hydrophobic and not biodegradable, and may have potential applications in flexible coatings.

Numerical simulation to correlate photopolymerization kinetics monitoring by RT-NIR spectroscopy and photocalorimetry

Photocalorimetry (DSC) and real time infrared (RTIR) spectroscopy are the two usual methods used to follow photopolymerization reactions. Kinetics obtained by DSC on thin samples and kinetics obtained by real time near-infrared (RT-NIR) spectroscopy on thick samples are not the same. The heat release during the photopolymerization induced a high temperature increase in thick samples because of the absence of temperature control. We think that this temperature offset is the main cause of this kinetic difference. In this paper, we want to verify this assumption. To reach this aim, conversion and temperature evolutions versus time were numerically simulated for a sample placed in the thermal conditions of NIR analysis by using experimental kinetic data obtained by photocalorimetry in isothermal mode. The boundary conditions were determined such as the simulated evolution of the sample temperature is the same as the experimental one. At last, conversion curves simulated to obtain these temperature profiles were compared to experimental results obtained by RT-NIR.

New polysiloxanes bearing heterocyclic groups—synthesis and curability

Abstract The synthesis of new polysiloxanes bearing thioether and heterocyclic functions (epoxy or oxetane) was performed. The reaction is a radical addition between a poly(dimethyl - co-methyl mercaptopropyl) siloxane and allyl or vinyl heterocyclic compounds. The corresponding sulfones were obtained by oxidation of thioether functions by using m -chloroperbenzoic acid. All the products were characterized by 1 H NMR, SEC and viscosimetry. The cross-linking of these products with isophorone diamine was studied at different temperatures. Thermal and mechanical properties were examined by dynamical mechanical and thermogravimetric analysis.

Kinetic studies of photoinitiated polymerization of a dimethacrylate oligomer

Abstract The kinetics of photoinitiated polymerization of a dimethacrylate oligomer with 2,2-dimethyl-2-hydroxyacetophenone (Darocur 1173) was studied by using isothermal photocalorimetry. First, an autocatalytic model was used and the influence of the reaction temperature on the m and n orders of the reaction and on the phenomenological rate constant k was investigated. Then, a mechanistic model was applied to calculate the k p and k t rate constants. Their evolution with conversion was studied at 50°C.