Differential Photocalorimeter Research Articles

Photocured characteristics of fast photocurable acrylic formulations and investigations by differential photo calorimeter

Bisphenol-A glycerolate diacrylate has been synthesized, characterized and formulated with acrylate monomers. Photocrosslinking characteristics of UV-curable acrylate monomers were investigated with the help of differential photocalorimeter equipped with UV radiometer using UV radiation of 365 nm at an intensity of 10 mWcm−2. The heat of photoreaction, curing rate and degree of conversion were studied using theoretical kinetic equations to investigate the effect of 2-ethylhexyl acrylate on photocuring behaviour of bisphenol-A glycerolate diacrylate, acrylic acid and methyl methacrylate. Curing rate reached its maximum value within 7.5 s, and more than 70% monomers were photopolymerized in all the formulations. Enthalpy of photopolymerization was found in the range of − 206 to − 171 J g−1, and maximum degree of conversion attained was 82–84% within a time span of 25 s. A comparison of DPC curves reveals that 2-ethyl hexyl acrylate has no significant effect on the curing rate of photopolymerization, however, a small decrease in degree of conversion was observed. Further, FTIR quantification of C=C bond conversion was performed in order to estimate the degree of conversion after 25 s. Specific gravity and mechanical properties of the casted films have also been reported. Glass transition temperatures were also recorded with the help of DSC, and a remarkable shift from 40.52 to 23.48 °C was observed imparting flexibility to the UV-cured compositions. The developed photocurable acrylic formulations have been used for preparation of laminated glasses which were analysed for fracture and adhesion test.

Benzylpyrazinium Salts as Photo-Initiators in the Polymerization of Epoxide Monomers

In order to study the capability of pyrazinium salt derivatives to act as photo-initiators of epoxide monomers, benzyl pyrazinium hexafluoroantimonate (BPH), benzyl 3,5-dimethyl pyrazine hexafluoroantimonate (BDH) and benzyl quinoxalinium hexafluoroantimonate (BQH) were synthesized by the Menschutkin reaction of benzyl bromide with pyrazine, 2,6-dimethyl pyrazine, and quinoxaline, followed by exchanging with hexafluoroantimonate (SbF6). BPH, BDH, and BQH exhibited characteristic ultraviolet (UV) absorbance as well as exothermic peaks as a function of irradiation time in a differential photo-calorimeter (DPC). In the absence of photo-irradiation, cyclohexene oxide (CHO) underwent slow polymerization at 25 °C using BPH derivatives, but quantitative conversion was achieved even after a 5-min photo-irradiation. In addition, photo-irradiation was required for the photo-polymerization of CHO and styrene oxide (STO), which was characterized by a short induction period followed by a very rapid and exothermic polymerization. While glycidyl methyl ether (GME) required long induction periods, glycidyl phenyl ether (GPE) underwent rather slow and/or no photo-polymerization. The reactivity order of the monomers was CHO > STO >> GME >>> GPE, and the reactivity order for the photo-polymerization of CHO was BPH > BQH > BDH. It was found that BPH, BDH, and BQH could serve as photo-latent initiators for CHO, STO and GME, respectively.

SYNTHESES OF UV-CURABLE HYPERBRANCHED POLYSILOXANES AND STUDIES ON THEIR PHOTO-CURING BEHAVIOR

UV-curable hyperbranched polysiloxanes were synthesized via hydrolysis of γ-methacryloxyprop-yltrimethyloxysilane (A-174) by controlling the amount of water.Macromolecular structures of the polymers obtained were characterized and confirmed by FT-IR, ~1H-NMR spectra and multi-angle laser light scattering technology(MALLS).The results indicated that the hyperbranched polysiloxanes carrying a large amount of functional vinyl groups could be cured under UV-irradiation.Their photo-initiated curing kinetics were studied by isothermal differential photo calorimeter (DPC) test.It was found that both the polymerization rate and the ultimate conversion first increased and then decreased with the increase in the molecular weight of the polymer and the photoinitiator concentration.The increase in UV-light intensity can lead to increase of both the polymerization rate and the ultimate conversion,and particularly, the polymerization rate is proportional to the square root of light intensity.Although elevated temperature can indeed improve the polymerization rate and the ultimate conversion,the effect of temperature on polymerization rate is not prominent.The total exponent of the photo-polymerization of the polymer 3# is about 3,and the apparent activation energy is 16.9 kJ/mol,calculated from an autocatalytic model.

Fast cure kinetics of a UV-curable resin for UV nano-imprint lithography: Phenomenological model determination based on differential photocalorimetry results

The fast cure kinetics of an ultraviolet (UV) light-curable resin for UV nano-imprint lithography (UV-NIL) was measured using a differential photocalorimeter (DPC). A simple phenomenological model was formulated to describe the curing behaviors of the UV-curable resin, i.e., the initial fast reaction rate at a small degree of cure and the autocatalytic reaction rate at a larger degree of cure. Kinetic model parameters were best fitted to the measured cure rate by using an error minimization technique. The practical applicability of the phenomenological model developed herein was demonstrated by a good agreement between the measured and modeled curing behaviors of the UV-curable resin. The effect of cure conditions on the estimated kinetic model parameters was also investigated.

Kinetic Study on UV-curing of Hyperbranched Polysiloxane

Ultraviolet (UV) curing kinetics of hyperbranched polysiloxane (HBP) initiated by 2-Hydroxy-2-methyl-1-[(4-isobutyl)phenyl]-1-propanone (Trade name: IHT-PI 185) was studied by using Differential Photo Calorimeter (DPC). The effects of photoinitiator concentration, UV irradiation intensity, environment temperature and atmosphere on curing behaviors were investigated. It was found that both curing rate (R) and ultimate vinyl conversion percentage (C) first increase and then tend to stabilize within 3 wt% of photoinitiator concentration. Higher UV irradiation intensity can lead to higher values of R and C. Particularly, R is proportional to the square root of irradiation intensity at initial stage. Although raising temperature could raise the values of R and C, the effect of temperature on R is not marked. Oxygen possesses a notable inhibition effect on curing, however, induction period can be reduced by enhancing irradiation intensity. Curing kinetics was studied using Ameliorated Autocatalytic Model attaching a diffusion term. It is found that the model is suitable to describe the autocatalysis effect at the initial stage and the termination stage controlled by diffusion process. The kinetic parameters including total apparent curing exponent and apparent activation energy calculated by model above are c.a. 6 and 13.15 KJ/mol, respectively.

The Analysis of Photocuring Behavior of Polyester Acrylate by Means of Differential Photo Calorimeter (DPC) and Rigid-Body Pendulum Rheometer (RPT)

This study aims to understand the different photocuring behaviors of acrylated polyester by adding different photoinitiators and monomers. Differential photo calorimeter (DPC) is used to understand the exothermal effects during photocuring. The self-catalyst model of dynamic analysis software was then used to obtain the relationships between reaction speed, reaction extent, and rate of reaction. In addition, this study also tried to understand the formation of photocuring resin from the rigid-body pendulum rheometer (RPT) experiment. The results showed that the extent of reaction, conversion rate and speed varies directly with the concentration of the photoinitiator and monomer. The reaction level of propoxylated pentaerithritol triacrylate was higher than propoxylated neopentyl-glycol diacrylate. Moreover, the method using RPT shows better view of the molecule reaction status inside the photopolymer.

Superior real time method to evaluate photo‐curing resin by means of rigid‐body pendulum rheometer

AbstractThe objective of this article is to establish a new method in evaluating photo‐polymerization resin reaction behavior, and to use the trends resulting from past evaluation methods and those already known to prove the feasibility of this method. Another objective is to compare the data gathered using the differential photo calorimeter (DPC) method and RPT on different photo‐polymerization resin systems to illustrate that the application of RPT on photo‐polymerization resin studies is more suitable. Experiment results show that the trends through the real time method using oxide series acrylate research through rigid‐body Pendulum Rheometer, the photo‐curing behavior under the various parameters of monomer functionality, and photo‐initiator concentration can all be observed. Comparing the DPC and RPT methods on polyester acrylate series, when the oligomer of tetra‐functional polyester acrylate is added with a different ratio of the monomer of propoxylated neopentyl‐glycol di‐acrylate, DPC evaluation methods show that the differences in observation are minimal. However, when RPT was applied, not only were the differences in reaction speed observed, but also the differences in crosslinking and other data in the hardening process when the balanced time was achieved during the oscillations procedure. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 3402–3407, 2006

Behavior of quaternary ammonium salt photobase generators on initiating free radical photo‐polymerization

AbstractSeries of quaternary ammonium tetraphenyl borates salt photobase generators (PBGs) were synthesized using p‐methoxyphenacylmethylene and 2‐naphthoymethylene as chromophores, and triethylene diamine, pyridine or 3‐methyl pyridine as tertiary amine. The kinetics for polymerization of trimethylolpropane triacrylate (TMPTA) monomer using PBGs as free radical photo‐initiator was monitored by differential photo‐calorimeter (DPC). It was found that all the quaternary ammonium tetraphenyl borate salt photobase generators synthesized could initiate free radical polymerization of the acrylate monomer TMPTA by exposure to UV irradiation, but the activity was relatively low. Addition of a small amount of polar solvent to the system could largely increase the polymerization rate and final conversion. Photo‐polymerization was also improved by increasing light intensity or raising reaction temperature. PBGs with p‐methoxyphenacylmethylene as chromophore had higher absorbance at around 280 nm and showed higher activity in initiating photo‐polymerization than those with N‐(2‐naphthoylmethyl) as chromophore. Copyright © 2006 Society of Chemical Industry

Effects of polymerization initiator complexation in methacrylated β-cyclodextrin formulations

Objectives. Methacrylated β-cyclodextrin (MCD) is a candidate dental monomer that can complex molecules within its hydrophobic cavity. This study determined the effects of complexation of polymerization initiators such as camphorquinone (CQ) and ethyl-4-dimethylaminobenzoate (4E) with MCD on the flexural strength (FS) and degree of conversion (DC) of resulting dental composite formulations. Methods. Complexation of CQ and 4E with MCD was studied by thin layer chromatography. A mass fraction of 44% 2-hydroxyethylmethacrylate or triethyleneglycoldimethacrylate was mixed separately with a mass fraction of 56% MCD to produce a workable formulation. The mixture was activated with varied amounts of CQ and 4E. One part by mass of the activated resin formulation was mixed with three parts by mass of glass filler. Specimens for FS were prepared by filling molds with composites and curing for 2 min. The cured specimens were immersed in 37 °C water for 24 h and FS was measured with an Instron machine at a crosshead speed of 0.5 mm/min. DC in MCD-based resin formulations was measured with a differential photocalorimeter under nitrogen. Results. MCD appears to form inclusion complexes with CQ and 4E. As a result, FS and DC of MCD-based composites vary significantly as a function of the concentration of polymerization initiators used in the formulations. Significance. Complexation of polymerization initiators with MCD can influence the FS and DC in MCD-based dental formulations and should be taken into consideration when evaluating MCD as a dental monomer.

UV photo curing of N, N′-bismaleimido-4, 4 ′-diphenylmethane

The photo curing of a formulation consisting of N, N ′-bismaleimido-4, 4 ′-diphenylmethane (BMI), which is most widely used in commercial thermal curing formulations, was performed. Parameters, such as initiator, co-initiator and temperature, which affect the curing rate and enthalpy, were studied using differential photocalorimeter. BMI undergoes copolymerization with 4-hydroxybutylvinylether (HBVE), when exposed to UV radiation, in presence of the photo initiator, Triphenylphosphine oxide (TPO). Diallylbisphenol A has been observed to be an efficient co-initiator, which improves the reaction rate coefficient and enthalpy of the photo curing process for the system BMI/HBVE/TPO.

Studies on the kinetics of radical initiated photocopolymerisation of di(vinyl 2-hydroxy propanoate) ether of bisphenol-A and monomers

Di(vinyl 2-hydroxy propanoate)ether of bisphenol-A (DEBA) was prepared by reacting diglycidyl ether of bisphenol-A (DGEBPA) with acrylic acid using triphenyl phosphine as catalyst. Divinylester monomer was copolymerised with four different monomers, viz. methyl methacrylate (MMA), n-butyl acrylate (BA), vinyl acetate (VAc) and acrylic acid (AA), using benzoin as photoinitiator. The kinetics of radical initiated photocopolymerisation were studied by differential photocalorimeter (DPC). The thermogram data obtained from DPC were used to calculate kinetic parameters, order of the reaction (n), independent order to encompass autocatalytic reaction (m) and the apparent rate constant (k) for the copolymerisation at different temperatures for each monomer. A change in the kinetic model from autocatalytic to Nth order was observed with increase in the fraction of conversion. A comparison of rate of conversion for copolymerisation with different monomers reveals that acrylic acid has a tendency to undergo faster copolymerisation whereas methyl methacrylate has relatively less tendency to copolymerise with DEBA.