Monomer Exponent Research Articles

Non‐Ideal Polymerization Kinetics of a Cationic Double Charged Acryl Monomer and Solution Behavior of the Resulting Polyelectrolytes

AbstractThe radical polymerization of bis‐1,3(N,N,N‐trimethylammonium)‐2‐propylmethacrylate dichloride revealed non‐ideality with 0.59 and 4.4 for the reaction orders of the initiator and monomer concentration, respectively. Further, autoacceleration was observed from less than 10% conversion onwards. Degradative chain transfer to the monomer was concluded to explain the initiator exponent. Monomer association and electrostatic effects are hypothesized to govern the monomer exponent and autoacceleration. The exponential concentration dependent increase of the viscosity of the monomer solution and the relatively low overall activation energy Ea = 31.5 kJ · mol−1 support the hypothesis. Counterion activity measurements confirmed strong counterion condensation as expected for a charge distance of 0.12 nm.magnified image

Magnetic field effects on the free radical solution polymerization of acrylamide

Systematic polymerization experiments quantified magnetic field (MF) influences on the free radical solution polymerization of acrylamide for various polymerization conditions. The type of initiation, the initiator concentration, the monomer concentration, and the viscosity of the aqueous medium were the subject of variation. The initiator efficiency (Φ) increased up to 60% and the initiator exponent of the overall rate expression raised from 0.1 to 0.28 when a weak MF of 0.1T was applied to photochemical initiation. However, no appropriate effect was observed for thermal initiation. Kinetic analysis proved a reduction of the termination rate coefficient (kt) up to 40%. Photochemically initiated polymerizations in media of enhanced viscosity revealed the highest increment of the initiator efficiency ratio ΦMF/Φ and the most pronounced reduction of ktMF/kt. On the contrary, the propagation rate coefficient (kp) and the monomer exponent were not influenced by MF. Despite considerable increase of the polymerization rate in MF, no reduction of the molar mass was found. Compensation of increased ΦMF and decreased ktMF are suggested as explanation. The singlet–triplet intersystem crossing mechanism for radical pairs served to explain the MF effects.

Radical polymerization of vinyl acetate using p-acetylbenzylidene triphenylarsonium ylide as an initiator

p-Acetylbenzylidene triphenylarsonium ylide initiated radical polymerization of vinyl acetate in dioxane has been carried out at 65±0.1°C in polymerization tubes for 8 h under nitrogen. The initiator and monomer exponents are 0.44 and 1.5 respectively. The overall activation energy and value of k 2 p/ k t are 35 kJ mol −1 and 6.06×10 −3 l mol −1 s −1 respectively. The ylide is believed to dissociate to generate phenyl radicals which initiate the radical polymerization of vinyl acetate.

UV-curable powder coating

A combination of Michler's ketone and benzoyl peroxide was used as photoinitiator for photopolymerization of methyl methacrylate at 40°. Spectrophotometric analysis indicated equilibrium complexation between the initiator components; the complex is considered to be the actual initiating species, giving free radicals by photo-decomposition. The observed initiator exponent of 0.21 and monomer exponent of > I in various solvents reveal non-ideality in the photopolymerization kinetics. The non-idealities are interpreted in terms of initiator dependent chain termination mainly by primary radicals, in addition to the usual bimolecular termination.

Kinetics and mechanism of radical polymerization of methylmethacrylate using p-acetylbenzylidene triphenylarsonium ylide (p-ABTAY) as an initiator

Solution polymerization of methylmethacrylate (MMA) initiated by p-acetylbenzylidene triphenylarsonium ylide in dioxane was carried out at 60±0.2 °C up to 10 hrs. in a polymerization tube under a nitrogen atmosphere. The values of the initiator and the monomer exponent were computed as 0.46 and 1.03, respectively. The overall activation energy and kp2/kt were calculated as 53 KJ/mole and 1.19 × 10−2 L/mol·s, respectively for the polymerization.

Photopolymerization of methyl methacrylate using a morpholine-sulfur dioxide charge-transfer complex as the photoinitiator

Photopolymerization of the vinyl monomer (M) of methyl methacrylate (MMA) was kinetically studied by using near-UV/visible light at 40°C and employing a morpholine (MOR)-sulfur dioxide (SO 2 ) charge-transfer(C-T complex as the photoinitiator. The rate of polymerization (R P ) was found to be dependent on the morpholine: sulfur dioxide mole ratio; the 1: 2 (MOR-SO 2 ) complex acted as the latent initiator complex C which underwent further complexation with the monomer molecules to give the actual initiating complex I. Using the 1: 2 (MOR-SO 2 ) C-T complex as the latent initiator, the observed kinetics may be expressed as R P [MOR-SO 2 ] 0.27 [M] 1.10 . Benzoquinone behaved as a strong inhibitor. Polymers obtained tested positive for the incorporation of a sulphonate-type end group. Polymerization followed a radical mechanism. Kinetic nonideality as revealed by a low initiator exponent and monomer exponent of greater than unity was explained on the basis of a prominent primary radical termination effect.

Cationic photopolymerization of 1,2-epoxy-6-(9-carbazolyl)-4-oxahexane

Photopolymerization of 1,2-epoxy-6-(9-carbazolyl)-4-oxahexane (ECOH) initiated with diphenyl iodonium tetrafluoroborate and cyclopropyldiphenyl sulfonium tetrafluoroborate has been studied. The influence of diols on photopolymerization of ECOH has been examined. The results show that in the presence of 1,2-ethanediol (ED) reaction proceeds by the activated monomer mechanism. The monomer exponents were established for photopolymerization of ECOH in 1,2-dichloroethane with the iodonium salt and for that in the presence of ED.

Photopolymerization of methyl methacrylate using morpholine–bromine charge transfer complex as the photoinitiator

Photopolymerization of methyl methacrylate (MMA) was kinetically studied using near UV/visible light at 40°C and by employing the morpholine (MOR)–bromine (Br2) charge transfer (CT) complex as the photoinitiator. The rate of polymerization (Rp) was dependent on the morpholine:bromine mole ratio; the 1:2 (MOR–Br2) CT complex acted as the latent initiator complex C which underwent further complexation with monomer molecules to give the actual initiator complex, I. Using a 1:2 (MOR–Br2) CT complex as the latent initiator, the initiator exponent for bulk photopolymerization of MMA was 0.08 and the monomer exponent determined from studies of photopolymerization in a carbon tetrachloride diluted system was 1.20. Benzoquinone behaved as a strong inhibitor and the polymers tested positive for the incorporation of bromine atoms as end groups. Polymerization followed a radical mechanism. Kinetic non-ideality was revealed by low (≪0.5) initiator exponent and a monomer exponent of greater than unity; it was explained in terms of primary radical termination.

Analysis of nonideal kinetics in the polymerization of methyl methacrylate using some complex initiator systems based on a pyridine–sulfur dioxide charge transfer complex

The kinetic nonideality in the polymerization of methyl methacrylate was studied with the use of pyridine-sulfur dioxide charge transfer complex as the initiator under different conditions. The following systems were studied: (1) aqueous polymerization of methyl methacrylate (MMA) with the use of a pyridine-sulfur dioxide charge transfer complex as initiator, (2) photopolymerization of MMA initiated by the pyridine-sulfur dioxide complex in the presence of carbon tetrachloride, (3) photopolymerization of MMA in bulk and in a pyridine-diluted system with pyridine-sulfur dioxide alone and in combination with benzoyl peroxide as a photoinitiator. Polymerization in all these cases proceeded by radical mechanisms. The kinetic parameter /kt for the aqueous system was 3.65 L mol−1 s−1, and for nonaqueous systems were 1.27 × 10−2 to 1.40 × 10−2 L mol−1 s−1. The monomer exponent and initiator exponent for ideal free radical polymerization systems are 1.0 and 0.5, respectively. In the system studied, the ideal kinetics were followed at specific concentration ranges of both monomer and initiator. At different concentration ranges, the systems behave nonideally. The kinetic nonidealities in monomer exponents, i.e., lower or higher than unity, were explained on the basis of (1) the rate-enhancing effect of different solvents, and (2) a radical generation step by in situ initiator monomer complexation reaction. The kinetic nonidealities in initiator exponent were analyzed and interpreted in terms of (1) primary radical termination, and (2) degradative initiator transfer with little reinitiator. Analysis of kinetic data shows that the degradative initiator transfer effect is more prominent in the present systems. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 67: 585–595, 1998

Analysis of nonideal kinetics in the polymerization of methyl methacrylate using some complex initiator systems based on a pyridine-sulfur dioxide charge transfer complex

The kinetic nonideality in the polymerization of methyl methacrylate was studied with the use of pyridine-sulfur dioxide charge transfer complex as the initiator under different conditions. The following systems were studied: (1) aqueous polymerization of methyl methacrylate (MMA) with the use of a pyridine-sulfur dioxide charge transfer complex as initiator, (2) photopolymerization of MMA initiated by the pyridine-sulfur dioxide complex in the presence of carbon tetrachloride, (3) photopolymerization of MMA in bulk and in a pyridine-diluted system with pyridine-sulfur dioxide alone and in combination with benzoyl peroxide as a photoinitiator. Polymerization in all these cases proceeded by radical mechanisms. The kinetic parameter /kt for the aqueous system was 3.65 L mol−1 s−1, and for nonaqueous systems were 1.27 × 10−2 to 1.40 × 10−2 L mol−1 s−1. The monomer exponent and initiator exponent for ideal free radical polymerization systems are 1.0 and 0.5, respectively. In the system studied, the ideal kinetics were followed at specific concentration ranges of both monomer and initiator. At different concentration ranges, the systems behave nonideally. The kinetic nonidealities in monomer exponents, i.e., lower or higher than unity, were explained on the basis of (1) the rate-enhancing effect of different solvents, and (2) a radical generation step by in situ initiator monomer complexation reaction. The kinetic nonidealities in initiator exponent were analyzed and interpreted in terms of (1) primary radical termination, and (2) degradative initiator transfer with little reinitiator. Analysis of kinetic data shows that the degradative initiator transfer effect is more prominent in the present systems. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 67: 585–595, 1998

Photopolymerization of methyl methacrylate using pyridinium chlorochromate (PCC) as the photoinitiator

Photopolymerization of the vinyl monomer (M) methyl methacrylate (MMA) was studied at 40 °C using pyridinium chlorochromate (PCC) as the photoinitiator. Observed dependence of rate of polymerization, R p , on concentrations of PCC and MMA may be expressed as R p ∝ [PCC] 0.21 · [M] 1.0. PCC-induced photopolymerisation of MMA proceeds via instantaneous complexation between the initiator (PCC) and the monomer (MMA). Chain initiation actually takes place by radicals derived from photodecomposition of the said complex and the PCC-MMA complex is believed to be the actual initiating species. The polymers formed tested positive to the sensitive dye-partition test for the presence of halogen (chlorine) atom end groups in polymers. Nonideality in the polymerization kinetics in respect of initiator exponent < 0.5 is explained on the basis of significant termination by degradative initiator transfer over and above the normal bimolecular mode of termination. Monomer exponent of unity precludes consideration of primary radical termination as the cause of kinetic nonideality.

Photopolymerization of methyl methacrylate with the use of morpholine-chlorine charge transfer complex as the photoinitiator

Polymerization of methyl methacrylate (MMA) was kinetically studied under photo condition using near UV visible light at 40°C and employing morpholine (MOR)–chlorine (Cl2) charge transfer (C-T) complex as the photoinitiator. The rate of polymerization (Rp) was dependent on morpholine/chlorine mole ratio; the 1 : 2 (MOR–Cl2) C-T complex acted as the latent initiator complex, C, which underwent further complexation with the monomer molecules to give the actual initiator complex, I. Using 1 : 2 (MOR-Cl2) C-T complex as the latent initiator, the initiator exponent evaluated for bulk photopolymerization of MMA was 0.071 and monomer exponent determined from studies of photopolymerization in benzene diluted system was 1.10. Benzoquinone behaved as a strong inhibitor and the polymers tested positive for the incorporation of chlorine atom end groups. Polymerization followed a radical mechanism. Kinetic nonideality as revealed by low (≪0.5) initiator exponent and a monomer exponent of greater than unity were explained in terms of primary radical termination effect. © 1997 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 35: 1681–1687, 1997

Hydroxy(tosyloxy)iodo]benzene as Thermal initiator for the Radical Polymerization of Methyl Methacrylate

Abstract The thermal polymerization of methyl methacrylate in a solution of N,N-dimethylacetamide has been studied using [hydroxy(tosyloxy)- iodo]benzene (HTIB) as the initiator. The rate of polymerization was a direct function of the monomer and initiator concentrations. The initiator and monomer exponent values expressing this dependence were found to be 1.0 and 0.8, respectively. The overall activation energy of polymerization was estimated to be 45 kJ·mol−-1. The polymerization was inhibited in the presence of hydroquinone. The effect of various solvents on the polymerization rate was studied. The polymer prepared with HTIB (0.47 × 10−3 mol·L−-1) had a number-average molecular weight of 138,000 and a glass transition temperature of 106°C. The polymer showed good thermal stability as determined by thermogravimetric analysis.

Polymerization of styrene by photoexcited safranine T without additives

AbstractStyrene can be photopolymerized with methanolic solutions of safranine T(STH+) in the absence of any additives. Under these conditions the monomer acts as an electron donor for the excited singlet state of STH+, and after electron transfer an initiating semireduced STH+ radical is produced. The experimentally determined monomer exponent of α = 2 indicates additional deactivation reactions of the primary radicals. The polymerization rate depends on the dye concentration also in those regions, in which all light is already absorbed. Presumably, this dependence is caused by a comproportionation reaction between STH+ and substituted leuco‐safranine T formed in the course of polymerization. © 1993 John Wiley &amp; Sons, Inc.

Polymerization of methyl methacrylate using isatoic anhydride–bromine donor–acceptor complex as the photoinitiator

AbstractIsatoic anhydride (IA) alone did not initiate photopolymerization of methyl metacrylate (MMA) at 40°C when exposed to visible light for about 180 min. But IA, when used in combination with bromine (Br2) as the initiator, initiated the photopolymerization of MMA readily under the same conditions. This behavior was explained by the formation of a donor‐acceptor type of complex between IA and Br2 in the presence of MMA. The polymerization was found to proceed via a free radical mechanism and the radical generation process was considered to follow an initial complexation reaction between the initiator components and monomer. The complex initiator showed nonideal kinetics for the present system (initiator exponent &lt; 0.5) and was analyzed. The monomer exponents varied from 0.83 to 1.15 normally depending on the nature of solvent used. Initiator‐dependent chain termination was significant as well as the bimolecular mode of chain termination. © 1993 John Wiley &amp; Sons, Inc.

Photocrosslinking of silicones. VI. Photocrosslinking kinetics of silicone acrylates and methacrylates

AbstractThe photoinduced radical crosslinking of silicones containing pendant acrylate and methacrylate groups has been investigated with calorimetric and ESR measurements. Oxygen very strongly influences this process, which leads to a prolonged induction period and a pseudo first‐order termination reaction between polymer radicals and oxygen. Kinetically, such reaction steps are responsible for light intensity and monomer exponents, both of unity. In the absence of oxygen, second‐order processes take place between polymer and primary radicals. The results of conversion‐time and reaction‐rate time measurements using stationary irradiations and postpolymerization experiments agree with the corresponding kinetic expressions. Long‐lived polymer radicals and their decay have also been determined with ESR techniques. Long‐chain spacer groups, which link the unsaturated ester moiety at the silicone backbone, increase the crosslinking rate. The final conversions of the double bonds exceed high values in each case. © 1992 John Wiley &amp; Sons, Inc.

Light-induced polymer and polymerization reactions—46. Dye pigments as heterogeneous sensitizers for the photopolymerization of vinyl monomers

Three dyed organic pigments of the quinone, acridone and phthalocyanine series have been investigated for their usage as heterogeneous photo-initiators in vinyl polymerizations. Using surfactants, the pigments formed sols in aqueous solutions of acrylamide. By irradiation in the presence of typical reductants or oxidants for excited dye molecules, polymers are formed without any fading of the pigments. Compared with homogeneous photo-initiators, the polymerization quantum yields of these heterogeneous photo-initiators are low. The results of kinetic measurements and flash photolysis experiments of homogeneous solutions of the quinone pigment suggest photo-induced electron transfer processes as key steps of the polymerization initiation. An unusual monomer exponent of 2.1 has been found.

Mechanistic and kinetic studies on the polymerization of styrene initiated by dimethyl sulfonium 2‐pyridyl carbonyl methylide

AbstractDimethyl sulfonium 2‐pyridyl carbonyl methylide (Ypy‐s) initiated radical polymerization of styrene in dimethyl sulfoxide at 85±0.1°C for 6 h under a nitrogen blanket using dilatometric techniques has been studied. The initiator and monomer exponent values were calculated to be 0.5 and 1.2, respectively. The system follows ideal radical kinetics with bimolecular termination. The higher monomer exponent value is ascribed to significant solvent effects on the initiation rate. The overall activation energy and average value of k2p/kt are 52.0 kJ mol−1 and 1.0 × 10−3 litre mol−1 s−1, respectively. The polymerization was retarded in the presence of hydroquinone or benzene; dimethylformamide, however, enhanced the rate of polymerization. Kinetic data and ESR studies indicate that the overall polymerization takes place via triplet carbene formation which acts as a source of free radicals.

Photoinitiierte Polymerisation mit Dialkoxythiocarbonyldisulfiden – eine Polymerisationsreaktion mit Primärradikalabbruch

Photoinitiated Polymerization with Dialkoxy Thiocarbonyl Disulfides – a Polymerization Reaction with Primary Radical TerminationThe photoinduced free radical polymerization of methyl methacrylate (MMA) and some other vinyl monomers using dialkoxy thiocarbonyl disulfides (1–4) as photoinitiators was studied. The photolysis of these initiators leads to cleavage of the SS bond, which was determined by spin trapping experiments with phenyl tert‐butyl nitrone. No evidence was found for a further thermal decomposition of the primary alkoxy thiocarbonyl sulfide radicals (R·) at room temperature. In the absence of scavengers the primary radicals react back exclusively to the initial compounds, due to a strong cage effect. By means of UV spectroscopic measurements and in the presence of MMA the quantum yields of the initiator decomposition were detected to be 0.8. The polymerization of acrylic and methacrylic derivatives can be initiated by the R·, contrary to the situation with fumarates and maleates. The mechanism of MMA polymerization depends on the light intensity absorbed by the initiators. At high intensities the combination of primary and polymer radicals terminates the chain reaction. This follows from the measured monomer exponent of α = 2, the light intensity exponent of β = 0,2 and the number of thiocarbonyl end groups of 2 in the polymers isolated. Contrary to this, in the low intensity region the experimental data obey the ideal kinetic equation. Kinetic modelling gives evidence for an interaction of the monomer with the cage radicals.

Radical polymerization of styrene initiated by p-acetyl benzylidene triphenylarsonium ylide

The kinetics of the polymerization of styrene in bulk and in dilute systems in the presence of p-acetyl benzylidene triphenylarsonium ylide ( p-ABTAY) as radical initiator has been examined at 60 ± 0.1°C for 20 h under N 2. The values of the initiator exponent and the monomer exponent showed that the system follows ideal radical kinetics with bimolecular termination. The overall activation energy and average value of k 2 p k t are 64.6 kJ mol −1 and 0.10 × 10 −2 l mol −1 s −1, respectively. The ylide dissociates to produce phenyl radical, which brings about polymerization.