Benzophenone-sensitized photopolymerization of methyl methacrylate using dimethyl aniline–maleic acid combination as photoinitiator

Benzophenone (BP)-sensitized photopolymerization of methyl methacrylate (MMA) in near UV/visible light was studied at 40°C using dimethylaniline maleic acid (DMA—MA) combination as the photoinitiator. An instantaneous 1:1 complexation between DMA and MA takes place when they are mixed together in acetonitrile. Also, instantaneous complex formation occurs between DMA and MMA and between MA and MMA when they are dissolved in MMA in low concentrations, separately. Interestingly, when equimolar proportions of DMA and MA are mixed together in MMA, there is indication for further instantaneous complexation between (DMA—MMA) complex and (MA—MMA) complex forming the actual initiating species in the photopolymerization system. Initiator exponent was 0.28 and monomer exponent varied between 0.0 to 1.8 depending on the nature of the solvent and range of dilution used. Analysis of kinetic data indicates a free radical mechanism for the polymerization with initiator-dependent termination. Chain termination via degradative initiator transfer is quite significant; but the degradative effect becomes much less prominent in the higher range of initiator concentration indicating that the reinitiation reaction following the initiator transfer process assumes more proportionate significance as the initiator concentration is increased, probably as a result of higher reinitiation efficiency. Polymers obtained gave evidence for the incorporation of aromatic (amine) end groups in them.     

Photopolymerization of methyl methacrylate using benzophenone-dimethylaniline combination as photoinitiator

Photopolymerization of MMA at 35° was studied using benzophenone (BP)-dimethylaniline (DMA) combination as photo-redox initiator. Initiator exponent was 0.13; monomer exponent was < 1.0 in chlorinated solvents and > 1.0 in other solvents. Photoreduction of BP by DMA is considered to produce chain-initiating radicals and analysis of kinetic data indicates this process to be solvent and monomer dependent. Chlorinated solvents are indicated to be much more reactive than other solvents. The photopolymerization is also characterized by significant primary radical termination.     

Photopolymerization of methyl methacrylate and some other vinyl monomers with the use of chlorine as photoinitiator

Low concentrations (0.001–0.03M) of chlorine easily induce photopolymerization of MMA at 40°C. Kinetic data indicate that polymerization follows a radical mechanism involving complexation of monomer by the initiator and initiation takes place through radical generation during photodecomposition of the initiator-monomer complex. Termination appears to take place bimolecularly. The k_p²/k_t value for MMA polymerization at 40°C was found to be 0.83 × 10^?2. Rates of chlorine-initiated photopolymerization were found to decrease in the order MMA, EMA ? VA, Sty > MA.     

Photopolymerization of Methyl Methacrylate Using the Benzil-Dimethylaniline Combination as the Photoinitiator

Benzil (BZL)-dimethylaniline (DMA) exciplex interaction has been utilized to initiate the photopolymerization of methyl methacrylate at 40°C in bulk and in solution. Depending on the nature of the solvent used, the monomer exponent values varied between 0.47 to 2.76. Initiator exponent values were found to be 0.29 and 0.15 with respect to [BZL] and [DMA], respectively. A low value of k_p ²/k_t and the high initiator transfer constant values indicated significant initiator-dependent termination. The semipinacol radical formed during irradiation is thought to be mainly responsible for primary radical termination while the generated ion radicals are presumed to participate in degradative initiator transfer.     

Effect of benzophenone on the H2O2-induced photopolymerization of methyl methacrylate

Benzophenone (BP) in low concentrations (<0.001 mol 1^?1) produces a rate enhancing effect in the H₂O₂-induced bulk photopolymerization of MMA. R_p is proportional to [H₂O₂]^0.4 and [BP]^0.4, and $\text{k}{}_{\mathrm{p}}{}^2\text{k}{}_1$ at 30° is 1.00 × 10^?2 1.mol^?1 sec^?1. In diluted systems, different solvents produce different kinetic effects, reaction order with respect to monomer being negative for IPA and THF as solvent, positive but <1.0 for benzene and chloroform, 1.2 for acetonitrile, CCl₄ and t-butanol and 1.8 for DMA. The variable solvent effect is attributed to modification of the initiation process by the various solvents to different extents. Kinetic analysis of data for bulk photopolymerization gives evidence for primary radical termination and degradative initiator transfer.     

Investigation of the effect of reaction conditions on the synthesis of multiarm-star polyisobutylene-polystyrene block copolymers

New multi-arm star block copolymers comprising of rubbery polyisobutylene (PIB) midsegment and glassy polystyrene (PS) end blocks have been synthesized by carbocationic polymerization using a new multifunctional initiator, hexaepoxy squalene (HES), with TiCl₄ coinitiator, di-t-butylpyridine (DtBP) as a proton trap and N,N-dimethylacetamide (DMA) as an electron pair donor in methylcyclohexane (MeCHx)/methyl chloride (MeCl) solvent mixtures at −80 °C. It was found that reaction conditions, such as solvent composition, HES/isobutylene (IB) ratio and TiCl₄ concentration, have profound influence on initiator efficiency and functionality. Living conditions were achieved in the presence of DMA in MeCHx/MeCl 60/40 v/v, while in the absence of DMA, the M_n-conversion plot showed a considerable intercept. Depending on the reaction conditions, the PIB midblocks had 3-10 arms. Reaction rates increased with increasing solvent polarity and TiCl₄ concentration. Living narrow molecular weight distribution PIBs (M_w/M_n=1.1-1.2) were reacted with styrene (St) solution containing DtBP and DMA to yield multiarm-star PIB-PS block copolymers. Blocking was evidenced by SEC analysis and copolymers with 8.9-28.6 wt.% PS, M_n∼164,000-609,000 g/mol and M_w/M_n=1.32-1.88 were successfully synthesized.     

How the interplay of different control mechanisms affects the initiator efficiency factor in controlled radical polymerization: An investigation using organometallic Mo-based catalysts

Compound CpMoI₂(iPr₂dad) (iPr₂dad = iPrNCHCHNiPr), obtained by halide exchange from CpMoCl₂(iPr₂dad) and NaI, has been isolated and characterized by EPR spectroscopy, cyclic voltammetry, and X-ray crystallography. Its action as a catalyst in atom transfer radical polymerization (ATRP) and as a spin trap in organometallic radical polymerization (OMRP) of styrene and methyl acrylate (MA) monomers has been investigated and compared with that of the dichloro analogue. Compound CpMoCl₂(iPr₂dad) catalyzes the ATRP of styrene and MA with low efficiency factors f (as low as 0.37 for MA and ethyl 2-chloropropionate as initiator), while it irreversibly traps the corresponding growing radical chains under OMRP conditions. On the other hand, compound CpMoI₂(iPr₂dad) has a greater ATRP catalytic activity than the dichloro analogue and yields f = 1 for MA and ethyl 2-iodopropionate as initiator. Under OMRP conditions, it does not irreversibly trap the growing radical chains. This comparison serves to illustrate the general principle that low initiator efficiency factors, sometimes observed in ATRP, may result from the interplay of the ATRP and OMRP mechanisms, when the latter ones involves an irreversible radical trapping process.     

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 (R_p) 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     

Photopolymerization of methyl methacrylate using a combination of rhodamine 6G and benzoyl peroxide as photoinitiator in nonaqueous media

Photopolymerization of methyl methacrylate (MMA) in visible light was studied at 40°C using Rhodamine 6G—Benzoyl peroxide combination as photoinitiator. The photopolymerization proceeds by a free radical mechanism and the radical generation process occurs by an initial complexation reaction between the initiator components. Kinetic data indicated a lower-order dependence of R_p on initiator concentrations (initiator exponent < 0.5). Initiator-dependent chain termination was significant along with the bimolecular mode of chain termination.     

Alkyl halide/tertiary amine as novel initiators for free radical polymerizations of methyl methacrylate,methyl acrylate and styrene

A series of combinations of alkyl halide with tertiary amine such as ethyl α-bromophenylacetate/tris[2-(dimethylamino)ethyl)]amine (αEBP/Me₆TREN), ethyl 2-bromoisobutyrate/triethylamine (EBiB/TEA), and ethyl 2-chloropropionate/N,N,N′,N′,N′′-pentamethyldiethylenetriamine (ECP/PMDETA) have been developed as novel free radical initiators and used for the polymerizations of methyl acrylate (MA), methyl methacrylate (MMA) and styrene (St). The effects of the structure of alkyl halide and tertiary amine on the polymerization of MA were investigated. Gel permeation chromatograph (GPC) and proton nuclear magnetic resonance (¹H NMR) have been utilized to analyze the end group of the obtained poly(methyl acrylate). Electron spin resonance (ESR) spectroscopy was employed to identify the structure of the radicals produced by αEBP/Me₆TREN, and the results indicated that αEBP reacted with Me₆TREN via a single electron transfer (SET) nucleophilic mechanism to produce corresponding ethyl α-phenylacetate radicals which subsequently initiated the polymerization of MA. As both alkyl halide and tertiary amine are commercially available at low cost, non-explosive, and ease of use and storage in comparison with conventional azo, peroxide or persulfate initiators, the combination of alkyl halide and tertiary amine as a free radical initiator is promising for large-scale practical applications.     

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

Isatoic 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 < 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 & Sons, Inc.     

Photopolymerization of methyl methacrylate using triethylene tetramine-benzophenone combination as the photoinitiator

Photopolymerization of MMA at 40 was studied using triethylene tetramine (TETA)-benzophenone (BP) combination as the initiator. Initiator exponent is 0.5; monomer exponent is 1.0 in benzene, toluene, chlorobenzene, acetone and methyl ethyl ketone, < 1.0 in halomethanes (chloroform and carbon tetrachloride) and > 1 in methanol. Photoreduction of BP1(BP in the excited state) by ground state TETA via an exiplex formation is considered to produce chain-initiating radicals. Polymers obtained were found to bear amine end-groups. Termination takes place bimolecularly (initiator exponent being 0.5 in bulk as well as in diluted systems). The radical generation process is dependent on the nature of the solvent. The role of solvents in modifying the initiation or radical generation process has been examined and analysed.     

Polymerization of Methyl Methacrylate Using Acridone-Bromine Combination as the Photoinitiator

The photopolymerization of methyl methacrylate (MMA) in visible light was studied at 40°C using the acridone-bromine (acridone-Br₂) combination as the photoinitiator. 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 monomer and each initiator component (acridone and Br₂), followed by further interaction between these two initiator-monomer complexes. Kinetic data indicated a lower-order dependence of R on initiator concentrations (initiator exponent < 0.5). Initiator-dependent chain termination was signifi-cant along with the usual bimolecular mode of chain termination. The monomer exponent varied from about 1.00 to 2.00, depending on the nature of solvents used. The nonidealities in this system were also analyzed.     

Polymerization of methylmethacrylate with cetyl pyridinium bromide (CPB)-benzoyl peroxide (BZ2O2) combination as a redox initiator and with CPB as a lone photoinitiator

Polymerization of MMA was carried out in near-bulk and in fairly dilute solutions in DMF at 40° with (1) CPB-BZ₂O₂ combination as the redox initiator in the dark and (2) CPB as the sole photoinitiator in visible light. R_p was proportional to ([CPB] [BZ₂O₂])^0.18 for the redox polymerization and to [CPB]^0.35 for the photopolymerization both in near-bulk (10% DMF, v/v) and in high dilution (50% DMF, v/v). Polymerization was inhibited by hydroquinone in each case indicating a radical mechanism. Effect of several solvents/additives on the polymerization revealed that dimethyl formamide, acetonitrile and pyridine acted as rate enhancing solvents in the redox polymerization while in the photopolymerization they acted as normal diluents; benzene, methanol, acetone and chloroform exhibited inert nature while formamide and acetamide behaved as retarding additives in both types of polymerization. Initiator transfer of the degradative type reasonably explains kinetic nonidealities.     

Photopolymerization of methyl methacrylate and other vinyl monomers with the use of N-bromosuccinimide as photoinitiator

Polymerization of MMA was done in the presence of visible light (440 nm) with the use of N-bromosuccinimide (NBS) as the photoinitiator. The initiator exponent and intensity exponent were 0.5, and the monomer exponent was found to be unity. The polymerization was inhibited in the presence of hydroquinone. The average k_p²/k_t for this photopolymerization system was found to be 0.296 × 10^?2 and the activation energy of photopolymerization was 4.67 kcal/mole. Kinetic and other evidence indicate that the overall polymerization takes place by a radical mechanism. With NBS as the photoinitiator, the order of polymerizability at 40°C was MMA, EMA ? MA ? VA, and styrene could not be polymerized under similar conditions.     

Photochemistry of thioxanthones VI: A polymerization,spectroscopic and flash photolysis study on novel water-soluble substituted 3-(9-oxo-9H-thioxanthene-2,3-γ-4-yloxy)-N,N,N-trimethyl-1-propanaminium salts

The photopolymerization activity and photochemistry of nine novel water-soluble 3-(9-oxo-9H-thioxanthene-2,3-γ-4-yloxy)-N,N,N-trimethyl-1-propanaminium salts is examined in water and 2-propanol using absorption, luminescence and conventional microsecond flash photolysis techniques. For both the chloro and the methylsulphonate salts, photopolymerization activity in water follows the order of substitution 4- > 2- > 3-. Methyl substitution in the 1-position deactivates the molecule and this is reflected by a reduction in both the photopolymerization activity and luminescence (fluorescence and phosphorescence) quantum yields and the triplet lifetime. Intramolecular hydrogen-atom abstraction is the main competitive process suppressing photochemical activity. The longest wavelength absorption maxima and extinction coefficients and luminescence quantum yields are similar to those of water-soluble 2-substituted derivatives studied previously, indicating a lowest excited singlet state with strong n̄n̄^* character. On changing the solvent from 2-propanol to water all the fluorescence quantum yields are enhanced and this is consistent with a strong degree of charge transfer character in the lowest excited singlet state. From conventional microsecond flash photolysis results, transient absorptions below 400 nm are associated with the intermediate ketyl radical formed by the lowest excited singlet/triplet states of the thioxanthene molecule abstracting a hydrogen atom from the amine synergist (used in photopolymerization) while absorptions above 400 nm are associated with the radical anion intermediate formed by a concurrent electron abstraction process from the amine. The latter is confirmed through a detailed study on the effect of pH and amine concentration on transient production, as well as the effect of various amines of increasing ionization potential. Transient formation is only partly reduced in aerobic conditions and is consistent with our earlier findings and conclusions that photopolymerization activity is associated, in the main, with electron abstraction by the lowest excited singlet state of the thioxanthone molecule from the tertiary amine synergist. This is confirmed by a correlation between the photopolymerization activity and the ionization potential of different amines.     

Structure and thermal degradation of poly(vinyl chloride) synthesized by various polymerization catalyst

Relationship between the structure and the thermal stability of poly(vinyl chloride) synthesized by various polymerization catalysts was investigated. The Cp∗Ti(OPh)/MAO catalyst, n-butyllithium (n-BuLi), the Cu(0)/TREN/CHBr₃/DMSO catalyst, benzoyl peroxide/N,N-dimethylaniline (BPO/DMA), 2,2’-azobis(2.4-dimethylvaleronitrile) (V-65) was used as the polymerization catalyst. The temperature of 5% weight loss was in the following order; Cp∗Ti(OPh)₃/MAO (280 °C) > n-BuLi (264 °C) > V-65 (249 °C) > Cu(0)/TREN/CHBr₃/DMSO (215 °C) > BPO/DMA (209 °C), and the rate of weight loss was the reverse order of T_−5% in the isothermal degradation of the polymer from 160 °C to 220 °C. The T_−5% value of the polymer obtained from the polymerization with Cp∗Ti(OPh)₃/MAO catalyst increased with an increase of the molecular weight of PVC, in contrast to that PVC obtained with the radical initiator did not depend on the molecular weight of the polymer. The T_−5% value of PVC macromonomer was 285 °C, while the temperature of non-functionalized PVC was 262 °C, respectively. It is clear that the PVC macromonomer had a good thermal stability regardless of low-molecular weight.     

Three component ketocoumarin, amine, maleimide photoinitiator II

Three component photoinitiator systems containing N-substituted maleimide/ketocoumarin/tertiary amine have been used for the visible light photopolymerization of acrylate and thiol-ene monomers. Thin-film calorimetry studies were conducted. The polymerization exotherms of these systems with the blue (470 nm) and cyan (505 nm) LED light sources show that the multicomponent initiator package is an effective system for visible light polymerization of acrylate and thiol-ene monomers. Exotherms of a visible light initiator combination of camphorquinone/amine were recorded for comparison purposes.     

STUDY OF PHOTOSENSITIZED INITIATION SYSTEMS CONTAINING OXYGEN Ⅴ. THE EFFECT OF MERCAPTAN ADDITIVES

A kinetic study on the photopolymerization of methyl methacrylate (MMA) with benzophenone(BP)/triethylamine (TEA)/mercaptan systems as initiator has been carried out in the presence of oxygen.It was found that both aliphatic and aromatic thiols promote the photooxidation process, leadingto obvious decrease in induction period of photopolymerization. The rate-aereleration of aromaticthiols is more effective than that of aliphatic ones, such as p-toluene thiol used as additive increasesthe relative quantum yield φ_(O2)/φ_(N2) to 1.8.     

Synthesis and photoinitiating behavior of hyperbranched polymeric photoinitiators bearing coinitiator amine

A series of benzophenone (BP)‐terminated hyperbranched polyester (BoltornTM P1000), bearing amine moieties as synergists by reacting with piperidine, were synthesized as yellowish liquids with low viscosity, and used as polymeric photoinitiators (HPPIs). For comparison, acrylate groups were introduced to the terminals of hyperbranched polyester for obtaining a polymerizable photoinitiator. The chemical structures were characterized by FTIR and ¹H NMR spectroscopy. HPPIs and BP exhibited the similar absorptions by UV–vis spectroscopy. The photoinitiating behavior of HPPIs with trimethylolpropane triacrylate (TMPTA) as a trifunctional monomer was investigated by using photo‐DSC analysis. The results indicated that the maximum photopolymerization rate and unsaturation conversion of TMPTA initiated by HPPIs were both lower than that by BP. Among them, the HPPI with double tertiary amine moiety of BP moiety was found to be the most efficient photoinitiator. Additionally, the films cured with bisphenol A epoxy acrylate EB605 initiated by HPPIs were uniform and possessed high T_g from DMTA. Copyright © 2010 John Wiley & Sons, Ltd.