Rate constants for the addition of the 2‐hydroxy‐2‐propyl radical to alkenes in solution

Héberger, Károly; Fischer, Hanns

doi:10.1002/kin.550251105

Cited by 68 publications

(56 citation statements)

References 36 publications

Supporting

Mentioning

Contrasting

Unclassified

Order By: Relevance

“…These constants were used in the simulation of TR EPR spectra of spin-adducts ( Figure 3) and are in agreement with the reported values for radical adducts to double bonds. 4,24,25 The line width of the TR EPR of the spin adducts shows an alternation (Figure 3). In particular, the outermost components of the multiplets are narrower than the inner components.…”

Section: Direct and Tx-sensitized Photolysis Of Tmdpo In The Presencementioning

confidence: 99%

Direct and Sensitized Photolysis of Phosphine Oxide Polymerization Photoinitiators in the Presence and Absence of a Model Acrylate Monomer: A Time Resolved EPR, Cure Monitor, and PhotoDSC Study

et al. 2000

View full text Add to dashboard Cite

The effect of triplet sensitizers on the photoinitiated polymerization (cure) of a model acrylate monomer, isobornyl acrylate (IBOA), has been investigated. Time-resolved electron paramagnetic resonance (TR EPR) spectroscopy was employed to investigate the initiation of polymerization. Cure monitoring and photodifferential scanning calorimetry (photoDSC) were employed to follow the course of the polymerization. Thioxanthen-9-one (TX) and 2-isopropylthioxanthen-9-one (ITX) were found to be effective sensitizers of the photopolymerization, which was initiated by radicals produced from (2,4,6-trimethylbenzoyl)diphenylphosphine oxide (TMDPO) and bis(2,4,6-trimethylbenzoyl)phenylphosphine oxide (BAPO). TR EPR experiments demonstrated that the mechanism of sensitization involves T-T energy transfer from TX (or ITX) to TMDPO or BAPO followed by formation of radicals by R-cleavage of the photoinitiators. Direct photolysis of TMDPO and BAPO results in an absorptive chemically induced dynamic electron polarization (CIDEP) pattern due to the triplet mechanism (TM) of polarization of the substituted benzoyl and P-centered radicals produced by R-cleavage of the photoinitiators. TR EPR demonstrates that the same radicals were produced during direct and sensitized photolysis. However, a different CIDEP pattern is produced by photosensitization, namely an emissive/absorptive (E*/A) pattern. A TR EPR study of solutions containing phosphine oxide initiators and IBOA under direct and photosensitized conditions demonstrated that the polarized primary P-centered radicals add to the double bond of IBOA with the formation of polarized secondary radical adducts. Both primary and secondary radicals exhibit the same polarization pattern as the primary radical precursors, i.e., A in direct photolysis and E*/A in the presence of a sensitizer. The rate of polymerization of neat IBOA was followed by cure monitoring. In the presence of ITX the rate of cure increases significantly compared to direct photolysis of same. The heat evolved in the polymerization of IBOA photoinitiated (direct and sensitized) with TMDPO was monitored by photoDSC, and at early times was found to be higher in the sensitized photopolymerization. Time-intermittent UV irradiation allowed an estimation of the ratio of termination to propagation rate constants (k t /k p ) during dark periods of polymerization. The observed decrease of k t /k p with the progress of polymerization is discussed. The results suggest that photosensitization may provide a means of manipulating and controlling the parameters of photocuring of acrylates.

show abstract

Section: Direct and Tx-sensitized Photolysis Of Tmdpo In The Presencementioning

confidence: 99%

Direct and Sensitized Photolysis of Phosphine Oxide Polymerization Photoinitiators in the Presence and Absence of a Model Acrylate Monomer: A Time Resolved EPR, Cure Monitor, and PhotoDSC Study

et al. 2000

View full text Add to dashboard Cite

show abstract

“…The adduct radical 7c produced only a very weak signal, probably because the addition of the ketyl radical 2c to vinyl pivalate (7a) is relatively slow. For example, it is known that for a compound of similar structure, vinyl acetate, a rate constant of addition of ketyl radicals k add ) 7500 M -1 s -1 has been found in 2-propanol at 296 K. 38 Thus, the rate of addition of 2-hydroxy-2-propyl radicals to 7a is probably slower than the spin-lattice relaxation of reactive radicals, and spin polarization disappears before addition occurs.…”

Section: Tr-esr Experimentsmentioning

confidence: 99%

“…We report here a systematic study using standard photoinitiators (Scheme 1) of the addition of two well-studied radicals (phosphinoyl [35][36][37] and 2-hydroxy-2-propyl [38][39][40] ) to the bifunctional monomer, vinyl acrylate. The radicals were photochemically generated from precursors that are known to give strong spin polarized radicals.…”

Section: Introductionmentioning

confidence: 99%

Electron Spin Resonance and Laser Flash Photolysis Study of Radical Addition to Vinyl Acrylate and Related Alkenes

2001

View full text Add to dashboard Cite

Addition of two radicals (diphenyl phosphinoyl and 2-hydroxy-2-propyl) to the bifunctional alkene, vinyl acrylate, was studied by both time-resolved (TR) and steady-state (SS) ESR and laser flash photolysis (LFP). The adduct radicals are predominately a result of tail addition (addition to the unsubstituted carbon atom) of the acrylate double bond. Chemical structures of the adducts were established by comparison of the observed ESR spectra with those of adducts of the same reactive radicals to structurally related alkenes, tert-butyl acrylate and vinyl pivalate, which have only one type of double bond. Adducts of bulky phosphinoyl radicals to the acrylates demonstrate hindered rotation and a cis-trans isomerization at room temperature. The structure of the adduct radicals and the reactivity of the two radicals are discussed. Absolute rate constants for the addition of the phosphinoyl radical to the alkenes were measured by LFP in ethyl acetate at 296 K. A rate constant of k add ) (33 ( 1) × 10 6 M -1 s -1 was found for vinyl acrylate. The latter value is ∼1.5 times higher than that for tert-butyl acrylate (k add ) (22 ( 1) × 10 6 M -1 s -1 ) and ∼17 times higher than that for vinyl pivalate (k add ) (2.0 ( 0.1) × 10 6 M -1 s -1 ). These rate constants are consistent with conclusions derived from the ESR data. The results provide some insights into free radical polymerization of vinyl acrylate and vinyl ethers.

show abstract

“…For example, Buxton and Green [26] reported a value of k = 4.2 N 10 7 mol -1 N dm 3 N s -1 for the addition of an alkyl radical to acrylamide. Héberger and Fischer [27] noted that the rate constants for the addition of the 2-hydroxy-2-propyl radical vary with alkene substitution within more that 6 orders of magnitude depending on the polarity of the substituent and for some olefins they determined values in the range of 10 7 -10 8 mol -1 N dm 3 N s -1 .…”

Section: Resultsmentioning

confidence: 99%

Kinetics of the early stages of high-energy radiation initiated polymerization

Takács¹,

Wojnárovits

Dajka

2000

Macromol. Chem. Phys.

View full text Add to dashboard Cite

We describe our method based on pulse radiolysis with optical detection developed for the examination of the kinetics and mechanism of the first steps of high‐energy radiation initiated polymerization. The absorption spectra of the intermediates were obtained in cyclohexane solution of hexanediol diacrylate (HDDA) of different concentrations. In dilute solution (10 mmol·dm–3) and short time (10 μs) after the pulse, the spectrum of the monomer radicals was observed. On increasing the monomer concentration, the maximum of the spectrum was shifted to longer wavelength indicating the start of the oligomerization reaction. The increase in the time of observation resulted in a similar shift in dilute solution. From the kinetic curves the rate coefficients of termination for the monomer radicals (2·kt,m) and average rate coefficients of termination for the oligomer radicals of different chain length (2·kt) were determined. The average rate coefficient of termination was found to decrease in time (that is with increasing chain‐length).

show abstract

Rate constants for the addition of the 2‐hydroxy‐2‐propyl radical to alkenes in solution

Cited by 68 publications

References 36 publications

Direct and Sensitized Photolysis of Phosphine Oxide Polymerization Photoinitiators in the Presence and Absence of a Model Acrylate Monomer: A Time Resolved EPR, Cure Monitor, and PhotoDSC Study

Direct and Sensitized Photolysis of Phosphine Oxide Polymerization Photoinitiators in the Presence and Absence of a Model Acrylate Monomer: A Time Resolved EPR, Cure Monitor, and PhotoDSC Study

Electron Spin Resonance and Laser Flash Photolysis Study of Radical Addition to Vinyl Acrylate and Related Alkenes

Kinetics of the early stages of high-energy radiation initiated polymerization

Contact Info

Product

Resources

About