Macromol. Chem. Phys.200,1005–1013 (1999) 1005

Light-induced polymerisation of photoinitiator-free vinylether/maleimide systems

Christian Decker*1, Florence Morel1, Sonny Jo¨nsson2, Shan Clark3, Charles Hoyle3

1 Laboratoire de Photochimie Ge´nerale, Universite´ de Haute-Alsace, 3, rue Werner – 68200 Mulhouse,France

2 Fusion UV Systems Inc, Gaithersburg, MD, USA3 Polymer Science Dept., University of Southern Mississippi Hattiesburg, Mississippi, USA

(Received: August 4, 1998; revised: October 5, 1998)

SUMMARY: The photo-induced copolymerisation of electron donor/electron acceptor monomers has beenstudied by real-time infrared spectroscopy. With stoichiometric maleimide-vinyl ether mixtures, the reactionwas found to proceed within seconds upon UV exposure. For systems with an excess of vinyl ether, the twomonomers disappeared at essentially the same rate, to generate an alternating copolymer. In such photoinitia-tor-free systems, the initiating radicals are mainly formed by hydrogen abstraction by the excited maleimidemolecules. Highly crosslinked polymer networks have been obtained by light-induced copolymerisation ofbismaleimide and divinyl ether monomers. One of the distinct characteristics of this type of radical-inducedpolymerisation, beside the absence of any added photoinitiator, is that it is less sensitive to oxygen inhibitionthan the conventional UV-curable acrylate resins.

IntroductionMost monomers do not undergo homopolymerisationwhen they are exposed neat to UV radiation because ofboth their low absorbance in the UV range and a poorlyefficient production of initiating species. Therefore, thephotosensitive systems currently used in UV-curing appli-cations contain photoinitiators in their formulation. Asthe unreacted photoinitiator may affect the longtermproperties of UV-cured polymers, growing attention hasbeen given to photoinitiator-free formulations undergoingfast polymerisation upon UV exposure. A series of suchUV-curable systems consisting of a combination of elec-tron donor and electron acceptor monomers has beenrecently developed by Jo¨nsson et al.1–6) The most thor-oughly studied system consists of a stoichiometric mix-ture of a vinyl ether (VE) monomer (donor) and anN-substituted maleimide (MI) monomer (acceptor). Thereactivity of some VE/MI based systems was found to beas high as that of the widely used acrylate resins contain-ing a radical-type photoinitiator. Hydrogen abstractionplays a key role in the polymerisation efficiency, both inthe initiation step and in the propagation step through achain transfer reaction:

where DH represents either one of the two monomerswith labile hydrogen atoms and P9 a growing polymer

radical. The photopolymerisation ofN-alkylmaleimides isreported to proceed through hydrogen abstraction fromthe triplet of the maleimide7), with formation of two car-bon-centered radical sites. Both of them are expected toadd to the carbon-carbon double bond of the VE and MImonomers and thus initiate the polymerisation.

The reaction kinetics has been followed so far byphotocalorimetry, a technique which monitorsin situ theoverall heat flux evolved by the polymerisation of thetwo monomers1–4). It is possible to follow in real time thedisappearance of each one of the two monomers bymeans of infrared (RTIR) spectroscopy, and thus obtainimportant information on the mechanism of the copoly-merisation8). In this paper, we report on a kinetic study byRTIR spectroscopy on the light-induced polymerisationof photoinitiator-free vinyl ether/maleimide formulations,in an attempt to further elucidate the basic mechanism ofthis process.

Experimental part

Materials

The following monomers were used in this study: 4-hydroxy-butyl vinyl ether (HBVE) and divinyl ether of triethylenegly-col (DVE-3) from ISP, butylmaleimide andtert-butylmale-imide from Aldrich, 5-hydroxypentylmaleimide (HPMI) andtriethyleneglycol bismaleimide (TEGBMI) from Ciba,2-ethyl carbonate ethylmaleimide (ECEMI) from USM and aliquid bismaleimide with a 36 carbon cycloaliphaticbranched structure (Q-bond) from Quantum Materials. Thechemical formula of the various VE and MI monomers uti-lised in this study are given in Fig. 1. While the selected

Macromol. Chem. Phys.200, No. 5 i WILEY-VCH Verlag GmbH, D-69451 Weinheim 1999 1022-1352/99/0505–1005$17.50+.50/0

1006 C. Decker, F. Morel, S.Jonsson,S.Clark,C. Hoyle

vinyl ethersdo not absorblight above250nm, all the male-imide monomersexhibit a strong UV absorbancein the300nm region. The light emitted by the mercury lamp isthereforemainly absorbedby themaleimidemonomer.

Irradiation

The photopolymerisable formulation, comprisedof a givenmixture of VE and MI monomers,wascoatedonto a poly-(propylene)film at a typical thicknessof 10 lm. In mostexperiments,a secondpoly(propylene)film was laminatedon top of the liquid resin to preventthe diffusion of atmo-sphericoxygen.The samplewasplacedin the compartmentof an infraredspectrophotometerwhereit wasexposedfor afew secondsto the UV radiationof a mediumpressuremer-cury lamp (HOYA-SCHOTT-UV-200 s). The light intensityat the samplepositionwasin the range7 to 270mW N cm–2,as measuredby a radiometer(InternationalLight IL-390).Upon UV exposure,the maleimideundergoesrapid photo-bleaching(Fig. 2), thus allowing the incident light to pene-trate deeperinto the sample.SomeUV-curing experimentswerealsocarriedout with anon-lineIST-MINICURE setup,at a light intensity of 600mW N cm–2 and a belt speedsetbetween5 and60 m/min.

Analysis

The polymerisationreactioninducedby UV irradiation wasfollowed in situ by RTIR spectroscopy9). The disappearanceof eachof thetwo monomerswasmonitoredcontinuouslybysettingthewavelengthof theIR detectionat thevaluewhere

the relateddoublebondexhibitsa characteristic peak:1623cm–1 for the vinyl ether, 697 cm–1 for the maleimide,and1644cm–1 for theacrylate.Fig. 2 showstypical IR spectraofthe MI andVE monomersused,beforeandafter UV expo-surefor a giventime.Thespectrophotometerbeingsetin theabsorbancemode,conversionversustime curvesaredirectlyrecordeduponUV exposure of thesample.Fromtheslopeofthesecurves,the actual rate of polymerisation(Rp) can beevaluatedat any stageof the reaction.In most systems,Rp

defined as the maximum polymerisationrate is attainedinthe10 to 30%conversionrange.This analyticalmethodper-mits oneto determinealsoaccuratelythefinal monomercon-version, andthus the amountof residualunsaturationin theUV-curedpolymer.

Fig. 1. Chemicalformulaof themonomersused

Fig. 2. IR spectra of the maleimide and vinyl ether doublebond, before and after UV exposure. Light intensity = 45mW N cm–2

Light-inducedpolymerisation of photoinitiator-freevinyl ether/maleimidesystems 1007

Results

Influenceof thechemicalstructure of theVE andMImonomers

In the light-inducedpolymerisation of photoinitiator-freemixturesof MI andVE monomers,the generation of theinitiating radicals is consideredto proceedby hydrogenabstraction by theexcitedmaleimidemolecules. A possi-ble reaction scheme of the hydrogen abstraction fromexcited state N-alkylmaleimides, recently proposed byHoyle et al.6), is shownin Chart1. Although we have not

determinedthe spin configurationof triplet N-alkylmale-imide, the triplet maleimide has been proposed byMcGlynn et al.10) to be an electronic n,p* configuration.Thechemical structureof themonomers, in particular thepresenceof labile hydrogens, should be a key factor inthepolymerisation efficiency. In addition, thepresenceoftwo reactive groups on eachmonomer, i. e. divinyl ethers(DVE) and bismaleimides(BMI), is also likely to affectthepolymerisation kinetics,with formationof a tridimen-sional polymer network.

Photopolymerisation of monofunctional vinyl etherandmaleimidemonomers

If the copolymerisation is alternating, one would expectthe two monomers to exhibit similar conversion versustime profiles upon UV exposure. The kinetic curvesrecorded by RTIR spectroscopy for each monomer(Fig. 3) showthat this is indeedtrue for a stoichiometricmixture of HBVE andt-BuMI irradiatedat a light inten-sity of 45 mW N cm–2. It shouldbe noted that the male-imide monomer polymerises slightly faster and moreextensively than the vinyl ether monomer, probablybecauseof theadditionalformation of someMI homopo-lymer and 2 + 2 cycloaddition reactions11). To increasethereactivity of theformulation, t-BuMI wasreplacedbyhydroxypentylmaleimide (HPMI) which contains ab-

stractablehydrogenatomson thea-carbonadjacent to theOH groupin the N-substituted chain.The polymerisationwasfoundto proceed15 timesasfast,asshown in Fig. 4.Since HBVE and HPMI have similar hydroxyalkylchains,usingHMPI in placeof t-BuMI would resultin anincrease(essentially doubling) in the abstractable hydro-gen concentration. Accordingly, the rate increasewithHMPI could be dueto: (1) enhancementof intermolecu-lar hydrogenabstraction dueto the increasein total con-centration of abstractable hydrogens,or (2) the introduc-tion of anintramolecular hydrogenabstraction process, or(3) an increasein the triplet statepopulationfor HPMIcomparedto t-BuMI (preliminary laserflashanalysissug-geststhat t-BuMI mayhavea low triplet yield, comparedto otherN-substitutedaliphaticmaleimides).

Additional experiments suggest that the hydrogenatomsfrom the CH2—OH groups aremainly abstracted:with hydroxyethylmaleimide, the polymerisation pro-ceedsnearlyasfastaswith hydroxypentylmaleimide,andmuch fasterthanwith t-BuMI. With butyl-maleimide,thepolymerisation is only twice as fast as with t-BuMI,

Chart1: Hydrogenabstractionfrom excitedstateN-alkylmale-imides

Fig. 3. Polymerisationprofilesrecordedby RTIR spectroscopyuponUV exposureof theHBVE/t-BuMI combination(laminatedfilm). I = 45mW N cm–2

Fig. 4. Influence of the chemical structureof the maleimidemonomeron the light-inducedcopolymerisation with HBVE.I = 45 mW N cm–2. Laminatedfilm

1008 C. Decker, F. Morel, S.Jonsson,S.Clark,C. Hoyle

which contains no abstractable hydrogens.Finally, byassociating 2-ethyl carbonate ethylmaleimide (ECEMI)to HBVE, a fast copolymerization was found to occurupon UV exposure, as shownin Fig. 4. The triplet yieldof thesevariousN-substituted maleimides was found toincreasein the following ordert-BuMI a HEMI a HPMIa ECEMI, in good agreement with the polymerisationdataof Fig. 5.

It should bepointedout that thepolymersformeduponUV exposure of stoichiometric mixtures of monofunc-tional VE andMI monomers were found to be over 90%insoluble in organic solvents.A chain transfer reactionmustbe responsiblefor this effect, asit creates newradi-cal sitesby hydrogen abstraction on the polymer chain,andon the monomersaswell, thusleading to the forma-tion of cross-linked polymers. By reducing themolecularmobility in the solid polymer formed, crosslinking maybe responsible for the premature endingof the polymeri-sationand the observed amountof residualunsaturationin theUV-curedsample.For theHBVE/t-BuMI combina-tion, an additional factor is the low initiation efficiency.Indeed,when a radical photoinitiator was addedto thissystem,a MI conversion superior to 90% was reachedwithin 20 s (seelastsection andFig. 14).

Photopolymerisationof difunctionalvinyl etherandmaleimidemonomers

In most UV-curing applications, multifunctional mono-mers are used to generate highly resistant cross-linkedpolymers.Whena stoichiometricmixtureof divinyl etherof triethyleneglycol (DVE-3) and triethyleneglycol bis-maleimide (TEGBMI) wasexposed to UV radiation, thepolymerisation of both monomers was found to proceedas fast as with the very reactive HBVE/HPMI system(Fig. 5). However, the formation of the tridimensional

polymer network, with its related mobility restrictions,leads to a premature ending of the chainreaction, so thatthe UV-curedpolymer containsa relatively large amountof residualunsaturation (8% and25% of the original MIand VE double bond content, respectively). A pictoraldepiction of the structure of the net poly[maleimide-alt-(vinyl ether)]formedis shownschematically in Fig. 6.

Similar results have been obtained by replacingTEGBMI by a liquid bismaleimide (Q-bond) which is aC36 hydrocarbon branchedchain end-capped by male-imide groups.This telechelic monomeris quite misciblewith vinyl ethers,thusprecluding thesolubility andcrys-tallisation problemsencounteredwith other solid bisma-leimide monomers. In associationwith DVE-3, Q-bondcopolymerisesasefficiently asTEGBMI uponUV expo-sure, with essentiallythe sameconversion versustimeprofile. Therateof polymerisation wasfoundto decreaseasthe film thicknesswasincreased,asexpectedfrom theinner filter effect of the UV-absorbing maleimide mono-mer. Fortunately, the fast photobleaching at 300nmcausedby the polymerisation of the maleimide moietyleads to an increasedpenetration of the incident UVradiation, thusallowing several millimeter thick samplesto be cured in lessthan 1 min by frontal polymerisationunder intenseillumination.

Influenceof themonomerfeedratio

Whether polymerisation occurs by a cross-propagationmechanismor by homopolymerisation of a donor-accep-tor complex, thereaction rate should bedependent on theinitial ratio of the two monomersandreachits maximumvalue for the stoichiometric composition. Fig. 7 showstheMI polymerisationprofilesrecordedby RTIR spectro-scopy for the HBVE/t-BuMI combination, at differentmonomercompositions. In orderto work under the samelight absorbance conditions, the sample thickness(l) hadto beadjustedto match thevariationof theMI concentra-tion (absorbance= e N l N [MI] l 0.9 at 300nm). The twomonomerswerefound to polymeriseat the samerate, aslong as the molar ratio MI/ (VE + MI) was lessthan 0.4(Fig. 8). The amounts of VE and MI polymerisedwereidentical (Fig. 9), thus implying theformationof analter-nating copolymer. For highervalues, the rateof polymer-isation of t-BuMI wasalwayslarger than that of HBVE,probablybecauseof anadditional homopolymerisation ofthe maleimide in excess.In a separateexperimentwefound that photolysis of neat highly purified t-BuMIresults in formation of about 22% cyclodimer (by GC)andpresumably78%polymer(at a conversionof t-BuMIof slightly lessthan10%MI). This suggeststhat, for sys-tems with high concentrationsof t-BuMI, initiation mayoccur, at leastin part,by abiradical cyclodimerprecursor.Also, therecould be somehydrogenabstraction from the

Fig. 5. Polymerisationprofilesof theVE andMI doublebondsuponUV exposureof theDVE-3/TEGBMI mixture

Light-inducedpolymerisation of photoinitiator-freevinyl ether/maleimidesystems 1009

methyl groups(intermolecularor intramolecular) or evenhydrogenabstraction from an impurity. However, it isnoted that the t-BuMI usedto generate the cyclodimerwas purified beforeusing. The exact initiation mechan-ism for the pure t-BuMI remains to be verified by laserflash, intermediatetrapping,andquenching experiments.In the presenceof a radical-type photoinitiator, t-BuMIwas found to polymerise readily when exposed to UVradiation. The polymer formed should therefore consistof a mixture of an alternating MI/VE copolymer, a MI

homopolymer anda MI/VE copolymer with isolatedVEunits, as illustrated by the following reaction schemebasedon a cross-propagationmechanism.

The alkyl radicalR9 producedby hydrogenabstractionof the excited MI is alsoexpected to initiate the copoly-merisation by reactingwith theVE andMI double bonds.If copolymerisation proceedsby homopolymerisation ofa donor-acceptorcomplex [A-D], the samealternatingcopolymer would be formed, togetherwith somehomo-

Fig. 6. Structure of the alternating copolymer network formed upon UVexposure of a mixtureof VE andMI difunctionalmonomers

Fig. 7. Influence of the initial maleimide concentration (inwt.-%) on thephotopolymerisationof theHBVE/t-BuMI system

Fig. 8. Variation of the maximum rate of polymerisation ofHBVE and t-BuMI with the monomerfeed composition uponUV exposure.I = 45mW N cm–2 (0 : VE; h : MI)

1010 C. Decker, F. Morel, S.Jonsson,S.Clark,C. Hoyle

polymer andthe 2 + 2 cyclodimer whenmaleimide is inexcess,but according to differentkineticswith respecttothe two monomer concentrations12). (We note that wehave not confirmed a cross-propagationversuspolymeri-sation of donor-acceptor complex. For convenience,wesimply usethecross-propagationprocesshere.)

A similar behaviour was observed with difunctionalVE andMI monomers (DVE-3/Q-bond), except for a fas-ter homopolymerisation of the neat bismaleimide uponUV-exposure than with t-BuMI (50% conversion within10 s). Fig. 10 and 11 show the polymerisationprofilesrecordedat variousmonomerfeedcompositions, by fol-lowing the disappearance of the VE and MI doublebonds, respectively. Here again,the two monomers werefoundto polymeriseat identicalrates,with [VE]polymerised=[MI] polymerised, aslong asthevinyl etherconcentrationwasat leasttwice that of maleimide (Fig. 12). The UV-curedsample containedlargeamounts of unreactedvinyl ether,besides the copolymer formed. The maximum rate ofpolymerisation of each monomer was reached for thestoichiometric composition. In formulations containinganexcessof maleimide,a more completeoverall reactionwas achieved, because the bismaleimide homopoly-

Fig. 9. Influenceof the monomerfeedratio on the amountofVE andMI monomerspolymerised uponUV exposure.HBVE +t-BuMI. Laminate. I = 45 mW N cm–2. Exposuretime = 90 s(0: VE; h: MI)

Fig. 10. Influence of the initial maleimide concentration(inwt.-%) on the vinyl etherpolymerisationuponUV exposureoftheDVE-3/Q-bondsystem

Fig. 11. Influence of the initial vinyl ether concentration(inwt.-%) on the maleimidepolymerisationupon UV exposure oftheDVE-3/Q-bondsystem

Light-inducedpolymerisation of photoinitiator-freevinyl ether/maleimidesystems 1011

merisesreadily. As expected,the relative amount of MIhomopolymer in the UV-cured material was found toincreasewith the MI content of the monomer feed. Acompromise was achieved for a stoichiometric mixture,with a high final conversion (›90%) anda relatively lowamountof homopolymer(a 10%).

Influenceof thelight intensity

Oneof thedistinctadvantagesof light-inducedpolymeri-sation is that the initiation rate (r i) can be easily variedovera wide rangeby means of the light intensity (I) : r i =Ui I whereUi is the initiation quantumyield. An increaseof the light intensity from 7 to 270mW N cm–2 leads to afaster and more complete polymerisation(Fig. 13). Themaximumrateof polymerisationof both monomers (Rp),usually reached at 10% conversion,was found to obeythe following kinetic law for the DVE-3/Q-bond system:Rp = k I 0.6[M], asshown in Fig. 14.

The value of the exponent is slightly greater than0.5,the value which was expected if termination were tooccur solely by bimolecular radical interaction. The

slightly higher value (0.6) is most probably due to thecontribution of a monomolecular termination process,i. e., a trapping of the polymer radicalsin the tridimen-sional polymer network.

For samples having received the same dose, e.g.500mJN cm–2, a more extensive cure hasbeenobservedwhen UV irradiation was performed at high light inten-sity: 94%MI conversionat 270mW N cm–2, comparedto87% at 7 mW N cm–2. This effect was attributed to agreaterrise of the sampletemperatureunderintenseillu-mination,becausethepolymerisationheatis evolvedin ashorter time13).

Anotherbeneficial effect of operating underhigh lightintensityandshortexposureconditions is that it reducesthe importance of oxygen inhibition in these radical-inducedreactions. It canbeseen in Tab.1, which reportsthe Rp values at various light intensities under air-satu-ratedandO2-freeconditions,that thepolymerisation is 25times as slow in the presenceof air as in the laminatedsample at 7 mW N cm–2, but only 3 times as slow at270mW N cm–2. By further increasing the light intensityup to 600mW N cm–2 using an industrial UV-curing line,

Fig. 12. Influenceof themonomermolar ratio on thepolymer-isationrateof a DVE-3/Q-bondmixture (0: VE; h: MI)

Fig. 13. Influenceof the light intensityon the photopolymeri-sationkineticsof aDVE-3/Q-bondstoichiometricmixture

Fig. 14. Light-intensity dependenceof the rateof polymerisa-tionof theDVE-3/Q-bondsystem.(f: VE; g: MI)

Tab.1. The rate of polymerisation of the DVE-3/Q-bond sys-tem exposed to UV radiationin the presenceof air or in O2-freeconditions

Light intensityin mW N cm–2

Rateof polymerisationin mol/kg/s

laminate air

�Rp�laminate

�Rp�air

7 0.32 0.013 2515 0.55 0.032 1730 1 0.05 2046 1.3 0.097 1362 1.5 0.12 12.592 1.9 0.22 9

125 2.1 0.35 6190 2.6 0.7 4270 3.4 1.15 3

1012 C. Decker, F. Morel, S.Jonsson,S.Clark,C. Hoyle

nearlycomplete polymerisationof the bismaleimide wasachieved both under O2-free conditions(99%) andin thepresenceof air (97%).Theseresults arefully in line withpreviousobservations on similar systemswhich showedthat the radical-induced polymerisation of the MI/VEcombination is less sensitive to oxygen inhibition thanthatof acrylate-basedresins14), thusmakingthis photoini-tiator-freesystemparticularly well suited for theUV-cur-ing in air of thin films.

Influenceof anaddedphotoinitiator

The addition of a radical-type photoinitiator to a vinylether/maleate formulation has beenpreviously found toaccelerate drastically the copolymerisation upon UVexposure12). A similar behaviour was observed with thevinyl ether/maleimide stoichiometric combination, whent-BuMI was selected as electronacceptormonomerandHBVE aselectrondonor. The addition of as litt le as0.1wt.-% of a monoacylphosphine oxide (Lucirin TPO)provedto besufficient to increasethepolymerisation rateof both monomers tenfold (Fig. 15). This result demon-stratesthat the low photosensitivity of the photoinitiator-freeHBVE/t-BuMI formulation is primarily dueto a veryinefficient productionof initiating radicals.With themostreactiveHBVE/HPMI andDVE-3/Q-bondcombinations,theadditionof Lucirin TPOwasfoundto have a lesspro-nouncedeffect on the polymerisation kinetics: a 20%increaseof Rp in the presenceof 0.1 wt.-% of addedphotoinitiator, and a doubling of the reaction rate at 0.8wt.-% TPO.

It can be concludedfrom this study that the effect ofaddinga photoinitiator to a VE/MI mixture will primarilydependon thechemical structureof themaleimidemono-mer:a strongacceleratingeffect if theMI monomercon-tainsno labile hydrogens, anda marginal effect if theMImonomercontains abstractable hydrogens.This trend is

illustrated in Fig. 16 which showshow the formulationreactivity varieswith the photoinitiator concentration. Itshould benoticedthat,whentheHBVE/HPMI or DVE-3/Q-bondformulation wasexposedto filteredlight contain-ing only wavelengths longer than 360nm, no polymerformation could be detected in the photoinitiator-freesample,while polymerisation occurredin thesample con-taining 0.5%Lucirin TPO.Therefore,the latter formula-tion wasmore easilycureduponexposureto sunlight.

ConclusionA stoichiometric combination of mono- or difunctionalN-substitutedmaleimide and vinyl ethermonomers wasshown to undergo rapid copolymerisation whenexposedto UV radiationin the absenceof any added photoinitia-tor. The initiation processinvolvesthe abstraction by theexcited maleimide molecule of the labile hydrogensofthe two monomers. The sametype of reactionmust beresponsibleof branchingandinsolubilisation of thepoly-mer by a chain transferreaction. When vinyl ether is inexcess,thetwo monomerspolymeriseat exactly thesamerate, with formation of an alternating copolymer. Whenmaleimide is in excess,a competitive homopolymerisa-tion reactiontakesplace,its efficiency dependingon thechemical structure of the N-substitutedchain. The factthat polymerisation is accompanied by a fast photo-bleaching of the light-absorbing maleimide monomerallows thick specimens to becuredby frontal polymerisa-tion. Basedon its distinct characteristics, onecanexpectthis type of photocurable systemto find its main indus-trial applicationsas protective coatings,as quick-settingadhesivesandcomposites, andasphotoresiststo producehigh resolution relief images.

Fig. 15. Influence of an added photoinitiator on the light-inducedpolymerisation of HBVE/t-BuMI

Fig. 16. Influence of the photoinitiator concentrationof thelight-inducedpolymerisationof VE/MI system.I = 45mW N cm–2. Laminate

Light-inducedpolymerisation of photoinitiator-freevinyl ether/maleimidesystems 1013

Acknowledgement:Theauthorswish to thankFusionUV-SYS-TEMSINC. for supportof thiswork.

1) S. Jonsson,W. Schaeffer, P. E. Sundell, M. Shimose, J.Owens,C. E. Hoyle, Proc. RadTech Conf. Orlando 1994,p. 194

2) M. Shimose,C. E. Hoyle,S.Jonsson,P. E. Sundell,J.Owens,K. Vaughn,ACSPolym.Mater. Sci.Eng. 72, 470 (1995); M.Shimose,C. E. Hoyle,S.Jonsson,P. E. Sundell, J.Owens, K.Vaughn,Polym.Prepr. (Am.Chem. Soc.,Div. Polym.Chem.)32 (2), 485(1995)

3) S.Jonsson,P. E. Sundell,J.Hultgren,D. Sheng,C. E. Hoyle,Progr. Org. Coat. 27, 107(1996)

4) S. Jonsson,J. E. Ericsson,P. E. Sundell,M. Shimose,S. C.Clark,C. Miller, J.Owens,C. E. Hoyle,Proc.RadTechConf.Nashville1996

5) S. Jonsson,G. Doucet, G. Mattson,S. Clark, C. Miller, C. E.Hoyle, F. Morel, C. Decker, Proc. RadTech Europe Conf.1997,p. 103

6) C. E. Hoyle, S. C. Clark, S. Jonsson,M. Shimose,Polymer38, 5695(1997)

7) H. Aida, I. Takase,T. Nozi, Makromol. Chem. 190, 2821(1989)

8) C. Decker, F. Morel, S. Jonsson,S. C. Clark, C. E. Hoyle,Polym.Mater. Sci.Eng. 75, 198(1996)

9) C. Decker, K. Moussa,Macromolecules22, 4455(1989)10) C. Seliskar, S.P. McGlynn,J. Chem.Phys.55, 4337(1971)11) Y. Kanaoka,Y. Hatanka,J. Org. Chem.41, 400(1976)12) C. Decker, D. Decker, Proc. RadTech Conf. Orlando 1994,

p. 602; C. Decker, D. Decker, Polymer38, 2229(1997)13) C. Decker, D. Decker, F. Morel, in: Photopolymerization,

Fundamentals and Applications, ACS Symp. Series 673,p. 63 (1997)

14) S. Jonsson,C. Hasselgren,V. S. Ericsson,M. Johnson, S.Clark, C. Miller, C. E. Hoyle, Proc. RadTech’98 Proc. Chi-cago1998,p. 189