Synthesis of Telechelic Polymers Initiated With Selected Functional Groups by Catalytic Chain Transfer ALEXEI A. GRIDNEV,1 WILLIAM J. SIMONSICK, JR.,1 STEVEN D. ITTEL2 1 DuPont Performance Coatings, Marshall Laboratory, 3401 Grays Ferry Avenue, Philadelphia, Pennsylvania 19146 2 DuPont Central Research and Development, Experimental Station, Contribution Number 8014, Wilmington, Delaware 19880-0328 Received 1 January 2000; accepted 1 March 2000 ABSTRACT: Catalytic chain transfer is found to be useful for making telechelic oli- gomers with a variety of initiating groups in a one-step reaction procedure. Two olefinic components are required, the first being a normal free-radical-polymerizable monomer such as a methacrylate. The second is a vicinal or other olefin generally considered to be unreactive in free radical polymerizations. Under conditions of radical polymeriza- tion in the presence of a CCT catalyst, the copolymer that results incorporates predom- inantly one molecule of the second component at the initiation of each polymer chain. The terminal end group is a geminal double bond. This geminal-disubstituted end group is radically polymerizable and would allow the preparation of functionalized arms on graft polymers. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 1911–1918, 2000 Keywords: polymers; catalytic chain transfer; oligomer; telechelics; functional groups; hydride; cobalt chelate; graft-polymers; radical polymerization INTRODUCTION monomer.5 From a technological or commercial point of view, the high rate constants translate Catalytic chain transfer (CCT)1 remains one of into low concentrations of impurities in the final the most rapid and more selective catalytic pro- product. Generally, removal of the catalyst resi- cesses in radical polymerization. Its catalytic ef- dues from the resulting macromonomers or oli- ficiency (i.e., ratio of the rate constant of catalyzed gomers is a challenging problem made even more versus noncatalyzed reaction) is about 1010, difficult by the higher viscosities of high poly- which is comparable to the efficiency of enzymatic mers. In typical polymer applications, catalyst catalysis.2 In many cases, the rate constant of residue levels must be kept low to avoid color and Ϸ 8 ⅐ CCT, ka 10 L/mol s, is believed to be con- catalyst residues can cause problems in subse- 3 trolled by diffusion. Oligomers as low as dimers quent curing chemistry or polymer modification. and trimers can be obtained with CCT catalyst The removal of residual parts-per-million levels of concentration as low as 0.05 weight percent of the CCT catalyst residues from low viscosity products 4 monomer. For comparison, other catalytic reac- is relatively straight forward6 and requires rela- tions in radical polymerizations, like living radi- tively small quantities of sorbents and solvents. cal polymerization, require catalyst concentration The first reaction of the CCT process, hydrogen at the level of more than 2–3 weight percent of the abstraction from the propagating radical, Rn, by cobalt catalyst, LCo (where Pn is the correspond- ing polymer molecule with a terminal double Correspondence to: A. A. Gridnev bond, and LCo-H is the hydrido-Co(III) form of Journal of Polymer Science: Part A: Polymer Chemistry, Vol. 38, 1911–1918 (2000) 7 © 2000 John Wiley & Sons, Inc. the CCT catalyst) is well investigated. 1911 1912 GRIDNEV, SIMONSICK, AND ITTEL ka the radical or olefin. Thus, the more stable radi- Rn ϩ LCo O¡ Pn ϩ LCoOH (1) cals of MMA or polyMMA may follow a reaction pathway more akin to the three-center interme- diate while the concerted mechanism is more ap- The second reaction of the CCT catalytic cycle, propriate in the case of cyclic olefins that form transfer of the abstracted hydrogen atom to new less stable radical species. Recent discoveries in monomer, is the reaction of catalyst regeneration chemistry of vitamin B12 suggest that multiple and also chain initiation. mechanisms or more correctly, a continuum of reaction pathways are available to apparently similarly reactions whenever cobalt chelates are kr 11 M ϩ LCoOH ¡ R ϩ LCo (2) involved. In this article, we are reporting some 1 practical utilization of reaction 2 without regard to the exact mechanism, which may well vary for the different substrates employed. The hydrogen atom transfer from Co(III)-H to yield Co(II) and a new monomer radical is not yet well understood (M is the vinylic monomer, R1 is the monomeric radical). The difficulty arises from EXPERIMENTAL the very high reactivity of the cobalt hydride and its resulting low concentration in the reaction medium. Under normal condition of radical poly- Mass Spectrometry merization, its concentration is below detection ϩ 7(a),8 K IDS is an acronym for Potassium Ionization of limits. Despite the low steady-state concen- ϩ Desorbed Species.12 All K IDS experiments were tration, the addition of LCo-H to double bonds performed on a quadrupole mass spectrometer was thoroughly investigated.9 The radical formed (Finnigan model 4615B GC/MS, San Jose, CA). in reaction 2 yields a relatively stable adduct with An electron impact source configuration operat- Co(II) to give a Co(III)-R complex and the result- Ϫ ing at 200 °C and a source pressure of Ͻ 1 ⅐ 10 6 ing Co-alkyl chelate is often formed with domina- Torr was used in all experiments. tion of one isomer. This selectivity indicates that We present an abbreviated experimental pro- hydrogen transfer (reaction 2) goes through a con- ϩ cedure for the K IDS technique because a more certed mechanism followed by homolytic cleavage detailed procedure has been published else- of the CoOC bond (3): where.13 Commercially available (Finnigan, San Jose, CA) direct-exposure probe filaments were coated with a 10% w/w slurry of Al2O3, 2KNO3, and 2SiO2 in acetone. The coated filaments were (3) dried and conditioned by heating the filament to approximately 500 °C under vacuum. Neat sam- where EWG is an electron-withdrawing group. ples (0.1 mg) or 10% w/w solutions (0.2 ␮L) were On the other hand, hydrogen transfer from deposited onto a stainless steel ribbon adjacent to radical to catalyst by reaction 1 is believed to the conditioned filament. The filament and sam- proceed by a three-center intermediate as indi- ple were inserted into the ion source of the mass cated by kinetic data for reaction 17(h) and the spectrometer and a 1.3-A current applied to the substantial isotope effect, Ϸ 3.5.10 Thus it would filament. The application of a high current to the seem that CCT contradicts the principle of micro- filament causes resistive heating of the filament scopic reversibility that requires both forward with subsequent Kϩ emission from the alumino- and reverse reaction to have the same intermedi- silicate matrix. The sample, which is in close ate state. proximity to the filament, is heated and intact This apparent dichotomy regarding the princi- large organic molecules are desorbed. The organic ple of microscopic reversibility indicates that the molecules collide with Kϩ and are cationized. Ions reversible hydrogen exchange process between are seen as [M] Kϩ, the mass of the analyte, plus radicals and the cobalt catalyst can follow differ- 39 Da, the mass of potassium. For these studies, ent reaction pathways depending on the elec- the mass spectrometer was scanned from 100– tronic and steric nature of both the catalyst and 1000 Da/s. Under these conditions, we obtained TELECHELIC POLYMERS BY CATALYTIC CHAIN TRANSFER 1913 ϩ Figure 1. K IDS mass spectrum of copolymer of MMA2 copolymerization with BMA in the presence of CCT catalyst. between three and five scans per sample that Copolymerization of MMA2 and BMA were averaged to yield the reported spectra. A solution of 8 mg of (tetra-p-anisylporphin)cobal- t(II), 24 mg of AIBN, 2 mL of MMA2 and1mL Materials BMA in 10 mL of chloroform was degassed by three freeze-pump-thaw cycles and sealed in a VAZO-88௡ [azo-bis(cyclohexanecarbonitrile)] was Ϫ flask at 10 2 Torr residual pressure. The flask recrystallized from methanol and chloroform at was immersed into an isothermal circulating bath temperatures below 23 °C. MMA was vacuum for5hat75°C.Thecontent was analyzed by distilled immediately prior to the experiments. ϩ K IDS and the results are presented in Figure 1. Other olefins (Aldrich) were used as received. Cat- As is readily seen, the product is a mixture of alyst (triphenylphosphine)-bis(diphenylglyoximato)- MMA -initiated BMA macromonomers and homo- Co(III)chloride was made as reported earlier.7(e) 2 BMA macromonomers. Conversion of BMA was Another CCT catalyst, tetrakis(n-heptyloxyphe- approximately 90% and conversion of the MMA nyl)porphin cobalt(II), was obtained from Dr. 2 was approximately 10–15%. G. V. Ponomarev (Institute of Biophysics RAN). MMA oligomers were prepared by a standard Copolymerization of Olefins and MMA CTC polymerization of MMA utilizing bis(meth- ylglyoximato)Co(III)isopropyl.4 The resulting In a typical experiment,a5mLreaction flask product was vacuum distilled to yield pure dimer equipped with a Teflon௡ stopcock and magnetic (MMA2) and trimer (MMA3), leaving higher oli- stirrer was charged with 3 mg tetrakis(n-hep- gomers behind in the residue. tyloxyphenyl)porphyrinCo, 16 mg VAZO-88௡, 1.8 mL of the nonhomopolymerizable olefin and 0.08 mL of MMA. The sample was degassed by three freeze-pump-thaw cycles and the reaction flask was sealed at 10Ϫ2 Torr pressure. The flask was placed into an oil bath and kept at 100 °C for 1 h. Then the flask was chilled, another 0.08 mL of MMA was added and the flask was degassed the same manner as described above. After1hanother0.08 mL of MMA was added 1914 GRIDNEV, SIMONSICK, AND ITTEL followed by the degassing and temperature logical question was whether this fast H-ex- treatment.