Novel Hybrid Monomers Bearing Cycloaliphatic Epoxy and 1-Propenyl Ether Groups Sure ´ sh K. Rajaraman, William A. Mowers, and James V. Crivello* Center for Polymer Synthesis, Department of Chemistry, Rensselaer Polytechnic Institute, Troy, New York 12180 Received July 9, 1998; Revised Manuscript Received October 23, 1998 ABSTRACT: The synthesis of a novel series of hybrid monomers containing cationically polymerizable cycloaliphatic epoxide and 1-propenyl ether functional groups in the same molecule has been conducted. Detailed structure-reactivity studies of the diaryliodonium salt-induced cationic photopolymerizations of these monomers indicate that the rate of epoxide ring-opening polymerization is markedly enhanced by the presence of the 1-propenyl ether group. At the same time, the polymerization of the 1-propenyl ether groups in such hybrid monomers is retarded. A mechanism involving the free-radical-induced decomposition of the photoinitiator has been proposed which serves to amplify the rate of the photoinitiated cationic epoxide ring-opening polymerization. Introduction In recent years, work in this laboratory has been directed toward the design of novel monomers specifi- cally for use in photoinitiated cationic polymerizations. 1-4 Of particular interest are monomers that undergo very rapid photopolymerizations. These monomers have many potentially important uses in applications such as photocurable coatings, adhesives, and printing inks. Our initial work in this area focused on cycloaliphatic epoxides since these monomers undergo photoinitiated cationic polymerization at the highest rates of all known epoxides and also because the resulting polymers have excellent adhesion, chemical resistance, and mechanical properties. 5 For this reason, these monomers have become the mainstay of many industrial photocuring applications. Conversely, there is an increasing demand for epoxide monomers that undergo even more rapid photopolymerizations. Accordingly, we have undertaken a program to design and synthesize such monomers. One recent approach we have taken for the design of new, more reactive epoxide monomers has been to incorporate other types of cationically polymerizable functional groups into these monomers. We call such monomers “hybrid” monomers. To enhance the reactiv- ity of an epoxy monomer, it would appear reasonable to incorporate a functional group with an intrinsically higher reactivity. Previous studies from this group have shown that monomers containing the 1-propenyl ether group are among the most reactive functional groups known. 6 Their cationic polymerization rates exceed those of all epoxides, including the most reactive cy- cloaliphatic epoxides. Although hybrid monomers con- taining the glycidyl ether group and a 1-propenyl ether moiety in the same molecule have been synthesized, 7,8 there are no known examples of monomers containing both a cycloaliphatic epoxide and a 1-propenyl ether functional group. The goal of the present investigation was to prepare such hybrid monomers and conduct a detailed investi- gation of their behavior in photoinitiated cationic po- lymerization. It was of special interest to determine whether the two types of functional groups would exhibit cooperative or differentiated reactivity during polymerization. Experimental Section Materials and Characterization Techniques. All or- ganic reagents employed in this investigation were reagent quality and were used as purchased from the Aldrich Chem- ical Co. (Milwaukee, WI) unless otherwise noted. 1,2,3,6- Tetrahydrobenzyl alcohol was purchased from Fluka-US (Mil- waukee, WI) and was used as received. The photoinitiators (4-n-undecyloxyphenyl)phenyliodonium hexafluroantimonate (IOC11) and (4-n-decyloxyphenyl)phenyliodonium hexafluo- roantimonate (SOC10) were prepared as described previ- ously. 9,10 1 H NMR spectra were obtained using Varian XL-200 and XL-500 spectrometers at room temperature in CDCl3. All chemical shifts are reported relative to tetramethylsilane as an internal standard. Gas chromatographic (GC) analyses were performed on a Hewlett-Packard HP-5840A gas chromato- graph equipped with a 15 m × 0.53 mm × 1.5 μm film thickness cross-linked methyl silicone gum column and a flame ionization detector. Differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA) measurements were carried out under nitrogen and air at heating rates of 5 and 20 °C/min, respectively, using a Perkin-Elmer DSC-7 TGA-7 thermal analysis system. Elemental analyses were performed by Atlantic Microanalysis, Inc. (Norcross, GA). Synthesis of Model Compounds and Monomers. A summary of the characteristics of the monomers and model compounds prepared in this study is presented in Table 1. Synthesis of (2-Oxapent-4-enyl)cyclohex-3-ene (CA). Method A. Into a 500 mL round-bottom flask equipped with an overhead stirrer, a thermometer, and a nitrogen inlet were placed 56.085 g (0.5 mol) of distilled 1,2,3,6-tetrahydrobenzyl alcohol, 90.75 g (0.75 mol) of allyl bromide, 100 mL of toluene, and 30 g (0.75 mol) of sodium hydroxide. The reaction mixture was stirred at room temperature for 15 min. Then, 3 g (0.01 mol) of tetra-n-butylammonium bromide was added and the reaction mixture slowly heated to reflux (65 °C) and main- tained at that temperature for 8 h. The reaction mixture was cooled and filtered to remove the sodium bromide that pre- cipitated during the reaction. The filtrate was poured into 500 mL of distilled water, the organic layers were separated, and the aqueous layer was extracted with fresh toluene. The combined organic layers were washed with three 200 mL portions of distilled water, and the organic phase was dried over anhydrous sodium sulfate. Then , the excess allyl bromide * To whom correspondence should be addressed. 36 Macromolecules 1999, 32, 36-47 10.1021/ma981078r CCC: $18.00 © 1999 American Chemical Society Published on Web 12/17/1998