6856
Macromolecules 1999, 32, 6856-6859
Polymerization of Methyl Methacrylate and Its Copolymerization with E-Caprolactone Catalyzed by Isobutylalumoxane Catalyst Bin Wu,†,# Robert W. Lenz,*,‡ and Baki Hazer§,⊥ Departments of Chemistry and Polymer Science and Engineering, University of Massachusetts, Amherst, Massachusetts 01003; Department of Chemistry, Zonguldak Karelmas University, 67100 Zonguldak, Turkey; and TUBITAK-Marmara Research Center, P.O. Box 21, Gebze, 41470 Kocaeli, Turkey Received February 8, 1999
Introduction In recent years, ring-opening polymerization of lactones has attracted increasing interest because many of the polyesters obtained from these polymerization reactions are potentially biodegradable. For example, [R,S]-β-butyrolactone can be polymerized by alumoxane catalysts into a semicrystalline and biodegradable polyester.1 Polycaprolactone obtained from the ring-opening polymerization of -caprolactone (CL) has found uses as materials for controlled release drug delivery systems.2 CL can be readily polymerized by many different catalysts3-8 and copolymerized with L-lactide to form a biodegradable block copolymer.9 On the other hand, vinyl polymers such as poly(methyl methacrylate), PMMA, are not biodegradable. It would be very desirable to combine the biodegradability of the polyesters and the excellent application properties of polyvinyls. Efforts have been made toward the copolymerization of lactones and vinyl or vinylidene monomers. This type of copolymerization is known as “hybrid copolymerization.”10 In a hybrid copolymerization, the reactive species with different characters and reactivities coexist. Solaro and co-workers10 attempted the copolymerization of MMA with different lactones using diethylaluminum sulfate (DEAS), triisobutylaluminum (TIBA), and TIBA/H2O as the catalysts. In their study physical mixtures of homopolymers were obtained, and there was no evidence that any copolymer was formed during the copolymerization. However, as Solaro and co-workers pointed out, the study provided a way of obtaining in situ polymer alloys of PMMA and polyesters, and therefore semibiodegradable polymer blends can be produced. Despite the lack of evidence, they believed that block copolymers of MMA and the lactones might have formed and acted as a compatibilizer for the polymer alloys. Alumoxanes are the reaction products of a trialkylaluminum with water as shown in the following general reaction equation:
The specific structures of the alumoxanes are not known, but there is generally no simple formula of the type shown above that can be used to represent the real structure of alumoxanes because the products of the hydrolysis can consist of many different types of oligomeric compounds, which may have linear, cyclic, or even cage structures.11,12 Alumoxanes are known to activate the transition metal catalysts used for the ZieglerNatta polymeirzation of olefins, especially for the polymerization of ethylene to the linear polymer and of propylene to the highly isotactic polymer.13 As mentioned above, alumoxanes can polymerize [R,S]-β-butyrolactone,1 and it was found that isobutylalumoxane was a good catalyst for the ring-opening polymerizaton of CL.14 It is natural, therefore, to think of using isobutylalumoxane to copolymerize CL and MMA. In this paper, we report on our study of the polymerization of MMA and the copolymerization of MMA and CL catalyzed by isobutylalumoxane. Experimental Section Chemicals. Isobutylalumoxane was purchased from Akzo Nobel Chemicals as 1 M solution in toluene (Al/O ) 1/0.8). Toluene used for the polymer synthesis was refluxed with sodium for at least 48 h and distilled before use. CL and MMA were purchased from Aldrich, dried over CaH2 for 24 h, and distilled under reduced pressure. Homopolymerization of MMA. All the glassware used for the polymerization was oven-dried for 24 h and flame-dried under vacuum with argon purge for at least three cycles. A 100 mL Schlenk tube was charged with 3 mL (0.028 mol) of MMA dissolved in 30 mL of toluene, and an appropriate amount of isobutylalumoxane solution was added to the MMA solution at room temperature under argon atmosphere using a syringe. The reaction mixture was heated to the desired temperature while being magnetically stirred. The reaction Table 1. Reaction Conditions and Polymer Yields of MMA Homopolymerization rxn ID IBAOa (mol %) rxn temp (°C) rxn time (h) yieldb (%) 1 2 3 4 a
1 5 5 10
60 60 50 60
