Preparations, Thermal Properties, and T g Increase Mechanism of Inorganic/Organic Hybrid Polymers Based on Polyhedral Oligomeric Silsesquioxanes Hongyao Xu, †,‡ Shiao-Wei Kuo, † Juh-Shyong Lee, † and Feng-Chih Chang* ,† Department of Applied Chemistry, National Chiao-Tung University, Hsin Chu, Taiwan, and Department of Chemistry, Anhui University, Anhui, 230039, China Received February 21, 2002 ABSTRACT: A series of novel hybrid poly(acetoxylstyrene-co-isobutylstyryl-POSS)s (PAS-POSS) and poly(vinylpyrrolidone-co-isobutylstyryl-POSS)s (PVP-POSS) are synthesized and characterized. The POSS content in these hybrids can be controlled by varying the monomer feed ratio. The polyhedral oligosilsesquoixane (POSS) moiety can effectively increase the T g of the resultant organic/inorganic hybrid polymer at a relatively high POSS content and produce the hybrid copolymer with narrower molecular weight distribution. The FTIR spectra are used to investigate the structure-property relationship of these hybrid polymers, and the T g enhancement mechanism is discussed in detail. Introduction Polymeric hybrid materials have attracted great interest recently due to their advantageous performance relative to the nonhybrid counterparts. Typical hybrid materials may contain a cross-linked inorganic phase bonded (often covalently) with an organic phase. 1,2 Recently, polyhedral oligosilsesquoixanes (POSS)-based hybrid polymers 3-13 have received increasing attention among the academic community and industries because of the unique structure of the POSS macromer, which is a well-defined cluster with an inorganic silica-like core (Si 8 O 12 ) surrounded by eight organic corner groups. This POSS macromer can be easily functionalized with a wide variety of organic groups that can be employed as monomer or comonomer in a typical polymerization. The preparation and properties of POSS-based hybrid poly- mers can be designed and controlled at the molecular level. Many POSS-based hybrid polymers have been prepared and possess a number of desirable properties. 3-9 However, only a few papers have reported their T g increase behavior. 3-5 In the study, we will report the syntheses of a series of new POSS-based hybrid poly- mers and the structure-property relationship of these hybrid polymers. Experimental Section Materials. Isobutylstyryl polyhedral oligosilsesquioxane (POSS) was purchased from the Hybrid plastic Co. Inc., which was stored in a dried box before use. Vinylpyrrolidone and acetoxystyrene were purchased from Aldrich, distilled from calcium hydride under reduced pressure, and stored in sealed ampules in a refrigerator. High-purity azobis(isobutyronitrile) (AIBN) was kept in a dried box and used as received. Spectroscopic grade THF and toluene were predried over 4 A molecular sieves and distilled from sodium benzophenone ketyl immediately prior to use. All other solvents were purchased from Aldrich and used without further purification. Instrumentation. Thermal analyses were carried out on a DSC from DuPont (DSC-9000). The scan rate was 20 °C/ min within the temperature range 30-260 °C. The sample was quickly cooled to 0 °C from the melt for the first scan and then scanned from 20 to 280 °C at 20 °C/min. The glass transition temperature is obtained at the midpoint of the specific heat increment. FTIR spectra were measured with a spectral resolution of 1 cm -1 on a Nicolet Avatar 320 FT-IR spectro- photometer using KBr disks or pellets at room temperature. Weight- and numer-average molecular weights (M w and Mn) and polydispersity index (Mw/Mn) were determined by a Water 510 gel permeation chromatograph (GPC). 1 H NMR spectra were recorded on a Bruker ARX300 spectrometer using the chloroform-d solvent. Polymerizations. All polymerization reactions were car- ried out under nitrogen using a vacuum-line system. Poly- (vinylpyrrolidone-co-isobutylstyryl-POSS) (PVP-POSS) and poly(acetoxystyrene-co-isobutylstyryl-POSS) (PAS-POSS) were prepared by a conventional free radical polymerization tech- nique. For comparison, the homopoly(vinylpyrrolidone) (PVP) and homopoly(acetoxystyrene) (PAS) were also synthesized as shown in Scheme 1. Typical experimental procedures for these polymers are given below. In a typical reaction, 9.8 mmol of vinylpyrrolidone (VP) and 0.22 mmol of POSS monomer in toluene (dried toluene, 7 mL) were polymerized using the AIBN initiator (1 wt % based on monomer) at 80 °C under a nitrogen atmosphere for 24 h. The product then was poured into excess cyclohexane under vigorously agitation to precipi- tate the copolymer, then purified in THF/cyclohexane, and dried in a vacuum oven. A 58.4 wt % yield was obtained through this procedure. Determination of Component Contents. 12,14 IR analysis was used to determine the respective component contents of these polymers. The pure poly(acetoxystyrene) (PAS), poly- (vinylpyrrolidinone) (PVP), and poly(isobutylstyryl polyhedral oligosilsesquioxane) (POSS) samples were prepared following similar procedures mentioned above. To establish a calibration curve, a series of POSS/PVP and POSS/PAS mixtures with known amounts of POSS were prepared. To ensure intimate mixing, PVP, PAS, and POSS were first dissolved in a solvent and then cast into a thin film. The carbonyl stretching vibration of the PVP is located at 1680 cm -1 . The POSS moiety exhibits a “robust” absorption centered at 1109 cm -1 . The carbonyl absorption band of the PAS is located at 1760 cm -1 . These carbonyl bands at 1680 and 1760 cm -1 were adopted as internal standards for POSS/PVP and POSS/PAS mixtures, respectively. The ratios of band areas, A 1109/A1680 and A1109/ A1760, were plotted against the mole fraction of the POSS in the POSS/PVP and POSS/PAS mixtures, and the results are shown in Figure 1a,b. These plots gave a linear calibration † National Chiao-Tung University. ‡ Anhui University. * To whom correspondence should be addressed: e-mail changfc@cc.nctu.edu.tw, Tel 886-35-131512, Fax 886-35-723764. 8788 Macromolecules 2002, 35, 8788-8793 10.1021/ma0202843 CCC: $22.00 © 2002 American Chemical Society Published on Web 10/03/2002