Research Summary 

1. Fluoropolymers for 157 nm photolithography. Building transparent single layer resists for 157 nm photolithography requires an understanding of how each component of the resist work together. Because of the strong absorbance of the unsaturated structures (phenols and carboxylic acids) at 157 nm, the incorporation of fluoro onto a polymer backbone has been an overriding concern in resist design. Fluorine-containing polymers are highly transparent at 157 nm and fluorocarbinols, whose pKa values are comparable to those of phenols, can be used as acidic functional groups in the design of chemically amplified and aqueous base developable resists. In order to balance transparency with other desirable traits such as etch resistance, adhesion and dissolution contrast, a series of fluoropolymer systems were developed. Main approaches used are as follows: (1) incorporating hexafluoroisopropynol group to acrylate and styrene systems; (2) introducing fluoro and trifluoromethyl onto the carbon next to carbonyl; (3) making trifluoroacrylates; (4) prepare new monomers with both electron-rich and electron-deficient double bonds for cyclopolymerization; (5) using perfluorocyclicdiketones to make fluoropolymers consisting of cyclic in the main chain (Scheme 1).

2. Macrocyclic Thioether Imide Oligomers. The processing of aromatic polyimides especially from the melt was quite difficult. Thus, many attempts have been directed towards novel, linear polyimides that are soluble in organic solvents or melt processable. Ring-opening polymerization (ROP) offers many advantages over other polymerization methods, such as the elimination of the solvents, the absence of generated volatile by-products, and the possibility of reaching high molecular weight in a short reaction time, in some cases, molecular weight and polydispersity of the resultant polymers can be well controlled. Free-radical ring-opening polymerization (FRROP) provides a possibility of using reactive processing techniques to transform cyclic oligomers directly into commercial objects by extrusion or molding without release of volatile products and residue of metal ions. Therefore, a new series of macrocyclic thioether imide oligomers was synthesized with high yield via nitro displacement reaction of symmetric and nonsymmetric dinitrodiimide with 1,4-benzenedithiol(Scheme 2). The nature of cyclic structure was confirmed by means of 1H NMR, GPC and MALDI-TOF-MS spectra. Ring-opening polymerization of the cyclic oligomers carried out at elevated temperature in the presence of 2,2¡¦-dithiobis(benzothiazole) (DTB) afforded polyimide with essentially the same mechanical and thermal properties as that of linear analogue prepared independently.

3. Linear & Hyperbranched Polyimides. Five new kinds of AB-type and an AB2-type monomer were successfully synthesized from 4-nitrophthalonitrile and corresponding phenols. The linear and hyperbranched polyimides were prepared via a two-step method in which the direct polycondensation reaction was carried out in N-methylpyrrolidone (NMP) in the presence of diphenyl(2,3-dihydro-2- thioxo-3-benzoxazolyl)phosphonate (DBOP) as a condensation agent. Thermal and mechanical properties of the resulting polymers were studied in detail. The properties such as degree of branching, density as well as dielectric constant of the resulting hyperbranched polyimide were also investigated.

4. Aliphatic Polyesters. Aliphatic polyesters have long been studied as biodegradable polymers. Due to their excellent biocompatibility and biodegradability, they have been widely used in the biomedical field. However, common polyesters do not have functional pendant groups to allow further chemical modification or to the ability to conjugate with drugs and other bioactive residue. This limits their application. Recently, a new kind of aliphatic polyester containing functional pendant groups, mainly carboxylic, amino, thio and hydroxyl groups, have been studied with an aim to develop functional aliphatic polyesters and to broaden their applications.
We prepared a new polyester containing chloromethyl pendant group. a-Chloromethyl-a-methyl-b-propiolactone (CMMPL) was synthesized via chlorination, hydrolysis and lactonization of a,a-dihydroxymethylpropionic acid successively. The ring-opening polymerizations of CMMPL were carried out by using different initiators. Copolymerizations of CMMPL with e-caprolactone (CL) and trimethylene carbonate (TMC) were studied and random copolymers with similar composition as the feed ratio were obtained by carefully optimizing the copolymerization conditions. The sequence distribution of P(CMMPL-co-CL) was analyzed by 13C NMR spectra, and the result confirms that P(CMMPL-co-CL) is of random nature. After modification of P(CMMPL-co-CL) with pyridine, the hydrophilicity was enhanced as evaluated by dynamic contact angle (DCA) measurement. The isothermal and non-isothermal crystallization kinetics of P(CMMPL) was studied by DSC, and the rheological behavior of P(CMMPL) and P(CMMPL-co-CL) was also examined.

Well-Defined Polymeric Materials (1D, 2D and 3D structures) ------ Toward controlling the Polymer Size, Shape and Function;
Biomaterials and Biomedical Engineering ------ Targeted Drug delivery systems, Tissue Engineering.
Intelligent Materials ------ Smart response to the environmental variances, such as pH, thermal, photo, electro, ultrasonic, magnetic, and other special substances;
High-Performance Materials-Nanomaterials ------ Polyimide, Polyamide, Epoxy Resin, Polyphenylsulfide, Polyphenyloxide and so on;