The Effect of Polymerization Conditions on the Density and Tg of Bisphenol-A and Hexafluoroisopropylidene-containing Polybenzoxazines

Transcription

1 Effect of Polymerization Conditions on the Density Changes and Tg of Bisphenol-A... The Effect of Polymerization Conditions on the Density and Tg of Bisphenol-A and Hexafluoroisopropylidene-containing Polybenzoxazines Mantana Kanchanasopa and Nantaya Yanumet The Petroleum and Petrochemical College, Chulalongkorn University Bangkok 10330, Thailand Kasinee Hemvichian and Hatsuo Ishida* Department of Macromolecular Science and Engineering Case Western Reserve University Cleveland, Ohio , USA Received: 26th January 2001; Accepted: 22nd May 2001 SUMMARY The volumetric expansion of bisphenol-a and aniline-based benzoxazine (BA-a) has been studied by comparing the room temperature density of the cured BA-a under different polymerization conditions with the amorphous BA-a monomer. The glass transition temperatures (Tg) of BA-a at various degrees of polymerization have been investigated by differential scanning calorimetry (DSC). The degrees of conversion at different polymerization temperatures were compared with the respective glass transition temperatures. It was found that substantial development of Tg occurs at low degrees of conversion. A fluorinated polybenzoxazine was synthesized from the ring-opening polymerization of hexafluoroisopropylidene-containing benzoxazine monomer. The properties of the fluorine-containing polymer were compared to those of nonfluorinated polybenzoxazine. Fluorine incorporation had a profound effect on the glass transition temperature of polybenzoxazine. The thermal stability also improved upon fluorination. INTRODUCTION Traditional phenolic materials, which are the condensation reaction products of phenol and formaldehyde, exhibit good heat-resistant, flame retardant, and dielectric properties. They are widely used in electrical devices, appliances, and construction. The use of inexpensive raw materials is of particular attraction. While the advantages of phenolic resins are considerable, they have also shortcomings. These include release of water and ammonia during polymerization, poor molecular design flexibility, poor shelf life, and brittleness. Polybenzoxazines are an alternative to traditional phenolic resins and other thermosetting resins such as epoxies, unsaturated polyesters and even to high performance polymers like bismaleimides and *To whom correspondence should be addressed. polyimides. Benzoxazine was first synthesized by Holly and Cope in from a phenolic derivative, a primary amine and formaldehyde. However, the use of benzoxazine as precursor to phenolic resin did not start until 1973 when Shreiber 2 reported the formation of oligomeric phenolic compounds made from benzoxazines. Riess et al 3 studied the synthesis and reaction of monofunctional benzoxazine compounds. They reported that monofunctional benzoxazines formed only oligomeric materials. They theorized that the side reaction of the ring opening reactions compete with the chain propagation and lead to low molecular weight products. While benzoxazine chemistry is not new, no paper had been published on the physical and mechanical properties of polybenzoxazines until Ning and Ishida studied bifunctional benzoxazine precursors 4. The bifunctional benzoxazine leads to high molecular weight polymers. Polybenzoxazines provide a chemical and structural framework with great Polymers & Polymer Composites, Vol. 9, No. 6,

2 Mantana Kanchanasopa, Nantaya Yanumet, Kasinee Hemvichian and Hatsuo Ishida molecular design flexibility 5. The benzoxazine precursors exhibit low viscosity, which is advantageous from a processing point of view. The majority of monomers undergo volumetric shrinkage upon polymerization. However, zero shrinkage or volumetric expansion can be desirable in many applications, such as coatings, composites, and precision casting. Shrinkage causes residual stress and may lead to premature debonding and microcracks. Bailey et al. 6-9 reported spiro ortho esters and spiro ortho carbonates that polymerize via a ring-opening reaction, showing volumetric expansion. They hypothesized that the strained ring of the monomer opened and occupied a larger volume afterwards. These spiro ortho compounds were often mixed with epoxy resins in order to counter the shrinkage of the epoxy. An example is work of He et al. where norbornene-spiro-orthocarbonate (NSOC) was copolymerized with an epoxy resin 10,11. They found that the room temperature density of the polymer was lower than that of the monomer, while the Tg and the mechanical properties decreased as the amount of NSOC increased. In addition to the aforementioned mechanism of volumetric expansion, it is thought that the reduction of shrinkage in the glassy state (<Tg) during the cooling process by lowering the Tg of the copolymer significantly contributed to the observed results. The shrinkage in the glassy region leads to internal stresses since the molecular motion of the network segments was mostly restricted in this region. In general, better mechanical properties are reported with materials showing lower shrinkage The room temperature density (ρ RT ) of an epoxy resin with various curing conditions was studied by Pang and Gillham 14. The ρ RT of a polymer depends on many factors, such as curing time, curing temperature, and cooling rate after the curing reaction. They found that, at low Tc, the ρ RT of both fast and slow-cooled specimens increased gradually with curing time due to the densification of the material in the liquid and rubbery states. The density levels off when the material reaches the glassy state at a specified Tc. A different event occurs at moderate Tc. However, the increased ρ RT as a function of curing time is found for fastcooled samples. This is contrary to the slow-cooled samples where the ρ RT decreased as a function of curing time. Both the fast and slow-cooled samples showed decreased ρ RT at a higher Tc. These phenomena can be explained by the effect of glass transition temperature and crosslink density on the thermal shrinkage during the cooling step of the polymerization reaction. Ishida and Allen reported while using dilatometric measurements that the maximum shrinkage for isothermally cured BA-a or the volumetric expansion coefficient in the glassy state were lower than for epoxy 15. The near-zero shrinkage at room temperature of fully cured BA-a was observed when the volumes at room temperature of the amorphous monomer and the polymer cured at 140 C were compared. At the isothermal curing temperature of 140 C, the material underwent approximately 3% shrinkage upon polymerization until it reached the vitrification point. The greatest cure shrinkage was found at this temperature. Above 140 C, the cure shrinkage was lower. And above 195 C, the material cures either with no shrinkage or possibly even some expansion. The BA-a materials are polymerized with low shrinkage under isothermal conditions. Ishida and Low reported the effect of intramolecular hydrogen bonding on the volumetric expansion of benzoxazines by systematically varying the type of primary amine used in synthesis 16. There is intramolecular hydrogen bonding between the phenolic OH and the nitrogen of the Mannich base 17,18. The strength of this hydrogen bonding depends on the electronegativity of the amine group that is attached to the nitrogen. The stronger the hydrogen bonding, the greater the volumetric expansion. In addition, the steric effect of the amine group also influences the volumetric changes during cure. Both near-zero volumetric changes (or expansion) upon polymerization and fast development of Tg at low conversions are observed for polybenzoxazines and are rare among many known polymers. Nearzero volumetric changes are commonly observed for many benzoxazine resins 15,16. However, the effect of conversion on the Tg of polybenzoxazines has not been studied to date. Thus, in addition to the bisphenol-a based benzoxazine, a fluorinated benzoxazine is also studied for comparison. Incorporation of fluorine into polymers can cause a significant change in the polymer properties. Thus, if similar behaviour is observed in the fluorinated benzoxazine, the likelihood of observing the high Tg increase at low conversions for other benzoxazines may be high. The fluorine-containing polymers are also attractive in the optical and electronic packaging material industries. The low moisture absorption due to the hydrophobicity of fluorine-containing polymers has been reported 19. The effect of fluorination on thermal stability enhancement has also been investigated 20. Owing to the aforementioned results, the synthesis and characterization of fluorinated polymers have 368 Polymers & Polymer Composites, Vol. 9, No. 6, 2001

3 Effect of Polymerization Conditions on the Density Changes and Tg of Bisphenol-A... been applied to a number of high performance polymeric materials, such as polyimides, polyamides, polyethers, and polybenzoxazoles 21. In the past, an effort to synthesize the benzoxazine monomers from fluorinated primary amines has been made 22. It was found that, under neutral conditions, the fluorinated primary amines were exceptionally unreactive. This can be explained by the fact that a high basicity of primary amines is required for ring formation of the benzoxazine monomer. In this case, the high electronegativity of fluorine acts to reduce the basicity of the primary amines, resulting in a very low yield of benzoxazine monomers. In this work, the bisphenolcontaining hexafluoropropylidene group was used. After the synthesis and characterization, the fluorinated benzoxazine monomer was polymerized via a ring-opening polymerization. Since no fluorinated polybenzoxazines have been reported in the literature, the effect of fluorination on the thermal properties was also evaluated. The thermal properties of fluorinated benzoxazine polymers were characterized by differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). The aim of this work was to study effect of curing conditions on volumetric expansion. The glass transition temperature of polybenzoxazines is studied by varying the curing temperature and curing time. EXPERIMENTAL Bisphenol-A, aniline (99.5%), 1,4-dioxane, diethylether, chloroform, sodium sulphate and formaldehyde aqueous solution (37%) were purchased from Aldrich. 2,2-Bis(4-hydroxyphenyl) hexafluoropropane (bisphenol-af, 97%) was purchased from PCR, Inc. Paraformaldehyde was purchased from Fluka. All chemicals were used without further purification. The benzoxazine based on bisphenol-a and aniline was synthesized by the method reported elsewhere 4 according to the following scheme. The monomer, bis-(3,4-dihydro- 6-phenyl-2H-1,3-benzoxazinyl)isopropane is abbreviated as BA-a. The benzoxazine based on bisphenol-af and aniline was also prepared by the solventless method 23. The monomer, bis-(3,4- dihydro-6-phenyl-2h-1,3-benzoxazinyl)hexafluoroisopropane is abbreviated as BAF-a and was synthesized according to the method reported by Liu and Ishida 24. Formaldehyde is the common component for both benzoxazines. The crude benzoxazines were purified according to a reported method 4. The monomers were prepared according to the chemical scheme shown below in Scheme 1. Approximately 2 grams of purified benzoxazine monomer was degassed in an aluminium pan in a vacuum oven at 100 C for 6 hours. They were then cooled to room temperature. The degassed material was cured isothermally at 135, 145, 155, 165, 175, and 185 C for 1 to 10 hours in an oven. The volumetric expansion of cured samples was studied by density measurement according to ASTM D792 (Method A). By comparing the density of the monomers with that of the polymer, the shrinkage or expansion of the BAa material can be determined. Only the bubble-free samples were used for this measurement. The temperature of the water bath was kept constant at 24±1 C for all density measurements by water displacement. Seven samples for each condition were used for this measurement and the average value is reported. A Fourier Transform infrared (FTIR) spectrophotometer (Bomem Michelson MB110) was used to obtain infrared spectra. The spectrophotometer was equipped with a liquid nitrogen cooled, medium band-pass mercurycadmium-telluride (MCT) detector. Co-addition of 100 scans was sufficient to obtain good signal-tonoise ratio, at a fixed resolution of 4 cm -1. All recorded spectra were displayed in the absorbance mode. The benzoxazine sample was mixed with KBr powder and pressed into a pellet for examination. The 1 H nuclear magnetic resonance (NMR) spectrometer used was a Varian XL-200 NMR spectrometer with a proton frequency of 200 MHz. The deuterated chloroform with 1% tetramethylsilane was used as the solvent. The sample was further examined by size exclusion chromatograph (SEC) (Waters 486 Scheme 1 where R = CH 3 or CF 3 Polymers & Polymer Composites, Vol. 9, No. 6,

4 Mantana Kanchanasopa, Nantaya Yanumet, Kasinee Hemvichian and Hatsuo Ishida instrument) equipped with a three Styrogel columns of molecular weight ranging from 50 to 100,000 at a flow rate of 1 ml/min, with an ultraviolet absorption detector fixed at 254 nm. The thermal properties of the benzoxazine samples were studied by a modulated differential scanning calorimetry (MDSC) (TA Instruments model 2920) by purging with nitrogen gas at a rate of 60 ml/min. Approximately mg of the BA-a or BAF-a samples were placed in a pressure pan. Experiments were run from 30 C to 350 C at a heating rate of 10 C/min. Thermogravimetric analysis (TGA) was performed by a High Res TGA 2950 thermogravimetric analyzer (TA Instruments) at a heating rate of 20 C/min under a nitrogen atmosphere with a flow rate of 90 ml/min. RESULTS AND DISCUSSION The detailed characterization of the benzoxazine structure by FTIR and SEC is presented elsewhere 4. Although not shown in this paper, a SEC chromatogram using a UV detector shows the strongest peak at 10 min retention time, which is assigned to the difunctional BA-a benzoxazine monomer. The shoulder of the strongest peak which occurs at a shorter retention time represents dimers and higher oligomers. The purity computed by comparing the area under the highest peak to the shoulder is 98%. Figure 1 shows representative DSC thermograms of the uncured and isothermally cured BA-a at the curing temperature Tc of 155 C for 2 hours. The Tg appears as an endothermic shift over a temperature interval in the DSC thermogram. In this study, Tg was taken as the midpoint of the step-transition. The residual heat of reaction of the remaining reactants ( H r ) appears as an exothermic peak. The heat of polymerization is estimated by drawing a straight line connecting the baseline before and after the peak and integrating the area under the curve. The area of the exothermic peak of the uncured sample is the total heat of reaction ( H t ). From the value of H t, H r, and cure time (t), it is possible to calculate the fractional conversion or extent of reaction (α) and rate of reaction (dα/dt) of the curing reaction as: and α= 1 Hf H Hf dα H = t dt t Figures 2 and 3 show the DSC thermograms of the materials cured at 155 C for different times and the materials cured for 3 hours at isothermal Tc of 155, 165, 175, and 185 C, respectively. From these figures, it is found that both Tg and H r change monotonically with Tc and curing time. These phenomena are illustrated by the plot of Tg vs. curing time in Figure 4. During curing, the glass transition temperature of the curing system will continuously increase until it approaches the curing temperature. Then the reaction mode will change from chemical reaction control to diffusion control when the viscosity of the reacting system becomes high, and even stop at the temperature at which Tg equals Tc, which is defined as vitrification. Vitrification takes place in materials cured at lower temperatures than the ultimate glass transition temperature (Tg ). t (1) (2) Figure 1 DSC thermograms of uncured BA-a (top) and BA-a isothermally cured at 155 o C for 2 hours (bottom) Heat flow (mw) Figure 2 DSC thermograms of BA-a cured at 155 o C for 3-6 hours; from top to bottom Heat flow (mw) Temperature ( C) Temperature ( C) 370 Polymers & Polymer Composites, Vol. 9, No. 6, 2001

5 Effect of Polymerization Conditions on the Density Changes and Tg of Bisphenol-A... Figure 3 DSC thermograms of BA-a cured for 3 hours at isothermal curing temperatures of 155, 165, 175, and 185 o C; from top to bottom Heat flow (mw) Figure 5 Relationship between extent of reaction and glass transition temperature of BA-a cured at Tc = 155 ( ), 165 ( ), 175 ( ), and 185 o C ( ) Tg ( C) Temperature ( C) Fractional conversion Figure 4 Glass transition temperature of BA-a cured at Tc = 155 ( ), 165 ( ), 175 ( ), and 185 o C ( ) Tg ( C) Time (h) The fractional conversions and Tg values of isothermally cured BA-a at different Tc temperatures are plotted in Figure 5. The Tg of BA-a was found to be around 170 C. Unexpectedly, the evolution of the Tg as a function of the fractional conversion shows the opposite trend to that of epoxy resin 14,25,26. Gillham and his coworkers reported that the Tg of an epoxy resin increased very slowly until fractional conversion, after which it increased rapidly. At very high conversions, the reaction leads to increased crosslink density and thus influences the Tg of the epoxy resin significantly, whereas at the lower conversion, the reaction contributes mostly to build uncrosslinked molecules. This is contrary to what was found with the polybenzoxazine where the 10 major increase in Tg takes place during the early stages of polymerization. When the normalized glass transition temperature, cured uncured Tg Tg uncured Tg Tg is calculated for an arbitrarily set fractional conversion of 0.5, 80% of the glass transition temperature development has already taken place for the polybenzoxazine whereas only 28% is found for an epoxy resin 25. This implies that a very high conversion is not necessary for the polybenzoxazine to reach a Tg close to Tg. This early development of Tg, and associates mechanical and physical properties, is advantageous from the processing point of view. The molecular reason for this unusual phenomenon is not known at this time but it is hypothesized that the extensive inter and intramolecular hydrogen bonding in polybenzoxazine is responsible. As soon as the degree of polymerization exceeds 3, the oligomers possess multifunctional phenolic hydroxyl groups which can form hydrogen bonding networks. Since no free hydroxyl group is found in the FTIR spectrum of the partially cured benzoxazine resin, they must all participate in hydrogen bonding. A complication arises, however, since intramolecular hydrogen bonding cannot participate in increasing the apparent molecular weight. Hence, the relative ratio of the inter and intramolecular hydrogen bonding becomes an important criterion for the apparent molecular weight development through intermolecular hydrogen bonding. At the present Polymers & Polymer Composites, Vol. 9, No. 6,

6 Mantana Kanchanasopa, Nantaya Yanumet, Kasinee Hemvichian and Hatsuo Ishida time, no quantitative data on this ratio is available. However, qualitatively, a strong intermolecular hydrogen bonded IR band is observed, and thus it is safe to assume that a large number of hydroxyl groups are participating as intermolecularly hydrogen bonded groups 18. It is obvious that the apparent molecular weight of the intermolecularly hydrogen bonded molecules develops much faster than the molecular weight based on covalent bonds alone. It is also important to recognize the stiffening role of the strong chelated intramolecular hydrogen bonds, O H N. It is for these reasons that the Tg of polybenzoxazine develops quickly at very low fractional conversions. Interestingly, a model epoxy resin that yields one hydroxyl group in every chemical repeat unit upon polymerization exhibits the intermediate situation. Again, at the fractional conversion of 0.5, 40% of the glass transition temperature development was observed, further implying that hydrogen bonding may indeed be a major parameter for this phenomenon. The average room temperature density (ρ RT ) of the monomer and cured BA-a are shown in Table 1. By comparing the ρ RT of this amorphous monomer and polymer, the volumetric expansion upon polymerization of BA-a was found to be around 1-2% depending on the polymerization conditions. The plot of density vs. curing time is shown in Figure 6. Similar trends are observed for samples cured at 155, 165 and 175 C. The ρ RT decreases as a function of curing time and it is nearly constant at the lower density for long curing times, due to the effect of the diffusion controlled reaction and lower rate of polymerization. Comparing the ρ RT of BA-a cured for the same time at various Tc temperatures, it was found that the higher the Tc, the lower the ρ RT due to Table 1 The average room temperature density (ρ RT ) of the monomer and cured BA-a, for different curing conditions Cure time (h) C 165 C 175 C 185 C Figure 6 Density of BA-a cured at Tc = 155 ( ), 165 ( ), 175 ( ), and 185 o C ( ) Density (g/cm 3 ) Curing time (h) the increased percent conversion. Gillham and his coworkers studied extensively the effect of crosslink density on the volume of epoxy resin. They reported that increased crosslink density lead to volumetric expansion 14. The free volume measurement by positron annihilation also supports this statement 18. It is interesting to note that the ρ RT of the cured BA-a at 185 C shows the opposite trend to the other Tc temperatures. At this temperature, the ρ RT tends to increase during the prolonged curing time. A plot of density vs. Tg is shown in Figure 7. Most of the data fit the curve except for the material polymerized at 185 C. It is possible that the polymerization reaction at Tc < Tg is slightly different from that at Tc > Tg. The polymerization preferentially takes place at the ortho position of the phenolic structure. The para position is unavailable since it is occupied by the bond with the quaternary carbon of bisphenol-a. Although quite unreactive, the meta position is nonetheless available and can react when the conditions are favourable. Increased temperature might provide a sufficient condition for the meta position to react as well. If this reaction takes place, the local structure of the benzoxazine networks would be quite different from that of the ortho-dominated structure. Further study is needed to verify this hypothesis. This fast development of Tg at low conversions is unusual. In order to examine whether or not this is a common phenomenon among benzoxazine resins, bisphenol-af-based benzoxazine (BAF-a) was used to compare with bisphenol-a-based benzoxazine 372 Polymers & Polymer Composites, Vol. 9, No. 6, 2001

7 Effect of Polymerization Conditions on the Density Changes and Tg of Bisphenol-A... Figure 7 Relationship between density of BA-a cured at Tc = 155 ( ), 165 ( ), 175 ( ), and 185 o C ( ) and glass transition temperature Density (g/cm 3 ) Tg ( C) (BA-a). The fluorinated benzoxazine monomer has been successfully synthesized by the solventless method 22 using 2,2-bis(4-hydroxyphenyl) hexafluoropropane. The thermal behaviour of the BAF-a benzoxazine polymer was investigated by DSC. All samples were subjected to isothermal curing for a specified period of time in an oven. Four different polymerization temperatures of 155, 165, 175, and 185 C were used. Polymerization times varied from 10 min to 10 h. H T for the BAF-a benzoxazine monomer was J/g. The variation of Tg with polymerization time under four different isothermal conditions is shown in Figure 8. From the comparison between these two polybenzoxazines, we found that, under the same curing conditions, the Tg of the BAF-a polybenzoxazine was about C higher than that of the BA-a polybenzoxazine. Another interesting observation found as a result of the fluorination of polybenzoxazine is that the glass transition temperature obtained from each polymerization temperature was much higher than the cure temperature itself (Tg > Tc). This unusual property has also been reported for some other classes of polymer 27,28. The residual heat of reaction decreased as the cure time increased. The residual heat of reaction can be transformed in to the fractional conversion by equation (1). The increase of fractional conversion with time was similar to that of Tg, implying that there is a correlation between Tg and fractional conversion. In order to see the relationship between Tg and the fractional conversion, the Tgs of samples cured isothermally at four different temperatures are plotted in Figure 9 versus the corresponding fractional conversion. From Figure 9, it is obvious that there was a relationship between Tg and conversion which was independent of cure temperature. The relationship between the glass transition temperature and the conversion has been studied for some classes of thermosetting polymers, especially epoxy resin 29. Again, the trend observed for BAF-a-based polybenzoxazine is the opposite of that for epoxy resins. However, the increase in Tg as a function of fractional conversion for BAF-a is not as pronounced as for BA-a. Figure 8 Tg of partially cured BAF-a polybenzoxazines cured isothermally at different temperatures, 155 ( ), 165 ( ), 175 ( ), and 185 o C ( ), plotted vs. time Tg ( C) Time (h) Figure 9 Tg of partially cured BAF-a polybenzoxazines cured isothermally at different temperatures plotted vs. the corresponding fractional conversion Tg ( C) Fractional conversion Polymers & Polymer Composites, Vol. 9, No. 6,

8 Mantana Kanchanasopa, Nantaya Yanumet, Kasinee Hemvichian and Hatsuo Ishida Figure 10 TGA thermograms of BAF-a and BA-a polybenzoxazines Residual weight (%) The benzoxazine monomer was synthesized from a bisphenol containing a hexafluoroisopropylidene group. The bisphenol-af-based polybenzoxazine obtained demonstrated a large increase in the glass transition temperature compared to the bisphenol- A-based polybenzoxazine. The Tg of bisphenol-abased polybenzoxazine was found to be higher than the cure temperature itself, which was not observed in bisphenol-a-based polybenzoxazine. The development of the Tg of bisphenol-af-based polybenzoxazine takes place at a low conversion. This is the opposite of the trend observed with an epoxy resin. In addition, the incorporation of a fluorine-containing group was found to improve the thermal stability of polybenzoxazine Temperature ( C) A thermogravimetric analysis was performed in order to see the effect of fluorination on the thermal stability of polybenzoxazine. The result is shown in Figure 10. From the TGA thermogram of BA-a polybenzoxazine, weight loss started at around 290 o C, and a marked decomposition was seen in the range of C. The char yield of this polymer under a nitrogen atmosphere at 800 C was 30%. For BAF-a polybenzoxazine, the polymer began to lose weight at 330 C, and a notable decrease of weight was observed in the range of C. At 800 C, the char yield of this polymer was determined as 57%. From the comparison, it is obvious that the char yield of fluorinated polybenzoxazine was about 28% higher than that of the nonfluorinated analogue. This increase in char yield implies that fluorination had the same effect on the improvement of thermal stability of polybenzoxazine as it does in many other polymers. CONCLUSIONS The density of the BA-a benzoxazine measured at room temperature was investigated as a function of curing time and isothermal curing temperature. The 1-2% volumetric expansion of cured BA-a was found as a function of curing conditions. The higher the conversion, the higher the volumetric expansion. Vitrification occurred in the system cured at lower temperatures than 170 C, which is the ultimate glass transition temperature of the cured BA-a. At Tc = 175 C and 185 C (Tc>Tg), vitrification did not occur, so the reaction reached nearly 100% conversion at this cure temperature. At 185 C, minor volumetric shrinkage was observed at prolonged curing times, possibly due to different curing mechanism. ACKNOWLEDGMENT The authors gratefully acknowledge the partial financial support of the Royal Thai Government. The authors are also indebted to the partial financial support of the NSF Center for Molecular and Microstructure of Composites (CMMC) which is jointly established by the State of Ohio and EPIC, representing industrial members. REFERENCES 1. Holly F.W. and Cope A.C., J. Amer. Chem. Soc., 66, (1944), Shreiber H., Ger. Offen (1973); and Ger. Offen (1973) 3. Riess G., Schwob J.M., Guth G., Roche M., and Lande B., in Advances in Polymer Science, B.M. Culbertson and J.E. McGrath, Eds., Plenum, New York (1986) p Ning X. and Ishida H., J. Polym. Sci., Polym. Chem. Ed., 32, (1994), Ning X. and Ishida H., J. Polym. Sci., Polym. Phys. Ed., 32, (1994), Bailey W.J. and Katsuki H., ACS Div. Polym. Chem., 14, (1973), Bailey W.J., Katsuki H. and Endo T., ACS Div. Polym. Chem., 15, (1974), Bailey W.J., Polym. Preprints, 18, (1977), Bailey W.J., Mater. Sci. Eng., A126, (1990), He P., Zhou Z. and Pan C., J. Mater. Sci., 24, (1989), Polymers & Polymer Composites, Vol. 9, No. 6, 2001

9 Effect of Polymerization Conditions on the Density Changes and Tg of Bisphenol-A He P. and Zhou Z., J. Mater. Sci., 26, (1991), Shimbo M., Ochi M. and Shigeta Y.J., J. Appl. Polym. Sci., 26, (1981), Shimbo M., Ochi M., Inamura T. and Inoue M., J. Mater. Sci., 20, (1985), Pang K.P. and Gillham J.K., J. Appl. Polym. Sci., 37, (1989), Ishida H. and Allen D.J., J. Polym. Sci., Polym. Phys. Ed. (in press) 16. Ishida H. and Low H.Y., Macromolecules, 30, (1997), Dunkers J., Zarate E.A. and Ishida H., J. Phys. Chem, 100, (1996), Wirasate S., Dhumrongvaraporn S., Allen D.J. and Ishida H., J. Appl. Polym. Sci., 70, (1998), Mercer F.W. and Goodman T. D., High Perform. Polym., 3, (1991), Nagai A., Nishimura S., Takahashi A. and Mukoh A., J. Polym. Sci. Part C: Polym. Lett., 28, (1990), Bruma M., Fitch J.W. and Cassidy P.E., J. Macromol. Sci. Rev. Macromol. Chem. Phys., C36 (1), (1996), Liu J.P., Ph.D. dissertation, Case Western Reserve University, (1995) 23. Ishida H., U.S. Pat. 5,543,516, Aug. 6 (1996) 24. Liu J.P. and Ishida H., Polym. & Polym. Compos. (submitted) 25. Venditti R.A., Gillham J.K., Chin E. and Houlihan F.M., J. Appl. Polym. Sci., 53, (1994), Wisanrakkit G. and Gillham J.K., in Polymer Characterization; Physical Property, Spectroscopic, and Chromatographic Methods, C.D. Craver and T. Provder, Eds., Advances in Chemistry Series 227, American Chemical Society, Washington D.C., (1990), Wisanrakkit G. and Gillham J.K., J. Appl. Polym. Sci., 41, (1990), Shen S.B., Ph. D. dissertation, Case Western Reserve University, (1995) 29. HaleA., Macosko C.W. and Bair H.E., Macromolecules, 24, (1991), 2610 Polymers & Polymer Composites, Vol. 9, No. 6,

10 Mantana Kanchanasopa, Nantaya Yanumet, Kasinee Hemvichian and Hatsuo Ishida Designers, Processors, Engineers, Sales/Marketing Personnel For more details contact: Gill Tunnicliffe Training Business Co-ordinator Rapra Technology Limited Shawbury, Shrewsbury, Shropshire SY4 4NR, UK Want to know more about Thermoplastic Elastomers? Where are they used and why? Tel: +44(0) Fax: +44(0) or What is their potential? Understand the basic polymer science Learn about suppliers, processes, costs and applications Training Courses 376 Polymers & Polymer Composites, Vol. 9, No. 6, 2001