Neat Resins

Electrical, electronic, and technical appHcations use polycarbonates for a variety of purposes. The woddwide market is about 156,000 t aimuaHy. Because of exceHent electrical properties (dielectric strength, volume resistivity), and resistance to heat and humidity, polycarbonate is used for electrical connectors (qv), telephone network devices, oudet boxes, etc. Polycarbonate had been popular for use in computer and business machine housings, but the use of neat resin has been largely supplanted by blends of polycarbonate with ABS. OveraH, however, the total use of polycarbonate continues to increase. 

Mechanical Properties. Properties of typical grades of PBT, either as unfiUed neat resin, glass-fiber fiUed, and FR-grades, are set out in Table 8. This table also includes impact-modified grades which incorporate dispersions of elastomeric particles inside the semicrystalHne polyester matrix. These dispersions act as effective toughening agents which greatly improve impact properties. The mechanisms are not fiiUy understood in all cases. The subject has been discussed in detail (171) and the particular case of impact-modified polyesters such as PBT has also been discussed (172,173). 

Mechanical Properties. The performance of various polyester resin compositions can be distinguished by comparing the mechanical properties of thin castings (3 mm) of the neat resin defined in ASTM testing procedures (15). This technique is used widely to characterize subtle changes in flexural, tensile, and compressive properties that are generally overshadowed in highly filled or reinforced laminates. 

Bayer marketed PPS compounds in the United States under the trade name Tedur, but the company has exited the PPS business. PPS is also marketed in the United States by GE Plastics, whose source of neat resin is Tosoh Corporation of Japan. GE Plastics markets PPS under the trade name Supec PPS. Patent activity by Tennessee Eastman describes an alternative process for the production of poly(phenylene sulfide/disulfide), although samples of such product have not appeared as of early 1996. Both Phillips and Hoechst Celanese have aimounced plans to debotdeneck their existing U.S. faciUties in order to meet anticipated market growth. 

The roster of PPS suppHers in Japan is much larger than in the United States. Multiple market presences in Japan include TOPPS (Toray PPS, formerly TO—PP, which was a joint venture between Toray and Phillips) Dainippon Ink and Chemicals, Inc. Tosoh Tohpren Kureha/Polyplastics and Idemitsu. PPS marketed by Toray is sold under the Torelina trademark. Production capacity in Japan was estimated in 1995 at 11,400 t of neat resin per year. At the time that this capacity was created, the situation in Japan was characterized by overcapacity and underutilization. Additionally, further PPS capacity was brought on by Sunkyong in Korea, which is marketing a low cost PPS product. Although excess PPS capacity still exists in Japan, market growth has narrowed the gap between supply and demand. 

The neat resin preparation for PPS is quite compHcated, despite the fact that the overall polymerization reaction appears to be simple. Several commercial PPS polymerization processes that feature some steps in common have been described (1,2). At least three different mechanisms have been pubUshed in an attempt to describe the basic reaction of a sodium sulfide equivalent and -dichlorobenzene these are S Ar (13,16,19), radical cation (20,21), and Buimett s (22) Sj l radical anion (23—25) mechanisms. The benzyne mechanism was ruled out (16) based on the observation that the para-substitution pattern of the monomer, -dichlorobenzene, is retained in the repeating unit of the polymer. Demonstration that the step-growth polymerization of sodium sulfide and /)-dichlorohenzene proceeds via the S Ar mechanism is fairly recent (1991) (26). Eurther complexity in the polymerization is the incorporation of comonomers that alter the polymer stmcture, thereby modifying the properties of the polymer. Additionally, post-polymerization treatments can be utilized, which modify the properties of the polymer. Preparation of the neat resin is an area of significant latitude and extreme importance for the end user. 

The methanol is coUected overhead and the neat resin is extmded from the reactor in a batch or continuous process. The larger volume firms employ continuous operations with outputs per line of 11,000—14,000 t/yr (68). 

Fig. 1. Maximum moisture content as a function of relative humidity for Narmco 5208 neat resin. (Loos and Springer (19))...

Fig. 3. Liquid water uptakes for a TGDDM-DDS neat resin at increasing applied hydrostatic relative pressures. (22)...

Fig. 5. First (open circles) and second (full circles) equilibrium moisture sorptions in the DGEBA-TETA neat resin. The dotted line is eq. (1)...

Fig. 10. Liquid water sorptions for DGEBA-TETA neat resin under thermal cycling...

Fig. 11. Water vapour sorption kinetics in the same external conditions for as cast and hygrothermally damaged DGEBA-TETA neat resin...

Typical tension stress-strain curves of baseline and irradiated unidirectional T300/934 composites tested in [0] and [90] orientations at three different temperatures (121 are shown in Figures 11 and 12. Irradiation had essentially no effect on the fiber-dominated tensile modulus of the [0] specimen and caused only a small (10-15%) reduction in strength at the low and elevated temperatures. For the matrix-dominated [90] laminates, irradiation caused a very substantial decrease in strength at three test temperatures (-38% at -157°C, -26% R.T., -13% 121°C). Irradiation increased the modulus at -157°C and R.T. (10 - 15%), but lowered it at 121°C (-15%). These results are consistent with results obtained on the neat resin specimens discussed above. 

Figure 10. Neat resin tensile response of 934 resin specimens. (Reproduced from reference 13.)...

About 1970, research was initiated under Air Force funding on acetylene-terminated imide oligomers (ATI) which could be thermally chain extended through the acetylenic end-groups (33, 34). This effort resulted in the development of HR-600 (Eq. 9) and subsequent commercialization by Gulf Oil Chemicals Company in the form of Ther-mid -600. Neat resin properties of HR-600 are presented in Table IV while preliminary composite properties are given in Table V. 

Although HR-600/Thermid-600 provided promising neat resin and composite properties, major processing problems have plagued these as well as other acetylene-terminated oligomers. Resin flow and wetting is inhibited due to the reaction of the terminal ethynyl groups prior to the formation of a complete melt or soft state. This becomes even more severe due to heat transfer problems as... 

Inserts can be incorporated into the mould before injection or placed after demoulding into a moulded hole. For neat resins, the first solution is generally avoided because of the big difference between the coefficients of thermal expansion of metals and plastics. In both cases, inserts and embossing must obey some general rules. Among these, some, but not all, are recalled below ... 

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