Semi-IPN

Semi-gloss alkyd paint formulation, 18 6 It Semi-interpenetrating network (IPN) approaches, 10 436 Semi-IPN (interpenetrating polymer network) hydrogels, 13 733 Semikilled steels, 23 291 Semimoist pet foods, 10 849 Semipermanent cells, 14 228 Semiphorone, 14 583 Semiportable mri system, 23 860-861 Semiregenerative reforming operations, 25 166... 

Silicone co-polymer networks and IPNs have recently been reviewed.321 The development of IPNs is briefly described, and the definitions of the main (non-exclusive) classes of the IPNs are cited. Examples of latex IPNs, simultaneous and sequential IPNs, semi-IPNs, and thermoplastic IPNs are provided. The use of silicone-silicone IPNs in studies of model silicone networks is also illustrated. Networks in which siloxane and non-siloxane components are connected via chemical bonds are considered co-polymer networks, although some other names have been applied to such networks. Today, some of the examples in this category should, perhaps, be discussed as organic-inorganic hybrids, or nanocomposites. Silicone IPNs are discussed in almost all of the major references dealing with IPNs.322-324 Silicone IPNs are also briefly discussed in some other, previously cited, reviews.291,306... 

Full-IPNs have higher compressional strength (2929 g load for 50 % compression) than the corresponding semi-IPNs (1883 g load for 50 % compression) [42],... 

Pseudo or semi-IPNs are combinations of linear with crosslinked polymers resulting in various degrees of interpenetration. (28-34)... 

Figure 1. Effect of different compositions of PU/VMGC on the tensile strength of semi-IPN coatings with or without opposite charge groups.

Figure Micrographs of semi-IPN with and without opposite charge groups by scanning electron microscopy (SEM),...

Figure 3.17 Tg behavior of semi-IPNs cured at 210°C Tgs of (O) BPACY-rich phase, (O) PEI-rich phase and (O) homogeneous state...

With controllable strength of the self- and hetero-associated hydrogen, a molecular level penetrated semi-interpenetrating polymer networks (semi-IPNs) of ST-VPDMS with poly(N-vinylpyrrolidone) (PVPr) were prepared by condensation of the self-associated silanols.13... 

Semi-interpenetrating Polymer Network (Semi-IPN) Synthesis ... 

A novel attempt was made to realize different IPN architectures in a composite system of cellulose/poly(AT-vinyl pyrrolidone-co-glycidyl methacrylate) (CELL/P(VP-co-GMA)) [73]. The copolymer-rich compositions (4-19 wt % CELL) were synthesized successfully via photopolymerization in the gel state of cellulose impregnated with a monomer mixture of VP and GMA, resulting in the development of a semi-IPN-like organization (Fig. 5a) within the copolymerized bulks. An additional treatment of the as-polymerized composites ([O]-series) with 50% formic acid or 3% sodium hydrox-... 

Fig. 5 Schematic illustrations of different IPN architectures attainable for CELL/P(VP-co-GMA) composites, a Semi-IPN b Full-IPN c Joined-IPN...

Exclusively mechanically interlocked linear polymer blends, typically, are not thermodynamically phase stable. Given sufficient thermal energy (Tuse>Tg), molecular motion will cause disentanglement of the chains and demixing to occur. To avoid phase separation, crosslinking of one or both components results in the formation of a semi-IPN or full-IPN, respectively. Crosslinking effectively slows or stops polymer molecular diffusion and halts the phase decomposition process. 

Bismaleimide-Linear High Tg Thermoplastic Semi-IPNs. . 170... 

When the blend is prepared with a linear polymer and a crosslinkable monomer, a semi-interpenetrated polymer (semi-IPN) network is obtained and this concept has been applied to a linear heterocyclic polymer and a crosslinkable thermostable oligomer [111]. The linear heterocyclic polymers exhibit high glass transition temperatures, good fracture toughness (Table 6), but the high viscosity above Tg make them difficult to process. 

Table 6. Thermomechanical properties of some linear polymers used for the preparation of semi-IPNs with BMIs and BNIs...

Table 7. End-capped oligomers used for the preparation of thermostable semi-IPNs...

The BMIs and BNIs which were used for the semi-IPN preparations are summarized in Table 7. By heating, the melt viscosity of such oligomers decreases before the crosslinking and allows the process with classical tools. Two questions arise Is it possible to get an intimate mixture of crosslinked BMI or BNI with a linear heterocyclic polymer and what will be the behavior of such semi-IPNs ... 

A mixture of a BMI (Compimide 796) with 4,4 -bis(orf/zo-propenylphe-noxy)benzophenone (TM 23) was blended in solution with Udel 700 (polysul-fone from Union Carbide), Ultem 100 (General Electric polyether imide), and PH 10 (Bayer polyhydantoin) (Fig. 35). The thermoplastics were introduced at various concentrations up to 33%. A phase segregation did not appear with PH 10, but two phases were observed with Ultem. With both semi-IPNs the observed Glc were found to be four- to fivefold the Glc of the neat BMI [113]. 

An increase in the Klc and Glc of BMI-MDA was again observed by blending with Ultem 1000. After crosslinking the semi-IPN exhibited phase separation and a complex morphology [118]. 

As shown in a previous section, fluorinated nadimides exhibit the best thermo-oxidative behavior. NR 150 linear polymers are prepared by reaction of HFDE and a mixture of para- and raefa-phenylenediamine. A semi-IPN was prepared by addition of a 150 °C staged PMR-15 to a solution of the NR 150 precursor. The solution was used for the composite manufacture. After curing at 250 °C, the DSC diagram showed two peaks in agreement with a non-miscible system. After curing, the Glc of the blend is higher than that of pure PMR-15 (Table 8) [119]. 

LARC TPI is a linear polyimide prepared with BTDA and 3,3 -diaminobenzo-phenone. The polyamide acid intermediate was used to prepare a semi-IPN with the PMR-15 reactants. After curing the blend exhibited a twofold Tg and an improved value of Glc (Table 8). 

The role of the miscibility of semi-IPN components on the mechanical properties has been discussed. The linear bisnadimide was a benzhydrol bisnadimide (Fig. 33). Three polyimides prepared from the same diamine and three different dianhydrides (Fig. 37) were used as linear components. The blends were cured up to 300 °C in a similar fashion to the bisnadimide alone. The results for the blend containing 20% by weight of linear polymers are summarized in Table 9. The non-miscible character of the components gives a phase segregation leading to the best toughness [121]. 

The semi-IPN concept has also been used in order to improve the high-temperature adhesive properties of a flexible polyimide. Polyimide prepared with isophthaloyldiphthalic anhydride and mefa-phenylenediamine presents good adhesive properties but is limited to 270 °C. By blending it with a bisnadimide... 

Table 8. Thermomechanical properties of semi-IPNs from PMR-15 (Tg=339 °C,Glc= 87 J m 2) after curing...

Table 9. Some properties of BBN 1500 based semi-IPNs...

Pascal T, Sillion B (1994) Heat resistant semi-IPNs. In Klempner D, Frisch KC (eds) Advances in interpenetrating polymer networks, Vol IV. Technomic, Lancaster, p 141... 

---