Solid-state polycondensation vacuum

Besides the pressure (vacuum) and the flow rate of the gas, temperature is the major experimental variable in SSP and is of the highest importance for the economy of the process. Temperature dependence data for the solid-state polycondensation process are shown in Figures 5.4-5.7. According to the results... 

Solid-state polycondensation (SSP) is thus a technique applied to thermoplastic polyesters to raise their molecular weight or IV. During solid-state polycondensation, the polymer is heated above the glass transition temperature and below the melt temperature of the polymer either under an inert gas or under vacuum. Increasing the intrinsic viscosity requires a residence time of up to 12 h under vacuum or under inert gas, at temperatures from 180 to 240 °C. 

High-molecular-weight polyesters cannot be made by polymerization in the molten state alone - instead, post-polymerization (or polycondensation) is performed in the solid state as chips (usually under vacuum or inert gas) at temperatures somewhat less than the melting point. The solid-state polycondensation of polyesters is covered in detail in Chapters 4 and 5. 

Waste of polyesters and polyamides may have suffered from the hydrolytic depolymerization. Thus, it may be necessary to increase the molecular weight by solid-state polycondensation under high vacuum, or by reactive coupling using such di-functional agents as di-glycidyls. Prior to melt processing, the resins should be dried to less than 0.01 wt% of moisture, re-stabilized and (if compounded with immiscible polymers) compati-bilized. 

Materials. Completely aromatic random copolyester CPE-1 was synthesized by melt polycondensation, where TPA, PHQ, and HBA (45, 45, and 10 mol %, respectively) were used as initial components. To increase the molecular mass, the final stage of polycondensation was carried out in the solid state in vacuum at 260°C. Varying the duration of this final stage, one obtaines samples with different molecular weight. The molecular weight was estimated from the measurement of relative viscosity of copolyester solutions (0.5 g/dl) in a trifluoroacetic acid-chloroform (60 40%) mixed solvent. For the CPE-1 samples studied, the specific viscosity was 2.7, 3.4, 4.4, 4.7, and 6.4. We studied highly oriented CPE-1 fibers. The fibers were... 

Certain polyamides and polyesters can be prepared by solid-state polycondensation step polymerization, usually by heating the appropriate monomer or monomer salt. For example, nylon 11 can be prepared by heating crystals of 11-aminoundecanoic acid (melting point =188 C) at 160°C under vacuum. Polyaddition step polymerization of conjugated dialkene monomers can be induced in the solid state by exposure of the monomer to ultra-violet radiation. For example, irradiation of crystalline 2,5-distyrylpyrazine yields quantitatively a highly crystalline linear cyclobutane polymer... 

Heterochain polymers of the type -(M-X) - contain polar M-X bonds (for reviews see [1,2,12-15]). Such polymers are often prepared by polycondensation of a bifimctional metal halide (M = B, Si, Ge, Sn, Pb, Sb, Ni, Pd, Pt, Ti, Hf) with a bifunctional Lewis base such as a diol, diamine, dihydrazine, dihydrazide, dioxime, diamideoxime, dithiol, diacetylene (Eq. 7-2). Another possibilitiy is the polyaddition of a bifunctional metal hydride to bifunctional alkenes (Eq. 7-3). Mn and mg containing poly(p-xylylenes) of the composition -(-CH2-C6H4-CH2-M-) - were produced by solid-state UV-photopolymerization of a cocondensated mixture of p-xylylene with Mn or mg at 80 K [16]. Prolonged storage of the polymers at ambient temperature under vacuum led to gradual decomposition. 

This is the preferred method for the synthesis of both, aliphatic and aromatic polyesters derived from CHDM. The reaction is usually accomplished in two steps. The first step is carried out under a pressure which depends on the diacid or the dimethyl ester derivative used for the synthesis. Usually an excess of diols to diacid (1.2-2.2 1) is employed so a mixture of short oligomers is produced. In the second polycondensation step, which is carried out at higher temperatures and under vacuum, the oligomers react to generate the polymer and the excess of diol is removed. If the resulting polyester is crystalline it may be subjected to solid state postpolycondensation (SSP) in order to increase the molecular weight. 

In the vacuum deposition of the precursors PMDA and ODA at temperature of 120-145 °C reaction of polycondensation to P AA with opening of the anhydride ring of PMDA takes place (Ac-Sn2 -reaction). These processes are to great extent accelerated and controlled in the thermal treatment of the condensed solid phase which represents PAA, with regard to their transformation to PI by means of reaction of polycyclodehydration in solid state to linear PI [7,10,11]. The FTIR spectra of individual films of PMDA, ODA and PAA are shown in figure 2. 

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