Solid-state polymerization Solution polycondensation

Polycondensation can be carried out by various polymerization techniques including melt polymerization, solution polymerization, interfacial polymerization, emulsion polymerization and solid-state polymerization. These polymerization processes will be summarized briefly in the following paragraphs. 

Beyond polycondensation and chain-growth polymerizations, further selections must be made whether to use bulk (mass), solution, emulsion or interfacial, suspension, graft and solid-state polymerizations ring opening, free radical, anionic or cationic. 

The choices are not always optimal. Solution and interfacial polycondensation polymerizations are used when bulk polymerization is too exothermic, as noted earlier. Polymerization combines processes such as polycondensation, bulk, graft, and solid-state polymerization or copolymerization. Three solid-state polymerization methods include... 

It is important to characterize because it is possible to use PET with relatively low molar mass obtained by solution polycondensation to make fibers or films. For the manufacture of bottles and tire cords, PET obtained by solid-state polymerization possessing a higher molar mass must be used. 

Just as the products of polycondensation are greatly varied, so are the reaction conditions used in their production. Some are produced in the melt (many polyamides and polyesters), some initially in the melt but with extensive polymerization continuing in the solid state (polyurethane foams and elastomers), in solution (some polyurethane fibres) or in non-homogeneous liquid systems (some polycarbonates, very high melting polyamides). 

It was found meanwhile that nearly every slim unbranched polymer chain, such as poly(trimethylene oxide) [224], poly(l,3-dioxolane) [225], poly(tetramethylene oxide) [226], polyethylene imine) [227], poly(3-hydroxy propionate), poly (4-hydroxybutyrate) and poly(6-hydroxyhexanoate) [228,229], poly(butylene succinate) [229], polyadipates [230], nylon-6 [231], and even oligomers of polyethylene [232], form a-CD ICs with channel structures. In all of these cases, inclusion is a heterogeneous process, since the guest polymer and its CD complex are almost insoluble in water. Therefore, extensive sonication had to be applied to accelerate the diffusion process. The polymer was also dissolved in an organic solvent, e.g., nylon-6 in formic acid, and this solution was added to the solution of a-CD [231], Alternatively, a monomer, such as 11-aminoundecanoic acid, was included in a-CD and polymerized to nylon-11 by solid state polycondensation within the channels of the IC. Thus, the IC of nylon-11 was formed under conservation of the crystal packing [233-235],... 

Finally, in a position at the interface of solid-state and polymer science are the remarkable linear chain compounds [LiMo3Se3]n, which can be dissolved in polar solvents such as propylene carbonate, DM SO, or N-methylformamide to form burgundy solutions. These species contain polymeric [Mo3Sc3] anions (6.25) that consist of polycondensed MogSes polyhedra (Fig. 6.12) [61, 62]. 

Type of polymerization polycondensation (step-growth) or chain-growth (addition) free-radical, ionic solution including interfacial, emulsion, suspension, bulk (mass) continuous or batch graft, solid state... 

Polycondensation is a typical method for polyimide syntheses, which need aromatic tetracarboxylic acids and aromatic diamines as monomers. Figure 10.1 shows that the polymerization process goes through two reactions The ring-opening polyaddition of aromatic diamines to aromatic tetracarboxylic dianhydrides in solution at room temperature gives soluble precursor polyamic acids, followed by solid-state thermal cyclodehydration to polyimides. 

The polyether-ester polyamic acid imidization process in a solid state under microwave irradiation was studied by Yu et al. [73]. The prepolymer, polyether-ester polyamic acid, was prepared by the polycondensation of poly(tetramethylene ether)glycol di-p-aminobenzoate (Polyamine-650, Polaroid, Co.) and pyromellitic acid dianhydride (PMDA) at room temperature in DMF solution. Later, the prepolymer solution was cast on polytetrafiuoroethylene plates to form 200 pm thin films that were imidized under microwave irradiation in a household microwave oven at 60 °C. The temperature was measured by means of a thermocouple applied to the film surface immediately after the intervals of microwave turn off It was found that microwave irradiation reduced both the reaction temperature and time. For example, during the solid phase thermal polymerization 68.3% polyamic acid was converted to polyimide at 155 °C, while under microwave irradiation 65 % of polyamic acid was reacted at 60 °C within 3 h [73]. 

Actual polymerizations are carried out in a variety of ways. These can be categorized as homogeneous and heterogeneous systems. Homogeneous systems include bulk and solution polymerization, whereas suspension polymerization, emulsion polymerization, bulk polymerization with precipitate, interfacial polycondensation, and solid-state polycondensation constitute the heterogeneous systems. 

Flory outlined [3] that the definition of polycondensation is necessarily based on kinetic aspects and not on the structure of polycondensates, because numerous polycondensates can also be prepared by ROP which usually proceeds as chain-growth polymerization. Flory s definition of step-growth polymerization is limited to polycondensations and polyadditions in the melt or in solution, and does not include solid-state polycondensations. Hory s definition of step-growth polymerizations is based on point 1. 

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