Poly condensations

The second category of polymerization reactions does not involve a chain reaction and is divided into two groups poly addition and poly condensation [4]. In botli reactions, tire growth of a polymer chains proceeds by reactions between molecules of all degrees of polymerization. In polycondensations a low-molecular-weight product L is eliminated, while polyadditions occur witliout elimination ... 

Among the polymeric stabilizers may be listed poly-condensed polymers based on alkyl phenols, aldehydes, and ketones of the aliphatic series, where = 1 - 8 and R,R means alkyl [24], Na, K, Ca phenolates of poly-condensed polymers [25], and also products of epichlor-ide with one or more aliphatic amines C3—C30 [26]. 

Maleic anhydride, 98 g (1.0 mol), 148 g (1.0 mol) of phthalic anhydride, and 160 g (2.1 mol) of 1,2-propanediol are poly condensed in a three-necked flask equipped with a mechanical stirrer, a nitrogen inlet, and a distillation head connected to a condenser and a receiver flask. The flask is placed in a salt bath preheated at 160°C. Water begins to distill and the temperature is then raised gradually to 190°C. The polycondensation is stopped (after about 15 h) when the reaction mixture has an acid number of 50 (see Section 2.3.8.4.1) (Scheme 2.54). A slightly different procedure is described in ref. 423. 

Melt poly condensation The reaction is carried out in a 250-mL stainless steel vessel with nitrogen inlet and mechanical stirrer. The vessel containing T4T-dimethyl (30 g, 72.8 mmol) and ethanediol (30 g, 0.48 mol) is heated up in an oil bath at 200°C. After 15 min reaction TiO -OCaJ I7 )4 (1.5 mL of 0.1 M solution in CH2C12) is added and subsequently the temperature is gradually raised to 260°C (l°C/min). After 10 min at 260°C the pressure is reduced (15-20 mbar) for 5 min. Then the pressure is reduced further (<2.5 mbar) for 45 min. The vessel is cooled down slowly to room temperature, maintaining the low pressure. After solidification, the polymer is ground (particle size <1 mm) and subsequently dried in a vacuum oven at 80°C. 

Note Several condensing agents for the direct poly condensation reaction such as diphenyl chlorophosphate-LiBr and tosyl chloride-DMF have also been developed by Higashi et al.311,312 (see Section 2.3.3.2). 

Poly condensations of trimethylsilyl 3,5-diacetoxybenzoate Trimethylsilyl 3,5-diacetoxybenzoate (15.52 g, 50 mmol) is weighed into a cylindrical reactor equipped with a glass stirrer and gas inlet and outlet tubes. The reaction vessel is placed into a metal bath preheated to 200°C. The temperature is raised in 20°C steps over a period of 1 h and finally maintained at 280°C for 3 h. Vacuum is then applied for an additional 0.5 h. Finally, the cold reaction product is powdered, dissolved in CH2Cl2-trifluoroacetic acid (volume ratio 4 1), and precipitated into cold methanol. 

Polysulfonation of self-polycondensation of 4-(phenylthio)benzenesulfonyl chloride was also used to prepare poly(arylene sulfide sulfone)s.245,246 Condensation of diphenyl sulfide with d -oxydibenzenesulfonic acid or d.d -thiodibcn/cnc-sulfonic acid247 or by poly etherification of poly condensation of DC DPS with d.d -dihydroxydiphenol sulfide occurred.5... 

CPE Produced by ADMET poly condensation.23 JSee ref 38 for reviews on metallocene PE catalysis. eFrom ref. 39. 

Greater size of the silica particles indicates higher extent of poly condensation that has taken place in the inorganic phase. The generation of silica particles is directly proportional to the alkoxysilane concentration and higher concentration of TEOS used for these investigations allows higher extent of... 

Synthesis of strictly alternating copolymers can be achieved via various polymerisation techniques including poly-condensation or Ziegler-Natta polymerisations [123, 124]. 

The ring structures undergo further (poly)condensation reactions. These polymerization reactions proceed rapidly until particles with diameters of typically 1-2 nm are formed. Schematically, the process can be summarized as shown in Figure 3.15. 

Finally, two accidents are mentioned that brought into play the poly-condensation of chioroacetone On a glass bottle), which was exposed to sun-... 

Test results for a series of reactions of polyfunctional amino acids with CDI in aqueous solution are reported in reference [51]. Serine and threonine did not poly-condense. Instead, via the iV-imidazolyl-carbonyl amino acids, L-2-oxooxazolidine-4-carboxylic acid or L-(+)-fraw,s-5-methyl-2-oxooxazolidine-4-carboxylic acid were obtained. 

Freeder, B. G. et al., J. Loss Prev. Process Ind., 1988, 1, 164-168 Accidental contamination of a 90 kg cylinder of ethylene oxide with a little sodium hydroxide solution led to explosive failure of the cylinder over 8 hours later [1], Based on later studies of the kinetics and heat release of the poly condensation reaction, it was estimated that after 8 hours and 1 min, some 12.7% of the oxide had condensed with an increase in temperature from 20 to 100°C. At this point the heat release rate was calculated to be 2.1 MJ/min, and 100 s later the temperature and heat release rate would be 160° and 1.67 MJ/s respectively, with 28% condensation. Complete reaction would have been attained some 16 s later at a temperature of 700°C [2], Precautions designed to prevent explosive polymerisation of ethylene oxide are discussed, including rigid exclusion of acids covalent halides, such as aluminium chloride, iron(III) chloride, tin(IV) chloride basic materials like alkali hydroxides, ammonia, amines, metallic potassium and catalytically active solids such as aluminium oxide, iron oxide, or rust [1] A comparative study of the runaway exothermic polymerisation of ethylene oxide and of propylene oxide by 10 wt% of solutions of sodium hydroxide of various concentrations has been done using ARC. Results below show onset temperatures/corrected adiabatic exotherm/maximum pressure attained and heat of polymerisation for the least (0.125 M) and most (1 M) concentrated alkali solutions used as catalysts. 

Benzyl alcohol contaminated with 1.4% of hydrogen bromide and 1.1% of dissolved iron(II) polymerises exothermally above 100°C. Bases inhibit the polymerisation reaction. In a laboratory test, alcohol containing 1% of HBr and 0.04% of Fe polymerised at about 150° with an exotherm to 240° C. Formation and iron-catalysed poly-condensation of benzyl bromide seems to have been implicated. See Benzyl bromide Molecular sieve, or Catalytic impurities See Other BENZYL COMPOUNDS, POLYCONDENSATION REACTION INCIDENTS... 

Figure 5. Schematic structure of a polysiloxane layer obtained by hydrolysis and poly condensation of monomeric alkylsilanes RSiX3 (X = Cl, OCH3, OC2H5).

These are obtained by poly condensation of dihydrazides of dicarboxylic acids (in an excess of hydrazine hydrate) ... 

In 1959 and 1960, Challa published the first results of quantitative experiments on the poly condensation equilibrium in PET [22, 41, 42], He determined the polycondensation equilibrium constant K at different temperatures and average degrees of polycondensation and found that this parameter depends only slightly on temperature, but increases significantly with increasing degree of polycondensation. The monomer BHET was found not to follow the principle of equal reactivity. 

Many publications have appeared on the kinetics of transesterification, dealing with either PET or model compounds. A selection of these papers is summarized in Table 2.5. The overall reaction order of polycondensation is 3, being 1 each for ester, alcohol, and catalyst [43], The reaction rate of poly condensation is generally limited by the rate of removal of EG from the reaction mixture. A... 

Hoftyzer and van Krevelen [100] investigated the combination of mass transfer together with chemical reactions in polycondensation, and deduced the ratedetermining factors from the description of gas absorption processes. They proposed three possible cases for poly condensation reactions, i.e. (1) the polycondensation takes place in the bulk of the polymer melt and the volatile compound produced has to be removed by a physical desorption process, (2) the polycondensation takes place exclusively in the vicinity of the interface at a rate determined by both reaction and diffusion, and (3) the reaction zone is located close to the interface and mass transport of the reactants to this zone is the rate-determining step. 

Laubriet et al. [Ill] modelled the final stage of poly condensation by using the set of reactions and kinetic parameters published by Ravindranath and Mashelkar [112], They used a mass-transfer term in the material balances for EG, water and DEG adapted from film theory J = 0MMg — c ), with c being the interfacial equilibrium concentration of the volatile species i. 

The chemistry of the solid-state polycondensation process is the same as that of melt-phase poly condensation. Most important are the transesterification/glycolysis and esterification/hydrolysis reactions, particularly, if the polymer has a high water concentration. Due to the low content of hydroxyl end groups, only minor amounts of DEG are formed and the thermal degradation of polymer chains is insignificant at the low temperatures of the SSP process. 

Ravindranath and Mashelkar 121 Unsteady state Solid-state poly condensation Particle... 

Laubriet et al. 111 Continuous Poly condensation, finisher Tube reactor, disc type... 

Mallon and Ray 123 Continuous Solid-state poly condensation Tube reactor... 

Rieckmann and Volker 8 Semi-batch Poly condensation Crucible of TGA... 

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