Monofunctional chain-terminating

Polyester plasticizer n. Any of a broad class of plasticizers characterized by having many ester groups in each molecule. They are synthesized from three components (1) A dibasic acid such as adipic, azelaic, lauric, or sebacic acid. (2) A glycol (dihydric alcohol). (3) A monofunctional chain terminator such as a monobasic acid. Molecular weights are low - from 500 to 5,000. Polyester plasticizers are noted for their permanence and resistance to extraction. 

Monofunctional, cyclohexylamine is used as a polyamide polymerization chain terminator to control polymer molecular weight. 3,3,5-Trimethylcyclohexylamines ate usehil fuel additives, corrosion inhibitors, and biocides (50). Dicyclohexylamine has direct uses as a solvent for cephalosporin antibiotic production, as a corrosion inhibitor, and as a fuel oil additive, in addition to serving as an organic intermediate. Cycloahphatic tertiary amines are used as urethane catalysts (72). Dimethylcyclohexylarnine (DMCHA) is marketed by Air Products as POLYCAT 8 for pour-in-place rigid insulating foam. Methyldicyclohexylamine is POLYCAT 12 used for flexible slabstock and molded foam. DM CHA is also sold as a fuel oil additive, which acts as an antioxidant. StericaHy hindered secondary cycloahphatic amines, specifically dicyclohexylamine, effectively catalyze polycarbonate polymerization (73). 

The condensation reaction is promoted by certain polar solvents and of the many which have been tested dimethyl sulphoxide appears to be the most effective. As usual with linear condensation polymers molecular equivalence and near-absence of monofunctional material is necessary to ensure a high molecular weight. Moisture and alcohols can also have a devastating effect on the molecular weight. In the case of water it is believed that 4-chlorophenyl 4-hydroxyphenyl sulphone is formed which functions as an effective chain terminator. Gross contamination with air is also believed to reduce the maximum attainable molecular weight as well as causing intense discolouration. 

A related technique involves incorporation of monofunctional poly(etliylene oxide) chains as nonionic, internal emulsifier groups. Even PMDI can be dispersed in water using this nonionic method (Scheme 4.24). High-molecular-weight (ca. 2000 g/m) monols are usually used which act as chain terminators and long, hydrophilic tails which function as an emulsifying agent. 

Monomers that participate in step growth polymerization may contain more or fewer than two functional groups. Difunctional monomers create linear polymers. Trifiinctional or polyfunctional monomers introduce branches which may lead to crosslinking when they are present in sufficiently high concentrations. Monofunctional monomers terminate polymerization by capping off the reactive end of the chain. Figure 2.12 illustrates the effect of functionality on molecular structure. 

The degree of polymerization is dictated by the ratio of liquid resin (cmde DGEBPA) to bisphenol A an excess of the former provides epoxy terminal groups. The actual molecular weights attained depend on the purity of the starting material. Reactive monofunctional groups act as chain terminators. 

The Addition of a Monofunctional Compound The monofunctional compound (e.g., —B) acts as a chain terminator since it produces molecules with unreactive ends. Let us consider A-A and B-B with BX. The initial total number of molecules is given by ... 

According to the reactants, either diblock or triblock copolymers can be obtained. For instance, PEO-fc-PDMS-b-PEO triblock copolymer and PEO-PDMS diblock copolymers were prepared in high yields by hydrosilylation of a telechelic PDMS which exhibits SiH functions (Mn = 1000) with monofunctional allyl-terminated PEO with Mn = 350 and 500 and telechelic diallyl PEO (Mn = 600), respectively [123]. Their dilute solution properties were investigated. Similarly, interesting PS-b-PDMS thermoplastics have been synthesized from a polystyrene fitted at chain end with a vinyl silane function which reacts with a PDMS bearing SiH end-groups [124]. In addition, hydrosilylation has been used to prepare original copolymers from a,co-disilyl-PDMS 25 and either a,oj-diallyl-polysulfone [125] or a,oj-diallyl poly (L-lactide) (PLLA) as follows [126] ... 

Catalytic chain transfer is a versatile tool that complements other means of polymerization. It allows the synthesis of the large variety of structured polymers shown in Figure 11. The primary outlet for CCT is to control molecular weight in free-radical polymerizations without the use of stoichiometric chain terminators (sections 1—3). All of the products can be considered to be monofunctional in that they are all terminated by unsaturation. The unsaturation... 

Since 1-propanol is monofunctional and reacts with "matched dissociation isocyanate" (at internal urethane chain positions) as well as "unmatched isocyanate" (at polymer chain terminal positions) its effects include cleavage of some polyurethane chains in the process of generating more urethane groups. As a result, polymer DP, melt viscosity, and torque drop until the shortstop is consumed, or escapes the mixture by volatilizaton. Figure 9 shovjs that the more 1-propanol used to shortstop the polymerizations, the more pronounced the polymer reversion was. 

Monofunctional alcohols may also be cured with epoxyslloxanes, although they act as chain terminators and slow UV cure iSgOH/oxlrane ratios approach 1. This effect is Illustrated for the M N /octanol system in Table VIII below ... 

Monofunctional hydroxyl terminated polyethylene oxide chains with degree of polymerization from 5 to 20 are reacted with pMDI, or simply with MDI, to provide surface active agents. The resulting surface active agent is then mixed with pMDI to provide a resin which is dispersible in water, resulting in an oil-in-water emulsion [51]. Such emulsions are stable for brief periods, 1 to 2 hours, before the water reaetion eauses gelation. Emulsifiable pMDI could be used where dispersion in water offers some benefit. For example, neat emulsifiable pMDI could be added directly to the blow line for medium density fiberboard production. Water emulsified pMDI has been used for improving resin distribution in particleboard or OSB manufacture however, this is not common industrial practice. 

Salt dehydration. Direct esterification requires high purity materials in equimolar amounts because esterifications rarely go beyond 98% completion in practice. To overcome this, hexamethylene diamine and a dibasic acid such as adipic acid can be reacted to produce a nylon salt, hexamethylene diammonium adipate. A solution of 0.5-mol diamine in a mixture of 95% ethanol (160 cm ) and distilled water (60 cm ) is added to 0.5-mol diacid dissolved in 600 cm of 95% ethanol over a period of 15 min. The mixture is stirred for 30 min during which time the nylon salt precipitates as a white crystalline solid. This can be recrystallized and should melt at 456 K. The pure salt can be converted into a polyamide by heating it under vacuum in a sealed tube, protected by wire gauze, at about 540 K in the presence of a small quantity of the diacid, e.g., 10 g salt to 0.55-g adipic acid is a suitable mixture. If a lower molar mass is desired, a monofunctional acid can replace the adipic acid and act as a chain terminator. 

If the amino end groups are removed, i.e., by reaction with acetic acid, then no transamidation is observed. Monofunctional compounds with this kind of effect are known in industrial parlance as regulators, stabilizers, or chain terminators. Their effectivity shows that direct transamidation between two amide groups is not significant. 

The proposed kinetic model of the postpolymerization describes the multiple experimental data well and is in good agreement with all the characteristics of the postpolymerization kinetics listed above. However, the introduction of two types of radicals sharply differing by characteristic life times into a kinetic scheme is an inevitable simplification of a real set of characteristic life times of active radicals. Fhrthermore, it cannot be indirectly re-passed on the kinetics of monofunctional monomer postpolymerization which, the same as stationary kinetics, can be characterized by differences from the kinetics of bifunctional monomer postpolymerization. The term hionomolecular chain termination , introduced in Refs. [ 55, 56] as an active center of the radical self-burial act in the act of chain propagation, did not have a theoretical basis via the relation of kx with k. ... 

In the polycondensation step, a monofunctional phenol (such as 3-5 mol% phenol, p-tert-butylphenol, p-cumylphenol) is added as a chain terminator to control the molecular weight of the final polycarbonate. Reaction partners are now end groups (chloroformate and phenolic -OH see above) and reaction rates decrease. The final polycondensation stages are catalyzed by tertiary amines. The amines react with the chloroformate end groups to form intermediate quaternary acylium salts which then react with phenolate to form carbonate and OH ions, hydrolyzing the chloroformate end groups, or to form a urethane in a side reaction [164]. Detailed mechanistic studies of the catalyst reaction were performed by Aquino et al. [173] and Kosky et al. [174]. 

The partition of phenols between the phases and its pH dependence [177]. Silva and Kosky [178] studied the reaction of hydrolysis taking into account the different phases and the partitioning of BPA between them. Monofunctional phenols with better solubility in the organic phase show a better efficiency as chain terminators. 

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