Poly high-molecular-weight polymers

Polylactide is the generaUy accepted term for highly polymeric poly(lactic acid)s. Such polymers are usuaUy produced by polymerization of dilactide the polymerization of lactic acid as such does not produce high molecular weight polymers. The polymers produced from the enantiomeric lactides are highly crystalline, whereas those from the meso lactide are generaUy amorphous. UsuaUy dilactide from L-lactic acid is preferred as a polymerization feedstock because of the avaUabUity of L-lactic acid by fermentation and for the desirable properties of the polymers for various appUcations (1,25). 

Isobutjiene was first polymerized ia 1873. High molecular weight polymer was later synthesized at I. G. Farben by decreasiag the polymerization temperature to —75°, but the saturated, unreactive polymer could not be cross-linked iato a useful synthetic elastomer. It was not until 1937 that poly(isobutylene- (9-isoprene) [9010-85-9] or butyl mbber was iavented at the Standard Oil Development Co. (now Exxon Chemical Co.) laboratories (1). 

The properties of three types of poly(methyl methacrylate) (sheet based on high molecular weight polymer, lower molecular weight injection moulding material and a one-time commercial copolymer) are given in Table 15.1. 

Reaction with additional monomers leads to the formation of larger rings (3, 4) and eventually to high molecular weight polymers, namely poly-... 

The nucleophilic aromatic substitution reaction for the synthesis of poly(arylene ether ketone)s is similar to that of polysulfone, involving aromatic dihalides and aromatic diphenolates. Since carbonyl is a weaker electron-withdrawing group titan sulfonyl, in most cases, difluorides need to be used to afford high-molecular-weight polymers. Typically potassium carbonate is used as a base to avoid the... 

GPC traces of poly(phenylmethylsilylenes) prepared in the ultrasonication bath are shown in Fig. 1. In contrast to thermal condensation, monomodal high molecular weight polymer is formed. Oligomeric cycles (mostly cyclic pentamer), formed usually in high yield (cf. Table 1), can be very easily separated from the reaction mixture by precipitation with isopropanol. The molecular weight of polysilanes decreases and polydispersity increases with temperature. 

LOV MOLECULAR WEIGHT MODEL COMPOUNDS. The mechanisms of radiation effects on polymers are frequently investigated by studies of low molecular weight model compounds. Analysis of the chemical reactions is much easier than with high molecular weight polymers. Thus, N-acetyl amino acids can be studied as model compounds for poly(amino acid)s and hence for proteins. 

With emulsion polymerization it is possible to prepare very high-molecular-weight polymers at high rates of polymerization. The required reaction temperatures are low and can even be below 20 °C when redox systems are used for initiation (see Examples 3-11). Polymer emulsions with solid contents of 50% and higher can be very stable. In many cases, e.g., poly(vinyl acetate), they are directly used as paints (paint latices), coatings, or adhesives (see Sect. 2.5.4). 

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