Isolation of Polymers

Regarding industrial methods for isolation of polymers, the reader is referred to the relevant literature. 

---

The Curtius rearrangement procedure described here is a modification of one reported by Winestock. The submitters have found this procedure to be considerably more reproducible when N,N-diisopropylethylamine is substituted for triethylamine. The procedure described for the preparation of trans-2,4-pentadienoic acid is a modification of an earlier one by Doebner. The submitters have found this method to give reproducibly higher yields, and to be more convenient, than other commonly used procedures for preparing this material. The use of dichloromethane as the extracting and crystallizing solvent greatly simplifies the isolation of polymer-free samples of the crystalline acid. 

The radical homo- and copolymerization of the ferrocene-containing monomer 154 allowed for the isolation of polymers containing pendent ferrocene moieties (Scheme 2.41).228 High molecular-weight polymers were obtained from AIBN-initiated reactions, whereas other cationic initiators gave only low molecular-weight materials. Electrochemical studies showed that homopolymer 155 underwent two oxidations at Ey2 = —0.13 V and Ey2 = +0.05V in... 

If, after the polymer has been formed, a transformation of one structure into another is possible (e.g., formation of an amorphous polymer with its subsequent crystallization), the kinetic characteristics of these transformations will, in their turn, exert the determining effect on the final structure of the polymer. Specifically, the supramolecular structure of a polymer produced in the course of its synthesis will change, depending on the relationship between the rates of three processes (1) chemical reaction of polymer formation, (2) isolation of polymer in a separate phase, (3) structural transformations inside the polymer phase. In the latter two processes, a significant role is played by the ratio between the rates of the formation and growth of the nuclei of one phase inside the other. This is the kinetic aspect of the problem of controlling the polymer structures during synthesis. 

Transformation of Anionic Polymerization into Cationic Polymerization. Richards et al. (26. 27, 73-75) proposed several methods for the transformation of a living anionic polymeric chain end into a cationic one. Such a process requires three distinct stages polymerization of a monomer I by an anionic mechanism, and capping of the propagating end with a suitable but potentially reactive functional group isolation of polymer I, dissolution in a solvent suitable for mechanism (2), and addition of monomer II and reaction, or change of conditions, to transform the functionalized end into propagating species II that will polymerize monomer II by a cationic mechanism (73). 

While all of the above-described purification methods have assisted in the isolation of polymer macrocydes, substantial efforts have been made to improve the synthetic methods and to allow the production of macrocydes with narrow polydispersities and increased cyclic purities [18-21]. In this chapter, an attempt will be made to review the general techniques for preparing cycUc polymers, and to highlight the methods which are presently at the forefront of research. 

Schematic representation of isolation of polymer chain trapped/confined between clay platelets by solvent extraction procedure.

The treatment of the dichlorosilane (39) with a slight excess of sodium dispersion in a high-boiling solvent allowed the isolation of polymers 40 with molecular weight (A/w) in the range 17000-38000, A/ / M = 2.9-5.3. Spectroscopic and analytic data are consistent with a chain unit with alternating disilyla-nylene and thienylene units. The latter are of interest as structures capable of photochemical reactivity of the Si-Si bond [68]. 

Mainchain ferrocene-based polymers have also been synthesized by polyaddition reactions." For example, the reaction of l,l -dimercaptoferrocene with 1,4-butandiyl dimethacrylate resulted in the isolation of polymer 13. 

The photolytic demetallation of polymers 3a-h was achieved in solutions of acetonitrile, or acetonitrile/DMF, resulting in the isolation of polymers 4a-h. The photolytic reactions were conducted for 4h, and after that time, there was no evidence of the cyclopentadienyliron moieties in the NMR spectra of the organic polymers... 

The azobenzene-fimctionalized complexes 55a-c (Scheme 18) were also reacted with nucleophiles 2d, 7, and 10, resulting in the isolation of polymers 57a-c, 58a-c, and 59a-c in excellent yields. These cyclopentadienyliron-coordinated polyaromatic ethers or ether/thioethers containing azobenzene chromophores in their sidechains displayed fair to excellent solubility in polar organic solvents such as DMF, DMSO, and acetonitrile. The polymers prepared using bisphenol A (2d) possessed the highest solubibty, while polymers prepared with 4,4 -thio-Z>/5-benzenethiol (7) and 1,8-octanedithiol (lOd) often formed gels. 

Completed polymerizations can be terminated at -78°C by introducing a protic material such as methanol or acetic acid in which case the product will have isobutyrate ester termini. Alternatively the mixture can be warmed to room temperature whereupon spontaneous termination occurs to form cyclic ketone ends (2). With THF solvent, isolation of polymer is accomplished by precipitation in water, hexane or methanol depending upon the sorts of contaminants or by-products one wishes to remove or, the polymer solution can simply be stripped free of solvent. 

Once a Type 1 proanthocyanidin polymer has been isolated by the above methods, the purity of a preparation may be gauged by the vanillin-hydrochloric acid assay (17, 25) or by the value in the A ax 270-280 region in water or methanol (25). This procedure has been shown to be effective for the isolation of polymers from a wide range of plant sources (25, 29, 37), and it is usually reasonable to assume that the constitution of the polymer so isolated is an average representation of the condensed tannins as they exist in that particular plant tissue. 

Reactions of dicobaltoctacarbonyl with a silicon-based polymer with aUcyne emits in the backbone have led to the isolation of polymers containing Co-Co bonds (scheme 41) ° ... 

However, scale-up synthesis of polymer-grafted nanoparticles was hardly achieved, because complicated reaction processes, such as centrifugation, filtration, and solvent extraction, are required for the synthesis and isolation of polymer-grafted nanoparticles, and a lot of waste solvent is generated. 

Monomer 89 (Scheme 10) is a ferrocenyl-substituted cyclic phosphazene, which is ring-opened to give a polyphosphazene with ferrocenyl moieties attached as side-chains to two positions on the polymer backbone. Attempted polymerization at 250°C resulted in no polymer formation however, a catalytic amount of a perchlorinated cychc phosphazene monomer under the same conditions resulted in the isolation of polymer 90. 

The properties of a number of vinyl, acrylate, and methacrylate polymers that incorporate ferrocenyl groups in their sidechains were also examined. " The incorporation of ferrocene moieties into these classes of polymers resulted in materials with glass transition temperatures much higher than that of their organic analogs.For example, radical polymerization of ferrocenyl methylacrylate (16) allowed for the isolation of polymer 17, whose glass transition temperature (Tg) was 197-210°C versus only 3°C for poly(methyl acrylate) (18). 

Schrock, Wrighton, and coworkers have reported that ring-opening metathesis polymerization (ROMP) of norbomene monomers fhnctionalized with ferrocenyl groups allowed for the isolation of polymers such as 55-58. Alternatively, polynorbornenes capped with ferrocenyl units could be produced by using a molybdenum initiator functionalized with ferrocene. When this polymerization reaction was terminated through the addition of octamethyl-ferrocenecarboxaldehyde, low molecular weight polymers such as 58 were isolated. 

Another class of coordination-type polymer containing ferrocene units in the backbone is shown in Scheme 42. Reaction of monomer 154 with the bipyridine-based monomer 155 resulted in the isolation of polymer 156. In the solid state, polymer 156 is thermally stable up to 240°C however, depolymerization occurs at about 85°C in toluene. 

The metallacyclization of CpCo(PPh3)2 (140) with the diacetylene (144) resulted in the isolation of polymer (145), which was thermally rearranged to produce 146. It was established that the first step of the rearrangement was the loss of the triphenylphosphine ligands fi om cobalt. In the presence of isocyanate, the cobaltacyclopentadiene rings were converted to 2-pyridone rings as shown in Scheme 39. 

Scheme 13 illustrates an alternative route to this class of conjugated metal-lopolymer. Using the strategy shown below, the ruthenium complex was reacted with the preformed polymer (59), resulting in the isolation of polymer 60. ... 

Developments in this field then became rapid due to those polymers bioactivity, and in the 1960s organotin polymers were reviewed Adrova et al. also described the incorporation of organotin moieties into the backbones of polymers using the strategy shown in Scheme 49. The reaction of monomer 194 with organotin hydrides such as 195 led to the isolation of polymer 196. This polymer had a degree of polymerization of approximately 25. 

---