TRUE COPOLYMERS

Preparation scheme for poly(pyrrole-styrene) copolymers as adopted by Nazzal and Street [138]. 

Stanke et al. After Reference [136, 137], reproduced with permission. 

In other work of relevance, Raspopov et al. [148] claimed to have synthesized a copolymer of Acetylene and ethylene via a Ziegler-Natta catalytic method, claiming conductivities of 10 S/cm for a 20 mole-% Acetylene content. However, it was not clear whether this was a true copolymer or just a P(Ac) network with PE serving as a host polymer. Similarly, in work of Aldissi et al. [1S2] in the production of P(Ac)/PStyr copolymers , it was not clear whether the end product was a true copolymer or a composite, since a percolation threshold, a term invalid for a copolymer, was claimed (ca. 16 v/v% P(Ac) for 10 S/cm conductivity). 

Cho et al. recently described [374] an interesting set of copolymers obtained by alternating units such as phenylene and vinylene with dihexylfluorenes these were targeted for photoluminescence (PL) applications. Well known organic reactions such as the Heck, Suzuki and Wittig reactions, were employed in the syntheses. Table 10-1 summarizes structural and PL information for some of these. 

Beggiato et at. [37S] recently described a unique set of copolymers having the following monomer components dithienopyrrole-dithenothiophene (DTP-DTT) DTP-thionaphtheneindole (DTP-TNI) DTT-TNI. Simpleelectrochemicalpolymeriza-tion from acetonitrile solutions of the monomers in the desired proportions was used. However, only the first combination, DTP-DTT, yielded CPs showing conductivity and electrochromism. 

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The results suggests that the copolymer has a graft structure and that the mastication medium involves three kinds of domains. The first is the inner domain of poly(vinyl chloride) which is only slightly penetrated by monomer. Polymerization is initiated by macroradicals created in the PVC domain causing the formation of a true copolymer. Short radical segments arising from transfer reactions migrate into the third external domain which consists practically entirely of pure monomer and there initiate polymerization. The second domain is the surface of the resin particle which is swollen by monomer. The free radicals created by bond rupture appear in this second domain. 

Tn copolymerization by a radical mechanism, random copolymers are obtained in almost every case, but true copolymers are not obtained in copolymerization by a cationic mechanism. Usually copolymers with considerable block character are obtained, or some homopolymer is formed together with the copolymer. 

Asphalt has been used as a major component in many coating formulations. These include epoxy-asphalts (much used in refineries) and urethane-asphalts. Of these the urethane-asphalts, some of which are true copolymers, are the most satisfactory substitutes for hot asphalt. They can be used at exposures higher in temperature than can hot asphalt due to their freedom from cold flow, and are reasonably good barriers. Like the asphalt emulsions and solvent putties, however, they can be penetrated, though at a much slower rate, by small molecule acids. Fluid (cold) applied membranes are discussed elsewhere in this volume. 

Since there are almost no ideal systems that lead to a perfect a/f-copolymer in radicalic reactions, these cases can be viewed as true copolymer formation. However, regarding their thermal decomposition, a/f-copolymers behave similarly to homopolymers. 

We have examined the microstructure of a number of dichlorocarbene adducts of both cis- and trans-polybutadiene using 13C NMR spectroscopy. Samples were prepared in a two phase system where dichlorocarbene was generated by the reaction of either concentrated aqueous or solid alkali metal hydroxide with chloroform in the presence of a phase transfer catalyst (14t). Monomer compositions and sequence lengths were obtained as for true copolymers and were correlated with glass transition temperature and phase morphology. 

The copolymerization of TXN and St was analysed in a number of papers 150,151 in terms of conventional reactivity ratios without paying attention to the proper characterization of copolymers and other factors discussed in this volume (cf. Chap. 15). Some additional information comes from the studies of similar systems, i.e. DXL-St copolymerization 152). Also in this case product characterization mainly involved solubility studies, although Yamashita et al. claimed that 1H-NMR spectra confirmed that the product is indeed a true copolymer. This claim was based on a rather limited analysis of H-NMR spectra, however, and was not confirmed by analysis of spectra of related models. Copolymerization conditions were as follows [DXL]0 = 0.7 - 3.7 mol l [St]0 = 4.5 — 2.7 mol l-1, [BF3 OEt2] = 2,5 10-2 mol 1 1, 25 °C, in toluene. After 2-8hrs, from 2% to 9% product with fr ] = 0.12 — 0.32 dl g-1 (viscosity determination conditions not specified) was obtained. 

The polymers contained, depending on the monomer ratio in the feed, from 26 to to 85 mol % DXL units and from 15 to 76 mol% St units. On the basis of overall product composition it was concluded that sequences containing up to 4 St units are present. Yamashita et al. reported the formation of copolymers with Mn as high as 332000153). These products were obtained at 72% yield using [DXL /fSt], = 10, however, copolymer formation was not proven. At lower [DXL]o/[St]0 ratios both yields and molecular weights were drastically reduced thus using [DXL /ISt], 1 1a copolymer with M = 3520 was obtained at 43 % yield. Additional and conclusive proof that the products obtained were true copolymers was obtained from analy-... 

More recently cyclic acetal-styrene systems were reinvestigated by the GPC technique 154,155). Using double detection (UV and RI), Yamashita et al. showed that products of copolymerization of styrene with tri- and tetraethylene glycol formals have a unimodal molecular weight distribution, and that the maxima of both RI and UV traces coincide indicating that the products are true copolymers. 

While MF resins have been known for a long time to be able to form true copolymers with PF resins, this has not been the case for UF resins. Until quite recently, copolymerization between PF and UF resins or urea was not thought to be likely [53], the system curing as a polymer blend only. However, applications of this type have been... 

The tendency considered in section 12.2 for polymers of different types to segregate applies for the true copolymers, i.e. excluding IPNs, just as it does to blends. If one component is a very minor component or if the polymer is a random copolymer, segregation does not generally take place, but in block copolymers in which the minor components form more than a certain proportion of the whole, segregation generally takes place in some range of temperatures. The important difference here is that... 

A copolymer with two or more constitutionally different monomeric units is not sufficiently characterized by its average composition alone. A product with, for example, a 50% proportion of component A and 50% of component B can be a true copolymer with a composition that is constant for all the molecules present, a true copolymer with different A B ratios among the component molecules, a polyblend from two homopolymers, or a corresponding mixture from two homo- or bipolymers. Consequently, copolymers have to be characterized according to their compositional... 

Equilibrium sedimentation studies are mostly used to investigate density differences in different macromolecules. The method has been used, for example, in research on the replication of N-labeled deoxyribonucleic acids. Theoretically, it is also suitable for distinguishing between polymer blends and true copolymers. In such studies, problems usually arise from the considerable back-diffusion and the wide molar mass distribution. The gradient curves are so strongly influenced by these two effects that there is considerable overlap in the curves for substances of differing densities. 

In addressing color control in true copolymers, it has also been shown that the colors of the neutral state for copolymers of 2,2 -bis(3,4-ethylenedioxythiophene) and 3,6-bis-(2-(3,4-ethylenedioxy)... 

The copolymers obtained are true copolymers and not a mixture of two homopolymers. This is indicated by the presence of a single glass transition temperature. For example, glass transition temperatures of polystyrene and poly(methylmethacrylate) are 100 and 114 °C. Single glass transition temperatures at 112 °C for polymer 19 (about 43% of cyclophosphazene) and 151 °C for polymer 20 (about 40% of cyclophosphazene) were detected. 

The formation of a true copolymer was disputed as polyacetylene particulates suspended in solution by dissolved polymer, such as polystyrene, were also found to form stable latex particles [58]. In order to... 

The formation of true copolymers was confirmed in all copolymers studied by C-NMR. The comonomers were present as isolated units arising from random-type incorporation of the comonomers. No consecutive comonomer units were detected by NMR, which means either that the concentration of comonomer dyads was below the sensitivity of the C-NMR measurements or that formation of the dyads was suppressed. In copolymerizations of ethylene and higher a-olefins, the bridged bis(indenyl)-type metallocene catalysts, such as rac-Et(Ind)2ZrCl2,... 

The method distinguishes between true copolymers and physical mixtures of copolymers. The method makes use of a characteristic IR rocking vibration due to... 

Physical blends of the two homopolymers, PE and polybutene-1 will not suffice because these have a different spectrum to a true copolymer with the same ethylene-butane ratio. An excellent method for preparing such standards is to copolymerise blends of ethylene and C-lahelled butane-1 of known activity. From the activity of the copolymer determined hy scintillation counting, its butane-1 content can be calculated. 

Interpolymer A type of Copolymer in which the two monomer units are so intimately distributed in the polymer that the substance is essentially homogeneous in chemical composition. An interpolymer is sometimes called a true copolymer. 

The main structural results on these copolymers were obtained for products of low styrene content 41,154) polymerized with Ti-based systems. In all cases the total polymer products can be separated into two parts atactic polystyrene (soluble in ketones) and the true copolymers. These products do not contain isotactic polystyrene 41), which verifies the suggestion that this atactic polystyrene is formed on cationic active sites rather than cm the usual Ziegler-type centers. Copolymers of low styrene content have the styrene units isolated independently from the rit2 value. This was proved by IR and NMR spectra studies. Styrene units absorb at frequencies characteristic for isolated groups at 550-560cm" and at 1075cm" when the styrene content is 5.7-19.1% 41,154), and give rise to a resonance at t 298 in the NMR spectrum (154). 

Physical characterization of a SCL-MCL PHA copolymer produced from glucose in recombinant E. coli expressing fatty acid biosynthesis enzymes and PHA synthase. The isolated polymer produced by frtty acid biosynthetic enzymes and a mutant PHA synthase was characterized by NMR, gel permeation chromatography (GPC), and differential scanning calorimetry (DSC). In order to determine the structure of the isolated polymer and to show that the polymer was a true copolymer rather than a blend of polymers, NMR was used. The mol% fractions of the secondary (C6) and tertiary (C8) monomer units were determined from the intensity ratio of tiie main-chain methylene proton resonance to methyl proton resonance in the H NMR spectra (Figure 3A). Supporting information for tertiary (C8) monomer units were obtained by C NMR analysis. As shown in Figure 3B, the C NMR spectrum was used to show that the polymer was a random copolymer rather than a blend of polymers. 

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