Synthesized copolymers

For the insertion of new types of functional groups which cannot be directly obtained by synthesizing copolymers from monomers,... 

Graft copolymers are usually prepared from copolymers whose backbone attaches functional groups which can be converted into grafting sites. A variety of techniques for synthesizing copolymers with backbone grafts have been investigated294. ... 

There is considerable interest in synthesizing copolymers. This is actually possible if organisms are confronted with mixtures of so-called related and unrelated substrates. Copolymers can also be synthesized from unrelated substrates, e.g., from glucose and gluconate. The 3-hydroxydecanoate involved in the polyester is formed by diversion of intermediates from de novo fatty-acid synthesis [41,42]. Related , in this context, refers to substrates for which the monomer in the polymer is always of equal carbon chain length to that of the substrate offered. Starting from related substrates, the synthesis pathway is closely connected to the fatty-acid /1-oxidation cycle [43]. In Pseudomonas oleovor-ans, for example, cultivated on octane, octanol, or octanoic acid, the synthesized medium chain length polyester consists of a major fraction of 3-hydroxyoc-tanoic acid and a minor fraction of 3-hydroxyhexanoic acid. If P. oleovorans is cultivated on nonane, nonanol, or nonanoic acid, the accumulated polyester comprises mainly of 3-hydroxynonanoate [44]. 

The first realization of this approach was reported by the Cambridge group, which synthesized copolymers 80 containing phenylene vinylene and dialkoxy(phenylene vinylene) units by the thermoconversion method [23,134], A 30-fold improvement in EL efficiency was observed for these copolymers compared with PPV 1 or MEH-PPV 13 devices fabricated in the same configuration (Chart 2.15). 

Burn and coworkers [173] synthesized copolymer 143, containing a similar electron deficient moiety (triazole) incorporated in the PPV backbone. They have reported an efficient blue emission from this polymer (APL = 466 nm (solution), 486 nm (film), PL = 33% (film)) although the efficiency of the PLED fabricated as ITO/PPV/143/A1 was not very high (CT>j ) reached 0.08% at a luminance of 250 cd/m2). 

Another example of efficient Forster energy transfer in Eu3+ complexes of fluorene copolymers (similar to the alternating copolymers described in Scheme 2.49) was demonstrated by Huang and coworkers [414] for random copolymers. They synthesized copolymers 336 with a different ratio between the fluorene and the benzene units in the backbone and converted them into europium complexes 337 (Scheme 2.50) [414]. The complexes 337 were capable of both blue and red emission under UV excitation. In solution, blue emission was the dominant mode. However, the blue emission was significantly reduced or completely suppressed in the solid state and nearly monochromatic (fwhm 4 nm) red emission at 613 nm was observed. 

Other thiophene-thiophene-5,5-dioxide copolymers were reported by Berlin et al. [544], who synthesized copolymers 443 and 444 with an alternating electron acceptor thiophene-5,5-dioxide unit and donor ethylenedioxythiophene (EDOT) units (Chart 2.107). The polymers absorbed at 535 nm (Eg = 2.3 eV) in chloroform solution and in films (which is consistent with their electrochemistry Eox 0.40-0.50 V, Emd -1.75-1.8 V AE 2.2-2.25 V) and emitted at 650 nm (<1> M (film) 1%). Such a high band gap (which exceeds that in PEDOT... 

The majority of those involved in research on siloxane-modified poly(arylene carbonates) have chosen to synthesize copolymers of arylene carbonates and polysiloxanes (2-17). 

Tsuda and coworkers350 used nickel(O) complexes to effect the [2 + 2 + 2] cycloadditions between two alkyne units and one alkene unit and employed this strategy to synthesize copolymers. Thus, the reaction of diyne 602 with A-octylmaleimide (603) catalyzed by Ni(CO)2(PPh3)2 afforded copolymer 604 with a maximum yield of 60% and a GPC molecular weight of as high as 35,000, which corresponds to n = 64 (equation 172). The exo,exo-bicyclo[2.2.2]oct-7-ene moiety of 604 arises through the reaction of the initially formed [2 + 2 + 2] adduct with another equivalent of A-octylmaleimide. 

Table 7 Compositions of the synthesized copolymers as determined by H NMR spectroscopy...

Use of Pseudomonas cepacia lipase (lipase PS) or Porcine pancreatic lipase does allow for the enzymatic ROP of lactide. Matsumura and coworkers reported polymers with extraordinarily high molecular weights (Mw up to 270 kDa) and very narrow PDI (<1.3) [135-137]. However, high temperatures (130°C) were needed to achieve good conversions, and polymerizations proceeded only when conducted in bulk. It is conceivable that another non-enzymatic mechanism contributed in these polymerizations. In fact, Koning and coworkers synthesized copolymers... 

Narrowing the bandgap of copolymers by alternation of electron-rich thiophene and electron-deficient benzo-l,2,3-thiadiazole units was used in the design of several LEPs whose optical and electronic properties could be tuned through such a modification. Cao and coworkers synthesized copolymers 599 and 600 (02MI2887 04MM6299), exploiting random copolymerization. 

On the other hand, it should be realized that radical copolymerization at heterogeneous conditions offers additional unique opportunities not available in homogeneous (solution) copolymerization. These include the intrinsic possibilities of exploiting the heterogeneities of the reaction system to control the chemical microstructure of the synthesized copolymers, making possible new paradigms for synthesis and production of polymeric materials. In this contribution, we discuss some new synthetic strategies, which have been developed in recent years to provide effective control of the chemical sequences. 

By varying the distance between nearest adsorption sites, rs, one can control the composition variation period of the synthesized copolymer. From the chemical correlators defined by Eq. 16, it is easy to find the average number of segments in the repeating chain sections, N, for different rs values. It is instructive to analyze the relation between N and rs. As expected, a power law N oc is observed. It is clear that exponent //. in this dependence should be between //, = 1 (for a completely stretched chain) and //. = v 1 with v 0.6 (for a random coil with excluded volume [75]). The calculation [95] yields yu 1.33 for N > 15. This supports the aforementioned assumption that the repeating chain sections are strongly stretched between the adsorption sites. The same conclusion can be drawn from the visual analysis of typical snapshots similar to that presented in Fig. 22. 

The use of copolymers as surfactants is widespread in macromolecular chemistry in order to compatibilize immiscible blends. These additives are sometimes named surfactants , interfacial agents or more usually compatibi-lizers . Their effect on improving different properties is observed interfacial tension and domain size decrease, while there is an increase in adhesion between the two phases and a post-mixing morphology stabilization (coalescence prevention). The aim of the addition of such copolymers is to obtain thermodynamically stable blends, but the influence of kinetic parameters has to be kept in mind as long as they have to be mastered to reach the equilibrium. Introducing a copolymer can be achieved either by addition of a pre-synthesized copolymer or by in-situ surfactant synthesis via a fitted re-... 

We have just discussed several methods for improving the mechanical properties of polymers. In addition to these techniques, one could think about synthesizing copolymers of styrene and less brittle monomer(s). Actually, we have already seen that this approach has been used with considerable success (see Chapter 5 and Table 5-2). Styrene-acrylonitrile (SAN) copolymers and acrylonitrile-butadiene-styrene (ABS) terpolymers have excellent impact strength. Although sometimes copolymerization is a viable option, oftentimes a completely different approach is called for. Let s see how. 

Forasmuch as 1,7- and 1,5-divinylcyclohexasiloxanes, used in polyaddition, represent mixtures of cis- and tram-isomers of the approximate 52 48 ratio, synthesized copolymers are atactic. Reprecipitation of copolymers from toluene solution by methyl alcohol has given viscous or solid (with regard to the value of flexible junction) transparent products with T sPec=0.09-0.29, well soluble in different organic solvents. It is found that at short length of dimethylsiloxane unit (n < 4), copolymer yields are slightly decreased that may be explained by partial proceeding of hydride polyaddition by intramolecular cyclization mechanism (see Tables 3 and 4). 

As a result of the reaction, synthesized copolymers possess r spec = 0.08 -0.26 and represent liquid or glassy-like light yellow transparent products, soluble in ordinary organic solvents. Some physical and chemical parameters, molecular weights and yields of synthesized copolymers are shown in Table 6. 

The reaction proceeding was also monitored by viscosity increase of synthesized copolymers. It was found that viscosity of copolymers and the hydride polyaddition degree increase with temperature rise to 70 - 90°C. In hydride polyaddition of a, -dihydridedimethylsiloxane to divinylorganotricyclodecasiloxane, conversion of =Si-H bond increases with temperature as follows from 85% (70°C) to 95% (90°C). Figure 7 shows time dependence of =Si-H concentration (%) decrease for various temperatures. 

Thermomechanical studies of synthesized copolymers indicate that the glass transition temperature of copolymers is decreased with an increase linear dimethylsiloxane backbone length, n (Figure 8). Since n=12 carbotricyclodecasiloxane fragments in copolymers cause no effect on the dimethylsiloxane backbone and Tg of copolymer 6 (Table 6) remains equal -123°C. 

Synthesized copolymers were studied by the X-ray diffraction method. Diffraction patterns of amorphous polymers (Figure 9) show that the interchain distance reaches its maximum (t/i=10.24 A) at short lengths of flexible dimethylsiloxane backbone, n. As the length of dimethylsiloxane backbone increases ( = 21), the interchain distance decreases and for copolymer 5 reaches 7.54 A (Table 6). 

Since initial dihydride- and dihydroxyorganosiloxanes, used in dehydrocondensation, represent a mixture of cis- and traws-isomers, synthesized copolymers possess atactic structure. As observed from the data, catalytic dehydrocondensation proceeds at a deeper level with formation of higher molecular products, than in the case of homofunctional products. 

When precipitated from toluene solution with methanol, synthesized copolymers are solid or viscous substances with r spec = 0.07-0.30, well soluble in usual organic diluters, with regard to dimethylsi-loxane unit value. Table 14 shows the yield, Tg and viscosity parameters of cyclolinear carbosilo-xane copolymers. 

Polyaddition was carried out at 60-70°C, and at the final stage the mixture was heated up to 100°C. The catalyst in amount 5x10-4 Pt mol/mol was added to vinylcyclosiloxane, heated up to 50°C. Some parameters of synthesized copolymers are shown in Table 16. 

The influence of diluting on mesogenic units with a non-LC-monomer was investigated by synthesizing copolymers of IV-6 and NbdMe in different ratios with initiator 2. The isotropization temperature decreased with increasing amounts of NbdME. Above a critical value (around 50% for this system), no LC-phase was observed [47]. 

Attempts to synthesize copolymers from D -DiSiAn in which n was >30 failed. Invariably, two immiscible o-dichlorobenzene solutions resulted. Typically, one phase contained low-molecular-weight polymer rich in poly(dimethylsiloxane), and the other contained high-molecular-weight material rich in organic block. Phase separation during polymerization was not encountered when the average siloxane blocks were less than 30 units long. 

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