Cyclic polymers Poly , example

Although rigid-rod poly(p-phenyleneterephthalamide) analogues having alkyl side chains did not contain cyclic polymers, the polycondensation of silylated m-phenylenediamine and aliphatic dicarboxyhc acid chloride afforded cyclic polyamides predominantly (Scheme 49) [187]. Furthermore, cyclic polymers were also produced in polycondensations for polyesters, poly(ether ketone)s, polyimides, and polyurethanes [183]. These examples are the products in polycondensation of AB monomers or in A2 + B2 polycondensations, but cyclization of oligomer and polymer was also confirmed in polycondensation of AB2 monomers [ 188-195] and in A2 + B3 [ 196-202] and A2 + B4 polycondensations [203-206], which afford hyperbranched polymers. 

If a one-dimensional spectrum does not provide sufficient information to determine the polymer structure, two-dimensional techniques, such as INADEQUATE, may be employed (see Sec. II.E.4). For example, this experiment was used to measure the sizes of the cyclic materials, poly(ethyl a-[(allyloxy)methyl] acrylate) and poly(allyl a-[hydroxymethyl] acrylate) carbon-carbon connectivities could be traced around the rings [100]. Such advanced techniques are particularly useful for characterizing the regiore-gularity of some polymers. Certain monomers, such as vinyl fluoride, can add to a growing chain in either a head-to-tail, ... 

Other attempts made by Rempp et al. [48, 49] and VoUmert et al. [50] used a similar method but changed the solvent conditions using, for example, a mixture of benzene and tetrahydrofuran (THF). This allowed good coupling for the synthesis of cyclic polymers with different building blocks such as poly(2-vinyl pyridine), polybutadiene, poly(dimethylsiloxane), poly(propylene oxide), poly(ethylene oxide), and a variety of other polymers (Scheme 4). 

After the report of poly[2.2]metacyclophane 3 described above, there were no reports on the synthesis of cyclophane-based ju-stacked polymers for over 15 years. In 2001 and 2002, polymerizations of thiophene-substituted [2.2]paracyclophanes were reported independently by two research groups [13-16]. Both groups synthesized jc-stacked polymers by electrochemical polymerization using cyclic voltammetry. For example, Audebert and coworkers reported that the electrochemical polymerization of monomer 5 deposited jr-stacked polymer 6 on a glassy carbon or indium-tin oxide electrode (Scheme 2) [13, 14]. 

Polyolefins with branched side chains other than P4MP1 have been prepared Figure 11.14). Because of their increased cohesive energy, ability for the molecules to pack and the effect of increasing chain stiffness some of these polymers have very high melting points. For example, poly-(3-methylbut-l-ene) melts at about 240°C and poly-(4,4-dimethylpent-l-ene) is reported to have a melting point of between 300 C and 350°C. Certain cyclic side chains can also... 

All of the soluble polymers (1 and 3-6) give high resolution NMR spectra (1H, 13C, and 31P) that are completely consistent with their proposed structures. As observed for other types of poly(phosphazenes), the 31P chemical shifts of these alkyl/aryl substituted polymers are consistently ca. 15-30 ppm upfield from those of the analogous cyclic trimers and tetramers. Some important structural information is provided by 13C NMR spectroscopy, particularly for the phenyl/alkyl derivatives 3 and 4. These polymers are rare examples of phos-phazenes that contain two different substituents at each phosphorus atom in the chain. Thus, they have the possibility of being stereoregular. The fact that the structures are completely atactic, however, is confirmed by the observation of three doublets in the P-Me region of the 13C NMR spectrum (ca. 22 ppm) in a 1 2 1 intensity ratio. 

Polymers are formed via two general mechanisms, namely chain or step polymerisation, originally called addition and condensation, respectively, although some polymerisations can yield polymers by both routes (see Chapter 2). For example, ring opening of cyclic compounds (e.g., cyclic lactides and lactams, cyclic siloxanes) yield polymers either with added catalyst (chain) or by hydrolysis followed by condensation (step). Many polymers are made via vinyl polymerisation, e.g., PE, PP, PVC, poly(methyl methacrylate) (PMMA). It could be argued that the ethylenic double bond is a strained cyclic system. 

A comparison of Tables 9-12 indicates that naturally occurring species tend to produce stable membranes more abundantly. We believe this is due to the cyclic nature and rigidity of the backbone, as will be discussed in the following section of the paper. Several trends are immediately obvious. For example, the hydrophobicity of the polymer appears to be a critical parameter. While polyacrylic acid can form a stable membrane with virtually all polycations, poly-methacrylic acid is much less effective. Similarly, propylene glycol modified alginate is less effective than sodium alginate. Furthermore, when the poly-... 

A rare exception to the dominance of enthalpic driving force is provided by the unstrained eight-membered ring (Me2SiO)4, which undergoes ROP to give poly(dimethylsiloxane). For this process, A//rop is approximately zero but the remarkable skeletal flexibility of the polysiloxane backbone makes the TAArop term favourable and entropy provides the driving force for ROP. Exceptional behaviour occurs in the extremely rare cases of monomers where the polymerisation is driven by entropy and A7/rop is unfavourable. In these cases, the formation of polymer is favoured at elevated temperatures. For example, cyclo-Sg will polymerise above 150 °C (where the favourable TAArop term dominates), but slowly depolymerises back to the cyclic Sg monomer at room temperature. ... 

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