Poly methylene Chains

In principle, the poly(methylene) chain would represent a more complex potential surface than that of pentane. The number of different conformations following this simple scheme is 3 . A typical polymer molecule may have 10000 carbons and thus 3 conformations, i.e. an enormously large 

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Cyclodextrins were also threaded onto polymeric threads. Wenz and Keller used poly(methylene) chains [80]. Equilibration of a-CDX with poly(iminotrimethylene-iminodecamethylene) was reached in c. 9 days. The dethreading by dialysis was not even complete after two weeks. To analyse the degree of threading, the CDX rings were blocked on the chains by partial acylation of the amino groups of the polymer. Consequently, a material containing 23 -NH(CH2)io-N(H)-(CH2)3- subunits was shown to entrap 37 CDX rings. 

The characteristic ratio of the poly(methylene) chain, which might be considered to be the simplest polymer molecule, as a function of chain length is shown in Fig. 4.4 for the simple models considered thus far. All save the simple freely jointed chain display end effects, manifest by an increase in Ci with chain length at small n, which will not be considered further. In what follows, only the asymptotic limit of the characteristic ratio for 00 (Coo) will be discussed. The values of for the freely jointed chain, the freely rotating chain and the chain with independent bond rotational potentials increase in value from 1 through 2 to ca 3-5. The latter value is, however, only ca one-half of the experimentally determined value of Coo=6-9 for poly(methylene). This serious discrepancy points to the fact that the bond rotational potentials are definitely not independent, i.e. the conformation of bond i depends upon the conformations of bonds (/—I) and (/-i-1). 

Fig. 4.8. The ratio of the mean square displacements for attached and free poly(methylene) chains (1) normal to the interface (2) parallel to the interface (after Feigin and Napper, 1979).

In several enzyme systems that catalyze the desaturation of stearic acid, oleic acid (cis-A -octadecenoic acid) is the sole product and the reaction is therefore characterized by positional and geometrical stereospecificity. The desaturating system of Corynehacterium diphtheriae has been found by Schroepfer and Bloch (1965) to have the additional property of selectively removing one particular hydrogen atom from each pair of hydrogens at carbons 9 and 10 of stearic acid. The enzyme can thus distinguish between the two hydrogen atoms attached to a carbon atom of a poly-methylene chain, and the system is a notable example of the stereospecificity of enzymatic reactions at meso carbon atoms (Levy et al., 1962). The chemical identity... 

Two-dimensional-IR spectra were used to study the orientation and the mobility of a ferroelectric liquid crystal dimer during switching by an electric field. The detailed mutual arrangements of different molecular segments (poly(siloxane), poly(methylene) chain, polysiloxane chain) in a smectic C phase were derived from the static spectra. Temperature and electric field strength dependencies of the mobility of these segments were established (163). 

Calculations have shown that proximity and orientation constraints are not serious in intramolecular reactions of pairs of terminal groups connected by a poly methylene chain. Hence, calculations based on a core-probability model show good agreement with experimental data. ... 

R.G. Snyder, M. Maroncelli, H.L. Strauss, V.M. Hallmark, Temperature and phase behavior of infiared intensities the poly(methylene) chain", /. Phys. Chem., 1986,90,5623-5630. 

Here m is the mode order (m — 1,3,5. .., usually 1 for polyethylenes), c the velocity of light, p the density of the vibrating sequence (density of pure crystal) and E the Young s modulus in the chain direction. The LAM band has been observed in many polymers and has been widely used in structural studies of polyethylenes [94—99,266], as well as other semi-crystalline polymers, such as poly (ethylene oxide) [267], poly(methylene oxide) [268,269] and isotactic poly(propylene) [270,271], The distribution of crystalline thickness can be obtained from the width of the LAM mode, corrected by temperature and frequency factors [272,273] as ... 

A theoretical investigation of the use of NMR lineshape second moments in determining elastomer chain configurations has been undertaken. Monte Carlo chains have been generated by computer using a modified rotational isomeric state (RIS) theory in which parameters have been included which simulate bulk uniaxial deformation. The behavior of the model for a hypothetical poly(methylene) system and for a real poly(p-fluorostyrene) system has been examined. Excluded volume effects are described. Initial experimental approaches are discussed. 

For poly(methylene), an exclusion distance (hard sphere diameter) of 2.00 A was used to prevent overlap of methylene residues. The calculation reproduced the accepted theoretical and experimental characteristic ratios (mean square unperturbed end-to-end distance relative to that for a freely jointed gaussian chain with the same number of segments) of 5.9. This wps for zero angular bias and a trans/gauche energy separation of 2.09 kJ mol". ... 

Recent advances in the development of well-defined homogeneous metallocene-type catalysts have facilitated mechanistic studies of the processes involved in initiation, propagation, and chain transfer reactions occurring in olefins coordi-native polyaddition. As a result, end-functional polyolefin chains have been made available [103].For instance, Waymouth et al.have reported about the formation of hydroxy-terminated poly(methylene-l,3-cyclopentane) (PMCP-OH) via selective chain transfer to the aluminum atoms of methylaluminoxane (MAO) in the cyclopolymerization of 1,5-hexadiene catalyzed by di(pentameth-ylcyclopentadienyl) zirconium dichloride (Scheme 37). Subsequent equimolar reaction of the hydroxyl extremity with AlEt3 afforded an aluminum alkoxide macroinitiator for the coordinative ROP of sCL and consecutively a novel po-ly(MCP-b-CL) block copolymer [104]. The diblock structure of the copolymer... 

The (co)polymerization of dienes can be a good method for the preparation of polymers with reactive vinyl groups, a method that enables the preparation of polymers possessing plural vinyl groups per polymer chain. A fluorinated bis(phenoxy-imine) Ti complex was shown by Coates and co-workers to convert 1,5-hexadiene to poly(methylene-l,3-cyclopentane-fti-3-vinyl tetramethylene), which contained multiple vinyl groups. As already discussed, Saito et al. and others revealed that bis(phenoxy-imine) Ti complexes favored secondary insertion. " This is probably responsible for the formation of 3-vinyl tetramethylene units. Likewise, the same catalyst system can form sPP-/ -poly(methylene-l,3-cyclopentane-z -3-vinyl tetramethylene) from propylene and 1,5-hexadiene. Very recently. 

F i g U re 4.3 The poly (dimethylsil-methylene) chain.10 Reproduced by permission of the American Chemical Society. 

Cyclopolymerisation leading to polymers with monocyclic units in the main chain proceeds in two steps the first step involves a 1,2-insertion of the coordinated a, ffl-diolefin via one olefinic bond, and the second step, which is a ringclosing reaction, involves an intramolecular insertion of the other olefinic bond undergoing coordination scheme (89) presents both steps for 1,5-hexadiene cyclopolymerisation leading to a cycloaliphatic polymer with poly(methylene-1,3-cyclopentane) structural units [30,450,497] ... 

In the case of the formation of a cycloaliphatic polymer with bicyclic units in the main chain, such as the polymer with poly[methylene-l,3-(2,5-methanocy-clohexane)] structural units obtained in the cyclopolymerisation of 3-vinyl-1,5-hexadiene, the intramolecular insertion, analogous to that presented in scheme (89), is followed by another intramolecular insertion involving a vinyl substituting group ... 

The equation for the diffusion coefficient in a gaseous state, Dc, is the starting point for the derivation of an equation for diffusion coefficients in an amorphous solid state (S). The homologous series of n-alkanes is used as a reference class of chemical compounds which asymptotically reach an unlimited molecular chain in the form of poly methylene. The diffusion coefficient, DSji, is derived theoretically for a member of the series with j carbon atoms at infinite dilution in a matrix of a n-alkane with i carbon atoms in the molecule. In addition, the diffusion in polymethylene, which is considered as the reference structure for all polymers is also derived theoretically. 

While, however, penta-methylene is the most stable ali-cyclic compound of the poly-methylene group it is hexa-methylene which is of special interest and importance. This importance is due to the fact that it is the connecting link between the ali-cyclic compounds (carbo-cyclic compounds not derived from benzene, i.e. the poly methylenes) and benzene itself. Thus it becomes the connecting link between the aliphatic open-chain compounds and the very large and important division including benzene and its derivatives. 

Elemental analyses of the polyformals agreed with or were reasonably close to the calculated values therefore, the polymers contained substantially no poly-(methylene oxide) in the chains. Since excess formaldehyde was used in preparing the prepolymers, presumably their chains were terminated with hydroxymethyl groups. Both water and formaldehyde must then be eliminated during the buildup of polymers ... 

The temperature independent relaxation time (t0) is also affected by the spacer length. The data of the liquid crystalline main-chain polyethers are in agreement with the data by Farrow et al. (291 on semicrystalline poly(methylene terephthalate) polymers. 

Crystallization-induced phase separation can occur for concentrated solutions (gels) of diblocks [58,59]. SAXS/WAXS experiments on short PM-PEO [PM=poly(methylene) i.e. alkyl chain] diblocks revealed that crystallization of PEO occurs at low temperature in sufficiently concentrated gels (>ca. 50% copolymer). This led to a semicrystalline lamellar structure coexisting with the cubic micellar phase which can be supercooled from high temperatures where PEO is molten. These experiments on oligomeric amphiphilic diblocks establish a connection to the crystallization behaviour of related nonionic surfactants. 

Waymouth and Coates employed the homogeneously catalyzed cyclopolymerization of 1,5-hexadiene giving poly (methylene-1,3-cyclopentane) as previously developed in his group in order to utilize the stereoselectivity of the monomer insertion for the construction of a polymer with main-chain chirality. The cyclopolymerization is a remarkable chain growth reaction during which a conventional... 

Poly(methylene-1,3 -cyclopentane) synthesized in the presence of (-)-(R,R)-3 and methylalumoxane revealed a molar optical rotation of [0] 4O5 = +51.0° (c 8.0, CHCI3), whereas the polymer analogously prepared using the enantiomer (+)-(S,S)-3 showed a value of [0]284O5 = -51.2° (c 8.0, CHCI3). These findings are consistent with the formation of polymers with main-chain chirality. [9a]... 

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