Poly , methylene carbons

The influence of molecular structure on the degradation mechanism of degradable polymers of poly(tri-methylene carbonate), poly (trimethylene carbonate-co-caprolactone), and poly(adipic anhydride) was explored by Albertsson and Eklund [7]. Measuring the change of the mass and the molecular weight for the... 

Backbone methylene carbons, poly(1-hexene), 141 Benzoyl peroxide catalyst, 13C NMR of PS, 190... 

Figure I indicates the approach used to synthesize poly(oxyethylene)-b-poly(pivalolactone) telechelomers. An acetal capped anionic initiator, X (13) polymerizes ethylene oxide (EO) to give 2> a potassium alkoxide of a masked polyether, and this "new" initiator is to be used to polymerize pivalolactone (PVL). Since potassium alkoxides are strong nucleophiles, they can randomly attack at both the carbonyl carbon and the 3-methylene carbon in lactones, (Figure 2) such a random attack would result in a pivalolactone segment containing irregularities. Lenz (15), and Hall (16), and Beaman (17) have investigated PVL polymerization and have shown that the less nucleophilic carboxylate anion is preferable in polymerizing PVL smoothly. The weaker carboxylate anion will attack only at the methylene...

In one example, the Tics of the non-crystalline methyl, methine and methylene carbons of iPP, 70% crystalline, were compared at room temperature with those of model atactic poly(propylene), hydrogenated poly(2-methyl-l,3-pentadiene) [163]. It was found that, within the experimental error, the Tic values of each of the carbons were the same in both polymers. The conclusion can then be reached that the fast segmental motion, at or near the Larmor frequency of... 

The simplest motional description is isotropic tumbling characterized by a single exponential correlation time ( ). This model has been successfully employed to interpret carbon-13 relaxation in a few cases, notably the methylene carbons in polyisobutylene among the well studied systems ( ). However, this model is unable to account for relaxation in many macromolecular systems, for instance polystyrene (6) and poly(phenylene oxide)(7,... 

The blend of poly(bisphenol A carbonate)-(poly(caprolactone) PC-PCL is particularly unusual in that both polymers are capable of crystallization and FT-IR has been used to study the state of order in these blends as a function of the method of preparation 254,255). In this case, PCL is a macromolecular plasticizer for PC. The PCL becomes progressively less crystalline as the concentration of PC increases. PC is amorphous if the blend is cast from methylene chloride but semicrystalline if cast from tetrahydrofuran. When PC in the pure form is exposed to acetone, it will not crystallize, but in the blend, exposure of acetone causes the PC to crystallize which emphasizes the additional mobility of the PC in the blend. 

Fig. 22. (a) Equilibrium spectrum of poly(tetramethylene oxide) at 0 °C in the range of the a-methylene carbon and (b) its crystalline component... 

Fig. 2., 3C-NMR spectrum of live poly(Bd)Li (DP = 2, 3, or 4). The signals at 92. 82, and 78 ppm have been assigned to the complexed terminal methylene carbon atom of various DP values. Note the absence of a signal at 110-114 ppm for the noncomplexed terminal methylene also absent in Fig. 1. (Bottom is aliphatic region top is olefin region.)...

Neither the first nor the second step in Scheme (42) has been directly observed, but it has conclusively been shown by studies of the number of the end groups in poly-THF initiated with triflic anhydride that one molecule of the anhydride gives two growing ends of the cationic and/or ester structure in one macxomolecufe. These structures are interconvertible. Recently, Smith separated and characterized two intmnediate products tetramethylene-bis-triflate, resulting from the attack of the anion on the o-methylene carbon atom in salt 42a, and the corresponding dicationic trimer... 

The target structures in the final example are fully aromatic polymeric hydrocarbons, consisting of all-carbon six-membered rings - so-called angularly annulated polyacenes 91 [55]. The structural difference between those and the methylene-bridged poly(phenylene)s is the replacement of the benzylic methylene bridges by vinylene moieties. 

Fig. 14 3D- H, C, F correlation of poly(l-chloro-l-fluoroethylene) with slices at 5( F) = -98.2 (a), -99.4 (b), -100.7 (c) (d) schematic illustration of the 3D spectrum with relative positions of the shoes. Each shce in (a)-(c) displays two correlation signals representing the two CHj groups adjacent to a CF moiety. The polymer tacticity can be determined as follows the splitting of each signal reveals the stereochemistry of individual CFCI-CH2-CFCI diads, the two protons at a methylene carbon being chemically inequivalent in meso (m) and chemically equivalent in racemic (r) diads. Consequently, the fluorine atoms can be assigned to rr (a), rm (b) or mm triads (c). The possible tetrad structures can be determined by looking for identical C-H cross-peaks in different F slices e.g. the A cross-peaks in (a) do not occur in the other two sUces therefore, the methylene group A shows only correlations with F atoms in mm triads and must be centred in an mmm tetrad, etc. Reproduced, with permission, from ret 100. Copyright 1996 American Chemical Society.

However, poly(l,6-heptadiyne)s were insoluble in any organic solvents and unstable with air oxidation, regardless of the catalysts and polymerization conditions used. Introduction of substituent on the methylene carbon at the 4-position of 1,6-heptadiyne solved the predescribed problems of poly(l, 6-hep-tadiyne) such as the insolubility and the facile oxidation to air. 

Figure 18. Transition temperatures from the glass ( ), crystalline (o), nematic (A) and smectic ( ) phases of poly 5- [n-[4"-(4" -nitrostilbeneoxy)alkyl]carbonyl )bicyclo[2.2. l]hept-2-ene)s (DP =27-42, pdi= 1.08-1.11) [187], 4-n-alkoxy-4 -nitro(stilbene) [228] and poly[3-[(( -(4 -(4"-nitrostilbeneoxy)alkyl)carbonyl)methylene-oxy)methyl]cyclobutene s (DP =61 -72, pdi= 1.14-1.16) [187] as a function of the number of methylenic carbons in their n-alkyl spacers.

When a polymer is altered by chemical reaction and the process is not carried to completion, the modified units are not necessarily distributed at random through the macromolecules. The partial conversion of polyVAC to poly(vinyl alcohol) gives a product in which the residual VAC units tend to occur in blocks [82] (see chapter 2). This conclusion was reached from CNMR studies of the materials dissolved in D2O. The methylene carbon resonances were used to determine the mean lengths of sequences of VAC and of vinyl alcohol units. 

Depolymerization (or reversion) occurs essentially at high temperatures, only in linear polymers having weak monomer-monomer bonds, or in tridimensional polymers having weak cross-link junctions (see Table 12.2). These are linear polymers containing the weakest aliphatic C-C bonds, i.e. involving tetrasubstituted carbon atoms, e.g. polyisobutylene (PIB), poly(methyl methacrylate) (PMMA), poly(or-methyl styrene) (PorMS), etc. These are also linear polymers containing heteroatoms, e.g. poly(oxy methylene) (POM), poly(ethylene terephthalate) (PET), poly(vinyl chloride) (PVC), etc., but also sulphur vulcanized elastomers. Cross-linking predominates mainly in unsaturated linear polymers, i.e. essentially polybutadiene and its... 

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