Molecular poly -based

Miller and co-workers have recently prepared nanometer-scaled molecular dumbbells based on poly(benzyl ether) dendrons (G1-G4) and oligoimide spacers [64], Their synthetic approach involved the coupling of amine-terminated oligoimides to dendrons with a carboxylic acid focal point. The resulting hybrid materials were found to be quite soluble thus allowing their analysis by cyclic voltammetry in DMF. Consistent with Roncali s observation, the kinetics of reduction of the oligoimide core was not found to be limited by the presence of the dendritic wedges. 

Some recent examples demonstrating the molecular dispersion of rod polymer molecules in coil polymer matrices due to ionic interactions were given by Parker et al. (1996). These systems were based on three types of ionic PPTA s (Figure 5.4) and polar polymers, such as poly(4-vinylpyridine) (PVP), poly(vinyl chloride) (PVC), poly(ethylene oxide) (PEO), and poly(styrene-co-acrylonitrile) (S-AN). Due to the ionic-dipole interactions the rod-coil polymer pairs formed molecular composites as revealed by optical clarity, polarized microscopy, Tg measurements, as well as TEM observations. More significantly the molecular composites based on amorphous matrix polymers (e.g., PVP) were all transparent and showed no phase separation upon heating. Therefore they are melt-processible. As would expected, the mechanical properties of the molecular composites were... 

Crystallites may also be considered to act as reinforcing fillers. For example, the rubbery modulus of poly(vinyl chloride) was shown by lobst and Manson (1970,1972,1974) to be increased by an increase in crystallinity calculated moduli in the rubbery state agreed well with values predicted by equation (12.9). Halpin and Kardos (1972) have recently applied Tsai-Halpin composite theory to crystalline polymers with considerable success, and Kardos et al (1972) have used in situ crystallization of an organic filler to prepare and characterize a model composite system. More recently, the concept of so-called molecular composites —based on highly crystalline polymeric fibers arranged in a matrix of the same polymer—has stimulated a high level of experimental and theoretical interest (Halpin, 1975 Linden-meyer, 1975). 

A Nykaenen, M. Nuopponen, A Laukkanen, S. P. Hirvonen, M. R3d ela, 0. Tlirunen, H. Tenhu, R Mezzenga, 0. Ikkala, and J. Ruokolainen, Thase Behaviour and Temperature-Responsive Molecular Filters Based on Self-Assembly of Polystyrne-Block-Poly(n-Isopropylacrylamide)-Block Polystyrene," Macromolecules. 40, 5827-5834(2007). 

One should keep in mind that mole Iraction-based activity coefficients become very small values for common polymer solutions and reach the value of 0 for Mj—> which means a limited applicability to at least oligomer solutions. Therefore, the common literature provides only mass fraction-based activity coefficients for (high-molecular) poly-mer/(low-molecular) solvent pairs. Furthermore, the molar mass Mj of the polymeric liquid is an average value according to the usual molar-mass distribution of polymers. Additionally, it is a second average if mixed stationary liquid phases are applied. 

Each of the two quantitative spectra of poly(ethylene glycol) (PEG) depicted in Fig. 41 exhibits an end-group (OH) resonance at 3.2 ppm and a main -O-CH2 CH2O- peak at 3.9 ppm. The molecular weights of these two products can easily be calculated by NMR, based on the relative intensity ratio of the end to main peaks. Rare spins ( C and Si) can also be used to determine molecular weight, as demonstrated for several polysilox-anes [117]. A commercially available on-line system tracks both density and melt index (which is related to molecular weight) based on wide-line H experiments [118]. GPC/NMR, a variant of LC/NMR, has been used to track the molecular-weight distribution of poly(methyl methacrylate) [119]. 

Molecular motion based on the electrochemical-induced ligand substitution reaction has been reported in a copper(I) rotaxane (Figure 37). This rotaxane is composed of a 2,9-diphenyl-l,10-phenanthroline-containing cyclic poly ether ring, a tetraphenylmethane-stoppered molecular string that contains another 2,9-disubstitnted phenanthroline chelate... 

Complete controlled of condensation polymerization by substituent effect-assisted CGCP was first demonstrated in the synthesis of N-alkylated poly(p-benzamide)s by polymerization of 4-(alkylamino)benzoic acid phenyl esters 14 [20]. Polymerization of phenyl 4-(octylamino)benzoate (14a) was carried out in the presence of a base and the initiator 15a, yielding poly(p-benzamide) with a low polydispersity and controlled molecular weight based on the feed ration of 14 to 15a ([14]o/[15a]o) (Scheme 11). 

Polypyridine, which is an n-type Ji-conjugated polymer, was also prepared by catalyst-transfer CGCP (Scheme 47). 5-Bromo-3-chloromagnesio-2-(2-(2-methoxyethoxy)ethoxy)pyridine 39 was polymerized with Ni(dppp)Cl2 in the presence of 2.0 equivalents of LiCl in THF at room temperature to yield poly 2-[2-(2-methoxyethoxy)ethoxy]pyridine-3,5-diyl with narrow molecular weight distributimi and cmitrolled molecular weight based on feed ratio of 39 to Ni(dppp)Q2 ([39]o/[Ni(dppp)a2]o) [135]. 

The introduction of short-chain branches into polyethylene by use of an alpha-olefin comonomer yields the commercially important polymer called linear low-density polyethylene (LLDPE). These short branches would also be expected to affect the entanglement molecular weight. Based on previously published data on poly (a-olefins) [10, 53], Fetters etal. [60] developed the following empirical equations for estimating the plateau moduli of polymers of this type, given only the average molecular weight per backbone bond, mj,. 

Experimental work on molecular composites has focused on attempting to kinetically delay the phase separation with a desirable morphology before the thermodynamics leads to complete immiscibility. Most of this work was initially performed as part of a program sponsored by the United States Air Force. For example, poly (p-phenylene terephthalamide) (PPTA) and poly (p-phenylene benozbisthiazole) (PBT) have been successfully dispersed in a Nylon 66 matrix.i 22 J y gf 23 reported that there are interactions present in a PPTA and Nylon 6 system and that phase separation can be thermally induced in molecular composites based on these two polymers. Thermally induced phase separation has also been observed in the PBT/ Nylon 6 system, when the melting temperature of the Nylon component is reached. Finally, Moore and Mathias reported a unique method for the preparation of molecular composites using an in situ polymerization process in which the anion of the PPTA was used as the initiator for the anionic polymerization of acrylamide in the formation of a Nylon 3 matrix. 

Table 9.3 lists the intrinsic viscosity for a number of poly(caprolactam) samples of different molecular weight. The M values listed are number average figures based on both end group analysis and osmotic pressure experiments. Tlie values of [r ] were measured in w-cresol at 25°C. In the following example we consider the evaluation of the Mark-Houwink coefficients from these data. 

---