Copolymer, composition molar mass average

Two general methods have been developed for the determination of copolymer composition and sequence, namely a method which uses a combination of mass spectral intensities and the chain statistics approach. " In the approach based on a combination of MS intensities one computes the average copolymer composition (molar fraction of A units in the copolymer), Ca-... 

Polymers vary by a number of characterization variables. The molar mass and their distribution function are the most important variables. However, tacticity, sequence distribution, branching, and end groups determine their thermodynamic behavior in solutions too. For copolymers, the chemical distribution and the average chemical composition are also to be given. Unfortunately, much less iirformation is provided with respect to the polymers or copolymers that were applied in most of the thermodynamic investigations in the original hterature. In many cases, the samples are characterized only by one or two molar mass averages and some additional information (e.g., Tg, T, Pb, or how and where they were synthesized). Sometimes even this information is missed. 

Consistent notation is adopted throughout this book. Diblock copolymers are written poly(monomer A) poly (monomer B) or PA-PB, where examples of PA and PB are illustrated in Fig. 1.2. Similarly, triblock copolymers are written poly(monomer A)-poly(monomer B)-poly(monomer C) or PA-PB PC. Deuterated blocks are denoted dpoly(monomer A) or dPA. The molar mass of a copolymer is denoted by M, or Af corresponding to the weight- or number-average respectively, and the composition is specified by the volume fraction of one component,/. In solution, the volume fraction of a copolymer is denoted [Pg.3]

Recently, Siu et al. [139] studied the effect of comonomer composition on the formation of the mesoglobular phase of amphiphilic copolymer chains in dilute solutions. The copolymer used was made of monomers, N,N-diethylacrylamide (DEA) and N,N-dimethylacrylamide (DMA). like PNI-PAM, PDEA is also a thermally sensitive polymer with a similar LCST, but PDMA remains water-soluble in the temperature range (< 60 °C) studied. At room temperature, copolymers made of DMA and DEA are hydrophilic, but become amphiphilic at temperatures higher than 32 °C. Before the association study, each P(DEA-co-DMA) copolymer was characterized by laser light scattering to determine its weight average molar mass (Mw) and its chain size ( Rg) and (R )). The copolymer solutions (6.0 x 10 A g/mL) were clarified with a 0.45 xm Millipore Millex-LCR filter to remove dust before the LLS measurement. 

The first method has the advantage that the ratio mol quencher/mol basic unit of polymer is reasonably well known from copolymer composition. The copolymer should be of the random (not block) type and the molar mass should be known in order to know the average number of quenching groups per macromolecule (if this number is 1, "ordinary kinetics are suspected to fail). 

All latex samples prepared by emulsion polymerization are characterized by a broad distribution of molar masses, and in the case of copolymer latexes, a distribution of copolymer composition. Since the diffusion coefficient for a polymer depends upon both the chain length and the chemical structure, the polymers in any one film sample will be characterized by a rather broad distribution of Dcm values. Experiments to detormine in such systems actually yield a value averaged over the distribution, Dts. As will be seen below, since different components of the system contribute to the measured signal at different times, and the fastest diffusing species dominate the diffusion at early times, experi-mental values of Detr decrease with the ext t of interdiffiision. For such sanqiles, one is normally less int sted in the absoluie values of than in how extonal... 

In the case of a homopolymer the most important characteristic is its size of molar mass. The molar mass (defined by various averages and especially the molar mass distribution) determines a large range of properties of the polymer material. Naturally this qqrlies to copolymers as well, but in this case the di nical composition also plays an important role. 

In order to obtain a phase diagram in conversion-composition coordinates, a particular system consisting of a diepoxide based on diglycidylether of bis-phenol A (DGEBA), a stoichiometric amount of a diamine (4,4 -diamino-3,3 -dimethyldicyclohexyl-methane, 3DCM), as a hardener, and a rubber based on a statistical copolymer of butadiene and acrylonitrile, will be considered [65]. The increase in the number-average molar mass for the polycondensation of a stoichiometric diepoxy-diamine mixture, is given by [65]... 

In order to interpret the resulting data, a model is developed for copolymers obtained by SEC fractionation, taking into account the fractionation conditions and specifically the number of fractions. The model predicts the composition and the ratio D(x) of the SEC fraction. D(x) is the ratio between the number-average and the weight-average molar mass, and x is the fraction number. The predictions of the model are compared with SEC-NMR and SEC-MALDI data for the random copolymer of styrene and MMA reacted at high conversion. 

For most of the results discussed below, the following is valid concerning COP, PC and mixtures if not otherwise stated. The thermotropic copolyester derived from p-hydroxybenzoate and poly(ethylene terephthalate) [10] containing 60 mol% PHB was used exclusively as the PLC component because this composition has the best mechanical properties [10,118] of these copolymers. It was obtained from Eastman Kodak, Kingsport, TN, and had an average molar mass estimated from solvent viscosity of about 19000 g mol . The sequence distribution was calculated from C-NMR as described by Lenz et al. [119] and was nearly random the statistical parameter which describes the randomness of the copolymer is = 1 for a block copolymer and P = 0 for a completely random copolymer. The copolymer used for the experiments had P = 0.15. 

Synthetic copolymers are always polydisperse, i.e. they consist of a large number of similar chemical species with different molar masses and different chemical composition. Further sources of polydispersity are differences in the number of short- and long-chain branches, tactidty, sequence length, and other characterization variables. When block copolymers are considered, additional polydispersities, for example, in block length, in the number of blocks, and in the arrangement of blocks, have to be taken into account. Owing to this polydispersity, characterization of copolymers does not usually provide the number of the individual molecules or their mole fractions, mass fractions, etc. but requires the use of continuous distribution functions or their averages. 

---