Molecular weight MWD and

In controlled polymer synthesis, in addition, it is particularly important that the control herein implies not only the simple regulation of molecular weights, MWD, and other structural factors but also the precise introduction of functional groups into specific positions of polymers with well-defined architectures. Namely, the control of one or more of these structural factors, then, leads to a variety of polymers of synthetic interest, as some of them illustrated schematically in Fig. 2 ... 

It should be mentioned that the relationships between average molecular weights, MWD, and the power-law index of the respective polymer melts are not clear and completely unexplored in case of wood-filled composites. For example, increasing viscosity does not always improve physical properties of products. It was found that the increase of MFI of polypropylene from 3 to 30 g/10 min did not alter the efficiency of wood fiber dispersion and did not result in an improvement of any measured property of WPC. On the contrary, a change of MFI for HDPE from 0.15 to 7.0 led to better wetting of wood fiber and superior mechanical properties of the WPC. 

The family of polyethylenes has many properties in common. Tables 4.4 and 4.5 show the relationship of these properties to molecular weight, MWD, and density. 

Living polymerization characteristics—controlled molecular weight, MWD and chedn architecture. 

It is noteworthy that the polymerization of DEA with amide enolates leads to well-defined water-soluble poly(DEA) without hydrophobic terminal groups as well as the control of molecular weight, MWD, and stereoregularity. Those novel polymer samples are unique and advantageous for investigating the effect of terminal functionality on water solubility and thermosensitivity. 

Thermoresponsive poly(OEVE) S3 tems stayed one step ahead of poly(NIPAM) (PNIPAM) systems to study the effects of molecular weight, MWD, and sequence distribution, since well-controlled polymerization of NIPAM was not achieved at that time. Thus, the findings with the VE systems were quite important for the understanding of LCST-type phase separation mechanism as well as for further design of stimuli-responsive polymers. Fine structures of stimuli-responsive polymers... 

N,N-diethylacrylamide (DEAAm) in polar and nonpolar solvents using alkyllithium initiators is complicated due to the presence of slow aggregation dynamics of the propagating amido enolate ion pairs similar to ester enolate ion pairs in alkyl (meth) acrylate polymerization. Attempts were made to use different initiators in combination with coordinating ligands to control the polymerization, and only minimum control on molecular weight, MWD, and the stereostructure of the polymers was obtained."""-"""... 

Most of the copolymers and polymers obtained by chemical modification reactions generally possess a two-dimensional distribution MWD (Molecular Weight Distribution) and CCD (Distribution of Chemical Composition). An analogous problem exists with polyolefins MWD and distribution of Short-Chain Branching (SCB). It is normally impossible that they can be adequately fractionated by both molecular weight (MWD) and by chemical composition (CCD). The problem is overcome by cross fractionation. The term cross-fractionation refers to any eombination of fractionation methods capable of evaluating the distribution in size and composition. 

The tailoring of PE properties in commercial processes is achieved mostiy by controlling the density, molecular weight, MWD, or by cross-linking. Successful control of all reaction parameters enables the manufacture of a large family of PE products with considerable differences in physical properties, such as the softening temperatures, stiffness, hardness, clarity, impact, and tear strength. 

Mechanical Properties. The principal mechanical properties are Hsted in Table 1. The features of HDPE that have the strongest influence on its mechanical behavior are molecular weight, MWD, orientation, morphology, and the degree of branching, which determines resin crystallinity and density. 

The bulk viscosity control parameter for CSM, as with other elastomers, is molecular weight M and molecular-weight distribution (MWD). Mooney viscosity for CSM is determined by selection of the polyethylene precursor. 

The primary molecular parameters affecting the processing and ultimate properties of PEs are type, content, and distribution of chain branching, molecular weight (MW), and molecular weight distribution (MWD). 

Molecular weight, temperature, and pressure have little effect on elasticity the main controlling factor is MWD. Practical elasticity phenomena often exhibit little concern for the actual values of the modulus and viscosity. Although MW and temperature influence the modulus only slightly, these parameters have a great effect on viscosity and thus can alter the balance of a process. 

Techniques were developed for the dilute solution characterization of polydlchlorophosphazene. The purity of the trimer has a significant effect on oligomer formation, polymerization time and polymer MW and MWD. The polymers prepared in this study have high molecular weights and broad molecular weight distributions and probably have similar, if not identical, chain structures. 

Among the main molecular structural variables in EPDMs that are stipulated by catalyst systems and that affect the vulcanizate tensile properties we may mention molecular weight (MW) and MWD, degree of unsaturation (LG=C 1) and its distribution in the polymer, composition (C S) and monomer sequence length distribution along molecular chains, and long-chain branching if present. Effect of... 

Recently, gel permeation chromatography (GPC) and other dilute solution techniques have been directly applied to the characterization of II (17-20). In our laboratory we have examined II prepared by the uncatalyzed bulk and solution polymerization processes. Polymers obtained from the former process have high molecular weights (MWs) and broad molecular weight distributions (MWDs, Mw/Mn=5). The dilute solution... 

Since its discovery in 1959 (1) and first application to synthetic organic polymers in 1964 (2), SEC has become the most widely used technique for routine characterisation of polymer molecular weights (MW) and molecular-weight distributions (MWD), as attested... 

The protected amine and primary amine ended polymers show the good molecular weight control and narrow MWD s one expects of anionic polymers. In addition, the hydrolysis of the protecting group does not disrupt polydiene backbones. Such procedures are also gel free. The polymers formed exhibit functionalities approaching the theoretical values, especially for low molecular weight (high amine content) polymers (Table VI), (14, 2). 

---