Molecular weight distribution glass transition temperature

POLYMER PROPERTIES Chemical composition Molecular weight Molecular weight distribution Glass transition temperature (T ) Density Average atomic number ... 

Solution PolymorS. A solution pol5mier s composition, solids content, viscosity, molecular weight distribution, glass-transition temperature, and solvent are of interest. Standard methods allow for all of these properties to be readily determined (171,172). 

Polymer—purity, molecular weight and molecular weight distribution, glass transition temperature (T ) or heat deflection temperature (HDT), and flow characteristics... 

The value of Tg is affected by polymer molecular weight (see Glass transition temperature), so, if the polymer has a broad distribution of molecular weight, the transition recorded by the DSC will tend to be broad rather than sharp (Fig. 2b, compare Fig. 2a). The glass transition temperature would usually be taken as a temperature at the point of inflection. 

Emulsion polymers provide a wide range in properties and low viscosity. Flexo and gravure inks are referred to as fluid inks because of their low viscosity. Molecular weight, Tg (glass transition temperature), and particle size distribution are key properties that are varied to meet specific ink requirements. 

Tsuji (2002) conducted an investigation into the hydrolysis of an amorphous form of PLA, to determine the effects of L-lactide content, tacticity and enantiomeric polymer blends. In this work four samples were prepared—poly(D,L-lactide), poly(L-lactide), poly(D-lactide) film and the blend sample of poly(L-lactide) and poly(D-lactide). The results are sununa-rized in Table 7.4, which also covers a complementary study that explored the effects of hydrolysis in terms of molecular weight and its distribution, glass transition temperature, crystallization temperature, melting temperature and mechanical properties. 

Various substituted styrene-alkyl methacrylate block copolymers and all-acrylic block copolymers have been synthesized in a controlled fashion demonstrating predictable molecular weight and narrow molecular weight distributions. Table I depicts various poly (t-butylstyrene)-b-poly(t-butyl methacrylate) (PTBS-PTBMA) and poly(methyl methacrylate)-b-poly(t-butyl methacrylate) (PMMA-PTBMA) samples. In addition, all-acrylic block copolymers based on poly(2-ethylhexyl methacrylate)-b-poly(t-butyl methacrylate) have been recently synthesized and offer many unique possibilities due to the low glass transition temperature of PEHMA. In most cases, a range of 5-25 wt.% of alkyl methacrylate was incorporated into the block copolymer. This composition not only facilitated solubility during subsequent hydrolysis but also limited the maximum level of derived ionic functionality. 

GPC measurements were used to demonstrate that a monomodal molecular weight distribution with a polydispersity of approximately 2 was obtained. The glass transition temperature was determined on a Perkin-Elmer DSC-2 using a heating rate of 10 C/min and the intrinsic viscosity was determined in NMP at 25°C. These data are summarized in Table I. 

Size-exclusion chromatography (SEC) has been also used as complementary technique for characterizing changes in the composition of synthetic resins due to aging. In particular, it enables the determination of molecular weight distributions and the glass transition temperatures of resins. 

In addition to the Bisphenol-A backbone epoxy resins, epoxies with substituted aromatic backbones and in the tri- and tetra- functional forms have been produced. Structure-property relationships exist so that an epoxy backbone chemistry can be selected for the desired end product property. Properties such as oxygen permeability, moisture vapor transmission and glass transition temperature have been related to the backbone structure of epoxy resins5). Whatever the backbone structure, resins containing only the pure monomeric form can be produced but usually a mixture of different molecular weight species are present with their distribution being dictated by the end-use of the resin. 

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