Glass transition temperature molecular architecture

How does the molecular architecture of the bisphenol molecule affect the glass transition temperature of polycarbonate ... 

Molecular architecture Free volume and flexibility as indicated by low glass transition temperatures 26, 29, 46, 47, 48... 

A third feature for solubility is molecular architecture, especially in the case of large compounds such as polymers. The polymer should exhibit large free volume with a high degree of flexibility. A good indication of polymer flexibility and high free volume is a low glass transition temperature. 

As biological systems have always been an inspiration for scientists, intracellular compartments (such as lysosomes or mitochondria) also have their artificial equivalents in polymer vesicles, called polymersomes. Polymersomes are spherical compartments with a bi- or monolayer membrane, generated by self-assembly of di- or triamphiphilic block copolymers in diluted aqueous conditions. To favor the formation of structures such as polymersomes, it is necessary to have a hydrophilic fraction of the copolymer mass of 25-40%, and polymer concentration above the critical micellar concentration. Other parameters that affect the self-assembly process, and therefore the final architecture of the polymer supramolecular assemblies, are the molecular weight of the copolymer (Af ), block lengths, solubility, and glass transition temperature (Tg) [21,22], The relative mass or volume fraction of each block is a key parameter in the formation of a self-assembled structure with a certain membrane curvature, and ultimately, with a specific architecture. The of the copolymer (and thus the block lengths) dictates the membrane thickness and polymersome properties, such as membrane fluidity, stabihty, and permeabihty [21,74],... 

Polymer blends can be classified as miscible or immiscible (Figure 7.1). These properties depend on the chemical structure, molar mass distributions and molecular architectures of the components. In principle, the constituents of these immiscible blends are separable by physical means. For miscible blends, however, the polymeric chains can be inserted into each of their own frameworks and exhibit a single glass transition temperature or have optical clarity, but only under specific conditions. 

Cooling past the glass transition temperature is accompanied by a dramatic change in the mechanical properties. The elastic modulus increases by a factor of 1000 when the polymeric liquid is cooled below Tg and the modulus of the glassy polymers is relatively insensitive to changes in molar mass and repeating unit structure. The actual value of Tg is, however, very dependent on the repeating unit, the molecular architecture and the presence of low molar mass species, as is shown in section 5.2. 

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