Quiz 2 REVIEW - Lecture 4 Crystallinity: polymers with...

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Lecture 4 Crystallinity: polymers with strong IMF; polymers cooled from melt state; compact structures; As crystallinity increases, polymer becomes more opaque due to scattering of light Crystallinity increases stiffness * higher young’s modulus * Less flexibility; diffusion rates are less permeable to molecules * necessary for drug delivery sometimes * Low penetration of h2o; slow hydrolysis Ex. PLGA, Polyethylene Teraflate Bone implants, bad for optics Amorphousness: called glassy polymers; brittle; when heated become soft; rubbery Lack crystalline domains that scatter light * transparent * Ex. Poly(methyl methacrylate) Optics, PMMA, PDMS, poly Syrene T m : crystalline melting point; temperature at which all crystalline regions melt; as crystallinity inc., so does Tm T g : glass transition temperature; temp at which a polymer changes from a solid glassy state to a rubbery state Heat capacity, density, permeability, dielectric constant, etc. change at Tg Silicones have low Tg and Tm, always fluid at relative temps (breast implants); Biodegradable polymers: PLGA (hydrolytically degradable because of esters bonds); proteins – peptide bonds PLGA put together by ester bonds Ester bonds are hydrolytically cleaved More hydrophobic (due to methyl group); looses water less; Slower rate of hydrolysis To increase rate of drug release, increase G amount because it is more hydrophilic driven by hydrolysis
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Quiz 2 REVIEW - Lecture 4 Crystallinity: polymers with...

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