Macromolecular Chemistry Berzelius Staudinger Carothers
³ = T 90 A ³ ³ = 89 T 80 B ³ ³ = 79 T 70 C ³ ³ = 69 T 60 D ³ ³ = 59 T 50 F ( ) - é ù x x = + T x 10 77 ê ú s ë û = x raw score = s standard deviation = x average of test scores Grading Question • The raw scores that you earn on the exams will be converted to Standard T-scores. Using T-scores removes bias in favor of the tests with the highest standard deviation. It represents the fairest way I know of to “grade on a curve”. This statistical approach is used in grading nearly all national exams such as the MCAT, SAT, GRE, etc. Each exam will be returned with a raw score and a T-score so that you will know exactly where you stand after each exam. The average of your T-scores will be used to determine the course grade according to the following table:
Some early Milestones • 1833 Berzelius coins term polymer • 1880-1900 Man made fibers by modification of natural material cellulose acetate, nitrocellulose, etc • 1900-1930 “Colloid Controversy” • 1910 Bakelite • 1920 Staudinger macromolecules • 1930- 1937 the Carothers period Neoprene, nylon,etc.
Natural Polymers • Natural polymeric materials have been used throughout history for clothing, decoration, shelter, tools, weapons, and writing materials • Examples of natural polymers: • Cellulose (wood, cotton) • Hair (wool) • Silk • Rubber • Horn • Modified natural polymers • Nitrocellulose (lacquer, smokeless powder) • Rayon, etc
Cellulose Cellulose is the most widely distributed plant skeletal polysaccharide. It constitutes over half of the cell wall material of wood. Cotton is almost pure cellulose. Cellulose is a linear polysaccharide of D-glucose units joined by b-1,4-glycosidic bonds.
Cellulose • The average MW of cellulose in 400,000 g/mol, corresponding to about 2200 D-glucose units per molecule. • Cellulose molecules act a lot like stiff rods and align themselves side by side into well-organized water-insoluble fibers. The -OH groups form numerous intermolecular hydrogen bonds adding strength to the network. • This arrangement leads to high mechanical strength and water insolubility, hence the strength and utility of wood and cotton fiber.
C e l l u l o s e - O H + S S = = - - + + C e l l u l o s e - O H C C e e l l l l u u l l o o s s e e - - O O - - C C - - S S N N a a c e l l u l o s e x a n t h a t e Rayon Rayon is made by first treating cellulose with carbon disulfide in base solution. N a O H C S 2 Then the solution of cellulose xanthate is passed through a small Orifice or slit into an acidic solution. H+ +
Shellac Bug Bug “do do” Lots of bug “do do”
Shellac natural polymer secreted by a southeast Asian lac beetle Excellent quality of moulding detail leads to: Early 78 rpm records 25% "shellac“, cotton filler, powdered slate, and a small amount of wax
The History of Novolac C.H. Meyer and/or L.H. Baekeland Discovered Novolac ca. 1900 ??? Baekeland Meyer
Bakelite Baekeland’s Phenol-formaldehyde resins, which he called Bakelite.
The Mayan Ball Game: life or death with a littlerubber ball… • The Ball Court was used for symbolic religious games. • It is formed of two parallel walls.
What are Polymers?? Coined the term "polymer" in 1833 to describe organic compounds that share identical empirical formulas but differ in overall molecular weight …a kind of “isomer”.. acetylene cyclobutadiene, benzene and styrene, for example. This concept lasted until Carothers. Jöns Jacob Berzelius (1779-1848)
The Association People Graham thought that cellulose and other colloids consisted of large numbers of structurally simple molecules held together by "association." ….also called “partial valency” ??!! Thomas Graham 1805-1869
Hermann Staudinger 1881-1965 The statement of a German chemist after a debate with Staudinger in 1926: ‘We are shocked like zoologists would be if they were told somewhere in Africa an elephant was found who was 1600 feet long and 300 feet high’. Staudinger received the Nobel Prize in chemistry in 1953.
Colligative Properties • Colligative properties of solutions are properties that depend upon the concentration of solute molecules or ions, but not upon the identity of the solute. Colligative properties include freezing point depression, boiling point elevation, vapor pressure lowering, and osmotic pressure.
h Osmometry Define a pressure P = r g h Semipermeable membrane: stops polymers, passes solvent.
(Ideal) ( N2 ) ( Real ) The gas law in review PV =NRT or PV/nRT = 1 1.0 PV/nRT P (atm) PV/nRT = 1 + BP + CP2 + DP3…..etc Virial fudge factors
Applying to “ideal solutions” r g h = P So…. P V / n R T = 1 or P = (n/V) R T n / V = m (Molar concentration) So…. P = m R T this is the van’t Hoff Relationship For molal m = n / V = c / M Where M = mass of solute per unit volume of solvent So…. P / c = R T / M and we can cheat…. P / c = R T /M + Bc + Cc2 + …..
Reduced osmotic pressure (/c) vs concentration (c) P / c RT M Slope = B C
Morphology • Many polymers tend to crystallize as they precipitate or are cooled from a melt • But, they are very large molecules, often with complicated and irregular shapes, which inhibits crystallization and tends to prevent efficient packing into exactly ordered structures • As a result, polymers in the solid state tend to be composed of ordered crystalline domainsand disordered amorphous domains
Polymer Morphology Amorphous Crystalline and semi crystalline
Morphology • Polymers with regular, compact structures and strong intermolecular forces, such as hydrogen bonds have high degrees of crystallinity. • as crystallinity increases, the polymer becomes more opaque due to scattering of light by the crystalline regions…for example, teflon -(CF2CF2)-“looks” white • Melt transition temperature, Tm: the temperature at which crystalline regions melt • as the degree of crystallinity increases, Tm increases
Crystallinity crystalline amorphous proportion of crystalline / amorphous strong influence on properties PE carrier bag - amorphous, toughened pipe 95% crystalline
Morphology • Example: poly(ethylene terephthalate), abbreviated PET can be made with crystalline domains ranging from 0% to 55% depending on how it is processed. It can have the properties of drink bottles or Dacron fiber.
Morphology • Amorphous PET is formed by cooling the melt quickly • plastic beverage bottles are PET with a low degree of crystallinity • By cooling slowly, more molecular diffusion occurs, chains become more ordered and crystalline domains form • PET with a high degree of crystallinity can be drawn into textile fibers and tire cords (dacron)
Morphology • Amorphous polymers are referred to as glassy polymers • they lack crystalline domains that scatter light and are transparent….Poly(methyl methacrylate) • they are weaker polymers and generally more flexibility • on heating, amorphous polymers are transformed from a hard glass to a soft, flexible, rubbery state • Glass transition temperature, Tg: the temperature at which a polymer undergoes a transition from a hard glass to a rubbery solid (ca. 100 degrees for polystyrene)