28. Polymerisation Flashcards
Define ‘condensation polymerisation’.
Addition reaction followed by elimination (eg. water, HCl). Monomers contain two functional groups capable of reacting with each other in two ways:
- groups found on the same molecule
- groups on different molecules (eg. nylon 6,6)
What are nylons and how are they made?
Polyamides made from the reaction between -NH2 and -COOH/-COCl.
How is nylon 6,6 made?
From 1,6-diaminohexane and hexanedioic acid/hexanedioyl dichloride.
How is nylon 6 made?
Not by condensation, by ring-opening polymerisation. Heating caprolactam in an N2 atmosphere. It breaks the chain and these monomers react to form nylon 6.
Caprolactam is made of 6-aminohexanoic acid.
Describe the properties of nylon.
Low-density, strong, elastic. Used in the clothing industry and in making rope.
Pulled into long fibres via cold drawing - polymer chains are lined up and H-bonds form (high tensile strength).
Describe the structure of Kevlar.
Polyamide with benzene rings - strong and flexible, resistant to fire and abrasion. Long chains line up and form H bonds.
(-CO-benzene-CO-NH-benzene-NH-)n
Used in bulletproof vests, biker leather, rubber in tyres.
Describe the features of amino acids in proteins.
Alpha amino acids, distinguished by their side chains (R groups).
The side chains can be non-polar, polar or electrically charged (acidic or basic).
Amino acids are amphoteric - their pH depends on the conditions (acidic +, basic -). In body tissues (pH7), the -NH2 and -COOH are ionised and their charges are balanced
Which type of polymer are proteins? What are their characteristics?
Condensation - dipeptides -> tri -> tetra -> polypeptide (many peptide links, made of amino acid residues).
The N-terminal end is the end with a free -NH2. The sequence is drawn starting here.
The polypeptide chain is unbranched, the amino acid sequence is unique + determined by DNA, there are specific functions.
Outline the secondary structure in proteins.
Regular structural arrangement, H bonds between NH and CO in neighbouring peptide bonds. They can be arranged as alpha-helices or beta pleated sheets.
Describe the structure of an alpha-helix.
CCNCCN backbone, some points flexible and allow free rotation. Twists into a spiral, rod-like structure.
H bonds lie between NH group and CO four residues down. Parallel to the long axis of the helix, stabilising the structure. Side chains stick out.
Describe the structure of a beta pleated sheet.
Antiparallel strands, bonds between -NH and -CO in different chains or different areas of the same chain.
Describe where secondary structures are mixed.
Eg. pepsin - has beta turns and randomly coiled areas between regions.
Describe the different types of bonding in proteins’ tertiary structures.
Disulfide bridges lock chains in place (covalent). Lie in the same chain or between different chains. Function outside cells (eg. digestive enzymes).
VDWs occur between non-polar residues. Many in the centre of the protein. Weak individually.
Hydrogen bonds occur between polar side chains (H-O or H-N).
Ionic/salt bridges occur between ionised side chains (basic/acidic).
What is produced when proteins are hydrolysed (acid and alkali)?
Reflux with excess dilute acid - original 2-amino carboxylic acids formed. -NH2 reacts with excess to form ammonium salts.
Reflux with excess dilute alkali - original sodium salts formed (eg. H2N-RCH-COO(-)Na(+) ).
Describe the structure of DNA.
Phosphoester link between phosphate group and ribose sugar. Nitrogenous base (A, T, G, C) linked to sugar. Strands run in opposite directions (3’ -> 5’ and vice versa).
A and T are planar with two rings, C and G have one. H bonds between these pairs keep the double helix together. So do VDWs between the pairs. The pairs are slightly out of line, allowing the double helix to bend.
What are the important features of DNA?
Polynucleotides (RNA too) which determine the structure and nature of chemical reactions.
- DNA can make copies of itself to be passed on
- Contains base sequences forming a code for protein synthesis.
Describe the process of DNA replication.
Chromosomes contain DNA. DNA replication occurs during cell division.
- H bonds and VDWs broken, helix unzips, nucleotide triphosphates (free nucleotides) pair with the unpaired bases and are joined by phosphodiester bonds, catalysed by enzymes. New strand complementary to template.
Semi-conservative - double helices have one new and one old strand.
How are polyesters formed? Describe some examples.
Condensation polymerisation between dicarboxylic acids and diols.
Terylene - benzene-1,4-dicarboxylic acid and ethane-1,2-diol. Antimony (III) oxide catalyst and 280°C.
PLA - 2-hydroxypropanoic acid. Raw material from starch, biodegradable alternative to oil-based plastics. Broken down by acid hydrolysis.
What are the differences and similarities between LDPE and HDPE?
- Made of non-polar polymer chains linked by VDWs.
LDPE - highly branched, cannot pack neatly, fewer IM forces, low density, low MP.
HDPE - unbranched, can pack neatly, more VDWs forces, high density, high MP. Used in water pipes.
natural + synthetic rubbers
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What are non-solvent-based adhesives and why are they better alternatives?
Traditional adhesives use organic solvents to dissolve a polymer which will stick two surfaces together - the solvent evaporates and leaves behind a solid. Ethyl ethanoate is often used, but other organic solvents can be flammable or toxic.
Non-solvents use a polymer containing Si-O bonds, which are hydrolysed by moisture in the air and form siloxane cross-linkages between chains (Si-O-Si). The products are called ‘silyl modified polymers).
Non-solvent-based adhesives: What are epoxy resins?
Thermosets - polymers forming giant covalent cross-link networks and cannot be melted or remoulded.
Formed by condensation of epoxyethane derivative and diamine pastes.
Non-solvent-based adhesives: What is superglue?
Uses addition with monomer methyl cyanoacrylate. Addition occurs across the C=C, initiated by the presence of moisture.
How are biodegradable plastics broken down?
Some are made of plant materials (PLA) that are digested easily.
Polyamides and polyesters can be broken down by acid hydrolysis (occurs due to rotting vegetation in landfills).
Small amounts of starch granules in the plastics are broken down by microorganisms, increasing the SA so that the rate of decomposition can be increased.
