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Interesting fact

Nylon was first introduced around 1939 and was in high demand to make stockings. However, as World War 2 progressed, nylon was used more and more to make parachutes, and so stockings became more difficult to buy. After the war, when manufacturers were able to shift their focus from parachutes back to stockings, a number of riots took place as women queued to get stockings. In one of the worst disturbances, 40 000 women queued up for 13 000 pairs of stockings, which led to fights breaking out!

Polymers

  1. The following monomer is a reactant in a polymerisation reaction:
    1. What is the IUPAC name of this monomer?
    2. Give the structural formula of the polymer that is formed in this polymerisation reaction.
    3. Is the reaction an addition or condensation reaction?
  2. The polymer below is the product of a polymerisation reaction.
    1. Give the structural formula of the monomer in this polymer.
    2. What is the name of the monomer?
    3. Draw the abbreviated structural formula for the polymer.
    4. Has this polymer been formed through an addition or condensation polymerisation reaction?
  3. A condensation reaction takes place between methanol and methanoic acid.
    1. Give the structural formula for...
      1. methanol
      2. methanoic acid
      3. the product of the reaction
    2. What is the name of the product? (Hint: The product is an ester)

The chemical properties of polymers

The attractive forces between polymer chains play a large part in determining a polymer's properties. Because polymer chains are so long, these interchain forces are very important. It is usually the side groups on the polymer that determine what types of intermolecular forces will exist. The greater the strength of the intermolecular forces, the greater will be the tensile strength and melting point of the polymer. Below are some examples:

  • Hydrogen bonds between adjacent chains Polymers that contain amide or carbonyl groups can form hydrogen bonds between adjacent chains. The positive hydrogen atoms in the N-H groups of one chain are strongly attracted to the oxygen atoms (more precisely, the lone-pairs on the oxygen) in the C=O groups on another. Polymers that contain urea linkages would fall into this category. The structural formula for urea is shown in [link] . Polymers that contain urea linkages have high tensile strength and a high melting point.
    The structural formula for urea
  • Dipole-dipole bonds between adjacent chains Polyesters have dipole-dipole bonding between their polymer chains. Dipole bonding is not as strong as hydrogen bonding, so a polyester's melting point and strength are lower than those of the polymers where there are hydrogen bonds between the chains. However, the weaker bonds between the chains means that polyesters have greater flexibility. The greater the flexibility of a polymer, the more likely it is to be moulded or stretched into fibres.
  • Weak van der Waal's forces Other molecules such as ethene do not have a permanent dipole and so the attractive forces between polyethene chains arise from weak van der Waals forces. Polyethene therefore has a lower melting point than many other polymers.

Questions & Answers

different structural formula
Lucas Reply
different type of structural formula
Lucas
primary,secondary and tertiary
Snowy
how does the earth revolute
Kevin Reply
What is the momentum
Given Reply
The product of the object's mass and it's velocity
Mvula
electric field def
FREENCO
what is secondary alcohol?
Raymond
is when Carbon that is bonded with OH is also bonded to 2 carbons of the chain.
Gontse
how is ester formed
Aubrey Reply
how is n ester formed
Aubrey
Alcohol reacts with a carboxylic acid
Texas
and the reaction is catalysed by sulphuric acid
Vhulenda
An ester is form when an alcohol reacts a carboxylic acid and sulphuric acid is used as a catalyst which therefore eliminates water.
Azola
an athlete with a mass of 70kg runs at a velocity of 45km . determine the athlete's momentum
Lesedi Reply
Is that a velocity or something else
msawenkosi
45km/h i guess
Texas
Change to m/s
Texas
45km/h = 12.5 m/s p=mv =70×12.5 =875 kg.m/s
Thato
what are the measures of the rates of reaction
Lesego Reply
Volume Concentration Temperature Pressure Surface Area
Thato
the principle of superposition of waves
Sfundo Reply
what is work
Kool Reply
is this a group chat
Nobuhle Reply
Hey can y'all define newton's 2nd law
mthebzification
If a resultant force act on an object...the object will accelerate in the direction of a resultant force,the acceleration of the object is directly proportional to the net force and inversely proportional to the mass of the object
mosa
how do you calculate tension force
Bulumko
use the formula Fnet=ma if there is tension connecting two objects
Sboniso
to calculate Tension, usually calculate acceleration first Draw separate free body diagrams for each body. Apply Fnet = ma to calculate Tension
Kevin
Hi people
Paul
when a resultant force acting on an object the object will accelerate in the direction of a force at an acceleration directly proportional to the force and invesly proportional to the mass of the object.
Raymond
Hey people
Kaytee
how does temperature affect the equilibrium position
Blessing Reply
an increased temperature increases the average kinetic energy thus in turn increases the number of effective collisions........
Lwando
so...which reaction is favored between endothermic and exothermic .when temperature is increased..?
Blessing
exothermic reaction because energy is realised to the surroundings as heat and light energy ....graphical so much energy is realised as reactants to form product and because temperature is high rate of reaction is fast which means there is a successful collision
Code
INTEMENDO - INCREASE IN TEMPERATURE FAVOURS ENDOTHERMIC DETEMEXO - DECREASE IN TEMPERATURE FAVOURS EXOTHERMIC
Thato
an object will continue in a state of rest unless it is acted upon an unbalanced force
Junior Reply
Newton's Law 1
Code
First Newton's Law
Azola
Newton's first law
Surprise
newton first law
Thinavhuyo
Newton's first law
Blessing
when pressure is increased what happen to volume
Siphelo Reply
decreases
Code
care to explain?
Mpati
if pressure is applied to a pistol , the volume will decrease and particles will collide more frequently with the wall of a container .Each time they collide with the wall they exert a force on them .More collision means more force and the pressure will increase , that Boyle's Law
Code
Because the volume has decreased , the particle will collide more frequently with the wall of a container and each time they collide with the wall of a container they exert a force on them.More collision means more force so the pressure will increase , that Boyle's Law
Code
what is the difference between momentum and a change in momentum?
Chavonne Reply
Change in momentum is the impulse of the object
Rachel
Momentum is a vector quantity equal to the product of the mass of the particle and its velocity
Mmola
How to name a branched molecule from right or left?
Vadin Reply
What's Free Fall
Senzo Reply
Free Fall means there is no acting force on that object.
Dingaletu
only gravitational force
Dingaletu
no external force acting on an object
Sphiwe
by only force of gravite
Sello
but gravitational force
Sphiwe
true
Lucky
a motion in which the only force acting is gravitational force
Blessing
and an object experiencing free fall is referred as a projectile
Blessing

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Source:  OpenStax, Siyavula textbooks: grade 12 physical science. OpenStax CNX. Aug 03, 2011 Download for free at http://cnx.org/content/col11244/1.2
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