Chemistry for Changing Times 11th Edition Hill and Kolb

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Announcements
Evaluations - Laura Lecture Chapter 10 Lab
Quiz Take at the end of class Take home Quiz 5
/ Worksheet Pick up at end of class Due
Thursday Thursday Complete Chapter 10 Discuss
Final
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Polymerization

• A ..-A-A-A-A-A-A-A-..
• The word polymer comes from the Greek. Poly
  means many. Mer comes from meros meaning parts.
  
• Polymers consist of many smaller molecules called
  monomers that are connected to form the larger
  (macro) molecule.
• Monomers are the building blocks of polymers!
• Polymers can be classified a number of different
  ways, including
• Natural versus Synthetic
• Addition Polymers versus Condensation Polymers

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Natural Polymers

• Many natural substances exist as polymers
  including
• starch
• cotton (cellulose)
• wood (cellulose)
• proteins
• Celluloid is one of the earliest synthetic
  substances that is a polymer. It is produced
  when natural cellulose is treated with nitric
  acid. Cellulose nitrate was used for billiard
  balls, mens fashion collars, and movie film.

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Synthetic Polymers Polyethylene

• Perhaps the most common synthetic polymer is the
  plastic, polyethylene.

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Synthetic Polymers Polyethylene Characteristics

• High density polyethylene (HDPE) exists as mostly
  linear molecules that pack closely together. It
  is used for milk jugs, bottle caps, toys, etc.
• Low density polyethylene (LDPE) is a more highly
  branched form of polyethylene. It is used to
  make plastic bags, plastic films, electric wire
  insulation, etc.

These two bottles, both made of polyethylene,
were heated in the same oven for the same length
of time. Which is made of HDPE and which is made
of LDPE?
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Addition Polymers

• Addition polymerization occurs when monomers add
  to one another in such a way that the resulting
  molecule contains all atoms that are present in
  the monomers. Addition polymers are all
  derivates of polyethylene.

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Addition Polymers

• Vinyl Polymers

Polytetrafluoroethylene (PTFE) insert PTFE
here
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Condensation Polymers

• In condensation polymerization, small molecules
  such as water, alcohols, ammonia, or HCl are
  released as byproducts.

Nylon is a polyamide. Most nylon is manufactured
as fibers.
Polyesters are condensation polymers made from
molecules containing alcohol and carboxylic acid
functional groups. The linkage is an ester.
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Condensation Polymers

• Phenol-formaldehyde resin was the first synthetic
  polymer. It was known as Bakelite in honor of
  its discoverer, Leo Baekeland. Leo Baekeland
  received a patent in 1909 for this polymer.

Polycarbonates are tough, clear polymers used in
protective helmets, safety glasses, and dental
crowns. Lexan is one such polycarbonate.
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Condensation Polymers

• Polyurethanes are similar to nylon. They may be
  elastomers (meaning both flexible and elastic) or
  tough and rigid, depending on the monomers used.
  Polyurethanes are used in foam rubber, skate
  wheels, and tough furniture finishes.

Epoxy resins are often sold as two-part liquids.
They make durable, clear coatings and are an
excellent adhesive. They are very strong when
cross-linked.
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Properties of Polymers

• Polymers have very high molecular weights. Since
  the strength of intermolecular forces increases
  with molecular weight, polymeric materials
  exhibit very strong intermolecular forces. For
  these reasons, polymeric materials exist as
  strong fibers and polymers form viscous solutions.

The molecules of crystalline polymers line up in
neat rows forming fibers of great strength.
Crystalline polymers tend to be very
rigid. Amorphous polymers, on the other hand,
have molecules that are randomly tangled.
Amorphous polymers tend to be soft and rubbery.

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Properties of Polymers

• The glass transition temperature (Tg) is the
  temperature above which the polymer is tough and
  rubbery, and below which it is like glass?hard,
  brittle, and stiff.

Some synthetic polymers can be converted to
fibers. Many can exhibit properties that are
superior to natural fibers. The majority of
fibers and fabrics used in the United States are
synthetic.
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Disposal of Plastics

• Most plastics do not decompose readily in the
  natural environment.
• Unwanted plastic waste can be dealt with by
  disposal in landfills, incineration,
  biodegradation, and recycling.

Landfills Plastics make up 11 by mass of solid
waste and 20 by volume. More than half of all
solid waste ends up in landfills. Landfill space
is becoming increasingly difficult to obtain.
Incineration Many plastic materials have
significant fuel value and incineration of solid
waste along with using the heat energy to
generate electricity is attractive. However, the
combustion of plastics and rubbers is not without
problems. Many of these materials exhibit toxic
gases when combusted. PVC plastic, for instance,
releases HCl gas when burned.
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Disposal of Plastics

• Degradable Plastics
• About half of our waste plastic comes from
  packaging. Expect to see more biodegradable and
  photodegradable plastics used for packaging in
  the near future.

Recycling Over the long term, recycling may be
the best way of dealing with waste plastics.
Recycled plastics can be separated into the
various types, chopped into flakes, melted, and
remolded or spun into fibers.
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Plastics and Hazards

• Many people are injured each year due to
  accidental ignition of plastics. Federal
  regulations require that childrens sleepwear be
  made of flame retardant materials.
• Some plastics release toxic gases during
  combustion. Firefighters must protect themselves
  from toxic gases.
• In the news. Recently plastic bottles have been
  in the news as for possible health hazards
• http//www.plasticsinfo.org/s_plasticsinfo/sec_lev
  el2_faq.asp?CID705DID2839
• typical plastic water bottles have plasticizers
• http//www.eartheasy.com/article_nalgene_bottles.h
  tml
• Nalgenes are polycarbonate based

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Plasticizers Pollution

• Certain plastics such as vinyl polymers are stiff
  and brittle plasticizers are chemicals that are
  used to make the materials more flexible. Many
  of these plasticizers have low volatility.
  Eventually these materials can become stiff and
  brittle as the plasticizers vaporize.

Early plasticizers were polychlorinated
biphenyls (PCB).
More recent plasticizers are less toxic, and
include phthalate esters.
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Plastics The Future

• It is difficult to imagine the world without
  synthetic polymers and plastics. Many are made
  from petroleum or natural gas. Much research is
  being conducted on developing synthetic polymers
  from renewable resources. These materials
  represent both hope and challenge for our future.