6.1 Types of copolymers and their synthesis

Copolymers are versatile polymers made from two or more types of monomers. They come in various forms, including random, alternating, block, and graft copolymers, each with unique properties and applications.

Synthesis methods for copolymers include chain-growth and step-growth polymerization. Monomer structure and reactivity greatly influence the final copolymer properties, while different techniques like living polymerization and emulsion polymerization offer distinct advantages in copolymer production.

Types of Copolymers

Types of copolymers

Top images from around the web for Types of copolymers

• 

  Phase manipulation of topologically engineered AB-type multi-block copolymers - RSC Advances ... View original

  Is this image relevant?

• 

  Frontiers | Block Copolymer Synthesis by the Combination of Living Cationic Polymerization and ... View original

  Is this image relevant?

• 

  Fluorescent labeling of biocompatible block copolymers: synthetic strategies and applications in ... View original

  Is this image relevant?

• 

  Phase manipulation of topologically engineered AB-type multi-block copolymers - RSC Advances ... View original

  Is this image relevant?

• 

  Frontiers | Block Copolymer Synthesis by the Combination of Living Cationic Polymerization and ... View original

  Is this image relevant?

1 of 3

Top images from around the web for Types of copolymers

• 

  Phase manipulation of topologically engineered AB-type multi-block copolymers - RSC Advances ... View original

  Is this image relevant?

• 

  Frontiers | Block Copolymer Synthesis by the Combination of Living Cationic Polymerization and ... View original

  Is this image relevant?

• 

  Fluorescent labeling of biocompatible block copolymers: synthetic strategies and applications in ... View original

  Is this image relevant?

• 

  Phase manipulation of topologically engineered AB-type multi-block copolymers - RSC Advances ... View original

  Is this image relevant?

• 

  Frontiers | Block Copolymer Synthesis by the Combination of Living Cationic Polymerization and ... View original

  Is this image relevant?

1 of 3

• Random copolymers have monomers randomly distributed along the polymer chain without any specific sequence or pattern (styrene-butadiene rubber)
  • Monomer distribution depends on reactivity ratios and feed composition
  • Properties often intermediate between those of the constituent homopolymers
• Alternating copolymers have monomers that alternate in a regular pattern, such as ABABAB (maleic anhydride-styrene copolymers)
  • Formed when monomers have similar reactivity and are fed in equimolar amounts
  • Tend to have unique properties distinct from the constituent homopolymers
• Block copolymers are composed of distinct homopolymer segments (blocks) covalently bonded together (polystyrene-b-polybutadiene)
  • Can have various architectures, such as diblock (AB), triblock (ABA or ABC), or multiblock (ABAB...)
  • Blocks can be arranged linearly or in more complex structures like star or comb shapes
  • Microphase separation of incompatible blocks leads to ordered nanostructures
• Graft copolymers have a main polymer backbone with side chains (grafts) of a different monomer (polyethylene-graft-polystyrene)
  • Grafts can be randomly or regularly distributed along the backbone
  • Graft density and length influence properties like wettability and mechanical strength

Synthesis and Properties of Copolymers

Synthesis methods for copolymers

• Chain-growth polymerization involves the sequential addition of monomers to a growing polymer chain (free radical, ionic, coordination)
  • Initiated by reactive species like free radicals, ions, or organometallic complexes
  • Propagation occurs rapidly, with high molecular weights achieved in a short time
  • Termination occurs by chain transfer, combination, or disproportionation
• Step-growth polymerization involves the stepwise reaction of monomers with functional groups to form dimers, trimers, and eventually long polymer chains (polyesters, polyamides)
  • Monomers must have complementary functional groups, such as diols and diacids or diamines and diacids
  • Polymer growth occurs slowly, with high molecular weights achieved only at high conversions
  • No termination step; polymerization continues until monomers are depleted or equilibrium is reached

Monomer influence on copolymers

• Monomer structure affects reactivity and stability of the growing polymer chain (resonance, inductive effects, steric hindrance)
  • Electron-withdrawing groups (nitrile, ester) increase monomer reactivity
  • Bulky side groups (tert-butyl) decrease reactivity due to steric hindrance
• Monomer structure influences final copolymer properties like glass transition temperature ($T_g$), crystallinity, and mechanical strength
  • Rigid, bulky monomers increase $T_g$ and decrease chain mobility (bisphenol A)
  • Flexible, linear monomers decrease $T_g$ and increase chain mobility (ethylene glycol)
• Relative reactivity of monomers affects copolymer composition and sequence distribution
  • Reactivity ratios ($r_1 = k_{11} / k_{12}$, $r_2 = k_{22} / k_{21}$) quantify the preference of a growing chain to add the same or different monomer
  • $r_1 \approx r_2 \approx 1$ leads to random copolymers, $r_1 \cdot r_2 \approx 0$ leads to alternating copolymers

Copolymerization techniques: pros and cons

1. Living polymerization enables precise control over molecular weight and dispersity and allows the synthesis of well-defined block copolymers (anionic, cationic, ring-opening)

   • Pros: Low dispersity ($Đ < 1.1$), control over block length and sequence
   • Cons: Requires stringent reaction conditions (moisture- and oxygen-free) and high-purity monomers

2. Emulsion polymerization uses water as a dispersing medium to produce high-molecular-weight copolymers with low viscosity (styrene-butadiene rubber)

   • Pros: Environmentally friendly, efficient heat dissipation, low viscosity
   • Cons: May require post-polymerization purification to remove surfactants and other additives

3. Controlled radical polymerization (CRP) provides control over molecular weight, dispersity, and copolymer architecture (ATRP, RAFT, NMP)

   • Pros: Tolerant to impurities and functional groups, can be conducted in various solvents
   • Cons: May require specialized initiators or chain transfer agents, slower than conventional free radical polymerization