3
Tacticity
• Asymmetric carbons have alternate configuration• Methylene hydrogens are racemic• Polymer stays in planar zig-zag conformation
R R R R R R R R
R R R R R R R R
R R R R R R R R
Isotactic
• All asymmetric carbons have same configuration • Methylene hydrogens are meso• Polymer forms helix to minimize substituent interaction
Syndiotactic
Atactic
• Asymmetric carbons have statistical variation of configuration
5
Major Developments in the 1950-60's
Living Polymerization (Anionic)• Mw/Mn 1• Blocks, telechelics and stars available
(Controlled molecular architecture)• Statistical Stereochemical Control• Statistical Compositions and Sequences• Severe functional group restrictions
8
Good monomers for anionic polymerizations
. labile a-protonIn the polymers
steric stabilizing effect as well
14
1,4 trans content increases crystallinity, Tm > 25oC.1,4 cis content suppress crystallinity, low Tg (-110oC), Tm ~12oC; used for synthetic rubber
Solvent and Counter Ion Effect
26
Additional Developments in the 1980's
"Immortal" Polymerization (Cationic)– Mw/Mn 1.05– Blocks, telechelics, stars– (Controlled molecular architecture)– Statistical Compositions and Sequences– Severe functional group restrictions
35
OR
+HI
OR
IZnI
OR
IOR
OR
ZnI
+
-
OR
I
ZnI
OR
dormantspecies
OR
IOR
ZnI
ORreactivespecies
(irriversible)
Strategy: prolong the life time of cationic propagating species by reversible formation of dormant species. (Note: anionic propagating species has a much longer life time).
40
Free Radical Initiated Polymerization
• Controlled Free Radical Polymerization• Broad range of monomers available• Accurate control of molecular weight• Mw/Mn 1.05 --Almost monodisperse• Blocks, telechelics, stars• (Controlled molecular architecture)• Statistical Compositions and Sequences
42
Iniferter approach
Otsu et al 1982
hn
recombination
exhibit living characteristics at low conversion, but PDI is broad as 3 can also initiate polymerizations.
43
The Key Concept in Living Radical Polymerization
formation of dormant propagating species reduces
the effective polymeric radical concentration and hence
minimize termination reactions
R is a capping agent ∙and does not initiate
chain growth
PDI= Mw/Mn=1+qM0/Mn = 1+q/n(Poisson distribution PDI = 1+1/n, slide 25)
(Page 144, Hiemenz and Lodge)
44
Stable Free Radical Polymerization (SFRP)or Nitroxide Mediated Polymerization (NMP)
+ radical initiator (BPO, AIBN)
N
O
SFRP Initiator System (e.g., biomolecular or unimolecular)
47
State of Art for SFRP
•MW > 105, PDI = 1.1-1.2•High reaction temperature (125-145oC)•Long reaction time (24-72 hr)•Low to moderate conversion (<70%)•Limited scope of monomers: St, MA, MMA etc. •functionalized alkoxyamine is required for block or telechelic polymer synthesis
lower temperature(60-80oC), shorter
reaction time (several hrs) and higher
conversion (>99%) are desired
49
Atom Transfer Reversible Polymerization (ATRP)
Basic components: vinyl monomers, metal catalyst/ligand and initiator
Example:
most common
51
State of Art for ATRP
•MW > 105 easily, PDI = 1.1-1.6•reaction temperature (70-130oC)•Low to moderate conversion (<80%)•Tolerant of functional groups, wide scope of monomers: St, MA, MMA, acrylamide, vinylpyridine (VP), acrylonitrile (AN) etc. (acrylic acid, vinyl halide, vinyl ether, a-olefin cannot be polymerized) •Availability of a variety of initiator and catalysts. •block polymers and telechelic polymers are readily prepared.•metal contaminant is sometime less desired
52
Reversible Addition-Fragmentation Transfer Polymerization (RAFT)
SFRP (NMP) and ATRP involves reversible termination
RAFT involves reversible chain transfer
53
Reversible Addition-Fragmentation Transfer Polymerization (RAFT) Mechanism
Basic components: vinyl monomers, radical initiator and RAFT chain transfer agent.The number of growing chain is determined by both CTA and initiator content.
Stability can be
controlled by Z
group
54
RAFT Chain Transfer Agent
RAFT polymerizations are compatible with a variety of activated (St, MMA, MA etc.) or unactivated vinyl monomers (VAc, NVP). RAFT is versatile and robust as compared to SFRP and ATRP. But CTA agents need to be individually synthesized.
Design of CTA structures allows for control of the relative rate of addition and fragmentation steps
55
Ring Opening Metathesis Polymerization (ROMP)
[Ru] or [Mo] or [W]catalyst
2nd Gen. Grubb’s catalystSchrock’s catalyst
62
Ring Opening Polymerization (ROP)
metal-mediated reaction
organic-mediated reaction
Aliphatic Polyester synthesis
(Waymouth, Hedrick)
(Coates, Chisholm, Tolman/Hillmyer, Bourissou)
63
Polypeptide synthesis
Ring Opening Polymerization (ROP)
Polypeptoid synthesis
HN
O
nHN
O
O
O
R Initiators
initiators: RNH2 HNTMS2 (Cheng, 2007) Ni(bipy)(COD) (Deming, 1997)
-nCO2
NO
O
OR -nCO2
RNH2 N
O R
n
N
NN
O
O
O
R R
Rn-2
-nCO2
NHC NN
iPr
iPr iPr
iPrNHC
Zhang, 2010
64
Coordination Polymerization
• Stereochemical Control• Polydisperse products• Statistical Compositions and Sequences• Limited set of useful monomers, i.e. olefins
• SINGLE SITE CATALYSTS
Ziegler-Natta Polymerization (50-60’s)
65
Commodity Polyolefins
Polyethylene
Low Density (1939-1945)LDPE
Packaging Film, wire and cable coating, toys, flexible bottles, house wares, coatings
High Density (1954) HDPE
Bottles, drums, pipe, conduit, sheet, film
Linear Low Density (1975) Shirt bags, high strength films LLDE
66
Polyolefins• Polypropylene (PP, 1954)
• dishwasher safe plastic ware, carpet yarn, fibers and ropes, webbing, auto parts
67
Ziegler-Natta (Z-N) Polymerization
Radical polymerization is inefficient due to stable radicals from chain transfer
71
Single Site Catalyst 1990
Allows for production of elastomeric polypropylene (PP)
Waymouth 1995
atactic PP isotactic PPMAOMAO
72
Single Site Catalyst in 2000-olefinethylene
+
CTA
Allows for production of thermoplastic
elastomer
Arriola, Carnahan, Hustad, Kuhlman, Wenzel (Dow Chemical, Freeport, TX)
73
Acknowledgement•MIT OpenCourseWare: Synthesis of Polymers by Dr. Paula Hammondhttp://ocw.mit.edu/courses/chemical-engineering/10-569-synthesis-of-polymers-fall-2006/lecture-notes/•Note by USM Dr. Daniel Savin and Dr. Derek Pattonhttp://www.usm.edu/polymerkinetics/•Note by LSU Dr. Daly•Polymer Chemistry, 2nd edition, Hiemenz and Lodge•Principle of Polymerization, 4th edition, Odian•Polymer Chemistry, 4th edition, Pan, Zheijiang University
•“Functional Polymers via Anionic Polymerizations.” Akira Hirao, 1997 ACS Symposium Series.•“New Polymer Synthesis by Nitroxide Mediated Living Radical Polymerizations.” Craig Hawker, 2001, Chem. Rev. •“Atom Transfer Radical Polymerization.” Krzysztof Matyjaszewski, 2001, Chem. Rev.•“Copper(I)-Catalyzed Atom Transfer Radical Polymerization.” Krzysztof Matyjaszewski and Timothy Patten, 1999, Acc. Chem. Res.•“Toward Living Radical Polymerization.” Graeme Moad, Ezio Rizzardo, San Thang, 2008, Acc. Chem. Res.•“Living Radical Polymerization by the RAFT Process.” Graeme Moad, Ezio Rizzardo, San Thang, 2005, Aust. J. Chem.•“Living ring-opening metathesis polymerization catalyzed by well-characterized transition-metal alkylidene complexes.” Richard Schrock, 1990, Acc. Chem. Res.•“The Development of L2X2RuCHR Olefin Metathesis Catalysts: An Organometallic Success Story.” Robert Grubbs, 2001, Acc. Chem. Soc.•“Organocatalytic Ring-Opening Polymerization.” Robert Waymouth, James Hedrick, 2007, Chem. Rev.•“Controlled Ring-Opening Polymerization of Lactide and Glycolide.” Didier Bourissou, 2004, Chem. Rev.•“Synthesis of Well-Defined Polypeptide-Based Materials via the Ring-Opening Polymerization of α-Amino Acid N-Carboxyanhydrides.” Nikos Hadjichristidis, 2009, Chem. Rev.