Phosphazenes as Fire Retardants in Aircraft Interiors

Harry Allcock, Catherine Ambler, Jonathan Taylor, Thomas Hartle, Clay Kellam, Robbyn Prange, Michael

McIntosh, Michael Coleman.Department of Chemistry and Materials Science and

EngineeringThe Pennsylvania State University

University Park, PA 16802Support, FAA (Dr. Richard Lyon)

Outline

• Why Phosphazenes for Fire Retardance?• Fire-proofing Polyurethanes• Block and Graft Copolymers for Fire-Resistant

Blends with Commercial Organic Polymers– Block copolymers– Polystyrene with pendent phosphazene units– Fire-resistant polynorbornenes by ROMP– Cyclolinear polyalkenes by ADMET– Polymers with phosphate side groups

• Conclusions and Future Directions

Why Polyphosphazenes?

• Side groups and skeletal architecture easily tailorable – wide range of properties

• Function through vapor and/or condensed phase fire retardance mechanisms

• Phosphorus plus nitrogen increases char yield

Three Types of PhosphazeneStructures for Fire Retardance

• Cyclic, small-molecule phosphazenes covalently bonded to an organic polymer

• Linear, high polymeric phosphazenes – Stand-alone use– Blends with conventional polymers

• Block Copolymers

Small-Molecule Cyclic Phosphazenes

NP

NPN

P

ORORRO

RO

ORORNaOR

NP

NPN

P

ClClCl

Cl

ClCl

RNH2

• Highly tailorable side groups, including functional groups for linkage to organic polymers

• Thermo-oxidatively stable• Applications include use as additives,

pendent functionalities, monomers for cyclolinear polymers

NP

NPN

P

NHRNHRRHN

RHN

NHRRHN

Polyphosphazene Synthesis

N P

Cl

ClN

PN

P

NP

Cl

ClCl

Cl

ClCl

N P

OR

OR

N P

NHR

NHR

250 °C

n

N P

OR

NR2

n n n

RO- Na+ HNR

2H NR2

RO- Na+

Living Cationic Polymerization

P N PCl3+PCl6

--

Cl

Cl

Cln Cl3P=NSiMe3 2 PCl5

n

• Polymerization of phosphoranimines• Molecular weight control through stoichiometry• Narrow polydispersities• Undergoes macromolecular substitutions• Living polymerization• Allows for synthesis of blocks, dendrimers, grafts, etc

Thermal Analysis Testing

Prototype Fire Resistant Materials

Oxygen Index (OI)Polyphosphazene

26

24

18

N P

nOC3H7

OC3H7

N P

nOC 4H 9

OC 4H 9

N P

nOC5H11

OC5H11

Prototype Fire Resistant Materials

32

43

46

59

Oxygen Index (OI)Polyphosphazene

N P OCH2CF3 OCH2(CF2)3CF2H

n

N P O Cl O Cl

Cl

n

N P O O Cl

Cl

n

N P O O

n

Phosphazene–Urethane Copolymers

+

- CO2

N=PO

O

n

COOH

COOH

N=PO

O

CO

NNH

CO

NH

n

H

COOH

OCN NH

CO

NH

Thermal Analysis

510122030

20202021.523

00.51.01.92.9

05102030

Char at 600o CLOI% Phosphorus% Phosphazene

Cyclic Phosphazene - Polyurethane Copolymers

PN

P

NP

N

OPhOHRO

OPhOH

OR

RO

HOPhO

+ OCNPh(OCH2CH2)nPhNCO

R = Ph, EtOEt,

PN

P

NP

N

OPhORO

OPhO

OR

RO

OPhO

C

C

C

ON

ONO

N

Ph

PhH

HPh

H

Cyclic Phosphazene-Polyurethane Copolymers

• Increased crosslinking ability

• Covalently bound, non-migrating

• Side group tailorablity

• Low cost

Thermal Analysis

Polyurethane + [NP(OPhOH)(OEtOEt)]3

0%10%

20%

Phosphinimine Chemistry

• Phosphinimine linkage -P=N-P-– Synergistic effects

• Polymerization of diphenyl-p-styrylphosphine– Free radical– Anionic– Wide range of copolymers possible

• Tailorability of phosphazene

Pendent Phosphazenes

N

PN

P

NP

OR

ORRO

RO

ORN

P

P

P

Toluene, AIBN

- N2

R = CH2CF3 R = C6H5

N

PN

P

NP

OR

ORRO

RO

ORN3

Acyclic Diene Metathesis (ADMET)

• Intermolecular metathesis of dienes

• Ethylene elimination favors high polymers

• Catalyst selection, reaction conditions very reactivity and polymer molecular weight

ADMET for Cyclolinear Phosohazenes

PNP

NPN

ClR

ClR

R R

PNP

NPN

RR

R R

Na+ -O+

O O

O CH2OR =

PNP

NPN

ClCl

ClCl

Cl Cl

O CH2Na+ -O+

Ring Opening Metathesis Polymerization

• Ring Opening Metathesis Polymerization –ROMP

• Metathesis of strained cyclic olefins

• Living polymerization

• Wide range of monomers available

Norbornene-Phosphazene Copolymers

N

PN

P

NP

OR

ORRO

O

ORRO

N

PN

P

NP

OR

ORRO

RO

ORO

Grubbs Catalyst

n

R = CF3CH2- (17)EtOOCPh- (18)CH3CH2- (19)Ph- (20)

Thermal Analysis

Thermal Analysis

Phosphorylated Phosphazenes

N Px

O

O

P

O

ORO

RO

P

O

OR

ORO

• Improve fire resistance of polyphosphazenes

• Immobilize fire retardant additive onto polymer backbone

• Functionalize side groups with phosphate derivatives

Prepolymer Synthesis

N P

Cl

Cl

N P

O

O

n n

N P

O

O

nN P

O

O

n

O

O

OH

OH

Na+-O O

- NaCl

BBr3

CH2Cl2

BBr3

CHCl3

Na+-O OCH3

OCH3

OCH3

- NaCl

Phosphorylation

ClP

O

OO

N P

O

O

x

OH

OHTHF

NEt3, CuCl

N P

P

O

OO

P

O

OO

x

O

O O

O

Polystyrene Additives

P NPNP

N

OO

O

OO

O

OO

O

O

O

O

PP

P

P

P

P

O

O

O

O

O

RORO

RORO

OROR

OROR

OROR

RORO

O

Trimer 2R = Ph

Trimer 1R = Et

Thermal Analysis

112

222428

102030

71217

192021

102030

4815

242625

102030

Trimer 2

TriphenylPhosphate

Trimer 1

1180----------% Char at 500 oCLOIWt %Additive

R = Et

R = Ph

Phosphazene Poly(ethylene oxide) Block Copolymers

R' (CH2CH2O)n CH2CH2NH2 + Br PR

RNSiMe3

R' = NH2 or CH3O R = OCH2CF3

-HBr

R' (CH2CH2O)n CH2CH2N(H)(R2P=NSiMe3)

CH2Cl2PCl5

R' (CH2CH2O)n CH2CH2N(H)[R2P=NPCl3+]PCl6

-

R' = NH(R2P=NSiMe3)R' = CH3O

Block Copolymers, Continued

R' (CH2CH2O)n CH2CH2N(H)[R2P=NPCl3+]PCl6

-

Cl3P=NSiMe3CH2Cl2

R' (CH2CH2O)n CH2CH2N(H)R2P[N=PCl2]m

NaOCH2CF3dioxane

R' (CH2CH2O)n CH2CH2N(H)R2P[N=PR2]m

R = OCH2CF3

Phosphazene-Styrene Block Copolymers

P N

R

R

P

R

R

P N

Cl

Cl

PCl3]+P N[Cl3

(Ph)2P=N

PPh2 P(Ph2)=NSiMe3

N P(Ph)2

n-Bu n-Bu

n-Bu n-Bu

1. nBuLi2. Ph2PCl

x

N3SiMe3

xx

2) NaR

1) 1/2

R = OCH2CF3

n-2

[PCl6]-

n

x x

Conclusions and Future Directions

• Phosphazene rings and polymer chains are highly effective fire retardant species

• They function by both vapor phase flame quenching and char formation

• A variety of options have been developed for the incorporation of phosphazene units into polymers both for stand-alone polyphosphazenes and material for blends and IPNs with normal organic polymers

• Future work will involve evaluation of the influence of the phosphazene components on physical properties and fire resistance of blends and IPNs, with a view for minimizing overall materials costs.