Macromolecular and Morphological Characterization of Medical Grade PEEK Polymers

Anuj Bellare1, Kim-Phuong Le2, Shi-Shen Yau2 & Stephen Spiegelberg3

1 Brigham & Womens Hospital, Harvard Medical School, Boston, USA

2 Stryker Orthopaedics, Mahwah, NJ

3 Cambridge Polymer Group, Inc, Boston, MA

April 25, 2013

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Financial Disclosure

Anuj Bellare - None

K-P Le & S-S Yau Stryker Orthopaedics

S. Spiegelberg Royalties from Zimmer, Corin, Renovis,Iconacy, Conformis, Mako

3

Poly (ether ether ketone) - PEEK

Tg ~ 143C

Tm ~ 335-345C

Micrometer level structure - spherulitic

Nanometer level structure - lamellae

High ultimate tensile stress, high modulus

Carbon-Fiber reinforced PEEK ~ modulus of cortical bone

Application in trauma, orthopedic and spinal implants

4

Micro- and Nano-structure

IMPINGED SPHERULITES

L

Stack of Lamellae

5

Objective

To measure molecular weight distribution and characterize

semi-crystalline morphology of various grades of PEEK

6

Materials and Methods

Four medical grade PEEK polymers

PEEK-1, PEEK-2, PEEK-3, PEEK-4

Gel Permeation Chromatography Mn, Mw, Mz

Density Measurements (ASTM D792)

Differential Scanning Calorimeter (ASTM F2026)

Fourier Transform Infrared Spectroscopy (ASTM D2778-09)

Small Angle X-ray Scattering L, D

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Molecular Characterization

ID Mn [g/mol] Mw[g/mol] Mz g/mol] PIPEEK1 35,726181 114,026121 209,294808 3.19PEEK2 34,314194 108,352470 227,540958 3.16PEEK3 42,0741448 115,91386 210,3171654 2.75PEEK4 30,278683 74,426432 124,2971617 2.46

PEEK-3 had highest Mn

PEEK-4 had lowest Mn and lowest PI

Mn = NiMi/Ni

Mw = NiMi2/ NiMi

Mz = NiMi3/ NiMi2

PI = Mw/Mn

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Small Angle X-Ray Scattering

1

10

100

0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9

PEEK-1 PEEK-2 PEEK-3 PEEK-4

Inte

nsity

[cou

nts]

q [1/nm]

Long Period L = 2/d ~ Inter-lamellar spacing almost same for all PEEKs

L

One Dimensional Correlation Function

p(r) (1 / 22A) q2I(q)cos(qr)dq0

-0.02

0

0.02

0.04

0.06

0.08

0.1

0 5 10 15 20

PEEK-1 PEEK-2

PEEK-3 PEEK-4

r [nm]One

dim

ensi

onal

corr

elat

ion

func

tion

-2.0E-02

0.0E+00

2.0E-02

4.0E-02

6.0E-02

8.0E-02

1.0E-01

0.0E+00 2.0E+01 4.0E+01 6.0E+01

p(r)

r [nm]

origin base linebase line

dPdr

slope=

Qfit

L

O. Glatter, 1977

L

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Crystalline Morphology

ID L[nm] XDSC [%] D[nm]PEEK1 12.2 41.81.7 5.10.2PEEK2 12.3 47.81.3 5.90.2PEEK3 12.4 42.50.8 5.30.1PEEK4 12.3 52.20.9 6.40.1

L

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Crystallinity and Lamellar Thickness

0

10

20

30

40

50

60

20000 25000 30000 35000 40000 45000

Mn [g/mol]

% C

ryst

allin

ity

0

1

2

3

4

5

6

7

Lam

ella

r th

ickn

ess [

nm]

XIR

Xdensity

Xdsc

Lamellarthickness

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Summary

All medical grade PEEK resins showed relatively small differences in molecular weights and morphology

PEEK-4 had the lowest Mn and highest crystallinity

Differences in crystallinity associated with differences in lamellar thickness

Consistent trend in crystallinity obtained from DSC, FTIR and density

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Future Work

Micrometer scale morphology Low voltage SEM

Alter crystallization conditions (nucleation/crystal growth)

Correlate crystalline morphology on the nano- and micro-scale with macroscopic mechanical properties

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