Oligomer synthesis

Synthesis of the all-aromatic ester-based reactive liquid crystalline oligomers end-capped with phenylethynyl reactive end-groups.1

DSC signals of the 5K oligomers series. First heat using a heating rate of 20 ºC/min.

Melt behavior of the oligomers

Thermal stability

Tg data were obtained from DMTA experiments and defined by the maximum of the E’’ peak.

Introduction

Thermal stability of the HBA/BP/TA(20)-9K cured thermosets, measured from room temperature to 600 ºC, under nitrogen atmosphere (red) and air atmosphere (blue), using a heating rate of 10 ºC/min.

Conclusions and future Work

Liquid crystal thermosets are a unique sub-set of high-performance polymers that combine desirable processing characteristics with outstanding thermo-mechanical properties after cure. LCTs are prepared via the so called reactive oligomer approach, where the oligomer backbone is terminated with latent end-groups that can react in a successive thermal post treatment step to form a network structure. In this work we have explored the most rigid, high Tg (~ 400 oC) LCT formulation known to data, i.e. based on 4-hydroxybenzoic acid (HBA), terephthalic acid (TA) and 4,4’-biphenol (BP).Herein we will discuss the thermo mechanical performance of these new polymers.

The reactive oligomer approach is an excellent method towards novel processable all-aromatic liquid crystalline polyesters based on all-para-substituted monomers (HBA/BP/TA).

High Tg (> 350 oC) and high thermal stability (Td5% (N2) > 475 oC) make this

class of polymers promising for demanding high-performance applications. All cured polymers show excellent storage moduli (E’) as function of

temperature and easily out performs PEKK. Melt and cure rheology analyses are in progress. One or two reactive oligomers will be selected and used as matrix in carbon

fiber reinforced composites.

Series 5000 g/mol - HBA/TA/BP• 60%/20%/20%• 50%/25%/25%• 40%/30%/30%• 30%/35%/35%

Series 9000 g/mol - HBA/TA/BP• 60%/20%/20%• 50%/25%/25%• 40%/30%/30%• 30%/35%/35%

75 150 225 300 375 450 525 6000

25

50

75

100

Wei

ght [

%]

Temperature [°C]

Air N

2

Thermo-mechanical behavior

Phase behavior

Nematic textures of HBA/BP/TA(25)-9K observed by polarized microscopy. A– Low viscous sample at 370 ºC during cure. B– Crosslinked sample at 550 ºC after the complete cure.

A B

5K Oligomers

Nitrogen Air

5% weight loss [ºC]

Char yield 595 oC [%]

5% weight loss [ºC]

HBA/BP/TA (20) 486 54 482

HBA/BP/TA (25) 490 50 475

HBA/BP/TA (30) 495 50 484

HBA/BP/TA (35) 487 49 475

9K Oligomers

Nitrogen Air

5% weight loss [ºC]

Char yield 595 oC [%]

5% weight loss [ºC]

HBA/BP/TA (20) 490 51 484

HBA/BP/TA (25) 497 53 484

HBA/BP/TA (30) 496 50 488

HBA/BP/TA (35) 491 48 486

5K OligomerOnset Temperature

[ºC]Peak maximum (TK-N )[ºC]

HBA/BP/TA (20) 252 311

HBA/BP/TA (25) 290 327

HBA/BP/TA (30) 301 328

HBA/BP/TA (35) 304 332

9K OligomerOnset Temperature

[ºC]Peak maximum (TK-N )[ºC]

HBA/BP/TA (20) 262 316

HBA/BP/TA (25) 306 346

HBA/BP/TA (30) 324 353

HBA/BP/TA (35) 328 363

100 150 200 250 300 350

20 25 30 35

Temperature [°C]

Exo

the

rm

KN

SamplesGlass Transition

Temperature Tg [ºC]

Storage modulus E’ at 300 ºC [GPa]

5K thermosets  

HBA/BP/TA (20) 378 0.65

HBA/BP/TA (25) 405 0.81

HBA/BP/TA (30) 419 0.79

HBA/BP/TA (35) 427  0.95

9K thermosetsGlass Transition

Temperature Tg [ºC]

Storage modulus at 300

ºC [GPa]

HBA/BP/TA (20) 357 0.59

HBA/BP/TA (25) 380  0.44

HBA/BP/TA (30) 425 1.5

HBA/BP/TA (35) 430 0.75

100 200 300 400 500

107

108

109

E' [

Pa]

Temperature (°C)

tan

E''

[Pa]

0,0

0,5

1,0

1,5

2,0

Representative DMTA scan for HBA/BP/TA(35)-5K. The experiment was performed under a N2 atmosphere using a heating rate of 2 ºC/min and a frequency of 1 Hz.

50 100 150 200 250 300 350 400 450100

101

102

103

104

105

106

107

108

109

1010

E' [

Pa]

Temperature (°C)

PEKK HBA/BP/TA(35)-5K

DMTA data showing HBA/BP/TA(35)-5K film (red) and a commercial available polyether-ketoneketone (PEKK) sample (black).

Aero

space

Eng

ineeri

ng

High Tg ester based liquid crystal thermosets:

synthesis and characterization

PhD Candidate: Martino MarchettiDepartment: ASMSection: Novel Aerospace MaterialsSupervisor: Prof. Theo DingemansPromoter: Prof. Theo DingemansStart date: 01-01-2013

1. Mazhar Iqbal, Theo J. Dingemans, European Polymer Journal, 2010, 46, 2174–2180.