Find out about.......Plastics, Polymer Engineering and Leadership: High Performance Thermoplastic Selection - Part 2D: Liquid Crystal Polymers (LCP) and High-performance Polyesters (Polycyclohexylene terephthalate

Hello and welcome to Part 2D of my High Performance Thermoplastics Selection blog series.

Overview - 6 major high performance thermoplastics families (“the magnificent six”)

In this blog post series we discuss six major high performance thermoplastics families (“the magnificent six”) which are outlined in the following enumeration

1. Introduction to High Performance Polymers

2. Short profile of the "magnificent six" families:

-Part 2A: Polysulfides (Polyphenylene sulfide - PPS), Polysulfones (PSU, PESU, PPSU), and Polyarylates (PAR)

-Part 2B: Imide-Based Polymers (PEI, PAI, PESI, TPI, PI) and Polybenzimidazoles (PBI, PBI+PEEK, PBI+PEKK)

-Part 2C: Polyether (PPE)

-Part 2C: Polyether (PAEK, PEEK, PEKK)

-Part 2D: Liquid Crystal Polymers (LCP) and High-performance Polyesters (Polycyclohexylene terephthalate - PCT)

-Part 2E: Semi- and Fully Aromatic Polyamides (PARA, PPA, Aramid)

-Part 2F: Polyhalogenolefins (PTFE, PCTFE, FEP, PVDF, ECTFE)

3. Key properties and design data for selection

4. Polymer Material Selection 4-stage funnel methodology (POMS-Funnel-Method)

5. Examples for Ultra- and high performance polymer selection

Let's start with LCP.

1) Liquid Crystal Polymers (LCP)

1.1 Introduction

Liquid Crystal Polymers (LCPs) are a class of high-performance thermoplastics characterized by their ability to form ordered (liquid crystalline) structures in the melt phase. This molecular alignment leads to exceptional mechanical and thermal properties, even at elevated temperatures.

LCPs are considered super engineering plastics and are widely used in electronics, automotive, and precision components.

Discovery of LCP - Friedrich Reinitzer and Otto Lehmann

In 1888, Friedrich Reinitzer, an Austrian chemist and botanist, observed unusual temperature-dependent behavior in cholesteryl benzoate. He noticed it melted into a hazy liquid at one temperature and then became clear at a higher temperature, exhibiting color changes upon cooling before solidifying. Puzzled by these two melting points, Reinitzer sent his findings and the material to German physicist Otto Lehmann. Lehmann used a heated microscope to further investigate and identified the hazy liquid as a new state of matter with crystalline properties, which he named a "liquid crystal." While this discovery by Reinitzer and Lehmann around the turn of the 20th century generated initial scientific interest and the identification of nearly 200 similar compounds, practical applications were not immediately apparent, leading to a decline in research focus.

1.2 Chemistry and Production

Not to be overlooked is the fact that every LCP has a unique chemical structure. This implies that although the term "liquid crystalline polymer" refers to the overall set of features, each manufacturer of LCP may have unique chemical structures and this is similar to polyamides. For example, PA6 and PA 4.6 show significantly differing thermal resistance, yet they both absorb more water than polyesters and have poorer dimension stability. While each polyamide has a unique chemical structure that determines its different thermal resistance, the amide-bonding group determines the increased water absorption property.

Looking into the literature [1] of polymer chemistry, we can distinguish between

-Type I LCP (HDT a 1.82 MPa > 260°C),

-Type II LCP (HDT = 210-260°C), and

-Type III (HDT < 210°C).

All three types contain a p-hydroxybenzoic group and are called “thermotropic” LCP ( in contract to “lyotropic” LCP = liquid crystals can be seen in solvent as a solution). The crystals stay solid in the melt phase and can be modelled as matchsticks during the injection moulding filling process. Applying shear to the polymer will result in a very good alignment of the matchsticks.

LCPs are typically aromatic polyesters or polyester-amides, which are built from rigid rod-like monomers (e.g., hydroxybenzoic acid, terephthalic acid derivatives).

Polymerization via:

Melt polycondensation
Occasionally solution polymerization

Key structural feature:

Highly anisotropic molecular chains
Self-aligning during processing → liquid crystalline phase

Some more history on the commercialization of LCP - Example Xydar

Xydar Liquid Crystal Polymer (LCP) is a high-performance thermoplastic, commercially introduced by Dartco Manufacturing Company in 1984. It is notable as one of the first melt-processable aromatic polyesters, characterized by its ability to form ordered, rigid-rod structures in the melt phase, providing superior high-temperature performance (melting points > 300°C) and chemical resistance.

The technology originated from research in the 1970s, with Dartco (a subsidiary of Dart Industries) obtaining a license for production from Carborundum.

Composition: Xydar is a Type I LCP, generally based on a copolymer of p-hydroxybenzoic acid (HBA) and related monomers, designed for high heat distortion temperatures (HDT).
Industrialization (1984): Dartco launched Xydar as a commercial product, targeting high-heat applications. In 1985, Dartco licensed Xydar to Nippon Petrochemical, which after establishing the JX Nippon group is since 2021 on the market as Eneos LC. Eneos focus selling LCP in China (80%), Japan and rest of Asia.
Amoco Acquisition (1987): At the end of 1987, Amoco Chemical Company acquired the patent rights to Xydar from Dartco.
Further Ownership Changes: The product line was later part of Solvay Advanced Polymers and is currently associated with Syensqo (formerly Solvay).

Xydar was part of the first wave of commercial liquid crystal polymers in the mid-1980s (alongside Celanese’s Vectra in 1985).

1.3 Properties of LCP

Thermal properties: CUT vs. HDT of LCP

The short term temperature resistance of engineering polymers can be improved by adding glass-fiber reinforcement, however the long term temperature resistance stays on a similar level. This is different with high heat plastics such as PEEK, PPS, LCP, Polyarylates (PAR), Polysulfones (PSU, PESU, PPSU), and Polyimides (PEI, PAI, PI). They combine a high short- and long term thermal resistance. Figure 1 compares the Continuous Use temperature (CUT) to the Heat Deflection Temperature (HDT; short term temperature resistance) of high performance and engineering polymers. LCP has an excellent short- and long-term temperature stability.

Figure 1: Thermal properties of LCP - comparison of short and long temperature.

Dynamic Mechanical Analysis (DMA):

LCP has a high heat deflection temperature (HDT; e.g. LCP-GF30: 282 °C at 1.8 MPa) and continuous use temperatures (CUT) up to ~200–300°CLCPs do not have a “glass transition” temperature in the classical way of definition (Alpha temperature transition enabling the movement of more than 40 C-atoms in backbone [3]). They have a liquid crystal temperature. Figure 2 shows the DMA curves of PESU (amorphous; Tg = 220°C), PEEK (semi-crystalline; Tg=143°C; Tm =334°C), and LCP (Tlc = 300-380°C). LCP does not have a glass transition temperature, nor a melting temperature. It has a liquid crystalline temperature where the crystals remain solid, however the linkages between the solid crystals can move [1]. If you examine in detail the literature, a small transition temperature of LCP was found at 120°C. LCP can keep a high mechanical strength level up to 300 °C, outperforming PEEK and PESU.

Figure 2: Dynamic Mechanical Analysis (DMA) of LCP, PEEK, and PESU.

Mechanical properties

LCP has a very high stiffness and strength with a self-reinforcing effect and as an example is the relationship of wall thickness and tensile strength of LCP:

The skin layer's thickness of LCP is almost 200 μm and is a result of the strong orientation of the solid crystal elements (“matchsticks”). The ratio of the skin layer to the total thickness increases proportionately as the thickness decreases. The skin layer has strong mechanical properties since it is made up of highly aligned fibrous semi-crystals of stiff rod molecules. Because of this, LCP's strength will progressively rise as its thickness decreases. Figure 3 shows this relationship of a LCP, and comparing it to a PBT and PESU. This is a common and unique feature of LCP that isn't seen in traditional polymers.

Figure 3: Relationship of wall thickness and tensile strength of LCP.

Low creep and excellent fatigue resistance
Highly anisotropic properties (direction-dependent)
Excellent dimensional stability
Thermal conductivity

Figure 4 shows the thermal conductivity of LCP+PTFE, LCP+MF30, LCP+GF30, and LCP+CF30 [9]. The thermal conductivity increases slightly for glass fiber reinforced LCP.

Figure 4: Thermal conductivity of different filled LCP grades as function of the temperature [9].

Electrical: Very low dielectric constant and loss (Figure 5), making LCP ideal for high-frequency (5G, RF) applications.

Figure 5: Dielectric constant of different LCPs [9].

Chemical: Excellent chemical resistance
Low moisture absorption
Unique feature: Self-reinforcing behavior due to molecular orientation. Know how in part design and material selection is needed to unfold the full potential of LCP.

1.4 Processing Methods

Injection molding (primary method)
Extrusion (films, fibers)
Thin-wall molding capability
Very low viscosity in melt → high flowability
Key processing aspect: Properties strongly depend on flow direction and orientation

1.5 Applications

Electrical & electronics: Connectors, sockets, SMT components, Lead-free reflow soldering of LEDs
High-frequency electronics: 5G antennas, RF components
Automotive: Sensor housings, ignition components
Industrial: Precision gears, micro-components

1.6 Economic Aspects

Higher costs compared to standard engineering plastics

Cost is justified by:

Miniaturization capability
High performance in demanding environments
Often replaces metals or ceramics in niche applications

1.7 Suppliers / Trade Names

Major global LCP suppliers include:

Celanese – Vectra®, Zenite®
Toray – SIVERAS™
Sumitomo Chemical - SUMIKASUPER ™ LCP
Polyplastics - Laperos®
Syensqo - Xydar®

2) Polycyclohexylene Terephthalate (PCT)

2.1 Introduction

PCT is a high-temperature, semi-crystalline polyester belonging to the engineering thermoplastics family. It is structurally similar to PET and PBT but offers higher thermal resistance and hydrolysis stability.

It is often positioned as a high-performance polyester for electrical and automotive applications.

Discovery of PCT

PCT was developed by Eastman Kodak and introduced in the early 1950s under the trade name KODEL II. While similar in structure to Polyethylene Terephthalate (PET), PCT features a cyclohexylene ring within its structure. This modification gives it a higher melting point (approximately 285°C), and better hydrolysis resistance. In 1980, General Electric Co. commercialized extrusion-grade PCT for use in construction materials and high-strength panels.

While initial applications were in fibers, PCT gained traction as a specialized injection molding resin due to its superior heat performance and ability to remain dimensionally stable. PCTs have high initial whiteness which can be further modified by additives. This results in high reflective values (>95% @ 460 nm). Therefore, PCTs are good material candidates for LED applications, where high reflectivity, combined with luminosity retention over the product service life is needed.

Replacing thermoset Electric and Electronic applications is possible too.

2.2 Chemistry and Production

Polymer: Polycyclohexylene dimethylene terephthalate

Produced by polycondensation of:

Terephthalic acid (TPA)
Cyclohexanedimethanol (CHDM)

Structure:

Aromatic + cycloaliphatic backbone

→ Provides:

High rigidity
Improved thermal resistance vs PET/PBT, excellent chemical resistance, and high crystallinity.

2.3 Properties of PCT

Thermal: high-temperature form stability (up to 256°C shortly), high melting point (~285°C), and excellent resistance to reflow soldering (~255°C). Also, good long-term heat resistance.
Optical properties: Figure 6 shows the high reflectance values according ASTM E1331 of two Lavanta® HPP grades [10].

Figure 6: Optical properties (Reflectance) of Lavanta® High Performance Polyester [10].

Mechanical: High stiffness and dimensional stability (PCT-GF15 reach a tensile modulus of 7 GPa with a tensile strength of 70 MPa and 1.2 % tensile strain).
Good creep resistance
Chemical: Resistant to automotive fluids and cleaning agents.
Good hydrolysis resistance (better than PET)
Electrical: High dielectric strength and High CTI (comparative tracking index).
Moisture behavior: Low water and moisture absorption, resulting in stable properties. (water absorption after 24 hours is typically 0.057 %; ASTM D570)

Figure 7 shows an engineering comparison for typical unfilled, semicrystalline Polyesters which can be used during material selection.

Figure 7: Engineering comparison for typical unfilled, semicrystalline Polyesters (PET, PBT, and PCT) which can be used during material selection.

2.4 Processing Methods

Injection molding (main process)
Fast cycle times (good flow behavior)

Compatible with:

Glass fiber reinforcement (20–30%)
Flame-retardant formulations

2.5 Applications

Electrical & electronics: Connectors, switches, relays
Automotive: Sensor housings, connectors, interior components which require high reflectivity
Lighting: LED reflectors (color stability advantage)
Industrial: High-temperature components as well as filaments and fibers (industrial use).

2.6 Economic Aspects

More expensive than PET/PBT
Less expensive than LCP

Attractive for:

High-temperature polyester niche with re-flow soldering
Drop-in replacement for PBT in some cases
Replacement of thermosets

Short material selection guide

PET: choose when higher strength/stiffness is needed and managing processing in careful way is possible.

PBT: choose when the best molding productivity and a strong all-round property balance is needed.

PCT: choose when thermal margin, hydrolysis resistance, high reflectivity (LEDs) and dimensional stability at high temperature matter most.

2.7 Suppliers / Trade Names

Key suppliers include:

Syensqo - Lavanta®
Celanese – Thermx®
Eastman – Eastar®
SK Chemicals – SkyPURA®

LCP and PCT: Key Comparison Insight

Figure 8 compares LCP and PCT for having a quick overview on the main properties.

Figure 8: Comparison of LCP and PCT.

Practical selection guidance for LCP and PCT

Choose LCP when:

When very high flow, very thin walls, micro-molding, excellent dimensional accuracy, or high-frequency electrical performance is needed. LCPs are also attractive when self-reinforcing behavior and low CTE are beneficial, and when the design can tolerate or exploit anisotropy.

Choose PCT when:

When a high-temperature polyester with more conventional semi-crystalline behavior, strong chemical resistance, good electrical performance, and compatibility with standard injection molding practice is needed. PCT is especially compelling for electrical and automotive connector applications where solder resistance matters but LCP-level miniaturization is not mandatory.

Final Engineering Takeaway

LCP = highest flow, highest miniaturization potential, anisotropic performance, premium cost → Best for electronics, RF, precision parts

PCT = high-temperature semi-crystalline polyester, balanced connector material, easier substitution path from other engineering polyesters → Best for connectors, automotive, and electrical applications

Check out the other parts of this series too:

The 11 Functional Groups of Polymers — A Primer for Polymer Engineers

-Part 2A: Polysulfides (Polyphenylene sulfide - PPS), Polysulfones (PSU, PESU, PPSU), and Polyarylates (PAR)

-Part 2B: Imide-Based Polymers (PEI, PAI, PESI, TPI, PI) and Polybenzimidazoles (PBI, PBI+PEEK, PBI+PEKK)

-Part 2C: Polyether (PPE)

-Part 2C: Polyether (PAEK, PEEK, PEKK)

Thanks for reading & #findoutaboutplastics

Greetings,

Herwig

📚My Polymer Material Selection Book - Available Here

📊 Discover your Polymer Material Selection score by taking quick test here

🎥Join my YouTube channel community