Reactive Mesogens for High Birefringence and UV Stability
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Solution Overview
Problem
Reactive mesogens (RMs) used in optical components for liquid crystal displays (LCDs) face challenges in achieving high birefringence while maintaining polymerizability and resistance to yellowing under UV light, particularly due to the reactivity of tolane groups which are unsuitable for many optical applications.
Innovation Solution
Development of RM compounds with specific chemical groups such as terphenyl structures, which can be polymerized via UV photopolymerization, forming high-birefringence films with improved resistance to yellowing when exposed to UV light, using formulations that include solvents and additives for enhanced properties.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stress or pressure
If tolane groups are incorporated into RM compounds to increase birefringence, then high birefringence is achieved, but yellowing or degradation occurs upon light exposure
Solution Approach 1:
The patent changes the chemical structure parameters by replacing tolane groups with terphenyl groups and modifying the mesogenic core structure. This structural parameter change maintains high birefringence while improving UV stability and resistance to yellowing, as the new structure is inherently more stable under light exposure
Solution Approach 2:
The patent creates composite RM molecules combining terphenyl groups with specific mesogenic units and polymerizable groups. This composite structure integrates the high birefringence property of terphenyl with the stability required for optical applications, achieving both high birefringence and UV resistance simultaneously
2Stress or pressure
If reactive groups are added to achieve high birefringence, then polymerizability is improved, but stability under UV light deteriorates
Solution Approach 1:
The patent modifies the chemical composition parameters by selecting specific polymerizable groups (acrylate, methacrylate, vinyl, epoxide, oxetane) that are inherently more stable under UV light. These groups maintain reactivity for polymerization while being less prone to degradation, thus improving both birefringence and UV stability
3Stress or pressure
If specific chemical groups are incorporated to increase birefringence, then optical properties are improved, but suitability for UV photopolymerisation decreases
Solution Approach 1:
The patent designs RM molecules that are multi-functional: the terphenyl group provides high birefringence, the mesogenic unit ensures liquid crystalline behavior, and the polymerizable group enables UV photopolymerization. This universal design allows a single compound to satisfy multiple requirements simultaneously - high optical performance and ease of manufacturing through UV curing
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The RM compounds and formulations achieve high birefringence and resistance to yellowing, making them suitable for advanced optical and electrooptical components, including LCDs, with improved performance in UV stability and optical clarity.
Implementation Method 1
The compounds of formula I1 are suitable for preparing polymers by in situ UV photopolymerisation
Data Source
Figure 1
AI summary
The invention relates to reactive mesogens (RMs) comprising a terphenyl group, to mixtures and formulations comprising them, to polymers obtained form such RMs and RM mixtures, and the use of the RMs, RM mixtures and polymers in optical or electroopticat components or devices, like optical retardation films for liquid crystal displays (LCDs).