Silicone Hydrogel Polymerization via Chain Transfer Agent
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Solution Overview
Problem
Current methods for producing silicone hydrogel contact lenses face challenges in consistently achieving desired physical and mechanical properties such as oxygen permeability, ion permeability, and modulus, due to issues with polymerization control leading to defects like cracks and voids, and high production costs.
Innovation Solution
A method involving a polymerizable fluid composition with a siloxane-containing macromer, a free radical initiator, and an organonitroxide, cured at elevated temperatures to produce silicone hydrogel materials with improved quality, reduced defects, and specific properties like oxygen permeability of at least 40 barrers and a modulus of 1.5 MPa or less.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If polymerization is performed at elevated temperature to increase productivity, then production speed improves, but polymerization control becomes difficult leading to defects such as cracks and voids
Solution Approach 1:
A chain transfer agent is introduced as an intermediary substance during polymerization to control the reaction at elevated temperatures. The chain transfer agent mediates between the high temperature conditions and the polymerization process, preventing uncontrolled runaway reactions while maintaining high production speed, and eliminating defects like cracks and voids that would otherwise form at elevated temperatures
2Manufacturing precision
If polymerization is performed slowly at low temperature to maintain material quality, then manufacturing precision improves, but productivity decreases
Solution Approach 1:
The polymerization parameters are changed by introducing a chain transfer agent that enables the reaction to proceed at elevated temperatures with controlled kinetics. This parameter change transforms the process from slow low-temperature polymerization to faster elevated-temperature polymerization while maintaining material homogeneity through the controlling effect of the chain transfer agent on reaction rate and heat generation
3Use of energy by moving object
If exothermic polymerization is performed without adequate heat dissipation, then energy efficiency improves, but temperature control becomes difficult leading to uncontrolled polymerization
Solution Approach 1:
The chain transfer agent acts as a mediator in the heat management of the exothermic polymerization process. It controls the reaction rate and heat generation, preventing thermal runaway while maintaining energy efficiency. The chain transfer agent ensures uniform temperature distribution by moderating the exothermic nature of the reaction, eliminating the need for complex cooling systems
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 method enables the production of silicone hydrogel contact lenses with consistent desired properties, reducing defects and production costs, while maintaining high oxygen permeability and ion permeability, and providing enhanced corneal health and comfort.
Implementation Method 1
a polymerizable fluid composition comprising (a) a siloxane-containing macromer with ethylenically unsaturated group(s), (b) a free radical initiator, and (c) an organonitroxide
Implementation Method 2
curing the polymerizable fluid composition at the elevated temperature in the tubes to form a polymer in a form of rod which is free of cracks and voids
Data Source
AI summary
The present invention provides a method and a formulation for consistently producing a silicone hydrogel material having relatively high oxygen permeability, relatively high ion permeability, and low modulus, and contact lenses prepared from a formulation of the invention or made of a silicone hydrogel material of the invention.