Trinseo : Cultivating a Circular Transformation

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Our Sustainability Strategy

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OUR CORE VALUES

At Trinseo, we believe in the power of ideas. We test the limits and break new ground to bring innovative solutions to life. We strive to help our industry cultivate a circular economy by shaping how we think about operations, product innovation, safety, and procurement.

Sustainability is intrinsic to who we are and what we do each day. As a global company, we have the customer base, network connections and technologies to deliver sustainably advantaged solutions that drive innovation. We are inspired every day by the challenges we help our customers solve through collaboration across our value chain partners, industry peers and other stakeholders. Our commitment to sustainability shapes everything we do and is embedded throughout our culture and business strategy.

Our success is founded on decades of experience in diverse material solutions that address our customers' unique challenges. Our worldwide network of local, agile teams can meet the needs of our global customer base across a variety of end markets, including automotive, consumer electronics, appliances, medical devices, packaging,

footwear, carpet, paper and board, lighting and building and construction. As we prepare for anticipated regulations for sustainability reporting and manufacturing, our processes continue to evolve in preparation, so our company and our customers are ready to make the transition. With the landscape of sustainability reporting continuing to shift, and to align with stakeholder priorities, we have centered our Core Impact Report around Trinseo's influence on the Environment, Economy and Society.

We are guided by our Sustainability Goals and our company's Core Values. Together, they set the foundation for our daily work, and have helped set the path forward for our sustainability strategy. Our vision, values and commitment to sustainability are our promise to conscientiously maintain ethical standards for everything we do and how we do it. By innovating not only our products but also how we approach materials solutions, we are helping to achieve a brighter tomorrow.

Throughout our Core Impact Report, we will showcase how Trinseo delivers on our promise to be a leader in Plastics, Engineered Materials and Latex Binders innovation to provide extraordinary value for our stakeholders and reduce our impact on the planet.

RESPONSIBLE CARE®	RESPECT & INTEGRITY	ACCOUNTABILITY
As a Responsible Care® company, we consider	We treat each other, our customers and	& VALUE CREATION
the health and safety of our employees and	our stakeholders with respect and dignity.	We believe that speed and agility combine
the protection of our communities to be our	We conduct all business activities with
with good decision-making to create
highest priorities. We strive to meet or exceed	the highest ethical standards and are
value. We feel ownership and take
the highest standards of environmental,	fully committed to complying with the
accountability for our company's success.
health and safety performance.	laws in the countries we operate.

INNOVATION	COMMITMENT TO CUSTOMERS
We believe that innovation through	By collaborating with our customers,
our technology and the creativity of our	we deliver value through our technology,
people powers our achievements and	innovation and solutions. While Trinseo is a
drives the success of our customers.	global company, we prioritize collaboration
	on a local level with our customers to provide
	bold solutions to their legacy challenges.

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Our 2030 Sustainability Goals

Trinseo's Sustainability Goals help our company cultivate a future driven by environmental stewardship, a sustainable workforce, responsible operations and value chain partnerships. Our goals are purposely strategic, ambitious and, yet, achievable. By utilizing our culture of discipline and science in setting and achieving these goals, we have set a strategic foundation for our sustainability roadmap.

In 2023, our Sustainable Workforce goals evolved to better meet the needs of the communities we work in and the employees we serve. While our goal for safety remains, we have expanded our workforce goals so they better reflect our strategy for recruiting, attaining, developing and retaining a diverse and talented workforce.

More details about our sustainability goals can be found at Trinseo.com/Sustainability.

CLIMATE CHANGE

By 2035, reduce by 35% Scope 1 & 2 GHG emissions1-2 intensity (2017 base year)

By 2030, increase the share of electricity from non-fossil sources3 from 5% to 30% (2017 base year)

By 2025, establish a management system for Scope 3 emissions4, and begin reporting and tracking Scope 3 emissions

SUSTAINABLE PRODUCT PORTFOLIO

By 2025, 30% of Trinseo's technology and R&D efforts will be aimed at circular economy solutions

By 2030, 40% of Trinseo's products will be sustainably advantaged5

By 2030, 50% of Trinseo's products will be used in applications that align with the United Nations Sustainable Development Goals

SUPPLIER RESPONSIBILITY

• By 2025, implement a Sustainability/CSR Due Diligence program for new key suppliers as an addition to the existing supplier on-boarding process
• By 2030, 80% of our existing suppliers with recurring spend of
  >$100K will be assessed and demonstrated to be compliant with our sustainability requirements

RESPONSIBLE OPERATIONS

• By 2030, reduce freshwater intake by 20%
• By 2030, reduce overall waste generation by 15%
• By 2030, reduce waste disposal to landfill to zero
• By 2030, all pellet-handling sites achieve zero pellet loss to the environment through Operation Clean Sweep®

SUSTAINABLE WORKFORCE

• By 2030, have 40% of management positions filled by women globally and increase the number of roles filled by underrepresented ethnic groups in the U.S.
• By 2030, achieve one or more years where the voluntary turnover rate for women is equal to or less than the global turnover rate.
• By 2030, establish talent programs to spotlight, develop and promote women and underrepresented racial and ethnic groups.
• By 2030, develop an enterprise-wide strategy to measure, understand and respond to employees' sense of inclusion, belonging and engagement.
• By 2030, achieve one or more years of zero recordable injuries for employees and contractors globally.

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1. Scope 1 GHG Emissions are direct emissions from owned or controlled sources.
2. Scope 2 GHG Emissions are indirect emissions from the generation of purchased energy.
3. Non-FossilSources refers to nuclear and renewable sources, such as solar, hydraulic, wind and tide.
4. Scope 3 GHG Emissions are all indirect emissions that occur in a company's value chain, including upstream and downstream emissions.
5. Sustainably Advantaged is defined as products that have recycled, renewable or degradable content contributing to a circular economy model; have reduced/eliminated raw material substances of concern; or contribute to GHG emission reduction or material intensity reduction.

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Our Intrinsic Value

INPUTS

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OUTPUTSOUTCOMES

FINANCIAL

$3,029.2 million total assets

Mission & Vision

$3.7 billion net sales

Our business strategy and investments continue to evolve as our company transforms into a specialty material and sustainable solutions provider. We are focused on maintaining a strong financial position with appropriate financial flexibility and liquidity, while continuing to prioritize

As a global specialty materials solutions provider, we empower our customers' bold, creative ideas by bringing them to life in smarter, more sustainable ways. Through our premier expertise and best-in-class materials, we unlock value for companies and consumers alike by taking big ideas and turning them into impactful innovations. Our commitment to sustainability shapes

OUR VALUE CREATION PROCESS

Trinseo's Value Creation Chart shows how we take in, create and transform value as a company focused on Environmental, Economic and Social. The chart uses an Integrated Reporting framework to illustrate how Trinseo delivers value to our stakeholders, which

is guided by our mission, vision and principles and impacted by societal trends, risks and opportunities.

$47.4 million year-over-year increase in cash balance

OPERATIONS

34 manufacturing plants

1 recycler

$69.7 million capex

Core Values

$154.3 million Adjusted EBITDA1

B score on Climate Change Score from CDP

1 program for Supplier Scope 3 GHG emissions

2 new Trinseo facilities joined Operation Clean Sweep®

growing margins and reducing earnings volatility through organic investments, strategic acquisitions or investments, as well as divestitures of businesses less suitable to our portfolio.

As our company continues to transition to a specialty, sustainable solutions provider, we are focused on reducing the environmental impact of our operations. Operation Clean Sweep® is fundamental to this, as we continue to incorporate additional facilities into this industry association effort to reduce plastic pellets lost to the environment.

Additionally, we worked with our suppliers to implement a Scope 3 emissions program to regularly

everything we do and is embedded in our culture and business strategy.

Our stakeholders know we embrace their innovative ideas and deliver value in many ways. This includes, but is not limited to:

FINANCIAL: Our economic merit comes from the profit we generate, but also the value that we deliver to our employees and stakeholders.

OPERATIONS: Consisting of our facilities, supply chain and customer relationships, Trinseo's operational value is defined

9th year as a member of Operation Clean Sweep®

INNOVATION

+40% technology and R&D efforts

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0 reportable loss of plastic pellets or flakes to the environment

3 Responsible Care® awards

122kT of sustainably advantaged materials sold

exchange information with our most critical suppliers to get better insight into their sustainability metrics, decarbonization strategy and sustainable portfolio. We continue to proactively develop and manage supply chain relationships through our Supplier Code of Conduct and Corporate Procurement Policy to mitigate supply chain risk and deliver sustainability of sourced goods.

• Delivering solutions that help our customers improve their end products but also reshape the world forever.
• Encouraging growth in our employees through mentorship, professional development and training opportunities that foster workforce talent and leadership advancement.
• Contributing to the regions where we operate as a responsible partner.
• Helping to cultivate a circular transformation by advancing our sustainability goals, which include expanding our recycling technologies to incorporate more recycled feedstocks and increasing our renewable and clean energy sources.

by how we generate satisfaction throughout the value chain.

INNOVATION: Trinseo's sustainably advantaged portfolio helps solve our customers' challenges and support their goals. Innovation incorporates both economic and environmental value through our delivery of tailored, creative solutions.

PEOPLE: We deliver value to our employees and the communities they live in through our dedication to equitable representation, professional development, social responsibility, safety and ultimately, performance.

ENVIRONMENT: We recognize that it is our responsibility to reduce our impact on the environment and institute practices that safeguard our ecosystem.

For more information about these topics, reference our 2024 Sustainability and Corporate Social Responsibility Report at Trinseo.com/Sustainability.

dedicated to circular economy solutions 11 R&D centers

2 new recycling technologies

2 scientific tools for environmental impact assessment

PEOPLE

63,430 hours of employee training

2 new Occupational, Health and Safety trainings

4 enhanced Sustainable Workforce goals

3 new Employee Resource Groups

ENVIRONMENT

18% of electricity sourced from renewable energy

11% of electricity self-generated through nuclear energy

425 GW electricity usage

1,392 TCM water consumed

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Societal Trends

Risks & Opportunities

1 new Latex Binders partnership announced

10 new ALTUGLAS™ and PLEXIGLAS® R-Life grades using mechanically and chemically recycled feedstocks

100% of Plastics & Latex Binder solutions have PCF calculations

30% of leadership roles filled by women

0.30 injury rate

1,574 employees earned Triple Zero Awards

6,001 hours of community service impacting communities where employees live and work

464,000 MT GHG emissions for Scope 1 & 2

10% decrease in total waste

30% reduction of water consumption

35,004 MT materials recycled (diverted from landfill)

Innovation and sustainability go hand-in-hand at Trinseo. We bring sustainably advanced solutions to life without compromising on performance. In 2023, we expanded our recycling technologies to pilot our polycarbonate (PC) dissolution and polymethyl methacrylate (PMMA) depolymerization facilities. By investing in R&D and expanding our recycling capabilities through our recycling facility, we can help contribute to a circular economy that advances closed loop manufacturing.

Trinseo is made up of difference-makers,self-starters, hard workers, forward thinkers and conscientious teammates who ignite ideas and inspire others. As we continue to prioritize an inclusive culture, we evolved our Sustainable Workforce goals to better meet the needs of the communities we work in and the employees we serve. While our goal for safety remains, we have expanded our workforce goals so they better reflect our strategy for recruiting, attaining, developing and retaining an inclusive and talented workforce.

We continue to commit to exceptional safety standards through proven training programs, and successfully implemented Fall Prevention and Line of Fire trainings.

In 2023, Trinseo began implementing its decarbonization strategy to address our Scope 1 and 2 emissions and calculate Scope 3 GHG emissions. Our facilities worked with the Procurement team to assess on-site opportunities for physical renewable energy supplies, which resulted in the installation of solar panels at our Hamina, Finland, facility in 2024. Additionally, our facilities also identified and completed Scope 1 reduction projects.

1. For a reconciliation of Adjusted EBITDA, which is a non-GAAP measure, to Net Income, see the About This Report section of the Sustainability Report.

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Delivering Financial Value to Our Stakeholders

BUSINESS UPDATES

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Trinseo's business strategy and investments focus on evolving our company into a specialty material and sustainable solutions provider-one that brings value to our customers, investors, employees and other stakeholders. By leaning into our premier expertise and best-in-class materials, we are poised to meet evolving market demands and our customers' unique needs.

Our company is focused on maintaining a strong financial position with appropriate financial flexibility and liquidity. To that end, we employ a disciplined approach to capital allocation and deployment of cash that strives to balance the growth of our business, and continued cash generation, while providing shareholder returns.

In 2023, Trinseo generated a $47.4 million year- over-year increase in our cash balance and saw the benefit of our previously announced asset restructuring, targeted inventory control and other initiatives. We continue to have access to capital resources. With the successful refinancing of our existing debt structure, we do not have any significant debt maturing until May 2028.

Amid uncertain market conditions, including a volatile geopolitical landscape and continued persistent underlying demand weakness, sustainability remains a key focus area of our long-term business strategy and an area where we are dedicated to growth. While we expect the costs of administering our sustainability program to increase as we continue to progress toward our goals and improve our sustainability initiatives and reporting, we remain firm in our commitment to this strategy.

Our employees and business teams play a critical role in creating our longer-term strategies for growth, including product and application development, new customers, technology strategy and investments and acquisitions.

As we look ahead to 2024, there are anticipated regulations within our industry and those we serve that will significantly shift how we address climate change and sustainability reporting. In preparation, we continue to actively monitor legislative changes that might affect our operations and end markets.

Trinseo's 10-K

Proxy Statement

We continue to focus on growing margins and reducing earnings volatility through organic investments, strategic acquisitions or investments, as well as divestitures of businesses less suitable to our portfolio.

Beginning in December 2022 and continuing through 2023, Trinseo implemented an asset restructuring initiative designed to reduce costs, improve profitability and reduce our exposure to cyclical markets and elevated natural gas prices. As part of this ongoing process, Trinseo closed its Terneuzen, the Netherlands, styrene plant in November 2023. With this closure, we no longer produce styrene and will purchase all necessary styrene from third parties. This decision will not only reduce our company's exposure to commodity volatility but will also lower our Scope 1 and 2 greenhouse gas emissions.

actions to transform our company into a higher growth, higher margin and less cyclical specialty and sustainable materials provider. In March 2024, we announced that we commenced a sale process for our 50% ownership in Americas Styrenics LLC ("AmSty"), a joint venture with Chevron Phillips Chemical Company LP, which is expected to ultimately lead to a sale of our interest no later than early 2025.

As we continue to evaluate opportunities that will help us transform into a specialty materials and sustainable solutions provider, we are leveraging the expertise and network of our recycler, Heathland B.V., to expand our recycling capabilities.

In April 2023, we announced the inauguration of a polycarbonate (PC) dissolution pilot facility in our Terneuzen, the Netherlands plant, which will manufacture recycled

NET SALES BY END MARKET	SALES VOLUME (KT)
9% Appliances
19% Automotive
22% Building & Construction / Sheet	2,106
5% Textile
1,915
3% Consumer Electronics	1,670

7% Packaging

5% Graphical Paper

7% Styrene / MMA Related

11% Board & Specialty Paper

12% Other

Additionally, Trinseo continues to evaluate strategic alternatives to divest all or a portion of our Styrenics business, which includes the Polystyrene and Americas Styrenics reporting segments. Separating the Styrenics business remains an integral part of Trinseo's transformation strategy, and we continue to evaluate

polymers. Eight months later, we announced the groundbreaking of our polymethyl methacrylate (PMMA) depolymerization facility at our Rho, Italy, facility. These announcements represent an important step in realizing our sustainability goals and helping

to cultivate a circular transformation within our industry.

2021

2022

2023

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Building Our Sustainable Operations

HUMAN RIGHTS & MODERN SLAVERY

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Trinseo's dedication to operating responsibly is integral to our business model. Every day, our ethical, responsible business practices empower us to improve our social and environmental impact throughout

the value chain. By leaning into our expertise and innovation, we are poised to meet evolving market demands while operating with excellence.

As we continue to advance our decarbonization strategy, we are exploring the implementation of clean energy sources and the expansion of our green energy certificates to more regions. We are evaluating our facilities for onsite physical projects and exploring offsite partnerships as part of our clean energy sourcing opportunities to reduce our Scope 2 greenhouse gas (GHG) emissions.

Our decarbonization strategy focuses on managing our Scope 3 GHG emissions. As a first step, we completed gathering our Scope 3 GHG emissions data in 2023 and are undergoing third-party validation. Additionally, since our Scope 3 emissions originate from the GHG emissions throughout our value chain, a critical component of our management plan is buy-in from our employees, suppliers and value chain partners.

In 2023, we launched theTrinseo Sustainability Academyfor internal trainings and external webinars with our company experts. Our internal trainings focused on increasing employee awareness of carbon emissions and sustainable procurement topics with development available at various levels. As part of our implementation strategy, we have established an annual training program focused on GHG emissions and sustainable procurement practices, metrics and strategies. While compulsory for all procurement, sales and supply chain employees, it is open to anyone on our workforce interested in the topic.

For external audiences, our Sustainability Academy connected industry professionals with Trinseo experts and our partners, such as EcoVadis, Eviden, Coexpan, Grupo Lantero and MEO. We covered topics such as Scope 3 GHG emissions and procurement, sustainability plastics solutions, mass balance and more. One of the main focuses of our external webinar series was a supplier engagement program, where we regularly exchange information with

our most critical suppliers to gain insight into their sustainability metrics, decarbonization strategies and sustainable products. Through these webinars, we facilitated the sharing of best practices with our broader supply base.

ETHICS & COMPLIANCE

Ethics and regulatory compliance underpin our approach to business, empowering responsible business practices that respect people, communities and the environment. This approach is intrinsic to our legacy of business excellence.

We hold ourselves to the highest standards of ethical behavior, and we expect the same from our people. Therefore, it is our policy that all Trinseo employees be lawful, highly principled, and socially responsible in business practices. Employees are expected to learn and comply with all corporate policies and laws applicable to their job responsibilities, and we provide extensive training and resources to make employees aware of these expectations, as well as mechanisms to report concerns relative to ethics and compliance. Key elements in this process include executive oversight, protection of those reporting potential violations, employee training resources, and an ethics and compliance hotline.

Our Code of Business Conduct lists our core values, outlines employees' accountability and provides key ethical principles and policies to assist employees in conducting business around the world. The code is designed as a supplement to the existing Trinseo policies and standards as well as the laws, rules and regulations in the countries in which we do business. Trinseo's Code of Business Conduct is extended to our suppliers through Trinseo's Supplier Code of Conduct.

Code of Business Conduct

All people deserve respect for their inherent dignity, rights and ambitions. This truth is foundational to our business excellence. Trinseo is committed to improving our practices to combat slavery and human trafficking in our supply chains or businesses. We have zero tolerance for slavery and human trafficking. Our policies reflect this commitment to acting ethically

in our business relationships.

Labor and Human Rights are key priorities for our business and stakeholders. We have due diligence processes in place to identify

and mitigate the risk of human trafficking, including a specific training program for relevant staff.

Furthermore, we are dedicated to combatting unlawful labor and child exploitation by adhering to all applicable child labor laws and regulations. We closely monitor hours of work, rates of pay and benefits to confirm compliance with applicable laws and regulations.

Trinseo's Procurement team checks for modern slavery abuses in its supplier screening via our partnership with Beroe, EcoVadis ratings and our integrated risk management tool.

Labor and Human Rights

Pellet loss to the environment is a critical issue for the plastics industry. Approximately 100 million spilled pellets reportedly enter waterways each year, posing a deadly threat to birds and marine animals. As a member of Operation Clean Sweep® (OCS) since 2014, Trinseo is committed to combatting pellet, flake and powder loss.

Recent increases in global focus placed on this issue have prompted the expansion of OCS, with support from the plastics industry. In early 2023, Plastics Europe launched the first European pellet loss certification scheme to strengthen OCS by harmonizing processes and procedures for controlling and documenting pellet loss across the plastics supply chain.

Trinseo prepared for these new European OCS certification requirements by introducing two new Trinseo facilities to the OCS program and completing internal gap assessments at all of our European pellet-handling sites. These additional measures supplement the pre- existing OCS management system at our facilities, which leverages a database of best practices to address areas at risk of potential losses. We also use quarterly meetings as an opportunity to review best practices, program improvements and equipment updates. Our European sites are preparing for certification in 2024.

In addition to the new facilities, we celebrated 13 sites reaching level four of the OCS program, which was our target for 2023. This level is designated within the program as advanced, indicating most requirements have been adopted. These sites signed

the OCS pledge in recognition of this achievement, with many hosting signing events to include employees.

We also expanded and refined our practices to better protect the environment and save valuable resources, including the installation of basket strainers, sieves, filters and other measures at key areas with pellet loss potential.

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Delivering Value Through Innovation

MEETING OUR SUSTAINABILITY GOALS

Our Operational sustainability goals are important to our stakeholders and remain a top priority for our company. Our Supply Chain and Procurement teams continue to advance efforts with our Sustainability/CSR Due Diligence program to help preferentially

select suppliers who mirror our commitment to ethical conduct, global corporate social responsibility and sustainability. We increased our collaboration with EcoVadis in 2023 to analyze and evaluate our suppliers using the EcoVadis platform. We have now assessed 90% of our top direct suppliers on key sustainability attributes that are standardized in the Trinseo Supplier Code of Conduct.

We continue to evaluate suppliers against policies and procedures such as the Supplier Code of Conduct and Corporate Procurement Policy. In 2023, we published an updated version of our Supplier Code of Conduct. This latest version features enhanced language and expanded topics, including Scope

3 GHG emissions and anti-corruption due diligence. These adjustments were made at the recommendation of Trinseo's Internal Audit team and shared with all suppliers.

Additionally, we continue to contract Beroe, Inc. to analyze records related to financial checks, anti-corruption, sanctions and due diligence records, EcoVadis business sustainability ratings, and health and safety alerts to evaluate our suppliers based on compliance with Trinseo's sustainability requirements.

As a long-standing member of Operation Clean Sweep®, we are committed to taking a leading role in addressing this core issue in the plastics industry. By 2030, we aim to have zero pellet loss to the environment at all of our pellet- handling sites.

Supplier Code of Conduct

Competition Law

Compliance

International Trade Policy

At Trinseo, our portfolio of diverse solutions combines innovation and sustainability to bring ideas to life. Our solutions drive success in several high-growth end markets, including the building and construction, medical, consumer goods and mobility industries. We strive to make solutions that are sustainable, without compromising on the performance or quality of our materials.

Knowing that our solutions are intrinsic to our customers' success, our approach to innovation incorporates sustainability regulations while aligning with global trends. As a result, our materials can be found in sustainable packaging, light-weighted cars, sustainable housing materials and critical medical devices.

Our customers and their end-users continue to demonstrate their interest in circular and sustainably advantaged solutions. In 2023, Trinseo sold 121.8kT of sustainably advantaged materials, which equates to 6.8% of all our portfolio sales that year. As we continue to evolve our sustainably advantaged solutions, access to high-quality waste streams remains a top priority. Trinseo's Heathland B.V., a leading collector and recycler of plastic waste in Europe, positions us to supply the necessary recycled feedstocks to our business units and provide our customers with sustainably advantaged solutions that they can count on.

Furthermore, Trinseo has expanded our scientific tools to track our environmental impact through Life Cycle Assessments (LCA) and Product Carbon Footprints (PCF), so we can consider how our products may impact customers, end users and the environment.

Developing solutions while relying less on fossil fuels and reducing our carbon footprint is essential to our innovation. This is a driving force behind our R&D efforts, as our business units collaborate to achieve our 2030 Sustainability Goals. Trinseo's R&D team continues to exceed our goal of investing more than 40% of our efforts in advancing circular economy solutions. Our Plastics Solutions, Polystyrene, Feedstocks, Latex Binders and Engineered Materials business units will continue to support our customers by investing in technology, research and partnerships that drive sustainable change. Their work has successfully introduced solutions that meet the unique needs of our customers and advance sustainability, including:

• Growth of our recycling technologies
• Expansion of sustainably advantaged solutions, including bio-based product lines and recyclate-containing materials
• Introduction of compostable materials

Our sites also regularly receive certifications that validate the sustainability claims of our solutions, demonstrating our greater commitment to providing value to our customers. Trinseo's Zhangjiagang plastics plants in China received ISCC+ certification for the mass balance approach to bio, bio-circular and circular acrylonitrile butadiene styrene (ABS).

WHAT IS MASS BALANCE?

The ISCC+ mass balance approach has become the recognized standard for tracking inputs and outputs when mixing sustainable and non-sustainable materials in the same production process. It is a chain of custody method to track sustainably advantaged materials through complex value chains and attribute it

to the finished goods. It is a scientific methodology applicable to and widely used by many industries.

DNV BUSINESS

ASSURANCE ITALY VALIDATES ENVIRONMENTAL CLAIMS

DNV Business Assurance Italy, an independent assurance and risk management company, visited Trinseo's Rho, Italy, plant to validate environmental claims for R-Life PMMA resins against the ISO14021 standard for recycled content. The successful verification means Trinseo is complying with requirements of the internationally recognized standards, and the Company's self-declarations are accurate.

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TRINSEO REIMAGINES RECYCLING

WITH DEPOLYMERIZATION AND

DISSOLUTION FACILITIES

As part of our ongoing commitment to sustainability, in 2023, we piloted our polycarbonate (PC) dissolution facility in Terneuzen, the Netherlands, and broke ground on our polymethyl methacrylate (PMMA) depolymerization plant in Rho, Italy.

Dissolution is a physical recycling process where the needed polymer is extracted using solvents. The extracted polymers are used as raw materials to make recyclate-containing solutions. Trinseo's dissolution technology takes pre- or post- consumer materials containing PC-such as a vehicle part or electronic device that contains other plastics, metal or even glass-and puts them directly into the solvent with little to no pre-treatment. The solvent dissolves the PC contained within those end-of-life parts while the non-PC materials remain, allowing them to be processed using other recycling methods. The extracted PC is 100% recycled and can be used for compounding into new materials for an array of applications, such as mobile phone casings, printer enclosures or automotive parts.

Depolymerization is a chemical recycling technology complementary to traditional mechanical recycling processes, which returns the polymer to its constituent monomer, methyl methacrylate (MMA). This enables recycling of a wider variety of PMMA-based solutions and helps reduce the manufacturing demand for virgin materials. Acrylics produced using the recycled MMA will be integrated as part of Trinseo's distinctive "R-Life" portfolio designed around a commitment to sustainability, which utilizes both mechanically and chemically recycled feedstocks. These products are used in applications across the mobility, building and construction and consumer goods industries, aligning with the growing industry and regulatory interest in products that are developed with sustainability in mind.

Both recycling technologies are a pivotal step toward reshaping the plastics industry as we focus on cultivating a circular economy.

BUILDING & CONSTRUCTION

Our partners in the building and construction industry require innovative and high-performing solutions. We offer a range of sustainably advantaged materials that are designed with safety, strength and aesthetics in mind.

In 2023, we successfully launched recyclate- containing solutions as part of our CALIBRE™ PC resins product portfolio. The innovative CALIBRE™ ECO products incorporate 50% or more of mechanically recycled feedstocks, and when compared to the all-prime solution, represents a reduction in global warming postential of approximately 37%, as supported by the PCF.

CONSUMER GOODS

Our solutions are intrinsic to countless consumer good applications produced by some of the most recognizable consumer brands, including consumer electronics, sanitary applications and footwear. We are known worldwide for our ability to consistently deliver quality, sustainably advantaged solutions.

As part of this commitment, we launched Trinseo's first compostable bio-hybrid binder for use in coated paper board products. The LIGOS™ BH

7340 SCE binder utilizes a proprietary method that introduces corn starch as a feedstock that imparts the binder with biodegradable properties that meet international standards and are supported by testing. Results show the binder fulfilled criteria for aerobic biodegradability under controlled compsting, fullfilling both the American standards of ASTM D6400 and D6868 and the international standard of ISO 18606 for compostability requirements.

We also launched several thermoplastic polyurethane (TPU) solutions designed to increase the amount

of recycled feedstocks in footwear applications. Trinseo's APILON™ 52 ECO grades are TPU compounds containing up to 70% mechanically recycled feedstocks that offer the same performance properties as all-prime material, making it

the perfect material for use in shoe soles.

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Partnerships are also critical to our ability to advance sustainability and provide value. In 2023, Trinseo entered a partnership with RWDC Industries, LLC, a biotechnology company, to bring polyhydroxyalkanoates (PHA) dispersion technology to target markets and use the technology to create water-based barrier coatings that are recyclable in traditional paper processes, organically recyclable via composting and biodegradable in soil and marine environments.

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MEDICAL

At Trinseo, we develop innovative products that benefit both providers and patients. Our medical- grade polymers, including our PC, ABS and PMMA resins, are designed to deliver consistent quality and crafted to meet customers' unique challenges.

In 2023, we began the commercialization process for MAGNUM™ ABS 8391 MED BIO80 resins for medical applications. Developed using a mass balance approach, we can accurately track the product's sustainability claims of utilizing up to

80% bio-circular attributed content. This innovative solution tackles the challenging problem of balancing sustainability and performance for diagnostic equipment housings, drug delivering devices and single- and multiple-use devices.

MOBILITY

Trinseo's longstanding expertise in the mobility industry allows us to keep customers ahead of the curve. Our solutions are specifically designed to meet consumer priorities, including electrification, range extension and sustainable design.

In 2023, we introduced the MEGOL™ ECO and BIO thermoplastic series, a sustainably advantaged portfolio of solutions for automotive interior and exterior applications. Solutions within this portfolio offer low fogging, odor, volatile organic compounds (VOC) and semi-volatile "fogging" compounds (FOG) emissions compared to their all-prime counterpart, while maintaining good mechanical properties and a short cycle time. Solutions are available in varying hardness levels.

Building on our sustainable offerings, Trinseo also launched new recycled content containing grades of one of our most universal and suitable PMMA resins for injection. Our recyclate- containing ALTUGLAS™ and PLEXIGLAS® R-Life V825T grades for automotive rear lights, pillars and trims can help equipment manufacturers and suppliers advance their sustainability goals.

Additionally, we expanded our PULSE™ Engineering product line by introducing PULSE™ GX90 ECO, available with 30% or 50% recycled content.

This grade of the PC/ABS engineered resins combines super low temperature ductility and high-heat performance to deliver a high-end solution for automotive interior applications. One characteristic of this grade compared to our other PULSE™ ECO Engineering Resins is its outstanding high-impact strength and high heat resistance equivalent to the all-prime GX90 solution.

18

MEETING OUR SUSTAINABILITY GOALS

Designed to deliver value to our customers, Trinseo's solutions help solve industry challenges and support our customers on their sustainability journey.

TRINSEO NAMED OUTSTANDING SUPPLIER

Trinseo teams work tirelessly to deliver best-in-class customer support. The China Aviation Lithium Battery (CALB), one of the world's top battery cell makers, awarded Trinseo with the Outstanding Supplier Award at its Global Partners Conference in 2023. The award is truly a testament to Trinseo's dedication to

Making a Difference for Our People

19

OUR 2030 SUSTAINABLE WORKFORCE GOALS

By 2030, have 40% of

management positions filled by

As part of our efforts toward achieving Trinseo's 2030 Sustainability Goals, we continue to dedicate our technology, innovation and R&D efforts to sustainable solutions.

Our continued commitment to explore new recycling technologies and introduce recycled feedstocks into the production of our latex binders, plastics and engineered

creating high-quality battery solutions, while highlighting our commitment to innovation and collaboration.

PRODUCT CARBON FOOTPRINT AND LIFE CYCLE ASSESSMENT FOR TRINSEO PRODUCTS

Trinseo employees are innovators, difference-makers and self-starters who ignite and inspire ideas. Our success is dependent on the investment we make in our best asset: our people.

One of the ways we engaged employees as part of our strategy was to launch our first three Employee Resource Groups (ERGs) for women, young professionals and LGBTQ+ employees and allies-an effort born from growing employee interest in

women globally and increase

the number of roles filled by

underrepresented ethnic groups

in the U.S.

By 2030, achieve one or more

materials will help us meet this goal.

Our R&D team exceeds our goal of investing more than 40% of our efforts in advancing circular and sustainably advantaged solutions. As we look ahead, Trinseo will continue to tailor our sustainable solutions to align with our customers' needs and global trends.

Trinseo promotes the responsible use of our material solutions to minimize potential harmful impacts from our products throughout their life cycles. We are actively seeking ways to help our customers understand the carbon footprint of our solutions throughout their life cycles. One area we invested is analyzing the PCF of our solutions

PCF provides a scientific lens for Trinseo and our customers to fully understand the carbon footprint of our solutions, enabling comparison between virgin materials and our sustainably advantaged solutions. After successfully piloting a PCF platform with Eviden in 2022, we started implementing it across our entire portfolio of material solutions.

The platform utilizes the data that we have in our systems, along with our supplier carbon emissions data when available, to deliver accurate

calculations from our manufacturing operations. This provides us and our customers with transparent data that allows for more informed decisions.

We completed PCF calculations for our plastics, latex binders and polystyrene solutions in 2023, and engineered materials solutions will follow. In addition, we continue to contribute to the development of public LCAs to help customers understand the impact of our products. LCAs are initiated and maintained by industry associations, such as Plastics Europe and Cefic, and are an average of data from several companies.

Our efforts aid the industry in determining the larger impact of plastics, engineered materials and latex products on the environment, including energy and raw material use, water consumption, emissions and waste.

As a global company, we are focused on building an energizing, inclusive environment that welcomes and celebrates differences. When employees bring their personal and unique perspectives and experiences to work, this leads to bold ideas that solve challenges. This philosophy is why we prioritize attracting, engaging, developing and retaining a talented, diverse pool of employees.

Driven by our dedication to human rights; equity and inclusion; and workforce elevation we expanded our 2030 Sustainability Goals for a Sustainable Workforce. These enhanced goals provide a new approach to achieving an inclusive workforce while continuing to prioritize safety. As our company continues to evolve, these aspirational goals will help us support and foster employees' talents

for professional advancement and leadership development while providing measurable results.

Additionally, as a critical milestone in our employee retention and development strategy, we implemented new employee programs that provide development and mentorship opportunities. Our Employee Experience Week showcased how our employees empower the latest societal advancements, and

we hosted informative global webinars throughout the year to foster mentorship, diversity, equity and inclusion (DEI) and professional growth.

connecting with their global peers. These communities are open to all employees, and are dedicated to fostering a more inclusive and supportive work environment. They support our strategic pillars to maintain global environments that make all our employees feel safe and welcomed, encourage career development and promote our Trinseo culture. Each ERG serves as a platform for members to connect, provide mentorship and advocate for issues important to their communities. The ERGs are each sponsored by a member of the executive leadership team and led by our employees.

Additionally, in 2023, we implemented new learning opportunities for our employees through LinkedIn Learning. These development opportunities, which supplement trainings held through our Learning Management System, support our above-average safety rating as well as employees' career aspirations. Trinseo employees engaged in over 63,000 hours

of training across our development opportunities, marking a 32.9% increase from 2022.

years where the voluntary

turnover rate for women is

equal to or less than the global

turnover rate.

By 2030, establish talent

programs to spotlight, develop

and promote women and

underrepresented racial and

ethnic groups.

By 2030, develop an enterprise-

wide strategy to measure,

understand and respond to

employees' sense of inclusion,

belonging and engagement.

By 2030, achieve one or

more years of zero recordable

injuries for employees and

contractors globally.

The above are aspirational goals.

Trinseo complies with all U.S. and

international laws with respect to

employment decisions.