Trinseo : Cultivating a Circular Transformation

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2 | TRINSEO 2024 SUSTAINABILITY REPORT

Contents

04 WELCOME

04 CEO Message

05 CSO Message

06 About Trinseo

08 Highlights from 2023

10 OUR SUSTAINABILITY STRATEGY

12 Our Approach to Sustainability

13 Governance

46 PRODUCTS & INNOVATIONS

1. Our Approach to Innovation

1. Key Product Updates
2. Our Facilities

1. Building & Construction

1. Consumer Goods

1. Medical

1. Mobility

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84 ENVIRONMENTAL PROTECTION

1. Our Approach to Environmental Protection
2. Environmental Reporting

1. Responsible Care
2. Product Safety & Stewardship

1. Climate Strategy

1. Circular Solutions

18 Stakeholder Analysis & Engagement

21 Material Topics

24 Sustainability Goals

27 Aligning Our Efforts with the SDGs

30 Our Sustainability Strategy Highlights

32 BUSINESS & OPERATIONS

35 Our Approach to Sustainable Operations

36 Financial Disclosures

37 Economic Performance

38 Ethics & Compliance

40 Supply Chain & Procurement

41 Quality Management

42 Privacy & Cybersecurity

43 Community Impact

58	PEOPLE	100 CORPORATE CITIZENSHIP
102 Our Approach to Corporate Citizenship
60	Our Approach to People
103 Community Highlights
62	Employee Reporting
105 Industry & Trade Associations
64	Labor, Employment & Compensation
	Policies

67	Talent Management	106 ABOUT THIS REPORT
109	GRI Content Index
72	Leadership Development
115	SASB Index
74	SAFETY	118	Non-GAAP to GAAP Reconciliation

1. Our Approach to EH&S Management

1. Safety Reporting

1. Safety Indicators

ON THE COVER

Fiddleheads are young, unfurled fern fronds that appear in early spring and represent a sign of hope in many cultures. As symbolized through the fiddlehead fern on our cover, we recognize that circularity is in its early stages, and we will continue to cultivate this transformation in the chemical industry.

4 |		| 5

Message from Our Chief Executive Officer

Message from Our Chief Sustainability Officer

Chemical manufacturing is an ever-evolving landscape as more regulators and investors focus on investing in a sustainability strategy. Trinseo is dedicated to bringing ideas to life in smart and sustainable ways that help our customers navigate these changing tides.

Amid uncertain market conditions, we remain steadfast in our journey to transform our company into a less cyclical business with higher growth and margin potential. Our year- to-date results were significantly impacted by persistent underlying demand weakness experienced across all

our reporting segments. However, this did not stop our sustainability progress.

We remain focused on becoming a specialty material solutions provider that prioritizes sustainability and innovation. To that end, we restructured our company to reduce earnings volatility and optimize assets to improve profitability. By maintaining an adaptive business strategy, we remain agile in our approach to sustainability. This further enables us to balance customer needs with sustainable innovation across our business segments.

I am incredibly proud of the work we accomplished in

2023. We expanded our recycling technologies to include polycarbonate (PC) dissolution and polymethyl methacrylate (PMMA) depolymerization-an investment in circular

solutions to help reduce plastic waste. Additionally, our methodical and scientific approach to decarbonization and clean energy is in full swing as we plan the next steps in our pathway to carbon excellence and green energy.

We continue to solidify our approach to upcoming sustainability regulation changes in the U.S. and Europe, including those for reporting. In 2022, Trinseo organized a team from across our business units and functions to help navigate these forthcoming changes. Throughout 2023, this team worked tirelessly to review our internal processes to help our company continue to prepare for these new regulations.

As I reflect on the year, I am confident that we are cultivating a sustainable future here at Trinseo. We are poised to support our industry through a circular transformation, and that is due to the hard work of our employees every day. As you read our Sustainability and Corporate Social Responsibility Report, I hope you are as optimistic about the future of Trinseo as I am.

Trinseo is a company of passionate, innovative people-an organization that I am proud to be part of. When faced with challenges, the dedication and engagement of our employees in advancing sustainability has never faltered. Because of this, our customers consider us leaders in sustainable materials innovation.

Sustainability is the backbone of our strategy at Trinseo and a key pillar of our future. From the Board down, everyone remains engaged in our efforts to reduce our carbon footprint, build a circular value chain, create a sustainable workforce and operate responsibly. We continue to prioritize work across the business units and functions to evolve our sustainability strategy through the dedication of our Sustainability Business and Services (SBS) team. We are unique in our approach to sustainability through this centralized team that supports our business units, functions and company overall. From the implementation of Product Carbon Footprint (PCF) and the extension of our mechanical recycling activities to piloting our PC dissolution and PMMA depolymerization recycling technologies, we have harmonized efforts across business units to leverage our strengths and keep moving forward.

Decarbonization remains a high priority for our company, and we are making fantastic progress in addressing our Scope 1, 2 and 3 greenhouse gas (GHG) emissions. Our team has taken significant strides forward with our value chain and customers to develop our Scope 3 baselines, and we are working internally to evaluate our facilities for Scope 2 investments in the years ahead. Our employees are passionate about our carbon excellence projects and are involved with researching the best approaches for their facilities to offset their footprint through alternative energy sources.

Our Sustainability and Corporate Social Responsibility Report showcases how sustainability remains embedded in our company, even during times of limited capital availability. We have cultivated a culture that is not afraid to question the status quo and encourages our employees to deliver innovative solutions.

We continue to drive innovation, and I am excited to see how we will transform our industry through ingenuity, perseverance and dedication.

FRANK BOZICH

FRANCESCA REVERBERI

President & Chief Executive Officer	Senior Vice President of Engineered Materials &
	Chief Sustainability Officer

6 | TRINSEO 2024 SUSTAINABILITY REPORT

About Trinseo

WELCOME | 7

Business Segments

Engineered Materials | Latex Binders | Plastics Solutions

At Trinseo, we believe in the power of ideas. As a global specialty materials solutions provider, we recognize our role in leading the sustainability journey ahead. We are inspired

We're bringing ideas to life in smarter, more sustainable ways using our premier expertise and best-in-class materials to unlock value for companies and consumers alike.

Polystyrene | Feedstocks | Americas Styrenics

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.

As a company, we are taking actionable steps to encourage our industry and value chain to advance sustainability through innovative materials solutions that break the mold on traditional limitations. This requires our continued investment in reducing emissions, developing a sustainable product portfolio, committing to supplier responsibility, evolving responsible operations and fostering a sustainable workforce. Trinseo remains dedicated to its investment in affordable and clean energy, responsible consumption and production, cultivation of key partnerships and climate action initiatives.

Our employees bring endless creativity to reimagining the possibilities with clients all over the world from Trinseo's locations in North America, Europe and Asia Pacific. We leverage this passion and our decades of expertise in specialty and sustainable materials to develop tailored solutions that benefit our customers and end consumers, empowering ideas that boldly challenge the status quo. Our investment in sustainable solutions is material to the everyday needs of people around the world and central to supporting a future circular economy.

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.

Our vision, values and commitment to sustainability are our promise to conscientiously maintain ethical standards for everything we do and how we do it. As a Responsible Care® company, we prioritize the health and safety of our employees and our communities. We strive to meet or exceed the highest standards of environmental and safety performance. Our adaptive strategic plan enables us to act with agility and accountability as we continue to invest in market-driven growth for sustainable products, new sustainably advantaged product development and recycling technologies, targeted acquisitions and divestitures and exciting new partnerships.

As part of our ongoing joint ventures, in 2023, Trinseo retained 50% ownership in Americas Styrenics, which is a leading polymer producer in its respective market. Trinseo PLC (referred to herein as "Trinseo," and together with its subsidiaries, the "Company") is a public limited company existing under the laws of Ireland and is listed on the New York Stock Exchange under the ticker symbol "TSE".

For more information about Trinseo and our product offerings, visit Trinseo.com.

Building &

Construction

Adhesives & Sealants

Bath, Pool & Spa

Building Materials

Coatings

Edgebands

Fiber Bonding

Infrastructure

Lighting & Diffusion

Safety & Security

Industries

Consumer Goods	Medical
Adhesives & Sealants	Diagnostic Equipment Housings
Building Materials	Drug Delivery Devices
Coatings	Medical Wearables
Consumer Electronics	Single & Multiple-use Devices
Fiber Bonding
Footwear
Furniture & Design
Home Appliances	Mobility
Lithium-ion Batteries	Automotive Interior & Exterior
Packaging	Automotive Lighting

GLOBAL FOOTPRINT				FINLAND
			Hamina
									SWEDEN
									Norrköping
									BELGIUM
									Tessenderlo
	U.S.A.				IRELAND
	Midland, MI				Dublin
Plastics Solutions	Wayne, PA						FRANCE
King of Prussia, PA						Paris
Latex Binders	Florence, KY						Serquigny*
Polystyrene	Louisville, KY								St Avold
Engineered Materials	Bristol, PA							Lacq*

NETHERLANDS

Hoek

Utrecht Terneuzen

GERMANY

Stade

Schkopau

Eschborn

Rheinmünster

KOREA

Seoul

Ulsan

JAPAN

Tokyo

Textiles & Carpet

Visual Communications

Paper & Board	Battery Charging Stations
Personal Care	Electrical Vehicle Battery Packaging
Textiles & Carpet	Lithium-ion Battery Coatings

Corporate and Sales Offices	Dalton, GA
Global Operating Center
= Manufacturing	MEXICO
= Recycling Facility
Mexico City
= R&D

• R&D activity takes place at an external shared site

ITALY

Mussolente

Rho

Porto Marghera

TURKEY

Istanbul

SWITZERLAND

Pfaeffikon

INDIA

Mumbai

SINGAPORE

INDONESIA

Merak

Jakarta

GREATER CHINA

Zhangjiagang

Shanghai

Taipei

Hsinchu

Guangzhou

Hong Kong

3,126	22	1	34	11	$3.7B
Employees	Sites	Recycler	Manufacturing	R&D	2023
			Plants	Facilities	Net Sales

Figures representative of Trinseo as of December 31, 2023

Map representative of Trinseo's 2023 global footprint

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Highlights from 2023*

WELCOME | 9

SUSTAINABILITY STRATEGY

• +5 new members joined the Sustainability Business and Services team
• + Scope 3 Council
• +2 new recycling technologies piloted

BUSINESS & OPERATIONS

• $47.4 million year-over-year increase in cash balance
• + Scope 3 GHG emissions supplier program implemented
• +2 Operation Clean Sweep® (OCS) compliant facilities

PRODUCTS & INNOVATIONS

BUILDING & CONSTRUCTION

>50% mechanically recycled

content in CALIBRE™ ECO PC Series

CONSUMER GOODS

• 1 Polyhydroxyalkanoates (PHA) dispersion partnership
• 70% mechanically recycled TPU feedstocks in APILON™ 52 ECO grades
• 1st compostable bio-hybrid latex binder solution

MEDICAL

• 1 mass balanced acrylonitrile butadiene styrene (ABS) medical solution

MOBILITY

• 7 new ALTUGLAS™ R-Life products using recycled feedstocks
• >30% recycled content in PULSE™ GX90 Engineered Resins

PEOPLE	ENVIRONMENTAL PROTECTION
	3,126 employees	23%↓ GHG emissions
	3 Employee Resource	12%↓ freshwater intake
	Groups established	5%↓ renewable energy sources

• 4 expanded 2030 Sustainability Goals

SAFETY	CORPORATE CITIZENSHIP
0.30 employee incident rate	6,000+ volunteer hours
18% ↓ transportation	101 organizations supported
incidents	Member of 60+ industry and trade associations

• 72% of teams received Triple Zero Award

*All comparisons are made against those reported in 2022, unless otherwise noted.

RETURN TO CONTENTS LIST

12 | TRINSEO 2024 SUSTAINABILITY

CORE VALUES

Our Approach

OUR SUSTAINABILITY STRATEGY | 13

Governance

Our core values are the foundation for our daily work, and we often look to them to guide our company forward in our sustainability strategy. They are embedded into our culture, helping to direct our commitment to Environmental, Economic and Social (EES):

RESPONSIBLE CARE®

As a Responsible Care® company, we prioritize the health and safety of our employees and our communities. We strive to meet or exceed the highest standards of environmental and safety performance.

RESPECT & INTEGRITY

We treat each other, our customers and our stakeholders with respect and dignity. We conduct all business activities with the highest ethical standards and fully comply with the law everywhere we operate.

Equal opportunity and diversity are important values at Trinseo. The Company is committed to respecting internationally recognized human rights, such as the UN

to Sustainability

At Trinseo, sustainability is a key pillar of our strategic direction. Our

2030 Sustainability Goals anchor our decisions across business units and functions, including those for operations, product innovation, safety and procurement. We are dedicated to cultivating a circular economy, and the work we accomplish throughout the years aligns with this guiding objective. Sustainability is intrinsic to who we are and what we do each day.

Our approach to sustainability is unique, as we treat each employee as an ambassador for our strategy. In 2023, we implemented the successful Trinseo Sustainability Academy (TSA) for our employees and external stakeholders. This webinar series utilizes experts from our business units and functions to educate stakeholders on relevant topics within sustainability and how we are implementing change.

As a global company, we have the customer base, network connections and technologies to deliver sustainably advantaged solutions that drive innovation. With our global footprint, we have local, agile teams around the world who can help our customers adapt to the ever-changing sustainability landscape. 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.

Trinseo utilizes a top-down approach for governance so that our sustainability strategy has a holistic approach that can be incorporated throughout our company, beginning with our Board of Directors (the Board) and our Executive Leadership Team (ELT). This is essential to our success.

As an international, publicly traded company listed on the New York Stock Exchange (NYSE), Trinseo is subject to the requirements of the U.S. Securities and Exchange Commission (SEC) and other regulatory bodies throughout the world.

Trinseo's Board periodically assesses the Company's governance against external standards. The Committee on Environmental, Health, Safety, Sustainability and Public Policy (the Committee) assists the Board in fulfilling its oversight responsibilities by assessing the effectiveness of programs and initiatives that support

the environment, health and safety, sustainability, corporate social responsibility, risk management, and climate change policies and programs at Trinseo. The Committee, which is chaired by an independent director, regularly advises the Board on matters related to these topics and reviews, approves and recommends for adoption the annual Sustainability and Corporate Social Responsibility Report.

Topics of importance explored by the Committee in 2023 included the Company's Material Topics for alignment with the 2021 GRI reporting disclosures framework; tracking

and benchmarking against Trinseo's sustainability goals; community risks and layer of protection analyses from facility operations; sustainability trends and target initiatives, new legislation and ongoing review of forthcoming reporting requirements; compliance and remediation program results and enforcement trends;

cybersecurity; crisis response and changes to sustainability governance; new acquisitions; implementation of a decarbonization and clean energy strategy; and tracking greenhouse gas (GHG) emissions and waste, energy and water consumption. The Committee also conducts an annual evaluation to improve Committee performance.

The ELT establishes the Company's overall annual objectives and priorities, as well as the annual budget and financial plan, which are approved by the Board. While there are changes from year to year, these are typically focused on Environmental, Health and Safety (EH&S), sustainability, financial performance, strategic planning and organizational effectiveness objectives.

More information about Trinseo's Board and the committees can be found in the Company's Proxy.

Universal Declaration of Human Rights and the UN Guiding Principles on Business and Human Rights. Trinseo also supports global efforts to eradicate modern slavery.

ACCOUNTABILITY &

VALUE CREATION

We acknowledge the ongoing global environmental and societal challenges within the industries we serve. These issues include climate change, plastic waste in the environment, a growing need for circular solutions, securing human rights throughout the value chain, increasing regulations and consumer demands, and more. Guided by our sustainability goals and company values, we focus on the EES impact we have on our employees, communities, customers, partners and other stakeholders. We take a strategic approach to how we handle these growing issues with our impact in mind.

Proxy Statement

Corporate Governance Guidelines

We believe that speed and agility combined with good decision-making create value. We take ownership and accountability for our company's success.

INNOVATION

We believe that innovation is essential to the growth of our business and our customers. Trinseo's innovation is powered by our advanced technology and the creativity of our people.

COMMITMENT TO CUSTOMERS

We are committed to our customers' success, delivering value through our personalized service, innovative solutions and technology.

Our 2024 Sustainability and Corporate Social Responsibility Report provides an opportunity to share our progress against these global challenges and be held accountable for our 2030 Sustainability Goals. We are passionate about transparent reporting that enables global continuity, so we again aligned our report with the Global Reporting Initiative (GRI) and the Sustainability Accounting Standards Board (SASB). Through the continued use of these frameworks for reporting, we can provide valuable comparable context around our sustainability efforts for our stakeholders that can show a purposeful, strategic approach to change.

In the coming pages of this report, we will showcase how our company is cultivating a circular transformation as an industry leader, guided by our sustainability goals and core values. By innovating not only our products, but also how we approach materials solutions, we are helping to achieve a brighter tomorrow.

Sandra Beach Lin

Member of the Board of Directors

Sandra Beach Lin became a director on Trinseo's Board in November 2019, and now is chair of the Committee on Environmental, Health, Safety, Sustainability and Public Policy. As Trinseo continues to embrace sustainability as an important element of its business strategy, Beach Lin believes the Company's holistic approach to sustainability oversight and implementation is critical to success.

"Our committee members are continuously educating ourselves as Trinseo pushes forward with its sustainability initiatives," said Beach Lin. "The Charter of the committee is very fulsome-within it we understand what is going on at Trinseo and within the world of sustainability. This means we learn on the job, since it's a fast-changing area."

In the years ahead, Beach Lin believes that Trinseo's scientific approach will make the Company successful. From collaboration across business units and functions to deliver innovative sustainably advantaged solutions to preparation for forthcoming regulatory compliance, the Company is dedicated to doing meaningful work that has measurable results.

"Trinseo is focused on the right things," said Beach Lin. "I'm very proud of the work the Company is doing throughout this journey. Everyone involved is focused on creating more sustainable products, more sustainable processes and providing transparency to all stakeholders."

14 | TRINSEO 2024 SUSTAINABILITY REPORT

SUSTAINABILITY BUSINESS

AND SERVICES (SBS) TEAM

Established in 2021, the SBS team is overseen by Trinseo's Senior Vice President, Engineered Materials and Chief Sustainability Officer (CSO), Francesca Reverberi. In 2023, the team was also led by Global Business Director for Engineered Compounds Sarmenio Saliba. The team develops and oversees Trinseo's sustainability strategy and provides sustainability services to the business units. Since then, the team has continued to grow as the Company invests in strategic sustainability initiatives, such as decarbonization, recycling innovation and circular solutions.

The team is directly responsible for oversight of each of Trinseo's five primary sustainability goal categories: Sustainable Product Portfolio, Supplier Responsibility, Climate Change, Responsible Operations and Sustainable Workforce. This oversight is coordinated through three strategic councils:

• Climate, Operations and Suppliers Council (COS)
• Sustainable Business Development Council (SBD)
• Environmental, Social and Governance (ESG) Council

In 2023, the team co-coordinated the implementation of the Scope 3 Council, which is a joint effort between SBS and the Supply Chain and Procurement teams. Alongside the councils, we have also established the Sustainable Feedstock Business, which utilizes the recycling technology and global network of our acquired business, Heathland B.V., to source sustainable feedstock solutions for our business units.

Under the leadership of the CSO, the SBS team has a direct line to the ELT and the Board that enables the team and its councils to coordinate with the corporate and business units on strategic direction, investment opportunities and communications.

SBS WELCOMES NINA KARABASH AS GLOBAL BUSINESS DIRECTOR

We welcomed Nina Karabash to the role of Global Business Director for Sustainability

• MMA in early 2024. She previously held the role of Sustainability Program

Director within the SBS team, and in her new position, she leads the team and the methyl methacrylate (MMA) business. She will drive sustainability growth initiatives forward and lead the polycarbonate

(PC) dissolution and polymethyl

methacrylate (PMMA) depolymerization projects, among other initiatives.

We are doing everything we can to keep Trinseo moving on its sustainability path- we are dedicated to this strategy. Our SBS team, and Trinseo's employees overall, are passionate about reducing the environmental impact of our solutions and operations through innovative initiatives, training

and collaboration."

Francesca Reverberi

CSO

OUR SUSTAINABILITY STRATEGY | 15

COS COUNCIL

This working group is responsible for reducing indirect and direct (Scope 1, 2 and 3) emissions, extending supplier responsibility and delivering responsible operations at Trinseo. In 2023, this council was instrumental in the development of the Company's decarbonization and clean energy strategies. The new Scope 3 Council is nested within this Council.

I am most proud of how much we accomplished in 2023. We are making good progress, and we are moving forward on our strategy. We are working together as a team to inform our employees about our decarbonization initiatives and cultivate a culture of understanding when it comes to Scope 1, 2 and 3. In 2024, we hope to achieve external validation for our work, which will be very rewarding."

TATIANNA YAM-YEE YUNG

Senior Project & Program Manager and Council Leader and Council Leader

SBD COUNCIL

This working group partners with the Company's business units to gather and analyze market intelligence on sustainable trends to deliver competitive solutions and supportive circular tools and services.

We are at the midpoint of our journey, but we anticipate more regulations coming in the next two years. So, we are starting to gear up to ensure we have the right resources in place and make changes where needed."

SOFIA SOTIROPOULOU RIEMANN

Global Sustainability Business Development Leader and Council Leader

ESG COUNCIL

The ESG Council oversees the strategic direction, implementation and reporting of the 2030 Sustainability Goals, as well as monitors ongoing global sustainability policy changes like the EU Green Deal and the forthcoming reporting requirements for the U.S. and Europe. It plays an important role in the Company's overall governance framework for Responsible Care® and EH&S; regulatory compliance; risk management; reputation; stakeholder relationships; and sustainability and corporate social responsibility (CSR) reporting.

Sustainability is the backbone of our company and at the forefront of conversation at Trinseo. As we prepare for new regulations around sustainability and reporting, this approach to sustainability is essential for employee and customer engagement. Our approach is helping us accelerate innovation in relevant areas like decarbonization and circular solutions."

WALTER VAN HET HOF

Global Industry Affairs, Public Policy & Corporate Sustainability Leader and Council Leader

SUSTAINABLE FEEDSTOCK BUSINESS

This business was established as the sustainable materials interface with downstream businesses. The unit is responsible for expanding its sustainable materials network and sourcing the required sustainable feedstock for our business units. In addition, it will take a principal role in building circular business models, managing a recycling operation and scaling up recycling technologies. While this business currently focuses on the supply of quality sustainable feedstock to our business units, the Company envisions that partnerships and acquisitions will strengthen this unit further and expand our sustainable offerings to the market.

We are exploring novel circular business models with customers to create efficient closed loop systems where end-of-life materials can be recovered and processed back into high value materials. Our expertise in sustainability continues to expand in order to support our internal business units, and by extension, our customers to meet the evolving landscape of the industry."

SARMENIO SALIBA

Global Business Director for Engineered Compounds

16 | TRINSEO 2024 SUSTAINABILITY REPORT

SUSTAINABILITY GOVERNANCE STRUCTURE

Board Committee

on EH&S, Sustainability and Public Policy

CEO and Executive Leadership Team

Alignment and Direction

SBS Team

Sustainable Feedstocks Business, Sustainability Goals Alignment, Progress and Direction

COSC	SBDC	Sustainable	ESGC
Feedstock Business

Sustainability Business Services

Tools (LCA, PCF, Mass Balance), Policy & Industry Relations, Reporting, Communications, Guidelines

Product Stewardship & Safety

TRACKING TRINSEO'S

SUSTAINABILITY PROGRESS

OUR SUSTAINABILITY STRATEGY | 17

Trinseo's sustainability efforts and reporting are led by the CSO in conjunction with the Global Industry Affairs, Public Policy & Corporate Sustainability Leader through the ESG Council. The Council continues to play an important role in the Company's overall governance framework with focus on:

• Tracking progress against the Company's 2030 Sustainability Goals while continuing to review and revise for relevance
• Facilitating quarterly assessment and alignment of Sustainability and CSR activities
• Providing strategic direction for sustainability strategies, work plans and external engagements
• Monitoring evolving sustainability reporting regulations and preparing the Company for compliance, as well as evaluating reporting frameworks for disclosure and transparency
• Supervising the development of Trinseo's Sustainability and CSR Report, including alignment of sustainability policies, standards and programs with the GRI framework
• Providing oversight of stakeholder analysis, stakeholder engagement and Material Topics and scope of impact

The ESG Council first convened in July 2018 under the name Sustainability Council. The Council is made up of senior leaders from across multiple company functions, including but not limited to EH&S, Investor Relations, Finance, Procurement, Operations, Human Resources and Legal and meets at least quarterly. It has the ability to add subcommittees and task groups as needed, and its charter is reviewed annually.

Board of Director Profiles

Environmental, Health, Safety, Sustainability and Public Policy Committee Charter

Nominating and Corporate

Governance Committee Charter

18 | TRINSEO 2024 SUSTAINABILITY REPORT

Stakeholder

Analysis &

Engagement

STAKEHOLDER ANALYSIS

Trinseo's relationships with its stakeholders provide immense value each year in our strategy development and the prioritization of our Material Topics. Recognizing this, we have engaged a variety of stakeholder groups throughout the year, including:

• Customers
• Communities
• Employees
• Government and regulatory bodies
• Industry and trade associations
• Shareholders and the investment community
• Suppliers

STAKEHOLDER ENGAGEMENT

The long-term success of our sustainability initiatives is dependent upon productive engagement with our internal and external stakeholders. As such, we foster an ongoing dialogue that helps guide our strategic priorities and efforts.

Our methods of engaging with our stakeholders vary according to specific needs and proximity, with priority on transparency, accuracy and purpose in all interactions. We review and analyze input from each group annually to identify new opportunities or risks related to sustainability. This includes meetings with customers to discuss our sustainability approach and their evolving needs.

Trinseo continued to connect with stakeholders through a hybrid approach in 2023. We maintained virtual dialogues through our Trinseo Sustainability Academy (TSA) webinars that invited customers, partners, employees and other stakeholders to learn about our sustainability efforts in decarbonization, circularity and reporting, among others. Additionally, we engaged customers at in-person events, such as conferences and trade shows, interviews, workshops and meetings, which helped us build strategies and drive innovation for our sustainable product portfolio.

SUSTAINABILITY COMMITMENT STATEMENT

Trinseo aims to be a sustainable specialty material solutions leader for our stakeholders, committed to:

• Innovating and developing new and improved products and processes that advance Trinseo's and our customers' commitments to sustainability and a circular economy
• Promoting the responsible use of our materials through product stewardship
• Improving our operations with respect to the environment, health, safety, the use of natural resources and our impact on climate change
• Maintaining a robust ethics and compliance program that values diversity and human rights for our employees and our communities
• Adhering to the principles of Responsible Care®
• Being a good neighbor in the communities where we operate

						OUR SUSTAINABILITY STRATEGY | 19
		DESCRIPTION		METHODS OF ENGAGEMENT		KEY TOPICS
				Meetings, visits, workshops, webinars,
	CUSTOMERS	Through our solutions and technology, our		and calls; Voice of Customer and		Recycling and circularity, recycled
		questionnaire outreach, including EcoVadis
		commitment and our actions, Trinseo is			materials, sustainability in the value
			and the Carbon Disclosure Project;
		focused on helping our customers realize their			chain, climate change and product
			innovation collaboration; trade shows;
		sustainability goals.			validation, regulation, and transparency.
			surveys; industry partnerships and
				conferences; and media and social media.
	COMMUNITIES	We encourage open dialogue with the		Community Advisory Committees; Volunteer		Safety, volunteering, community
			Days; educational community partnerships;		involvement, emergency response,
		communities we serve, and we invest in our
			charitable contributions; internet; Open Days;		proactive communications, and
		commitment to being good neighbors.
			and direct contact.		environmental and social justice.
	EMPLOYEES	our future means investing in our people.		media; and our Sustainability Report.		Business strategies, company financial
			opportunity, diversity and inclusion, and
		The engagement of our employees in the		Intranet and internet; meetings, employee		performance, sustainability, climate
		Company's sustainability strategy is vital to our		broadcasts and town hall meetings; webinars		change, professional development, job
		success. As such, we recognize that investing in		and trainings; email newsletters; social		opportunities, people resources, equal
						recruitment.
	REGULATORY	Trinseo prioritizes operating in compliance				Maintaining compliance; timely
	participate in local government action plans
		with all applicable laws, including permits,				reporting; monitoring new legislation and
		implementation of compliance with new				implementation of compliance programs
		laws and regulations, and reporting. We also
			In-person visits; reports; trainings and		for new laws, including but not limited
&	regarding energy reduction, energy transition		inspections; seminars; audits; emergency		to those pertaining to EH&S, ethics and
	GOVERNMENT		response planning and drills; assessments;		corporate compliance, customs and trade,
	and climate change, in addition to industry
		and outreach through industry associations.		data protection and privacy, diversity and
		standards that may align with better practices
					equal opportunity, and labor and human
		than government application. We translate these
					rights; and commitments to sustainability
		into country and site implementation plans
					action plans (climate change).
		around the world.
		Trinseo is a member of more than 60 industry
	INDUSTRY& TRADE ASSOCIATIONS	and trade associations, including the American
	Circular Solutions, and Styrene Information and
		Chemistry Council, Association of International				Board representation, advocacy,
		Chemical Manufacturers (AICM), the World		Working groups; board meetings;		contribution to working groups, industry
		Plastics Council, Plastics Europe, International		conferences; and events.		commitments and participation in
		Association of Plastics Distribution (IAPD), SCI
					sustainability organizations.
		Americas, Operation Clean Sweep®, Styrene
		Research Center (SIRC), among others.
	SHAREHOLDERS INVESTMENT& COMMUNITY			Quarterly investor conference calls; public
	We expect that the demand for sustainable		reports (including our Sustainability
			Report) and press releases; rating agency
		investment options will continue to be important			Company performance and strategy.
			publications; financial analyst phone calls;
		to investors.
			annual shareholder meetings; one-on-one
				meetings; and non-deal roadshows.
						Strategy, including discussions as a key
		While formal supply chain sustainability				component in our supplier relationship
	SUPPLIERS				management program, adherence to
	programs remain an important practice,
		Meetings and reviews; assessments;		Trinseo Supplier Code of Conduct or
	Trinseo believes a transparent, proactive
		webinars; and sustainability ratings.		comparable codes, Scope 3 greenhouse
	dialogue with suppliers offers an opportunity
				gas emissions and decarbonization
	for overall progress.
					initiatives, and supplier assessment and
						evaluation, including EcoVadis.