For the current week, the overall ratings of four chemicals stocks are worse, according to the Portfolio Graderdatabase. Each of these rates a “D” (“sell”) or “F” overall (“strong sell”).

PolyOne Corporation’s (POL) rating falls to a D (“sell”) this week, down from C (“hold”) the week prior. PolyOne is an international polymer services company with operations in North America, Europe, Asia, Australia, and South America. In Portfolio Grader’s specific subcategories of Earnings Growth, Earnings Momentum and Sales Growth, POL also gets an F. To get an in-depth look at POL, get Portfolio Grader’s complete analysis of POL stock.

Marrone Bio Innovations, Inc. (MBII) ratings are on the decline this week as the company earns an F (“strong sell”). Last week, it received a D (“sell”). The stock gets F’s in Earnings Momentum, Equity, Cash Flow and Sales Growth. For more information, get Portfolio Grader’s complete analysis of MBII stock.

This week, Kraton Performance Polymers, Inc.’s (KRA) rating worsens to an F from the company’s D rating a week ago. Kraton Performance Polymers produces engineered polymers and styrenic block copolymers. The stock gets F’s in Earnings Momentum and Earnings Surprise. To get an in-depth look at KRA, get Portfolio Grader’s complete analysis of KRA stock.

This week, Huntsman Corporation (HUN) drops from a C to a D rating. Huntsman manufactures differentiated and commodity chemical products. The stock gets F’s in Earnings Momentum, Earnings Revisions and Earnings Surprise. For more information, get Portfolio Grader’s complete analysis of HUN stock.

Louis Navellier’s proprietary Portfolio Grader stock ranking system assesses roughly 5,000 companies every week based on a number of fundamental and quantitative measures. Stocks are given a letter grade based on their results — with A being “strong buy,” and F being “strong sell.” Explore the tool here.