The ratings of four chemicals stocks are down this week, according to the Portfolio Grader database. Each of these rates a “D” (“sell”) or “F” overall (“strong sell”).

This week, PolyOne Corporation (POL) falls to a D (“sell”), worse than last week’s grade of C (“hold”). 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. The stock’s trailing PE Ratio is 44.30. To get an in-depth look at POL, get Portfolio Grader’s complete analysis of POL stock.

Marrone Bio Innovations, Inc.’s (MBII) rating falls this week to an F (“strong sell”), down from last week’s D (“sell”). In Earnings Momentum, Equity, Cash Flow and Sales Growth the stock gets F’s. For more information, get Portfolio Grader’s complete analysis of MBII stock.

The rating of Kraton Performance Polymers, Inc. (KRA) slips from a D to an F. Kraton Performance Polymers produces engineered polymers and styrenic block copolymers. The stock gets F’s in Earnings Momentum and Earnings Surprise. The trailing PE Ratio for the stock is 271.90. To get an in-depth look at KRA, get Portfolio Grader’s complete analysis of KRA stock.

This week, Huntsman Corporation’s (HUN) rating worsens to a D from the company’s C rating a week ago. 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.